| Gas turbine is a kind of constant volume power machinery.Its output power is closely related to the mass flow of the intake air.When the intake temperature increases,the air density decreases and the mass flow rate decreases.Reaulting the output power and the relative efficiency of the gas turbine decreases.Therefore,the inlet cooling technology arises at the historic moment.The finned tube heat exchanger studied in this paper is derived from the M251 S gas turbine inlet cooling system of a company in Chongqing.The finned tube heat exchanger is favored for its high heat transfer efficiency,compact structure and stable performance.The application of water-air finned tube heat exchanger to the intake cooling system of gas turbine can effectively solve the problems of unbalanced energy structure and poor economic benefit in this industry.Normally,gas turbine are designed under standard operating conditions(ambient temperature 15℃,atmospheric pressure 0.10135 MPa,and atmospheric relative humidity60%).Therefore,first of all,under the condition of air inlet temperature of 43 ℃(the highest summer temperature in Chongqing)and frozen water inlet and outlet temperature of 7℃/12 ℃.The air outlet temperature is 15 ℃.According to the theoretical calculation,a finned tube heat exchanger is designed to meet the requirements.Secondly,the model of heat exchanger was established by GAMBIT software.Because the overall size of the model is too large(6006 mm×4680 mm×1600 mm).The paper adopts several local threedimensional modeling to realize the numerical simulation calculation of the cooling process of heat exchanger.The air flow and heat transfer between fins of finned tube heat exchanger are studied.And the velocity,temperature and pressure field distribution are obtained,which provide theoretical guidance for practical application.The outlet temperature of the overall model will be calculated by using the weighted average of the outlet temperatures of the four locations.While the corresponding weight coefficient is the proportion of the outlet area of the local area with similar wall boundary conditions represented by the four locations to the outlet area of the overall model.Finally,the finned structure of the finned tube heat exchanger was optimized by orthogonal test,and the performance factor was used as the index to evaluate the performance of the heat exchanger.The results before and after optimization were compared and analyzed.The main results are as follows:(1)Among the four local models with different locations,the area ratio of position one(the symmetrical region in the middle of the heat exchanger)is the largest,up to 0.842.In terms of the outlet temperature of the four positions,position two(the middle area at the bottom of the heat exchanger)has the highest(17.10℃).Therefore,as long as the outlet temperature of the air in position two can meet the requirements,the overall model can meet the requirements of gas turbine inlet cooling.(2)The outlet temperature of the hot air at 43℃ after cooling is 16.75℃,which is1.75℃ higher than the ideal temperature at 15℃.In order to meet the cooling requirements,the flow rate of frozen water is adjusted from 0.19 m/s to 0.21 m/s.After adjustment,the outlet temperature was 14.38℃,which proved that the method of adjusting the water flow rate of frozen water to meet the air outlet temperature was effective.(3)Along the direction of cooling length,the air temperature gradually decreases and the decreasing range gradually decreases,starting from 12.27℃/320 mm in the first section of model to 1.86℃/320 mm in the fifth section.(4)The total pressure drop of 43℃ hot air is 210.38 Pa and the inlet velocity increases from 3.46 m/s to 5.76 m/s after cooling.(5)The heat transfer efficiency at different intake temperatures is calculated and analyzed.The results show that the heat transfer efficiency is closely related to the intake temperature of air,and the higher the intake temperature,the higher the heat transfer efficiency.(6)Based on the direct analysis of the orthogonal test results,it can be concluded that the fin spacing is the most important factor affecting the performance factor,followed by the fin height,and the fin thickness has the least effect.The optimized fin structure is CP/0.6/22/8(CP/fin thickness/fin height /fin spacing).Compared with CP/0.8/16/8 before optimization,the heat transfer coefficient and performance factor are increased by 7.79%and 15.7% respectively.(7)The optimized results show that taking the position one with the largest proportion as an example.After optimization,the air outlet temperature decreased from16.68℃ to 13.13℃,and the total pressure drop decreased from 214.25 Pa to 202.22 Pa,respectively. |
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