Horizontal Falling-film Evaporator Spray Uniformity Analysis And Small Mass Flow Falling-film Numerical Simulation

As a high efficiency heat transfer equipment the horizontal falling-film evaporator is inresearch and development. However, the law on falling-film flow and the heat and masstransfer are not quite clear, which restricts its application and extension. The key researchcontent in the paper is to design the structure of the horizontal falling-film evaporator, tostudy on the spray uniformity of its spray system, according these to establish geometricmodel and unit simulation model, and to explore preliminarily horizontal falling film flowand the performance of heat and mass transfer.Under ambient temperature and pressure, a hole-arrayed spray experiment set wasdesigned. Two kinds of flow experiment was done and the numerical simulation wasperformed in the corresponding condition, which verified the feasibility of VOF modelavailable in the FLUENT software, and provided reliability for solving horizontalfalling-film evaporator unit simulation model applying VOF model.The design for horizontal falling-film evaporator mainly includes heat transfer designand the structure design. An objective refrigerating capacity of a central air-conditioningchiller was given, through heat transfer calculation, the falling-film heat-transfer tubebundle layout and several main dimensions such as shell diameter, inlet and outlet diameterswere obtained. Where, the related parameters to tube bundle layout involves the number oftube passes, the tube rows in every tube pass and the tube number in a row, the tube numberof falling-film part, flooded part and total bundle, etc.The nozzle flow uniformity exerts an influence directly on the heat transfer effect ofthe horizontal falling-film evaporator. The flow of spray tubes and nozzles in the system atvarious cases were numerical simulated using FLUENT, and several fundamental factorsaffecting the nozzle flow uniformity were quantitatively compared and studied with the aidof average relative error which is a characteristic parameter. The factors are spray amount, spray nozzle diameter, whether installing pressure equilibrium tube or not and single pumpor binary pump.The physical model and the unit numerical model of horizontal falling-film evaporatorwere built and thermal boundary condition was loaded, under a small inlet mass flowboundary condition three-dimensional transient case for flow field and temperature fieldwas calculated with FLUENT. Considering no mass transfer function being involved inVOF model, a multiphase mass-transfer macro was defined and the UDF program wascompiled and hooked to FLUENT. Based on the simulation results, the flow and theperformance of heat and mass transfer were analyzed. The simulation and analysis could bea reference for new product development.