High Heat Transfer Rates Research Articles

Computational study and characteristics of magnetized gold-blood Oldroyd-B nanofluid flow and heat transfer in stenosis narrow arteries

Nanofluids are incredibly helpful to researchers because of their higher rates of heat transfer that have huge industrial usages. We discuss blood flow via a tiny artery with a stenosis in the appearance of heat and mass transfer in the existing critique. The non-Newtonian blood flow in narrow artery is mathematically investigated by depicting the blood as Oldroyd-B fluid. The major intention of this investigation is to investigate the impact of MHD in Oldroyd-B nanoliquid flow with gold (Au) nanoparticles (NPs) on stenosis arteries. The properties of heat transfer with joule dissipation are being examined. The base fluid for nanoparticles is blood. Appropriate transformations are exploited to convert the nonlinear PDEs that govern the system into nonlinear ODEs. The numerical results of these ODEs are determined using the Homotopy analysis method (HAM). Flow anticipates for every physical quantity is also investigated. Physical explanations are utilized to illustrate the physical effects of flow limitations versus assumed fluid flow. The results show that as the volume fraction, flow, and relaxation parameters increase, so does the velocity contour. The nanofluid temperature is decreased for the volume fraction and Prandtl number. In addition, the drag force and heat transfer explanations for blood flow dynamics are being investigated. As the flow parameter values increase, the Nusselt number decreases and the drag force increases. The modelling and numerical solution serves an essential role in trying to predict the cause of atherosclerosis.

Effects of higher order chemical reaction and slip conditions on mixed convection hybrid ferrofluid flow in a Darcy porous medium

Many researchers have been captivated by the ability of hybrid ferrofluid to increase heat and mass transmission, leading them to further examine the working fluid. This study is essential for figuring out how Fe3O4-CoFe2O4/H2O hybrid ferrofluid would behave thermally and massively when physical factors like a greater degree of chemical reaction (n) and slip boundary conditions are present through mixed convection stagnation point flow in Fe3O4-CoFe2O4/H2O hybrid ferrofluid toward a permeable vertical flat plate embedded in Darcy porous medium. The complexity of the partial differential equation for heat, flow, as well as mass transfer is reduce through similarity transformation into a system of ordianry differential equation, before being numerically solved using the built-in solver bvp4c in MATLAB for various values of the governing parameters. Dual solutions (first and second solution) are obtained as result produced in regions of opposing and assisting flow. Hybrid ferrofluids with additional CoFe2O4 nanoparticles have a higher heat transfer rate than ferrofluids and base fluid (water). Furthermore, a different order of chemical reaction greatly influences the mass transfer rate. Note that the presence of thermal and concentration slips reduce the heat transfer and mass transfer rate, accordingly, and delay the boundary layer separation.

Dynamics of heat transport in flow of non‐linear Oldroyd‐B fluid subject to non‐Fourier's theory

AbstractTo study non‐Fourier heat and mass transport in the stagnation point flow of magnetized Oldroyd‐B fluid due to stretching cylinder, the Cattaneo–Christov heat flux model is used in this investigation. Further, as the controlling agents for thermal and solutal transport in the fluid flow, the heat generation/absorption source and chemical reaction are also considered. The formulations of a such physical phenomenon are going to form the PDEs. Through appropriate similarity variables, these governing partial differential equations for flow and energy transport are converted into the ordinary differential. The analytical series solutions are obtained through the use of a homotopic approach. The graphical upshots are conducted for velocity fields, temperature, and concentration distributions. In addition, energy transport analysis is performed for two kinds of surface heating mechanisms, namely the prescribed surface temperature (PST) and constant wall temperature (CWT). The outcomes of the current investigation revealed that a higher rate of heat transfer is observed in the case of CWT as compared to PST. Moreover, the increasing values of thermal and solutal relaxation time parameters reduce the heat and mass transport in the fluid flow, respectively.

Nanofluid Flow and Heat Transfer between a Stationary Nonpermeable Disk and a Permeable Rotating Shrinking Disk with Radiation and Heat Generation Effects

The flow between bounded surfaces is known as internal flow. The internal flow between disks has many significant applications, such as gas turbine rotors, rotating machinery, food processing technology, and air cleaning machines. In the current study, the nanofluid flow between two disks, nonpermeable and stationary, and the other permeable, rotating and shrinking, is analysed. The governing partial differential equations and boundary conditions are proposed with the inclusion of radiation and heat generation effects. Then, similarity transformations are utilised in deriving the nonlinear ordinary differential equations and boundary conditions for computation using the bvp4c solver. Multiple solutions are obtained, and only the first solution is stable. The combination Mn-ZnFe2O4/C2H6O2 nanofluid is found to produce the lowest magnitude of skin friction coefficient and the highest heat transfer rate.

Out-of-Plane Biphilic Surface Structuring for Enhanced Capillary-Driven Dropwise Condensation.

Rapid and sustained condensate droplet departure from a surface is key toward achieving high heat-transfer rates in condensation, a physical process critical to a broad range of industrial and societal applications. Despite the progress in enhancing condensation heat transfer through inducing its dropwise mode with hydrophobic materials, sophisticated surface engineering methods that can lead to further enhancement of heat transfer are still highly desirable. Here, by employing a three-dimensional, multiphase computational approach, we present an effective out-of-plane biphilic surface topography, which reveals an unexplored capillarity-driven departure mechanism of condensate droplets. This texture consists of biphilic diverging microcavities wherein a matrix of small hydrophilic spots is placed at their bottom, that is, among the pyramid-shaped, superhydrophobic microtextures forming the cavities. We show that an optimal combination of the hydrophilic spots and the angles of the pyramidal structures can achieve high deformational stretching of the droplets, eventually realizing an impressive "slingshot-like" droplet ejection process from the texture. Such a droplet departure mechanism has the potential to reduce the droplet ejection volume and thus enhance the overall condensation efficiency, compared to coalescence-initiated droplet jumping from other state-of-the-art surfaces. Simulations have shown that optimal pyramid-shaped biphilic microstructures can provoke droplet self-ejection at low volumes, up to 56% lower than superhydrophobic straight pillars, revealing a promising new surface microtexture design strategy toward enhancing the condensation heat-transfer efficiency and water harvesting capabilities.

The first and second law analyses of thermodynamics for CoFe2O4/H2O flow in a sudden expansion tube inserted elliptical dimpled fins

In this paper, thermo-hydraulic performance and entropy generation of the sudden expansion tube with elliptical dimpled fins (DFs) at different directions was computationally performed at different Reynolds (Re) numbers ranging between 100≤Re≤2000 using cobalt ferrite/H2O (CoFe2O4/H2O) nanofluid (NF) (0.0≤φ≤ 2.0). The novelty of this study is to investigate the effect of the elliptical DF and its arrays in the sudden expansion tube in terms of thermodynamics laws (energy and entropy generations). While the sudden expansion ratio (D2/D1) is 2.5, elliptical dimple width (a) and height (b) show variations between 4 and 8 mm. In addition, the distances among elliptical DFs (P) are taken as P = 10, 15, and 20 mm while the diameter (D1) and length (L1) of the inlet tube are D1=8 mm and L1=375 mm. The diameter (D2) and length (L2) of the tube with the sudden expanding and elliptical DFs are D2=20 mm and L2=1125 mm, respectively. The study comprehensively exhibits results of the thermo-hydraulic performance and entropy generation based on numerical data. The results demonstrated that the highest heat transfer rate is recorded by the case of DT3, and DT3 enhances the convective heat transfer rate by 221%, and increases the pressure drop by 17.38% at Re=2000 compared to smooth tube (ST). It was observed that as the Re increases, the performance evaluation criteria (PEC) gradually increases too, and the highest PEC has been obtained for DT3 as 2.11 at Re=2000. The entropy generation (EnG) was also evaluated in terms of both geometric designs and volumetric concentrations. Moreover, the best total EnG was found around 17% for DT3 at the Re=1000 and φ=2.0% compared to ST using H2O. Consequence of the applied analyses, the use of elliptic DFs in a sudden expansion tube enhances the convective heat transfer rate and decreases total EnG.

Evaluation and comparison of thermal performance of latent heat storage units with shell-and-tube, rectangular, and cylindrical configurations

• Criteria are proposed to evaluate heat transfer, flow resistance, and irreversibility. • Shell-and-tube LHSU has the shortest phase change time and highest heat transfer rate. • Shell-and-tube LSHU achieves the highest j / f factor and the best thermal performance. • Cylindrical LHSU achieves the highest melting exergy efficiency of 81.5% • Shell-and-tube LHSU has the highest exergy efficiency of thermal store-release cycle. Latent heat storage plays a significant role in tackling the mismatch between energy supply and demand. Evaluation and comparison of the thermal performance of different shaped latent heat storage units (LHSU) are essential in the optimal design of LHSU. This study developed the numerical model of heat transfer and flow in shell-and-tube, rectangular, and cylindrical LHSU with the same PCM mass and heat transfer area. Two kinds of criteria, namely the j / f factor considering both heat transfer and flow resistance and the exergy coefficient evaluating irreversibility, are proposed to assess the performance of LHSU comprehensively. It shows that natural convection intensity in cylindrical LHSU is the highest, while the shell-and-tube LHSU exhibits the lowest phase change time and the highest heat transfer rate. The average j / f factor of shell-and-tube LHSU is 21.4% larger than that of rectangular LHSU and is twice as much as that of cylindrical LHSU. Therefore, the shell-and-tube LSHU achieves the best overall thermal performance. Moreover, cylindrical LHSU achieves the highest melting exergy efficiency of 81.5%, while shell-and-tube LHSU has the highest solidification exergy efficiency of 62.8%. Regarding the thermal storage and release cycle, the exergy efficiencies of shell-and-tube, rectangular, and cylindrical LHSU are 50.1%, 49.2%, and 48.5%, respectively. Therefore, shell-and-tube is the optimal shape to achieve the largest exergy efficiency of the thermal storage-release cycle. This study deepens the understanding of the thermal behavior of PCM packed in different shaped containers, obtains the optimal geometric configuration, and gives guidance to the optimal design of geometric parameters of the LHSU.

Double-diffusive stagnation point flow over a vertical surface with thermal radiation: Assisting and opposing flows.

In numerous industrial procedures, the main concern of design engineers is ensuring adequate heat and mass transfer, such as in the heating and cooling practices of solar water heaters, geothermal systems, extrusion of metal, insulation of buildings, electronics, turbines, aerodynamics, electronics, paper manufacturing, and glass fiber production. The unsteady double-diffusive mixed convection flow of boundary layer nanofluids above a vertical region near stagnation point flow is developed and examined here. The Brownian motion and thermophoresis effects are incorporated by using Buongiorno's model. In the thermal energy equations, diffusion of regular and cross types is also used. By the use of the local similarity method along with suitable similarity transformations, nonlinear unsteady partial differential equations are converted to nonlinear ordinary differential equations and are numerically solved by the Keller-Box method. The investigation expresses that these profiles of solute concentration and nanoparticle concentration, temperature, and velocity in their boundary layers, respectively, depending on several parameters. A graphic analysis of all these parameters' possessions on nature's boundary layers is depicted. The highest rate of heat transfer is obtained with negligible thermophoresis effect. Furthermore, it is perceived that an increase in Nc and Nt results in a reduction in the reduced Sherwood number of nanoparticles, whereas addition results in an increase in the Nb number. There is a reverse effect on the temperature field and layer thickness for heat generation. In the wake of the above-mentioned potential applications, the current study of fluid flow has been found to be very interesting and innovative in the analysis of the influence of Brownian motion and thermophoresis effects near stagnation point flow, which will further make revolutions in industrial fields. Moreover, Buongiorno's model predicts the characteristics of double-diffusive fluids in enhancing heat transfers. This investigation has been established as a result of the numerous industrial applications mentioned above.

Enhanced heat storage and heat transfer performance of wood-based biomass carbonized skeleton loaded with polyethylene glycol phase change material by surface modification

Thermal energy storage technology can shift the peak and fill the valley of heat, which lays the foundation for realizing the goal of “emission peak and carbon neutrality”. Among various thermal energy storage techniques, the latent heat storage technology based on composite phase change materials can provide large storage capacity with a small temperature variation, and shows great potential in solving the intermittency issue of renewable energy. As a sustainable and renewable material, natural wood has the advantages of a unique anisotropic three-dimensional structure, perfect natural channel, low price, and rich resources. Therefore, the carbonized wood obtained from high-temperature carbonization of natural wood is an excellent choice as a supporting skeleton of composite phase change materials. On the other hand, polyethylene glycol is widely used in energy storage because of its suitable phase transition temperature (46–65℃), high latent heat (145–175 J/g), and stable performance. In this study, carbonized bamboo is prepared at high temperatures. To improve heat storage, thermal conductivity, and photo-thermal conversion properties, the carbonized bamboo is functionalized by graphene oxide and reduced graphene oxide, respectively. Finally, polyethylene glycol is implanted into modified carbonized bamboo to form shape-stabilized phase change materials. Their microstructures, morphologies, and thermophysical properties are characterized. The experimental results show that graphene oxide and reduced graphene oxide can change the surface polarity of carbonized bamboo, thus reducing the interfacial thermal resistance between the carbonized bamboo skeleton and polyethylene glycol, and improving the encapsulation ratio, thermal conductivity, and photo-thermal conversion efficiency without affecting the crystallization behavior of polyethylene glycol. The encapsulation ratio of carbonized bamboo/reduced graphene oxide/polyethylene glycol ternary phase change material is as high as 81.11% (only 4.67% lower than the theoretical value), its latent heat of melting and solidification are 115.62 J/g and 104.39 J/g, its thermal conductivity is greatly increased to 1.09 W/(m·K) (3.7 times that of pure polyethylene glycol), accompanied by substantial growth in its photo-thermal conversion efficiency, reaching 88.35% (3.1 times that of pure polyethylene glycol). This research develops a biomass-derived porous composite phase change material with high heat storage density, high heat transfer rate, and high photo-thermal conversion ability.

WSe2 nanowires-based nanofluids for concentrating solar power

Tungsten selenide belongs to the family of inorganic compounds denominated transition metal dichalcogenides (TMDCs). There is emerging interest in these compounds in the field of optoelectronics, catalysis, sensing or energy storage, among others. Most works focus on the use of these materials in their 2D form but there is scarce research on the study of TMDCs nanomaterials with one-dimensional morphology. In this work, we explore the thermophysical properties of nanofluids based on 1D-WSe2 nanostructures with the aim of studying the feasibility of these nanofluids as heat transfer fluids in concentrating solar power plants. In this respect, nanofluids with a high heat transfer rate could increase the thermal efficiency of solar power plants, which would reduce the energy dependence on fossil fuels. Nanofluids of 0.02 wt%, 0.05 wt% and 0.10 wt% WSe2 concentrations have been prepared by the two-step method considering a thermal fluid used in solar power plants as the base fluid. The results of extinction coefficient evolution, ζ potential and particle size in suspension show a high colloidal stability over time of the prepared nanofluids mainly because of the high aspect ratio of the 1D-WSe2 nanomaterial. Additionally, the one-dimensionality and length of the synthesized nanowires favors the transport of heat in controlled directions, obtaining increases in thermal conductivity with respect to the base fluid of up to 16.8% in the highest concentration nanofluid. Improvements in isobaric specific heat of up to 15.7% and heat transfer of up to 20.8% compared to the base fluid have also been found. The results of this paper provide evidence that the presence of WSe2 nanowires induces increases in the thermal properties of the fluid commonly used in concentrating solar power plants without inducing agglomeration or sedimentation problems. Therefore, the nanofluids based on 1D-WSe2 nanostructures prepared in this work have a high potential to be used as heat transfer fluids in concentrating solar power plants based on parabolic trough collectors.

Ferrohydrodynamics Mixed Convection of a Ferrofluid in a Vertical Channel with Porous Blocks of Various Shapes

Numerical simulations of (water-Fe3O4) ferrohydrodynamics (FHD) mixed convection inside a vertical channel are performed. The magnetic field is produced by three sources positioned outside the channel’s right wall. The latter is provided with localized heat sources surmounted by variously shaped porous blocks: rectangular, trapezoidal, and triangular. The general model of Darcy-Brinkman-Forchheimer is employed to describe the fluid flow in the porous regions, and the resulting equations are numerically solved by the finite volume approach. The influence of significant parameters, including the magnetic number (Mn), the Richardson number (Ri), and the shape of blocks, is examined. The results essentially reveal that the enhanced heat transfer brought by the magnetic field and its intensity increase is suppressed by the augmentation of Ri until a critical value, rising with Mn, beyond which the global Nusselt number increases again. The mean friction coefficient increases with increased Mn and reduced Ri. Compared to the case with no magnetic field, the maximum enhancement in heat transfer rate is around 132% for the rectangular blocks, 146% for the trapezoidal blocks, and 160% for the triangular blocks, while the maximum increase in pressure drop is approximately 45% for all the shapes. The triangular shape seems the most efficient because it leads to high heat transfer rates and low mean friction coefficients; its performance factor is 2.32 for a dominant magnetic field and 2.62 for a dominant buoyancy force. The current research's conclusions will help optimize the operation of various thermal engineering systems, including electronic devices, where the improved heat removal rate will keep the electronic components at a safe operating temperature.

Thermal and thermodynamic optimization of the performance of a large aperture width parabolic trough solar collector using gaseous and supercritical CO2 as heat transfer fluids

• A coupled optical-thermal-fluid model of a parabolic trough collector is developed. • sCO 2 exhibits better thermal and thermodynamic performance compared to gaseous CO 2. • sCO 2 has comparable thermal performance relative to Therminol-VP1 above 80 bar. • Flow rates above 300 m 3 /h give receiver temperature gradients lower than 50°C. • New correlations for optimal thermal and thermodynamic performance are presented. The degradation of thermal-oil-based working fluids in parabolic trough solar collectors (PTSCs) systems at temperatures above 400 °C has accelerated the search for cost-effective and efficient heat transfer fluids (HTFs) for high-temperature applications. Carbon dioxide is abundant and has the potential to be used as a working fluid in PTSCs. In this work, the performance of a larger aperture width PTSC with CO 2 as the working fluid (either in gaseous or supercritical phase) is investigated. In this study, a PTSC system with an aperture width of 9 m (geometric concentration ratio of 113) was considered. The operating pressure is in the range of 40−100 bar, the HTF inlet temperatures are between 650 and 1000 K, and the flow rate varies from 32.6 to 653 m 3 /h. A thoroughly verified and validated computational model using a combination of Monte-Carlo ray tracing and computational fluid dynamics was used for the numerical study. In addition, the Realizable k- ε model was used for turbulence modeling. The results show that CO 2 at 80 bar has comparable thermal performance relative to current thermal oil-based HTFs. Results further show that supercritical CO 2 (sCO 2 ) has the best thermal performance compared to gaseous CO 2 . In addition, the entropy generation minimization method was used to determine the Reynolds number that minimizes the irreversibilities at a given operating pressure. At low pressures, much higher flow rates are required to achieve high heat transfer rates and reduce temperature gradients in the absorber tube. Furthermore, correlations have been developed for the optimal Reynolds numbers at which the entropy generation rate is minimum and the collector efficiency is maximum.

Magnetized Tri-hybrid Nanofluids flow with binary Chemical Reaction and activation Energy through the porous Surfaces

Hybrid nanofluids are important to researchers because of their industrial applications due to their high heat transfer rates. Tri hybrid different types of nanoparticles are discussed here with Newtonian fluids under the effect of MHD. The most important chemical reaction associated with mass transfer and activation energy parameters hasbeen discussed in detail. The current research focuses on two-dimensional fluids with heat transfer enhancement flowing over a porous surface. The mathematical modeling of the problem, as well as empirical relations for nanoparticle materials, is expressed as PDEs, which are then translated into ODEs using appropriate variables. The Runge–Kutta and shooting methods are combined to solve the problems of the created coupled differential system. Variations in nanoparticle volume fraction at the lower and upper walls of porous plates, as well as heat transfer rate measurements, are computed using controlling physical factors. The impact of flow-related variables on the axial, radial, and temperature components of velocity and temperature distribution is also assessed.

Investigation of Spirals Rectangular and Rectangular Tubes Collector Design in Photovoltaic Solar Cell Cooling Systems

As the primary basis for electricity production, fossil fuels continue to decline. Solar Photovoltaic (PV) can be developed by utilizing solar energy. However, solar PV has low efficiency due to overheating from solar irradiation. This article analyzed forced convection Sunwatt 50Wp solar PV water cooling to lower the PV temperature and increase efficiency. The heat exchanger uses a spiral and rectangular configuration mounted on the back of the Sunwatt 50Wp solar PV panel with water flow. Sunwatt 50Wp solar PV testing using a solar simulator at an intensity of 470 W/m2, 625 W/m2, 870 W/m2, and 1000 W/m2. The test results show a decreased working temperature on spiral cooling at all intensities compared to solar PV without cooling. This impacts the low-performance value of solar PV without cooling. The intensity of 1000 W/m2 has a high value due to the release of electrons from the atoms in the cell. These results impact increasing electricity efficiency in Sunwatt 50Wp solar PV by cooling. At high intensity, the temperature increases causing the ability to increase efficiency to decrease. However, water cooling can increase electrical efficiency because the particles are evenly distributed in the heat exchanger, which causes a high heat transfer rate.

Three-dimensional coupled flow and heat transfer in non-newtonian magnetic nanofluid: An application of Cattaneo-Christov heat flux model

This article has been fine-tuned with studying the three-dimensional laminar flow of a magnetic liquid over a stretching sheet with the influence of thermal radiation and Cattaneo-Christov heat flux. Moreover, this article mainly focuses on moderate saturation magnetization and low Curie temperature. The dynamics of propylene glycol –paraffin wax nanofluid + water mixture and zinc oxide (ZnO)-SAE50 Nano-lubricant fluid flow is examined. The modeling equations are converted into non-linear ordinary differential equations (ODEs) using the required similarity transformations. The Runge-Kutta-Fehlberg fourth-to-fifth order (RKF-45) technique is used to solve the resultant non-linear ODEs numerically. Numerous regulating factors that affect the velocity and temperature profiles are examined via graphs. Research of the present study has shown that Deborah number accounts for the decelerating radial and tangential flow of both nanolubricant and nanofluids. The ZnO-SAE50 Nano-lubricant flow shows high heat transfer and increases faster followed by propylene glycol – water mixture + paraffin wax nanofluid flow for the increase in values of radiation parameter. The ZnO-SAE50 Nano-lubricant flow shows high heat transfer rate than propylene glycol–water mixture-based nanoliquid for rising values of radiation parameter.

Numerical Analysis of Lid Driven Convective Heat Transfer and Fluid Flow around a Tilted Elliptical Cylinder

A study of the heat transport and fluid flow behaviour around a tilted elliptical cylinder that is located concentrically in a square enclosure whose top horizontal wall is driven by a lid in the positive x-direction is presented. Due to the disparities in the results of convective heat transfer in square cavities in the literature, this study seeks to investigate the combined effects of the Grashof number, Aspect ratio of the geometry, and Elliptical cylinder inclination angle on the dynamics of thermal and flow fields within the geometry investigated. COMSOL Multiphysics 5.5 version was used to resolve the non-dimensional transport equations, while simulations were performed to examine the implications of salient parameters such as the elliptical inclination angle , Grashof number and aspect ratio . The simulation outcomes are displayed as average Nusselt numbers, velocity streamlines, and isothermal contours. Findings from this study show that an increase in aspect ratio resulted in increased heat transfer at the elliptical cylinder wall, with the highest rate of heat transfer occurring when .0. Furthermore, the inclination angle increments when Gr= and led to a reduction in the average Nusselt number of the elliptical cylinder wall. At and AR ranges of , the value of the elliptical cylinder wall increased as the ellipse's inclination angle increased. The findings of this study have found use in heat transfer systems, particularly electronic cooling and nuclear technologies.

Opposed-flow flame spread over carbon fiber reinforced plastic with different carbon fiber orientations

Herein, carbon fiber reinforced plastic (CFRP) sheets with different carbon fiber (CF) orientations were combusted in an environment of variable opposed-flow velocity (Vg) and oxygen concentration, and the effects of the CF orientation angle (θ) on the flame spread characteristics were studied. The limiting oxygen concentration increased with θ and linearly decreased with increasing Vg. The flame spread rate (Vf) was the highest when the CF orientation corresponded to the flame spread direction (i.e., θ = 0 deg.) and increased with Vg. Conductive heat transfer sideways became more significant as θ increased, which signifies increased heat loss. Thus, the net heat transfer rates that directly contributed to the flame spread decreased, leading to low flammability and weak flame spread. Vf was calculated using our previous CFRP flame spread model. The calculated Vf was higher than the measured Vf, and the difference between them increased as Vg increased. This is because the flame height (Hf) decreased considerably with increasing Vg, resulting in high heat transfer rate from the flame and high Vf. The Hf model was thus revised based on the dataset of the opposed-flow flame spread tests; then, the calculated Vf agreed well with the measured Vf. The Vf for the buoyant-flow flame spread assuming Vg = 35 cm/s was also calculated using the flame spread model with the original and revised Hf models, and no significant difference was noted between the calculated and measured Vf. Thus, this study succeeded in improving the CFRP flame spread model to deal with both the opposed-flow flame spread and the buoyant-flow flame spread. This revised model will help understand the physics of the flame spread over CFRP sheets and assess the fire risk of CFRP products for fire safety.

Elektrikli Araçlarda Kullanılan Paralel ve Seri Kanallı Soğutma Plakalarının Performanslarının HAD Yöntemi ile Karşılaştırılması

In a cold plate low thermal resistance thus high heat transfer rate and also low pressure drop is desired. In this study, performances of three liquid cold plates with different configurations are investigated for the thermal regulation of li-ion battery cells in electric vehicle applications. The outer dimensions of the cold plates are kept identical in order to use the cold plates in the same battery module under series, parallel and series-parallel configurations. The performances of the cold plates are investigated by using Computational Fluid Dynamic (CFD) tools. ANSYS Fluent commercial software is used to calculate the flowfield and the thermal field inside the cold plates for various flowrates. The performances of the cold plates are obtained by 3D simulations that solve Navier-Stokes, energy and continuity equations in a steady manner. The flow is assumed to be laminar for all the cases since calculated Reynolds number stay in laminar flow limits. The results show that the pressure drop of the coolant liquid of parallel flow arrangement is significantly lower than the serial arrangement. However, high thermal resistance and low uniformity of the temperature through the cold plate is observed compared to the serial case, as expected. As a result, series-parallel configuration results show that the trade-off between pressure drop and heat transfer rate can be optimized by applying a serpentine shape while keeping the flow arrangement as parallel as possible and increasing the length of the cross channels.

Scrutinization of Stefan suction/blowing on thermal slip flow of ethylene glycol/water based hybrid ferro-fluid with nano-particles shape effect and partial slip

This study is aimed to examine thermal slip flow of mixture based hybrid ferro-fluid with shape effect of nano-particles and partial slip under the constant influence of Stefan suction/blowing impacts. Thermal slip flow is magnetized with applied time-dependent magnetic force in transverse direction of flow. Partial slip impact is considered on magnetized hybrid ferro-fluid. Additionally, spherical shaped nano-particles have been accounted to constitute the desired hybrid ferro-fluid whereas distinct shape nano-particle effect is analyzed and discussed for heat transfer efficiency. The flow governing highly nonlinear equations are transformed into ordinary differential equations using suitable similarity transform. Furthermore, motion and temperature profile for spherical shaped nano-particles of hybrid ferro-fluid are analyzed and discussed under the impression of suction and blowing effect. It is observed that in the event of mass suction S=1 and partial slip 0.2≤Sf≤0.6 reduced shear stress rates and high rates of heat transfer are obtained. It is concluded that high Lorentz force under suction/blowing effect contract thermal boundary of flow. Laminar shape nano-particle increase temperature profile when compared with other shapes of nano-particles.

Contribution degree analysis of phase change capsule size in packed bed

The phase change capsule packed bed has been widely studied by many scholars because of its simple structure and high heat transfer rate. This study aims to obtain the effect of phase change capsule size on the thermal properties of the packed bed and the variation of the contribution degree in the heat storage process. In this paper, three three-dimensional models of heat storage packed beds with different phase change capsules sizes are established and the thermal storage process is numerically simulated by Fluent. The simulation results are compared with the experimental results, and the results are in good agreement. By monitoring the temperature of the heat transfer fluid (HTF), the temperature of the phase change material (PCM), and the liquid phase fraction in the packed beds with different phase change capsule sizes, the indicators for characterizing thermal characteristics of heat storage devices, such as heat storage rate, heat storage density, instantaneous energy efficiency, and exergy efficiency, can be calculated. The comparative analysis shows that the thermal properties of the packed bed improve as the capsule size decreases. Then the contribution degree of phase change capsule size to the heat storage process of the packed bed is obtained by the chain rule. Results indicated that as the phase change capsule size decreases, its contribution degree increases gradually. Still, the degree of increase decreases, and the gain from the change in capsule size decreases. The contribution degree of the phase change capsule size is also numerically less than that of the inlet mass flow and temperature. In general, with the decrease of the phase change capsule size, the thermodynamic performance of the packed bed and the contribution degree of the phase change capsule size increase significantly, but the power consumption and cost of packed beds increase.