Study On Flow And Heat Transfer Characteristics Of Liquid Film On Rectangular Microgroove Plate With Herringbone Arrangement

The liquid film on the existing plate-type evaporative cooler is affected by the surface tension and contact angle,and will shrink into the stream in the smallest volume direction.The dry spot on the surface of the heat exchanger is not covered by liquid film,which seriously worsens the heat transfer effect.To increase the efficiency of heat transfer,it is necessary to increase the spreading area of liquid film on the surface of the plate.In order to achieve this effect,an innovative method is proposed to engraved a small rectangular groove on a flat surface.The microgroove will guide the falling liquid film to spread horizontally,thus increasing the heat transfer area and increasing the heat transfer efficiency.In this paper,the flow characteristics and heat transfer characteristics of the liquid film on rectangular microgroove plate with herringbone arrangement are studied by cold state experiment,heat exchange experiment and numerical simulation.the better design parameters of the groove are given in the range of research.The main research results are as follows.(1)Herringbone arranged rectangular microgrooves effectively guide the liquid film spreading horizontally,which increase the wetting area of liquid film.In the study range,when the design parameters of the microgrooves are: deep is 0.3mm,wide is 0.5mm,and the angle of Herringbone character is 120 degrees,the surface wetting area can be increased from 62%~89% on the surface of the light plate to 84%~94%.(2)The heat transfer effect of the liquid film on the flat surface is influenced by the design parameters of microgroove and the Reynolds number.At the lower Reynolds number,the dimensionless outlet temperature of the 60 degree herringbone rectangular microchannel plate is 1.4 times that of the light plate,when the Reynolds number is large,this parameter is 1.6 times the light plate.(3)The experimental results show that the existence of rectangular micro-grooves with herringbone arrangement can effectively improve the wetting area of liquid film on the surface of flat plate at different liquid distributing speeds.When the liquid distributing parameters are n=4 and v*=0.59m/s,the specific wet area of liquid film on the flat plate with herringbone grooves of 120 degree,90 degree and 60 degree is 47.1%,43.2% and 31.3% larger than that on the smooth plate.By comparing the plate temperature,the heat transfer effect of 120 degree herringbone micro-groove plate is the best.(4)Vibration is an effective method to improve the heat transfer efficiency of the liquid film on a plate surface.The frequency and amplitude of the vibration parameters have a comprehensive effect on the heat transfer efficiency.In the range of study,when the amplitude is 2.0mm and the frequency is 50 Hz,the heat transfer efficiency of the falling film is increased by 27% compared to the non vibration state.