Research On Heat And Mass Transfer And Match Properties Of Absorber In Absorption Heat Pump

Absorption heat pumps are widely used in different types of central heating systems with heat recovery.In these applications,the outstanding feature of its external parameter is that large temperature rise / drop of recycled water is used as heat source for the components.This feature will make matching problems become serious,affecting the thermal performance of the absorption heat pump.Absorption is a key component of the absorption heat pump,this study mainly focus on the heat transfer and mass transfer characteristics of absorber,and analyzing the impact of unmatched properties on the thermal properties of the absorber.Finally,the unmatched problems are supposed to be solved.Previous studies mainly focus on the micro mechanism of heat and mass transfer,there are quite few studies of suitable thermodynamic analysis method.In this paper,based on the idea of temperature level and entransy dissipation,thermodynamic new cognition and analysis are made for the heat and mass transfer process of absorber used in absorption heat pumps.The thermodynamic evaluation index of absorber is proposed to be the cooing water bulk temperature.The absorber upper limit temperature is defined,the goal of optimization of absorber is to make cooling water temperature close to the upper limit temperature as much as possible.The approach is to reduce the entransy dissipation and resistance of heat and mass transfer.The heat resistance includes resistance of limit of heat transfer capability and resistance of unmatched process.The unmatched properties are effected by unmatched flow rate,unmatched parameters,flow pattern and absorption type.Adiabatic absorption and parallel flow internal-cooling absorption have poor thermodynamic property,while the counter flow internal-cooling absorption can be optimized to have good performance.Match properties of one-dimensional countercurrent absorber are analyzed.Flow matching and parameter matching are defined to study the influence of different factors on the heat and mass transfer performance.Furthermore,analytical solution is derivate for three-way flow heat and mass transfer model,and the theoretical conditions to satisfy flow matching and parameter matching are derivate.The mass transfer process of solution absorbing water vapor is equivalent to heat transfer process between solutionand hypothetical fluid.Based on the equivalent process,the heat resistances of the two heat transfer process are calculated to define flow unmatched resistance and parameter unmatched resistance.Influence of different parameters on the heat resistance and thermodynamic performance is analyzed.On the large vacuum test bench of heat and mass transfer,experiments of horizontal falling film absorption and the new falling column adiabatic absorption are carried out.Based on the experimental results,the differences between the two forms of the absorption process parameters are analyzed.The heat and mass transfer coefficients are calculated and the correlations formulas are obtained.The analysis of match properties is extended from one-dimensional countercurrent absorber to the actual two-dimensional horizontal tube absorber.A two-dimensional absorber model is established to analyze the impact of the tube pass number.The actual structure of absorber will cause unmatched heat and mass transfer process.Based on the calculation of heat resistance,larger tube pass number makes better thermodynamic property and more close to the ideal counter flow.The resistance of flow pattern is defined.For the design of absorber structure,the tube pass number should be carefully analyzed to control unmatched heat resistance and to optimize the thermodynamic performance.