Research On The Mechanism Of Droplet Generation And Propagation During Gas-liquid Interaction In Air Conditioning

Reducing the energy consumption of air conditioning systems is still a hot topic at home and abroad,the use of direct contact air treatment devices(such as frost-free air source heat pumps)in the air conditioning system can reduce the energy consumption of the air conditioning system,however,the droplet entrainment problem in these devices has had a certain impact on their promotion and use,moreover,the current research on the mechanism of droplet entrainment in air-conditioning systems belongs to a relatively new field,therefore,the study of the liquid film flow and floating liquid mechanism in the packed tower in this paper has a certain significance to prevent the droplet entrainment.This paper uses CFD research methods to simulate the flow of liquid film and the generation of droplet entrainment,and uses high-speed cameras to conduct experimental research on the propagation of droplet entrainment.The main results are as follows:The calculation model built first is verified,then the flow characteristics of the liquid film on the packing plate under different working conditions are studied,the results show that the calculation model constructed in this paper is reliable.When the inclination angle of the triangular corrugated packing plate is 90° and 60°,the liquid film on the packing plate will break;When the inclination angle of the triangular corrugated packing plate is 45° and 30°,the liquid film flow on the packing plate is relatively stable;When the inclination angle of the packing plate is 90°,the isopotential line of the flow function will be peeled off at the end of the runner,when the inclination angle of the packing plate is 45°,the isopotential line of the flow function will be smoothly close to the wall of the corrugated plate.The spreading time of the liquid on the rectangular packing plate is longer than the spreading time of the liquid on the trapezoidal packing plate is greater than the spreading time of the liquid on the triangular packing plate;The liquid film spread on the triangular corrugated packing board is complete,and the liquid film spread on the rectangular and trapezoidal corrugated packing board has cracked in different degrees.When the wavelength of the triangular corrugated packing plate is10 mm and 5mm,a complete liquid film can be formed on the packing plate,but when the wavelength of the triangular corrugated packing plate is 2.5mm,the liquid film on the packing plate will break;The flow function equipotential lines on the 10 mm wavelength packing plate will fit smoothly to the wall of the packing plate,and the flow function equipotential lines on the 5mm and 2.5mm wavelength packing plates will appear in the corrugated groove of the packing plate.Calcium chloride solution failed to spread a complete liquid film on the triangular corrugated packing board,and water and glycol solutions could spread a complete liquid film.When the liquid phase inlet velocity is 0.05m/s,the liquid cannot form a complete liquid film on the packing plate;When the liquid phase inlet velocity is 0.1m/s,0.3m/s,0.5m/s,a complete liquid film can be formed on the packing plate.With the gradual increase of the liquid inlet flow,the range of liquid "ribs" on the triangular corrugated packing plate gradually expands.The gas-liquid interaction and the characteristics of droplet entrainment in the packing channel are studied.The results show that: when the gas outlet velocity is 0.5m/s and 1.5m/s,the velocity cloud diagram of the steady flow of the liquid film can be clearly seen on the surface of the packing plate on the lower side of the triangular corrugated packing channel,There are airflow vortices in the corrugated grooves of the lower packing plate,and there are low-speed areas in the corrugated grooves of the upper packing plate;When the outlet wind speed is 0.5m/s,the velocity cloud picture near the air inlet of the triangular corrugated packing channel is more turbulent;The turbulent kinetic energy near the interface between the liquid film and the air is relatively large;the turbulent dissipation rate in the entire channel is almost unchanged;In the triangular corrugated packing channel,as the inlet velocity of the liquid phase increases,the outlet velocity of the gas phase when droplet entrainment occurs slightly decreases;This article also describes the process and mechanism of the droplet entrainment in the triangular corrugated packing channel.The velocity contours in the trapezoidal corrugated packing channel with wavelengths of 10 mm and 12 mm are similar.There are airflow vortices at the corrugated grooves of the packing plate on the lower side of the channel,and low-velocity areas are present at the corrugated grooves of the packing plate on the upper side of the channel;Near the exit of the liquid film,the liquid film velocity cloud diagrams on the packing plate of two wavelengths diverge;The turbulent kinetic energy near the interface between the liquid film and the air and near the air inlet is relatively large;The turbulent dissipation rate in the entire channel is almost constant.Keep the amplitude of the trapezoidal corrugated packing plate unchanged,the gas outlet velocity when droplet entrainment occurs in the trapezoidal corrugated packing channel increases with the increase of the wavelength of the packing plate;Keeping the wavelength of the trapezoidal corrugated packing plate unchanged,the gas outlet velocity when droplet entrainment occurs in the trapezoidal corrugated packing channel decreases with the increase of the amplitude of the packing plate.Finally,the propagation characteristics of the droplets are studied.The results show that when the impact velocity is 0.3243m/s,the droplets produce "sub-droplets" after impacting the plate with a contact angle of 128.4°;When the impact velocity is 0.405m/s,the droplets produce "sub-droplets" after impacting the plate surface with contact angles of 73.1°,86.6°,and 128.4°;When other conditions are constant,the greater the contact angle between the surface of the board being hit and the water,the more likely the droplet will rebound;When other conditions are constant,the greater the impact velocity of the droplet,the easier it is to generate "subdroplets".When the impact velocity is 0.3463m/s,the phenomena that appear after the droplet collides with the droplet on the receiving plate with the contact angle of 63.4° and 73.1° are rebound,splash,fusion,and oscillation,the phenomena that occur after the droplet collides with the droplet on the receiving plate with a contact angle of 128.4° are fusion,rebound,splash,and oscillation in sequence.When other conditions are fixed,the smaller the contact angle between the receiving plate and the droplet,the more likely the droplet above to rebound after the center-to-center collision;When other conditions are constant,the greater the velocity of the droplet center-to-center collision,the easier it is to generate "child droplets" in the collision process.