تاثير نوار پيچيده شده بر چگالش بخار R-404A

چكيده انگليسي :

Effect of Twisted Tape on Condensation of R 404A Vapor Sina Yarmohammadi s yarmohammadi@me iut ac ir Sep 11th 2011 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 8311 IranDegree M Sc Language FarsiMohammad Reza Salimpour salimpour@cc ut ac irAbstractIn this thesis heat transfer and pressure drop during condensation of R 404A inside horizontal twisted tapeinserted tubes has been investigated experimentally The experimental set up which was used in this studywas a well instrumented vapor compression refrigeration cycle which utilized R 404A as refrigerant This setup consist of a test condenser which all the experiments were carried out on it In addition there is a primarycondenser and secondary condenser to achieve the required vapor qualities in order to investigate the effectoff vapor quality on heat transfer and pressure drop All these condensers are double pipe counter flow watercooled heat exchangers which refrigerant flows inside the internal cooper tube while water flows in theannulus The experimental investigation was carried out in the plain tube and four twisted tape inserted tube At each experiment several parameters were measured such as refrigerant mass velocity inlet and outletwater temperatures inlet and outlet refrigerant temperatures etc Heat transfer coefficients were calculatedby use of the collected data Also pressure drop between the inlet and outlet of test condenser is measured bydifferential pressure transmitter In order to verify integrity of the experimental set up Comparison betweenplain tube results and exiting correlation was done Investigation of the results for twisted tape inserted tubeshows that for the same mass velocity twisted tape ratio reduction increases both heat transfer coefficient andpressure drop Also for the same twisted ratio increase of mass velocity and vapor quality increase heattransfer and pressure drop A new correlation for the prediction of heat transfer coefficient and pressure dropwere developed by utilizing the gained results for the twisted tape inserted tubes Finally performanceevaluation was done and it is observed that at all conditions using twisted tape inserts are unfavorable However twisted tape inserts can be employed in specific application such as when because of limited space compact heat exchangers are needed and higher pumping power is reasonable An experimental investigationwas conducted to find the influence of twisted tape inserts on the pressure drop and heat transfer coefficientduring force convective condensation of R 404A vapor in a horizontal tube The test section was a doublepipe counter flow heat exchanger The refrigerant flowed in the inner tube and cooling water flowed in theannulus Experimental tests were carried out for plain tube and four tubes with twisted tapes inserts of 4 7 10 and 14 twisted ratio with mass velocities from 71 2 to 142 4 kg m2s and vapor qualities from 0 24 to 0 87 Investigation clearly showed that using twisted tapes inside the tubes increases pressure drop and heattransfer coefficient in the range of 89 to 239 and 29 to 72 respectively higher than that for the plain tubeon the nominal area basis An empirical correlation was developed to predict the increased pressure drop andheat transfer during condensation inside a horizontal tube in the presence of twisted tape inserts Bycomparing the predicted and experimental data it was found that the majority of the present data falls within 20 of the proposed correlations In addition the performance evaluation for the twisted tape inserted tubeswas accomplished Key words Heat Transfer Increase Condensation Twisted Tape Pressure Drop R 404A

يار محمدي، سينا

تاثير نوار پيچيده شده بر چگالش بخار R-404A

انتقال حرارت , افت فشار , ارزيابي عملكرد