Experimental Research On Performances Of Slit Fin-Tube Heat Exchanger Under Free And Restricted Air Inlet Conditions

Fin-tube heat exchangers are widely used in many industrial applications, such as metallurgy, chemical engineering and HVAC systems. The airside heat transfer and pressure drop characteristics of fin-tube heat exchangers are the key issue studied by many researchers in HVAC field. The performances of heat exchanger are influenced by its geometry structures and working conditions. The geometry structures include fin pitch(FP), fin thickness(tF), row number(RN) and step number(SN), the working conditions include inlet air conditions(dry bulb and wet bulb temperature), air flow rate, media temperature and flow rate inside the tube, the air inlet conditions(free air inlet and restricted air inlet) and inclination in installation.At present, there are mainly two methods in the researches on performances of heat exchangers: Experimental method and Numerical simulation method. Due to the complex flow pattern of the two fluids inside the heat exchanger, it is difficult to get reliable results through one numerical simulation method, so experimental method is widely used in the researches of heat exchangers.For use in air conditioning system, dehumidifying phenomenon will happen in fin and tube heat exchanger when fin surface temperature is lower than incoming air dew temperature. Under this condition, the heat transfer forms between the two fluids include sensible heat transfer and latent heat transfer, it is more complicate than dry condition under which only sensible heat transfer happens.The effect of free and restricted air inlet conditions is also included in this study. At the same time, there are different inclinations in installation of heat exchanger to reduce the space. So the effect of air inlet condition and the inclination angle on the airside performances of heat exchanger under wet condition is the main content in this study.The airside performances of heat exchanger under wet condition have been investigated through proper method in a constant temperature and humidity chamber. The airside heat transfer and pressure drop characteristics are presented in the form of heat transfer coefficient ha and the ratioεof pressure drop between wet condition and dry condition respectively.Based on the above purposes, the following works are included in this study:1) Under free air inlet condition, the effect of the heat exchanger inclination angleθon airside transfer coefficient ha and the ratioεis experimented.2) Under free air inlet condition, the effect of fin pitch, fin thickness, row number, step number on airside transfer coefficient ha and the ratioεis experimented.3) With stated inclination angel,the effect of air inlet condition (free air inlet and restricted air inlet) on airside transfer coefficient ha and the ratioεis experimented.4) Under restricted air inlet condition, the effect of air inlet angle on airside transfer coefficient ha and the ratioεis experimented.5) Under free air inlet condition, experimental data for different heat exchangers have been fitted and compared through three different methods.Some conclusions obtained from the study: under free air inlet condition, except whenθis 60°, the effect ofθon ha andεis neglectful; in the study, the effect of FP and RN on airside performances of heat exchanger are greater than that of other structure parameters; with different range ofθ(θ>0°,θ<0°), ha andεchange with different air inlet condition; Under restricted air inlet condition, the inlet angle has no influence on the airside performances of heat exchangers basically.