tailieunhanh - Two Phase Flow Phase Change and Numerical Modeling Part 3

Tham khảo tài liệu 'two phase flow phase change and numerical modeling part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 50 Two Phase Flow Phase Change and Numerical Modeling Inlet R507A Fig. 16. Case of application for circuiting In the event of frost formation it is expected to be more uniform and to occur over a longer period of time in comparison to ordinary synthetic refrigerants. With refrigerant R507A several iterative attempts were performed before obtaining a reasonable temperature drop. At least four circuits were found to be necessary to satisfy this condition. The four circuits selected were 2 rows each arranged in parallel. In such a case the circuits are well balanced and the temperature drop in the saturation temperature is of the order of oC in each circuit metres while it s only of the order of oC for CO2 in all the coil length 90 metres . Length m Fig. 17. Temperature distribution for air and R507A with coil length 51 Numerical Modeling and Experimentation on Evaporator Coils for Refrigeration in Dry and Frosting Operational Conditions Fig. 18. Evaporation level in different circuits Fig. 19. Effect of refrigerant on temperature glide Fig. 18 shows the amount of evaporation taking place in each circuit. CO2 uses only one circuit and evaporates 100 of the available refrigerant. R505A needs four circuits to deliver the same capacity. In this case only the frontal circuit works at full capacity. The other three are increasingly underused from the coil front to rear because of their exposure to .