تحليل تجربي انتقال حرارت در چگالش R-404A داخل لوله هاي مارپيچ

چكيده انگليسي :

Experimental Investigasion of Heat Transfer during Condensation of R 404A inside Helical Tubes Ali Shahmoradi ali shahmoradi64@yahoo com Date of Submission 17 January 2012 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Mohammad Reza Salimpour salimpour@cc iut ac irAhmad Saboonchi ahmadsab@cc iut ac irAbstractThe performance of heat exchangers can be improved to perform a certain heat transfer duty by heat transferenhancement techniques Helical coiled tubes can be found in many application systems chemical processingand medical equipment Helical coils can accommodate a large heat transfer area in a small space with highheat transfer coefficients and narrow residence The performance of heat exchangers can be improved by heattransfer enhancement techniques In general these techniques can be divided into two groups active andpassive techniques Due to the curvature of the tubes as XLG RZV WKURXJK FXUYHG WXEHV FHQWULIXJDO IRUFH LVgenerated A secondary ow induced by the centrifugal force has signi DELOLW WR HQKDQFH WKH KHDW FDQWtransfer rate R 404A is one of the greenhouse gases covered by the Kyoto Protocol R 404A is largelyaccepted as a substitute for R 22 in cooling and freezing applications Both its volumetric refrigeratingcapacity and saturation pressure values are quite comparable with R 22 s data making it an interestingalternative In this thesis the condensing heat transfer coefficient of alternative HFC R 404A inside helicalcoiled tube heat exchanger experimentally is investigated Effects of different coils pitches and curvatureradius in different average vapor qualities and mass velocities are inspected The test sections are helicallycoiled smooth tubes with length 3 20 m outer and inner diameters are 9 52 and 7 52 mm respectively Diameters of coils are between 8 7 and 15 3 cm and pitches of coils are between 1 5 and 3 5 cm Heattransfer coefficient and the quality of refrigerant in inlet and outlet of test section are calculated by usingenergy balance based on the energy rejected from the test section and pre condenser Totally162 test runswere conducted for condensation of R 404A vapor with three refrigerant mass velocities of 125 156 188kg m2s and different vapor qualities inside helical tube Data were collected for condensation of R 404Avapor inside helical tubes The local vapor qualities are measured at the inlet and outlet of test condenser byperforming energy balance along the test condenser and vapor quality is assumed to be the average of thesetwo values In this experimental study the effect of coil pitch is insensitive and is decreased by increasingmass velocity and average vapor quality The most enhancements in average heat transfer coefficient werefor observed for pitch 1 5 cm In this study it was seen that the curvature radius has a remarkable effect onheat transfer coefficient Morerer when the pitch is left unchanged with the increment of mass velocity theimpact of curvature radius reduction upon the average heat transfer augementation is reduced Actualy themost enhancement was achieved at mass velocity 125 kg m2s This investigation reveals that the increment ofaverage vapor quality and mass velocity of the refrigerant and also the reduction of curvature radius andcoiled tube pitch enhance the heat transfer coefficient Examining the effect of geometrry we saw that theeffect of curvature is more prominent than the effect of the coiled tube pitch Finally an empirical correlationwas proposed to predict the heat transfer coefficients during condensation of R 404A vapor in the coiledtubesKey Word Heat transfer coefficient condensation coil tube curvature radius pitch coil

شه مرادي، علي

تحليل تجربي انتقال حرارت در چگالش R-404A داخل لوله هاي مارپيچ

شعاع لوله , گام لوله