Modeling and Control Architecture Design of Multi-evaporator Pumped Two-phase System

Two-phase cooling systems are being explored actively as a promising technology for energy-intensive electronics systems. The latent heat of vaporization results in a high heat-transfer coefficient. However, the system may suffer a sudden increase in temperature when the heat flux exceeds the critical heat flux, causing a dramatic rise in surface temperature and a sudden reduction in heat-transfer coefficient. This can lead to burnout or system failure. This research focuses on control-oriented dynamic modeling of a pumped two-phase system with multiple evaporators. Further, the multi-evaporator pumped two-phase system is integrated with a vapor compression system. To avoid the appearance of critical heat flux, the exit quality of the evaporator must to be constrained to less than one, which means that only two-phase fluid is allowed at the outlet of the evaporator. This research uses the dynamic model to explore control architectures that provide avoidance of critical heat flux in two-phase cooling for multiple evaporators under dynamic heat loads

Experimental Evaluation of Silicon Expansion Valve Techonology

Residential and commercial buildings consume 40% of the energy used in the United States. Heating and cooling uses more energy than any other system in a building. Typically, 43% of a building utility bill goes to HVAC equipment. By combining proper equipment maintenance and upgrades with appropriate insulation, air sealing, and thermostat settings, energy usage can be cut from 20% to 50%. In this research, advanced valves and control algorithms are studied to improve the efficiency and reduce the energy consumption of vapor compression air conditioning and refrigeration systems. The characteristics of the new generation of MEMS based flow control devices have been tested on single and multi-evaporator systems. This research conducted a comprehensive set of experimental tests that identify the most effective elements of an advanced valve control strategy under a variety of operating conditions. The performance of the new MEMS actuators with different control strategies is compared with the standard mechanical valves and a commercially available superheat controller. Preliminary research results reveal efficiency gains with a cascaded control algorithm over both the thermal expansion valves and the commercial superheat controller

Reduced GWP Refrigerant for Residential and Commercial Air Conditioning Systems

R-410A is widely used in residential and light commercial air-conditioning, heat pump and chiller systems. Due to increasing concerns about climate change, various environmental regulations have been proposed to phase out this refrigerant. A new refrigerant, R-466A, has been developed, which offers high energy efficiency and low global warming potential (GWP), resulting in low overall environmental impact. This paper discusses the thermal properties as well as the performance of this new refrigerant in a representative air conditioning system showing the benefits of using this new refrigerant. The thermal stability, material compatibility and refrigerant/lubricant interactions of R-466A are also discussed. Finally, a simulation model is used to evaluate the lifetime thermal stability of R-466A under real operating conditions for a heat pump system

Modeling and Control Architecture Design of Multi-evaporator Pumped Two-phase System

Two-phase cooling systems are being explored actively as a promising technology for energy-intensive electronics systems. The latent heat of vaporization results in a high heat-transfer coefficient. However, the system may suffer a sudden increase in temperature when the heat flux exceeds the critical heat flux, causing a dramatic rise in surface temperature and a sudden reduction in heat-transfer coefficient. This can lead to burnout or system failure. This research focuses on control-oriented dynamic modeling of a pumped two-phase system with multiple evaporators. Further, the multi-evaporator pumped two-phase system is integrated with a vapor compression system. To avoid the appearance of critical heat flux, the exit quality of the evaporator must to be constrained to less than one, which means that only two-phase fluid is allowed at the outlet of the evaporator. This research uses the dynamic model to explore control architectures that provide avoidance of critical heat flux in two-phase cooling for multiple evaporators under dynamic heat loads