| The conventional air conditioning to deal with heat and moisture jointly present some about energy waste and humidity difficult controlled and air quality issues. Independent control of temperature and humidity in dry coil and Fresh air units system can solve these problems effectively. The fan coil unit with high-temperature col d water in pipes can meet the requirements of dry conditions. As a result of high temperature of inlet water in dry coil, heat transfer temperature difference and heat transfer rate shrink. To elimination of indoor sensible heat load, dry coil unit will increase the heat exchange area and volumes, which increase investment of equipment and Installation inconvenience.Parallel-flow heat exchanger has been acknowledged as the high heat transfer rate unit in the automobile air-conditioning system, adopt aluminium micro channel flat tube and shutter finned assembly design, can solve the problem about small heat transfer rate and big volumes of heat exchanger from the standpoint of enhanced heat transfer. In this thesis, heat exchanger performance situation of the fin - tube, serpentine and parallel-flow were analyzed in the basis of overall study. And the feasibility of Parallel-flow heat exchangers applied to the surface cooler were profoundly analyzed in dry conditions. Matching designed and calculation were executed for the Parallel-flow heat exchanger with the dry coil system, In addition, different process Parallel-flow heat exchangers were designed.Integrated performance test and comparison are done to the different process heat exchangers in dry conditions. Experimental system is composed of the air-loop system, water-loop system and data-processing system. When water flow is fixed, Heat transfer rate, temperature difference, the pressure drop resistance changes were tested with the variation of air velocity. When air velocity is fixed, Heat transfer rate, temperature difference, the resistance changes are tested with the variation of water flow. Deals with experimental data into performance curves, analyzing and comparing heat transfer and pressure drop performance of different process heat exchangers. From the test results, we can see that increase water flow count can enhance the heat transfer effect and the pressure drop resistance of heat exchanger in the same state of airside and waterside for. In the scope of test condition and flow, The single pass Parallel-flow heat exchanger's total heat transfer coefficient is 114.7~124.8 W m~2·K, the two pass's is 117.1~128.7 W m~2·K, the three pass's is 119.0~132.9 W m~2·K, the four pass's is 121.1~137.7 W m~2·K, the total heat transfer coefficient increases along with the flow pass increased 4%, The waterside heat transfer coefficient increases along with the flow pass increased 65%. At the same air velocity, the waterside pressure drop resistance increases along with the flow pass increased 40~280%. Therefore, In allowing water resistance range, Parallel-flow heat exchanger can improve heat transfer efficiency and will be better choice for surface cooler in dry conditions through the reasonable multipaths designed. |
