Authors: A-R.A. Khaled
Addresses: Mechanical Engineering Department, King Abdulaziz University, P.O. Box 80204, Jeddah 21589, Saudi Arabia
Abstract: Enhancement of heat and exergy transfers in double pipe exchangers with conical tubes is investigated. Different fluid combinations are selected. The momentum and energy equations for both fluids are solved mathematically and numerically. Both solutions are well matched. A parametric study including the effect of the thermal conductivity, thermal capacity and the tube to pipe diameters ratios is conducted. Different performance indicators are computed including the second-law efficiency. Large enhancement factors are obtained when the fluid of smaller thermal conductivity is placed in the annulus. For this case, heat and exergy transfers' enhancement factors may increase to 2.0 and 2.38 folds, respectively. Under same input power, the convergent tube increases heat and exergy transfers above those for conventional exchanger when thermal entry-regions are insignificant. However, the divergent tube does that when entry-regions are substantial. Finally, using conical tubes to enhance heat and exergy transfers inside double pipe exchangers are recommended.
Keywords: augmentation; heat transfer; exergy efficiency; double pipe heat exchangers; conical tube; second-law efficiency; thermodynamics; conical tubes; thermal conductivity.
International Journal of Exergy, 2014 Vol.15 No.2, pp.171 - 195
Received: 22 Jul 2013
Accepted: 31 Aug 2013
Published online: 31 Oct 2014 *