Ultra-Efficient Turbo-Compression Cooling
Shane Garland, Achyut Paudel, Torben Grumstrup
Industry Partners: Modine & Barber-Nichols
In thermoelectric power generation, only about 40% of the energy in the fuel is converted into electricity. In other words, the power plant operates at about 40% efficiency. The remainder of the energy is converted to low-grade waste heat that must be removed to maintain the power plant's efficiency. Most power plants use water from nearby rivers, lakes, or the ocean for cooling. The water may pass directly over tubes containing the plant's heated condenser water, and then be returned, warmer, to the original source, or it may be evaporated to carry off the heat in water vapor. In areas with limited water or under drought conditions, dry-cooling systems use air to remove heat from the plant's condenser water. However, present dry-cooling technology reduces the power plant's efficiency and requires costly equipment. With water supplies becoming increasingly strained in many areas, economical dry-cooling approaches that do not reduce the efficiency of power plans are critically needed. Innovative methods to allow cooling below the daytime ambient air temperature and improve heat exchange between air and the plant's recirculating condenser water will provide the keys to ensuring the continued efficiency of power generation while decreasing the burden on water supplies.
The team will develop a thermally powered supplemental cooling system for thermoelectric power plants that will enable dry cooling. The technology features a transformational turbo-compressor and low-cost, high-performance heat exchangers that are currently mass produced for the HVAC industry. To operate, low-grade waste heat from the power plant combustion exhaust gases, or flue gas, is captured and used to power a highly efficient turbo-compressor system. The compressor pressurizes vapor in a refrigeration cycle to remove up to 30% of the power plant cooling load. The cooling system utilizes proprietary technology to maximize the turbo compressor and total system efficiencies, enabling a low production cost and an overall smaller, less expensive dry-cooling system. As a result, the cooling system could allow thermoelectric power plants to maintain a high efficiency while eliminating the use of local water resources. Furthermore, due to its very high performance, the turbo-compression cooling system has potential applications in a range of other markets, including commercial HVAC systems, data center cooling, and distributed cooling industries.
Thermal Management of High Heat Flux Electronic Devices
Taylor Bevis, Torben Grumstrup, Bryan Burk, Matthew Todd
As electronics trend towards increased miniaturization and greater performance, the need for high-performance cooling of becomes critical. Waste heat generated by microprocessors, laser diodes, and other electronics must be removed from the device to enable optimal functionality and avoid catastrophic overheating. As devices get smaller and performance demands increase, the resulting heat fluxes become extremely high. Sophisticated heat-removal technologies must be employed to manage such fluxes by dissipating heat to the ambient at a rapid rate. Torben’s research focuses on research and development of such high-performance cooling techniques. He uses finite element analysis (FEA) software to create models of devices and the associated cooling structures. The models are a powerful tools for optimization of cooling techniques because they permit one to examine performance for a large assortment of configurations and parameters without manufacturing and testing physical devices. Moreover, results from experiments conducted by other lab members can be incorporated into the model to improve the realism and applicability of the results. The models provide valuable capability in ITS Lab’s effort to develop new and ever-higher performance cooling technologies. With electronics becoming smaller and ever more powerful, Torben’s research is working to meet the need for correspondingly improved cooling technologies.
Waste Heat Availability from a High Temperature Diesel Engine
Manufacturers continue to make incremental gains in internal combustion engine efficiency, but as much as 60% of the fuel energy may still be rejected to the environment as waste heat. Research on recovering this waste heat has produced disappointing results due to the low heat capacity rate of the exhaust gases and the low temperature of the coolant (~90°), which limit the average relative efficiency gains to less than 10%. Increasing the engine coolant temperature would greatly increase the availability of waste heat and could result in efficiency gains of over 20%. Therefore, I am building an experiment using a small diesel engine to measure the availability of waste heat as the engine coolant temperature is incrementally increased. An energy balance will be performed on the modified Daihatsu three-cylinder diesel engine, which uses a copper head gasket, upgraded engine oil seals, and custom oil and cooling systems. The results from the experiment will then be used to model the output of a waste heat recovery system and demonstrate the possible efficiency gains.
(left) Modified Daihatsu diesel engine. (right) Custom oil and cooling systems.
A Multi-Functional Electrolyte for Li-Ion Batteries
PARTNERS: Prieto Battery
The high thermal conduction resistances of lithium-ion batteries severely limits the effectiveness of conventional external thermal management systems. To remove heat from the insulated interior portions of the cell, a large temperature gradient is required across the cell, and the center of the electrode stack can exceed the thermal runaway onset temperature even under normal cycling conditions. One potential solution is to remove heat locally inside the cell by evaporating a volatile component of the electrolyte. In this system, a high vapor pressure co-solvent evaporates at low temperature prior to triggering thermal runaway. The vapor generated is transported to the skin of the cell, where it is condensed and transported back to the internal portion of the cell via surface tension forces. For this system to function, a co-solvent that has a boiling point below the thermal runaway onset temperature must also allow the cell to function under normal operating conditions. Low boiling point hydrofluoroethers (HFE) were first used by Arai to reduce LIB electrolyte flash points, and have been proven to be compatible with LIB chemistry. In the present study, HFE-7000 and ethyl methyl carbonate (EMC) are used to solvate 1.0 M LiTFSI to produce a candidate electrolyte for the proposed cooling system. Lithium titanate oxide (Li4Ti5O12), copper antimonide (Cu2Sb), and lithium iron phosphate (LiFePO4) are used in half and full cells with the candidate electrolyte for cycling and electrochemical impedance spectroscopy tests, and testing results show similar performance characteristics as compared with a conventional carbonate-only electrolyte (1.0 M LiPF6 in 3:7 ethylene carbonate/diethyl carbonate). The same battery active materials are evaluated in a custom electrolyte boiling facility to evaluate electrochemical performance, and test results show that full electrochemical cells operate similarly even when a portion of the more volatile HFE-7000 is continuously evaporated.
Physical and Electrochemical Parameter Measurements of Commercial Lithium-Ion Cells
Kevin Westhoff, Trevor Vernon
PARTNERS: Everett Jackson, Dr Amy Prieto, Dr Gregory Plett
Five commercial lithium-ion batteries (LIB) were disassembled and analyzed for specific physical and electrochemical parameters. Cell disassembly was completed in an Argon glove box. Detailed measurements were performed on the physical construction of the batteries with the goal of determining the volume of active material in each electrode. The open circuit potential (OCP) as a function of temperature and state of charge (SOC) for the cathode and anode active materials versus Li/Li+ was measured. These tests used ¾” half-cells cycled at a C/30 rate on an Arbin battery tester while under strict environmental temperature control. The diffusion coefficient of Li+ as a function of temperature and SOC in the active materials was measured using the Galvanostatic Intermittent Titration Technique (GITT). Nuclear Magnetic Resonance Spectroscopy (NMR) was used to determine the composition of the electrolyte, if enough of an electrolyte sample was harvested during cell disassembly. Extensive Scanning Electron Microscope (SEM) imaging was performed on the electrodes to determine the coating thickness and active material particle size. Additionally, Energy Dispersive Spectroscopy (EDS) was performed on all electrode samples to determine the elemental composition of the active materials. This data was then coupled with X-Ray Diffraction (XRD) crystallographic data to produce an equivalent unit cell of the active material in order to determine the theoretical lithium storage capacity. The composite electrode electronic conductivity was also determined as a function of temperature with a Gamry Reference 3000 Potentiostat.
Development of a sulfur tolerant diesel fuel reformer
This research involves development and testing of a sulfur tolerant, autothermal, diesel fuel reformer for primary use in unmanned submarine applications. An autothermal reformer converts a liquid hydrocarbon fuel into syngas, a mixture consisting primarily of hydrogen and carbon monoxide gas, by reacting a mixture of fuel, water, and air over a specialized catalyst bed. The desired end product in this case is hydrogen gas to be used to power a fuel cell. The hydrogen may be extracted from the effluent gas stream by pressure swing absorption, a cascade of water gas shift reactors, or by diffusion through a membrane.
It is desirable to run a reformer using a readily available hydrocarbon fuel. However, commercial diesel, JP-8, and other logistics fuels contain sulfur which is a poison to reactor and fuel cell components. Sulfur may be removed from the fuel by highly energy intensive processes such as hydrodesulfurization which do not scale down to the vehicle size easily. But there have been recent developments in sulfur tolerant reactor components, namely a catalyst developed by Dr. Farrauto’s research group in Columbia and a membrane developed by J. Douglas Way’ research group at Colorado School of Mines. The aim of my research is to design and test a thermally integrated system around these sulfur tolerant components and to test a simple method for in-situ sulfur abatement. Thus far I have developed a process flow diagram, defined, temperatures, pressures, and gas composition at all points in the system, proven system thermodynamic feasibility, defined autothermal operating conditions, sized a full size reactor and performed detailed heat exchanger design calculations on the full size reactor.
Methanation Energy Storage
It is anticipated that the future will see larger proportions of consumed electricity being derived from renewable sources. This electricity will be distributed from producers to consumers through the electric grid. A major constraint of the electric grid is that, in general, electricity must be consumed when it is produced. Outside of capacitors, it cannot simply be stored. Due to the large size of these electrical grids, supply and demand balancing become an issue. The intermittent and variable nature of many renewable electricity sources (such as wind and solar) makes it difficult to integrate these sources into the grid balancing equation. One solution to this problem is to develop new, efficient storage media for excess produced electricity from renewable sources, which can in turn be used to return electricity to the grid when supply lags behind demand. One promising technology is methanation, whereby energy is converted from electricity into chemical energy in the form of methane. This methane can be easily handled, stored, and converted back into electricity at some later date. We are constructing a techno-economic model of such a “methanation” plant in order to test its feasibility in real world situations.