| The ocean contains abundant renewable energy.As an effective way to utilize the low-level heat energy of the ocean,the seawater source heat pump(SWHP)system has important research significance and practical value.However,problems such as seawater corrosion,the high cost of maintenance of deep-sea water intake projects,and the possibility of affecting scenic waterways have greatly restricted the promotion of the SWHP system.At present,the capillary box heat exchanger(CBHE)made of PPR material has the advantages of large heat exchange areas,promising heat transfer performance,corrosion resistance and low cost.It is buried in the beach near the shore and used as the front-end heat exchanger of the heat pump system to form a closed heat pump system using seawater and soil heat sources.Under unsteady working conditions,the heat transfer process of the front-end heat exchanger of the seawater-soil dual source heat pump system is more complicated under the influence of tidal seepage and the heat storage effect of the surrounding environment.It takes a long time to calculate the numerical simulation,which does not meet the real-time and rapid control requirements of the air conditioning system,and is not suitable for engineering application.Therefore,it is of great significance to accurately grasp the thermal characteristics of the heat exchanger and reasonably simplify the model calculation to guide the design and optimization control of the seawater-soil dual source heat pump system.In this paper,the CBHE of seawater-soil dual source heat pump system is taken as the research object,and the dynamic thermal characteristics,simplified RC heat transfer calculation model and optimization design of the front-end capillary heat exchanger are studied.The main research work is as follows:(1)The unsteady flow and heat transfer model of the CBHE was established based on Fluent simulation software by taking a Qingdao seawater source heat pump testbed as the reference of the physical model and using reasonable assumptions.In order to verified the accuracy of the CFD model,the test of the pumping water temperature and flow was conducted.The simulation results agree with the measured data,hence,the CFD model simulated the system effectively.The effects of flow velocity,seepage velocity and backfill sand type on the heat transfer performance of the CBHE were analyzed.The results show that the seepage can effectively improve the heat transfer of the CBHE.For different backfilled sand,the greater the Peclet number,the better the heat transfer effect.(2)A simplified RC heating network model of the front-end capillary heat exchanger was established,and the parameters were identified according to the heat flow response characteristics of the CFD numerical simulation,and the parameter settings of the RC model were simplified.Use MATLAB software to write code to realize the calculation,and verify the accuracy of the simplified RC model through verification with numerical simulation results.(3)Based on the simplified RC heat network model,the unsteady thermal response of capillary heat exchanger was simulated under heating and cooling conditions respectively,and the heat flow response delay characteristics were analyzed.Through the global sensitivity analysis based on variance(Sobol method),the sensitivity of the design parameter changes of the model heat exchanger to the response of the output heat flow was studied.The result showed that: in the design,priority should be given to the embedded area of the CBHE.The thermal conductivity of sandy soil provides a theoretical basis for further optimizing the design of CBHE. |
PDF Full Text Request