The influence of viscous heating on the entransy in two-fluid heat exchangers

In the present work, water and olive oil are taken as working fluids to study the influence of viscous heating on the entransy dissipation caused by heat transfer in two-fluid heat exchangers. The results show that the influence of viscous heating on the entransy loss associated with heat transfer can not be neglected for the liquids having large dynamic viscosity. The viscous heating effect maintains the heat transfer ability of the working fluids, relatively reduces the entransy loss in heat exchangers; the viscous heating effect relatively augments the entropy generation due to heat transfer and the available energy destruction in heat exchangers. For the working fluid having large dynamic viscosity, the increasing rates of the entransy and entropy generation contributed by the viscous heating are even larger than those contributed by heat transfer, when the mass flow rate of working fluid reaches a certain value under the fixed heat transfer area condition. Thus, the entransy loss rate decreases and the growth rate of entropy generation increases as the mass flow rate of the working fluid increases. Under the same other conditions, the heat transfer entransy loss rate and entropy generation rate per unit heat transfer rate obtained when the fluid having a smaller heat capacity rate is cold fluid are less than those obtained when the fluid having a smaller heat capacity rate is hot fluid.