Components Of Entropy Generation Research Articles

Influence of Slip and Orientation on Entropy Generation Due to Natural Convection in a Square Cavity

Abstract Numerical simulations are performed to deduce the effects of slip wall and orientation on entropy generation due to natural convection (NC) in a square cavity for Rayleigh number (Ra) = 105. The laterally insulated square cavity, heated at the bottom wall and cooled at the top wall, is subjected to various orientation angles (ϕ) and slip velocities characterized by the Knudsen number (Kn). The two components of entropy generation, i.e., entropy generation due to heat transfer (SΘ) and entropy generation due to fluid friction (SΨ), are separately investigated by varying the orientation from 0 deg to 120 deg in steps of 15 deg and Knudsen number from 0 (no-slip) to 1.5 in steps of 0.5. Evidence indicates that, for most cases considered, entropy generation due to fluid friction (SΨ) dominates the one due to heat transfer (SΘ). It is observed that the slip velocity on the isothermal walls (us,iso) has a strong influence on SΘ whereas the variations in SΨ are closely connected to the change in the rate of shear strain. Interestingly, the presence of corner vortices and the secondary circulations near the core of the cavity are also found to affect the variation in entropy generation. The existence of active zones of SΘ in the vicinity of isothermal walls and their elongation and migration while changing the orientation is another unique characteristic noticed in this study. A new parameter called maximum velocity ratio (MVR) is also proposed to highlight the variation in velocity components within the enclosure.

Thermal improvement of linear Fresnel solar system utilizing Al2O3-water nanofluid and multi-way twisted tape

To enhance the thermal treatment of Linear Fresnel Reflector (LFR) unit, multi-way twisted tape (MWTT) was applied in current research. Twelve mirrors and one tube with trapezoidal cavity around it, generates new LFR unit. The operating fluid is Al2O3-water and for predicting the properties, temperature dependent formulas were employed. Finite volume simulations results in finding the distribution of velocity, temperature, entropy generation. Also, thermal performance was measured. The geometrical factors are number of wings (nw), revolution (TR) and width (ER) of tapes. To evaluate the modeling procedure, various examinations with numerical and experimental publications were verified. To extract the distribution of absorb flux, SolTrace and ANSYS FLUET have been utilized and they are in good agreement. The output of SolTrace demonstrates the path of rays and selecting higher number of rays results in higher accuracy. Highest absorb flux occurs in bottom of pipe. As mixing of fluid improves with rise of revolution and width of tapes, Nu increases and augmentation in interaction of fluid with wall enhances the friction factor. Increasing number of wings can enhance the secondary flow. So, stronger impingement with wall can augment the friction factor. Nu enhances with rise of nw about 4.384% when TR = 2, ER = 0.34,V˙ = 19. Augmenting TR makes Nu to increase about 7.135% when nw = 4, ER = 0.1, V˙ = 19. Besides, with selecting higher ER, friction factor augments about 20.019% at TR = 2, nw = 2, V˙ = 6.3. To evaluate the amount of available work of this solar unit, components of entropy generation (Sgen,f, Sgen,h) have been measured. Thermal irreversibility declines with increase of turbulent intensity while friction component increases. Thermal efficiency (ηth) augments with growth of TR, ER and nw while it decreases with enhance of inlet temperature. As Tin rises, ηthreduces about 31.51% when TR = 2, nw = 2, ER = 0.1, V˙ = 19. Inclusion of nano-powders can enhance the useful heat and ηthaugments about 0.153%.

Numerical examination for entropy generation of turbulent nanomaterial flow using complex turbulator in a solar collector

Influences of inserted turbulator on heat transfer and irreversibility have been scrutinized. The simulations have been carried out by using finite volume method for various diameter ratio and revolution. All models were examined under turbulent flow regime with involving alumina nanomaterial as testing fluid. Components of entropy generation were exhibited as contours and 3D profiles. Outputs prove that by augmenting friction due to augmenting inlet velocity, the amount of Bejan number declines Efficacy of pumping power is more significant for greater values of diameter ratio.

Entropy generation in the human lung due to effect of psychrometric condition and friction in the respiratory tract

Background and Objective: Entropy generation is associated with the irreversibility of any thermodynamic system. It provides an indication of lost energy and hence the efficiency of a system. In this paper, an attempt has been made to study the effects of specific humidity, relative humidity, ambient temperature change, breathing air friction with the respiratory tract on the entropy generation during the respiration process at different physiological conditions.Methods: To address the above issues, a human respiratory tract model with realistic length to diameter ratio at different branches has been considered. The analysis examines air flow rates of 6 lpm and 60 lpm during rest and exercise condition respectively; corresponding to breathing rates of 30 and 60 per minute, respectively. The body temperature has been considered at 36°C, and ambient condition of air has been taken at 25°C DBT and 50% RH. The respiratory tract geometry has been modelled on the basis of Weibel's experimental results.Results: It has been noticed that, at a particular Lewis number entropy generation per day decreases with the increase in specific humidity, again at a particular specific humidity entropy generation increases with the decrease in Lewis number. For a particular physical condition and Lewis number entropy generation decreases with the increase in relative humidity. In this work, it has been observed that negentropy increases with the increase in ambient temperature for a constant relative humidity, however the net entropy generation is always positive. This study reports that, maximum resistance of flow occurs where duct aspect ratio (i.e. tract diameter to length) is minimal. For a typical geometry of air passage, velocity of flow increases up to 3rd generation then it is decreases gradually till 23rd generation. Amount of entropy generation goes on reducing as the duct goes on bifurcating except for the third generation where a local peak in entropy generation is observed. This is a consequence of typical geometry of human respiratory duct. This work reveals that, at rest entropy generation due to conditioning of breathing air is higher than its frictional component and during heavy physical activity, entropy generation due to breathing air friction with the respiratory tract is higher than its air conditioning component.Conclusions: Entropy generation is significantly higher due to conditioning of breathing air than that of frictional effect with the tract. This is a preliminary attempt in quantifying this aspect and the authors believe that, these two components of entropy generation have a probable connection with the bronchial thermoplasty, which helps to treat the asthma.

Numerical Study of the Magnetic Field Effects on the Heat Transfer and Entropy Generation Aspects of a Power Law Fluid over an Axisymmetric Stretching Plate Structure

Numerical investigation of the effects of magnetic field strength, thermal radiation, Joule heating, and viscous heating on a forced convective flow of a non-Newtonian, incompressible power law fluid in an axisymmetric stretching sheet with variable temperature wall is accomplished. The power law shear thinning viscosity-shear rate model for the anisotropic solutions and the Rosseland approximation for the thermal radiation through a highly absorbing medium are considered. The temperature dependent heat sources, Joule heating, and viscous heating are considered as the source terms in the energy balance. The non-dimensional boundary layer equations are solved numerically in terms of similarity variable. A parameter study on the Nusselt number, viscous components of entropy generation, and thermal components of entropy generation in fluid is performed as a function of thermal radiation parameter (0 to 2), Brinkman number (0 to 10), Prandtl number (0 to 10), Hartmann number (0 to 1), power law index (0 to 1), and heat source coefficient (0 to 0.1).

Thermodynamics of premixed combustion in a heat recirculating micro combustor

A thermodynamic model has been developed to evaluate exergy transfer and its destruction in the process of premixed combustion in a heat recirculating micro combustor. Exergy destruction caused by process irreversibilities is characterized by entropy generation in the process. The entropy transport equation along with the solution of temperature and species concentration fields in the wake of flame sheet assumptions have been used to determine the different components of entropy generation. The role of thermal conductivity and thickness of combustor wall, and Peclet number on transfer and destruction rate of exergy is depicted in the process of flame stabilization via heat recirculation. The entropy generations due to gas phase heat conduction and chemical reaction are identified as the major sources of exergy destruction. The total irreversibility in pre-flame region is confined only within a small distance upstream of the flame. It has been observed that the local volumetric entropy generation is higher near the axis than that near the combustor wall. The second law efficiency is almost invariant with heat loss from the combustor, Peclet number, and thermal conductivity and thickness of combustor wall.