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Energy Efficiency and Conservation Technologies
Published in Swapan Kumar Dutta, Jitendra Saxena, Binoy Krishna Choudhury, Energy Efficiency and Conservation in Metal Industries, 2023
Jitendra Saxena, Binoy Krishna Choudhury
Second Law of Thermodynamics: It is impossible for a heat engine to produce a network in a complete cycle if it exchanges heat only with bodies at a single fixed temperature (Kelvin-Planck statement). Also, it is impossible to construct a device which, operating in a cycle, will produce no effect other than the transfer of heat from a cooler to a hotter body (Clausius statement). Second Law thus limits the efficiency of conversion of heat energy into mechanical work, and also gives rise to the concept of entropy. Entropy is a measure of dis-orderliness. It increases with irreversibility. Two main causes of irreversibility in industrial systems, such as that of metal industries, are heat transfer through finite temperature difference and friction. Therefore, no practical system can be reversible, nor attain the theoretical limit of thermodynamic efficiency of reversible processes. Entropy may be considered as the amount of unavailable energy within a given system.
Analysis of Thermal Energy Systems
Published in Steven G. Penoncello, Thermal Energy Systems, 2018
Compressors, pumps, and fans are designed to move fluids. Compressors and fans move gases while pumps move liquids. These devices accomplish fluid movement by utilizing an energy input. If the device is reversible and adiabatic, then all of the input energy can be focused on moving the fluid. In the case of a real-world device, the major sources of irreversibility are mechanical friction and fluid friction. Therefore, to move the fluid at the same rate, more energy is required in the real case. Using this reasoning, the isentropic efficiency of a compressor, fan, or pump can be expressed by, ηm=wsw=hout,s−hinhout−hin
Flow of Incompressible Fluids
Published in Raymond Mulley, Flow of Industrial Fluids—Theory and Equations, 2004
Thermodynamics teaches that fluid flow is an irreversible process. The sense of the word “irreversible”, in this case, is useful available mechanical energy has been transformed into internal energy, or heat flow, without useful work being extracted.The system and the environment cannot be restored to their original states without additional work being done. The irreversibility is generally the unavoidable flow of heat energy generated by turbulence to a lower temperature sink, either in the environment or in the same flowing fluid. There is no practical way of recovering this incremental internal energy as mechanical energy.
Thermal transport and magnetohydrodynamics flow of generalized Newtonian nanofluid with inherent irreversibility between conduit with slip at the walls
Published in Engineering Applications of Computational Fluid Mechanics, 2023
Mohamed Boujelbene, Sohail Rehman, Sultan Alqahtani, Sultan Alshehery, Sayed M. Eldin
Entropy generation (EG) and its consequences point to irreversibility in accordance with the second rule of thermodynamics. Any mechanism that causes a thermal system to lose available work always has some irreversibility. The EG measures this loss of available work. To prevent the loss of the energy output owing to fluid friction, magnetic irreversibility, and irreversible heat transfer, minimizing of entropy formation plays a crucial role in the designing of energy systems. In fact, system irreversibility reduces the maximum achievable performance of the thermal process, which can be explained by the fact that each energy activity results in the destruction of some useful energy. To minimize irreversible losses, many studies have focused on the entropy production in thermal systems. In this regard, Bejan (1980; Bejan, 2013) made a tremendous effort and introduced a magnificent number. The ratio of entropy formation due to fluid friction to thermal irreversibility is referred as the Bejan number . (Turkyilmazoglu, 2020) discussed the application of the second law to the subject of thermal transportation in porous metallic channels. Furthermore, the production/generation of entropy was employed in various research to explore the thermophysical properties of micro/mini-channels in order to understand more about the calibre of the available energy (Alrowaili et al., 2022; Chen & Jian, 2022; Guedri et al., 2022; Jing et al., 2019; P. Kumar et al., 2022; Zaman et al., 2022).
Entropy minimization study of Maxwell nanofluid flow using oxides nanoparticles under transpiration and magnetic dissipation effects
Published in Numerical Heat Transfer, Part A: Applications, 2023
Shahzad Munir, Muhammad Ahmed, Ammara Amin
Engineering systems can be complex, and their efficiency is usually measured by the lower values of irreversibility’s. The magnitudes of the irreversibility present during that procedure are determined by entropy production. The greater the degree of irreversibility, the greater the production of entropy. Efficiency decreases with the enhancement of entropy, and this is the reason why entropy minimization in the thermo-fluid field has become an important topic. Gibanov et al. [34] presented a naturally convective flow with magnetic flux in a cavity to estimate the entropy production rate. Attributes of applied magnetic field and irreversibility in viscous nanofluid on a stretching plate are stated by Iqbal et al. [35]. They carried out entropy analysis of engine-oil and ethylene glycol based nanoliquid with nanoparticles and showed that ethylene glycol based nanoliquid performed better than engine-oil. Muhammad et al. [36] examined the entropy analysis through curved surface for nanoliquid flow. In this analysis thermal radiation, Ohmic heating and viscous dissipation are also taken. Chen et al. [37] examined the irreversibility conditions of forced convective flow on a curved surface. Entropy of thermal solar collectors was analyzed by Aziz et. al [38]. They deduced that based nanofluid has low thermal conductivity ratio than the
Irreversibility Analysis Related to Heterogeneous Airflow and Heat Transfer during Room Cooling of Postharvest Apples
Published in Heat Transfer Engineering, 2022
Guan-Bang Wang, Xin-Rong Zhang
In the previous studies, the heterogeneity of airflow and temperature distribution is either simply shown by the numerical methods or evaluated by the statistical parameters, but the analysis of the related irreversibility is still not considered. Actually, the irreversibility analysis is commonly conducted in terms of the entropy generation with respect to different heat transfer problems. Amani and Nobari [25] numerically studied the local entropy generation rate (EGR) at different sections in the entrance region of curved pipes as well as the EGR per unit length of pipe, while the geometry was promoted to double-pipe heat exchangers to investigate the distributions of thermal and frictional EGR at different sections [26]. The combined heat transfer mechanisms within a rectangular enclosure were reported with local volumetric entropy generation caused by the thermal conduction, gas radiation, and fluid friction [27], while Salari et al. [28] modified the similar geometry with circular corners and quantitatively studied the entropy generation by dimensionless parameters. Moreover, the entropy generation was also investigated by dimensionless parameters inside the porous enclosures with inclined positions [29] and particular shapes [30].