The HVAC sector is dominated primarily by the vapor compression cycle. However, there are two primary concerns: first, they are driven by electricity and secondly, the refrigerants used in the vapor compression cycles have the potential to cause harm to the environment. Hence, widespread efforts are being directed toward the investigation of refrigerants with low ozone depletion potential as well as global warming potential, and also with low flammability and toxicity. Adsorption heat pumps have the potential to utilize waste heat and provide cooling and heating with minimal electricity use and few moving parts. Conventional embodiments of adsorption heat pumps restrict their applicability due to some key design limitations. The adsorption and desorption cycle times for such systems can be up to a few hours depending on the system size and working pair, making them impractical for applications such as space conditioning. Rapid cycling of the adsorbent beds increases the adsorbent system viability for HVAC applications by yielding a competitive performance. This research thrust involves the development of adsorption heat pumps incorporating adsorbent-coated microchannels.
Adsorbent bed using microchannels
A variant of this pump can be used to store energy. Depending on requirements, adsorption and desorption processes in this adsorbent bed can be triggered. Furthermore, such a heat pump design can be easily implemented in automobiles, where the radiator coolant can become the source for actuation of the heat pump, thereby eliminating the need of a dedicated compressor.
Microchannel-based temperature swing adsorption (TSA) processes, which involve alternating flow of gases and liquids have been shown to not only yield competitive or superior performance than the existing processes, but also to be environment-friendly as they use heat for their operation. To realize this potential, however, understanding of simultaneous interactions of gases and liquids with adsorbents on a fundamental level becomes critical. For example, when hot water heat transfer fluid (HTF) makes direct contact with the adsorbent that already has CO2 present in adsorbed phase; the CO2 is forced to desorb because of temperature rise and in a gaseous state encounters hot liquid water. Water also has some affinity for CO2 and therefore, CO2 from an adsorbed phase in the adsorbent is absorbed in bulk liquid water. Another factor adding to the complexity of the process is the competitive adsorption of water and CO2. In this case, relative kinetics of sensible heating and cooling of the adsorbent, adsorption and desorption of water and CO2 in the adsorbent and absorption of CO2 in water must be characterized, so that impurity removal using this approach can be understood and scaled up for commercial utility. Such a diverse characterization can be expanded to other working-coupling fluid pairs and adsorbent materials, and depending on gas separation applications, analogous processes can be designed.
Schematic of gas-liquid-adsorbent simultaneous interaction
While detailed fundamental multi-phase heat and mass transfer and fluid mechanics models can be developed using appropriate first principle approaches, experimental insights into the adsorption and absorption phenomena can be obtained using transient mass spectrometry. The overall research plan can include modeling and experimental research thrusts, wherein both activities would be complementary to each other.
Recently, wide band gap (WBG) semiconductor materials like silicon carbide (SiC) and gallium nitride (GaN) have been demonstrated to be excellent candidates for next generation electronic devices, which can deliver at least twice the power densities as compared to conventional silicon (Si) based semiconductors with a significantly better switching performance. However, existing electronic packaging and thermal management techniques need significant upgrades to handle higher voltages and greater heat dissipated, so that WBG semiconductor technology can be commercially viable. Conventional packaging techniques can be improved in terms of better materials that can handle the mechanical and thermal stress with improved reliability, better material stacking sequence so that heat spreading through the material layers can be optimized, and better cooling techniques that can dissipate high heat fluxes within a compact available volume. Integration of these approaches via experimental and computational analyses is the key to the development of high performance electronic systems.
Interface bond material developed for power electronic package