Sukrut P. Phansalkar
Indian Institute of Technology Kharagpur, Kharagpur 721302, India
P. K. Das
Department of Mechanical Engineering, Indian Institute of Technology, Kharagpur, West Bengal, 721302, India
Regenerative Heat Exchangers are a class of heat exchangers which are used to exchange thermal energy between two fluid streams with a large temperature difference. As they are mainly used as recovery devices, their importance need not be exaggerated from the concern of energy conservation and protection of the environment. Rotary Regenerators are very commonly used, mainly due to their capability of continuous heat exchange in contrast with fixed bed regenerators. Although for recuperators, a significant amount of work has been done to understand the mechanism of heat exchange and the inefficiencies arising due to longitudinal conduction, pressure leakages, and non-uniform flow, adequate attention has not been paid to study these important aspects in regenerators. In the present work, we study the effects of non-uniform velocity distribution at the inlet of the rotary regenerator on its performance. In the paper that follows, we have tried to model these non-uniformities using numerical simulations. Using the first principles, we have derived the modified energy equations to account for the non-uniform velocity by defining a local Non-Uniformity Factor α (which is the ratio of local velocity to mean velocity). This local change in convective coefficient (h) and velocity, does play a significant role in the reduction of the effectiveness by almost 8-10% at NTU values of 5 and more. This is a very important result and these effects have to be taken into account while designing the ducts of the heat exchangers especially at the places where high efficiency is needed.