TRANSIENT HEAT TRANSFER IN PIPES WITH TIME PERIODICALLY CHANGING BOUNDARY CONDITION

Abstract

Transient heat transfer in thermal entrance region of pipes with time periodically changing surface temperature is investigated. The problem is handled in a two-regional pipe for laminar, hydrodynamically developed flow by involving fluid axial conduction. The solution is made numerically by a finite-difference method. A parametric study is done to analyse the effects of Peclet number and angular frequency on heat transfer characteristics. The results show that, considerable amount of heat is diffused back towards the upstream region by axial fluid conduction, which causes preheating the fluid prior to the heated downstream region. The heat transfer characteristics, in all axial positions, including the preheated upstream and the fully developed region, are seen to change periodically in time, similar to the periodic change of the surface temperature in the downstream region. , , , .

Keywords

• Fluid axial conduction
• Time periodicaly changing boundary conduction
• Transient heat transfer
• Laminar flow heat transfer in pipe

BORULARDA ZAMANLA PERİYODİK OLARAK DEĞİŞEN SINIR ŞARTI İLE GEÇİCİ REJİM ISI TRANSFERİ

Abstract

Borularda ısıl gelişme bölgesi geçici rejim ısı transferi, zamanla periyodik olarak değişen cidar dış yüzey sıcaklığı sınır şartında incelenmiştir. Problem, iki bölgeli bir boruda, hidrodinamik olarak gelişmiş laminer akış için, eksenel akışkan iletimi dikkate alınarak ele alınmış ve sonlu farklar yöntemi ile sayısal olarak çözülmüştür. Peclet sayısı ve açısal frekansın ısı transferi karakteristikleri üzerindeki etkilerini belirleyebilmek için parametrik bir çalışma yapılmıştır. Elde edilen sonuçlardan akışkan eksenel iletimi nedeniyle borunun üst akış bölgesine, akışa ters yönde önemli ölçüde ısı transfer edildiği ve bunun akışkanın borunun ısıtılan alt akış bölgesine gelmeden önce ön ısıtılmasına neden olduğu görülmüştür. Ayrıca alt akış bölgesi dış yüzey sıcaklığındaki periyodik değişime uygun olarak, tüm ısı transferi karakteristiklerinin de, ön ısıtma ve tam gelişmiş bölge de dahil olmak üzere, tüm eksenel konumlarda zamanla periyodik olarak değiştiği görülmüştür.

Keywords

• Akışkan eksenel iletimi
• Zamanla periyodik olarak değişen sınır şartı
• Geçici rejimde ısı transferi

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