Study On Flow Heat Loss Characteristics Of Bath Wastewater In Pipe And Operation Characteristics Of Composite Heat Pump System

In the context of increasingly prominent energy and environmental issues,the recycling of bath wastewater is still very limited at home and abroad.A large amount of waste heat in bath wastewater is discharged directly without recycling,which will not only cause energy waste,but also easily cause environmental heat pollution.In actual engineering,it is the most common practice to use bath wastewater source heat pump to recover the waste heat from bath wastewater to prepare hot water for bath.In order to ensure the stability of the system,air source heat pump is often used for assistance at the same time.However,under different conditions,heat loss will occur during the flow of bath wastewater along the way,resulting in differences in the temperature of the final flow into the wastewater tank,which will affect the amount of heat that can be recovered,and then affect the selection of the unit and the operation of the system.Therefore,this paper numerically simulates the heat loss characteristics of bath wastewater in drainage pipes,and conducts experimental research on the operating characteristics of bath wastewater source-air source composite heat pump system.In terms of numerical simulation,a three-dimensional numerical model of flow and heat transfer in bath wastewater pipes was established,and the influence of factors such as insulation layer,depth ratio,ambient temperature,pipe slope,and pipe diameter on the flow heat loss characteristics in bath wastewater pipes was discussed.The results show that as the drainage process continues,the bottom of the pipe near the water side is more prone to heat accumulation than the top of the pipe near the air side,and the heat loss ratio and heat loss rate will gradually increase.The closer the drainage pipe is to the inner layer,the more intense the heat flux at the interfaces changes,and the closer it is to the outer layer,the more gentle it is.Compared with ordinary PVC pipes,PVC polyurethane insulation pipes can effectively reduce the temperature drop of bath wastewater along the way and the heat flux at the interfaces,and the longer the pipe length,the more obvious the heat preservation effect,but the heat loss ratio of the two has no different trend.As the depth ratio increases,the temperature drop of bath wastewater along the way will decrease significantly.For example,when the depth ratio is 0.1 and 0.3,the temperature drop is 56.86 and 21.5 times larger than that when the depth ratio is 0.5.The thermal influence range,the excess temperature of the insulation layer at the top and bottom of the pipe,the heat flux and heat loss rate of each interface will increase accordingly,but the temperature drop of bath wastewater along the way will decrease.As the ambient temperature decreases,the temperature drop of bath wastewater increases,and the heat flux at the interfaces increases,but the heat loss rate is not affected.With the increase of pipe slope,heat loss ratio and the heat flux at the interfaces increases,but the temperature drop of bath wastewater along the way decreases.Under the same flow rate,with the increase of pipe diameter,the temperature drop of bath wastewater will increase significantly,and the temperature drop of 110 mm and 160 mm PVC polyurethane insulation pipes is 5.68 times and 10.13 times that of 75 mm respectively.In terms of experimental research,based on the bath wastewater source-air source composite heat pump system,the effects of wastewater and clean water flow ratio,single preparation time,hot water tank level,and hot water tank temperature return difference on the operation of the bath wastewater source-air source composite heat pump system were explored.The results show that:under the constant clean water flow mode,appropriately increasing the wastewater flow can increase the heating capacity of the heat pump system,increase the clean water outlet temperature,and increase the coefficient of system performance of the system(COPs),but the imbalance between the wastewater flow and the clean water flow will easily make the system difficult to operate for a long time.In the equal flow ratio mode,increasing the wastewater flow and clean water flow synchronously can increase the heating capacity of the heat pump system,reduce system energy consumption,and increase COPs.The long-term stability of the system operation is better,but the temperature of the clean water outlet will be reduced.When the compressor of the bath wastewater source heat pump is preheated,the clean water from the municipal water supply network will flow directly into the hot water tank without being heated.The shorter the single preparation time,the greater the impact on the water temperature of the hot water tank.When the liquid level of the hot water tank is too low,the temperature drops quickly,and the water temperature of the heated water tank tends to be high.When the liquid level of the hot water tank is too low,the temperature drops quickly,and the temperature of the heated water tank tends to be high.The higher the liquid level of the hot water tank,the longer the single heating time and heating cycle of the air source heat pump,but setting a higher water level in the hot water tank does not save energy.With the increase of the temperature return difference of the hot water tank,the single heating time,heating cycle and system cycle power consumption of the air source heat pump will gradually increase.When the set value of the temperature return difference of the hot water tank is large,the temperature drop of the hot water tank can be slowed down,and the heating cycle can be lengthened,which can achieve a certain energy saving effect,but there may be a problem that the temperature of the hot water for bath changes too much.This paper aims to explore the influence of different factors on the flow heat loss characteristics of bath wastewater in pipes,and conduct research on the operating characteristics of bath wastewater source-air source composite heat pump systems,so as to provide a reference basis for the estimation of the residual heat of bath wastewater and the operation regulation of the bath wastewater source-air source composite heat pump system in actual engineering.