# A Review of Small-Scale Vapor Compression Refrigeration Technologies
## 2 Small-Scale Refrigeration Technologies
### Active Technologies
#### 2.2.9 VCR Systems  
VCR refrigerators include four main components: compressor, condenser, evaporator, and expansion device (Figure 10), as well as a refrigerant as working fluid. The refrigerant has a low boiling point and high latent heat, allowing it to absorb and release large amounts of heat while vaporizing or condensing, respectively.  
Along its path through the system, the refrigerant experiences four distinct processes. Superheated vapor at low pressure and temperature enters the compressor and leaves as high-pressure and temperature superheated vapor. The refrigerant then flows into the condenser, where it releases heat and cools down to the point of condensation, resulting in high-pressure subcooled liquid at the outlet. The refrigerant next undergoes an isenthalpic depressurization as it flows through the expansion device, reaching the evaporator as a low temperature mixture of liquid and vapor. In the evaporator, the refrigerant absorbs heat from the medium to be cooled, leaving as superheated vapor at low pressure and temperature, concluding the cycle and returning to the initial state.  
Advantages of a VCR system vs. alternative technologies include the following. (1) They can provide cooling to systems at temperatures below ambient. This is unlike other technologies (e.g., forced convection cooling) that only work at temperatures above ambient. Moreover, when compared with spray cooling, jet impingement, and flow boiling in microchannels, VCR is the only one capable of cooling the junction temperature below ambient temperature [10]. (2) VCR systems can reach higher COP than other technologies such as thermoelectric cooling [42]. (3) Long periods of large cooling capacity are achieved with low mass flow rates, and (4) heat is transported away from its source [43]. The main applications for small-scale VCR systems are electronics and personal cooling, and they have proven to be a viable option for reaching cooling capacities up to 1000 W [44]. Other commercially available applications of small-scale VCR systems include medical, laboratory, mobile air conditioning, farming, commercial, telecom, and industrial applications.  
Table 1 presents a summary of the information previously discussed on active technologies for small-scale cooling applications to highlight the most salient differences between  
Figure 10: Schematic of a basic VCR cycle.  
them. As can be seen, for some of the technologies, capacity is defined based on the heat flux density that they can dissipate (W/m2), while others use cooling capacity (W). It is important to emphasize that having a high heat flux density does not necessarily imply that cooling capacity will be high, and vice versa. It is also evident that some of the technologies share common applications; however, not all offer the same levels of capacity, performance, or efficiency. VCR systems often have an advantage compared to the others, by offering higher efficiencies and covering a broader range of applications.  
It is essential to mention that to have a better comparison between the different technologies in terms of energy efficiency and environmental impact, it is advisable to carry out a life cycle analysis, which provides an exhaustive evaluation from the extraction of raw materials to the final disposal of the system.  
Section 3 describes previous VCR system studies to illustrate the current status of this technology.