Research On Heat Transfer Performance Of A Water Tank With Helical Heat Exchangers For Double Heat Sources

With the maturity of renewable energy utilization technology and the increasingly urgent demand for distributed heating in central and southern China,a variety of heating and hot water systems with renewable energy have been widely used.In the system,a water tank with double helical heat exchangers plays a core part in the heat transfer process between heat sources and loads.It should be attached great importance to analyze its structure to improve its heat transfer performance,thus the heat transfer efficiency of the whole system can be improved.A water tank with double helical heat exchangers for double heat sources is studied,which is used in a double-heat-source heating and hot water system.Firstly,the physical model and mathematical model of the water tank are established.Then,the accuracy of the model was verified through experiment,by setting up a double-heat-source heating and hot water system and comparing the simulated and experimental values under three different working conditions.The structure of the original water tank was optimized,and the values of various factors were changed to build different models.The influence of different parameters on the heat transfer effect and temperature field of the water tank were studied.Different factors have different impact on Nu,and the same factor may have different impacts on Nu of the upper and lower coils.In the research,with the increase of the distance between the heating coil and the top of the tank,the distance between the solar coil and the bottom of the tank,the ratio between the bending diameter of the helical coil and the diameter of the water tank,and the screw pitch of the helical coil,Nu on the outer side of the upper and lower helical coils monotonously changes.Effects of different parameters on the heat transfer performance and the temperature field of the water tank were studied.The simulation results were used for fitting.The relationship between Nu on the outer side of the two helical coils and various factors was obtained,and the importance of each factor was analyzed.Nu is greatly influenced by the ratio of the direct inflow velocity,the screw pitch of helical coil,and the bending diameter of the helical coil to the diameter of the water tank.For Nu of the upper coil,the factors related to the upper part of the tank are more influential than those related to the lower part.For Nu of the lower coil,the factors related to the lower part of the tank are more influential than those related to the upper part.