Total Entropy Generation Research Articles

Energy storage, thermal-hydraulic, and thermodynamic characteristics of a latent thermal energy storage system with 180-degree bifurcated fractal fins

The low thermal conductivity of organic phase change materials limits the performance of latent thermal energy storage (TES) systems. Inspired by fractal theory, this study proposes an innovative 180° fractal fin for enhancing the thermal performance of latent TES systems. The effects of length ratios (l) and fractal levels (N) are numerically investigated employing the enthalpy-porosity method. Compared with traditional rectangular fins, the results indicate that the 180° fractal fins reduce the integral average value of the maximum velocity by 2.24%–48.51%, which indicates the suppression of natural convection by the latter. Increasing l and N result in a general increase in melting time. Compared to the TES systems without fins and with rectangular fins, the 180° fractal fins can respectively reduce melting time by up to 88.79% and 28.00%, increase integral average Nusselt number by up to 7.30 times and 34.21%, and enhance energy storage power by a maximum of 8.55 times and 38.71%. Moreover, flow viscous entropy generation can be neglected compared to thermal entropy generation. In contrast to rectangular fins, the employment of fractal fins leads to a maximum reduction of 90.06% and 99.10% in total frictional entropy generation and thermal entropy generation, respectively.

Examination of convective heat transfer and entropy generation performance in twisted elliptical tubes using response surface method

In this paper, the convective heat transfer (CHT) and flow properties of twisted elliptical tubes (TETs) are numerically simulated within the range of Reynolds numbers (Re) 710 to 4790. The effects of design parameters such as twist ratio (P/D), aspect ratio (A/B), and Re on the CHT and flow resistance properties of TETs are highlighted. The response surface method (RSM) is used to research the effect of interaction between design parameters on the performance of CHT in TETs and establish the relationship between the objective function, i.e., Nusselt number (Nu), friction factor (f), and design parameters. The objective function fitted by RSM are optimized by the non-dominated sequential genetic algorithm (NSGA-II) to obtain the Pareto optimal solution. Besides, the entropy generation minimization principle explores entropy generation characteristics to reveal the mechanism of CHT enhancement in TETs. The results show that the CHT performance, flow resistance, and total entropy generation in TET increase, decrease, and increase with the growth of Re, respectively. They all increase with the reduction of P/D or the growth of A/B. The maximum values of Nu and pressure drop (ΔP) occur when A/B = 2.16 and P/D = 11.90; the minimum value of total entropy generation is reached when A/B = 1.34 and P/D = 26.33; and the Pareto optimal solution corresponds to the best combination of design parameters of Re = 3980, P/D = 13.32, and A/B = 1.82.

Research on the influence mechanism of internal flow characteristics on energy conversion in radial energy recovery turbines under multiple conditions

The development of Energy Recovery Turbine (ERT) is of great significance for energy saving and emission reduction. The mutual influence mechanism between the flow characteristics and energy conversion of ERT has not yet been mastered. A radial ERT was selected as the research object and a mathematical model based on entropy generation theory was established to evaluate the energy loss of the ERT. The internal flow characteristics and energy loss mechanism of an ERT were studied. The results show that the entropy generation power of the impeller accounts for 17.4 %. The turbulent entropy generation power of the impeller accounts for 76.5 % of the total entropy generation power. The energy loss at the volute tongue is maximized due to the presence of two attached vortexes with opposite rotation directions. The area with significant energy loss in the impeller gradually shifts from hub and pressure surface to the suction surface as the flow increases. The performance degradation under overload conditions is relatively slow, as the flow impact on the pressure surface has a smaller impact on the blade's ability to perform work. Therefore, the hydraulic design should be carried out after appropriately reducing the rated flow rate when designing a radial turbine.

Thermal entropy generation and exergy efficiency analysis of rGO/water nanofluid in a tube under turbulent regime using experimental and fully connected neural network

Analyzing entropy generation is one of the most effective methods for examining how well thermal systems operate. To determine the ideal operating conditions, numerous researchers have examined the entropy generation of thermal systems. In this work, the effects of concentrations of reduced graphene oxide (rGO) nanoparticles on the formation of entropy in water-rGO nanofluid flow through a circular pipe with a constant wall heat flux boundary condition in turbulent regimes are investigated experimentally. rGOs were prepared from Hummer's technique. Experiments are conducted at particle volumes from 0.5 % to 2.0 %, mass flow rates from 0.0333 kg/s to 0.25 kg/s, and Reynolds numbers from 1800 to 21,000, respectively. Later, estimated data points were anticipated with a convolutional neural network (CNN). The model was analyzed through several performances like root-mean-square-error (RMSE), mean-square-error (MSE), mean-absolute-percentage-error (MAE), and the coefficient of determination (R2). Results indicated, with used by 2.0 vol% of nanofluid, entropy generation-thermal is reduced to 39.24 %, entropy generation-frictional is higher by 16.92 %, entropy generation-total is decreased by 37.82 %, and second law efficiency is augmented to 34.17 % at Reynolds number of 13,705, against base fluid data. The correlation coefficient R2 evaluated from CNN for thermal entropy generation, frictional entropy generation, total entropy generation, and exergy efficiency are 0.99297, 0.99924, 0.9989, and 0.99273, respectively.

Effect of magnetic field and key parameters values on natural convection and entropy generation of hybrid nanofluid in a corrugated enclosure

This work enlightens the magnetohydrodynamics (MHD) natural convective hydrothermal scenario and entropy generation analysis in a corrugated enclosure filled with MoS2–SiO2–water hybrid nanofluid. Three discrete uniform heaters are kept fixed to the enclosure bottom wall. The enclosure top wall and the remaining parts of its bottom wall are isothermally cooled. The enclosure has adiabatic vertical walls. A higher-order compact (HOC) finite difference technique is used to determine the solutions to the dimensionless governing equations. To demonstrate the accuracy of the mathematical model, experimental and numerical verifications are accomplished. The numerical investigation is accomplished for Rayleigh number ( Ra = 10 4 − 10 6 ), aspect ratios of heater length ( AR = 0.2 , 0.4 , 0.6 , 0.8 ), nanoparticle volume percentage ( ϕ = 0 − 4 % ), and Hartmann number ( Ha = 0 − 120 ). The numerical outcomes are presented and studied by means of isotherms, streamlines, and the average Nusselt number. Furthermore, local entropy generation resulting from heat transmission, fluidic friction, and magnetic field, along with overall entropy formation and Bejan number are analyzed. This study reveals that the aspect ratio AR = 0.2 enhances the convective flow process at Ra = 10 6 , even when a magnetic field is present. The heat transfer rate increases as a function of the Rayleigh number, while it exhibits a decreasing trend with the aspect ratio of heater length and Hartmann number. Total entropy generation reduces as the Hartmann number and aspect ratio of heater length increase. Bejan number graphs show a reverse pattern as compared to total entropy generation. It has been noted that an increase in the Hartmann number from 0 to 120 decreases the average Nusselt number and total entropy generation by 19.77 and 46.63%, respectively, for AR = 0.2 , Ra = 10 6 , and ϕ = 4 % .

Numerical Investigation of Hybrid Nanofluid Natural Convection and Entropy Generation in a Corrugated Enclosure with an Inner Conducting Block

Current work deals with a numerical analysis of convective heat transfer and entropy generation inside a rectangular cavity with a corrugated bottom filled with MoS2–SiO2-water hybrid nanofluid. Here, a conducting solid body is attached to the top wall, and discrete heaters are attached to the bottom wall of the cavity. The numerical solutions of the governing equations are derived utilizing a higher-order compact (HOC) finite difference scheme and validated with the existing computational and experimental results. Present numerical results are then studied in detail, emphasizing isotherms, streamlines, and local entropy generation with respect to specific parameters like Rayleigh number (103 ≤ Ra ≤ 106), the volume percentage of nanoparticles (0% ≤ Φ ≤ 4%), the thermal conductivity of solid body (1.95 ≤ ks ≤ 16.00) as well as the aspect ratio of heater length (AR = 0.2, 0.4, 0.6, 0.8). The impacts of key factors on the Bejan number, average Nusselt number, and overall entropy generation are also investigated. The results show that an increase in the thermal conductivity of the solid body from 1.95 to 16.00 increases the average Nusselt number and total entropy generation by 9.17% and 40.07%, respectively, for AR = 0.2, Ra = 106, and Φ = 4%. In addition, the average Nusselt number and total entropy generation decrease by 59.11% and 61.99%, respectively, for ks = 16.00, Ra = 106, and Φ = 4% when the aspect ratio of heater length increases to 0.8.

Performance evaluation criteria based on the first and second laws of thermodynamics

Numerical simulations were conducted to investigate the correlation between assessments based on the total entropy generation rate criterion and the thermal resistance criterion in the context of evaluating heat transfer performance. This study focused on a parallel plate channel heat sink with the lower wall subjected to a constant heat flux, under various flow constraints. The flow was assumed to be laminar and fully developed. The energy equation was discretized using the control volume-based power law scheme, and the resulting algebraic equations were solved by the line-by-line method. Optimal channel heights which lead to minimize irreversibility and temperature difference between heated wall and inlet fluid temperatures were determined by both the total entropy generation rate and thermal resistance criteria under four distinct flow constraints: identical mass flow rate, identical inlet velocity, identical pumping power, and identical pressure drop. The investigation revealed a lack of significant correlation between the optimal channel heights derived from assessments based on the total entropy generation rate and thermal resistance. Consequently, the utilization of the total entropy generation rate criterion for evaluating heat transfer performance, based in the second law of thermodynamics, instead of the thermal resistance criterion, based in the first law of thermodynamics, was deemed inappropriate. The total entropy generation rate criterion was based on the minimization of the irreversibility and served as an indicator of heat transfer quality. As a recommendation, it is suggested that results obtained from both the total entropy generation rate and thermal resistance criteria for assessing heat transfer performance be presented separately for each specific application.

Effects of Hydrogen, Methane, and Their Blends on Rapid-Filling Process of High-Pressure Composite Tank

Alternative fuels such as hydrogen, compressed natural gas, and liquefied natural gas are considered as feasible energy carriers. Selected positive factors from the EU climate and energy policy on achieving climate neutrality by 2050 highlighted the need for the gradual expansion of the infrastructure for alternative fuel. In this research, continuity equations and the first and second laws of thermodynamics were used to develop a theoretical model to explore the impact of hydrogen and natural gas on both the filling process and the ultimate in-cylinder conditions of a type IV composite cylinder (20 MPa for CNG, 35 MPa and 70 MPa for hydrogen). A composite tank was considered an adiabatic system. Within this study, based on the GERG-2008 equation of state, a thermodynamic model was developed to compare and determine the influence of (i) hydrogen and (ii) natural gas on the selected thermodynamic parameters during the fast-filling process. The obtained results show that the cylinder-filling time, depending on the cylinder capacity, is approximately 36–37% shorter for pure hydrogen compared to pure methane, and the maximum energy stored in the storage tank for pure hydrogen is approximately 28% lower compared to methane, whereas the total entropy generation for pure hydrogen is approximately 52% higher compared to pure methane.

Inhomogeneous flow model of natural convection, entropy generation, and heatlines visualization in wavy I‐shaped enclosure with rectangular heater

AbstractThe present investigation is on examination of the natural convection and entropy generation considering the heatlines visualization of nanofluid I‐shaped enclosure with two corrugated walls considering inner rectangular heater of three different heights. The influence of Brownian motion along with thermophoresis had been implemented using Inhomogeneous two‐phase model of nanofluid. The governing equations were solved numerically using COMSOL software. Influence of Rayleigh number , Buoyancy ratio number , Lewis number , heater length . The results indicate that the influence of Lewis number on heat transfer bettering is stronger at high Rayleigh number while its impact is negligible at a lower value of Rayleigh number (conduction mode). In addition, the total entropy generation gets its highest value at Lewis number . Bejan number, fluid flow strength and heat rate increase as the rectangular heater height increases. Also, higher heat transfer augmentation is taken when the heater height is while increasing the heater height to leads to more total entropy generation. The impact of heater height on total entropy generation is highly affected by Rayleigh number as increasing the heater height from into , total entropy generation increases by at while it increases by at .

Study of Bejan number and entropy generation for mixed convection of nanofluid flow inside a chamber under an inclined magnetic field

Examination of the efficiency and losses in heat exchange devices is pivotal. Therefore, the entropy generation (EYG) and Bejan number (Be) of mixed convective heat transfer of nanofluid flow in a rectangular cavity (RCY) are evaluated in this study. Five baffles are placed at the lower hot wall of the RCY. The cold upper wall moves and causes forced convection flow of nanofluid. The magnetic field (MFD) at different angles affects the nanofluid when the Hartmann number (Ha) changes from 10 to 40. The length of stepped baffles is changed, and the values of frictional EYG, thermal EYG, and total EYG are estimated. The simulations are done using the LBM and an in-house code. The results demonstrate that the improvement in Ha decreases the amount of frictional EYG, thermal EYG, total EYG, and Be. The total EYG and Be also increase as the MFD angle is increased. The increment in the Richardson number (Ri) reduces the frictional EYG and total EYG (61.8 %) and increases the value of thermal EYG. Enhancing the length of the baffles intensifies the amount of Be and total EYG (3.4 %) and thermal EYG, but decreases the frictional EYG.

Entropy generation for thermo-magnetic fractional order convective flow in complex porous enclosures: a numerical study

PurposeThis study aims to analyze the impact of fractional derivatives on heat transfer and entropy generation during transient free convection inside various complex porous enclosures, such as triangle, L-shape and square-containing wavy surfaces. These porous enclosures are saturated with Cu-water nanofluid and subjected to the influence of a uniform magnetic field.Design/methodology/approachIn the present study, Darcy’s model is used for the momentum transport equation in the porous matrix. Additionally, the Caputo time fractional derivative is introduced in the energy equation to assess the heat transfer phenomenon. Furthermore, the total entropy generation has been computed by combining the entropy generation due to fluid friction (Sff), heat transfer (Sht) and magnetic field (Smf). The complete mathematical model is further simulated using the penalty finite element method, and the Caputo time derivative term is approximated using the L1 scheme. The study is conducted for various ranges of the Rayleigh number (102≤Ra≤104), Hartmann number (0≤Ha≤20) and fractional order parameter (0<α<1) with respect to time.FindingsIt has been observed that the fractional order parameter α governs the characteristics of entropy generation and heat transfer within the selected range of parameters. The Bejan number associated with heat transfer (Beht), fluid friction (Beff) and magnetic field (Bemf) further demonstrate the dominance of flow irreversibilities. It becomes evident that the initial evolution state of streamlines, isotherms and local entropy varies according to the choice of α. Additionally, increasing Ra values from 102 to 104 shows that the heat transfer rate increases by 123.8% for a square wavy enclosure, 7.4% for a triangle enclosure and 69.6% for an L-shape enclosure. Moreover, an increase in the value of Ha leads to a reduction in heat transfer rates and entropy generation. In this case, Bemf→1 shows the dominance of the magnetic field irreversibility in the total entropy generation.Practical implicationsRecently, fractional-order models have been widely used to express numerous physical phenomena, such as anomalous diffusion and dispersion in complex viscoelastic porous media. These models offer a more accurate representation of physical reality that classical models fail to capture; this is why they find a broad range of applications in science and engineering.Originality/valueThe fractional derivative model is used to illustrate the flow pattern, heat transfer and entropy-generating characteristics under the influence of a magnetic field. Furthermore, to the best of the author’s knowledge, a fractional-derivative-based mathematical model for the entropy generation phenomenon in complex porous enclosures has not been previously developed or studied.

Turbulent Heat Transfer of Hybrid Nanofluid with Nano-Encapsulated Phase Change Material in a Square Channel

Investigation of turbulent mixed convection of different working fluids, namely, pure water, CuO/water nanofluid, n-octadecane/water nanofluid (or slurry), and a hybrid water-based suspension of CuO and n-octadecane nanoparticles in a uniformly heated vertical square channel is carried out. The shear stress transport/kappa-omega model is applied to simulate the turbulent flow. Eulerian–Lagrangian two phase model and homogeneous model are employed to simulate the nanofluid flow. It is shown that Eulerian–Lagrangian two-phase model predicts higher Nusselt number and friction factor than single-phase model and the results of two-phase model are closer to experimental data. It is found that a new hybrid nanofluid with dispersed nano-encapsulated phase change material particles provides better thermal and hydrodynamic performances compared to other nanofluids. Slurry containing 5% n-octadecane provides an improvement of nearly 37.2%, while hybrid nanofluid (1% CuO + 5% n-octadecane) offers added convective heat transfer enhancement of almost 60%. With increasing volume fraction, friction factor becomes slightly larger than that of pure water. For 5% n-octadecane/water and 1% CuO + 5% n-octadecane/water nanofluids, friction factor increases by 2.5% and 1.7%, respectively. Due to dominance of thermal entropy generation, total entropy generation reduces by increasing Reynolds number and volume fraction.

Effect of lubricating oil on non-azeotropic refrigerant in flow boiling: an entropy generation analysis

ABSTRACT Entropy generation analysis is a useful method for studying the relationship between heat transfer and pressure drop in flow boiling. The flow boiling process in an actual refrigeration system is inevitably affected by oil. Therefore, the effect of oil on entropy generation needs to be investigated. A new non-azeotropic ternary refrigerant mixture, R447A, was selected as working fluid. Subsequently, flow boiling entropy generation models of R447A with and without oil were established. The effects of individual parameters on entropy generation were investigated. The entropy generation per unit tube length under different conditions was proposed as the benchmark for comparison. The results show that there is an optimal mass flux corresponding to minimum entropy generation per unit tube length at a specific oil concentration, and optimal mass flux decreases with increasing oil concentration. The tube diameter also affects the optimal mass flux of the fluid with oil, which increases with decreasing tube diameter and is smaller than that without oil for the same diameter tube. When the oil concentration is 0–4.95%, the total entropy generation exhibits a decreasing trend. Therefore, within the scope of this research, the addition of oil is beneficial for reducing the entropy generation of heat exchangers.

Investigation of thermal performance and entropy generation rate of evacuated tube collector solar air heater with inserted baffles and metal foam: A CFD approach

This study investigates the impact of metal foam embedding into evacuated tube collector solar air heaters with inserted baffle (IBMF-ETC-SAH) on the device thermal performance using a computational fluid dynamics (CFD) approach. A three-dimensional model is employed to analyze the system under steady-state conditions. The key finding of this study is that the utilization of metal foam leads to a substantial increase in thermal performance, with an average improvement of approximately 300 %. The investigation examines the influence of metal foam porosity and pores per inch (PPI) on the performance of the IBMF-ETC-SAH across Reynolds numbers ranging from 6000 to 18,000. The results indicate that increasing the PPI from 20 to 40 at a constant porosity of 0.93 has negligible effects on device performance. However, the pressure drop increases by 48 % for a PPI of 40 compared to a PPI of 20. Furthermore, reducing the porosity from 0.95 to 0.9 leads to a 7 % enhancement in thermal performance. The IBMF-ETC-SAH exhibits a significant decrease in the total global entropy generation rate (EGR) compared to the device without metal foam. The maximum value of total EGR for the IB-ETC-SAH case is 2.32 times higher than the corresponding values for the IBMF-ETC-SAH case.

Performance evaluation of a blocked regulated lateral release channel for proton exchange membrane fuel cell based on entropy generation analysis

Oxygen-deficient regions at low voltage restrict the enhancement of proton exchange membrane fuel cell performance. To address this issue, a blocked regulated lateral release channel (BRLRC) is proposed to divert oxygen from blocked channel into oxygen-deficient areas. The implications of BRLRC on oxygen distribution, drainage capacity and output performance are investigated by adopting a three-dimensional multi-phase model. Through entropy generation analysis, multiple irreversible losses across varying locations for various flow fields are assessed. Structural optimization of BRLRC, focusing on parameters such as width, entrance, and junction positions of auxiliary channels, is conducted to boost net output power of the fuel cell. Results show that compared to the blocked channel, BRLRC further augments the output power, oxygen uniformity, drainage capacity and diminishes pump power. Analysis of cathodic entropy generation reveals that over 90% stems from mass transfer, with the catalyst layer as the main contributor, while BRLRC significantly reduces total entropy generation by mitigating mass transfer irreversibility. By accurately oxygen allocation, the structurally optimized BRLRC attains peak output power even with an oxygen concentration that is 7.5% lower than the maximal observed concentration. Building on this efficiency, when contrasted with the straight channel, BRLRC amplifies the maximum net output power by 9.04%, exceeding the 5.18% increase achieved by the conventional blocked channel.

Relaxation analysis and entropy simulation of triple diffusive slip effect on magnetically driven Casson fluid flow

ABSTRACT In this article, we explore a novel numerical solution of a triple diffusive flow of Casson fluid taking slip boundary condition on a stretching sheet along with suction and magnetic field effects. Total entropy generation in flow of viscous fluid under coupling effects of concentrations of two heterogeneous salts () is evaluated by different Bejan numbers. Magnetic Bejan number and mass Bejan number have been defined for the estimation of novel irreversibilities due to salts’ concentrations and magnetic retardation over the non-linearly stretching sheet. Order reduction and then finite difference techniques are employed on system of equations thus obtained. Persuasive iterative scheme, successive over relaxation method, encoded via MATLAB has been utilized to numerically simulate discretised system of ordinary differential equations. Significant impacts of prime parameters on entropy generation rate and different Bejan numbers are physically interpreted through graphs for both linear as well as non-linear stretching cases. Magnetic force tends to decrease the entropy generation rate while enhances the magnetic Bejan number considerably. Entropy generation rate in triple diffusion is higher than double diffusion. Outcomes may be useful in automobiles industries, waste-water treatment, petroleum industries, food processing mills and mechanical systems under controlled conditions.

Thermal management for multi-cores chips through microchannels completely or incompletely filled with ribs

Microchannels have attracted significant attention in the thermal management of integrated circuits due to their small geometrical size and high heat transfer efficiency. Motivated by further improving the thermal management capacity of microchannels in multi-cores chips with lower pressure drop penalty, in this paper, a comparative investigation on four different configurations was conducted through numerical simulation for the Reynolds number ranging from 200 to 800 to analyze the comprehensive effects of filling mode and rib arrangement on the flow and heat transfer characteristics, including microchannel completely filled with aligned ribs (MCFAR), microchannel incompletely filled with aligned ribs (MIFAR), microchannel completely filled with staggered ribs (MCFSR) and microchannel incompletely filled with staggered ribs (MIFSR). Moreover, the entropy generation rate is used to estimate the irreversibility of flow and heat transfer based on the second law of thermodynamics. Finally, the performance evaluation criteria (PEC) is adopted to estimate the overall performance. The results show the flow patterns in the MIFAR and the MIFSR are different from those in the MCFAR and the MCFSR due to the incomplete filling mode, which could induce more dramatic disturbance and further break the downstream boundary layer, thus the heat transfer could be enhanced with a lower pressure drop penalty. The analysis of entropy generation rate indicates that entropy generated by heat transfer contributes the majority of the total entropy generation thus enhancing the heat transfer is a more important and effective approach in reducing the irreversibility. Among the four configurations researched, the microchannel MIFAR shows the best overall performance (PEC = 1.76) when Re = 400.

Computational investigation of aspect ratio and inclination effects on natural convection heat transfer in nanofluid-filled rough wall cavities

Numerical analysis is performed to deduce the effect of aspect ratio (AR) and inclination of a rough-walled cavity on heat transfer, fluid flow, and entropy generation due to natural convection for Rayleigh number (Ra = 105). The cavity is filled with Al2O3-water nanofluid of 0.05 solid volume fraction. The natural convection process is caused by the temperature difference between the left hot wall and the right cold wall of the cavity. The walls are subjected to slip boundary conditions and the slip velocity is characterized by the Knudsen number (Kn = 0.5). The profile of the rough surface is generated by Weierstrass-Mandelbrot (W-M) function. Numerical simulations have been performed using Finite Element based software COMSOL Multiphysics 6.0. The AR is varied in the range of 0.5 to 4, and the inclination of the cavity is kept at 0°, 30°, and 60°. The numerical results are exhibited in terms of isotherms, streamlines, entropy generation due to heat transfer, and fluid friction irreversibilities. It is observed that the slip velocity on the walls has a strong influence on the fluid flow. Entropy generation due to fluid friction is found to increase with the rise in AR up to 2 and then it starts declining. The entropy generation due to fluid friction irreversibility at the center of the cavity is minimal, so the Bejan number is close to unity. Cavity with an inclination of 30° gives the maximum Nusselt number at any value of AR. Notably, the total entropy generation is observed to reach its maximum at α = 60° and minimum at α = 30°, offering comprehensive insights into the interplay of geometric and flow parameters within the cavity.

Use of machine learning in predicting heat transfer and entropy generation in a flat plate solar collector with twisted tape turbulator and ferrofluid under the influence of an external uniform magnetic field: A numerical study

The flat-plate solar collector is the most common and widely used model of solar collectors. This model of solar collectors is more popular than other solar collectors due to its easy installation and lower cost. It is possible to further reduce the cost and size of these systems by improving their performance. For this purpose, simultaneous application of external uniform magnetic field (MF), water-Fe3O4 ferrofluid, and twisted tape turbulator along with changing the cross-section of the serpentine absorber tube of a collector is proposed in the present research. The outlet temperature of working fluid, pressure drop of working fluid, the rate of thermal energy transferred to the flowing fluid in the collector along with the entropy production rate in the system due to fluid friction and heat transfer were considered as the performance parameters of the system. The effect of cross-section of absorber tube (circular, square, triangular), Reynolds number (Re = 500, 1000, 1500 and 2000), pitch distance of turbulator (δ = 150 mm, 200 mm and 250 mm), ferrofluid volume fraction (σ = 0, 1 %, 2 % and 4 %) and magnetic field intensity (0, 600, 900 and 1200 Gauss) on these parameters was investigated numerically using the finite volume method. In the investigations conducted in the absence of MF, collectors equipped with circular and triangular absorber tubes showed the best and worst thermal performance, respectively, while the lowest and highest total entropy production rate was associated with collectors equipped with circular and rectangular tubes, respectively. Moreover, the escalation in σ from 0 % to 4 % and under the MF effect showed an increase of 0.14 %, 8.62 %, 0.45 %, and 4.55 % in the outlet temperature, pressure drop, useful heat, and thermal entropy generation rate, respectively. While the frictional entropy generation diminished by 8.73 %. In addition, the intensification of MF intensity from 0 G to 1200 G led to enhance the outlet temperature, useful heat, and pressure drop, by almost 0.0014 %, 3.96 %, and 0.013 %, respectively at three different σ values. While total entropy generation rate reduces by 0.195 % as MF intensity increases from 0 G to 1200G. Meanwhile, the results of neural network modeling were presented as two second-order polynomial functions to predict the total entropy generation rate and useful heat under the MF effects.

Thermohydraulic and Irreversibility Analyses of Swirl Flows Utilizing Distorted Radial Fins: Entropy Generation and Entransy Dissipation Evaluation

The current investigation analyses the convective heat transfer performance, entropy generation, and entransy evaluation of swirl flows generated by distorted radial fins (DRF). As swirl flows and various vortical structures induce large temperature gradients, second law and entransy analyses are necessary to thoroughly evaluate their true thermodynamic influence on heat transfer enhancement. The results indicated that due to the influence of swirl flows and vortices, all angles of the DRF were capable of inducing intense fluid mixing, thinner thermal boundary layers, and turbulent eddies. It was found that overaggressive swirl flows may hinder local heat transfer performances, by enclosing low-velocity heated fluids within the thermal boundary layers. However, as these overaggressive swirl flows and strong vortices propagate downstream, beneficial fluid mixing was eventuated, favouring heat transport over large regions. In terms of thermal performances, the maximum heat transfer enhancement was exhibited by the α=45° DRF, improving the Nusselt numbers up to 59.3%. Accordingly, the highest performance evaluation criterion (PEC) of 1.269 was obtained by the α=45° DRF at the Reynolds number 2389, attributed to the centrifugal effects of the swirl flows. Optimal entropy generation numbers were also exhibited by the α=45° DRF at the highest studied Reynolds number, reducing total entropy generation by 36.81%. Lower entransy thermal resistances were also accredited to greater DRF angles due to the intense swirl effects. In essence, the study concludes that the effects of swirl flows and vortices significantly enhance heat transfer, whilst reducing both entropy generation and entransy dissipation rates, leading to optimal thermal performances.