Thermal Entropy Generation Research Articles

Thermal enhancement and entropy generation of an air-cooled 3D radiator with modified fin geometry and perforation: A numerical study

The increasing fuel prices have led researchers to work on the efficiency and development of heat-transferring devices. One such device is the hot water radiator, which is familiar in the domestic arena. The study aims to increase the efficiency and cooling performance of hot water 3D radiators by modifying the design of their fins and adding perforations for better fluid mixing. CFD simulations were carried out on the radiators with modified fin geometries (Wavy, Spike-rib, Cut-sections, Straight) and with two different intensities of perforation (19 and 38 perforations) for each case at varying inlet flowrates of the radiator. The numerical model in this study was validated with experimental work. The hydrothermal performance of each radiator was measured in terms of fin surface temperature, entropy generation, heat transfer rate, and thermal enhancement factor. The temperature distributions and fluid flow streamlines have also been shown. The results show that modifying the fin geometries augments the overall heat transfer rate by up to 131 % while perforating the fins boosts the rate to 134 %. Moreover, the radiation heat transfer is seen to have surpassed the convection heat transfer by 60–160 % for the modified radiator cases. Finally, the most efficient radiator is found based on the thermal enhancement factor, which is the spike-fin arrangement.

Thermal performances investigation on an ammonia-fuelled heat-recirculating micro-combustor with reduced chemical mechanism

This study addresses the challenges in utilizing ammonia as a CO2-free fuel. However, the drawbacks of ammonia are—low burning speed and nitrogen oxide emissions. To enhance ammonia's flammability in atmospheric micro-combustion, hydrogen is blended in the fuel. First, a simplified chemical reaction mechanism of ammonia consisting of 44-step reactions and 19 species specifically for ammonia is developed and validated using experimental data to reduce computational cost and time. Then, we proposed a heat-recirculating micro-combustor fueled by premixed hydrogen/ammonia/air. Five key parameters are identical to numerically studying the thermal performance, entropy generation, and NO emissions. The present findings confirm that higher inlet velocity boosts thermal performance (power output achieving 15.8 W at 7 m/s) and NO emissions peak at 3 m/s (0.0169). Unity equivalence ratio optimizes thermal performance, rich-fuel combustion reduces NO emissions. At the stoichiometric ratio, the power output is 8.34 W, with the highest NO emissions at 0.9 (0.168). Hydrogen blending has a small effect on the performance (8.5 W at ξm = 0.7, 0.51 W above ξm = 0.4), but effectively reduces NO emissions (ξm = 0.7 NO emissions around 30 % lower than ξm = 0.4). Furthermore, changing the material from steel to Corundum enhances power output by approximately 6 %, while longer heat recirculation improves thermal performance.

Second-law analysis of nanofluid-based photovoltaic/thermal system modeling and forecasting model based on artificial neural network

The PVT solar collectors can produce the thermal energy and power in a same frame. The improvement of the PVT's efficiency leads to reducing the system size and capital costs. To this end, this paper studied the irreversibilities of the Al2O3Cu/water hybrid nanofluid (NF) in a PVT solar collector considering two single and double serpentine channels (SS and DS). The influences of Re and nanoparticle concentration (φ) on the thermal and frictional entropy generation rates (S˙th and S˙fr) were investigated and the thermal, electrical and overall exergy efficiencies (ψth, ψe, ψov) of the PVT with SS and DS channels were compared and discussed. Based on the results, the DS channel exhibited S˙fr of almost 75 % lower than SS channel due to lower nanofluid inlet velocities and velocity gradients. In addition, S˙th for the DS channel is nearly 65 % lower and 26 % higher than that for the SS channel at Re numbers of 500 and 2000, respectively. Besides, the Re escalation from 500 to 2000 intensifies S˙fr by almost 94 % at different φs in the SS and DS channels. The increase in φ from 0 % to 1 % escalates S˙fr by almost 99.98 % times for two configuration regardless of the Re number. ψth of the DD channel is nearly 14.5 % and 12.77 % higher than that of the SS channel at Res of 500 and 2000, respectively. Besides, ψe of the PVT with the DS channel is 2.36 % higher than that with SS channel at Re=500 at four studied φs. Moreover, the maximum ψe for the PVT with the DS and SS were obtained as 22.29 % and 21.28 %, respectively, which are associated with Re=1500 and φ=0.25 %. Additionally, a predictive model was presented to determine the total entropy generation rate based in the Re and φ as the inputs.

Effect of non-uniform heating on conjugate heat transfer and entropy generation characteristics within a partially filled porous corrugated channel

The persistence of the present numerical investigation is to evaluate the thermal and total entropy generation characteristics of flow within a partially filled porous wavy channel with finite wall thickness subjected to non-uniform wall heat flux. The average Nusselt number and the total entropy generation increase with the permeability value of the porous medium (Da) irrespective of asymmetric wall heat flux amplitude and wavelength as well as with the variation in thickness ratio and thermal conductivity value of the solid substrate. However, the total irreversibility decreases for a high Darcy number value when the phase angle between the applied heat fluxes is varied. Moreover, the average Nusselt number decreases up to a critical value of phase angle followed by a gradual increment for Da = 10−5 and 10−3, respectively. On the contrary, the reverse trend can be seen for Da = 10−1. The optimal choice of nonuniform heat flux amplitude, wavelength, and phase angle for a high heat transfer rate with minimum irreversibility generation is found to be 10 W/cm2, 5 mm, and 180°, respectively for a thickness ratio of 0.5 and thermal conductivity value of 646.07 W/m·K independent of Darcy number.

Thermal convection and entropy generation analysis of hybrid nanofluid slip flow over a horizontal poignant thin needle with an inclined magnetic field: A numerical study

Hybrid nanofluids have emerged as a promising field of research in recent years, finding applications in various industries and sectors. The entropy generation and impact of an inclined magnetic field on a water-Ethylene Glycol (50:50) mixture-based nanofluid over a poignant thin needle has been investigated under slip conditions. The flow is swotted using thermal and velocity slip boundary conditions. The numerical effects of an inclined magnetic field on the flow of ferrous and aluminum oxide nanoparticles in a hybrid nanoliquid with as base fluids have been examined. The non-dimensional ODEs along with boundary conditions are solved by numerical technique based on the Runge–Kutta fourth-order method. Velocity profile has been analyzed for the magnetic parameter, inclined angle and volume fractions. The Bejan number provides insights into the balance between heat transfer and entropy generation in a system. From the numerical values of skin friction coefficient and Nusselt number, it is analyzed that [Formula: see text]O3 possesses 1.01% and 1.06% of high heat transfer rate and high surface drag force than [Formula: see text]O4. Heat transfer profile has been analyzed for entropy generation and the Bejan number. The applications of hybrid nanofluids are vast, and one specific area where they can be utilized is in horizontal needle systems.

Mixed convective thermally radiative viscoelastic hybrid nanofluid flow in a vertical channel: Entropy generation analysis

The utilization of a new category of nanofluids, termed hybrid nanofluid, has recently been adopted to elevate the heat transfer rate. This research aims to analyze the significance of thermal radiative flux and entropy generation on the flow of hybrid nanofluid within a vertical channel. Specifically, the Al2O3–TiO2/CMC-water hybrid nanofluid is assumed to be produced by suspending hybrid nanoparticles of alumina (Al2O3) and titanium oxide (TiO2) in CMC-water (0.0–0.4%). The equations governing the problem are converted into a set of ordinary differential equations by utilizing appropriate similarity conversions, which are then solved through the Homotopy Analysis Method (HAM). The Brinkman number’s significant influence on the Bejan number and the regulation of entropy in the system is discovered. The results of the skin friction coefficient, heat transfer rate, entropy generation, and Bejan number are depicted through graphical representation, covering a wide range of parameter values.

The parametric optimization of a pin-fin heatsink in the presence of ultrasonic vibration based on the second law of thermodynamic

The goal of this numerical study is to investigate the effect of ultrasound waves on the entropy generation aspects in a water-cooled pin-fin heatsink. The effect of the number and locations of ultrasound transducers (32 different scenarios), Re number (500–2000) and frequency of ultrasound waves (F = 15–30 kHz) are investigated on the thermal and frictional entropy generation rates. It was revealed that different configurations with the transducers on two, three, and four walls entail a low thermal entropy generation rate, however, most of which have a high frictional entropy generation rate with the exceptions for case#27 and two other scenarios that bring a moderate frictional entropy generation rate. Therefore, case#27 was selected as the optimum configuration from the second thermodynamic law points of view. For the studied range of Re, the thermal entropy generation ratefor the optimum case is 21–47% lower than that for the base case at F = 30 kHz. While the frictional entropy generation rate for the optimum case escalates to 11–247 folds of the base case for Re numbers of 500–2000. In addition, the escalation of frequency from 15 to 25 kHz reduced the thermal and frictional entropy generation rates by 5.31% and 40.22%, respectively.

Numerical investigation of the effect of perforation inclination angle on the performance of a perforated pin-fin heatsink using two-phase mixture model

The numerical analysis of water/silver nanofluid (NF) flow in a perforated pin-fin heatsink (PFHS) is performed considering the nanoparticle concentration (φ) of 1% and seven different perforation inclination angles (γ). The configuration with the best hydrothermal performance and the lowest entropy generation rate at different values of Reynolds number (Re) is determined using the two-phase mixture technique. According to the results, the γs of 45º and -45º exhibit the highest heat transfer coefficient (h) and the lowest thermal resistance factor and mean CPU temperature at four studied Res of 500, 1000, 1500, and 2000. Consequently, the highest hydrothermal performance evaluation criterion (PEC) was obtained for the heatsink with γ of 45º followed by γ of -45º at Re of 500; the increase in Re reduced the PEC due to the pressure drop. PEC of the heatsink with γ of 45º was almost 11.06–16.63% higher than that with γ of 0º. In addition, γ of -15º and 45º provided the lowest frictional and thermal entropy generation rates (S˙fr and S˙th) at Re of 1500 and then 2000. S˙fr and S˙th for γ of 45º were 1401% and 97% lower than those for γ of 0º at Re=1500.

Heat transfer enhancement in pillow-plate type heat exchanger with SCWSCs using an entropy and exergy generation approximation technique

The design and development of the Pillow-plate heat exchanger (PPHE) are attracting more interest in the research and scientific communities in recent years. In this manuscript, a new investigation is performed to examine the heat transfers and fluid flow characteristics for different streamwise lengths with Staggered Circular Welding Spot Configurations. To analyze the heat transfer and friction factor parameters total of 25 different designs of dh/XL is considered, 1000 ≤Re≤ 16,000. In addition, to optimizing the exergy efficiency and thermal evaluation factor, some dimensional and non-dimensional thermodynamic and thermal-hydraulic influencers, including thermal and frictional entropy generation, thermal and frictional exergy destruction, Nusselt number, friction factor, Bejan, entropy generation number are calculated by considering the second law efficiency approach based on thermo-dynamics for turbulent single-phase water flow in PPHE as wavy surface using SST transition k−ω method and entropy and exergy approximation technique. Based on the computational results obtained, increasing the streamwise lengths with SCWSPs, the ‘elliptical recirculation vortex’ is essential and significantly enhances the thermal performance factor. The maximum exergy and thermal performance factor are improved by 41.58% and 1.54 in the dh/XL = 0.078 and 0.044 at Re = 1000, respectively.

Hydrothermal characteristics, entropy and kinetic energy investigation in a sinusoidal cavity for variable wavelengths and solid volume fraction using Cu-water nanofluid

The use of thermofluids in a cavity under magnetohydrodynamics (MHD) with the natural convective flow has been extensively researched, with numerous attempts made by researchers. However, none have examined the role of nanofluid concentrations on a sinusoidal cavity with variable wavelengths at two walls using Cu-water nanofluid with MHD. Therefore, the present study evaluated nanofluid concentration impact in a sinusoidal cavity for three different wavelengths under magnetic field conditions and Rayleigh numbers using Cu-water nanofluid. Four different solid volume fractions (ϕ = 0.02, 0.04, 0.06, 0.08), three different wavelengths (λ = 2, 3, 4), three different Rayleigh numbers (Ra=103,104, 105) have been considered for the study using the finite element method. The LBB-stable element is used to approximate velocities, pressures, and temperatures. The numerical results have been validated from the past study. The variation of kinetic energy, average Nusselt number, viscous, thermal, magnetic, and total entropy generation for various wavelengths has been shown for varying the concentration of nanofluid and Hartmann number. Additionally, the effect of Rayleigh numbers on the entropy generations for three different wavelengths has been presented. The results revealed that the heat transfer rate, kinetic energy, and entropy generation rise with the decreased value of volume concentrations for most of the cases. It is also noticed that these parameters also negatively effect due to the magnetic field. Therefore, with the rise of the Hartmann number, the fluid flow, thermal parameters, and entropy generation decrease. Moreover, Ra has a notable role in entropy generation. Entropy generations have been found higher for Ra=105, and the lowest is found for the case of Ra=103.

Convective heat transfer enhancement and entropy generation analysis for radiative flow of ferrofluid inside the enclosure with non-uniform magnetic field

The present work consists of investigating the thermal performance and entropy generation for the non-isothermal radiative-convective flow of magnetic-ferrofluid inside the cavity exposed to the variable magnetic field. The effects of Lorentz and Kelvin forces for magnetized liquid are associated with magnetohydrodynamic (MHD) and ferrohydrodynamic (FHD) are examined during this study. The penalty method is used to eliminate pressure terms from governing nonlinear system of partial differential equations, and then Galerkin finite element is utilized to reduce the system into a system of algebraic equations, which is then solved with the help of Newton Raphson method to obtain the required (unique) solution. The obtained results show that the thermal mixing and entropy generation increases with an increase in the magnetic number Mnf. The concentration of ferroparticles volume fraction (ϕ) from 0 to 0.05 increases the heat transfer rate by 62.78% and decreases the total entropy generation by 57.3%. The maximum 93.62% augmentation in the heat exchange rate is obtained at ϕ=0.05 and Mnf=103. The results of the present work can be used in obtaining geometric parameters and optimizing designs for effective energy transfer in chemical reactors, solar collectors, nuclear magnetic resonance imaging, heat exchangers, and dye removal from textile wastewater.

Entropy generation of Al2O3/water nanofluid in corrugated channels

The flow of nanofluids in a corrugated channel has been shown to have a significant impact on heat transfer performance, and has therefore become an important area of research. The ob- jective of this paper is to understand the thermal behavior of Al2O3/water nanofluid in a sinu-soidal and square channel and to identify ways to optimize heat transfer performance in such configurations. For this purpose, a numerical simulation was conducted using ANSYS-Fluent software 16.0 on entropy generation and thermo-hydraulic performance of a wavy channel with the two corrugation profiles (sinusoidal and square). The analyses were carried out under laminar forced convection flow conditions with constant heat flux boundary conditions on the walls. The influence of various parameters, such as particle concentration (0–5%), particle di-ameter (10nm , 40nm and 60nm), and Reynolds number (200 < Re < 800) on the heat transfer, thermal, and frictional entropy generation, and Bejan number was analyzed. Moreover, the distribution of streamlines and static temperature contours has been presented and discussed, and a correlation equation for the average Nusselt number based on the numerical results is presented. One of the most significant results obtained is that the inclusion of nanoparticles (5% volume fraction) in the base fluid yielded remarkable results, including up to 41.92% and 7.03% increase in average Nusselt number for sinusoidal and square channels, respectively. The sinusoidal channel exhibited the highest thermo-hydraulic performance at Re= 800 and φ= 5%, approximately THP= 1.6. In addition, the increase of nanoparticle concentration from 0% to 5% at Re= 800 and dnp= 10nm, diminishes the total entropy generation by 28.39 % and 22.12 % for sinusoidal and square channels, respectively, but when the nanoparticle diameter decreases from 60nm to 10nm at ϕ= 5% and Re= 800, the total entropy generation in the sinusoidal channel decreases by 34.85%, whereas in the square channel, it decreases by 20.05%. Therefore, rather than using a square channel, it is preferable and beneficial to use small values of nanoparticle diameter and large values for each of ϕ and Re in the sinusoidal wavy channel. Overall, the study of nanofluid flow in a wavy channel can provide valuable insights into the behavior of nanofluids and their potential applications in a variety of fields, including manufacturing, energy produc-tion, mining, agriculture, and environmental engineering.

Second Law Investigation in a Non-Newtonian Liquid Flow in a Porous Channel with Circular Obstacle

The problem of non-Newtonian fluid flow has taken considerable interest and has been the subject of several work in latest years due to its various requests in different fields of engineering, in particular the interest in the problems of heat transfer in non-Newtonian liquids, such as lubrication, hot rolling, cooling problem and drag reduction. Here, mixed convection heat transport and its related entropy production in a porous channel with circular obstacle saturated via non-Newtonian power law liquid has been scrutinized. The influences on entropy production of the power law index, the Reynolds number, the Rayleigh number and the Darcy number are investigated. Being a novelty of this work, an optimization study of the thermodynamic irreversibility as a function of the channel inclination angle and the power law index is undertaken. The governing equations of the problem are solved employing the COMSOL software. Outcomes illustrate that the governing parameters strongly affect the entropy production. The thermal entropy generation is maximal at low value of power law index and high value of Reynolds number. The effect of Reynolds number become insignificant at relatively high power law index. At fixed Reynolds number value, a rise in the power index (n) leads to a reduce in the thermal entropy. This decrease is tiny, at low value of Reynolds number (Re) and turn into increasingly considerable as Re rises. The streamlines show the existence of two recirculation zones just after the circular obstacle, whose existence depends on both Re and power law index. Results show that the greatest variation relating to the inclination angle is for power law index equal to 0.4. Results indicate also that, at low Darcy number and relatively high power law index, the intrinsic effect of the modified Darcy number on Darcy viscous irreversibility become pronounced giving a sharp increase in the total entropy production.

On the cooling performance and entropy generation characteristics of a heat sink under ultrasonic vibration: Exploring the impact of porous medium

Ultrasonic vibration and porous medium utilization are both proven to be beneficial techniques to improve cooling performance of heat sinks. Present work aims at exploring the impacts of using porous medium in heat sinks under ultrasonic vibration effect on the cooling performance and entropy generation characteristics, hence, the interrelation of these two techniques is evaluated. Simulations are performed for a constant Reynolds number (Re=2000) and ultrasonic vibration frequency (f = 30 kHz), whereas five different porosities (ε=0.75 to 0.95) along with five different pore diameters (dp=1 to 17 mm) determining the permeability of the porous structure are considered. The results are compared to the non-porous case to determine the effects of porous medium on the ultrasonically vibrated heat sink. It is found that using porous medium increases convective heat transfer coefficient by up to 84.5% attaining a temperature reduction of 10.22 K. Low porosity along with high pore diameter attains an effective cooling, while high porosity with high pore diameter ensures lower pumping power requirement, which is only 1.2-folds of the non-porous case. Frictional entropy generation rises by up to 23% due to porous structure restricting fluid flow depending on its porosity and permeability, while thermal entropy generation can be even decreased below that of non-porous case by 8% with appropriate choice of parameters. Yet, considering the total irreversibility, the frictional entropy generation is significantly dominant compared to the thermal entropy generation. Overall, using ε=0.95 and dp=17 mm along with 30 kHz of ultrasonic vibration is recommended for significantly enhanced heat transfer together with lowest possible pressure drop penalty and low thermal entropy generation.

Influence of nanofluids on the thermal performance and entropy generation of varied geometry microchannel heat sink

A microchannel heat sink (MCHS) is a compact, effective cooling device that meets the heat dissipation requirements of high-power electronic equipment. This paper investigates the impact of utilizing Al2O3/water, MgO/water, and TiO2/water nanofluids in a rectangular MCHS. To ensure an acceptable comparison, the flow rate is kept constant at 2 m/s. The heat sink base is subjected to 90W of steady heat dissipation, which produces the desired performance result. The vol. concentration of nanofluids ranges from 0 to 8%. The study covers a wide range of MCHS geometries; channel height (Hch) and its width (Wch) ranging from 200 to 800 μm and 100–500 μm respectively. The problem is modeled, validated, and analyzed. The use of nanofluids maximizes the heat transfer performance to 24.95% and minimizes thermal resistance and total entropy generation (TEG) to 15.01%, and 19.96% respectively. TEG decreases to 53.15% when Hch increases and the same increases to 198% when Wch increases. Nanofluids at highest vol. concentration as well as increase in Hch and Wch penalize the system maximum by demanding more pumping power (Ω) by 25.58%, 173.36%, and 39% respectively. Al2O3/water and MgO/water nanofluids deliver better performance and are recommended for future applications. Finally, the authors suggest concentration and geometric parameter ranges for optimality of the thermal performance.

Natural convection and entropy generation of hybrid nanofluid in double annulus separated by a thin rotating partition under magnetic field

The present study analyzes the impacts of using a rotating partition on the natural convection and entropy generation of nanofluid filled double annulus under magnetic field by using finite volume method. Effects of various pertinent parameters such as Rayleigh number (Ra: 104 – 6×105), rotational Reynolds number (Rew: 0-100), Hartmann number (Ha: 0–60), fin height (Hf:0.1–0.5) and fin number (Nf:4–20) on the thermal performance improvements are numerically assessed. The contributions of rotations to the overall thermal performance become different depending upon the activation of rotations and magnetic field effects. Depending on whether rotations exist, magnetic field effects have different impact on the behavior of heat transport and entropy generation. Thermal performance reduction amounts become 40% without magnetic field when comparing the rotating and stationary interface cases. Fins further improve the thermal performance up to 23% depending upon the existence of magnetic field while rises with existence of magnetic field and increasing its strength for the case of non-rotating interface while it shows opposite behavior for rotating interface case. When the location of the interface becomes closer to the outer surface of the annulus, reduction of the entropy generation up to 68% can be obtained. Artificial neural network based model provides successful estimation of thermal performance and entropy generation when considering the impacts of rotating interface.

Identification of invisible fatigue damage of thermosetting epoxy resin by non-destructive thermal measurement using entropy generation

To quantify carbon fiber-reinforced plastic (CFRP) fatigue, herein, we investigate the relationship between fatigue and an epoxy resin used in CFRPs. Generally, fatigue is related to the entropy, which comprises the mechanical entropy, calculated from the dissipated energy and temperature, and thermal entropy, calculated from the relationship between specific heat capacity and temperature. According to previous studies, mechanical entropy generation and thermal entropy generation are equal. Herein, 100 cyclic loading tests are conducted on epoxy resin specimens consisting of 4,4’-DDS and bisphenol a diglycidyl ether. The dissipated energy is determined based on stress – strain curves, and mechanical entropy generation is quantified. An equation for the relationship between the specific heat capacity and temperature is developed based on the Debye model, and the increase in specific heat capacity is calculated for equal mechanical and thermal entropy generations. Generally, differential scanning calorimetry is used for specific heat capacity measurements; however, because these measurements are performed by cutting the specimen, a nondestructive measurement method is required. In this study, the specific heat capacity is measured using lock-in thermography (LIT), and the measured and estimated values are comparable. Thus, fatigue can be estimated by quantifying the thermophysical properties, and the lock-in thermography method is a suitable thermophysical property measurement method for this application.

Three‐dimensional numerical simulation of free convection and entropy generation in a cubic cavity containing a heat source

AbstractThe present article provides a three‐dimensional numerical investigation of thermal convection and entropy generation. The lattice Boltzmann method, coupled with the finite difference approach, is applied to perform numerical simulations. The validation of these numerical approaches for thermal convection simulation and entropy calculation is performed by comparing our numerical results with those in the published literature for the case of benchmark problems. The physical geometry studied in this paper concerns a hot obstacle having the shape of a plus sign (+) placed in the center of a cubic enclosure. This cube is filled with air of a Prandtl number of 0.71 and characterized by two cold vertical walls. The heat exchange between the fluid and the hot body is studied as a function of the Rayleigh number (). The performed simulations show that the heat transfer rate can be increased by about 429% by switching from to . The entropy generation due to fluid friction, heat transfer, and total entropy are also calculated and discussed. For an irreversibility coefficient , the analysis of the results showed that for low values of the Rayleigh number (), the entropy production due to temperature gradients predominates over that produced by viscous effects. In the cases of and , entropy generation is due to both fluid friction and heat transfer. However, when the Rayleigh number becomes large (), entropy generation due to viscosity predominates over entropy production related to heat exchange. These results have important implications for the optimization and design of heat transfer systems in various industrial applications.

Numerical Analysis on Detonation Wave and Combustion Efficiency of Pulse Detonation Combustor With U-Shape Combustor

Abstract The research work is carried out for deflagration and detonation combustion processes at different equivalence ratios of hydrogen–air mixtures in a pulse detonation combustor (PDC). Furthermore, the U-shape channel curvature radius and thickness effect on detonation wave propagation are also investigated. This numerical simulation has been done using a SIMPLE algorithm with the finite volume discretization method and laminar finite rate chemistry for volumetric reaction in the Ansys Fluent platform. The numerical result shows that the U-bend radius of R = 3.5 cm can enhance the faster deflagration-to-detonation transition. So far, the fully developed detonation wave was found near the curvature area of the detonation tube having a width of W = 8 cm. This enhanced detonation wave velocity reaches 2775 m/s, which is higher than the C-J detonation velocity. Furthermore, the entropy generation has been analyzed in two modes of the combustion process. The entropy generation number of 0.76 and 0.7 is obtained from the deflagration and detonation combustion processes. However, the entropy production rate is less in the detonation combustion process, but thermal entropy generation is more in the deflagration combustion process with a magnitude of 3.5 kJ/kg K for an equivalence ratio of φ = 1.5. A combustion efficiency of 78% is found in the detonation combustion process, which is comparatively higher than the deflagration process.

Investigation into the effects of hydrophobicity on thermohydraulic characteristics and entropy generation of hybrid nanofluid with the magnetic property in a micro-heat sink under a magnetic field

The cooling of devices is a big challenge in the electronics industry, and most process units (graphical are central process units) experience defects under harsh temperature conditions, so dissipating generated heat under various working conditions should be studied seriously. This study investigates the magnetohydrodynamics of hybrid ferro-nanofluids in the presence of hydrophobic surfaces in a micro-heat sink. To scrutinize this study, a finite volume method (FVM) is applied. The ferro-nanofluid includes water as a base fluid and multiwall carbon nanotubes (MWCNTs) and Fe3O4 as nanoadditives, which are used in three concentrations (0, 1, and 3%). Other parameters such as the Reynolds number (5–120), Hartmann number (magnitude of the magnetic field from 0 to 6), and hydrophobicity of surfaces are scrutinized for their impacts on heat transfer and hydraulic variables as well as entropy generation variables. The outcomes indicate that increasing the level of hydrophobicity in surfaces leads simultaneously to improved heat exchange and reduced pressure drop. Likewise, it decreases the frictional and thermal types of entropy generation. Intensifying the magnitude of the magnetic field enhances the heat exchange as much as the pressure drop. It can also decrease the thermal term in entropy generation equations for the fluid, but increase the frictional entropy generation and adds a new term, magnetic entropy generation. Incrementing the Reynolds number improves the convection heat transfer parameters, although it intensifies the pressure drop in the length of the channel. Also, the thermal entropy generation and frictional entropy generation decrease and increase with an increasing flow rate (Reynolds number).