Study On Structure Optimization And Characteristics Of Asymmetric Plate Heat Exchanger For District Heating

Plate heat exchanger is a very competitive heat exchange equipment,because of its high heat exchange efficiency,compact structure and other advantages,has been widely used in the field of urban central heating.In practice,however,a pipeline network of water supply and return water temperature difference is about 50℃,the secondary network around 25℃,between primary side and secondary side water supply and return water temperature difference is very big,this leads to a plate on both sides of the flow as well as the import and export of pressure drop are make a big difference,on both sides of the plate heat exchanger is completely symmetrical structure of the traditional design can’t meet such asymmetric condition.Therefore,scholars at home and abroad have developed the asymmetric plate heat exchanger with two different widths of the channel,its structure can achieve a good match with the actual conditions,so as to improve the overall performance of the heat exchanger.At present,the research on the structural characteristics and optimization design of the asymmetric plate heat exchanger is still lacking.In this paper,an asymmetric plate heat exchanger with large or small sinusoidal ripples on its surface is taken as the research object.Combined with its structural characteristics,the parametric design of asymmetric corrugated plates is analyzed theoretically.On this basis,six different asymmetrical three-dimensional two-channel calculation models of plate heat exchangers were established.Through numerical simulation,the flow heat transfer performance of each asymmetric plate heat exchanger at different flow rates is studied and compared,and the comprehensive heat transfer performance and economic benefits are analyzed,which provides a train of thought for the optimal design and selection of asymmetric plate heat exchanger.Firstly,the characteristics of the flow passage section are characterized by the ratio of the flow passage cross-sectional area on both sides of the asymmetric plate heat exchanger,which was defined as the asymmetric factor a.Parameterization was carried out on the contour curve of the plate corrugation,and the functional expression of the corrugation profile curve of the plate was obtained.According to the actual working conditions of central heating,heat exchanger plates with different asymmetric factors a were established by adjusting the corrugated parameters of plates.Secondly,the effects of a and the inlet flow rate on the internal flow and heat transfer characteristics of the asymmetric plate heat exchanger were studied by numerical simulation.Results show that,With the increase of a,the average heat transfer coefficient on the hot fluid side gradually increases,while on the contrary,the cold side decreases.but for the total heat transfer coefficient,in addition to the plate with a of 3.0 due to the decrease of the effective contact area of heat transfer effect is poorer,the rest of the heat transfer performance of different type of asymmetric structure does not have obvious difference,and the heat transfer performance along with the increase of flow rate are increasing.The change of a changes the pressure drop distribution of the flow channels on both sides.The pressure drop of the hot fluid side gradually increases with the increase of a,while the pressure drop of the cold fluid side gradually decreases.The pressure drop on both the hot and cold sides showed an exponential growth trend with the increase of the flow rate,while the pressure drop on the hot fluid side increased with the increase of a.On the contrary,the growth trend of the cold fluid side gradually flattened.The results show that the asymmetrical plate reduces the pressure distribution difference between the hot and cold sides in the asymmetrical condition,and the resistance of the large flow side is significantly reduced,up to about 60%,owing to the reduction of the flow channel contacts.Finally,the comprehensive properties of the asymmetric plate heat exchanger was analyzed,and the introduction of classical evaluation index comprehensive heat transfer performance of heat transfer factor of different asymmetric factor for the comprehensive performance of a heat exchanger when comparing analysis,found that at an unequal flow rate,an asymmetric plate heat exchanger reduces the cold-side drag noticeably with overall heat exchange guaranteed,and its general performance is better than that of a symmetric one,which can be increased by 6.6%to 28.7%.Further,the plate with an asymmetric factor a of2.5 reaches its peak performance for central heating among the different asymmetric structures selected.The energy coefficient is used as the energy consumption evaluation index to analyze the energy consumption of different asymmetric plate heat exchangers.It is found that the energy consumption performance of the asymmetric plate heat exchanger is better than that of the symmetric plate heat exchanger under the same flow rate,and the energy saving advantage of the asymmetric plate heat exchanger is further expanded with the increase of the flow rate.The energy saving performance of the asymmetric plate with a of 1.5 is more outstanding.In addition,based on the principle of technical economics,this paper analyzes and evaluates the economy of the asymmetric plate heat exchanger by using the cost present value dynamic evaluation analysis as the economic performance evaluation index.The results show that with the increase of the total flow,the board area decreases,the initial investment decreases,but the total cost increases exponentially.At the same flow rate,compared with the traditional symmetrical plate exchanger,the economic advantage of the asymmetric plate exchanger is very obvious(the total investment can be saved 18%at q_m1=0.1kg/s).At the low flow rate(q_m1=0.1kg/s),the economic advantage of the asymmetric plate exchanger with a value of 2.5 is the best,while the economic performance of the asymmetric plate exchanger with a value of 1.5 is better at the higher flow rate.