بررسي عددي اثرات گام پره، گام هاي عرضي، طولي و تعداد آن در يك مبادله كن حرارتي پره صفحه اي با لوله تخت

Numerical Investigation of the Effects of Fin Pitch, Transverse, and Longitudinal Pitchs and their Numbers in a Plate-Fin Flat-Tube Heat Exchanger

در كار حاضر اثرات گام پره، گام هاي عرضي و طولي لوله و همچنين تعداد گام طولي در يك مبادله كن حرارتي پره صفحه اي با لوله تخت مورد بررسي قرار گرفت. جريان سيال آرام، دايم و تراكم ناپذير فرض شد. معادلات پيوستگي، مومنتوم و انرژي براي جريان سيال و معادله هدايت براي پره با استفاده از روش عددي حجم محدود حل شد. نتايج بي بعد نشان داد كه افزايش گام پره سبب 132/68% افزايش ضريب j كلبورن و 1353% كاهش ضريب اصطكاك f مي شود. همچنين افزايش گام عرضي باعث 203/83% افزايش ضريب j و 24/22% كاهش ضريب f مي شود. با افزايش گام طولي لوله، ضريب j 84% و ضريب f 32% كاهش مي يابد. نتايج بعددار نشان داد كه با افزايش گام پره مقدار انتقال حرارت 2/2% كاهش و عملكرد حرارتي، 75% افزايش مي يابد. افزايش گام عرضي لوله، باعث افزايش انتقال حرارت و عملكرد حرارتي به ترتيب 341%و 255% مي شود. افزايش گام طولي لوله سبب 71% كاهش انتقال حرارت و 79% كاهش عملكرد حرارتي مي شود. افزايش تعداد گام طولي لوله، N، سبب افزايش نرخ انتقال حرارت مي شود؛ ولي براي 28

In the present work, the effects of fin pitch, transverse pitch, longitudinal pitch and the number of the longitudinal pitch in a plate-fin flat tube heat exchanger were studied. The fluid flow was assumed laminar, steady, and incompressible. Continuity, momentum, and energy equations for fluid flow and conduction equation for fin were solved, using the finite volume method. Dimensionless results showed that increasing the fin pitch causes to increase of the j-Coulburn coefficient by 132.68% and reduces the friction coefficient rate by 13.35%. Also, increasing transverse tube pitch causes to increase of j coefficient by 203.83% and reduces 24.22% of the f coefficient. By increasing longitudinal tube pitch, j and f coefficients are reduced 84% and 32%, respectively. Dimensional results showed that by increasing fin pitch, heat transfer is reduced 2.2% and thermal performance, Q/w_p, is increased by 75%. Increasing transverse tube pitch causes to increase heat transfer and thermal performance about 341% and 255%, respectively. Increasing longitudinal tube pitches result in decreasing the heat transfer and thermal performance about 71% and 79%, respectively. Increasing the number of longitudinal tube pitches, N, causes to increase of the heat transfer rate, but for N>28, no sensible increase in heat transfer rate is observed therefore, N>28 is not recommended. Maximum thermal performance is achieved at N=5 and for N>5 thermal performance is decreased.