Enhancement of Heat Transfer Performance for Fin-Tube Heat Exchangers Using Dimpled/Protruding Fin Surface

Abstract

In this study, effect of dimpled/protruding fin on heat transfer performance and flow characteristics for a fin-tube heat exchanger was numerically investigated. Circular dimple/protrusion and two different dimple/protrusion aspect ratio (a/b) such as 0.667 and 1.50 in a double row arrangement were investigated in order to obtain the most feasible dimple/protrusion design parameter. The diameter of the circular dimple is 2.8 mm. The cross-sectional area of the oval dimples is equal to the cross-sectional area of the circular dimples. Simulations were carried out in the laminar flow conditions at four Reynolds (Re) numbers including 500, 1000, 1500 and 2000. Numerical calculations were performed with Ansys Fluent 19.2 using RNG k-ε turbulence model. Average Nusselt number ((Nu) ̅), lateraly-averaged Nu number distributions on the surface, thermal performance factor (TPF) and flow characteristics were comprehensively investigated. Results were compared with the flat fin surface. Numerical results revealed that dimple/protrusion fin increases heat transfer up to 26.63% compared to the flat surface. However, it was determined that the most feasible design for enhancement heat transfer is circular dimpled/protruding fin design for the fin-tube heat exchangers according to TPF results. 

Keywords

• Heat Exchanger
• Heat Transfer
• Vortex Generator
• Computational Fluid Dynamics

Kanatlı-Borulu Isı Değiştiricilerinde Çukurlu/Çıkıntılı Kanat ile Isı Transfer Performansının Arttırılması

Öz

Bu çalışmada kanatlı-borulu ısı değiştiricisinde çukurlu/çıkıntılı kanatın ısı transfer performansına ve akış karakteristiklerine etkisi sayısal olarak incelenmiştir. En uygun tasarım parametresini belirlemek için kanat üzerine dairesel ve 0,667 ile 1,50 olmak üzere iki farklı ovallik oranlı (a/b) çukurlar çift sıralı olarak yerleştirilerek ısı transfer performansına etkisinin araştırılmıştır. Dairesel çukurun çapı 2,8 mm olarak belirlenmiştir. Oval çukurların kesit alanı ise dairesel çukurla eşit tutulmuştur. Hesaplamalar 500, 1000, 1500 ve 2000 olmak üzere 4 farklı Reynold (Re) sayısında laminar akış rejiminde yapılmıştır. Sayısal hesaplamalar Ansys Fluent ile RNG k-ε türbülans modeli kullanılarak gerçekleştirilmiştir. Ortalama Nusselt sayısı ((Nu) ̅), yüzey üzerinde yanal ortalamalı Nu sayısı dağılımları, termal performans faktörü (TPF) ve akış karakteristikleri ayrıntılı olarak incelenmiştir. Sonuçlar çukur olmayan düz yüzeyli kanatçık ile karşılaştırılmıştır. Sayısal sonuçlar, yüzey üzerine yerleştirilen çukurların/çıkıntıların düz yüzeye göre ısı transferini %26,63’e kadar arttıracağını ortaya koymuştur. Bununla birlikte, TPF incelendiğinde ısı transferi artışında en uygun tasarımın dairesel çukurlu/çıkıntılı kanat tasarımının olduğu tespit edilmiştir.

Anahtar Kelimeler

• Isı Değiştirici
• Isı Transferi
• Girdap Üreteci
• Hesaplı Akışkanlar Dinamiği

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