The optimum performance of R410A and R32 refrigeration cycles is studied in this paper. A theoretical model for the coefficient of performance is derived first. Then, the L9(34) orthogonal table of Taguchi method is used for performance analysis. In the experimental design, four factors and three levels are considered. The range of each factor is given as: 0.81.0 MPa for evaporator pressure, 2.12.7 MPa for condenser pressure, 010°C for degree of superheating, and 010°C for degree of subcooling. Finally, a predicted model of COP is proposed for both R410A and R32 systems. According to the response table and ANOVA table, two significant factors contributed to COP are found as evaporator pressure and condenser pressure. Meanwhile, the optimum COP calculated from predicted model has a good agreement with the data of cycle theory. In addition, the value of optimum COP is 1% higher for R32 system through comparison.

One of the active approaches for regulating heat transfer in a convection-dominated cavity system is to use a periodic moving object. This study conducted a numerical study on the impact of an oscillating air-supply guide vane on the transient behaviour of thermo-hydraulic field within a square cavity with single inlet and outlet ports. The CFD package software, ANSYS FLUENT, was employed to perform the numerical simulation. The numerical analysis focused on the effect of frequency and amplitude of an oscillating guide vane on the internal flow distribution and heat transfer performance. According to the numerical results, it is known that the instantaneous Nusselt number presents cyclical changes. Moreover, the instantaneous Nusselt number increases with the increase of amplitude as the frequency is fixed. At fixed amplitude, the instantaneous Nusselt number decreases as the frequency increases.

Helical coil heat exchanger has been widely used in water heating purpose due to its higher heat transfer performance. Parameters, such as coil number, Reynolds number, and coil pitch are known as the key to the heat transfer. However, there is relatively rare study to stress on the heat transfer characteristics under a fixed heat transfer area condition. In this study, an experimental apparatus for a helical coil heat exchanger was established to study the shell side heat transfer performance for both counter and parallel flow patterns. The experiment was conducted under various coil diameters, coil numbers, coil pitches, and coil heights, while restricting on the same heat transfer area. The results show that the coil side heat transfer coefficient strongly related to coil diameter, coil pitch, coil curvature, and the Reynolds number. The results also verified the influence of coil curvature and coil pitch to the heat transfer performance.