Experimental Study Of Evaporator Performance Of Surface Water Condensing Heat Source Heat Pump

The global crisis of environmental pollution and energy shortage urgently requires the development and utilization of clean energy to solve.Building energy consumption occupies1/3 of China’s total social energy consumption,and heating and air conditioning energy consumption is an important part of building energy consumption,so the implementation of clean heating to reduce energy consumption is an important measure for energy saving and emission reduction.Heat pump technology is undoubtedly the preferred way of clean heating.Surface water source heat pumps are stable in operation and simple in system structure,but the surface water temperature in northern areas in winter is below 4℃,and its sensible heat is not enough to supply heat to heat users,so the application is limited.Considering the huge latent heat dissipated by water condensation and the abundant surface water resources in some areas,the research of surface water condensation heat source heat pump is of great significance.As an important component for extracting latent heat of condensation in a condensing heat pump,the condensing heat evaporator is a hot topic of research today.However,there are various shortcomings of existing condensing heat evaporators.In view of the shortcomings of the existing surface water condensing heat source heat pump evaporators,this paper innovative proposes a new type of condensing heat evaporator with icing outside the tube,hydrophobic coating to inhibit ice adhesion and hydrophobic coating combined with hot melt de-icing method,and builds an experimental platform by taking the heat exchange unit to study the icing law of the proposed new type of condensing heat evaporator and to derive the optimal operation and structural parameters.The article precedes with a systematic introduction to surface water condensation heat source heat pumps as well as surface water sources.The preliminary theoretical calculation of the condensing heat evaporator,the heat exchange unit and the experimental test bench were set up to test the influence of operation and structural parameters on the performance of the condensing heat evaporator,and the optimal operation conditions and ice formation and melting laws were derived.In order to solve the problem of thick ice layer and easy ice adhesion,hydrophobic coating is introduced,and the hydrophobic coating is compared and contact angle is tested;the icing situation with and without hydrophobic coating is tested,and the test results show that hydrophobic coating can effectively inhibit ice adhesion;the de-icing efficiency can be improved by using the method of hydrophobic coating assisted by hot melt;numerical simulation is performed by Fluent,and the optimal operating parameters obtained from the heat exchanger unit experiment are brought into the analysis.Numerical simulations using Fluent were carried out to analyze the heat transfer performance of the overall structure of the condensing heat evaporator.The final conclusion is as follows:(1)The heat transfer performance of the condensing heat evaporator is judged by the thickness of the ice layer outside the tube,the ice content rate(IPF),the heat exchange rate and the heat transfer coefficient.(2)It is proved through experiments that surface water inlet flow rate of 0.4m/s,inlet temperature of 3℃ and refrigerant evaporation temperature of-6℃ are the optimal operating parameters.(3)It is proved through experiments that the reduction of heat exchanger tube diameter and heat exchanger tube spacing is beneficial to the extraction of heat of condensation.This paper determines that the heat exchanger tube diameter and tube spacing are 10 mm and80mm respectively as the best structural parameters of the condensing heat evaporator.(4)The hydrophobic coating has a significant effect in inhibiting icing and weakening the adhesion of ice on the outer wall of the heat exchanger tube,which can significantly reduce the de-icing time in the later stage of de-icing.After 25 min of the experiment,the ice thickness was 67.7% higher without hydrophobic coating than with hydrophobic coating in the icing experiment;in the de-icing experiment,the efficiency of hydrophobic coating combined with hot-melt de-icing method was increased by 50% compared with the conventional hot-melt de-icing method.(5)It was found that the heat transfer efficiency was highest within the first 15 min,and decreased within 15～25min.But after 25 min the ice layer is too thick and the solidification heat transfer is hindered.Therefore,according to different needs,it is recommended to choose15 min or 25 min as the de-icing cycle,and the choice can be based on the difficulty of the de-icing method and the cost of de-icing.