Second Law Optimization of a Sensible Heat Thermal Energy Storage System With a Distributed Storage Element—Part 1: Development of the Analytical Model

1991 ◽  
Vol 113 (1) ◽  
pp. 20-26 ◽  
Author(s):  
M. J. Taylor ◽  
R. J. Krane ◽  
J. R. Parsons
Keyword(s):  
Energy Storage ◽  
Analytical Model ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Distributed Storage ◽  
Storage System ◽  
Energy Storage System ◽  
Sensible Heat ◽  
Storage Element ◽  
Thermal Energy Storage System

This study explores the behavior of a flat-slab, sensible heat thermal energy storage system, the physical design and operation of which have been optimized to minimize the production of entropy by thermodynamic irreversibilities. Unlike many previous studies, the present work includes the entropy production by transient heat conduction within the storage element; that is, the analytical model is based on a distributed, as opposed to a lumped, storage element. The work is presented in two parts. The development of the analytical model required to compute the figure of merit, which is called the entropy generation number, in terms of the design and operational parameters of the system is presented in Part I. In Part II, the numerical solution of the analytical model is discussed and the results of an optimization study are presented and interpreted.

Second Law Optimization of a Sensible Heat Thermal Energy Storage System With a Distributed Storage Element—Part II: Presentation and Interpretation of Results

1991 ◽  
Vol 113 (1) ◽  
pp. 27-32 ◽  
Author(s):  
M. J. Taylor ◽  
R. J. Krane ◽  
J. R. Parsons
Keyword(s):  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Distributed Storage ◽  
Storage System ◽  
Energy Storage System ◽  
Storage Element ◽  
Thermodynamic Performance ◽  
Thermal Energy Storage System ◽  
Dwell Period

This study explores the behavior of a flat-slab, sensible heat thermal energy storage system, the physical design and operation of which have been optimized to minimize the production of entropy by thermodynamic irreversibilities. The analytical model is developed in Part I of this work. This part includes a description of the numerical model and the presentation and interpretation of the results of a system optimization study. The major results of this study show that: 1) any Second Law model of a thermal energy storage system must include a distributed storage element in order to make realistic estimates the thermodynamic performance of the system; 2) unconstrained optimization of the design of a thermal energy storage system tends to yield a system that is undesirably large, but by constraining the number of transfer units (NTU), it is possible to design systems of a realistic size without seriously degrading the thermodynamic performance; 3) counterflow systems operated without a dwell period are the most efficient type of system; and 4) the use of a dwell period with a counterflow system, or the operation of a system in parallel flow instead of counterflow, degrades the thermodynamic performance of the system and increases the required system size (NTU) in comparison to a counterflow system operated without a dwell period.

The Optimum Design of Stratified Thermal Energy Storage Systems—Part II: Completion of the Analytical Model, Presentation and Interpretation of the Results

1992 ◽  
Vol 114 (3) ◽  
pp. 204-208 ◽  
Author(s):  
R. J. Krane ◽  
M. J. M. Krane
Keyword(s):  
Energy Storage ◽  
Heat Exchanger ◽  
Analytical Model ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Storage System ◽  
Energy Storage System ◽  
Thermal Energy Storage System ◽  
Thermal Energy Storage Systems ◽  
Performance Gains

This investigation is presented in two parts. The basic analytical model is developed in Part I. Part II includes the completion of the analytical model and the results of an optimization study performed with this model. The results show that: 1) Significant performance gains, that is, reductions in the entropy generation number on the order of 10 percent, are possible by employing perfectly stratified thermal energy storage systems that are designed on the basis of the second law of thermodynamics. 2) These performance gains are mainly due to the complete elimination of the entropy generation due to heat transfer through finite temperature differences within the storage element. 3) In general, the optimum design of a perfectly stratified thermal energy storage system requires the use of a very large heat exchanger; however, it is possible to employ a much smaller than optimum heat exchanger without seriously degrading the superior performance of the system. 4) The operation of a stratified system is quite flexible because it has no optimum storage time. 5) The optimum values of the capacity rate ratios, (φR)opt and (φR)opt, for a perfectly stratified thermal energy storage system are in general not equal to unity; however, this finding is shown to be in concert with Bejan’s theory of “remanent” irreversibilities for a heat exchanger.

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