Optimization Of Liquid Distribution And Its Influence On The Heat And Mass Transfer Of The Heating Tower

The heating tower heat pump(HTHP)is a new and efficient air conditioning heat/cold source.It has the advantages of low investment cost and high facility availability and has a bright prospect in hot-summer and cold-winter zone of China.The heat and mass transfer mechanism of the heating tower is similar to that of the cooling tower.The heat exchange progress of both happens when the air directly contacts the spilled solution/ water on the surface of the filling.The initial uniformity of the liquid has a decisive influence on the heat exchange area in the filling.The heating tower is designed according to the winter condition,and its mass flow density is less than that of the cooling tower.If the nozzle of the conventional cooling tower is used,the problem of insufficient utilization surface area of the filling will inevitably arise,and the overall heat exchange efficiency of the heating tower will be reduced.Therefore,in this study the nozzles for heating tower are optimized from the aspect of layout,structure,and a new kind of nozzle is designed for the heating tower.Three approaches,including theoretical analysis,numerical simulation and experimental research,are used to optimize the liquid distribution uniformity of the heating tower.The results of this study provide a new idea for the optimization of heat and mass transfer in a cross-flow heating tower and a reference for the theory and simulation study of liquid distribution in the filling.The mathematical model of the heating tower liquid circulation system was established,and the relationship between the mass flow and energy consumption of the system was studied.The power consumption of the gravity liquid distribution and the pressure liquid distribution are both calculated and compared with each other,and the result shows that the gravity liquid distribution is more energy-efficient than the pressure liquid distribution.In order to improve the initial liquid distribution in the filling and utilization of the surface area of the filling,the structure and layout of the liquid nozzles are optimized and a new type of nozzle is designed for the heating tower.The liquid distribution characteristics test platform is built,the liquid distribution characteristics of the new nozzle and the traditional nozzles and the liquid distribution law under different flow rates were tested.The uniformity of the new nozzle and the traditional ones was calculated and compared,and the superiority of the new nozzle liquid was verified.Based on the heat and mass transfer mechanism of the heating tower,the heat and mass transfer models under different liquid distribution uniformity are established.The heat and mass transfer processes under different liquid uniformity are analyzed in theory,and the effect of liquid non-uniformity on the characteristics of the heating tower is studied.The results show that,under the endothermic and hygroscopic condition,the heat exchange amount in an uneven distribution(the uniform distribution coefficient is 1)is completely reduced by 11.69% compared with the full uniform condition(the uniform distribution coefficient is 0,and it is only 0.25% different from the condition when the uniform distribution coefficient is-1.Consequently,the heat exchange amount of the heating tower relates to the change of the fluid distribution density along the air flow direction,and it is irrelevant to the direction of the distribution uniformity.A heating tower heat pump experiment system is set up for the study,and different types of nozzles are used in the experiment.Under different liquid uniformity,the effects of liquid/air mass flow rate on the heat and mass transfer of the heating tower were studied experimentally.The experimental expressions of the heat and mass transfer coefficients of heating towers with new nozzles or conventional nozzles were fitted.The experiment results show that the heat exchange amount of the heating tower with new nozzles is increased by 16.93% compared with the heating tower with single-layer nozzles,and it is increased by 50.56% compared with the heating tower with plum-shaped nozzles.