Study On Frosting Performance Of Heat Pump In Cold Region

Air source heat pumps are widely used in the world because of their high efficiency and environmental protection.But in the cold and wet areas use air source heat pump,outdoor units of its coil surface frost is inevitable,its surface frost phenomenon is very serious,and the frost layer will be more and more thick,it increases the thermal resistance of thermal conductivity of heat exchanger,seriously hindered the evaporator heat exchange with the environment,thus affect the efficient operation of the heat pump equipment.The frost layer not only leads to the decrease of system efficiency,but also increases the defrost energy consumption and the maintenance and management cost of the system.This thesis is based on the heat pump frost defrosting problem to carry out research.The frosting condition of water vapor on the cold surface is not only related to the ambient temperature and humidity,but also to the surface characteristics of the cold surface.Through surface treatment technology,changing the surface characteristics of the material,the frosting process of cold surface can be controlled,the frosting time can be delayed,so as to reduce the adverse impact of frosting on the operation of the air source heat pump system,improve the operating efficiency and working stability of the system,and it also has many advantages such as anti-pollution,anti-corrosion.In the dissertation,the contact Angle of different coating materials or finned materials treated by different processes was measured,and the frosting experiment platform was set up.By observing the process of droplet formation and initial frost crystal growth on the surface of three different materials with contact angles of 21.13 °,57.14 ° and 120.87 ° at temperatures of 5 ℃,0 ℃,-5 ℃,and-10 ℃,respectively,the frost formation characteristics of the surface and the frost mass per unit area changing with time were obtained.When the test time is less than 15 minutes,the finned surface with contact angle less than 90°got larger crystal size and denser frost coverage.However,the finned surface with contact angle greater than 90 ° has smaller crystal size and sparse frost coverage.When the test time reached 120 minutes respectively,the surface with contact angle less than 90°has been completely covered with frost layer,and the frost layer is dense,relatively compact,and the air is not easily circulated.However,the frosting on surface of fin with contact angle greater than 90 °is relatively loose and porous,and the air is relatively easy to circulate.The fin frosting experiment in different temperature and humidity was carried out as well,The results show that the larger the contact angle is,the smaller the frost mass per unit area is.When the contact angle of fins is greater than 90 °,the hydrophobic fins have obvious effect of delaying frost formation in the early stage of frost formation,and the ability of restraining frost formation is more obvious in the frosting process.The lower the ambient temperature and the lower the relative humidity,the less the frosting mass per unit on the fin surface.