افزايش انتقال حرارت در كندانسور R-404A توسط سيم پيچ

چكيده انگليسي :

Heat Transfer Enhancement of a R 404A Condenser Using Coiled Wires Hesam Gholami h gholamilehdarboni@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 coefficient and pressure drop during condensation of R 404A insidehorizontal tube and coiled wire inserted tubes has been investigated experimentally Theexperimental set up which was used in this study was a well instrumented vapor compressionrefrigeration cycle which utilized R 404A as refrigerant This set up consist of a test condenserwhich was a 1000 mm long double tube counter flow heat exchanger while the refrigerant flowedin the inner copper and cooling water flowed in the annulus and all the experiments were carriedout on it In addition there is a primary condenser and secondary condenser to achieve the requiredvapor qualities in order to investigate the effect off vapor quality on heat transfer and pressuredrop All these condensers are double pipe counter flow water cooled heat exchangers whichrefrigerant flows inside the internal cooper tube while water flows in the annulus Theexperimental investigation was carried out in the plain tube and five coiled wire inserted tube thatdata were collected for different mass velocities of 71 2 89 106 8 124 6 and 142 4 kg m2 s andin each mass velocities for six different vapor quality At each experiment several parameters weremeasured such as refrigerant mass velocity inlet and outlet water temperatures inlet and outletrefrigerant temperatures etc First category included springs with 10 mm coil pitch and 0 5 1 0and 1 5 mm thickness and exhibited effect of wire diameter on heat transfer and pressure dropduring condensation of R 404A inside horizontal coiled wire inserted tubes and second which hadsprings with equal diameter of 1 0 mm thickness and variant coil pitch of 8 10 and 13 mm showedeffect of spring pitch on heat transfer and pressure drop during condensation of R 404A insidehorizontal coiled wire inserted tubes Heat transfer coefficients were calculated by use of thecollected 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 Comparisonbetween plain tube results and exiting correlation was done Result of experiments showed usingcoiled wire increases average heat transfer coefficient up to 60 with compare to plain tube Fromresults it was found that the coiled wire inserts increase the pressure drop up to 1200 relative tothe plain tube values on a nominal area basis Investigation of the results for coiled wire insertedtube shows that for the same mass velocity wire diameter increment and coiled pitch reductionincrease both heat transfer coefficient and pressure drop Also increase of mass velocity and vaporquality increase heat transfer and pressure drop A new correlation for the prediction of heattransfer coefficient and pressure drop were developed by utilizing the gained results for the coiledwire inserted tubes Finally performance evaluation was done and it is observed that at allconditions using coiled wire inserts are unfavorable However coiled wire inserts can be employedin specific application such as when because of limited space compact heat exchangers are neededand higher pumping power is reasonable Key words Heat Transfer Increase Condensation coiled wire Pressure Drop

غلامي، حسام

افزايش انتقال حرارت در كندانسور R-404A توسط سيم پيچ

چگالش , مبردها