Frictional Entropy Generation Rate Research Articles

Numerical Simulation of Nanofluid Flow in a Channel Using Eulerian–Eulerian Two-Phase Model

In this article, laminar forced convection heat transfer in two-dimensional channel is investigated numerically. This investigation provides significant insight into recognizing the key parameters affecting the properties of the second law of thermodynamics, Darcy friction factor, performance evaluation criterion (PEC) and heat transfer. Because changes in the volume fraction of nanoparticles are significant, the Eulerian–Eulerian two-phase model is considered to simulate nanofluid flow. To enhance heat transfer, single jet and twin jets of ethylene glycol–SiO2 nanofluid are used. The pure ethylene glycol flows from the channel inlet and mixes with the flow of single jet or twin jets. The effects of the number of jet injection (single or twin), the concentration of nanoparticles and inlet velocity of jets are assessed using computational fluid dynamics. Jet injection with constant heat flux can lead to decrease in the general thermal and increase in the frictional entropy generation rates. With jet injection into the ethylene glycol flow, Nusselt number, Darcy friction factor and PEC increase. The nanoparticles’ addition to ethylene glycol increases the heat transfer from the target surface.

Numerical investigation of the effect of corrugation profile on the hydrothermal characteristics and entropy generation behavior of laminar forced convection of non-Newtonian water/CMC-CuO nanofluid flow inside a wavy channel

The force convection flow of non-Newtonian water/Carboxy-Methyl Cellulose (CMC)-CuO Nanofluid (NF) in three wavy channels and a straight channel was numerically investigated. The two dimensional governing equations were solved in the computational domain using the FLUENT software. The influence of Re and nanoparticle concentration (φ) on the pressure drop (ΔP), Nu, and global thermal and frictional entropy generation rates (Ṡg,th and Ṡg,f) were studied for different Re and φ values. The results showed that the influence of Re on the Nu is much higher than that of φ. The increasing of the Re and decreasing of φ, results in increasing the Nu for four channels of the study. Besides, the sinusoidal channel has the highest Nu as compared to the other channels. Also, the highest pressure drop and total global entropy generation rate were obtained for the trapezoidal channel.

RETRACTED: Free convection of non‐Newtonian nanofluid flow inside an eccentric annulus from the point of view of first‐law and second‐law of thermodynamics

AbstractThe current work aims to perform the hydrothermal and entropy generation (EG) characteristics in a naturally cooled eccentric horizontal annulus filled with non‐Newtonian water‐magnetite/CNT nanofluid (NF). The wall temperature of both cylinders is constant and the temperature of the outer cylinder is lower than that of the inner cylinder. The impacts of vertical eccentricity, nanoadditive concentration (φ) and Rayleigh number () on the first and second‐laws performance features of the annulus are investigated numerically. It was found the average Nusselt number (), the global thermal EG (TEG) and the global frictional EG (FEG) augment with boosting both the and φ. In addition, it was depicted that the negative eccentricity is desirable and undesirable from the perspective of the first and second‐laws of thermodynamics. Moreover, the outcomes revealed that the first‐law/second‐law performance of the aqueous magnetite/CNT NF is better/weaker than that of the aqueous magnetite NF. Furthermore, for all the examined cases, the TEG rates are much higher than the FEG rates, and as a result, the pattern of total EG changes follows the TEG. Among all the studied cases, the minimum total EG was 4 W/K, which belonged to the case of = 0.9%, = 0%, = 103 and = 0.001.

Entropy and thermal performance analysis of PCM melting and solidification mechanisms in a wavy channel triplex-tube heat exchanger

This paper aims to perform the entropy analysis and thermal performance evaluation of a wavy-channels triplex-tube latent heat storage heat exchanger (LHSHE) during melting and solidification mechanisms. The system with different wave amplitudes was examined for different temperatures and Reynolds numbers of the heat transfer fluid (HTF). Water is passed in the inner and outer tubes in opposite directions and the PCM is placed in the middle tube. The heat exchanger was analyzed based on the temperature, liquid fraction and velocity of the PCM as well as thermal (ST‴) and frictional (Sf‴) entropy generation rates. The results show that for a higher wave amplitude, shorter melting and solidification times are achieved. Both frictional and thermal entropy generation rates increase to the maximum values and then decrease during the melting and solidification. The frictional entropy generation rate reaches almost zero quickly during the solidification. For both melting and solidification, the magnitude of ST‴ is significantly higher than Sf‴ in the phase change problem. The maximum values of ST‴ are 0.05 and 0.13 W/Km3 for the melting and solidification mechanisms, respectively, for the dimensionless wave amplitude of 0.3. The results show the crucial role of entropy generation on the performance of the LHSHE.

The entropy generation analysis of forward and backward laminar water flow in a plate-pin-fin heatsink considering three different splitters

The application of splitters has been proven to be useful to control the separated wake downstream of the pin-fins. This paper aims to evaluate the thermal (Ṡth) and frictional (Ṡf) irreversibility rates in the fluid flow inside the plate-pin-fin heatsinks (PPFHSs). To this end, the numerical analysis of forward and backward water flow inside the PPFHS with three different attached splitters was performed considering Re of between 50 and 250. The main objective was to determine the locations with intense thermal and frictional entropy generation rates inside the fluid flow geometry. Based on the results, the frictional entropy generation rate is significantly lower than that the thermal term. Also, the pin-fin with arched splitter has the minimum thermal irreversibilities as compared to straight and wavy splitters. Furthermore, the major irreversibilities are associated with the locations near the pin-fin lateral and frontal surfaces as well as the plate fin walls and heatsink upper case and lower base. Moreover, it was shown that for all considered cases and two flow directions, the increasing of the Re results in decreasing and increasing the thermal and frictional entropy generation rates, respectively.

Hydrothermal and entropy generation specifications of a hybrid ferronanofluid in microchannel heat sink embedded in CPUs

The objective of this numerical work is to evaluate the first law and second law performances of a hybrid nanofluid flowing through a liquid-cooled microchannel heatsink. The water-based hybrid nanofluid includes the Fe3O4 and carbon nanotubes (CNTs) nanoparticles. The heatsink includes a microchannel configuration for the flow field to gain heat from a processor placed on the bottom of the heatsink. The effects of Fe3O4 concentration (φFe3O4), CNT concentration (φCNT) and Reynolds number (Re) on the convective heat transfer coefficient, CPU surface temperature, thermal resistance, pumping power, as well as the rate of entropy generation due to the heat transfer and fluid friction is examined. The results indicated higher values of convective heat transfer coefficient, pumping power, and frictional entropy generation rate for higher values of Re, φFe3O4 and φCNT. By increasing Re, φFe3O4and φCNT, the CPU surface temperature and the thermal resistance decrease, and the temperature distribution at the CPU surface became more uniform. To achieve the maximum performance of the studied heatsink, applying the hybrid nanofluid with low φFe3O4and φCNT was suggested, while the minimum entropy generation was achieved with the application of nanofluid with high φFe3O4and φCNT.

Heat transfer of nanofluid through helical minichannels with secondary branches

Heat transfer, fluid flow characteristics and entropy generation of water-Al2O3 nanofluid for cylindrical heat sinks with helical minichannels that have secondary branches are investigated experimentally. The minichannels helix angles are 45, 60 and 90 degrees; the volume fraction of nanoparticles variation is 0.05% – 0.1%; the Reynolds number range is between 113 to 478. The effects of the helix angle of minichannels, Reynolds number and nanoparticle volume fraction are studied. The heat transfer enhances with increasing Reynolds number, decreasing helix angle and increasing volume fraction of nanoparticles. However, with increasing Reynolds number, increasing helix angle and decreasing nanoparticles volume fraction, the friction factor decreases. The experimental results show that the secondary branches decreased the friction factor and Nusselt number. The maximum enhancement of Nusselt number in helix angle 60 and 45 for pure water are 31.1% and 51.3% greater in comparing with the straight minichannel, respectively; moreover, maximum enhancement of the Nusselt number of nanofluid compared with the pure water was about 14.3% for 0.1% vol. The thermal entropy generation rate decreases and, the frictional entropy generation rate increases with increasing the nanoparticles volume fraction and decreasing the helix angle. Furthermore, two new correlations are obtained for the Nusselt number and friction factor.

A numerical investigation on the influence of nanoadditive shape on the natural convection and entropy generation inside a rectangle-shaped finned concentric annulus filled with boehmite alumina nanofluid using two-phase mixture model

The goal of this work is to numerically study the hydrothermal and entropy generation specifications of boehmite alumina (γ-AlOOH) nanofluid flowing in a finned concentric annulus using the two-phase mixture model. Different shapes for the nanoadditives are examined including cylindrical, brick, blade, platelet and spherical. The impacts of nanoadditive shape and volume concentration $$(\varphi )$$ , Rayleigh number $$({\text{Ra}})$$ and application of fins on the streamlines, isotherms, Nusselt number as well as both the local and global rates of entropy generation due to the heat transfer and fluid friction are examined. The results indicated that the addition of fins and employing a higher $${\text{Ra}}$$ and $$\varphi$$ cause a higher average Nusselt number and generation rate of thermal entropy. Moreover, it was found that, except for $${\text{Ra}} = 10^{3}$$ , the generation rate of frictional entropy intensifies by utilizing fins. Moreover, the frictional entropy generation rate was enhanced using a higher $${\text{Ra}}$$ and $$\varphi$$ . The results depicted that the impact of fins on the Nusselt number and entropy generation is not varied by the nanoadditive shape and concentration. Furthermore, it was concluded that the best nanoadditive shape is cylindrical and platelet, respectively, based on the first and the second laws of thermodynamics.

Heat transfer and entropy generation of water–Fe3O4 nanofluid under magnetic field by Euler–Lagrange method

The Euler–Lagrange method is considered to simulate the water–Fe3O4 nanofluid inside a circular tube. The non-uniform magnetic field is employed to a part of the tube. The effects of Reynolds number, concentration and magnetic field are investigated. The obtained results show that by increasing the magnetic field strength, global frictional entropy generation rate enhances. Meanwhile, with the application of the magnetic field, the frictional entropy generation rate in the central region of the tube and the vicinity of the wall decreases and increases, respectively. Additionally, the Bejan number is approximately 1 near the outlet. Also, there is a non-uniform distribution for nanoparticles, and the concentration of nanoparticles in the tube center is higher than the wall adjacency. Moreover, the wall temperature of the tube decreases in the part where the magnetic field is applied. The use of nanoparticle leads to an increase in the convective heat transfer coefficient. The velocity of the nanofluid in the central part of the tube decreases with the application of the magnetic field. But, the flow velocity near the wall increases with increasing magnetic field strength.

Free convection heat transfer and entropy generation analysis of water-Fe3O4/CNT hybrid nanofluid in a concentric annulus

Purpose This paper aims to numerically investigate the heat transfer and entropy generation characteristics of water-based hybrid nanofluid in natural convection flow inside a concentric horizontal annulus. Design/methodology/approach The hybrid nanofluid is prepared by suspending tetramethylammonium hydroxide-coated Fe3O4 (magnetite) nanoparticles and gum arabic (GA)-coated carbon nanotubes (CNTs) in water. The effects of nanoparticle volume concentration and Rayleigh number on the streamlines, isotherms, average Nusselt number and the thermal, frictional and total entropy generation rates are investigated comprehensively. Findings Results show the advantageous effect of hybrid nanofluid on the average Nusselt number. Furthermore, the study of entropy generation shows the increment of both frictional and thermal entropy generation rates by increasing Fe3O4 and CNT concentrations at various Rayleigh numbers. Increasing Rayleigh number from 103 to 105, at Fe3O4 concentration of 0.9 per cent and CNT concentration of 1.35 per cent, increases the average Nusselt number, thermal entropy generation rate and frictional entropy generation rate by 224.95, 224.65 and 155.25 per cent, respectively. Moreover, increasing the Fe3O4 concentration from 0.5 to 0.9 per cent, at Rayleigh number of 105 and CNT concentration of 1.35 per cent, intensifies the average Nusselt number, thermal entropy generation rate and frictional entropy generation rate by 18.36, 22.78 and 72.7 per cent, respectively. Originality/value To the best knowledge of the authors, there are not any archival publications considering the detailed behaviour of the natural convective heat transfer and entropy generation of hybrid nanofluid in a concentric annulus.

Entropy generation of boehmite alumina nanofluid flow through a minichannel heat exchanger considering nanoparticle shape effect

This paper aims to study the effect of nanoparticle shape on the entropy generation characteristics of boehmite alumina nanofluid flowing through a horizontal double-pipe minichannel heat exchanger. Boehmite alumina (γ-AlOOH) nanoparticles of different shapes (cylindrical, brick, blade, platelet, and spherical) are dispersed in a mixture of water/ethylene glycol as the nanofluid. The nanofluid and water flow in the tube side and annulus side of the heat exchanger, respectively. The effects of the Reynolds number and nanoparticle concentration on the frictional entropy generation rate, thermal entropy generation rate, total entropy generation rate and Bejan number are numerically analyzed for different nanoparticle shapes. The obtained results demonstrated that the nanofluids containing platelet shape and spherical shape nanoparticles have the highest and lowest rates of thermal, frictional, and total entropy generation, respectively. Additionally, it was found that the rates of thermal, frictional, and total entropy generation increase with an increase in the Reynolds number, while the opposite is true for the Bejan number. Furthermore, it was inferred from the obtained results that the increase of nanoparticle concentration results in higher frictional and total entropy generation rates and lower Bejan number.

Second law analysis of turbulent convection flow of boehmite alumina nanofluid inside a double-pipe heat exchanger considering various shapes for nanoparticle

The main objective of this research is to study the effects of nanoparticle shape on the entropy generation characteristics of boehmite alumina nanofluid flow in a horizontal double-pipe heat exchanger. The examined boehmite alumina nanofluids include dispersed cylindrical, brick, blade, platelet and spherical nanoparticles in a mixture of water/ethylene glycol. The nanofluid and water flow through the tube side and annulus side of the heat exchanger, respectively. Two-phase mixture model is applied to precisely simulate the behavior of nanofluid. The effects of the various Reynolds numbers, nanoparticle concentrations and nanoparticle shapes on the frictional, thermal and total entropy generation rates as well as the Bejan number are numerically investigated. The results indicated that the highest and lowest frictional entropy generation rate belongs to the nanofluids with platelet shape and spherical shape nanoparticles, respectively, while the nanofluid containing spherical shape and platelet shape nanoparticles represented the maximum and minimum thermal and total entropy generation rates. Furthermore, it was inferred that the frictional entropy generation rate is enhanced with an increase in nanoparticle concentration, whereas except for nanofluid with spherical shape nanoparticles, the opposite is true for thermal and total entropy generation rates and Bejan number.

Irreversibility characteristics of nanofluid flow under chaotic advection in a minichannel for different nanoparticle types

Abstract This study aims to investigate entropy generation for flow of three different nanofluids in a chaotic minichannel. Fluid particles in this channel move in chaotic trajectories, which can intensify the flow mixing. The results show that the contribution of heat transfer to entropy generation is greater than that of friction. With increasing the concentration, thermal entropy generation decreases for the alumina–water and Cu–water nanofluids, while intensifies for the magnetite–water nanofluid. With increase in Reynolds number for all nanofluids, thermal entropy generation decreases while frictional entropy generation increases. With the concentration increment, frictional entropy generation rate has an ascending trend for the alumina–water and magnetite–water nanofluids, while has a descending trend for the Cu–water nanofluid. Moreover, as Reynolds number increases from 50 to 200 at concentration of 1%, total entropy generation reduces 66.25%, 65.9% and 68.9% for the magnetite, alumina and Cu nanofluids, respectively. Based on the second law of thermodynamics, the Cu–water nanofluid is a more appropriate coolant owing to smaller total entropy generation. Moreover, use of the Cu–water and alumina–water nanofluids is more suitable at greater concentrations, while employing the magnetite–water nanofluid is only recommended at low concentrations.

Heat transfer and entropy generation analysis of a protruded surface in presence of a cross-flow jet using Al2O3-water nanofluid

The heat transfer and entropy generation in a rectangular duct with protrusions have been investigated numerically by employing a cross-flow jet and Al2O3 nanofluid as a coolant. The duct Reynolds number has been varied from 6,000 to 20,000. In an effort to obtain the heat transfer improvement, the nanofluid volume fraction has been varied from 0% to 5%. Also, three different nozzle positions have been tested to choose a good location for a maximum heat transfer enhancement. The effects of duct Reynolds number, nozzle Reynolds number, as well as the volume fraction of nanofluid on heat transfer and entropy generation rate, have been quantified. It has been observed that Reynods number (duct and nozzle) and nanofluid volume fraction significantly influence the heat transfer enhancement. The entropy generation for the cross-flow arrangement has been quantified in terms of total, thermal and frictional entropy generation rates. The entropy generation the for the cross-flow and non-cross-flow situations have been compared. The performance evaluation criterion based on the relative strengths of mechanical and thermal energies have been delineated. The results from the present study may be utilized to obtain suitable process parameters in terms of enhanced thermodynamic performance for the nanofluid based thermal systems.

Numerical investigation of entropy generation to predict irreversibilities in nanofluid flow within a microchannel: Effects of Brownian diffusion, shear rate and viscosity gradient

In the present contribution, irreversibilities caused by heat transfer and friction for the water-TiO2 nanofluid flow in a circular microchannel are investigated by evaluating entropy generation rates. The effects of viscosity gradient, non-uniform shear rate and Brownian diffusion on particle migration are taken into account in order to examine the effect of nanoparticle arrangement on entropy generation rates. The results show that nanoparticle migration alters concentration distribution and consequently, changes entropy generation rates. Nanoparticle migration increases concentration of the particles in central regions, and this migration is more noticeable for higher mean concentrations and larger particles. Thermal entropy generation rate intensifies with increasing wall heat flux and particle size while decreases with increasing concentration. Frictional entropy generation rate increases by concentration increment and decreases by particles enlargement, while it changes trivially by increasing wall heat flux. Frictional entropy generation rate is larger than thermal entropy generation rate in the microchannel under study and therefore, total entropy generation mostly stems from friction. Thus, total entropy generation rate decreases by particles enlargement, which is a positive result according to second law of thermodynamics. Eventually, a model for entropy generation rates is developed using the numerical data by means of Artificial Neural Network (ANN).

Second Law Analysis of Nanofluid Flow within a Circular Minichannel Considering Nanoparticle Migration

In the current research, entropy generation for the water–alumina nanofluid flow is studied in a circular minichannel for the laminar regime under constant wall heat flux in order to evaluate irreversibilities arising from friction and heat transfer. To this end, simulations are carried out considering the particle migration effects. Due to particle migration, the nanoparticles incorporate non-uniform distribution at the cross-section of the pipe, such that the concentration is larger at central areas. The concentration non-uniformity increases by augmenting the mean concentration, particle size, and Reynolds number. The rates of entropy generation are evaluated both locally and globally (integrated). The obtained results show that particle migration changes the thermal and frictional entropy generation rates significantly, particularly at high Reynolds numbers, large concentrations, and coarser particles. Hence, this phenomenon should be considered in examinations related to energy in the field of nanofluids.

Local entropy generation rate through convective heat transfer in tubes with wire coil inserts

Purpose – The purpose of this paper is to present a numerical analysis of the flow and heat transfer in a tube with a wire coil insert. A second law analysis of the results is accounted for, in order to assess the local and overall entropy generation in relation with the increased pressure drop and convective heat transfer. A wire coil with p/D=1.25 and e/D=0.076 is selected as insert device. A Reynolds number range between 100 and 1,000 is investigated, which corresponds to the typical operating regimes in the risers of liquid solar collectors. Different wall heat fluxes and inclination angles allow to analyze the potential impact of mixed convection in the presence of tube inserts. Design/methodology/approach – Three-dimensional numerical simulations are performed using a finite-volume solver, assuming laminar flow conditions. Pure water and a mixture of water and propylene-glycol (20 percent) are used as working fluids, with temperature-dependent properties. Fanning friction factor, Nusselt number and local entropy generation results are obtained in the fully developed region. Findings – The friction factor results are successfully compared with a well-known experimental correlation for wire coil inserts. The earlier onset of transition is devised at Re > 300. Nusselt number augmentations between 2.5- and 6-fold are reported with respect to the smooth tube. The mixed convection regime encountered in the smooth tube for the operating conditions investigated is canceled in the wire coiled tube, owing to the opposed effect of the swirl flow induced and the bouyancy forces. Frictional, heat transfer and overall entropy generation rates are computed locally in the fully developed region, allowing to relate these results with the flow structures in the mixed convection smooth tube and in the wire coiled tube. A threefold decrease in the entropy generation rate is reported for tubes with wire coil inserts. Originality/value – An holistic understanding of the heat transfer enhancement in tubes with wire coil inserts is provided through the analysis of the flow pattern, Fanning friction factor, Nusselt number and local entropy generation rates. The reduced entropy generation in the enhanced tube serves as a performance criteria to confirm the positive effect of wire coil inserts in heat transfer for the operating regime under investigation, in spite of the increased pressure drop.

Investigating non-Newtonian nanofluid flow in a narrow annulus based on second law of thermodynamics

The present research attempts to study the convective heat transfer and analysis of the second law of thermodynamics for the non-Newtonian nanofluid flow containing TiO2 nanoparticles within a narrow annulus. The base fluid is solution of 0.5wt% Carboxymethyl Cellulose (CMC) in water. The employed nanofluid is of the pseudo-plastic behavior, and power law model is utilized for apparent viscosity. The convective heat transfer coefficient increases by increasing Reynolds number and nanoparticle concentration. In higher concentrations, due to intensified shear-thinning behavior, and consequently, flatter velocity profile, convective heat transfer increases with a greater rate by an increase in concentration. Thermal, frictional and total entropy generation rates, both local and integrated, are assessed at different Reynolds numbers, concentrations and heat fluxes. The results show that increasing the concentration and Reynolds number leads to a decrease in thermal entropy generation rate and an increase in frictional entropy generation rate. The profile of thermal entropy generation rate at the annulus cross section is flatter at higher Reynolds numbers; while the same occurs for frictional entropy generation rate at lower Reynolds numbers. The lower the Reynolds number, the more evident the effect of heat flux change on total entropy generation rate. At low heat fluxes, the total entropy generation rate increases by increasing the concentration. However, at high heat fluxes, the total entropy generation rate decreases by concentration increment that can be beneficial from the second law viewpoint. Moreover, the effect of changing the value of heat flux on Bejan number is greater at higher concentrations.

Prediction of entropy generation for nanofluid flow through a triangular minichannel using neural network

Heat transfer characteristics and second law of thermodynamics are evaluated for the water–Al2O3 nanofluid flow in a triangular minichannel under constant wall heat flux. The effects of parameters such as Reynolds number, particle size, wall heat flux, and particle concentration on entropy generation rates are investigated. By increasing the Reynolds number and the concentration and by reducing the particle size, the convective heat transfer coefficient enhances. The thermal entropy generation rate decreases when the concentration and the Reynolds number are increased, while it increases when the heat flux and the particle size are increased. However, the frictional entropy generation incorporates a trend which is totally in contrast with the thermal entropy generation. The effect of Reynolds number change on the frictional entropy generation rate is more significant than that of concentration. At higher Reynolds numbers, changing of the concentration alters the frictional entropy generation rate more significantly. By changing the particle size, the total entropy generation rate incorporates a minimum value (i.e. optimum value). The Bejan number has large values near the walls, and the effect of changing the particle size on the Bejan number is more noticeable at the greater concentrations. In addition, at the cross sections near the inlet, the Bejan number is negligible in large parts of central regions of the channel, and increases along the channel length. Based on the data obtained, the model of entropy generation rates was developed in terms of effective parameters using Artificial Neural Network (ANN).

Cooling performance investigation of electronics cooling system using Al2O3–H2O nanofluid

In this study, the cooling performance of Al2O3–H2O nanofluid was experimentally investigated as a much better developed alternative for the conventional coolant. For this purpose the nanofluid was passed through the custom-made copper minichannel heat sink which is normally attached with the electronic heat source. The thermal performance of the Al2O3–H2O nanofluid was evaluated at different volume fraction of the nanoparticle as well as at different volume flow rate of the nanofluid. The volume fraction of the nanoparticle varied from 0.05vol.% to 0.2vol.% whereas the volume flow rate was increased from 0.50L/min to 1.25L/min. The experimental results showed that the nanofluid successfully has minimized the heat sink temperature compared to the conventional coolant. It was noticed also that the thermal entropy generation rate was reduced via using nanofluid instead of the normal water. Among the other functions of the nanofluid are to increase the frictional entropy generation rate and to drop the pressure which are insignificant compared to the normal coolant. Given the improved performance of the nanofluid, especially for high heat transportation capacity and low thermal entropy generation rate, it could be used as a better alternative coolant for the electronic cooling system instead of conventional pure water.