Heat pump sludge drying based on belt through-flow drying model
The through-flow drying experiments of sludge samples at various temperatures have been carried out by using a constant temperature and humidity box,and the moisture diffusion coefficient is concluded from the obtained sludge drying characteristic curve.By analyzingthe moisture and heat transfer and the balance in the multi-layer belt through-flow drying process,a thermodynamic model describing its steady operation state is constructed.According to the characteristics of belt drying,a reverse diffusion iterative algorithm from bottom to top is designed to calculate the moisture distribution in sludge layer,and then the coupling calculation of the humidity field and the temperature field is finished.The distribution of the average moisture content of the sludge along the belt length is obtained,and the temperature and humidity changes of the through flowing air are investigated.Subsequently,in the theoretical analysis of the drying and dehumidifying heat pump system,the solution steps of the thermodynamic model of multi-layer belt through-flow drying are added in,the best evaporation temperature and the best dehumidification energy efficiency under different inlet temperature and humidity conditions have been acquired.Finally,a constrained working condition is selected to do drying process analysis.The results show that thinning the sludge layer and shortening the drying time are benefit to the rise of productivity and energy efficiency.
multi-layer belt through-flow dryingdrying characteristics of sludgeheat pump systemthermodynamic numerical modelreverse iteration
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