Study On A Novel Anti-fouling Wastewater Source Heat Pump Using Air As Medium

With the development of urbanization and industrialization,a large amount of sewage containing rich waste heat energy is produced from industries,commercial sites and people’s daily.In today’s environment protection and energy saving,we can consider using heat pump to recycle waste heat from sewage to meet the daily heat demand.However,it is necessary to pay attention to the poor water quality when using sewage as the heat source.The fouling deposited on the surface of heat exchangers will lead to a serious decline in heat exchange efficiency and even cause the shutdown of the heat pump unit.The development of a simple,reliable,low-cost wastewater source heat pump which can completely solve the problem of scaling is the key to promote wastewater source heat pumps.In order to solve the problem of fouling and clogging in the heat exchanger in the process of wastewater heat recovery,this paper proposes an efficient anti-fouling wastewater source heat pump system with air as the medium,which can realize the direct contact heat transfer between the air and wastewater and make full use of the latent heat of the wastewater due to the phase change.In this paper,the system schematic diagram of the efficient anti-fouling sewage source heat pump and the detail diagram of the wastewater tower were described at first.Based on the schematic diagram,the construction of the experimental prototype was completed,and the specific selection of each component of the experimental prototype was given,and the control device and measuring instrument of the experimental prototype were introduced.The operating performance tests of the experimental prototype were carried out.The influence of sewage temperature,preset temperature of hot water,sewage flow rate and circulating air flow rate on system performance was studied.The performance of the system in recovering the heat of bath wastewater was analyzed,proving that it has good performance of wastewater heat recovery.Then,the long-term performance test of the experimental prototype was carried out.The quality of the sewage used in the experiment and the performance of the system under clean conditions were introduced.The changes of heat transfer rate of the evaporator,total heat resistance of the evaporator,evaporating temperature of the refrigerant,COP of the system,and heat transfer rate of the wastewater tower were given based on the monitoring data during long-term operation.The quality of condensed water at the evaporator is compared with that of sewage used in the experiment.The quality of the condensed water at the evaporator was compared with that of sewage used in the experiment,proving that the system has good anti-fouling performance.Finally,COMSOL was used to simulate the air flow field in the wastewater tower.The model was simplified reasonably,and the correctness of the model was proved by comparing with the experimental data.Based on the model,the influence of the number of baffles and baffle spacing on the air side pressure drop of the wastewater tower was studied,and the prediction formula of the pressure drop was obtained.The research of this subject is of great significance for people to understand the operation characteristics of this new type of sewage source heat pump system,which provides reference basis and theoretical support for the development of efficient and anti-fouling sewage heat exchange equipment with air as the medium.This project comes from the research project of "national key research and development program funding"(project number: 2017YFC0702900).