Total Entropy Generation Research Articles

Experimental study and numerical simulation of internal flow dissipation mechanism of an axial-flow pump under different design parameters.

This research uses CFD (computational fluid dynamics) to simulate an axial-flow pump and analyzes its internal flow dissipation. The results show that under different operating conditions, with increasing tip cascade density, the pump head gradually increases. With increasing tip cascade density, the pump efficiency gradually decreases under small discharge conditions, and the high-efficiency zone of the axial-flow pump gradually narrows when the pump is operated under large discharge conditions. Under the design operating conditions, the highest efficiency of the axial-flow pump reaches 86.15%. The total entropy generation of the impeller, guide vane, and outlet pipe decreases and then increases with increasing discharge. Meanwhile, the total entropy generation of the impeller is 3.37W/K, which is the largest among different over-water flow components, accounting for 47%. The turbulence entropy generation (EGTD) ratios of the impeller, guide vane and outlet pipe are 42%, 59%, and 65% under the design operating conditions, respectively. Finally, the results of numerical simulation are reliable as verified by a model test. The research results have implications for improving the efficiency of axial-flow pumps.

Thermal and irreversibility analysis of non-Newtonian fluid within trapezoidal cavity containing heated cylinder

In this article, the mixed convection transport of the Carreau fluid in the presence of a magnetic field and a heated circular cylinder within a trapezoidal cavity is examined. Finite element analysis is used via COMSOL Multiphysics software to simulate the two-dimensional flow. The heat equation is formulated by incorporating the effects of viscous dissipation and Joule heating. The upper and lower surfaces of the cavity are adiabatic, while the left and right sides are assumed to be cold. The temperature distribution and flow field within the cavity are visualized through the plotting of isotherms, streamlines, and total entropy generation. The graphical representations are performed to examine the impacts of physical parameters on temperature, flow field, and total entropy generation, including the Reynolds number , Weissenberg number ( 1.0 ≤ We ≤ 6.0 ) , Power law index ( 0.1 ≤ n ≤ 5.0 ) , Hartman number ( 1.0 ≤ M ≤ 50 ) , and Richardson number ( 0.2 ≤ Ri ≤ 5.0 ) and ( 0.2 ≤ Rc ≤ 0.8 ) . It is found that the Joule heating and Richardson number are the main reasons to increase the thermal performance within the cavity. The r ( 100 ≤ Re ≤ 500 ) ising values of power law index and Weissenberg numbers caused to reduce the velocity field, irreversible effects and circulation within cavity. While the entropy is augmented by elevating the Eckert and Hartmann numbers. Furthermore, heat transfer improved with the increased magnetic field and Eckert number.

Hybrid Nanofluid Flow in Microchannel With Fins: Thermal-Hydraulic, Entropy Generation and Energy Management Analysis

This study aims to numerically analyze the thermal-hydraulic performances and total entropy generation of mono-nanofluid and hybrid nanofluid in microchannel heat sinks (MCHS) with fins for laminar flow regime. Besides, the performance evaluation plots (PEPs) are plotted to explore the possibilities of energy saving for mono-nanofluid and hybrid nanofluid flow in MCHS with different fin configurations. The two-phase model is adopted to model the flow of nanofluid in the MCHS. The fin height, fin number, and nanoparticles loading are varied to investigate their effect on the heat transfer, flow characteristic, and entropy generation in the MCHS. It is discovered that 1.0% Al2O3–Cu hybrid nanofluid gives the least total entropy generation if compared to water and Al2O3 mono-nanofluid owing to the significant heat transfer enhancement it offered. The MCHS with 5 fins and a fin height of 0.8 mm configuration is found to be the optimal design for heat removal in this study. Moreover, the plotted PEPs show that the use of Al2O3–Cu hybrid nanofluid and Al2O3 nanofluid (with the concentration range of 0.1%–1.0%) in the MCHS can save energy at either constant pressure drop or flow rate.

Thermal-Hydraulic Characteristics of an Earth Air Heat Exchanger: An experimental analysis

The pipe layout design has a great effect on the thermal-hydraulic characteristics of earth air heat exchanger (EAHE) systems. So, in the current study proposed four new buried pipe design configurations; low to high to low, high to low to high, spiral, and circular, in addition to the straight or uniform for comparison. These five configurations are tested and analyzed experimentally depending on the thermo-hydraulic performance for summer cooling requirements with variation of Re in the range of 18041 – 40843. The results show that changing the uniform design of the EAHE with fixed pipe length enhances both the heat transfer process and pressure loss values. At the same operating conditions, the circular design has the best performance compared to the other ones. For all pipe shapes, the cooling effect increases with the increase of air Re. The thermal- hydraulic performance of the circular design pipe is higher than that of the other pipe designs. The highest coefficient of performance (COP) average values that can be obtained at Re = 18041 is 3.05 for circular shape and enhances by 48.08 % compared to uniform shape. The effectiveness of EAHE with circular shape is improved by about 3.52 % compared to uniform shape at Re = 18041. Spiral design is optimum design based on the Nu value which reaches about 48 with enhancement 12.56% and 0.34 % compared to uniform and circular shapes respectively, at Re = 40843. The hydrothermal performance factor is highest in the case of circular shape with value about 21.9 at Re = 21257. By increasing Re, the drawbacks of the increasing in the total entropy generation are reflected negatively on the exergy efficiency. The specific cost of the circular shape at Re = 40843 is the optimum value by about 0.7 $/W. Spiral and circular shapes have a decrease of CO2 emissions less than uniform shape by percentage varied from 2.93 % to 13.84% for decrease in the Re from 21257 to 40843. It is concluded that using EAHE with four new shapes is highly efficient in increasing cooling capacity and energy consumption in buildings.

Convection flow of NE-phase change material-water mixture in evacuated tube solar collector manifold: Numerical analysis of MHD double-diffusive convection and exothermic reaction

This study investigates the convection flow of nano-encapsulated phase change material (NEPCM)-water mixture in an evacuated tube solar collector manifold, focusing on the effects of magnetohydrodynamic (MHD) double-diffusive convection and exothermic reaction. Computational fluid dynamics simulations using the Galerkin finite element method were employed to analyze temperature and concentration distributions, fluid flow, melting zone of PCM nanocapsules, Nusselt number, Sherwood number, entropy generation, and thermal performance. The numerical analysis considers a range of dimensionless parameters, including Rayleigh number (Ra=103−105), Lewis number (Le=0.1−10), buoyancy ratio (Nz=1−5), nanoparticle concentration (ϕ=0.01−0.035), fusion temperature (ϴf=0.1−0.9), Stefan number (Ste=0.1−0.9), Hartmann number (Ha=0−50), magnetic field inclination angle (γ=0°−90°), and Frank-Kamenetskii number (FK=0−2.5). Results show that increasing Ra enhances the average Nusselt number (Nuav) by up to 156.1 % and the average Sherwood number (Shav) by up to 104.5 %, while increasing the total entropy generation by up to 13,155 %. Increasing FK reduces Nuav by up to 42.2 % but increases Shav by up to 13.1 %. The Lewis number and buoyancy ratio significantly influence the hydrothermal performance, with Nuav exhibiting non-monotonic behavior and Shav increasing by up to 240.9 % as Le increases. The nanoparticle concentration enhances Nuav by up to 49.7 %. Interestingly, the magnetic field effects are less pronounced than in previous studies, with Ha having a minor impact on Nuav and Shav. These findings have significant implications for the design and optimization of evacuated tube solar collectors and other thermal energy storage systems, potentially leading to improved efficiency and performance in real-world applications.

Entropy generation in Casson nanofluid flow over a lubricated wall in the presence of induced magnetic field and activation energy

ABSTRACT The research on entropy generation in a mechanical system is quite imperative owing to its immense applications in the production of advanced cooling devices and medical appliances. The basic need on this research is how to optimize the irreversibilities within the systems and channelize that energy towards the benefit. This study elucidates the entropy generation analysis of a Casson nanofluid near a stagnation point over a lubricated vertical wall. A thin film of shear-thinning liquid with power law index of 0.5 is employed on the wall to ensure the lubrication. The effect of induced magnetic field and the chemical reaction stimulated by the activation energy is also incorporated within the flow. The non-linear PDEs of the substantive problem along with the compatible interfacial and boundary conditions are reverted into ODEs with the aid of suitable similarity transformation, and then cracked numerically using the sixth-order Runge Kutta method assisted with Nachtsheim–Swigert shooting practice. One of the significant findings reveals that the fluid friction irreversibilities in the entropy generation are diminished with the magnetic parameter and the Casson parameter, whereas the thermal irreversibility predominates over the total entropy generation for the escalating values of the activation energy parameter.

Magnetic field effects on double-diffusive mixed convection and entropy generation in a cam-shaped enclosure

This study investigates double-diffusive mixed convection and entropy generation under magnetic influence within a novel cam-shaped enclosure, with applications in automotive engineering. The unique geometry creates distinct flow patterns that enhance heat and mass transport. Using the Galerkin finite element method, we analyzed the effects of key parameters, including buoyancy ratio, Reynolds number, Hartmann number, magnetic field inclination angle on average Nusselt and Sherwood numbers, and total entropy generation. Results show that increasing the buoyancy ratio and Reynolds number enhances heat transfer, while the Hartmann number significantly impacts flow characteristics and entropy generation. The magnetic field inclination angle exhibits a non-linear effect on heat transfer and entropy production. These findings provide valuable insights for optimizing heat transfer systems in complex automotive geometries.

Artificial intelligence and numerical study of the heat transfer and entropy generation analysis of NEPCM-MWCNTs-Water Hybrid Nanofluids inside a quadrilateral enclosure

In the present investigation, the primary objective is to assess the synergistic impact of a novel hybrid nanofluid composed of nano-enhanced phase change material, multi-walled carbon nanotubes, and water. The governing equations are transformed into dimensionless forms for a more generalized analysis. To solve the problem, the Galerkin finite element method is employed, offering a robust numerical approach. A dataset of 1000 records was created by numerically solving the model for various combinations of control parameters. Using the dataset, a neural network was trained to learn the relationship between control parameters and heat transfer rate. The evaluation outcomes are comprehensively illustrated through key parameters, including local and average Nusselt numbers, total entropy generation, contours, and streamlines in the range of 103<Rayleigh number<105, 0<nanotube concentration<0.025, 0<nano capsule concentration <0.025, and 0.1<non-dimensional fusion temperature <0.7. Remarkably, the results indicate a substantial improvement in the heat transfer rate of the suspension for a hybrid concentration of 5%, showcasing an impressive 13% enhancement in contrast to the water host fluid's performance. Notably, the observed rise in entropy generation is relatively moderate, only a 5% increase.

Research on the Internal Flow Characteristics of an Electric Coolant Pump

Abstract To investigate the internal flow characteristics of an automotive electronic coolant pump, numerical simulations were performed utilizing the ANSYS CFX commercial software suite. The study delved into the velocity distribution, pressure pulsation intensity characteristics, and entropy generation of the electronic coolant pump under varying operational conditions. The findings revealed that with an increase in the flow rate, the coolant flow velocity within the pump also escalated. Concurrently, the separation flow at the trailing edge of the blade diminished, while the flow velocity at the trailing edge of the pressure surface escalated. Notably, the impeller and volute emerged as the primary sites generating pressure pulsations, with pressure pulsation intensity within the pump surpassing that of the design condition in off-design scenarios. Furthermore, entropy generation predominantly manifested at the impeller, volute, and front pump chamber locations, with the impeller exhibiting minimal total entropy generation under design conditions. These insights serve as crucial reference points for optimizing the design of automotive electronic coolant pumps.

Numerical investigation on effects of swirl and offset ratio on hydro-thermal transport phenomena and irreversibility generation of turbulent jet flow

The combined influence of offset jet and imposition of swirling motion is crucial because many macro-level electronic devices and heat exchanger systems involve such types of configuration. The mutual impact of the offset ratio and swirl number along with a range of Reynolds numbers is taken into account to briefly discuss the primary laws (first and second) of thermodynamics associated with the prescribed problem. An open channel with variable nozzle height is assumed under forced convective flow conditions. The flow physics associated with the prescribed problem has been solved numerically with an improvised [Formula: see text] turbulent (shear stress transport) model. The intricate interplay between the swirl intensity and the offset upon the thermal and entropy generation characteristics has been revealed in the average Nusselt number, local variation of skin friction coefficient, and total entropy generation by varying the distinct embedded control parameters. The results indicate that a higher range of Reynolds number leads to a high value of average Nusselt number unrelatedly of swirl number and offset ratio. However, the improvement of thermal performance does not depend only upon the heat transfer characteristics but also the total irreversibility should be optimized. In that regard, a swirl ratio of 0.5 with an offset ratio of 3 provides optimized configurations irrespective of all other parameters.

Numerical analysis of magnetohydrodynamic mixed convection and entropy generation in a curvelinear lid-driven cavity with carbon nanotubes and an adiabatic cylinder

Mixed convection convection is a vital subject and it is beneficial in many engineering applications. The current paper addresses this subject with a novel geometry and very vital variables including magnetohydrodynamic influences on the forced/free convection as well as the reproduction of irreversibilities in an enclosure filled with water/carbon nanotubes (CNT) and a nonadiabatic cylinder. The top wall is split from the middle and moves in different directions to drive the isotherms which are generated from the bottom wall and cold from the vertical surfaces. The numerical analysis was carried out using finite element method; the variables are Reynolds number (40–200), Richardson number (0.01–10), Hartmann number (0–62), inclined magnetohydrodynamic angle (0–60), volume concentration (0–0.08) while Prandtl number has kept constant at 6.2. The results show that the transformation of heat, as well as the fluid flow, are largely influenced by the change of variables, where increasing Reynolds number, Richardson number enhances heat and increases the flow circulation. Furthermore, heat transfer enhances by 57 % when increasing Ri from 0.1 to 10 at Re=41 and this enhancement increases to 62.5 % at Re = 200. Furthermore, increasing the concentration of the carbon nanotube can cause heat transfer but decrease the circulation of the fluid. In contrast, the transfer of heat as well as the flow streams are remarkably decreased with the increase of the Hartmann at zero inclination angle; however, the value of the Nusselt average increases with the increase of the inclination angle. Moreover, the value of Nusselt average decreses by 34.7 % when increasing Ha from 0 to 62 at Re = 200. Furthermore, the total entropy generation increases as Richardson number, Reynolds number, and volume concentration increase; in contrast, detraction with the rise of the MHD.

Thermal performance analysis of sinusoidal corrugated channels: A comparative study of thermo-hydraulic and entropy generation

The physical properties of working fluids—in terms of the Prandtl number—play a crucial role in determining their thermal performance in the internal flow, especially their viscosity. This study first considers the thermo-hydraulic and entropy generation of a sinusoidal corrugated channel in two configurations: symmetrical (raccoon) and asymmetrical (serpentine). Results are presented for different ranges of operating parameters, such as 100≤Re≤700 and 0.72≤Pr≤90, and for geometrical parameters such as the wave amplitude-to-wavelength ratio 0.2≤α≤0.6. In addition, the results of the two channels were compared with each other's and with the straight channel. Control transport equations are solved using finite element methods. It was found that the flow inside the wavy channels generated re-circulatory reigns, and their size was affected by the wave parameters as well as the Reynolds number. Also, employing high values of Pr extremely enhanced the heat transfer rate (HTR) of the wavy channels over the straight for all values of α and for both raccoon and serpentine channels. In addition, the results indicated that raccoon channels have higher HTR and performance factor compared to the serpentine channel. Finally, the thermal entropy generation dominated over the viscous entropy generation and its decrease with both Reynolds number and Prandtl number for raccoon and serpentine channels. This study focused on the heat transfer enhancement of the corrugated channels due to their importance in many industrial applications where the heat dissipation is critical to their work, including heat exchangers and heat sinks. Thus, the current numerical simulation primarily suggests utilizing the raccoon channel over the serpentine one, due to its higher thermal performance and nearly the same total entropy generation.

Analysis of magneto-natural convection and second law of thermodynamics of Cu-Al2O3-hybrid nanofluid in a vertical wavy cabinet having a localized non-uniform heat source

Improvements in thermal transference rate and minimization of entropy generation are critical issues in many industrial and engineering applications where heat transfer coefficient is essential to achieve optimal performance and minimal energy consumption. In the present investigation, a computational analysis has been conducted to analyze the impact of magnetic field on magneto-free convection and entropy generation inside a vertical wavy cabinet filled by Cu-Al2O3/H2O hybrid nanosuspension. In the geometry of this model, vertical boundaries of the chamber are designed as wavy and kept as cooled temperature (Tc), whereas the horizontal boundaries are modeled as square and are designed to be thermally adiabatic, except the centrally heated portion on the bottom wall. The centered bottom heated section is supposed to be isothermal with linearly changing temperature, and it changes linearly from Th1 to Th2, whereas it is modelled as a non-isothermal condition. The main focus, in this investigation, is on the entire chamber filled with the combination of hybrid nanoparticles regarded the volumetric concentration of copper and alumina nanoparticles (Cu-50 %+Al2O3-50 %) along with base liquid (H2O). The transformed dimensionless partial differential equations were solved by using finite volume method (FVM) with power law differencing scheme. The simulated flow and temperature fields are scrutinized by streamlines, isotherms, entropy formations, total entropy generation and average convective Nusselt number associated with varying number of undulations (0 ≤ N≤3) volume fraction of hybrid nano liquid (0 ≤ φ ≤ 0.04) magnetic orientation angles (0° ≤ ς ≤ 135°), Hartmann number (Ha = 0 and 50), and dimensionless temperature drop (Ω = 0.001–0.1). From this study, it is found that the average Nusselt number and entropy generation increase as the solid volume fraction of hybrid nanoadditives increases, while opposite trend is observed when the values of Hartmann number rises. The findings show that growth of undulation number (N) causes the reduction of convective heat transfer rate as well as average entropy production intensity. The obtained outcomes concluded that hybrid nano liquid is more effective and finest choice for the improvement of cooling of heat transfer process and minimal energy loss than single nanoliquid. According to the new proposed criterion (TPC), the results show that square-shaped enclosure (N=0) manifests the better cooling performance among the considered governing parameters. The novelty of this study is to scrutinize the flat/ vertical wavy boundaries of the cabinet which can be represented as a model of heat transfer controller, in which it manages the thermal and flow field characteristics. Predominantly, the isothermal line source is used to boost the overall convective heat transfer which is applied in buildings and fluid-mounted heaters. Additionally, many investigators have focused only on the enhancement of heat transfer. As it is known, to increase the thermodynamic efficiency of a system, optimization of entropy generation is an excellent tool which reduces the loss of energy. Hence, it recently does a good engineering sense to highlight an entropy irreversibility.

Active cooling of hot integrated circuits using a rotating cylinder and NEPCM-water mixture: Numerical analysis of the impact of phase change and Magnetohydrodynamics on double-diffusive mixed convection

Efficient cooling of integrated circuits is crucial for maintaining optimal performance and longevity of electronic devices. This study addresses this challenge by investigating the double-diffusive mixed convection around a hot integrated circuit (using) a nano-encapsulated phase change material-water mixture for enhanced heat absorption. The cooling process is carried out by a cylinder rotating at a constant speed inside a square cavity surrounded by the NEPCM-water mixture. Using the Galerkin finite element method, we numerically analyzed the influence of various parameters, including the Reynolds number (10≤Re≤100), Richardson number (0.1≤Ri≤10), Hartmann number (0≤Ha≤80), NEPCM volume fraction (0.01≤ϕ≤0.035), Lewis number (0.1≤Le≤10), buoyancy ratio (1≤Nz≤5), fusion temperature (0.1≤ϴf≤0.9), and Stefan number (0.1≤Ste≤0.8), on the average Nusselt number (Nuav), average Sherwood number (Shav), total entropy generation (Stotal), and Bejan number (Be). The results demonstrate that increasing Re and Ri enhances Nuav and Shav by up to 175 % and 162 %, respectively, while applying a magnetic field (increasing Ha) suppresses heat and mass transfer rates by up to 58 % and 50 %, respectively. Increasing ϕ improves Nuav by up to 34 % with minimal impact on Shav. The Le and Nz govern the coupling between heat and mass transfer processes, with Le substantially influencing Shav and Nz affecting both Nuav and Shav. The ϴf exhibits a non-monotonic effect on Nuav, suggesting an optimal fusion temperature, while Ste shows an inverse relationship with Nuav. The Stotal is significantly influenced by Re, Ri, Ha, and ϕ, while Be is affected by Re, Ri, Ha, and ϕ to a lesser extent. These findings provide valuable insights into the complex interplay of forced and natural convection, magnetohydrodynamics, and NEPCMs in the active cooling of hot electrical elements. The results can be applied to optimize cooling system designs, potentially leading to more efficient and effective thermal management in electronic devices.

On the effect of wave amplitude and corrugation profile of certain types of corrugated channels on thermal performance and entropy generation

This study aims to examine experimentally and numerically the thermal-hydraulic performance and entropy generation of wavy channels: sinusoidal and triangular, and compare them with respect to the straight channel. Various wavy amplitudes and corrugation profiles are considered in a sinusoidal wavy channel and a triangular wavy channel and assessed with the straight channel. Experimental test rig is built and the experiments are carried out on laminar air flow and used to verify the simulation results. The main findings show that the HT rate, fluid flow, and entropy generation are affected by the corrugation profile and wave amplitude of the wavy channel. The maximum Nusselt number of 11.17 occurred in a sinusoidal wavy channel with a wave amplitude equal to 1.75, and high friction factor also happens in this model. It was found that the sinusoidal and triangular wavy channels with A = 0.75 and a flow rate range of 1–1.75 have the highest overall thermal performance factor. Also, the total entropy generation of the straight channel was lower than all corrugated channel models. In conclusion, it has been found that the best compromise between enhanced HT and the accompanying increase in both pressure drop and entropy generation is occurred in case of A = 0.75 at flow rate ranged from 1 to 1.67 LPM.

Effects of strain and pressure on entropy generation in laminar flames

The mitigation of combustion noise is crucial for preventing thermoacoustic instabilities in rocket and gas turbine engines. Entropy noise, arising from entropy fluctuations within the engine, serves as a prominent noise source. Therefore, understanding the mechanisms governing entropy generation in flames becomes imperative for identifying the roots of indirect combustion noise. While previous studies have broadly examined various pathways of entropy generation under different canonical configurations of laminar flames, surprisingly, the effect of strain and pressure has been overlooked. This aspect is analyzed in the present work. Building upon previous analysis, the entropy source term of the reacting flow is decomposed into three sub-terms: the unsteady heat release term (Se,1), the sensible enthalpy term (Se,2), and the partial entropy term (Se,3). The extent to which these three sub-terms contribute to entropy generation is thoroughly analyzed. Simultaneously, the scaling laws of the three sub-terms with respect to strain rate and pressure are investigated. The inclusion of detailed chemical kinetics as well as flame structure in the simulation dataset allows for in-depth investigation into the mechanism of the strain and pressure effects. Three canonical laminar flame configurations – the freely propagating premixed flame, the premixed counterflow flame, and the counterflow diffusion flame – are investigated. The following main conclusions are drawn: the heat release term is the leading constituent of the entropy source; the sensible enthalpy term is negligible; and the partial entropy term is secondary while non-negligible. Under strain and pressure variations, the contribution of the partial entropy term to total entropy production can greatly off-set the total entropy source or even qualitatively affect the strain/pressure response of the entropy generation, i.e., the strain response of the premixed flame and pressure response of the hydrogen non-premixed flame.Novelty and significance statement1. Conducted a systematic investigation of entropy production due to chemical reactions under the influence of strain and pressure variations.2. Revealed that the partial entropy term, often overlooked in previous studies, can surpass the heat release term in certain configurations, emerging as the leading constituent of the total entropy generation source.3. Identified dominating reactions contributing to entropy production for two different fuels of hydrogen and methane.

Thermal energy storage, heat transfer, and thermodynamic behaviors of nano phase change material in a concentric double tube unit with triple tree fins

The contribution of this study is the proposal of a synergistic composite enhancement strategy involving tree fins and nanomaterials to improve the low thermal performance of phase change material (lauric acid) in a typical double tube latent heat thermal energy storage unit. The effects of nanoparticle concentrations and tree fin branching angles on the fluid dynamics, melting time, heat transfer, energy storage, and entropy generation characteristics were investigated. By employing tree fins, the melting time was respectively reduced by up to 60.20% and 36.05% compared to the finless case and the rectangular fins, while the energy storage power was respectively boosted by up to 143.36% and 37.45%. The increase of nanoparticle concentration was beneficial for melting heat transfer, and the dendritic fins with a bottom angle of 90° and a top angle of 30° yielded the highest energy storage performance. The total entropy generation of the melting process was mainly governed by the thermal entropy generation, and it showed a decreasing trend with the increase of time. In contrast to the finless configuration, the incorporation of fins diminished the integrated entropy generation value. Similarly, an elevation in nanoparticle concentration also led to a reduction of the integrated entropy generation value.

Theoretical analysis of entropy generation in multilayer insulations: A case study of performance optimization of variable density multilayer insulations for liquid hydrogen storage systems

Liquid hydrogen (LH2) is a promising and economical clean energy for achieving global carbon neutrality. Multi-layer insulation (MLI) with high performance is essential for the safe storage and operation of LH2. To perform a better optimization of MLI, the second law of thermodynamics becomes a complement to the first law of thermodynamics. However, very few studies have carried out the optimization of MLI performance through the second law of thermodynamics. For the sake of achieving more efficient optimization of MLI as well as revealing the fundamental indicators limiting the performance of MLI, this paper analyzes the characteristics of entropy generation produced by the solid heat conduction, thermal radiation, and residual gas conduction distributed in the MLI schemes by a validated layer-by-layer model.For a 40-layer MLI arranged with a constant layer density of 20 layers/cm, the first 15 layers near the cold boundary occupy more than 98% of the total entropy generation, providing an effective range of layers for thermodynamic optimization. Besides, an optimization of variable-density MLI (VDMLI) separated into two segments based on the entropy generation minimization is conducted. The optimal VDMLI has substantially lowered the entropy generation from the solid heat conduction but at the cost of increasing the entropy generation from radiation and residual gas conduction. This study provides a reliable optimization method of MLI, which allows the safe storage of clean energy with a low boiling temperature.

On the measurement of total entropy generation for determining fatigue fracture

A novel approach to measuring the rate of plastic work during fatigue using a thermodynamic modeling framework is presented. The temperature profile and temperature gradient are utilized to measure the total accumulated entropy throughout the fatigue degradation process. It is shown that for cases in which temperature does not reach a steady state condition, such as very low-cycle fatigue (VLCF), or in instances of a low-temperature rise, the model can reliably quantify the total entropy generation. Experimental tests are conducted on carbon steel 1018 flat dog-bone specimens using a fully reversible bending fatigue tester and aluminum 6061-T651 cylindrical dog-bone specimens under tension–compression cyclic loading. The obtained results demonstrate the model’s capability to accurately measure the plastic work rate, eliminating the need to capture the initial temperature slope or interrupt the fatigue test to measure the cooling rate.

Buoyancy-driven heat transfer and entropy analysis of a hydromagnetic GO-Fe3O4/H2O hybrid nanofluid in an energy storage enclosure partially filled with non-Darcy porous medium under an oblique magnetic field

Purpose Thermal energy storage systems use thermal energy to elevate the temperature of a storage substance, enabling the release of energy during a discharge cycle. The storage or retrieval of energy occurs through the heating or cooling of either a liquid or a solid, without undergoing a phase change, within a sensible heat storage system. In a sensible packed bed thermal energy storage system, the structure comprises porous media that form the packed solid material, while fluid occupies the voids. Thus, a cavity, partially filled with a fluid layer and partially with a saturated porous layer, has become important in the investigation of natural convection heat transfer, carrying significant relevance within thermal energy storage systems. Motivated by these insights, the current investigation delves into the convection heat transfer driven by buoyancy and entropy generation within a partially porous cavity that is differentially heated, vertically layered and filled with a hybrid nanofluid. Design/methodology/approach The investigation encompasses two distinct scenarios. In the first instance, the porous layer is positioned next to the heated wall, while the opposite region consists of a fluid layer. In the second case, the layers switch places, with the fluid layer adjacent to the heated wall. The system of equations for fluid and porous media, along with appropriate initial and boundary conditions, is addressed using the finite difference method. The Tiwari–Das model is used in this investigation, and the viscosity and thermal conductivity are determined using correlations specific to spherical nanoparticles. Findings Comprehensive numerical simulations have been performed, considering controlling factors such as the Darcy number, nanoparticle volume fraction, Rayleigh number, bottom slit position and Hartmann number. The visual representation of the numerical findings includes streamlines, isotherms and entropy lines, as well as plots illustrating average entropy generation and the average Nusselt number. These representations aim to provide insight into the influence of these parameters across a spectrum of scenarios. Originality/value The computational outcomes indicate that with an increase in the Darcy number, the addition of 2.5% magnetite nanoparticles to the GO nanofluid results in an enhanced heat transfer rate, showing increases of 0.567% in Case 1 and 3.894% in Case 2. Compared with Case 2, Case 1 exhibits a 59.90% enhancement in heat transfer within the enclosure. Positioning the porous layer next to the partially cooled wall significantly boosts the average total entropy production, showing a substantial increase of 11.36% at an elevated Rayleigh number value. Positioning the hot slit near the bottom wall leads to a reduction in total entropy generation by 33.20% compared to its placement at the center and by 33.32% in comparison to its proximity to the top wall.