The Determination of the Thermal Characteristics of the Microchannel Heat Exchangers for Single-Phase R600a Flow

Yıl 2021, Cilt: 24 Sayı: 3, 797 - 810, 01.09.2021

Anıl Başaran Ali Yurddaş

https://doi.org/10.2339/politeknik.719887

Cited By: 1

Öz

In this study, the mathematical modeling of microchannel heat exchangers (MCHEs) has been experimentally examined for applications where there is a single-phase refrigerant flow such as pre-heating/cooling, superheating/subcooling. A mathematical simulation model has been developed for louvered fin MCHEs where the working fluid is R600a, which estimates the outlet temperature, total heat transfer capacity and entropy generation of the R600a. To imrpove the accuracy of the model, different mass velocities in the passes and uniform air velocities at the face of MCHE have been taken into consideration in the proposed model. Different from other models in the literature, a calculation system created by two discretization level has been applied to take into account these effects. Non-uniform air velocities have been taken into consideration via dividing the face of the MCHE into airflow regions in the model. Experimental study has been performed to validate the model results. It concluded that the model predicts the outlet temperature with an average absolute deviation within ±10% for all investigated test conditions. It is found that the taking into consideration non-uniform air velocity improves accuracy of the model. The entropy generation mechanisms in the MCHE have been investigated and it has been determined that the contribution of the fluid flow irreversibility to entropy generation is quite low compared to heat transfer irreversibility.

Anahtar Kelimeler

Mathematical simulation model, microchannel heat exchanger, isobutane (R600a), thermal characteristics, experimental validation

Tek Fazlı R600a Soğutkan Akışı İçin Mikrokanal Eşanjörün Matematiksel Modellemesi

Öz

Bu çalışmada, özellikle iklimlendirme sistemlerinde ön ısıtma/soğutma, aşırı kızdırma/soğutma gibi tek fazlı soğutkan akışının olduğu uygulamalar için mikrokanal eşanjörlerin matematiksel modellemesi deneysel doğrulamalı olarak ele alınmıştır. Çalışma akışkanının R600a olduğu panjurlu kanatlı mikrokanal eşanjörler için R600a’nın çıkış sıcaklığını, toplam ısı transfer kapasitesini ve entropi üretimini tahmin eden bir matematiksel benzetim modeli geliştirilmiştir. Modelin doğruluk hassasiyetini arttırmak için geçişlerdeki farklı kütle hızları ve uniform olmayan hava hızı modelde dikkate alınmıştır. Bu etkileri dikkate almak için literatürde yer alan diğer modellerden farklı olarak iki seviye ayrıklaştırma ile oluşturulan bir hesaplama sistemi modelde uygulanmıştır. Modelde mikrokanal ısı eşanjörünün ön yüzü hava akış bölgelerine bölünerek uniform olmayan hava hızları dikkate alınmıştır. Model sonuçlarını doğrulamak için deneysel çalışma yapılmıştır. Deneysel doğrulama sonucunda modelin, incelenen tüm test koşulları için çıkış sıcaklığını ±%10 aralığında bir ortalama mutlak sapma ile öngördüğü sonucuna varılmıştır. Mikrokanal ısı eşanjörünün, ısı transfer performansını tahmin etme kabiliyeti, deneylerle değerlendirilmiş, uniform olmayan hava hızının modele dahil etmenin, modelin doğruluk hassasiyetini arttırdığı görülmüştür. Mikrokanal ısı eşanjöründeki entropi üretim mekanizmaları incelenmiş ve akışkan akımı tersinmezliklerinin entropi oluşumuna katkısının, ısı transfer tersinmezliklerine kıyasla oldukça düşük olduğu tespit edilmiştir.  

Anahtar Kelimeler

Matematiksel benzetim modeli, mikrokanal ısı eşanjörü, izobutan (R600a), ısıl karakteristik, deneysel doğrulama

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