Thermodynamic design of a mesoscale vapor compression cooling device

• Published in: Applied thermal engineering 2019-01, Vol.147, p.509-520
• Main Authors: Yee, Ricardo P., Hermes, Christian J.L.
• Format: Article
• Language: English
• Subjects: Circuits; Compressors; Computational fluid dynamics; Computer simulation; Conduction heating; Conduction model; Conductive heat transfer; Conservation equations; Cooling; Design; Empirical analysis; Energy conservation; Evaporators; Fluid flow; Heat exchanger; Heat exchangers; Miniaturization; Optimization; Orifices; Refrigerating system; Refrigeration; Temperature distribution; Thermal cycling; Thermodynamics; Thermoelectric cooling; Three dimensional models; Two dimensional models; Vapor compression refrigeration
• ISSN: 1359-4311; 1873-5606
• DOI: 10.1016/j.applthermaleng.2018.09.073

•A study of downscaling a vapor compression refrigeration system is presented.•A system simulation model was advanced considering distributed heat exchangers.•Semi-empirical compressor and fixed-orifice submodels were also adopted.•System packaging and cycle architecture were designed based on simulations.•The proposed design has a COP 5 times higher than those of Peltier coolers. This paper presents a thermodynamic methodology for designing a vapor compression refrigeration system aiming at mesoscale cooling. A cycle simulation model was developed assuming at first 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 calculated the heat leakage from the condenser to the evaporator, 2-D heat conduction models provided 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 surrounding air 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 analyzed in this work.