Second law analysis of a cyclic regenerator in presence of longitudinal heat conduction in matrix

Abstract

The present analysis gives an account of exergy destruction in regenerative heat exchangers used in cryogenic applications from the view point of Second Law of Thermodynamics. Unlike the previous studies, the present work considers the solid storage matrix with temperature variation along both spatial and temporal co-ordinates. The present analysis also considers the effect of matrix longitudinal heat conduction on the Second Law behaviour. Finite longitudinal conductivity, which results from the distribution of temperature in the matrix, acts as a major non-ideality associated with the analyses done so far. The present analysis shows that the introduction of longitudinal conduction ensures the optimization of charging period for the regenerator. This makes it possible to optimize the regenerator performance globally to produce optimum combination of N tu and charging time. It is also observed that a decrease in longitudinal conductivity reduces the optimum charging time. Thus the non-existence of thermodynamic optima at the absence of longitudinal conduction is explained adequately.