Thermodynamic Design of a Mesoscale Vapor Compression Cooling Device

This paper presents a thermodynamic methodology for designing a vapor compression refrigeration system aiming at electronics cooling. A cycle simulation model was developed firstly assuming isentropic compression and isenthalpic expansion, whereas the heat exchangers (condenser and evaporator) were modelled following a distributed approach. Whilst a 3-D heat conduction model calculates the heat leakage from the condenser to the evaporator, 2-D heat conduction models provide the temperature distribution (and the heat transfer rates) at the cold and hot ends. The fluid flow was modelled as 1-D considering both the momentum and the energy conservation equations to design the heat exchangers geometry and circuitry considering the heat and fluid flow trade-offs that take place when the system is scaled down. Subsequently, semi-empirical sub-models for variable-speed compressors and fixed-orifice expansion devices were incorporated to the cycle simulation model, which was then used to assess the effect of the components characteristics (expansion orifice size, compressor stroke and speed) on the system COP. When the case where a 5×5 cm heat source at 40°C with the surroundings at 25°C is considered, the optimal design provides a cooling capacity of 110 W with a COP of 1.6. If compared to a thermoelectric device available on the market operating at the same conditions, the thermoelectric cooler provided a COP of 0.3, nearly 5 times lower than that provided by vapor compression system designed by means of the thermodynamic methods presented in this work