Düz tüp içerisinde burulmuş şerit kullanarak ısı geçişinin iyileştirilmesi

Abstract

Tüp içerisinde ilave parça kullanımı, hidrolik kayıp zafiyeti pahasına taşınım ısı geçişi katsayısını arttırmak için kullanılan tekniklerden biridir. İlave parça geometrisinin ve akış koşullarının güçlü bir işlevi olan bu müşterek etki, toplam sistem performansını iyileştirmek için ayrıntılı şekilde analiz edilmelidir. Bu çalışma, ısıtma/soğutma elemanı kompaktlığının önemli olduğu soğutma uygulamalarında sıkça kullanılan düz tüpe (13 mm çaplı ve 1200 mm uzunluğunda) burulmuş şerit ilavesi akabinde termo-hidrolik özelliklerinin analizi için sayısal bir araştırma sunmaktadır. Burma oranının termo-hidrolik performans üzerindeki etkisi, soğutma uygulamalarının genelinin çalıştığı 5.025−14.871 Reynolds sayısı aralığında incelenmiştir. Benzetim sonuçlarının doğrulanması deneye dayalı Dittus-Boelter denklemi ile karşılaştırılmış (düz tüp için) ve iyi bir uyum elde edilmiştir. Sonuçlar, 6−9 arası burma oranındaki değişimin belirtilen çalışma koşullarında düz tüpe göre sürtünme faktörünü ve Nusselt sayısını sırasıyla %197−245, %180−220, %163−189 ve %156−179 ve %32−54, %28−46, %28−33 ve %28−33 arttırdığını göstermektedir. Hidrodinamik kuvvetlere karşı ısı geçiş miktarının artırılmasının ölçütü olan performans değerlendirme ölçütü, burma oranı artışına bağlı olarak 0.90−1.02, 0.89−1.00, 0.91−0.96 ve 0.92−0.96 arasında değişmiştir. Performans değerlendirme ölçütündeki maksimum artış, en düşük Reynolds sayısı ve burma oranında elde edilmiştir. Performans değerlendirme ölçütü Reynolds sayısının artışıyla azalmakta ancak burma oranı arttırılarak yükseltilebilmektedir. 

Keywords

• Isı geçişi iyileştirme,Burulmuş şerit,Burma oranı,Performans değerlendirme ölçütü

Enhancement of heat transfer using twisted tape insert in a plain tube

Abstract

The use of insert within a tube is one of the techniques enhancing the convective heat transfer coefficient at the expense of hydraulic loss penalty. This mutual effect which is a strong function of insert geometry and flow conditions is to be analyzed in detail to improve the overall system performance. This study presents a numerical investigation for analyzing the thermo-hydraulic characteristics of twisted tape insert in a plain tube (with a 13-mm-diameter and 1200-mm-long) which is widely used in refrigeration applications where the compactness of heating/cooling element is significant. The effect of twist ratio on the thermo-hydraulic performance was conducted for the Reynolds number range of 5,025−14,871 where most of refrigeration applications are operated in. The verification of the simulation results was compared to Dittus-Boelter empirical equation (for the plain tube case) and good agreement was obtained. Results indicate that the variation of the twist ratio between 6−9 increases the friction factor and Nusselt number 197−245%, 180−220%, 163−189% and 156−179%, and 32−54%, 28−46%, 28−33% and 28−33% relative to the plain tube case, respectively for the specified operating conditions. The performance evaluation criteria, which are measure of enhancing heat transfer against hydrodynamic forces, changed between 0.90−1.02, 0.89−1.00, 0.91−0.96 and 0.92−0.96 based on the twist ratio rise. The maximum enhancement in the performance evaluation criteria was obtained at the lowest Reynolds number and twist ratio. The performance evaluation criteria lower with increasing Reynolds number but can be increased by increasing the twist ratio.

Keywords

• Heat transfer enhancement,Twisted tape,Twist ratio,Performance evaluation criteria

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