Simulation Study Of The Performance Of Heat Pipe Heat Exchangers

With the development of industrialization,the problem of energy shortage has gradually surfaced.How to use energy more efficiently is the test we face.As an energy exchange device,the heat exchanger is slowly entering the public eye.How to optimize the design to make it run more efficiently has become a research hotspot.In this paper,a heat pipe heat exchanger is designed according to the application scenarios and application scope of the heat exchanger,and the structure is optimized.Heat pipe is a kind of enhanced heat exchange equipment.Because of its excellent heat transfer performance,it is often used in waste heat recovery system,but it is seldom used in liquid-liquid conditions.In this paper,a heat pipe exchange with a single arcuate baffle is designed.The heat exchanger is also searching for the optimal combination of baffle size and arrangement.According to the research experience of tube heat exchangers,the height and spacing of the baffle notches are critical to the overall performance of the heat exchanger.The simulation research is based on the CFD software,and the overall heat transfer performance is studied through the FLUENT numerical simulation method,and the velocity,temperature and pressure distribution diagrams are obtained and the working conditions are analyzed.In order to verify the rationality of the model design and comprehensively evaluate the overall efficiency of the heat exchanger,the JF evaluation factor is introduced.The JF factor can be combined with the heat transfer coefficient and pressure loss of the heat exchanger to comprehensively evaluate the performance of the heat exchanger and find the optimal solution.The following is the main research content of this article.(1)Firstly,the heat pipe heat exchanger with baffle plate is compared with the heat pipe heat exchanger without baffle plate,and it is concluded that the heat exchange rate is greatly improved after the baffle plate is added,which verifies that the baffle plate is added feasibility.(2)Then conduct a simulation study on the layout of the inlet and outlet of the heat pipe heat exchanger,and obtain four working conditions by permuting and combining the inlet and outlet of the evaporator and condenser.Comparing the JF factors under the four working conditions,the working conditions of the evaporator top in and bottom out,and the condenser top in and bottom out were finally selected in the four working conditions.(3)Under the working condition that the evaporator and the condenser are both top-in and bottom-out,different baffle notch heights are selected to compare the heat transfer performance under the in-line working condition of the heat pipe bundles,and the poor performance notch height is eliminated according to the JF factor.The baffles are 0.5D and0.15 D.The simulation shows the heat transfer,pressure loss,and JF factor of baffles with a notch height of 0.4D and 0.25 D under in-line and cross-line conditions,respectively.It is concluded that under the same working conditions and the same inlet parameters,the heat exchange of the fork row is greater than that of the in-line row,and the resistance is also greater than that of the in-line row.(4)In order to further determine the specific value of the notch height of the baffle,a model with the notch height of the baffle of 0.4D,0.35 D,0.3D,0.25 D was established to compare the flow conditions and heat exchange under different working conditions.Finally,the best baffle is obtained when the notch height is 0.3D.The baffle gap is small,the flow velocity through the gap is large,the heat exchange effect is good,but the pressure loss is also very large at the same time,the fluid can better scouring the tube bundle laterally,and the heat exchange is more sufficient.When the notch height of the baffle is too large,the fluid passing through the baffle will not have too much pressure loss,and the longitudinal flow is more,and the heat exchange effect is slightly worse.(5)Then determine the baffle spacing.The baffle spacing range is usually between0.5D～1.0D and not less than 50 mm.Therefore,models with spacings of 50 mm,75 mm,100mm,125 mm and 150 mm have been established.The flow above 125 mm has a large dead water area,and the resistance of 50 mm is too large.The final study range is set to 70 mm,80mm,90 mm and 100 mm.The resistance decreases with the increase of the baffle spacing,but when it exceeds 90 mm,the resistance increases instead.After comparing the JF factor,it is obtained: When the notch height is 0.3D,the model with the baffle spacing of 90 mm is the best.This study concludes that when determining the temperature difference and speed,the smaller the spacing of the baffles and the reduction of the height of the baffle gaps will lead to an increase in heat exchange and an increase in resistance.When the entrance temperature of the condensing section is 20℃,the entrance temperature of the evaporation section is 40℃,the internal flow velocity of the hot end of the heat exchanger is 0.20m/s,and the flow velocity of the cold end is 0.15m/s,the upper inlet and lower outlet of the evaporation section and the upper inlet and lower outlet of the condensing section are adopted.During the layout,the baffle notch height is 0.3d,and the baffle spacing is 90 mm,and the overall heat transfer performance is better.