Fluidized Descaling Of Sewage Heat Exchangers Based On Shape Factors Of Solid Particles

The use of renewable energy to reduce HVAC energy consumption is of great significance to reducing carbon emissions.Urban sewage is an ideal low-grade heat source for heat pumps,and sewage source heat pumps can extract waste heat from sewage.Due to the poor quality of urban sewage,the problem of heat exchanger fouling in the actual application of sewage source heat pumps cannot be avoided.The fouling of the heat exchanger not only reduces the heat exchange efficiency of the system,but also increases the initial investment and system operation and maintenance costs,which seriously affects the promotion and application of sewage source heat pump technology.Therefore,the effective removal of dirt on the heat exchange surface of the sewage heat exchanger is an urgent problem to be solved.Based on the literature research on sewage heat exchanger fouling,this paper analyzes the types of fouling,the formation mechanism of fouling,the structure of fouling layer,the factors affecting fouling growth,and the prediction model of fouling deposition.Different fouling monitoring methods and heat exchanger descaling methods are compared.In this paper,the shell and tube sewage heat exchanger is used as the research object,and the photosensitive resin particles of different shapes are used as the solid particles.The flow characteristics experiment of the horizontal single-tube liquid-solid circulating fluidized bed and the sewage heat exchanger descaling experiment are carried out.The main work content and conclusions are as follows:(1)In this study,we designed and built a liquid-solid circulating fluidized bed experiment platform with a horizontal transparent test tube.Using the ccd camera image acquisition method,the fluid velocity,particle addition volume percentage,pipe inner diameter,particle type and solid particles were studied.The influence of the flow characteristics in the pipeline.The experimental results show that fluid velocity is the main factor that affects the flow characteristics of particles in the pipeline.With the increase of fluid velocity,the unbalanced rate of particle distribution decreases,and the axial relative velocity of particles first decreases and then increases.The experiment tested particle addition volume percentage and particle shape have no regular influence on the particle distribution imbalance rate and the particle axial relative velocity.In the three pipeline inner diameter working conditions tested in the experiment,the particle distribution is more uniform under the pipeline inner diameter of 40 mm,and the particle axial relative velocity is higher under the pipeline inner diameter of 25 mm.The experimental results provide a reference for the determination of the operating parameters of the fluidized descaling of the sewage heat exchanger.(2)This research designed and built a horizontal liquid-solid circulating fluidized bed sewage heat exchanger experimental platform,using the fouling thermal resistance method to monitor the fouling thermal resistance in the heat exchanger,and using fluidized on-line descaling technology to control the structure The fouling sewage heat exchanger is used for the experimental research on descaling.The research results show that the fluidized online descaling technology can effectively remove the fouling deposited in the sewage heat exchanger.In the descaling condition of Somos1 particles,Somos2 particles,Somos3 particles and Somos4 particles,the fouling resistance of the heat exchanger was reduced by49.13%,50.42%,49.72%,41.53%,respectively.Among the particle shapes tested in the experiment,the particles with sharp edges and corners have the best descaling effect,and the scratching effect of the particles on the dirt is the main way to remove soft dirt.The solid phase particles of photosensitive resin material have low hardness,which can effectively remove the soft dirt deposited on the heat exchange surface,but the ability to remove hard dirt is weak.In order to obtain ideal descaling efficiency and descaling effect,particles with sharp edges and corners and suitable material hardness should be selected as the solid phase.