Browsing by Author "Bandhauer, Todd M., advisor"

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Open Access
A computational examination of conjugate heat transfer during microchannel flow boiling using finite element analysis
(Colorado State University. Libraries, 2018) Burk, Bryan E., author; Bandhauer, Todd M., advisor; Windom, Bret C., committee member; Henry, Charles S., committee member
As technology advances, electronic components continue to produce more heat while at the same time growing smaller and being arranged in ever more compact packages. This has created the need for new thermal management systems able to both dissipate the large heat loads and meet the diminishing size requirements. Microchannel heat exchangers have become an integral part of such advanced cooling systems as they provide an exceedingly large surface area over which heat transfer can occur while maintaining a diminutive size. Current microchannel devices primarily use single-phase flow to dissipate the heat. As heat loads increase, so too must flow rates. Due to associated issues with extremely large pressure drops and high pumping power requirements, the practical capacity of single-phase microchannel coolers has largely been met. One particularly promising avenue forward is to utilize flow boiling with similar microchannel heat exchanger designs. The very high latent heat of vaporization associated with phase change for many fluids allows for a large amount of heat to be dissipated in flow boiling using a relatively low flow rate as compared to single-phase systems, drastically reducing the issues related to pressure drop. Additionally, two-phase heat transfer is associated with much higher heat transfer coefficients, allowing for smaller heat transfer surface areas (and thus smaller overall devices) and lower driving temperature differences for the same heat removal rates. Microchannel flow boiling studies to date have assumed 1D heat conduction through the heat exchanger material and have developed correlations to predict average heat transfer coefficients. Unfortunately, with the high heat fluxes expected in the near future, and with heat loads being applied at small, localized hotspots, the 1D assumption is no longer valid. Conjugate heat transfer must be considered, and local heat transfer coefficient correlations are necessary for the design of future thermal management systems. This thesis describes a first of its kind computational model that uses finite element analysis to analyze the conjugate heat transfer problem, complete with local heat transfer coefficients. This work serves as both proof of concept and an evaluation of the predictive capabilities of five published heat transfer correlations when applied locally to a high heat flux microchannel heat exchanger that has been previously tested. Modeling results show highly variable local heat flux profiles along the microchannel walls, confirming the need to consider conjugate heat transfer. Significant heat spreading resulted in peak local heat fluxes of roughly 0.5× that of the uniformly applied heat flux with 31.4% - 64.1% of total applied heat dissipated outside the region projected directly above the heater. As determined via local temperature comparisons, the correlation from Agostini and Bontemps provides the best overall agreement with average root mean square temperature differences of 2.6°C, though trends suggest that this difference may increase as heat flux increase further than those values tested here.
Open Access
A multi-functional electrolyte for lithium-ion batteries
(Colorado State University. Libraries, 2016) Westhoff, Kevin A., author; Bandhauer, Todd M., advisor; Bradley, Thomas H., committee member; Prieto, Amy L., committee member
Thermal management of lithium-ion batteries (LIBs) is paramount for multi-cell packs, such as those found in electric vehicles, to ensure safe and sustainable operation. Thermal management systems (TMSs) maintain cell temperatures well below those associated with capacity fade and thermal runaway to ensure safe operation and prolong the useful life of the pack. Current TMSs employ single-phase liquid cooling to the exterior surfaces of every cell, decreasing the volumetric and gravimetric energy density of the pack. In the present study, a novel, internal TMS that utilizes a multi-functional electrolyte (MFE) is investigated, which contains a volatile co-solvent that boils upon heat absorption in small channels in the positive electrode of the cell. The inert fluid HFE-7000 is investigated as the volatile co-solvent in the MFE (1 M LiTFSI in 1:1 HFE-7000/ethyl methyl carbonate by volume) for the proposed TMS. In the first phase of the study, the baseline electrochemical performance of the MFE is determined by conductivity, electrochemical stability window, half and full cell cycling with lithium iron phosphate (LiFePO4), lithium titanate oxide (Li4Ti5O12), and copper antimonide (Cu2Sb), and impedance spectroscopy measurements. The results show that the MFE containing HFE-7000 has comparable stability and cycling performance to a conventional lithium-ion electrolyte (1 M LiPF6 in 3:7 ethylene carbonate/diethyl carbonate by weight). The MFE-containing cells had higher impedance than carbonate-only cells, indicating reduced passivation capability on the electrodes. Additional investigation is warranted to refine the binary MFE mixture by the addition of solid electrolyte interphase (SEI) stabilizing additives. To validate the thermal and electrochemical performance of the MFE, Cu2Sb and LiFePO4 are used in a full cell architecture with the MFE in a custom electrolyte boiling facility. The facility enables direct viewing of the vapor generation within the channel in the positive electrode and characterizes the galvanostatic electrochemical performance. Test results show that the LiFePO4/Cu2Sb cell is capable of operation even when a portion of the more volatile HFE-7000 is continuously evaporated under an extreme heat flux, proving the concept of a MFE. The conclusions presented in this work inform the future development of the proposed internal TMS.
Open Access
A techno-economic study on the waste heat recovery options for wet cooled natural gas combined cycle power plants
(Colorado State University. Libraries, 2018) Paudel, Achyut, author; Bandhauer, Todd M., advisor; Quinn, Jason C., committee member; Reardon, Kenneth F., committee member
Increasing ambient temperature is known to have negative impacts on the performance of gas turbine and combined cycle power plants. There have been multiple approaches to mitigate this performance reduction. One such method involves cooling of the gas turbine inlet air. There are several different commercial techniques available, but they are energy intensive and require large capital investments. One potential option for cost reduction is to recover the waste heat emanating from the power plants to operate thermally activated cooling systems to cool the turbine inlet air. In this study, a 565 MW natural gas combined cycle power plant subjected to different waste heat recovery scenarios and gas turbine inlet chilling is assessed. A simplified thermodynamic and heat transfer model is developed to predict the performance of an evaporatively cooled NGCC power plant at varying ambient conditions. By taking typical meteorological year (TMY3) hourly weather data for two different locations – Los Angeles, California and Houston, Texas – the yearly output for this plant is predicted at a 100% capacity factor. The feasibilities of different waste heat recovery (WHR) systems including a gas turbine exhaust driven absorption chiller, a flue gas driven absorption chiller, a steam driven absorption chiller, and an electrically driven vapor compression chiller are assessed by calculating the Levelized Cost of Electricity (LCOE) for each scenario. In each of these cases, a parametric analysis was performed on the COP and the costs ($ per kWth) of the system. In these cases, the COP was varied from 0.2 to 2.0 (increments of 0.2), whereas the costs were varied logarithmically from $10 to $10,000 per kWth. The results of the analysis showed that for a fixed WHR system cost (i.e., $ per kWth), the system powered by flue gas generated the lowest LCOE, followed by the electrically-driven vapor compression chiller, steam-heated chiller, and finally, the gas turbine exhaust driven chiller for both geographic locations at all COP combinations. The analysis also investigated the impact of fixed investment cost, and the flue gas system again yielded the smallest LCOE and yielded a lower LCOE than the baseline case (no WHR) over a wide range of COPs. The maximum costs each of these systems could tolerate before the LCOE is higher than the baseline case was also determined. The flue gas driven absorption system had the highest tolerable costs at all COP combinations, followed by the vapor compression, steam, and gas turbine exhaust driven systems. As such, the flue gas powered system was identified as the most economic system to reduce the LCOE from the baseline case for a wide range of COP combinations at high tolerable costs for these two locations.
Open Access
Analysis and control co-design optimization of natural gas power plants with carbon capture and thermal energy storage
(Colorado State University. Libraries, 2022) Vercellino, Roberto, author; Herber, Daniel R., advisor; Bandhauer, Todd M., advisor; Quinn, Jason C., committee member; Coburn, Timothy C., committee member
In this work, an optimization model was constructed to help address important design and operation questions for a novel system combining natural gas power plants (NGCC) with carbon capture (CC) and hot and cold thermal energy storage (TES) units. The conceptualization of this system is motivated by the expected evolution of the electricity markets towards a carbon-neutral electricity grid heavily penetrated by renewable energy sources, resulting in highly variable electricity prices and demand. In this context, there will be an opportunity for clean, flexible, and cheap fossil fuel-based generators, such as NGCC plants with CC, to complement renewable generation. However, while recent work has demonstrated that high CO2 rates are achievable, challenges due to high capital costs, flexibility limitations, and the parasitic load imposed by CC systems onto NGCC power plants have so far prevented its commercialization. Coupling TES units with CC and NGCC would allow to store thermal energy into the TES units when the electricity prices are low, either by subtracting it from the NGCC or by extracting it from the grid, and to discharge thermal power at peak prices, from the hot storage (HS) to offset the parasitic load of the CC system and from the cold storage (CS) for chilling the inlet of the NGCC combustion turbine and increase the output of the cycle beyond nominal value. For the early-stage engineering studies investigating the feasibility of this novel system, a control co-design (CCD) approach is taken where key plant sizing decisions (including storage capacities and energy transfer rates) and operational control (e.g., when to store and use thermal energy and operate the power plant) are considered in an integrated manner using a simultaneous CCD strategy. The optimal design, as well as the operation of the system, are determined for an entire year (either all-at-once or through a moving prediction horizons strategy) in a large, sparse linear optimization problem. The results demonstrate both the need for optimal operation to enable a fair economic assessment of the proposed system as well as optimal sizing decisions due to sensitivity to a variety of scenarios, including different market conditions, site locations, and technology options. After detailed analysis, the technology shows remarkable promise in that it outperforms NGCC power plants with state-of-the-art CC systems in many of the scenarios evaluated. The best overall TES technology solution relies on cheap excess grid electricity from renewable sources to charge the TES units -- the HS via resistive heating and the CS through an ammonia-based vapor compression cycle. Future enhancements to the optimization model are also discussed, which include additional degrees of freedom to the CC system, adapting the model to evaluate other energy sources and storage technologies, and considering uncertainty in the market signals directly in the optimization model.
Open Access
Economic impact of thermal energy storage on natural gas power with carbon capture in future electricity markets
(Colorado State University. Libraries, 2022) Markey, Ethan James, author; Bandhauer, Todd M., advisor; Quinn, Jason C., committee member; Herber, Daniel R., committee member
As policies evolve to reflect climate change goals, the use of fossil fuel power plants in expected to change. Specifically, these power plants will need to incorporate carbon capture and storage (CCS) technologies to significantly reduce their carbon emissions, and they will be operated flexibly to accommodate the growing concentration of renewable energy generators. Unfortunately, most CCS technologies are very expensive, and they impose a parasitic heat load on the power plant, thereby decreasing net power output and the ability to operate flexibly. This research evaluated the economic potential of using hot and cold thermal energy storages (TES) to boost the net power output and flexibility of a natural gas combined cycle (NGCC) power plant with CCS capabilities. Resistively heated hot TES was used to offset the parasitic heat load imposed on the NGCC by the CCS unit while vapor compression cooled cold TES was used to chill the inlet air to the power plant. Thermodynamic models were created for the base NGCC + CCS power plant, the hot TES equipment, and the cold TES equipment, to determine key performance and cost parameters such as net power output, fuel consumption, emissions captured, capital costs, and operational costs. These parameters were then used to simulate the operation of the power plant with and without the TES technologies in accordance with fourteen electricity pricing structures predicted for different future electricity market scenarios. The difference in net present value (NPV) between the base NGCC + CCS power plant and power plant with the TES technologies was used as the primary economic metric in this analysis. The NPV benefit from increased revenue due to TES utilization was found to outweigh the NPV penalty from the additional capital costs. This positive economic result was attributed to the low cost of the TES equipment and the ability to charge the storages using cheap electricity from high levels of renewable output. The results have shown that hot TES increased NPV in 12 of 14 market scenarios while the cold TES increased NPV in 14 of 14 market scenarios. A combination of both hot and cold TES yielded the largest increases in NPV.
Open Access
Effect of phase change material on dynamic thermal management performance for power electronics packages
(Colorado State University. Libraries, 2021) Hollis, Justin Ralph, author; Bandhauer, Todd M., advisor; Marchese, Anthony, committee member; Young, Peter, committee member
High temperature silicon carbide (SiC) die are the most critical and expensive component in electric vehicle (EV) power electronic packages and require both active and passive methods to dissipate heat during transient operation. The use of phase change materials (PCMs) to control the peak junction temperature of the SiC die and to buffer the temperature fluctuations in the package during simulated operation is modeled here. The latent heat storage potential of multiple PCM and PCM composites are explored in both single-sided and dual-sided package configurations. The results of this study show that the addition of phase change material (PCM) into two different styles of power electronics (PE) packages is an effective method for controlling the transient junction temperatures experienced during two different drive cycles. The addition of PCM in a single-sided package also serves to decrease temperature fluctuations experienced by the package as a whole and may be used to reduce the necessary number of SiC die required to divide the heat load, lowering the overall material cost and volume of the package by over 50%. PCM in a single-sided package may be nearly as effective as the double-sided cooling approach of a dual-sided package in the reduction of both peak junction temperature of SiC as well as controlling temperature variations between package layers.
Open Access
Generalized pressure drop and heat transfer correlations for jet impingement cooling with jet adjacent fluid extraction
(Colorado State University. Libraries, 2022) Hobby, David Ryan, author; Bandhauer, Todd M., advisor; Olsen, Daniel B., committee member; Prawel, David, committee member; Venayagamoorthy, Karan, committee member
Jet impingement technologies offer a promising solution to thermal management challenges across multiple fields and applications. Single jets and conventional impinging arrays have been studied extensively and are broadly recognized for achieving extraordinary local heat transfer coefficients. This, in combination with the versatility of impinging arrays, has facilitated a steady incline in the popularity of jet impingement investigations. However, it is well documented that interactions between adjacent jets in an impinging array have a debilitating effect on thermal performance. Recently, in an attempt to mitigate the jet interference problem, a number of researchers have created innovative jet impingement solutions which eliminate crossflow effects by introducing fluid extraction ports interspersed throughout the impinging array. This novel adaptation on classical impinging arrays has been shown to produce dramatically improved thermal performance and offers an excellent opportunity for future high-performing thermal management devices. The advent of jet-adjacent fluid extraction in impinging arrays presents a promising improvement to impingement cooling technologies. However, there have been very few investigations to quantify these effects. Notably, the current archive of literature is severely lacking in useful, predictive correlations for heat transfer and pressure drop which can reliably describe the performance of such impinging arrays. Steady-state heat transfer and adiabatic pressure drop experiments were conducted using nine unique geometric configurations of a novel jet impingement device developed in this work. This investigation proposes novel empirical correlations for Darcy friction factor and Nusselt number in an impingement array with interspersed fluid extraction ports. The correlations cover a broad range of geometric parameters, including non-dimensional jet array spacing (S/Dj) ranging from 2.7 to 9.1, and non-dimensional jet heights (H/Dj) ranging from 0.31 to 4.4. Experiments included jet Reynolds numbers ranging from 70 to 24,000, incorporating laminar and turbulent flow regimes. Multiple fluids were tested with Prandtl numbers ranging from 0.7 to 21. The correlations presented in this work are the most comprehensive to date for impinging jet arrays with interspersed fluid extraction. Nusselt number was found to be correlated to impinging jet Reynolds number to the power of 0.57. The resulting correlation was able to predict 93% of experimental data within ±25%. During adiabatic pressure drop experiments, multiple laminar-turbulent flow transition regions were identified at various stages in the complex jet impingement flow path. The proposed Darcy friction factor correlation was separated into laminar, turbulent, and transition regions and predicted experimental data with a mean absolute deviation of 20%. The heat transfer and pressure drop correlations proposed in this investigation were used in a follow-on optimization study which targeted an exemplary impingement cooling application. The optimization study applied core experimental findings to a microchip cooling case study and evaluated the effects of geometry, flow, and heat load parameters on cooling efficiency and effectiveness. It was discovered that reducing non-dimensional jet height results in all-around improved cooling performance. Conversely, low non-dimensional jet spacing results in highly efficient but less effective solutions while high non-dimensional jet spacing results in effective but less efficient cooling.
Open Access
High efficiency air delivery system for solid oxide fuel cell power generation
(Colorado State University. Libraries, 2024) Mitchel, Lars Jared-Brian, author; Bandhauer, Todd M., advisor; Windom, Bret C., committee member; Cale, James, committee member
Distributed power generation systems can be used in the electric grid to reduce peak loads, raise power quality, and reduce/eliminate transmission losses. One distributed energy system with distinct advantages is a Solid Oxide Fuel Cell (SOFC) integrated with an Internal Combustion Engine (ICE) which has the capability to operate at electric efficiencies as high as 70%. This research aimed to produce and test a high efficiency air delivery system that supports the SOFC-ICE to generate power on the scale of 80 kW. The air balance of plant (BOP) system utilized low speed scroll-type rotating compressors and brazed plate and frame heat exchangers for efficient preheating. The scroll compressors were modeled in GT-Suite and the remaining air BOP system was modeled with thermodynamic and heat transfer equations. Then testing was done on the compressors and heat exchangers to validate the model so that the air BOP system performance could be accurately predicted within a range of conditions. Both compressors were run from a range of 20 g/s to 60 g/s with the heat through the system being swept from 100°C to 600°C which yielded compressor efficiencies over 60% and heat exchanger effectiveness over 0.90. The validated model was then used to make predictions about system performance at on and off-design conditions.
Open Access
High heat flux phase change thermal management of laser diode arrays
(Colorado State University. Libraries, 2016) Bevis, Taylor A., author; Bandhauer, Todd M., advisor; Williams, John D., committee member; De Miranda, Michael A., committee member
Laser diodes are semiconductor devices than convert electrical work into light emitted at a specific wavelength over a small spectral bandwidth at a high intensity. A small array of laser diodes can be fabricated on an internally reflective bar that emits light through one edge. If a large number of edge-emitting bars are packed closely together and arrayed to emit light towards the same target, a very high brightness (i.e., light power per unit area) can be achieved, which is useful for a wide range of applications, including advanced manufacturing, inertial confinement fusion energy, and pumping laser gain media. The principle limit for achieving higher brightness is thermal management. State of the art laser diodes generate heat at fluxes in excess of 1 kW cm-2 on a plane parallel to the light emitting edge. As the laser diode bars are packed closer together, it becomes increasingly difficult to remove the heat generated by the diodes in the diminishing space between neighboring diode bars. In addition, the wavelength of the laser diode changes with temperature, and minimizing the variation in wavelength among diodes in very large arrays is very challenging. Thermal management of these diode arrays using conduction and natural convection is practically impossible, and therefore, some form of forced convective cooling must be utilized. Cooling large arrays of laser diodes using single-phase convection heat transfer has been investigated for more than two decades by multiple investigators. Unfortunately, either large temperature increases or very high flow velocities must be utilized to reject heat to a single phase fluid, and the practical threshold for single phase convective cooling of laser diodes appears to have been reached. In contrast, liquid-vapor phase change heat transport can occur with a negligible increase in temperature and, due to a high enthalpy of vaporization, at comparatively low mass flow rates. However, there have been no prior investigations at the conditions required for high brightness edge emitting laser diode arrays: heat fluxes >1 kW cm-2 and a volumetric heat generation rate >10 kW cm-3. In the current investigation, flow boiling heat transfer at heat fluxes up to 1.1 kW cm-2 was studied in a microchannel heat sink with plurality of very small channels (45 × 200 mm) for a phase change fluid (R134a). The high aspect ratio channels (5:1) were manufactured using MEMS fabrication techniques, which yielded a large heat transfer surface area to volume ratio in the vicinity of the laser diode. To characterize the heat transfer performance, a test facility was constructed that enabled testing over a wide range of fluid properties and operating conditions. Due to the very small geometric features, significant heat spreading was observed, necessitating numerical methods to determine the average heat transfer coefficient from test data. The heat transfer correlations were predicted well (mean absolute error, MAE, of ±38.7%) by the correlation of Bertsch et al. This correlation was modified to account for the effect of fin conduction, in the calculation of average heat flux, which yielded an improved MAE of ±8.1%. The new correlation was then used to investigate a range of potential phase change fluids and an alternative microchannel geometry for the laser diode phase change heat exchanger. Finally, a next generation test section design and operating conditions are proposed which are expected to improve diode array brightness up to 5.3× over the state of the art with R134a. If ammonia is used at the working fluid instead of R134a, the brightness could potentially increase by more than 17× over the state of the art.
Open Access
Investigation of liquid cooling on M9506A high density Keysight AXIE chassis
(Colorado State University. Libraries, 2021) Gilvey, Zachary Howard, author; Bandhauer, Todd M., advisor; Marchese, Anthony, committee member; Simske, Steve, committee member
Forced convection air-cooled heat sinks are the dominant cooling method used in the electronics industry, accounting for 86% of high-density cooling in data centers. However, the continual performance increases of electronics equipment are pushing these air-cooled methods to their limit. Fundamental limitations such as acoustics, cooling power consumption, and heat transfer coefficient are being reached while processor power consumption is steadily rising. In this study, a 4U, 5-slot, high density computing box is studied to determine the maximum heat dissipation in its form factor while operating at an ambient air temperature of 50°C. Two liquid cooling technologies were analyzed in this effort and compared against current state-of-the-art air-cooled systems. A new configuration proposed using return jet impingement with dielectric fluid FC72 directly on the integrated circuit die shows up to a 44% reduction in thermal resistance as compared to current microchannel liquid cooled systems, 0.08 K W-1, vs 0.144 K W-1, respectively. In addition, at high ambient temperatures (~45°C), the radiator of the liquid cooled system accounts for two thirds of the thermal resistance from ambient to junction temperature, indicating that a larger heat exchanger outside the current form factor could increase performance further. The efficiency of the chips was modeled with efficiency predictions based on their junction temperature. On a system level, the model showed that by keeping the chassis at 25°C ambient, the overall power consumption was significantly lower by 500W. Furthermore, the failure rate was accounted for when the chip junction temperature was beyond 75°C. FC72 jet impingement on the die showed the best performance to meet the system cooling requirements and kept the chips below 75°C for the highest ambient temperatures but consumed the most pumping power of all of the fluids and configurations investigated. The configuration with microchannels bypassing TIM 2 showed near the same performance as jet impingement with water on the lid and reduced the junction temperature difference by 5°C when compared to baseline. When the fluid was switched from water to a water glycol 50/50 mixture, an additional thermal resistance of 0.010 K W-1 was recorded at the heat sink level and a higher mass flow rate was required for the GC50/50 heat exchanger to achieve its minimum thermal resistance.
Open Access
Modeling and design of a power boosted turbo-compression cooling system
(Colorado State University. Libraries, 2021) Roberts, Nickolas Richard, author; Bandhauer, Todd M., advisor; Quinn, Jason C., committee member; Cale, James, committee member
Waste heat recovery technologies have the potential to reduce fuel consumption and address increased electricity and cooling demands in shipboard applications. Existing thermally driven power and cooling technologies are simply too large to be installed on ships where space for new equipment is extremely limited. This study addresses major shipboard challenges through the modeling and design of a volume optimized turbo-compression cooling system (TCCS). The TCCS is driven by low-grade waste heat in the shipboard diesel generator set jacket water and lubrication oil and was designed to be a drop-in replacement of electric chiller systems. A case study of a marine diesel generator set and electric chiller is presented, including annual engine loading and seawater temperature profiles. Three TCCS integration options and five working fluids (R134a, R1234ze(E), R1234yf, R245fa, R515a) were evaluated over the range of case study conditions using a fixed heat exchanger effectiveness thermodynamic model. The hybrid thermally and electricity driven "power boosted" TCCS reduced electricity consumption for cooling by over 100 kWe. Plate and frame heat exchanger models were used to size and optimize the system to fit within the volume of a commercial centrifugal chiller of equal cooling capacity. The system used R134a, provided 200-tons of cooling, and had an electric coefficient of performance (COP) of 9.84 at the design conditions. Optimized heat exchanger and pipe geometries were fixed, and the model was run over the range of case study conditions to determine annual fuel savings of 92.1 mt yr-1 and a weighted average generator set power density improvement of 11.0%. Heat exchangers, turbomachinery, and piping were solid modeled to demonstrate that the system fits within the required footprint (40.6 ft2) and volume (267 ft3). The designed system was estimated to cost $295,036 in equipment and $442,554 in total installed costs. The resulting payback period was 5.77 years while operating for only 3,954 hours per year. Over a 15-year period, the net present value and internal rate of return were $176,734 and 16%, respectively.
Open Access
Plate frame and bar plate evaporator model validation and volume minimization
(Colorado State University. Libraries, 2019) Simon, John Robert, III, author; Bandhauer, Todd M., advisor; Quinn, Jason, committee member; Carter, Ellison, committee member
Vapor compression chillers are the primary cooling technology for large building applications. Chillers have a large up front capital cost, with the heat exchangers accounting for the majority of the cost. Heat exchanger cost is a function of size, and therefore, a reduction in heat exchanger size can be correlated to a reduction in chiller capital cost. Few investigations focus on the reduction in heat exchanger size for vapor compression systems. Therefore, this investigation aims to decrease the size of chillers by predicting the minimum evaporator volume for a fixed performance. Only the evaporator was minimized because it was assumed that a similar process could be performed for the condenser in a future study. The study focused on a simple vapor compression cycle, and implemented high fidelity heat exchanger models for two compact heat exchanger types: brazed bar plate and gasketed plate and frame. These models accounted for variable fluid properties, phase change, and complex geometries within the evaporator core. The models used in this investigation were developed based on liquid-coupled evaporators in an experimental vapor compression system, and validated using collected data. The bar plate model was validated based on sizing and pressure drop to mean absolute errors of 14.2% and 14.0%, respectively. The plate frame model was validated for sizing to mean absolute errors equal to 7.9%; however, due to measurement uncertainty, pressure drop was not validated. The heat exchanger models were integrated into a simple vapor compression cycle model to determine the minimum required evaporator volume. Both heat exchanger types, in parallel and counter flow arrangements were minimized in this study. The minimum volume was achieved by varying the ratio between core length and number of channels. It was found that for both heat exchanger types, the parallel flow arrangement resulted in a smaller volume than the counter flow arrangement. Furthermore, the bar plate heat exchanger resulted in an optimum volume 91% smaller than the plate frame counterpart.
Open Access
Prediction and mitigation strategies for the transient thermal performance of low thermal resistance microchannel evaporators
(Colorado State University. Libraries, 2024) Anderson, Caleb Del, author; Bandhauer, Todd M., advisor; Venayagamoorthy, Karan, committee member; Windom, Bret, committee member; Wise, Daniel, committee member
Microchannel flow boiling heat transfer offers an effective thermal management solution for high heat flux microelectronic devices such as laser diodes. The high heat transfer rates, nearly isothermal flow conditions, high surface area-to-volume ratios, and lower required pumping powers facilitate smaller component systems while more efficiently cooling devices and reducing packaging stresses associated with thermal expansion when compared with single-phase cooling systems. Although much study has been dedicated to optimizing steady state flow boiling performance, the typically highly transient operation of these microelectronic devices leads to unsteady spikes in heat flux and, subsequently, in device temperatures and may potentially exacerbate flow instabilities present at steady state. The low thermal capacitance of the package that often accompanies the low thermal resistance of microchannel evaporators increases the potential for device damage and failure since large temperature swings are more likely. Predicting and mitigating the transient response of a low thermal resistance microchannel evaporator is paramount to practical application as a thermal management technique. In this work, temperature, pressure, and flow visualization measurements during stepped heat loads on two, low thermal resistance, microchannel evaporators revealed the presence of severe vapor backflow, large temperature overshoots, and impacted flow dynamics at the onset of nucleate boiling (ONB) despite the stability and high performance of the device under steady state heating conditions. These overshoots were exacerbated with higher heating rates and reduced subcooling but were generally improved with higher flow rates. Applying a slower heating rate greatly improved the transient thermal response, reducing both peak temperature and vapor backflow. Channel and inlet orifice geometry were found to greatly impact the performance, with smaller channels and smaller orifice-to-channel restriction ratios resulting in intensified vapor backflow and temperature spikes, despite offering improved steady state performance. A computational model embedded in a reduced order design tool was created and validated with the experiments. Two separate models were created due to the different transient conditions observed between the two tested microchannel evaporators. The models allow predictive modeling of these evaporators to determine the impact of the transient heating behavior on microchannel evaporator devices. The effect of incorporating gallium-based, solid-liquid Phase Change Materials (PCMs) was studied semi-empirically by simulating the performance of a virtual test section with predicted properties of a microchannel evaporator combined with gallium and gallium-composite foam PCMs. Properties of the PCMs were estimated and used to predict the test section thermal response under a range of PCM volumes. Models assuming single phase performance were conducted initially and the resulting predicted heat rate to the fluid applied experimentally to the test section heater to determine the temperature response. It was found that the simulated addition of the PCM slightly reduced the ONB temperatures but did not affect the peak temperature experienced by the device. The applied heating rate, however, did not consider the increased thermal resistance to the refrigerant fluid during the transient vapor backflow regime. The effect was most pronounced in the PCMs with the largest exposed surface area and with thermal conductivity-enhanced PCM composites comprised of gallium infiltrated in a copper foam matrix. Additional PCM models utilizing the transient flow boiling model were subsequently run on a series of representative heat load test cases comparing the performance of a gallium-nickel and gallium-copper composite with similar dimensions to the earlier simulations. Key assumptions included the same ONB temperatures and vapor backflow conditions as the baseline cases without PCMs. The models predicted significantly lowered peak device temperatures due to the heat absorption into the PCM during the transient vapor backflow phase. The effect was dependent on the PCM thickness, latent heat, and thermal conductivity, reflecting trade-offs in material. In addition, peak temperature variability observed experimentally across multiple trials at the same nominal testing conditions was greatly reduced with the inclusion of a PCM.
Open Access
Technoecomonic optimization and working fluid selection for an engine coolant driven turbo-compression cooling system
(Colorado State University. Libraries, 2018) Young, Derek Nicholas, author; Bandhauer, Todd M., advisor; Quinn, Jason C., committee member; Burkhardt, Jesse, committee member
The abundance of low grade waste heat presents an opportunity to recover typically unused heat energy and improve system efficiencies in a number of different applications. This work examines the technoeconomic performance of a turbo-compression cooling system designed to recover ultra-low grade (≤ 100°C) waste heat from engine coolant in large marine diesel engine-generator sets. In addition, five different working fluids (R134a, R152a, R245fa, R1234ze(E), and R600a) were studied for this application to better understand the effects of fluid properties on technical and economic system performance. A coupled thermodynamic, heat exchanger, and economic model was developed to calculate the payback period of the turbo-compression cooling system. Then, the payback period was minimized by optimizing the surface area of the heat exchangers by varying the effectiveness of the heat exchangers. The sensitivity of the payback period to the heat exchanger effectiveness values was quantified to inform future design considerations. The turbo-compression cooling system with R152a had the lowest payback period of 1.67 years and an initial investment of $181,846. The R1234ze(E) system had the highest cooling capacity of 837 kW and the highest overall COP of 0.415. The R152a system provided cooling for $0.0060 per kWh which was nearly 10 times cheaper than the cost of cooling provided by a traditional electrically driven vapor compression system onboard a marine vessel.
Open Access
Technoeconomic analysis of a steam generation system with carbon capture
(Colorado State University. Libraries, 2019) Giugliano, Luke, author; Bandhauer, Todd M., advisor; Jathar, Shantanu, committee member; Tong, Tiezheng, committee member
Industrial steam generation consumes large amounts of natural gas (NG) and contributes significantly to CO2 emissions. Existing boiler technology is relatively inefficient, and its continued adoption could potentially be hampered by carbon emissions taxes due to the difficulty in CO2 separation from the dilute exhaust gas stream. This paper presents an alternative approach to steam generation that combines a membrane reactor (MR) to produce hydrogen from steam methane reforming (SMR), resulting in a concentrated CO2 exhaust. The performance of the system is evaluated using a coupled thermodynamic and technoeconomic analysis of an industrial-scale SMR plant to produce hydrogen in a MR used primarily for the purpose of steam generation (SG). The proposed SMR-MR-SG system converts NG to clean-burning hydrogen (H2), burns H2 to generate steam, and captures and concentrates CO2. Unused NG and H2 are recycled back into the system with uncaptured CO2 to increase efficiency. The SMR-MR-SG is compared to two baseline systems: a natural gas industrial boiler system (BS), and the same boiler system with integrated CO2 capture (BSC). The SMR-MR-SG improves on the BS by increasing efficiency from 86% to 97% and reducing NG and water consumption by 14% and 55%, respectively. Additionally, the SMR-MR-SG uses cryogenic separation and gas recycling to completely eliminate CO2 emissions with a 3.0% energy penalty, much less than comparable systems with carbon capture. The SMR-MR-SG has a capital cost about three times the BS and twice the BSC, but makes up for it quickly with reducing operating costs. Using a conservative prediction of carbon tax, the SMR-MR-SG has a payback period of 1.86 and 1.26 years and a discounted lifetime cost reduction of 42% and 43% relative to the BS and BSC, respectively. A sensitivity analysis showed that the results are most heavily influenced by the amount of carbon tax implemented in the future, with no carbon tax corresponding to a payback period of 8.05 years relative to the BS. The results of this modelling study show that the SMR-MR-SG could be a direct replacement for common industrial boiler systems as a new, efficient, and clean steam generation system.
Open Access
Thermal management of discretized heaters using CuW microchannel heat sinks and FC3283 for laser diode applications
(Colorado State University. Libraries, 2024) Amyx, Isabella Gascon, author; Bandhauer, Todd M., advisor; Dumitrache, Ciprian, committee member; Venayagamoorthy, Subhas Karan, committee member
Single-phase cooling using microchannel heat sinks (MCHS) has become a popular approach for overcoming the thermal challenges associated with high-powered microelectronic devices. Thermal management is one of the largest barriers to higher power densities in electronics and frequently limits overall device performance. The implementation of forced convective cooling via single-phase liquid cooling in MCHS reduces the thermal resistance resulting in lower device temperatures at high-power conditions, which can decrease the package size and extend the lifespan of devices. The goal of this effort was to investigate practical cooling solutions for laser diode bars. This study examined the effectiveness of a copper tungsten (CuW) microchannel heat sink paired with a dielectric coolant (FC3283) for dissipating both discrete and uniform heat fluxes up to 600 W/cm2 across a 0.25 cm2 surface area through a numerical and experimental study. CuW was chosen as the MCHS material because it is thermal expansion matched to GaAs, which is a common laser diode substrate. FC3283 serves as a dielectric coolant that is compatible with power electronics cooling. Reasonable agreement was found between the numerical model and the experimental results. The resulting thermal resistance ranged from 0.15 cm2 K/W at the highest flow rate to 0.26 cm2 K/W at the lowest flow rate. The resulting thermal performance from this study proved to be insufficient for maintaining optimal temperatures for laser diode applications. Using the validated model, cooling fluid and geometry modifications proved to have a significant impact on the heat transfer coefficients. This study revealed the importance of considering discrete heat sources separately from uniform heat sources and proved that CuW microchannels can be a promising cooling option toward future advancements of laser diode bars and other high-power microelectronics when using a low viscosity and high thermal conductivity, dielectric cooling fluid and an optimized geometry.
Open Access
Transient modeling of an ambient temperature source centrifugal compressor steam generating heat pump
(Colorado State University. Libraries, 2024) Ryan, Kelly Patrick, author; Bandhauer, Todd M., advisor; Windom, Bret C., committee member; Herber, Daniel R., committee member
As the US electricity grid transitions to renewable power generation, electrifying end-uses that are currently fossil fuel fired presents a promising path towards deeper decarbonization, and next generation high temperature heat pumps are a viable solution for decarbonizing fossil fuel fired steam boilers. These next-gen systems require a higher degree of design complexity and more finely tuned control strategies than existing systems, and therefore can benefit from complex transient modeling that has not been previously implemented for these types of systems. A transient study of a novel steam-generating heat pump with steam delivery temperature of 150°C was conducted using physics-based simulation software. The model used manufacturer supplied performance data to calibrate each competent, providing reliable preliminary validation to the model. The model was set up to match the configuration of a prototype system constructed at Colorado State University. It was found that the results of the transient model agreed well with the steady state model of the heat pump at the design point. Transient conditions including cold startup to full load operation, full load operation to part load operation, and part load operation back to full load operation were modeled and the system was found to operate with stability. Compressor and expansion valve performance was investigated. Compressors were found to operate within their performance maps for both steady and transient operation. A control strategy was developed for the expansion valves to prevent liquid ingestion when transitioning to turndown operation. The system COP was predicted for both full and part load operation and in transition between them.
Open Access
Viability and sustainability of desalinating produced water in the oil and gas industry
(Colorado State University. Libraries, 2025) Grauberger, Brandi M., author; Bandhauer, Todd M., advisor; Tong, Tiezheng, advisor; Sharvelle, Sybil, committee member; Quinn, Jason C., committee member
Unconventional oil and gas extraction consumes considerable amounts of water, with up to 11 million gallons of freshwater used for the fracturing of a single well. Millions of gallons can come back to the surface of a well as flowback and produced waters, which are collected and disposed of through deep well injection. Water reallocation and reduction of resource waste can be aided by treating produced water from these operations but is rarely practiced. In particular, treating produced water to zero-liquid-discharge allows for management of dry wastes and generates a clean water source as its only other product. Eliminating the disposal of brines from produced water management would eliminate the need for deep well injection, which has shown to be an unsustainable option for produced water management. A major barrier to produced water treatment is the cost and availability of energy for treatment. Other barriers arise from an incomplete understanding of the system. Specifically, environmental and social impacts of produced water treatment are not understood. For example, it is not known if the discharge of treated produced water will have a negative effect on drinking water supplies or flow of rivers and streams. Without solving these challenges, produced water will continue to be disposed into injection wells, wasting the potential to reduce freshwater consumption, and further threatening seismic stability and access to freshwater reserves in oil and gas producing regions. This work completes three major analyses to understand the potential of produced water desalination. First, the accessibility of waste heat from the oil and gas industry, which is limited due to spatial and temporal disparities in waste heat and produced water production, was quantified and compared to energy requirements for produced water treatment. The results show that there is potential for waste heat utilization by membrane distillation, a thermal-membrane desalination technology option, in the oil and gas industry for produced water desalination with appropriate waste heat storage system integrations. The next major evaluation is of the economic and environmental impacts for multiple zero liquid discharge desalination options. Economic results show that the existing technology of mechanical vapor compression is difficult to reliably challenge, in terms of cost. However, environmental emissions can be much improved when using waste heat as an energy source for desalination or when treating with electrodialytic crystallization. Finally, this work evaluates options for zero liquid discharge desalination in the oil and gas industry using a triple bottom line sustainability framework. This framework considers the economic, environmental, and social competitiveness of technologies in multiple stakeholder-preference scenarios, which weight the importance of the three categories in different ratios. Results show that the use of waste heat is paramount to the consideration of membrane distillation as a technology option in the oil and gas industry. Further results show that the comprehensive consideration of economic, environment, and social impacts provide context to overall fit of technology options in the oil and gas industry. More detail of each major objective of this work are shared in the following paragraphs. The use of waste heat has been proposed to reduce the energy footprint of membrane distillation for flowback and produced water treatment. However, its feasibility has not been fully understood for produced water treatment. Accordingly, the third chapter of this work performed systematic assessments through thermodynamic modelling of waste heat capture, storage, and transportation for decentralized produced water treatment at well pads located in the Denver-Julesburg Basin. A wide range of sensible, phase-change, and thermo-chemical storage materials were assessed for their effectiveness at the utilization of waste heat from on-site hydraulic fracturing engines and natural gas compressor stations, in order to overcome the temporal or spatial mismatch between waste heat availability and produced water generation. Results show that the type of storage material being used can have a high impact on the efficiency of waste heat utilization and the treatment capacity of membrane distillation. Sensible storage materials only utilize sensible heat capacities, while phase-change materials have improved performance because they are able to additionally store latent heat. However, sensible and phase-change storage materials lose 11–83% of heat due to conversion inefficiencies caused by their changing temperatures. Thermo-chemical materials, on the other hand, have the highest potential for use because they collect and release heat at constant temperatures. Three thermo-chemical storage materials (magnesium sulfate, magnesium chloride, and calcium sulfate) were identified as those with the best efficiencies due to their elevated discharge temperatures which reduce the energy consumption of membrane distillation. In addition, these materials have high volumetric energy storage density, which enables capture and transportation of waste heat from remote locations such as natural gas compressor stations to the well sites, yielding up to 70% reduction in transportation costs relative to moving produced water to centralized treatment facilities at natural gas compressor stations. The third chapter of this work demonstrates the importance of selecting appropriate energy storage material for leveraging low-grade thermal energy such as waste heat to power membrane distillation for decentralized wastewater treatment. With more certainty given in the possibility and logistics of using waste heat for the membrane distillation system in the oil and gas industry, further analysis was needed to evaluate new technologies with existing brine desalination technologies in terms of replacement potential. Four technologies were considered: mechanical vapor compression with a crystallizer, electrodialytic crystallization, membrane distillation with a crystallizer using electrical heating, and membrane distillation with a crystallizer using waste heat. The fourth chapter of this work evaluates the economic and environmental competitiveness of said technologies. Zero liquid discharge desalination has garnered considerable attention for its potential to mitigate the impact of water scarcity while minimizing environmental consequences associated with ill-managed brine wastes. In the fourth chapter of this work, the economic and environmental competitiveness of an electrodialytic crystallization system designed in recent works was evaluated. It was found that when compared to existing zero liquid discharge technologies, electrodialytic crystallization could compete economically with the potential to reduce costs of zero liquid discharge by over 60% in optimal conditions. However, this high economic competitiveness is not consistent in more conservative operating scenarios. Furthermore, electrodialytic crystallization has 42% lower global warming potential than existing technologies. Scenario and sensitivity assessments completed in this chapter identify the operating parameters of electrodialytic crystallization that greatly affect economic and environmental impacts. Most notably, improvements to the cost and performance of ion exchange membranes will provide the highest benefit to electrodialytic crystallization competitiveness. With appropriate concentration of future research on these high-impact areas, the economic and environmental viability of electrodialytic crystallization should continue to increase in the coming years and electrodialytic crystallization will compete with existing zero liquid discharge technologies to provide a low-cost, efficient, and low-impact replacement to existing technologies. This chapter also shows the limited viability of membrane distillation with a crystallizer in replacing existing zero liquid discharge technologies due to high costs. In either case of electrical heating or waste heat use for membrane distillation, energy costs or infrastructure costs stemming from high energy intensity of membrane distillation result in costs far exceeding those of existing technologies. Through economic and environmental analysis expand the understanding of the potential for technologies to reach industrial application, further analysis can be leveraged to evaluate the fit of technologies into specific applications based on multiple stakeholder perspectives of the system needs. In the fifth chapter of this work, technology options were qualitatively evaluated under a stakeholder-informed triple bottom line sustainability perspective Chapter 5 of this work evaluates proposed technical solutions to produced water desalination and considers the additional economic, environmental, and social barriers that exist within the oil and gas industrial system. The consideration of these three impact areas (i.e., economic, environmental, and social) are defined as the triple bottom line considerations. The drivers, pressures, states, impacts and responses framework, first developed by the European Environmental Agency and later updated by the United States Environmental Protection Agency, was used to support the work of chapter 5 by organizing broad system considerations collected from stakeholder-generated literature into an orderly and approachable list of system indicators to evaluate technology compatibility within the applied system. System indicators are quantified, and overall system compatibility scores are calculated based on a variety of stakeholder preference scenarios. The results show that, given current models, emerging technologies have the potential to compete with existing zero liquid discharge technologies when applied to the oil and gas industry for produced water desalination under applications where stakeholders have low economic preference. Careful consideration of stakeholder preferences is necessary because technologies rank differently based on weightings of economic, environmental, and social impact importance. In summary, through thermodynamic and system modeling, techno-economic analysis, life cycle assessments, and triple bottom line sustainability considerations, four zero liquid discharge desalination technology options for the oil and gas industry (i.e., mechanical vapor compression with a crystallizer, electrodialytic crystallization, membrane distillation with a crystallizer using electrical heating, and membrane distillation with a crystallizer using waste heat) were evaluated for the Denver-Julesburg Basin in Northern Colorado. Overall, development of ion exchange membranes with improved performance for electrodialytic crystallization and developments in lowering membrane distillation energy intensity will determine the future economic competitiveness of electrodialytic crystallization and membrane distillation, respectively, as desalination technology options over mechanical vapor compression. However, when evaluating triple bottom line sustainability, results show potential for applications where there is lower preference to economic performance. In such applications, electrodialytic crystallization and membrane distillation with a crystallizer using waste heat consistently compete with mechanical vapor compression-based systems. Further understanding of the applied system needs and stakeholder preferences will determine overall applicability of technologies into the system.
Open Access
Waste heat driven cooling at beef processing facilities
(Colorado State University. Libraries, 2021) Colosimo, Samuel Paul, author; Bandhauer, Todd M., advisor; Jathar, Shantanu, committee member; Dillon, Jasmine, committee member
Waste heat recovery technologies present an opportunity to utilize typically wasted energy to reduce overall energy consumption by producing mechanical work, electricity, heating, or cooling. In this study, the technoeconomic performance of a turbo-compression cooling system (TCCS) driven by waste heat from boiler exhaust gas produced at beef processing facilities is investigated. The cooling produced by the TCCS is integrated to the primary refrigeration system (PRS) of a beef processing facility to provide condenser subcooling, which enhances the performance of the PRS and produces refrigeration energy savings. Further savings are produced by rejecting condenser heat from the TCCS to feedwater entering the boiler, allowing for a reduction in boiler natural gas consumption. Process level natural gas and water data was collected at a beef processing plant and used to calculate waste heat availability and boiler water flow rate. TMY3 weather data for five cities was used to model a beef plant refrigeration system with a condenser cooling tower. To justify the installation of a TCCS, the performance and economics of the system are compared to three technologies: an electrically driven dedicated mechanical subcooler (DMS), an organic Rankine cycle (ORC), and a feedwater economizer (FWE). The results of this study show that a TCCS used to subcool the PRS yielded the highest annual savings of the four technologies. A coupled thermodynamic, heat transfer, and economic model was produced to determine the capital cost, payback period, and net present value of each technology. Then, an optimization study was carried out for the TCCS, DMS, and ORC to minimize payback period and maximize net present value by varying the effectiveness values of the heat exchangers. The feedwater economizer was found to have the lowest average payback period of 0.92 years at an initial investment cost of $50,815. The average net present value of the FEW across the five cities was found to be $245,000. The ORC had the second lowest payback period of 1.82 years at an initial investment cost of $95,000. To achieve such a low payback period, the ORC produces almost no electricity, generating revenue solely through boiler feedwater heating. The net present value of the ORC was the second lowest at $175,000. The TCCS was found to have the third lowest average payback period of 2.22 years at a capital cost of $328,000, and the highest net present value of $429,000. The DMS was found to have the slowest payback period of 3.88 years at an investment cost of $465,000, and the lowest net present value of $84,000.
Open Access
Waste heat driven turbo-compression cooling
(Colorado State University. Libraries, 2018) Garland, Shane Daniel, author; Bandhauer, Todd M., advisor; Marchese, Anthony J., committee member; Carlson, Kenneth H., committee member
Waste heat recovery systems utilize exhaust heat from power generation systems to produce mechanical work, provide cooling, or create high temperature thermal energy. One waste heat recovery application is to use the exhaust heat from a Natural Gas Combined Cycle Power Plant (NGCC) to drive a heat activated cooling system that can offset a portion of the plant condenser load. There are several heat activated cooling systems available including absorption, adsorption, ORVC, and ejector, but each has disadvantages. One system that can overcome the disadvantages of typical heat activated cooling systems is a turbo-compression cooling system (TCCS). In this system, the exhaust heat enters an organic Rankine cycle at the boiler and vaporizes the fluid that passes through a turbine. The turbine power is directly transferred to a compressor via a hermetically sealed shaft that is made possible by a magnetic coupling. The compressor operates a vapor-compression system which provides a cooling effect in the evaporator. The hermetic seal between the turbine and compressor allows for two separate fluids on the power and cooling cycles, which maximizes the efficiency of the turbine and compressor simultaneously. This study presents a thermodynamic modeling approach that makes system performance predictions for the baseline design case, and for off-design performance conditions. The off-design modeling approach uses turbo-compressor performance maps and a heat exchanger UA scaling methodology to accurately simulate system operation for a broad range of temperatures and cooling loads. A 250 kWth cooling capacity TCCS was constructed and tested to validate the modeling approach. The test facility simulates a 138:1 scaled NGCC power plant configuration in which the TCCS extracts 106°C waste heat from the flue gases and produces a cooling effect that offsets a portion of the NGCC condenser load. The design target for the test facility was to achieve a COP of 2.1 while chilling water from 17.2°C to 16°C at an ambient temperature of 15°C. Although the final design point was not tested for this study due to facility limitations, the off-design performance methodology was utilized to predict the performance for an ambient condition of 27.5°C and power and cooling cycle mass flow rate range between 0.35 kg s-1 - 0.5 kg s-1 and 0.65 kg s-1 – 0.85 kg s-1, respectively. The comparison between the experimental and modeling data suggested strong correlation over the data range presented with a maximum error in COP of only 2.0% among the selected data points. Future experimental data over a larger range of ambient temperatures and system conditions is suggested to further validate the system modeling. Regardless, the results in the present study show that the TCCS compares favorably with other heat activated cooling systems.