Entropy Generation Minimization Research Articles

Entropy generation minimization of hybrid nanofluid mixed convection flow in lid-driven square enclosure with heat-generating porous layer on inner walls

PurposeThis study aims to numerically scrutinize the entropy generation minimization and mixed convective heat transfer of multi-walled carbon nanotubes–Fe3O4/water hybrid nanofluid flow in a lid-driven square enclosure with heat generation in the presence of a porous layer on inner surfaces, considering local thermal non-equilibrium (LTNE) approach and the non-Darcy flow model.Design/methodology/approachThe dimensionless governing equations for hybrid nanofluid and solid phases are solved by applying the finite volume method and semi-implicit method for pressure-linked equations algorithm.FindingsThe roles of the internal heat generation in the porous layer, LTNE model and nanoparticles volume fraction on mixed convection phenomenon and entropy generation are introduced for lid-driven cavity hybrid nanofluid flow. Based on the investigation of entropy generation and heat transfer, the minimum total entropy generation and average Nusselt numbers are found at 1 ≤ Ri ≤ 10 where the effect of the forced and free convection flow directions being opposite each other is very significant. When considering various nanoparticle volume fractions, it becomes evident that the minimum entropy generation occurs in the case of φ = 0.1%. The outcomes of LTNE number reveal the operating parameters in which thermal equilibrium occurs between hybrid nanofluid and solid phases.Originality/valueThe analysis of entropy generation under various shear and buoyancy forces plays a significant role in the suitable thermal design and optimization of mixed convective heat transfer applications. This research significantly contributes to the optimization of design and the advancement of innovative solutions across diverse engineering disciplines, such as packed-bed thermal energy storage and thermal insulation.

Effect of solid obstacle and thermal conditions on convective flow and entropy generation of nanofluid filled in a cylindrical chamber

PurposeOne of the major challenges in the design of thermal equipment is to minimize the entropy production and enhance the thermal dissipation rate for improving energy efficiency of the devices. In several industrial applications, the structure of thermal device is cylindrical shape. In this regard, this paper aims to explore the impact of isothermal cylindrical solid block on nanofluid (Ag – H2O) convective flow and entropy generation in a cylindrical annular chamber subjected to different thermal conditions. Furthermore, the present study also addresses the structural impact of cylindrical solid block placed at the center of annular domain.Design/methodology/approachThe alternating direction implicit and successive over relaxation techniques are used in the current investigation to solve the coupled partial differential equations. Furthermore, estimation of average Nusselt number and total entropy generation involves integration and is achieved by Simpson and Trapezoidal’s rules, respectively. Mesh independence checks have been carried out to ensure the accuracy of numerical results.FindingsComputations have been performed to analyze the simultaneous multiple influences, such as different thermal conditions, size and aspect ratio of the hot obstacle, Rayleigh number and nanoparticle shape on buoyancy-driven nanoliquid movement, heat dissipation, irreversibility distribution, cup-mixing temperature and performance evaluation criteria in an annular chamber. The computational results reveal that the nanoparticle shape and obstacle size produce conducive situation for increasing system’s thermal efficiency. Furthermore, utilization of nonspherical shaped nanoparticles enhances the heat transfer rate with minimum entropy generation in the enclosure. Also, greater performance evaluation criteria has been noticed for larger obstacle for both uniform and nonuniform heating.Research limitations/implicationsThe current numerical investigation can be extended to further explore the thermal performance with different positions of solid obstacle, inclination angles, by applying Lorentz force, internal heat generation and so on numerically or experimentally.Originality/valueA pioneering numerical investigation on the structural influence of hot solid block on the convective nanofluid flow, energy transport and entropy production in an annular space has been analyzed. The results in the present study are novel, related to various modern industrial applications. These results could be used as a firsthand information for the design engineers to obtain highly efficient thermal systems.

Heat Transfer and Entropy Generation Minimization in a Lid-Driven Enclosure Filled with Nanofluid

Heat Transfer and Entropy Generation Minimization in a Lid-Driven Enclosure Filled with Nanofluid

Experimental investigation on the thermal and flow performance of a thermodynamically-balanced packed bed humidification system

In this paper, a packed bed humidification system filled with corrugated wire mesh was experimentally investigated to obtain a better humidification performance. To thermodynamically balance the simultaneous heat and mass transfer process, multiple water injection bypasses were fabricated at different packing heights based on the entropy generation minimization method. In addition to the inlet water temperature, the influences of the liquid–gas ratio and injection ratio on the humidification capacity, energy effectiveness, and pressure drop were respectively studied and discussed. The experimental and comparison results demonstrated that the established humidification device was robust and superior. It was summarized that raising the number of injections can significantly elevate the humidification capacity, and synchronously magnify the pressure drop for all the cases, while the effectiveness behaved a reverse trend. Additionally, a higher value of the inlet water temperature could increase the humidification capacity and effectiveness, as well as the pressure drop. And, an elevation amplitude of the humidification capacity emerged as 35.51% for the double water injections with a maximum value of 1.48 × 10−2 kgs−1 once the liquid–gas ratio increased from 1 to 1.36, while the value was 39.13% as the injection ratio raised from 0.33 to 0.7. Furthermore, it was illustrated that increasing the mass flow rate of the liquid will reduce the effectiveness when the heat capacity rate ratio is larger than 1, and the effectiveness can reach 0.97 at Twi = 70 °C. In the process of thermodynamic balancing, the increase in the pressure drop of humid air should receive more attention for the designer and researcher related to the packed bed humidifier.

Optimization of entropy generation and thermal mechanism of MHD hybrid nanoliquid flow in a sinusoidally heated porous cylindrical chamber

The present computational investigation explores the fluid and thermal characteristics along with entropy generation due to buoyancy-driven magnetohydrodynamic (MHD) convective flow of aqueous hybrid nanoliquid filled in a nonuniformly heated porous cylindrical chamber. The fluid motion in the enclosure is modeled by Brinkman — extended Darcy model. The modeled equations are resolved by finite difference approach. The computations are conducted for Rayleigh number (103–105), Hartmann number (0–50), Darcy number (10−5–10−1), different nanoparticle shapes and nanoparticle volume fraction (Ag/MgO: 0–0.05) to understand the characteristic of flow, thermal and irreversibility distribution. With vast numerical simulations, the outcomes reveal that though the buoyancy force is greater, the fluidity cannot be enhanced unless the permeability and magnetic field strength are optimally maintained. As Ra,Ha and Da is varied respectively from 103 to 105, 50 to 0 and 10−5 to 10−1, the fluidity has been enhanced by 99.39%,83.26% and 99.79%. Among all considered parametric combinations, it has been noticed that the choice of Ha=0,Ra=105,Da=10−1 with proper ratio of nanoparticles enhance the system efficiency. However, minimal entropy generation can be achieved with greater Hartmann and lower Darcy numbers. Furthermore, it has been found that blade shaped nanoparticles lead to increase the performance of thermal system.

Thermal performance of Oldroyd-B hybrid nanofluid in solar energy-based water pumping systems and entropy generation minimization

The growing need for reliable energy supply to enhance productivity in industrial and residential sectors underscores the importance of conserving solar energy. This can be achieved through measures such as optimizing solar collector coatings and optical heat processes. The environmental risks posed by fossil fuels, like coal and diesel, for electricity generation, further highlight the urgency of seeking alternative solutions. Solar energy has emerged as a highly promising option, capturing global attention for its potential to improve productivity and sustainability. The study focuses on examining aluminum alloy-titanium alloy/ethylene glycol hybrid nanofluid in the flow of non-Newtonian Oldroyd-B through a parabolic trough surface collector located in the solar water pumps (SWP). The Galerkin weighted residual method was utilized to solve the group of equations that describe momentum, energy, and entropy generation. The findings show that the hybrid nanofluid leads to better thermal radiative performance compared to the ordinary nanofluid. Therefore, the implications of these findings are substantial, particularly in the fields of thermal engineering and renewable energy. By offering insights into the efficient utilization of solar energy in water pumping systems and the reduction of entropy generation, this research has the potential to drive innovations that enhance the sustainability and performance of such systems.

Experimental study of the thermal characteristic of a double tube heat exchanger with tapered wire coil inserts using PCM-dispersed mono/hybrid nanofluids

ABSTRACT An experimental study involving tapered wire coil inserts in a double-tube heat exchanger using water-based phase change material (PCM)-dispersed mono/hybrid nanofluids is conducted. The effects of the wire coils (WC) with nanofluids on the hydrothermal performance of this system are studied for different coil arrangements: converging wire coils (CWC), diverging wire coils (DWC), and converging-diverging wire coils (CDWC) and different Reynolds numbers. The experimental results indicate that among all the tested coil arrangements, the DWC presents a higher thermal performance factor (TPF) than the other arrangements. Using the DWC, the TPF of the Al2O3+PCM hybrid nanofluid is augmented by 3.98%, 9.61%, and 3.04% as compared to that for the plain wire coil (PWC), CWC, and CDWC, respectively. Besides, the DWC configuration exhibits the minimum entropy generation among all arrangements. For the Al2O3+PCM hybrid nanofluid using the DWC, the entropy generation is decreased by approximately 13.36%, 9.78%, and 5.78% as compared to that of the PWC, CWC, and CDWC at a volumetric flow rate of 15 lpm.

Improving performance of air conditioning system by using variable-circuit heat exchanger: Based on the Chinese APF standard

For finned-tube heat exchangers, owing to the extremely different refrigerant pressure drop characteristics between condensation and evaporation processes, the optimum refrigerant circuits of these two conditions are different. However, for a typical heat pump type air conditioner, refrigerant circuit of the conventional heat exchanger (CHX) is fixed no matter what operation condition is conducted. To solve this problem, a modified variable-circuit heat exchanger (VCHX) is developed for air conditioner outdoor unit applications. The VCHX, for which the refrigerant circuit can be easily switched by using a globe valve, could provide better matching characteristics between refrigerant circuit and operation condition variations. With a developed simulation model, refrigerant circuit of the VCHX is optimized by using the entropy generation minimization theory. Then, comparative experimental works were conducted to investigate the performance of VCHX and CHX systems in detail. Experimental results show that the presented VCHX is more suitable for high heating capacity and low cooling capacity applications. Based on the Chinese APF (annual performance factor) Standard, the VCHX system yields 6.5% higher APF value over CHX system. Significantly, economic analysis indicates that the investment payback period of VCHX system is 1.46 year, which is much lower than the designed lifetime of a residential air conditioner. In general, the VCHX technique has a great application potential for improving the overall performance of a heat pump type air conditioner.

Topologically Optimized Anode Catalyst Layers of Proton Exchange Membrane Water Electrolyzers

Climate change and global warming are ongoing global problems that will severely impact the environment if they are not addressed seriously. Replacing traditional fossil fuels with clean and sustainable energy from renewable energy sources, such as wind and solar, is necessary to reduce carbon emissions. However, these renewable energy sources are intermittent and thus require a system to help stabilize power generation. In this regard, hydrogen, the most sustainable form of clean energy, is proposed as a potential energy carrier. In such a system, water electrolyzers are used together with fuel cells. This allows hydrogen to be produced and stored in times of excess power generation. When there is demand and insufficient power generation, the produced hydrogen will be converted into electricity using fuel cells, resulting in a stable power grid. Although fuel cells have been improving significantly, water electrolyzers are an essential bottleneck for the widespread commercialization of the hydrogen economy.Due to the intermittency of renewable energy, the water electrolysis system applied to renewable energy should be able to turn on and off depending on renewable energy sources. As a result, low-temperature water electrolysis has gained widespread attention. Due to its potentially high-performance and high-purity hydrogen gas, the proton exchange membrane water electrolyzer (PEMWE) is one of the most promising technology for producing clean hydrogen. However, concerning widespread industrial use, PEMWE is affected by high costs due to its high loadings of expensive iridium-based catalysts. Therefore, it is necessary to improve its performance. As PEMWE technology grows, the working current density is inevitably higher. When the current density is higher, the amount of oxygen and hydrogen that must be removed from the cell must be more significant to deliver water to the reaction site efficiently. To meet the demands of the application, it is crucial to design an efficient electrode, especially at the anode, where the water must be supplied to the catalyst layer, and, at the same time, it is necessary to transfer oxygen gas from the reaction area to the flow channel.Topology optimization, an emerging tool to optimize physical systems, has recently been applied to systems with multi-physics. However, attempts to implement the approach in the system with reactions still lacked in the literature. Only a few studies were interested in utilizing such an approach in electrochemical energy device applications. Roy et al. [1] used topology optimization to develop the porous electrode. According to the findings, the developed electrode outperformed the traditional electrode. However, topology optimization is just a numerical approach. Our research group showed how a topologically optimized structure of porous reactors connected to the situation of the most uniform and minimum entropy generation [2]. To utilize topology optimization with PEMWE, a model for the anode catalyst layer is necessary. Although there are existing models to simulate the phenomena of PEMWE [3,4], to the best of our knowledge, studies have yet to look into how to model the phenomena inside the anode catalyst layer of the PEMWE.Therefore, the main goal of this study is to develop a model to simulate the physics of the anode and utilize it in topology optimization to search for the optimal structure of the anode catalyst layer. The optimization problem was formulated to maximize the cell performance by controlling the volume fractions of ionomer and catalyst materials. Figure 1a-c displays the heterogeneous structure obtained by topology optimization. The electrochemical reaction increased by approximately 40% compared to a case with the homogeneously distributed electrode. The topologically optimized structure was similar to the structure proposed by Dong et al. [5], where their ordered structure with Ir loading of 0.2 mg cm−2 can significantly decrease the overpotentials compared with conventional MEA with an Ir loading of 2 mg cm−2. Therefore, such a structure might be a way forward for high-performance PEMWE system. Acknowledgment The authors would also like to express their gratitude to Office of the Permanent Secretary, Ministry of Higher Education, Science, Research and Innovation (OPS MHESI) (Grant No. RGNS 65-084), Thailand Science Research and Innovation (TSRI) and King Mongkut’s University of Technology Thonburi. This work was partially supported by Grant-in-Aid for JSPS Fellows number 22J20603 and JSPS KAKENHI Grant number 21H04540 References [1] Roy, T., et al., Struct. Multidiscipl. Optim. 65 (2022) 171.[2] Charoen-amornkitt, P., et al., Int. J. Heat Mass Transf. 202 (2023) 123725[3] Lopata, J., et al., J. Electrochem. Soc., 168 (2021) 054518.[4] Lopata, J.S., et al., Electrochim. Acta, 424 (2022) 140625[5] Dong, S., et al., Nano Lett. (2022) (In Press) Figure 1

Optimization of inserted coiled tube three-fluid heat exchanger using genetic algorithms

The three-fluid heat exchanger is a multi-stream heat exchanger that provides three streams at different temperatures for certain usage objectives. Recently, optimizing heat exchangers generally and three-fluid heat exchangers especially have received great attention in the energy field. The current study objective is to get the optimal mass flow rate of the three streams to minimize the entropy generation number and maximize effectiveness. Optimization is performed on the inserted coiled tube type for 24 cases with different usage objectives and different mass flow rate constraints. The optimization is done using an analytical approach for the temperature profiles and a regressed model for the overall heat transfer coefficients. Single-objective and multi-objective genetic algorithms are the optimization algorithms. The result shows that cooling the hot fluid is the most efficient usage objective; however, heating the intermediate-temperature fluid is the less efficient usage objective. Also, the study shows that the entropy generation number is dependent on the mass flow rate constraint. The maximum effectiveness of 0.693 occurs when the usage objective is cooling the hot fluid. In this case, the mass flow rate of the cold and the intermediate-temperature fluids are maxima while the mass flow rate of the hot fluid is minimum. The minimum entropy generation number 0.0486 occurs when the mass flow rate of the cold fluid is maximum while the mass flow rate of the hot fluid and intermediate-temperature fluid are minimal.

Heat and mass transfer with entropy optimization in hybrid nanofluid using heat source and velocity slip: a Hamilton–Crosser approach

The modeling and analysis of hybrid nanofluid has much importance in industrial sector where entropy optimization is the key factor in different processes. This mechanism is also used in medical industry, where it can be used for separation of blood cells (red and white blood cells, platelets and plasma) by centrifuge process, treating cancers, and drug transport. In light of this importance, current study is focused on mathematical modeling and analysis of blood based hybrid nanofluid between rotating disks with various shapes of nanoparticles. The shape factors are taken into account with Hamilton–Crosser model as spherical, brick, cylinder and platelet in the current scenario, with special reference to entropy optimization. In order to solve modeled nonlinear and non-dimensional system, optimal homotopy analysis approach is utilized through Wolfram MATHEMATICA 11.3 software. Error estimation and convergence analysis confirms that obtained semi-analytical solutions are valid and reliable. Velocity, temperature and concentration profiles are analyzed against important fluid parameters. Fluid velocity decreased in all directions when unsteady parameter mathbb {B} and Darcy number Da increased while the slip parameters zeta _{1} and zeta _{2} decreased the nanofluid velocity. It is observed that in case of brick shaped nanoparticles, fluid temperature is enhanced as compared to other shape factors in the study. Minimal entropy generation is captured in case of spherical nanoparticles, while highest heat transfer is observed in platelet shaped nanoparticles. Furthermore, numerical optimization of entropy is performed against different values of hbar and volume fractions varphi _{Rd} and varphi _{Al}. Minimized entropy is recovered to be zero when hbar =-0.6, varphi _{Rd}=2% and varphi _{Al}=1%.

Enhanced heat transfer analysis of hybrid nanofluid over a Riga plate: Incorporating Lorentz forces and entropy generation

The Riga plate, comprising a configuration of electrodes and permanent magnets, can induce a wall-parallel Lorentz force through external electric and magnetic fields, enabling effective control of fluid flow. This paper focuses on studying the flow characteristics of Al2O3-Cu/water hybrid nanofluid past a Riga plate in the presence of strong suction. The mathematical model incorporates a two-phase approach to describe the behavior of the nanofluid, while considering the Grinberg-term to account for the wall parallel Lorentz force generated by the Riga plate. Several influential factors such as entropy generation, viscous dissipation, heat flux, thermal radiation, slippage, and convective boundary conditions of temperature are considered in our investigation. Entropy generation within thermodynamic systems contributes to energy losses resulting from various factors, including frictional forces, viscosity, and chemical reactions. Minimizing entropy generation is crucial to enhancing system performance. To address the research problem, we utilize dimensionless parameters and assume strong suction to simplify the governing partial differential equations. The dimensionless model is subsequently solved numerically using the Adams-Bashforth technique. Additionally, a comprehensive graphical analysis is conducted to examine the impact of various dimensionless parameters on the flow fields. This study highlights the importance of controlling fluid flow using the Riga plate in the presence of suction and investigates the behavior of a specific nanofluid under these conditions. The results provide valuable insights into the influence of key parameters on the flow characteristics. We conclude that effective utilization of the Riga plate can lead to significant enhancements in fluid flow control. Moreover, the study contributes to reducing energy losses through minimizing entropy generation. The novelty of this work lies in its comprehensive approach, considering multiple influential factors and employing a two-phase model for the nanofluid. Additionally, the inclusion of the Grinberg-term to account for the wall parallel Lorentz force adds to the uniqueness of the study. This research expands upon previous efforts in the literature by providing a more comprehensive analysis of the fluid flow control using the Riga plate, incorporating a broader range of factors, and presenting a numerical solution approach.

Natural convection and entropy generation in a trapezoidal region with hybrid nanoliquid under magnetic field

PurposeThis paper aims to study numerically the steady natural convective heat transfer of a hybrid nanosuspension (Ag-MgO/H2O) within a partially heated/cooled trapezoidal region with linear temperature profiles at inclined walls under an effect of uniform Lorentz force. This investigation is useful for researchers studying in the area of cavity flows to know features of the flow structures and nature of hybrid nanofluid characteristics. In addition, a detailed entropy generation analysis has been performed to highlight possible regimes with minimal entropy generation rates.Design/methodology/approachThe governing equations formulated using the Oberbeck–Boussinesq approach and single-phase nanoliquid model are transformed to a non-dimensional form by using non-dimensional variables. The obtained equations with appropriate boundary conditions are resolved by the finite difference technique. The developed code has been validated comprehensively. Analysis has been performed for a wide range of governing parameters, including Rayleigh number (Ra = 105), Prandtl number (Pr = 6.82), Hartmann number (Ha = 0–100), magnetic field inclination angle (φ = 0–?/2) and nanoparticles volume fraction (φhnf = 0 and 2%).FindingsIt has been shown that inclined magnetic field can be used to manage the energy transport performance. An inclusion of nanoparticles without Lorentz force influence allows forming more stable convective regime with descending heat plume in the central zone, while such a regime was performed for clear fluid only for moderate and high Hartmann numbers. Moreover, the average overall entropy generation can be decreased with a growth of the Hartmann number, while an addition of hybrid nanoparticles allows reducing this parameter for Ha = 30 and 50. The average Nusselt number can be increased with a growth of the nanoparticles concentration for low values of the magnetic field intensity.Originality/valueGoverning equations written using the conservation laws and dimensionless non-primitive variables have been resolved by the finite difference approach. The created numerical code has been verified by applying the grid independence test and computational outcomes of other researchers. The comprehensive analysis for various key parameters has been performed.

Heat Transfer and Entropy Generation in a Lithium-Ion Battery Pack Against Battery Spacing and Discharge Rate

Abstract Three-dimensional continuity, momentum, and energy equations have been solved in a battery pack of a unit module with 3 × 3 × 3 and 4 × 4 × 4 Li-ion cells to obtain the flow field and temperature distribution around the batteries. The battery spacing to hydraulic diameter ratio in x, y, and z directions have been varied in a wide range from 0.04458 to 0.08172, 0.00833 to 0.07133, and 0.007496 to 0.08052 for 4 × 4 × 4 cells, and 0.06 to 0.11, 0.0111 to 0.09649, 0.01 to 0.11 for 3 × 3 × 3 to obtain the optimum configuration for maximum heat transfer and minimum entropy generation. Air is pumped through the battery pack as a transport medium for heat transfer with Reynolds number (Re) varying in the laminar range from 400 to 2000. The results are plotted in terms of the average surface Nu over the battery surface and average volumetric temperature of the battery and air. It is found that the temperature of the battery pack remains almost constant against Sx. However, a significant rise in battery temperature is observed when we increase Sy. The scenario becomes different when spacing is varied in the z-direction. An optimum spacing for the minimum temperature of the battery pack is obtained at Sz/Dh = 0.03. The temperature variation trend is almost identical in 3 × 3 × 3 and 4 × 4 × 4 cells; however, the absolute temperature inside the pack is lower in 3 × 3 × 3 cells. In each case, the maximum temperature is seen on the batteries located at the top and bottom corners of the outlet. Among all the cases, the maximum temperature of 355 K has been found in 4 × 4 × 4 cells with a 3.6C discharge rate at Sy/Dh of 0.07133. Different discharging rates (1C, 2C, 3.6C, and 4C) have been considered to generate different amounts of heat inside the battery. However, it is numerically and theoretically proved that Nu and the nondimensional volumetric average temperature inside the pack are independent of the heat generation rate inside the battery pack.

Entropy minimization study of Maxwell nanofluid flow using oxides nanoparticles under transpiration and magnetic dissipation effects

Entropy generation is a measure of the irreversibility and inefficiency in a thermodynamic process. Minimizing entropy generation is desirable as it indicates a more efficient and optimized system. The present study focuses on flow dynamics and entropy minimization analysis in the MHD Maxwell nanofluid flow over the elastic surface with transpiration effects at the surface boundary. Furthermore, effects of important quantities such as magnetic field, electrical conductivity, joule heating, viscous dissipation, and heat source/sink are also considered. Two different types of nanofluids copper oxide-water and iron oxide-water are used, whereas the volume fraction of both nanofluids and base fluid are same. Similarity solutions are achieved by using similarity variables to transform the governing PDE’s systems into dimensionless ODE’s systems. The MATLAB algorithm bvp4c is used to perform numerical computations of nonlinear systems. Significant results of different parameters, such as volume fraction of nanoparticles, Eckert number, and magnetic parameter on entropy analysis, Bejan number, and velocity/temperature are comprehensively presented and discussed through graphs. It is realized that entropy minimization is possible for smaller values of nanoparticles volume fraction and Eckert number. The current analysis and data has significant uses in reducing energy losses in petroleum and chemical engineering systems such as production enhancement, thermal energy storage, energy efficient cooling systems.

Optimization of Dimensions of Smooth and Twisted-Tape-Inserted Tubes for Heat Transfer with NaCl/KCl/MgCl2 Molten Salts by Principle of Entropy Generation Minimization

Abstract The entropy generation minimization principle is used as the criterion to optimize the flow and heat transfer of solar collectors and heat exchangers that use molten salts NaCl–KCl–MgCl2 and KCl–MgCl2. The Gnielinski correlation for the Nusselt number versus Reynolds number, as well as the Moody friction factor given by Petukhov, was used for the calculation of the convective heat transfer coefficient and pressure loss due to friction in smooth tubes. For twisted-tap-inserted tube, equations of Nu and friction factor provided by Manglik and Bergles were used. The objective function, the entropy generation rate of the heat transfer system, was expressed as the function of Reynolds number, Prandtl number, heating flux, tube diameter, etc. As a result of the analysis, the optimum Reynolds number was determined and thereby to determine the optimum Nusselt number, convective heat transfer coefficient, friction factor, and tube diameter, which also allows the calculation of optimum flow velocity. The analysis was conducted in the fluid temperature range of 500–700 °C, which covers the operation temperature for supercritical CO2 power cycles in concentrated solar power (CSP) system. Optimized results from the smooth tube and twisted-tap-inserted tube are compared, which is important to the design of solar receivers for CSP systems.

Entropy Generation Minimization of Two-Phase Flow Irreversibilities in Hydrocarbon Reservoirs

The efficient use of available energy in hydrocarbon extraction processes is essential to reducing overall emissions in the petroleum industry. The inefficient design of an extraction process leads to higher emissions per unit mass of hydrocarbon recovery. Fluid friction and heat transfer are irreversible processes that are vital in decreasing the overall system’s operational efficiency. To reduce these irreversible energy losses in the petroleum reservoir production’s life, contributing factors such as the characteristic features of a reservoir formation, reservoir fluids, and production rate are investigated in this paper. This study examines irreversible energy loss in porous media and wellbore formations using entropy generation minimization at various stages of production and thermodynamic conditions, eventually achieving higher hydrocarbon recovery factors. Entropy production is used to develop predictive models that calculate reservoir and wellbore energy losses for multiphase flow. The proposed models consider oil and water as the working fluids in a porous medium and a wellbore. This paper also investigates the thermophysical effects around the wellbore by incorporating Hawkin’s model. A sensitivity analysis assessed the impact of rock and fluid properties and thermodynamic conditions such as temperature, wettability, and capillary pressure on the total entropy generation. The findings reveal that the capillary pressure significantly impacts the oil and water recovery factor and total entropy production. Additionally, the capillary pressure strongly influences the reservoir production life. The two-phase models show that as the recovery factor increases, the total entropy production decreases at lower production rates. This article helps to address the impact of irreversible processes on multiphase hydrocarbon reservoir operational efficiency. Furthermore, the results obtained from the numerical-simulation model open up a new research area for scholars to maximize the recovery factor using entropy generation minimization in heterogeneous reservoirs.

Optimised Electro-Osmotic Flow in Rectangular Microchannels with Smoothed Corners

Electro-osmotic flows are a means of circulating polar fluids through microchannels without resorting to mechanical pumping. The lack of moving parts, of noise and the ease of integration in silicon chips make them an interesting option for microchip cooling and miniaturized total analysis systems. This paper describes an optimization in terms of first- and second-law analysis of the cross-section of a microchannel subject to electro-osmotic flow. Starting from rectangular cross-sections of different aspect ratios, its corners are progressively smoothed and the resulting Poiseuille and Nusselt numbers computed. Performance evaluation criteria are then used to assess the change in, among others, heat transfer rate, temperature difference between wall and bulk fluid, and equivalent pumping power. The entropy number is also computed and the results commented. It is found that the latter criterion highlights a configuration of minimum entropy generation, whereas the trends of the heat transfer and temperature difference are opposite to that of the equivalent pumping power.

Optimization Analysis of Thermodynamic Characteristics of Serrated Plate-Fin Heat Exchanger.

This study explores the use of Multi-Objective Genetic Algorithm (MOGA) for thermodynamic characteristics of serrated plate-fin heat exchanger (PFHE) under numerical simulation method. Numerical investigations on the important structural parameters of the serrated fin and the j factor and the f factor of PFHE are conducted, and the experimental correlations about the j factor and the f factor are determined by comparing the simulation results with the experimental data. Meanwhile, based on the principle of minimum entropy generation, the thermodynamic analysis of the heat exchanger is investigated, and the optimization calculation is carried out by MOGA. The comparison results between optimized structure and original show that the j factor increases by 3.7%, the f factor decreases by 7.8%, and the entropy generation number decreases by 31%. From the data point of view, the optimized structure has the most obvious effect on the entropy generation number, which shows that the entropy generation number can be more sensitive to the irreversible changes caused by the structural parameters, and at the same time, the j factor is appropriately increased.

The effects of staggered triangular ribs induced vortex flow on hydrothermal behavior and entropy generation in microchannel heat sink

For dissipating the increasing heat in high flux microelectronic device, an original microchannel heat sink with staggered triangular ribs induced vortex flow is designed. In this work, the width (Wch) and height (Hch) of a single microchannel with staggered triangular ribs (MC-STR) are both 0.2 mm, as well as the width (Wr), height (Hr) and length (Lr) of the triangular rib are in ranges of 0.025–0.15 mm, 0.012–0.072 mm and 0.06–0.16 mm, respectively. The influences of the relative rib width (Wr/Wch), relative rib height (Hr/Wch) and relative rib length (Lr/Wch) on the hydrothermal behavior and entropy generation in MC-STR are numerically analyzed at the Reynolds number (Re) of 243–639. The results show that the increases in Wr/Wch and Hr/Wch can effectively improves the thermal performance, and reduce augmentation entropy generation number, but increase the flow resistance. In addition, the rise of Lr/Wch has weak effect on hydrothermal behavior and entropy generation. Overall, the MC-STR with Wr/Wch = 0.5, Hr/Wch = 0.3 and Lr/Wch = 0.5 at Re = 639 yields the highest performance evaluation criterion (1.502). Moreover, the minimum augmentation entropy generation number (0.236) is achieved at MC-STR with Wr/Wch = 0.5, Hr/Wch = 0.36 and Lr/Wch = 0.4 as Re = 639.