# A Review of Small-Scale Vapor Compression Refrigeration Technologies
## 3 Small-Scale Vapor Compression Refrigeration (VCR) Systems
### Components
#### 3.4.2 Condensers  
The condenser transfers heat between the refrigerant at the compressor discharge (at high temperature and pressure) and the surrounding environment. The refrigerant condenses as it transfers heat to the environment, and this process occurs approximately at constant temperature and pressure, reaching a saturated or subcooled liquid state at its outlet. In large-scale refrigeration equipment, there are different designs for this device; however, in most small-scale systems, condensers are typically microchannel heat exchangers. Figure 20: (**a**) Schematic of a linear compressor and (**b**) miniature linear compressor used by [PERSON] [54]. Several works have reported the use of microchannel heat exchangers, describing manufacturing methods, thermo-hydraulic performance, applicability [89], and numerical simulations [90]. Entropy generation analyses have also been conducted [13]. In addition, different designs have been proposed, including the addition of metal foams on the air side to enhance heat transfer [91] compared to louvered fins [92]. Other publications focused on the working fluids used, pressure drop, and optimization of these devices for both single-phase and two-phase flow [37]. Microchannel heat exchangers can achieve very high heat transfer rates, and therefore their study and use have extended to various applications such as the military, bio-engineering, medical, nuclear, and solar cells [93], as well as the cooling of computer components and information technologies, high power semiconductor devices, laser diode arrays, fuel cells, and the topic of this review: miniature VCR systems [94]. Another advantage of microchannel heat exchangers in small-scale refrigeration systems, either as condensers, evaporators, or both, is the reduction in refrigerant mass in the system, maintaining high heat transfer rates, as mentioned in the previous paragraph. We next describe relevant research involving the use of microchannels as condensers in small-scale refrigerators. A brazed aluminum multichannel parallel-type condenser with two-refrigerant passes [61] showed major improvements in heat transfer coefficient and heat exchange vs. a finned tube condenser. The finned tube condenser weighed 1.7 kg and dissipated 300 W of heat vs. 400 W for the multichannel condenser weighing less than 0.4 kg. The comparison showed that the parallel-type condenser was even more suitable for the miniature refrigeration system subject of study. More detailed information about this device such as dimensions and weight (130 \(\times\) 140 \(\times\) 16 mm\({}^{3}\) and 0.26 kg) were then presented by [PERSON] et al. [62]. Similarly, an aluminum microchannel condenser was used in the system proposed by [PERSON] and [PERSON] [14]. This model was even more compact, at 100 \(\times\) 100 \(\times\) 16 mm\({}^{3}\). There are other works where microchannel heat exchangers have also been used as condensers; however, they provide little detail on the characteristics of the devices, such as an aluminum microchannel multi-louvered fin heat exchanger (0.260 m wide, 0.238 m height, 0.0211 m deep) presented by [PERSON] [60] or the one used by [PERSON] et al. [50] with a thermal resistance of approximately 0.5 \({}^{\circ}\)C/W. Figure 21 shows different designs of microchannel condensers. Other types of condensers have been evaluated. [PERSON] et al. [55] considered a tube in tube-type condenser. [PERSON] [54] used a finned tube heat exchanger made of copper with aluminum louvered fins as condenser and pre-condenser, with the particularity that both were mounted together into a single device, as can be seen in Figure 22. Similarly, [PERSON] et al. [47] used the same type of condenser. However, little geometric information is given. Figure 21: Microchannel condensers: (**a**) design 1 and (**b**) design 2.