The entropy generation analysis is an approach to optimize the performance of different thermal systems by investigating the related irreversibilities of the system. This paper provides a concise review of the entropy generation analysis performed for different solar thermal energy systems including solar collectors, solar heaters, solar heat exchangers, and solar stills. The mathematical formulation and the equations for calculating the entropy generation are briefly presented. Moreover, main passive techniques including the usage of nanofluids, porous materials, and inserts which are used to improve the efficiency of different solar systems are discussed. It is shown that using entropy generation minimization method is an efficient tool to find the optimal design of solar systems. The current review aims to motivate researchers in the field of solar energy for using entropy generation analysis to reduce the lost work and consequently improving the system performance.

Entropy generation analysis of different solar thermal systems

In this paper, radiative entropy generation in a high temperature parallel plate system containing H2O, CO2 and soot with non-gray wall was investigated. Based on Discrete Ordinates method and Narrow Band k-distribution model, the spectral radiative entropy generation rate and radiative entropy generation rate due to different physical processes were given. The effects of CO2, H2O, soot, spectral emissivity of wall, as well as medium temperature on radiative entropy generation were evaluated. Some conclusions were obtained as below. The irreversibility of emission and reflection process on wall has main contribution on radiative entropy generation rate of system. The radiative entropy generation rate increases with the mole fraction of gas and volume fraction of soot. CO2 has less effect on total radiative entropy generation rate, but H2O and soot particle have more effect on total radiative entropy generation rate. The radiative entropy generation rate increases with the increase of total hemispherical absorptance of wall. The radiative entropy generation rate and dimensionless radiative entropy generation increase with the increase of non-uniformity of medium temperature distribution and difference of gas temperature and soot temperature.

Evaluation of radiative entropy generation in a high temperature system including H2O, CO2 and soot with non-gray wall

Effect of discrete heating-cooling on magneto-thermal-hybrid nanofluidic convection in cylindrical system

Entropy optimized flow of Darcy-Forchheimer viscous fluid with cubic autocatalysis chemical reactions

Simulation of combined convective-radiative heat transfer of hybrid nanofluid flow inside an open trapezoidal enclosure considering the magnetic force impacts

Numerical analysis of entropy generation through non-grey gas radiation in a cylindrical annulus

The present work is focused on the interaction between natural convection and thermal radiation in a participating medium through a cylindrical annulus. The Ray Tracing method through the quadrature T10 has been adopted in association with the Statistical Narrow Band correlated-k (SNBCK) model to solve the radiative part of the problem. Special attention is given to entropy generation and its dependency on the various governing parameters including the inner cylinder temperature, the outer cylinder radius, emissivities of the annulus walls, and the gas pressure. The results show that radiation remarkably affects the structure of the fluid flow and the temperature distribution, enhancing heat exchanges in the annulus. Moreover, it is found that the volumetric entropy generation due to radiative processes of medium should not be neglected and is comparable to the volumetric entropy generation due to heat conduction. It is also shown that increasing the emissivities of the cylinders intensifies entropy generation due to radiation through walls, but on the other hand doesn’t affect the volumetric entropy generation.

Effect of combined natural convection and non-gray gas radiation on entropy generation through a cylindrical annulus

This article reports a numerical analysis of combined natural convection and non-gray gas radiation within a cylindrical enclosure, isothermally heated and cooled on various arc lengths of the side...

https://journals.sagepub.com/doi/pdf/10.1177/1687814019895417

Effect of combined natural convection and non-gray gas radiation on entropy generation in a circular enclosure with partial heating:

The current study reports a numerical analysis of free convection of air in an isothermal horizontal cylinder, cooled and heated at different wall locations. Three heater sizes are discussed in this study. The first heated zone is spread across one-quarter of the sidewall; the second is uniformly distributed over the half of the wall and the third active wall covers three-quarters of the cylinder. Five various locations are considered and examined for each active zone of the sidewall. The computation is carried out for Rayleigh number ranging from 102 to 106. Numerical results characterizing heat transfer and flow features are achieved using an iterative model developed in COMSOL Multiphysics. The effect of Rayleigh number on heat transfer and fluid flow characteristics within the cavity are investigated. Particular attention is paid to the influence of heater location and heater size on energy efficiency. It is found that the mean Nusselt number and dimensionless velocity increase when increasing the Rayleigh number. Moreover, the optimal level of energy efficiency is achieved if the heating zone is centered at the upper part of the cylinder, regardless of the heater size. It is also shown that the optimal configuration providing higher energy efficiency is obtained when three-quarters of the sidewall are locally heated, and more precisely, if the active zone is centered at the top of the cylinder.

Natural Convection in a Horizontal Cylinder with Partial Heating: Energy Efficiency Analysis

A computational approach for the modelling of combined gas radiation and laminar natural convection heat transfer within a rectangular enclosure is presented. One wall among the others is maintained at a constant higher temperature (Th) while the others are of a constant lower temperature (Tc). The discrete-ordinate method (DOM) through S12 directions is applied to resolve the radiative transport equation (RTE) while the 'statistical narrow band correlated-k' (SNBCK) model is adopted to provide gas radiative properties. The effect of radiative contribution, the enclosure tilt angle, the boundary and geometry conditions are presented. Special attention is given to the effect scales of these parameters on the average Nusselt numbers. The results show that radiative effect remarkably contributes to the acceleration of the vortexes, improving heat exchanges at walls.

Khouloud Jarray

Papers

Numerical analysis of entropy generation through non-grey gas radiation in a cylindrical annulus

Effect of combined natural convection and non-gray gas radiation on entropy generation through a cylindrical annulus

Effect of combined natural convection and non-gray gas radiation on entropy generation in a circular enclosure with partial heating:

Natural Convection in a Horizontal Cylinder with Partial Heating: Energy Efficiency Analysis

Natural convection analysis through a radiatively participating media within a rectangular enclosure