Measurement Method And Experimental Research Of Performance Of Heat Transfer And Pressure Drop For Fin-Tube Heat Exchanger

The performance of heat transfer and pressure drop of a heat exchanger is the key issue for energy saving, and there are many studies in this field. Due to the complicated structure of the heat exchangers, it is difficult to setup a precious math model for the study. Based on the experimental study, this paper setups the highly accurate Enthalpy Difference Lab, and measures the performance of heat exchangers.The Enthalpy Difference Lab is setup including four systems: air system, water system, wind tunnel measurement system and signal control and data collection system. All the conditions are controlled by PID controllers. The four PID controllers are debugged to raise accuracy, and the set-points of P, I, D parameters are got. Also, problems about dry bulb temperature control in winter and the fluctuation of wet bulb temperature are solved. Because of the influence of sensors'accuracy on the measurement, the calibration for each sensor is finished. At last, the control accuracy of temperature is within±0.1℃, and accuracy of the face air velocity is within 0.01m/s.The sensor accuracy, stable condition of environment and the performance stability and repeatability of heat exchangers will affect the test result of heat exchanger simultaneously. Stable condition of environment is guaranteed by the controllers. To analyze the performance stability and repeatability for the different heat exchangers, three heat exchangers are tested to confirm the measuring method with dry-wet cycles.The fin pitch and fin thickness of the exchanger are the key parameters for heat transfer and pressure drop. Four heat exchangers with different fin pitch and fin thickness are tested, and the results are shown as below:(1) Under dry condition, with decreasing of the fin pitch, heat transfer area increases and the coefficient of heat transfer increases. However, the pressure drop increases.(2) Under wet condition, when the face air velocity is 1.0m/s, the fin pitch should be better than 1.5mm. Once the fin pitch reduces to 1.2mm, the heat transfer area increases, but the heat transfer performance deteriorates in the airside. At the same time, the pressure drop is much higher.(3) Under the fin pitch of 1.5mm, when the fin thickness increases to 0.115mm from 0.108mm, but the number of fin doesn't change, the influence of fin thickness on the heat transfer area in the airside and the through area of air is little. As a result, the heat transfer and pressure drop performance of heat exchangers change little.