Düz tüp içerisinde burulmuş şerit kullanarak ısı geçişinin iyileştirilmesi

Tüp içerisinde ilave parça kullanımı, taşınım ısı geçişi katsayısını arttırmak için hidrolik kayıp zafiyeti pahasına 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 donanım kompaktlığının önemli olduğu soğutma uygulamalarında sıkça kullanılan burulmuş şerit ilavesi yapılmış düz bir tüpün (13 mm çaplı ve 1200 mm uzunluğunda) termo-hidrolik karakter analizinin sayısal olarak incelenmesini sunmaktadır. Burma oranının termo-hidrolik performans üzerindeki etkisi, soğutma uygulamalarının ekseriyetinin çalıştığı 5.025−14.871 Reynolds sayısı aralığında incelenmiştir. Benzetim sonuçlarının doğrulanması deneye dayalı Dittus-Boelter denklemi ile kıyaslanmış (düz tüp için) ve iyi bir uyum elde edilmiştir. Sonuçlar, burma oranının 6−9 arasındaki değişimi, belirtilen çalışma koşullarında düz tüpe kıyasla 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 göstermiştir. Hidrodinamik kuvvetlere karşı ısı geçiş miktarının artırılmasının bir ölçütü olan performans değerlendirme kriteri, 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 kriterindeki maksimum artış, en düşük Reynolds sayısı ve burma oranında elde edilmiştir. Performans değerlendirme kriteri Reynolds sayısının artışıyla azalmakta ancak burma oranının arttırılmasıyla yükseltilebilmektedir.

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

The use of insert within a tube is one of the techniques enhancing the convective heat transfer coefficient at theexpense of hydraulic loss penalty. This mutual effect which is a strong function of insert geometry and flowconditions is to be analyzed in detail to improve the overall system performance. This study presents a numericalinvestigation 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 theheating/cooling component is significant. The effect of twist ratio on the thermo-hydraulic performance wasconducted for the Reynolds number range of 5,025−14,871 where most of refrigeration applications are operatedin. The verification of the simulation results was compared to Dittus-Boelter empirical equation (for the plain tubecase) and good agreement was obtained. Results indicate that the variation of the twist ratio between 6−9 increasesthe 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. Theperformance 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 maximumenhancement 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 increasingthe twist ratio.

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