Heat Transfer Characteristics Of Helical Coil Heat Exchanger For Seawater-source Heat Pump

A kind of self-developed helical coil heat exchanger(HCHE) was proposed and applied in a seawater heat pump(SWHP) system in this study through experiments and mathematical simulations. HCHE heat transfer performance under summer condition, winter non-icing condition was studied. Winter icing condition was also studied because winter seawater temperature is close to freezing point in some north coastal areas.Mathematical models of HCHE under winter icing condition and winter non-icing condition were developed at first. An experimental HCHE system was built in International Cruise Terminal, Tianjin port. Temperature distributions along tube length direction under winter icing condition and winter non-icing condition and ice layer thickness distribution along tube length direction under winter icing condition was recorded during test period. The recorded data was applied in the mathematical models to solve the convective heat transfer coefficient of HCHE and seawater outside the tube. The value of convective heat transfer coefficient during test period was calculated to be between 427.8 W/(m2?K) and 712.8 W/(m2?K) when the seawater flow rate ranges from 0.07 m/s to 0.38m/s while between 582.8 W/(m2?K) and 853.9 W/(m2?K) when the seawater flow rate ranges from 0.21 m/s to 0.53 m/s.Mathematical model of HCHE under summer condition was developed secondly. Performance tests were conducted with the built experimental system in summer to obtain the temperature distribution along tube length direction. The test data was applied in the model to solve the convective heat transfer coefficient of HCHE and seawater outside the tube. The result shows that the coefficient ranges from 451.7 W/(m2?K) to 762.4 W/(m2?K) when the seawater flow rate ranges from 0.09 m/s to 0.47 m/s.Heat transfer characteristics of HCHE in seawater were predicted based on the summer condition model and winter non-icing condition then. Some numerical simulations were undertaken to analyze the influence of tube length, tube diameter, liquid flow rate in the tube, liquid temperature at the tube inlet and seawater temperature on the heat exchange efficiency of HCHE. Distribution law of ice layer outside the heat exchanger tube under winter icing condition was also studied through numerical simulations.Finally, a case study of an office building in Nanjiang district, Tianjin Port, was introduced to elaborate on the design method of SWHP systems with HCHE. Energy-Plus, an energy simulation software was applied to calculate the annual load of the building. Three different types of SWHP systems utilizing direct intake, infiltration intake, and HCHE were studied. Methods of life cycle assessment and annual cost were utilized to give an economic analysis and an energy-saving assessment of them.