# A Review of Small-Scale Vapor Compression Refrigeration Technologies
## 3 Small-Scale Vapor Compression Refrigeration (VCR) Systems
### Small-Scale Vapor Compression Applications
#### 3.1.1 Electronics Cooling
[56] developed a hybrid cooling system by coupling a compact loop heat pipe with a mini vapor compression system to overcome the issues related to system layout onboard helicopters and aircraft. The first system was used to cool a hot spot on integrated modular avionics, and the second was used to reject the heat to the cold sink, as can be seen in the illustrative representation of the system in Figure 14. One of the most innovative aspects of this system lies in the use of a thermal connector or plug evaporator, disconnecting the heat load and the available heat sink and locating it in a different aircraft partition. The authors found that ambient temperature strongly affects the performance of the system; however, under different scenarios, they managed to keep the temperature below 120 \({}^{\circ}\)C for an ambient temperature of 55 \({}^{\circ}\)C.  
A very singular meso-scale VCR system design stacked a rotary vane-type compressor, a film-wise condenser, an expansion nozzle, and a microchannel evaporator, similar to the scheme shown in Figure 15[57]. Additionally, three heat pipes were incorporated with the condenser and the evaporator was designed by the Taguchi method to further increase heat transfer. The overall dimensions of the system were 60 \(\times\) 60 \(\times\) 100 mm\({}^{3}\) and the selected refrigerant was R123. A maximum cooling capacity of 80 W was determined  
Figure 14: Illustrative representation of the hybrid cooling system. Figure 13: Schematic representation of the refrigeration system. experimentally, keeping the temperature of the heat source at 46 \({}^{\circ}\)C and reaching COPs up to 2.15. [PERSON] et al. [58] integrated a miniature cooling system comprising vapor compression and thermosyphon loop for electronics cooling in avionics. This device has the particularity that it can change its operating mode depending on the thermal load and ambient temperature. At low heat load and ambient temperature, it works in a thermosyphon loop for energy conservation and switches to vapor compression mode at high heat load and ambient temperature for safety. The system consists of an evaporator made of multi-hole aluminum flat tubes, a forced convection micro-channel condenser, a micro rolling rotor compressor, an electronic expansion valve, a check valve, and two solenoid valves, with a total weight of 2.8 kg. In experimental tests, the dynamic characteristics of the two operating modes and the switching mode were studied, and among the most relevant results, it was found that the thermosyphon loop mode can handle a heat load of 600 W with an efficiency of 35.7, with input work invested in operating the fan, while the vapor compression mode has 1000 W of cooling power with COP of 3.1 considering fan and compressor input work, both at 20 \({}^{\circ}\)C ambient temperature. As can be seen, the number of applications where a vapor compression refrigeration system is needed for the cooling of electronic components is vast, and more will surely emerge as the technology advances and the demand for efficient systems with high heat removal rates rises, since the COP of these systems is a strong function of the temperature difference between the heat source and the sink and only a relatively weak function of the technological miniaturization of the components.