O. KINCAY, M. S. CELLEK, O. ACIKGOZ, A.S. DALKILIC, S. WONGWISES

INVESTIGATION ON THE RELATION BETWEEN EXERGY LOSS AND NTU

Bu çalışmada karşıt ve paralel akışlı ısı değiştiricilerinde ekserji kaybı ve ısı akısı arasındaki ilişki ve bunların oranları bir boyutsuz sayı ile ifade edilmektedir. Oran şeklindeki bu boyutsuz sayı ile NTU arasındaki ilişki; ısıl kapasiteleri ve giriş sıcaklıklarının fonksiyonu olarak formüle edildi. Parametrik durum ve deneysel çalışmalar ile elde edilen bulgular diyagramlar aracılığıyla irdelenmiştir. Ekserji kayıplarının ısı akısına oranı, azalan ısı kapasitesi oranı ile artmaktadır. Karşıt akışlı ısı değiştiricisinin, aynı ısı değiştiricisi için paralel akışlı ısı değiştiricisinden daha düşük bir ekserji kaybına sahip olduğu tespit edilmiştir. Isı değiştiricisinde akışkana nanopartikül ilave edildiğinde, etkenlik hafifçe artar ve bu nedenle gerekli ısı transfer alanı azalır. Ayrıca yoğuşma veya kaynama durumlarında etkenliğin en üst seviyeye ulaştığı gözlemlenmiştir. Bunun yanında, sıcak ve soğuk akışkanların sıcaklıkları oranının artmasıyla ekserji kayıplarının da arttığı tespit edilmiştir. Bu çalışmada model ve bulgular hem parametrik bir analiz hem de detaylı bir tablo ile ortaya koyulan deneysel veriler ile desteklenmektedir.

EKSERJİ KAYBI VE NTU ARASINDAKİ İLİŞKİNİN İNCELENMESİ

In this study, the relation between exergy losses and heat flux and their ratio are expressed as a dimensionless number for counter and parallel flow heat exchangers. The relation between the proposed dimensionless number and the number of transfer units (NTU) is formulated as a function of heat capacity and inlet temperatures. The findings based on this research are scrutinized via diagrams both as parametric case and experimental studies. The proportion of exergy losses to heat flux increases with a decreasing heat capacity rate. It has been found that the counter-flow heat exchanger has a lower exergy loss than the parallel one for the same heat exchanger. It was seen that when nanoparticles were added in the fluid used in the exchanger, the effectiveness slightly increased and therefore the necessary heat transfer area decreased. It was also observed that under condensing or boiling states the effectiveness reached its top level. Moreover, it was found that for increasing values of the temperature rates of hot and cold fluids the exergy losses also increased. The model and findings are supported both by a parametric analysis and experimental data revealed in a detailed table in the paper.

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