# 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  
The growing demand for electronic devices in ever-increasing applications is due to the constant improvement of technology, increasing accessibility and affordability, as well as the need for constant connectivity and immediate access to information. In this sense, the number of transistors that make up these chips had been doubling approximately every 18 months for several years according to [PERSON]'s law. However, this trend has slowed down in recent years, and it is even believed that it will end as the transistors reach atomic scale and manufacturing costs continue to increase [45]. In consequence, an increase in power consumption and therefore greater heat flux densities have been observed; in fact, the International Technology Roadmap for Semiconductors, ITRS, predicted that by 2022 the average power consumption for a typical stationary chip would be over 400 W and over 800 W by 2026 [42]. Efficient and powerful refrigerating solutions such as vapor compression cooling have been proposed and evaluated. With the aim of solving this problem, [PERSON] and [PERSON] [14] demonstrated a miniature VCR system measuring 300 \(\times\) 230 \(\times\) 70 mm\({}^{3}\) and 3.5 kg in weight with a cooling capacity of 200 W and R134a as a refrigerant. They conducted a series of systematic tests to find the best system characteristics, prioritizing cold plate temperature. Optimum system conditions were 1800 mm capillary tube length, 100 g refrigerant charge, and 2858 rpm compressor speed. With these conditions and 200 W heat load, the cold plate could be maintained at 60 \({}^{\circ}\)C for many hours with a COP equal to 8.5. The second law efficiency of the system was measured at 23-31%, mainly due to compressor irreversibility. Figure 11a shows an illustrative representation of this system. A similar work used a variable speed compressor for R134a, a microchannel condenser, a capillary tube, and a microchannel heat sink as an evaporator [46]. The authors focused their attention on the surface temperature of the heat source, achieving a suitable range between 54 and 73 \({}^{\circ}\)C when the heating power was 200 W. The authors found that slower compressor speeds reduced power consumption and led to improved coefficient of performance (as high as 9.0). It is finally noted that it is critical to control the refrigerant temperature at the evaporator inlet to avoid droplets that may damage the electronic device if the temperature is below the dew point. Figure 11b shows the experimental equipment built for this research. [PERSON] et al. [47] tested a miniature cooling system with 2.5 kg weight and 250 \(\times\) 200 \(\times\) 120 mm\({}^{3}\) size. The system used a spiral-tube evaporator of their own design. At test conditions of mass flow and ambient and chilled water temperatures, their experiments showed a 63 W cooling capacity with 24.5 W input power (COP = 2.57) and 40 g optimal refrigerant charge. Seeking a system with even smaller dimensions that could fit into the free space of a personal computer, a miniature refrigeration system was developed with commercially available components and R134a as the working fluid [48]. Cooling capacity and COP were measured between 121-268 W and 2.8-4.7, although these values were expected to be lower according to the design specifications of the compressor. The largest losses originated in the rotary compressor, which was not designed for the test conditions. This experimental setup was also used to validate a MATLAB numerical model [49]. [PERSON] et al. [50] successfully fitted a miniature refrigeration system into a notebook computer. The system used isobutane as the working fluid and the tests were conducted with a thermal load close to 50 W. The results showed that the system could reach COP greater than 2.25 at evaporating (50 \({}^{\circ}\)C) and condensing (90 \({}^{\circ}\)C) temperatures higher than typically used. [PERSON] et al.