External Condensation of HFE 7000 and HFE 7100 Refrigerants in Shell and Tube Heat Exchangers

Abstract

The paper describes the results of experimental studies of media as an intermediary in heat exchange taking place in low volume conditions. Their properties predestine them both as a future-proof for transporting and storing heat materials. The paper concerns the current topic related to the miniaturization of cooling heat exchangers. There are many studies in the literature on the phase transition of refrigerants in the flow in pipe minichannels. However, there is a lack of studies devoted to the condensation process in a small volume on the surface of pipe minichannels. The authors proposed a design of a small heat exchanger with a shell-and-tube structure, where the refrigerant condenses on the outer surface of the pipe minichannels cooled from the inside with water. It is a response to the global trend of building highly efficient, miniaturized structures for cooling and air conditioning heat exchangers. Two future-proof, ecological replacements of the CFC refrigerants still present in the installations were used for the experimental research. These are low-pressure fluids HFE 7000 and HFE 7100. The tests were carried out in a wide range of changes in thermal-flow parameters: G = 20–700 kg·m−2s−1, q = 3000–60,000 W·m−2, ts = 40–80 °C.

The Effect of Microencapsulated PCM Slurry Coolant on the Efficiency of a Shell and Tube Heat Exchanger

“…The results of the authors' own research showed that the heat transfer in exchangers during the condensation of refrigerants was characterized by an increase in efficiency in relation to single-phase systems [36]. It is also known that the use of mixtures of MPCM and water as a coolant has a positive effect on the intensity of heat transfer in heating/cooling (thermal) devices.…”

“…MPCM slurry is presented in Figure 3. The physical and chemical properties of the HFE 7000 refrigerant are presented in [36], while the properties of the MPCM slurry, i.e., viscosity, density, heat conductivity, specific heat, and heat of fusion, as well as the procedure for their determination have been presented in a number of previous studies [38][39][40][41][42].…”

“…Accordingly, the following dependence of the heat flux absorbed in the heat exchanger by the coolant on the temperature of the cooling medium at the inlet was obtained (Figure 4). In earlier studies [36], the value of αc was determined experimentally as the heat transfer coefficient from the side of the condensing medium. In this study, the authors determined the heat transfer coefficient from the side of the MPCM slurry-the heat transfer fluid αexp.…”

“…At the same time, a significant increase in the value of the heat transfer coefficient αc of the cooling medium (Figure 4), calculated according to Formula (3), was observed. In earlier studies [36], the value of α c was determined experimentally as the heat transfer coefficient from the side of the condensing medium. In this study, the authors determined the heat transfer coefficient from the side of the MPCM slurry-the heat transfer fluid α exp .…”

“…where L-exchanger length, n-number of cooling channels, λ-heat conduction coefficient of the channel wall material (copper), d i -internal diameter of the minichannel, d e -external diameter of the minichannel, α c -heat transfer coefficient of HFE 7000 [36], and ∆t-the difference in temperatures in the exchanger calculated as the difference between the saturation temperature of the refrigerant t s and the average temperature of the cooling medium (water) t f . It is noted (Figure 5) that the value of the heat transfer coefficient of the slurry when the PCM was in the form of a solid or in the form of a liquid had a mean value 7% higher than that of the water.…”