Second law analysis of compressible flow through circular ducts of variable cross-section.

摘要

Efficient utilization of energy is primary objective in designing a thermodynamics system. This useful energy can be destroyed due to the intrinsic irreversibility associated within the process components. Unfortunately irreversibility cannot be avoided, but it can be minimized in order to save the available energy. The minimization can be achieved if the irreversibility can be identified in the process components. Second law analysis provides a useful tool to identify the irreversibility in any thermal system. This study presents the investigation of local and total entropy generation in compressible flow through constant area duct and diffuser. Air is used as fluid. Uniform heat flux and constant wall temperature are two different thermal boundary conditions. Two dimensional solution of velocity and temperature fields are obtained using CFD code FLUENT. The distribution of the entropy generation rate is investigated throughout the volume of the fluid as it flows through the diffuser. Region of high entropy production in diffuser has been predicted. Entropy generation increases with increase in inlet Mach number, wall temperature and wall heat flux. The main parameter considered here is the desired inlet expansion angle corresponding to the minimum entropy generation at specified conditions. The numerical results indicate that by successfully predicting the distribution of irreversibility, re-design efforts can be more carefully focused on specific regions with highest entropy production.