Numerical Simulation Of The Condensation Heat Transfer Of Condensing Gas Water Heater

In the constant advancing industrialization in our country and the rapid development of national economy,the serious shortage of energy problem and environmental pollution has become the issue which can not be ignored.Developing clean and efficient energy chain of industrial structure is the inevitable trend of sustainable development of our country,under the policy of "energy conservation and emissions reduction",the condensing gas water heater arises at the historic moment.Compared with the traditional gas water heater,the condensing gas water heater make full use of the sensible heat and latent heat in flue gas by reducing exhaust temperature which greatly improving the energy utilization.Its thermal efficiency has significantly improved and its theory of thermal efficiency can reach 110%,what's more,the low exhaust temperature is effective to reduce the environmental pollution problems.This article focuses on the thermal performance of condensing heat exchanger of commercial JSQ21-QL12 LJW type condensing gas water heater.The research methods of this aricle incudes the theoretical study ?experimental tests and numerical simulation of the thermal performance.First of all,analyze the heat transfer performance of the water heater machine theoreticaly based on the fluid mechanics and heat transfer fluid knowledge of sample structure performance of condensing heat exchanger,then construct the thermal test experiment platform according to the relevant specification requirements of condensing gas water heater,concluding and summarizing the relationships of the fluid velocity?excess air coefficient and condensing temperature drop with taking the condensing heat exchanger as research focus,Using the pretreatment software Gambit to build 3d grid model of the condensing heat exchanger,then export the grid model to the FLUENT software with the initial conditions setted,running a series of numerical simulation.After the convergence of the condenser model,setting some sections which easy to observe the performance of the fluid flow.analyze the condenser heat transfer conditions of the internal heat cavity according to the graph of temperature distribution and velocity distribution.Comparing the simulation results and experimental results to verify the credibility of the simulation results.At the last,put forward a series of improvement opinions according to the analysis results of sample condenser.In this paper,the main research contents include the followings.(1)Analyze thermal performance and structure of the condensing gas water heater and the thermal properties and structure of condenser theoreticaly,change the gas flue from down-top flow to a top-down flow in the condenser samples,as the same as the flow direction of condensed water which will be advantageous to discharge the condensed water,changing the downstream heat changes to countercurrent heat exchange.Based on the comprehensive economic considerations,retain the original water heater machine structure.(2)Set up the platform of condenser thermal performance test.Conclude the internal relationships between the temperature drop of the condenser ?the coefficient of excess air and the smoke temperature under different fluid velocities and fluid temperatures which has already be setted in initial conditions,in the last,research the different effects on the thermal efficiency under different factors of the condensing gas water heater.(3)Carry out the numerical simulation on the condenser,the simulation results show that the side of the flue gas cavity has a poorer heat transfer condition,so the flue gas temperature has a uneven distribution.Because the position of gas import is on the right side,the flue gas are easy to produce gas vortex on the left side of the chamber,and the heat exchange is stagnated.(4)when the fluid flow in the heat exchange tube and do heat exchange,the front rows of heat exchange tubes which near the side of the gas cavity have a stronger exchange intensity than some heat exchange tubes which are back away from the side of cavity.The reason is that the somke flow through the front rows of heat exchange tubes have a more faster speed and more lower static pressure than the back heat exchange tubes,so the flow rate of flue gas in front row of heat exchange tubes is small,and its speed is also slow which made the heat exchange is sufficient.According to above researches,conclude some improvement Suggestions about the structure design of the sample condenser for optimization to strengthen heat transfer,in the last,some limits of researches are added in view of insufficiency of this article.