An Optimization Research On Casted Heat Exchanger Used In Seawater Source Heat Pump System

The ocean is a huge repository of renewable energy. The specific heat capacity ofseawater is larger than air, so seawater is very suitable as a heat source. In a heatpump system, using seawater as heat source/sink can greatly alleviate the pressure ofthe air conditioning electricity consumption in the coastal cities, and bring hugeeconomic and environmental benefits. Therefore, with the development of the heatpump technology in our country, seawater source heat pump (SWHP) can replace thetraditional boiler heating and chiller cooling from a technical point. The use ofrenewable energy could be realized. For this, performance and optimization structuraldesign of casted heat exchanger (CHE) used in SWHP are studied in this thesis.Firstly, via the site test of seawater and air temperature in Tianjin coastal areas,seawater temperature distribution along the different depths in summer and winter inTianjin is got. The direct SWHP system can’t be run in the icing condition in winterdue to the low seawater temperature, so CHE used in SWHP is presented in thispaper.According to heat transfer analysis of CHE, mathematical models were built insummer condition and winter icing condition. Using Thomas algorithm, thedistribution of temperature along the CHE can be calculated. The fluid temperaturedistribution along the CHE might be calculated by dividing the whole pipe into smallparts in order to calculate fluid inlet and outlet temperature profile along the pipe canbe calculated.Secondly, in order to validate the mathematical model of CHE, an experimentalrig was established to measure the heat transfer performance. The calculatedtemperature distribution along CHE and corresponding test data in summer operationis compared. The simulation results show great agreement with experimental data.Using the mathematical model, the heat transfer performance of CHE was calculatedand analyzed at different pipe length and diameter, inlet temperature and flow rate ofsecondary refrigerant as well as seawater temperature. In winter，when the seawatertemperature was so low, the outside of the pipe may freeze. The heat transferperformance of CHE in the icing and no-icing condition was studied. It is observedthat icing outside the pipes is the most influential factor on the heat transferperformance.Thirdly, in the icing condition in winter, taking the pipe diameter, length andnumber of pipes as variables, the objective function was established, aimed at minimizing the total cost that including the initial investment cost and operation cost.Finally, a SWHP system with CHE was applied as a rehabilitation program of theproject in front of a wharf in Tianjin Port was introduced. Three programs includingthe existing system, a seawater source heat pump system with the casted heatexchanger and direct seawater source heat pump system were compared and resultsshowed the adoption of seawater source heat pump system with the casted heatexchanger for heating and cooling could save the operation cost, and reduce theemission of pollutants. So it has not only environmental protection but also economyprofit.