In order to solve the problems arising from the use of HFC-based refrigerants, it is a new alternative refrigerant. Among natural refrigerants, hydrocarbon-based refrigerants are highly flammable, ammonia refrigerants are explosive and toxic, and carbon dioxide refrigerants have very high operating ...
In order to solve the problems arising from the use of HFC-based refrigerants, it is a new alternative refrigerant. Among natural refrigerants, hydrocarbon-based refrigerants are highly flammable, ammonia refrigerants are explosive and toxic, and carbon dioxide refrigerants have very high operating pressure. It has a drawback. However, the HFO-based R-1234yf refrigerant has a GWP of 4, an ODP of 0, no toxicity, and has the advantage that the decomposition rate in the atmosphere is decomposed and disappears in a short time compared to that of the existing R-134a for 14 years.
This paper investigates the heat transfer and pressure drop characteristics for the optimum design of a refrigeration and air conditioning system using R-1234yf as the working fluid, which can replace Freon-based refrigerants, and refrigeration using R-1234yf as the working fluid. The purpose of this paper is to provide basic data for optimal design of refrigeration and air conditioning equipment. For this purpose, it was manufactured as a system consisting of a refrigerant pump, preheater, evaporator, and condenser, and the evaporator has three types of inner diameters of 3.7, 5.3, and 6.8 [mm], and two types of heat exchanger with the inner diameters of the condenser: 3.7, 5.3 [mm]. In order to understand the heat transfer and pressure drop characteristics of the evaporator and condenser, the evaporation and condensation characteristics according to changes in vapor quality, heat flux, mass flux, saturation temperature, and pipe diameter were analyzed.
The following main conclusions were drawn. First of all, when looking at the flow pattern, intermittent flow was dominant in the low quality at the inlet of the evaporator, and annular flow dominated in the high quality. The local heat transfer coefficient increased as the mass flux and heat flux of R-1234yf increased in the whole quality range. In addition, it was found that the heat transfer coefficient increased as the tube diameter decreased in the entire quality region. The results obtained by the experiment on the evaporation heat transfer of R-1234yf in a horizontal tube were compared with the correlations suggested by Shah, Gungor-Winterton, Kandlikar, Jung, Liu-Winterton, Saitoh et al. The average dietary error was 13.63%, showing the best agreement.
In the comparison of the pressure drop between R-1234yf and R-134a, the pressure drop of R-134a was large. The evaporation pressure drop decreased as the saturation temperature of R-1234yf increased in the entire quality. For all tube diameters, the pressure drop increases with the mass flux and heat flux of R-1234yf. In addition, as the tube diameter decreased, the pressure drop increased, and as a result of comparing the local pressure drop of R-134a of R-1234yf with each other, the pressure drop of R-1234yf was lower than that of R-134a in the entire quality. As a result of comparing the evaporation pressure drop of R-1234yf in the pipe of inner diameter of 3.7 [mm], 5.3 [mm], 6.8 [mm] and the value predicted by other correlations, the average error with the correlation of Choi-Domanski was –15.3%.
While the R-1234yf was condensed in the condenser, most of the slug flow was observed at low mass flux, and most of the annular flow at high mass flux. The heat transfer coefficient according to the change of the saturation pressure showed a tendency to decrease as the pressure of R-1234yf increased. In addition, the local heat transfer coefficient of the inner diameter of 3.7 [mm] was higher than that of the inner diameter of 5.3 [mm]. In the comparison of the heat transfer coefficients of R-134a and R-1234yf, it can be seen that the local condensation heat transfer coefficient of R-134a is large at the total vapor quality. As a result of comparison with the conventional condensation heat transfer correlation, the predicted value and the experimental value by the correlation of Dobson-Chato and Basher et al. showed good agreement within the error range of ±10%. Therefore, it was found that the correlation of Dobson-Chato and Basher et al. can be used as it is to design a condenser using R-1234yf. The pressure drop of R-1234yf in the condenser increased as the pipe diameter decreased. From the comparison of the pressure drop between R-134a and R-1234yf, it can be seen that the frictional pressure drop of R-134a is greater than that of R-1234yf in most quality.
In order to solve the problems arising from the use of HFC-based refrigerants, it is a new alternative refrigerant. Among natural refrigerants, hydrocarbon-based refrigerants are highly flammable, ammonia refrigerants are explosive and toxic, and carbon dioxide refrigerants have very high operating pressure. It has a drawback. However, the HFO-based R-1234yf refrigerant has a GWP of 4, an ODP of 0, no toxicity, and has the advantage that the decomposition rate in the atmosphere is decomposed and disappears in a short time compared to that of the existing R-134a for 14 years.
This paper investigates the heat transfer and pressure drop characteristics for the optimum design of a refrigeration and air conditioning system using R-1234yf as the working fluid, which can replace Freon-based refrigerants, and refrigeration using R-1234yf as the working fluid. The purpose of this paper is to provide basic data for optimal design of refrigeration and air conditioning equipment. For this purpose, it was manufactured as a system consisting of a refrigerant pump, preheater, evaporator, and condenser, and the evaporator has three types of inner diameters of 3.7, 5.3, and 6.8 [mm], and two types of heat exchanger with the inner diameters of the condenser: 3.7, 5.3 [mm]. In order to understand the heat transfer and pressure drop characteristics of the evaporator and condenser, the evaporation and condensation characteristics according to changes in vapor quality, heat flux, mass flux, saturation temperature, and pipe diameter were analyzed.
The following main conclusions were drawn. First of all, when looking at the flow pattern, intermittent flow was dominant in the low quality at the inlet of the evaporator, and annular flow dominated in the high quality. The local heat transfer coefficient increased as the mass flux and heat flux of R-1234yf increased in the whole quality range. In addition, it was found that the heat transfer coefficient increased as the tube diameter decreased in the entire quality region. The results obtained by the experiment on the evaporation heat transfer of R-1234yf in a horizontal tube were compared with the correlations suggested by Shah, Gungor-Winterton, Kandlikar, Jung, Liu-Winterton, Saitoh et al. The average dietary error was 13.63%, showing the best agreement.
In the comparison of the pressure drop between R-1234yf and R-134a, the pressure drop of R-134a was large. The evaporation pressure drop decreased as the saturation temperature of R-1234yf increased in the entire quality. For all tube diameters, the pressure drop increases with the mass flux and heat flux of R-1234yf. In addition, as the tube diameter decreased, the pressure drop increased, and as a result of comparing the local pressure drop of R-134a of R-1234yf with each other, the pressure drop of R-1234yf was lower than that of R-134a in the entire quality. As a result of comparing the evaporation pressure drop of R-1234yf in the pipe of inner diameter of 3.7 [mm], 5.3 [mm], 6.8 [mm] and the value predicted by other correlations, the average error with the correlation of Choi-Domanski was –15.3%.
While the R-1234yf was condensed in the condenser, most of the slug flow was observed at low mass flux, and most of the annular flow at high mass flux. The heat transfer coefficient according to the change of the saturation pressure showed a tendency to decrease as the pressure of R-1234yf increased. In addition, the local heat transfer coefficient of the inner diameter of 3.7 [mm] was higher than that of the inner diameter of 5.3 [mm]. In the comparison of the heat transfer coefficients of R-134a and R-1234yf, it can be seen that the local condensation heat transfer coefficient of R-134a is large at the total vapor quality. As a result of comparison with the conventional condensation heat transfer correlation, the predicted value and the experimental value by the correlation of Dobson-Chato and Basher et al. showed good agreement within the error range of ±10%. Therefore, it was found that the correlation of Dobson-Chato and Basher et al. can be used as it is to design a condenser using R-1234yf. The pressure drop of R-1234yf in the condenser increased as the pipe diameter decreased. From the comparison of the pressure drop between R-134a and R-1234yf, it can be seen that the frictional pressure drop of R-134a is greater than that of R-1234yf in most quality.
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