Friction Irreversibility Research Articles

Investigation of the nanofluid convective flow and entropy generation within a microchannel heat sink involving magnetic field

In this research, by studying the thermodynamics' laws, the thermal efficiency of microchannel was investigated employing the entropy analysis. Water is used as a base fluid with Al2O3 nanoparticles. Forchheimer -Brinkman model has been applied to include porous zone effect in momentum equations. The two-energy-equation model, which consists of two coupled equations, one for fluid and one for solid phase was employed. The analytical approach is applied to solve energy and momentum equations. The goal for using this method is the existence of nonlinear terms in equations. The effects of magnetic field, Reynolds number, α and ε on the parameters affecting irreversibility were studied. Then, it was concluded that by augmenting the Reynolds number to Reop, Ns decreases. Beyond Reop, the rise in Re enhance the Sgen and declines efficiency of the system. However, applying the magnetic field is beneficial between Re = 1.1 and Recr, and reduces the generated entropy. It was also observed that with the increase of α, Ns takes an upward trend. Increasing the ε value from 0.25 to 0.5 results in the downward trend of Ns, however, in high ε (0.75), Ns rises noticeably with augment of frictional irreversibility.

Turbulent nanofluid flow through a solar collector influenced by multi-channel twisted tape considering entropy generation

To enhance the performance of solar collectors, multi-channel twisted tape has been employed in this paper. Our main focus has been on the entropy generation of nanofluids. Inserting such device separates the nanofluid and a longer duration in pipe occurs. The number of channels and revolutions, the Reynolds number and the pipe diameters were considered as effective parameters. Results pointed out that more turbulence mixing occurs with greater values of the diameter ratio. Thermal irreversibility augments when reducing the number of channels. Because of more nanofluid gliding near the surface, frictional irreversibility enhances with increasing pumping power.

A numerical study on non-homogeneous model for the conjugate-mixed convection of a Cu-water nanofluid in an enclosure with thick wavy wall

Conjugate heat transfer due to the mixed convection and conduction of a Cu-water nanofluid in a thick-wall enclosure is conducted numerically based on the non-homogeneous model for nanofluids. We consider an enclosure with a thick wavy hot left side wall with the right vertical wall being allowed to move vertically downwards to develop a shear driven flow. This in combination with the horizontal temperature gradient leads to a mixed convection within the enclosure. The wavy geometry is transformed to a square domain by the co-ordinate transformation method and the governing equations along with the specified boundary conditions are solved using the finite volume method. The Richardson number and Reynolds number, which governs the mixed convection, are varied up to a moderate range at different choices of the nanoparticle volume fraction and its size, solid-to-fluid conductivity ratio, wave length and amplitude of the wavy interface. The heat transfer characteristics of the nanofluid is analyzed by evaluating the entropy generation and Bejan number. Results show that the impact of the dispersion of nanoparticles on the mixed convection is pronounced for a higher range of the Richardson number and nanoparticle volume fraction. The heat transfer and entropy generation both enhances with the increase of wave amplitude and wave number, however, the heat transfer enhancement rate dominates the entropy generation rate. Entropy generation due to heat transfer is more significant than that of fluid friction irreversibility for all the cases addressed here.

Numerical assessment into the hydrothermal and entropy generation characteristics of biological water-silver nano-fluid in a wavy walled microchannel heat sink

The objective of this numerical assessment is to examine the hydrothermal and irreversibility behaviour of a biologically synthesized water-silver nano-fluid in a wavy microchannel heat sink (MCHS). The green tea leaf extract is utilized to prepare silver nanoadditives. The impacts of nanoadditives volume fraction, Reynolds number, amplitude and wavelength of the channel on the convective heat transfer coefficient, CPU surface temperature, pumping power, as well as the thermal, frictional, and total irreversibilities are investigated. The results show that enhancing the Reynolds number and nanoadditives fraction intensifies the performance of heat sink by boosting the convective heat transfer coefficient of the working fluid which favorably reduces the CPU surface temperature and the rate of thermal and total irreversibilities and importantly leads to the temperature uniformity of the CPU surface. However, increase in Reynolds number adversely affects both the pumping power and the frictional irreversibility in the system. In addition, it is found that the nano-fluid always has a better cooling performance in comparison with the pure water. Moreover, it is reported that augmenting the wavelength results in an increase in the hydrothermal performance of nano-fluid and decrease in the global total entropy generation rate.

Lattice Boltzmann simulation of 3D natural convection in a cuboid filled with KKL-model predicted nanofluid using Dual-MRT model

Purpose This study aims to investigate the three-dimensional natural convection and entropy generation in a cuboid enclosure filled with CuO-water nanofluid. Design/methodology/approach The lattice Boltzmann method is used to solve the problem numerically. Two different multiple relaxation time (MRT) models are used to solve the problem. The D3Q7–MRT model is used to solve the temperature field, and the D3Q19 is used to solve the fluid flow of natural convection within the enclosure. Findings The influences of different Rayleigh numbers (103 < Ra < 106) and solid volume fractions (0 < f < 0.04) on the fluid flow, heat transfer, total entropy generation, local heat transfer irreversibility and local fluid friction irreversibility are presented comprehensively. To predict thermo–physical properties, dynamic viscosity and thermal conductivity, of CuO–water nanofluid, the Koo–Kleinstreuer–Li (KKL) model is applied to consider the effect of Brownian motion on nanofluid properties. Originality/value The originality of this work is to analyze the three-dimensional natural convection and entropy generation using a new numerical approach of dual-MRT-based lattice Boltzmann method.

Potential of gear-ring turbulator in three-dimensional heat exchanger tube from second law of thermodynamic viewpoint

Purpose This paper aims to use the second law of thermodynamic to evaluate the potential of gear-ring turbulator in a three-dimensional heat exchanger tube. Accordingly, a numerical simulation is performed to obtain the irreversibilities in a three-dimensional heat exchanger tube equipped with some gear-ring turbulators for turbulence regime. Design/methodology/approach A numerical simulation is performed to obtain the irreversibilities in a three-dimensional heat exchanger tube equipped with some gear-ring turbulators for turbulence regime. The analysis is carried out based on shear stress transport (SST) k-ω turbulent model. The influences of different parameters containing tooth number, free-space length ratios and Reynolds number on frictional and thermal irreversibilities and Bejan number are discussed. Findings The results indicated that the thermal irreversibility reduces by decreasing the tooth number. For example, the thermal entropy generation decreases about 25.81 per cent by decreasing the tooth number in the range of 24 to 0 at Re = 6,000. Moreover, the frictional entropy generation decreases by increasing the tooth number as the gear with more tooth number causes a lower flow disturbance. Originality/value The present study arranged a numerical work to study the potential of a gear-ring turbulator in a heat exchanger tube from first and second laws of thermodynamic viewpoint. The turbulent flow is considered for this problem. The literature review showed that the usage of a gear-ring turbulator in a heat exchanger tube is not investigated from the second law of thermodynamic viewpoint by previous studies. As a result, the influences of different parameters containing tooth number, free-space length ratios and Reynolds number on frictional and thermal irreversibilities and Bejan number are discussed.

Modelling Study on Internal Energy Loss Due to Entropy Generation for Non-Darcy Poiseuille Flow of Silver-Water Nanofluid: An Application of Purification.

In this paper, an analytical study of internal energy losses for the non-Darcy Poiseuille flow of silver-water nanofluid due to entropy generation in porous media is investigated. Spherical-shaped silver (Ag) nanosize particles with volume fraction 0.3%, 0.6%, and 0.9% are utilized. Four illustrative models are considered: (i) heat transfer irreversibility (HTI), (ii) fluid friction irreversibility (FFI), (iii) Joule dissipation irreversibility (JDI), and (iv) non-Darcy porous media irreversibility (NDI). The governing equations of continuity, momentum, energy, and entropy generation are simplified by taking long wavelength approximations on the channel walls. The results represent highly nonlinear coupled ordinary differential equations that are solved analytically with the help of the homotopy analysis method. It is shown that for minimum and maximum averaged entropy generation, 0.3% by vol and 0.9% by vol of nanoparticles, respectively, are observed. Also, a rise in entropy is evident due to an increase in pressure gradient. The current analysis provides an adequate theoretical estimate for low-cost purification of drinking water by silver nanoparticles in an industrial process.

Lattice Boltzmann simulation for hydrothermal analysis of free convection within dumbbell-shaped heat exchanger

The lattice Boltzmann simulation of nanofluid flow and heat transfer during natural convection within a dumbbell-shaped heat exchanger is carried out. The heat exchanger is filled with CuO–water. The KKL model is employed to predict the thermo-physical properties of nanofluid. In order to perform a comprehensive hydrothermal investigation, different post-processing approaches such as heatline visualization, total entropy generation, local entropy generation based on local fluid friction irreversibility and heat transfer irreversibility, average and local Nusselt variation are employed. In the present investigation, it is tried to present the impact of different influential parameters like Rayleigh number, solid volume fraction of nanofluid and thermal arrangement of internal fins-bodies on the fluid flow, heat transfer rate and entropy generation.

Convection of heat and thermodynamic irreversibilities in two-phase, turbulent nanofluid flows in solar heaters by corrugated absorber plates

The effects of simultaneous implementation of corrugated walls and nanoparticles upon the performance of solar heaters are investigated. Triangular and sinusoidal wall profiles along with varying concentration of nanoparticles are analyzed. The multi-phase mixture and the SST κ-ω models are used to simulate turbulent nanofluid flows inside the corrugated channels. The staggered computational grid is employed for storing the velocity and pressure terms at cell faces and cell center, respectively. The governing equations are first discretized by employing a second-order upwind differencing technique and are then solved by means of pressure-based finite volume approach. The convergence criterion is also presented for the validation of obtained results. The effects of wall profiles and nanoparticle concentration on the pertinent parameters including Nusselt number, pressure drop, performance evaluation criterion (PEC), and thermal and frictional irreversibilities are studied. This reveals that, in general, the triangular duct features superior heat transfer and inferior hydraulic characteristics in comparison with the sinusoidal duct. It is demonstrated that as long as the base fluid (water) is used the highest value of PEC corresponds to the straight duct. Yet, by introducing nanofluids the PEC values of the corrugated ducts exceed those of the straight duct. The analysis further shows that on the basis of the performance evaluation criterion, the sinusoidal duct appears to be a better choice in comparison with the triangular duct. However, the situation is reversed when thermodynamic irreversibilities are considered. It is argued that vortex formation in the two investigated wavy walls and shear layer developed in the triangular case are the essential physical reasons for the observed thermal, hydraulic and entropic behaviors.

Conjugated heat transfer and entropy generation of Al2O3–water nanofluid flows over a heated wall-mounted obstacle

The present study reports numerical simulations of water-based Al2O3 nanofluid flowing in a 2D channel with a heated wall-mounted obstacle. The conjugated heat transfer problem including forced convection within the fluid and conduction inside the obstacle is numerically solved using the mixture model with temperature-dependent properties. The model has been first carefully validated against published data. Then, the fluid flow and heat transfer have been investigated for six nanoparticle volume fractions $$\varphi$$ up to $$1.8\%$$ and bulk Reynolds numbers within the range $$100 \le Re \le 1600$$ . The results show that only the Reynolds number has an influence on the hydrodynamic field, especially on the reattachment length behind the obstacle. The heat transfer rate increases with increasing nanoparticle concentrations and/or Reynolds number. The second law analysis is employed to study the heat transfer and fluid friction irreversibilities. The average entropy generation increases linearly with the Reynolds number. Increasing the nanoparticle volume fraction reduces the thermal entropy generation while the frictional one increases. Finally, the benefit of using this nanofluid is discussed regarding five merit criteria.

Heat transfer enhancement and entropy generation analysis of Al2O3-water nanofluid in an alternating oval cross-section tube using two-phase mixture model under turbulent flow

Heat transfer and turbulent flow of Al2O3-water nanofluid within alternating oval cross-section tube are numerically simulated using Eulerian-Eulerian two-phase mixture model. The primary goal of the present study is to investigate the effects of nanoparticles volume fraction, nanoparticles diameter and different inlet velocities on heat transfer, pressure drop and entropy generation characteristics of the alternating oval cross-section tube. For numerical simulation validation, the numerical results were compared with experimental data. Also, constant wall temperature boundary condition was considered on the tube wall. In addition, the comparison of thermal-hydraulic performance and the entropy generation characteristics between alternating oval cross-section tube and circular tube under same fluids were done. The results show that the heat transfer coefficient and pressure drop of alternating oval cross-section tube is more than base tube under same fluids. Also, these two parameters are increased when adding Al2O3 nanoparticle into water fluid, at any inlet velocity for both tubes. Furthermore, compared to the base fluid, the value of the heat transfer enhancement of nanofluid is higher than the increase of friction factor of nanofluid at the same given inlet boundary conditions. The results of entropy generation analysis illustrate that the total entropy generation increase with increasing the nanoparticles volume fraction and decreasing the nanoparticles diameter of nanofluid. The generation of thermal entropy is the main part of irreversibility, and Bejan number with an increase of the nanoparticles diameter slightly increases. Finally, at any given inlet velocity the frictional irreversibility is grown with an increase the nanoparticles volume fraction.

Second law of thermodynamics analysis for nanofluid turbulent flow inside a solar heater with the ribbed absorber plate

Employing rough surfaces and nanofluids in solar heater ducts are recognized as effective techniques to improve thermal performances of these devices. In this paper, the second law of thermodynamics analysis is performed for nanofluid turbulent flow in a solar heater duct with rib roughness on the absorber plate. The effects of different parameters including rib height, rib wedge angle, rib pitch, Reynolds number, and nanofluid concentration on thermal and frictional irreversibilities are investigated. The results indicated that the thermal entropy generation decreases about 11.1% by using nanofluid with concentration of 0.04. The frictional and thermal entropy generations decrease by increasing the rib pitch. Moreover, the thermal entropy decreases about 21.05% by increasing the rib height in the range of 0.025–0.033 for Re = 3200. Finally, it is found that the thermal entropy generation decreases by increasing the wedge angle of the rib.

Heat transfer intensification using CuO-water nanofluid in a finned capsule-shaped heat exchanger using lattice Boltzmann method

The natural convection fluid flow and heat exchanger in a capsule-shape heat exchanger is investigated. The lattice Boltzmann method is used to simulate the fluid flow and heat transfer in the enclosure. To predict the thermal conductivity and dynamic viscosity of CuO-water nanofluid, the KKL-model is utilized which is able to apply the Brownian motion of the nanoparticles. In order to carry out a comprehensive analysis, the heatline visualization and entropy generation are used to detect the path of heat energy and find the optimum conditions, respectively. The influences of different effectual parameters such as Rayleigh number103<Ra<106, nanoparticle concentration0<φ<0.04, different thermal arrangements of implanted fins on the studied cases such as fluid flow, heat transfer, heat transfer irreversibility map, fluid friction irreversibility map, local Nusselt variation map, average Nusselt number and the total entropy generation are investigated comprehensively.

Effect of specific heat variations on irreversible Otto cycle performance

Considering internal irreversibility loss, friction loss and heat transfer loss, an irreversible Otto cycle model is built up by using finite-time thermodynamics with air standard assumption. Using the various irreversible losses in the cycle to compute the entropy generation rate, the optimal ecological function performance of the cycle is studied when the specific heats of working fluid are nonlinear relation with its temperature. Some important expressions, including ecological function, entropy generation rate, efficiency and power output, are obtained. The cycle ecological function performances with constant specific heats, specific heats changed with linear and nonlinear relations of its temperature are compared. Moreover, the impacts of internal irreversibility loss, friction loss and heat transfer loss on ecological function performance are analyzed. The results show that optimization of the exergy-based ecological function not only represents a compromise between the power output and the rate of entropy generation but also represents a compromise between the power output and the thermal efficiency, the specific heat models have no qualitative effect and only have quantitative effect on the performance characteristics of ecological function versus power output and ecological function versus efficiency, and the ecological function, power output and efficiency decrease with the increase of heat transfer, friction and internal irreversibility losses.

Effect of pressure drop and longitudinal conduction on exergy destruction in a concentric-tube micro-fin tube heat exchanger

A numerical study is carried out to predict the heat transfer characteristics and various exergy losses in a micro-fin concentric-tube double pipe heat exchanger. The results are compared with the experimental data from the literature and are found to be in a good agreement. The study is extended to include the effect of pressure drop and longitudinal conduction on the exergy losses. Furthermore, Ethylene Glycol-Water as a hot fluid is considered to investigate the effect of higher viscosity on the frictional irreversible losses. It is found that, at lower mass flow rates, fluid frictional irreversibility can be ignored for a low viscous fluid; however, there is a substantial exergy loss for a highly viscous fluid. At higher mass flow rates, fluid frictional irreversibility dominates over thermal irreversibility for both the fluids investigated in this study.

Lattice Boltzmann method based on Dual-MRT model for three-dimensional natural convection and entropy generation in CuO–water nanofluid filled cuboid enclosure included with discrete active walls

In the present study, the three-dimensional natural convection and entropy generation in a cuboid enclosure included with various discrete active walls is analyzed using lattice Boltzmann method. The enclosure is filled with CuO–water nanofluid. To predict thermo-physical properties, dynamic viscosity and thermal conductivity, of CuO–water nanofluid, the KKL model is applied to consider the effect of Brownian motion on nanofluid properties. In lattice Boltzmann simulation, two different MRT models are used to solve the problem. The D3Q7-MRT model is used to solve the temperature filed, and the D3Q19 is employed to solve the fluid flow of natural convection within the enclosure. The influences of different Rayleigh numbers 103<Ra<106 and solid volume fractions 0<φ<0.04 and four different arrangements of discrete active walls on the fluid flow, heat transfer, total entropy generation, local heat transfer irreversibility and local fluid friction irreversibility are presented comprehensively.

Magneto-Nanofluid Dynamics in Convergent-Divergent Channel and its Inherent Irreversibility

The effects of Cu-nanoparticles on the entropy generation of steady magnetohydrodynamic incompressible flow with viscous dissipation and Joule heating through convergent-divergent channel are analysed in this paper. The basic nonlinear partial differential equations are transformed into a system of coupled ordinary differential equations using suitable transformations which are then solved using power series with Hermite- Padé approximation technique. The velocity profiles, temperature distributions, entropy generation rates, Bejan number as well as the rate of heat transfer at the wall are presented in convergent-divergent channels for various values of nanoparticles solid volume fraction, Eckert number, Reynolds number and channel angle. A stability analysis has been performed for the shear stress which signifies that the lower solution branch is stable and physically realizable, whereas the upper solution branch is unstable. It is interesting to remark that the entropy generation of the system increases at the two walls as well as the heat transfer irreversibility is dominant there whereas the fluid friction irreversibility is dominant along the centreline of the channel.

Free convection heat transfer and entropy generation analysis of MWCNT-MgO (15% − 85%)/Water nanofluid using Lattice Boltzmann method in cavity with refrigerant solid body-Experimental thermo-physical properties

The local and volumetric heat transfer and entropy generation analysis of natural convection is carried out using Lattice Boltzmann method in a cavity with refrigerant rigid body and filled with MWCNT-MgO (15% −85%)/Water nanofluid. To increase the accuracy of the results and avoid wrong predictions of theoretical correlations, the thermo-physical properties of nanofluid are measured experimentally in five solid volume fractions of 0.25, 0.5, 1, 1.5 and 2vol% in a temperature range of 300 to 340 (K). To utilize these results, some correlations for dynamic viscosity and thermal conductivity in terms of temperature and solid volume fraction are developed and used in the numerical simulations. The considered cavity is heated with constant and uniform temperature from side walls, the top and bottom walls are insulated and the refrigerant rigid body has constant and uniform cold temperature. The influences of different governing parameters such as Rayleigh number, solid volume fraction and refrigerant rigid body configuration on the local Nusselt variation, fluid friction irreversibility map, heat transfer irreversibility map, average Nusselt number, volumetric entropy generation, Bejan number, fluid flow and temperature field are resented comprehensively. It is concluded that the configuration of refrigerant rigid body has pronounced effect on the fluid flow, heat transfer and entropy generation. Furthermore, the Nusselt number has direct relationship with Rayleigh number and solid volume fraction, and the entropy generation has direct and reverse relationship with Rayleigh number and solid volume fraction, respectively.

A Numerical Study on Entropy Generation in Two-Dimensional Rayleigh-Bénard Convection at Different Prandtl Number

Entropy generation in two-dimensional Rayleigh-Bénard convection at different Prandtl number (Pr) are investigated in the present paper by using the lattice Boltzmann Method. The major concern of the present paper is to explore the effects of Pr on the detailed information of local distributions of entropy generation in virtue of frictional and heat transfer irreversibility and the overall entropy generation in the whole flow field. The results of this work indicate that the significant viscous entropy generation rates (Su) gradually expand to bulk contributions of cavity with the increase of Pr, thermal entropy generation rates (Sθ) and total entropy generation rates (S) mainly concentrate in the steepest temperature gradient, the entropy generation in the flow is dominated by heat transfer irreversibility and for the same Rayleigh number, the amplitudes of Su, Sθ and S decrease with increasing Pr. It is found that that the amplitudes of the horizontally averaged viscous entropy generation rates, thermal entropy generation rates and total entropy generation rates decrease with increasing Pr. The probability density functions of Su, Sθ and S also indicate that a much thinner tail while the tails for large entropy generation values seem to fit the log-normal curve well with increasing Pr. The distribution and the departure from log-normality become robust with decreasing Pr.

Lattice Boltzmann simulation of natural convection and entropy generation in cavities filled with nanofluid in existence of internal rigid bodies-Experimental thermo-physical properties

The lattice Boltzmann simulation of natural convection heat transfer in cavities with active internal rigid bodies and filled with DWCNTs-water nanofluid is performed. The thermo-physical properties of the nanofluid, thermal conductivity and dynamic viscosity, are measured experimentally by means of modern measuring devices in different solid volume fraction of 0.01%, 0.02%, 0.05%, 0.1%, 0.2%, and 0.5% and a temperature range of 300 to 340. Two sets of correlations for thermal conductivity and dynamic viscosity are developed and used in the numerical simulations. The influences of different governing parameters such different arrays of rigid bodies, different concentrations of nanofluid and temperature differences of side walls on the fluid flow, temperature filed, Nusselt number and entropy generation are presented. The local fluid friction irreversibility and heat transfer irreversibility contours are depicted graphically which show the concentration of two components of total entropy generation. It is concluded that the array of refrigerant bodies has significant influence on streamlines and isothermal lines. Moreover, the effects of rigid body arrays on the average Nusselt number, total entropy generation and heatlines are considerable. The Nusselt number and entropy generation are highest at Case B. Also, the Nusselt number has direct relationship with Rayleigh number and solid volume fraction. On the other hand, the total entropy generation has direct and reverse relationship with Rayleigh number and solid volume fraction, respectively.