Simulation Research On Heat And Mass Transfer Of Hydrophobic Membrane Plate-and-Frame Absorber

At present,research on energy conservation and emission reduction has attracted worldwide attention,and absorption refrigeration systems can use environmentally friendly renewable energy and refrigerants to prevent damage to the ozone layer.Therefore,it is speculated that the application of absorption refrigeration systems will increase in the future.However,compared with the vapor compression system,the absorption refrigeration system has a higher cost,and for large-scale applications,the available time is very short.Therefore,the application of absorption refrigeration technology in cooling applications is still relatively small,especially in mobile applications.In the refrigeration or air-conditioning sector,absorption refrigeration has not received much attention.The main disadvantages of the absorption refrigeration system are the small unit cooling capacity and the large volume of machinery and equipment.These conditions limit its application in mobile equipment,small-volume commercial and residential buildings.Therefore,in the future,there is an increasing need to design an absorption refrigeration system that can be applied on a small scale and has a small space requirement.In order to solve this problem,the research of hydrophobic membrane plate-and-frame absorber is particularly important.The research background and research progress of the hydrophobic membrane absorber are introduced,and the heat transfer inside the hydrophobic membrane plate-and-frame absorber was analyzed at the same time.The qualitative mechanism,the physical model is determined,and the mathematical model of the solution and cooling water channels is established through reasonable assumptions.After considering the changes in the physical properties of the lithium bromide aqueous solution,a numerical model of the hydrophobic membrane plate-and-frame absorber was established based on the COMSOL platform,and the accuracy of the model was verified by comparison with previous studies.The influence of constant physical properties and variable physical properties parameters on the calculation process is explored,and the necessity of variable physical properties calculation is proved.The influence of diffusion coefficient and thermal conductivity on absorption is explored by changing the diffusion coefficient and thermal conductivity under normal physical conditions.The result shows that the absorption rate increases with the increase of the diffusion coefficient and thermal conductivity.By changing the cooling water temperature and the solution inlet concentration to create different temperature and concentration conditions,the influence of concentration and temperature on absorption is explored.Compared with temperature,concentration has a greater impact on absorption.It also explores the effect of geometric parameters(channel height,length,etc.)and membrane parameters(film thickness,porosity,etc.)on the performance of hydrophobic membrane plate-and-frame absorber at different concentrations.The influence of the absorption rate with these parameters under different concentration conditions is obtained.The height of the cooling water channel is changed under different solution channel heights,and the average absorption rate of the lithium bromide aqueous solution at the solution-membrane boundary is used as the standard to explore the influence of the cooling water channel height on the absorption.If the solution channel is higher than 0.4mm,the cooling water channel is designed to be 0.4mm to reduce the volume of the absorber while the absorption rate remains unchanged.If the solution channel is less than 0.4mm,the The cooling water channel is designed to be 0.4mm,which can effectively increase the absorption rate and make the absorption effect better.In order to explore the influence of the surface morphology of the membrane on the absorption,the solution-membrane contact surface was set as a sine wave and found that there are two main factors affecting the absorption The first is the fluctuation of the solution-membrane contact surface.When a high-concentration solution is retained in the protrusion,it is difficult to be taken out of the channel with the flow of the solution,thus hindering the absorption.The higher the protrusion at the solution-membrane junction,the lower the absorption rate.The second point is the disturbing effect caused by the fluctuation of the solution-membrane contact surface.The solution passes through the solution-membrane interface and will fluctuate up and down with the wave in the interface.The effect of perturbation accelerates the mixing speed of the absorbed water vapor and the solution.The absorption rate increases,and as the wave amplitude becomes larger,the disturbance will also become larger.The interaction of these two factors together has an impact on the absorption rate at the solution-membrane junction.The amplitude of the wave becomes larger,and the disturbance effect is enhanced,and the retention effect on the solution will also increase.Therefore,the absorption rate increases or decreases depending on which effect is greater.In order to explore the influence of the shape of the cooling wall on the absorption,the cooling water-solution interface is set as a sine wave.Due to the existence of the wave crest,the flow of the cooling water is hindered,and the cooling water that has absorbed heat is stuck inside the wave crest and cannot flow out of the channel.The temperature is taken away inside,and the influence of disturbance on the absorption process of the contact surface of the solution film is not obvious.Therefore,the absorption rate increases slightly under certain conditions,but the amplitude is not large.The solution channel was bent to explore the influence of the bending damage of the absorber on the absorption,and it was found that the weak bending can effectively increase the absorption rate,but as the degree of bending continues to deepen,the absorption rate gradually begins to decrease.The calculated maximum absorption rate is generated when the wave amplitude is 0.05 mm,which is 4.5% higher than the absorption rate when it is not bent.