Experimental Study On Heat Transfer Performance Of Spiral Tube-in-tube Condenser In Air-source Heat Pump

Heat pump technology is an effective energy-saving method, it is widely used for heating and domestic hot water heating, condenser, as a key component of heat pump water heater, its heat transfer effect directly affects the performance of whole system. Because of its compact structure, high heat transfer efficiency, secondary flow and simple production, spiral tube-in-tube heat exchanger has a broad application prospect in the heat pump, refrigeration and air conditioning industry. It has the important practical value for energy-saving operation of a heat pump water heater, the design of the spiral tube-in-tube heat exchanger and application that the heat transfer characteristics of spiral tube-in-tube condenser in heat pump water heater was researched.A air-source heat pump water heater, using R22as the working medium, was designed and set up, and a spiral tube-in-tube heat exchanger was used for condenser, R22flows in annular space between the inner and the outer tubes, water flows in inner tube, they adopts a counter-current arrangement. The heat transfer characteristics of spiral tube-in-tube condenser was experimental tested in different inlet water temperature and in different volume flow of water, and the experiment was conducted at the range of water flow from0.4to O.53m3/h, the range of water temperature from17℃to34℃The variations of total heat transfer rate, total heat transfer coefficient with the change of water temperature and water flow were experimentally tested, the results show that the total heat transfer rate and the total heat transfer coefficient of spiral tube-in-tube condenser decrease with the increase of inlet water temperature, for the water flow of0.53m3/h, when the water temperature rises from17℃to34℃, the total heat transfer rate and the total heat transfer coefficient were reduced by about22.5%and22.5%respectively. And the total heat transfer rate and the total heat transfer coefficient increase with the increasing water flow rate, the water temperature is17℃, the total heat transfer rate and the total heat transfer coefficient increase by about20%and25%respectively when the water flow varies from0.4m3/h to0.53m3/h, and the overall heat transfer coefficient increases by about19%when the water flow increases0.25times.The variations of condensation heat transfer coefficient of refrigerant in spiral annular space with the change of vapor quality, water temperature and water flow were experimentally tested, and it indicates that the local condensation heat transfer coefficient of R22in spiral annular space increases with the decrease of vapor quality. The water flow is0.53m3/h, the local condensation heat transfer coefficient decreases by about12%to10%when water temperature rises from17℃to34℃. And the local condensation heat transfer coefficient of R22in spiral annular space increases with the increasing water flow, under the same water flow, the condensation heat transfer coefficient of refrigerant increases with the decreasing water temperature, the condensation heat transfer coefficient increases by about16%when water flow increases0.22times; and the condensation heat transfer coefficient increases by about4%when water flow increases0.08times.Application documents within the flow channel in the similar development in heat transfer calculation formula, through the reasonable correction, calculate the refrigerant in the annular channel in local condensation heat transfer coefficient, and comparing with the experimental results, the results show that the water temperature is17℃, tube inlet flow rate is0.53m3/h, R22in spiral casing condensation heat transfer coefficient of annular space, relative levels strengthened tube No.1, No.2, No.3tube condensation heat transfer coefficient increased by about60%,35%,24%respectively;R22in spiral casing annulus of condensation heat transfer coefficient is relatively revised spiral pipe, casing condenser low finned tube outside the condensation heat transfer coefficient increased by28.7%and6.8%, respectively.This paper provides the reference and theoretical basis for the optimization and design of spiral tube-in-tube heat exchanger; it has a certain guiding significance on the energy-saving operation of the air conditioning and heat pump system. And it also has reference significance for the study on spiral tube-in-tube heat exchanger under the same or similar conditions.