Heat Transfer最新文献

In recent times, bioconvection has numerous uses, like, biological and biotechnological problems. The present study describes the magnetic bioconvective Buongiorno's flow model with microorganisms in a stretchable area with convective heat transfer and second-order velocity slip in a non-Darcian porous regime. Here, the influence of variable viscosity, viscous dissipation, Joule heating, and heat source/sink are considered in the occurrence of higher-order chemical reactions. Employing proper similarity transformations leading equations are transformed to dimension-free form. The transformed equations are solved via MATLAB bvp4c problem solver. This study's main objective is to graphically analyze the effects of different pertinent factors on the density of motile microorganisms, velocity, concentration, temperature, number of motile microorganisms' density, skin friction, mass transport rate, and heat transport rate. The main findings drawn from this study are viscosity $��\left(��-�\; �5�\; �\le �\; �{\theta }_r�\; �\le �\; �-�\; �1��\; �\right)�$ and magnetic parameter $��\left(��0.5�\; �\le �\; �M�\; �\le �\; �3��\; �\right)�$ lowers the fluid velocity. Biot number $��\left(��0.4�\; �\le �\; �B_i�\; �\le �\; �0.6��\; �\right)�$

A numerical investigation of the Nusselt number, heat transfer augmentation efficiency, and friction factor in a laminar flow tube with triangular perforated nail head twisted tape (TPNHTT) is reported using ANSYS 19.2 Fluent. The effects of triangular cut (each side 3 mm) in the middle pitch of the tape along the height, diameter, and top diameter of the nail head (10, 2, and 2.5 mm, respectively) have been explored for (300 ≤ Re ≤ 1800) in a tube of 22 mm diameter. In this paper, implementation has been done with a TPNHTT varying width (14 ≤ b ≤ 20) twist ratio (TR) ranging from (3 ≤ TR ≤ 6), inserts in a tube for laminar flow. Twisted tape (TT) produces a swirl flow associated with fluid resulting in heat transfer enhancement and pressure drop characteristics other than that for the plain tube (PT). The performance of the Nusselt number and friction factor increased up to 123.62% and 495.30%, respectively, on the application of TPNHTT as compared with PT. A maximum thermal performance efficiency of 2.98 has been achieved using the twisted-tape ratio of the current tube in laminar flow at a Reynolds number of 1700. In addition, correlation equations (11) and (12) have been developed for the friction factor and Nusselt number valid for 300 ≤ Re ≤ 1800, 14 ≤ b ≤ 20, and 3 ≤ TR ≤ 6. The study has proved that applying TT is an upgraded approach for laminar convection heat transfer. This novel work finding will be supportive for researchers to design the latest heat exchangers.

In this work, an approximate solution is given to compute the gas emissivities and absorptivities for H₂O–CO₂–CO mixtures. The proposed model is valid for temperatures from 300 to 2700 K and pressure path-length $��\left(�\; �P_x�\; �L�\; �\right)�$ from 0.06 to 40 atm m. In the calculation of the analytical solution (AS), the nonlinear methods of Galerkin and Ritz were implemented based on the residual solution of the differential roots of the Finite Element Method. For each point value $��(�\; �P_x�\; �L�\; �;�\; �T�\; �)�$ using the AS, the spectral absorptivity $��a_{\lambda }�$ and emissivity $��{\epsilon }_{\lambda }�$ were determined, while for the gas mixture the emissivity $��{\epsilon }_m�$ and absorptivity $��a_m�$ were computed using the Hottel Graphical Method (HGM) and the proposed method. In the emissivity calculations, t

The effect of an internal heat source linearly dependent on the solid fraction on the onset of convection in a composite air-porous channel with vertical throughflow has been analyzed. We considered boundaries to be insulating to temperature perturbations. The governing equation that satisfies the air-porous configuration is analyzed by the normal mode approach, solved by the regular perturbation technique for linear stability, and the critical internal Darcy–Rayleigh number for the onset of stationary convection has been derived. The paper aims to analyze the effects of parameters like heat source size, depth ratio, Darcy number, throughflow direction, solid fraction, and Prandtl number on stationary convection in a composite air-porous configuration. Understanding these influences can illuminate thermal behaviors in intricate systems and inform applications in heat transfer and fluid dynamics. The observed stability configuration decreases monotonically due to increasing the effect of the depth ratio and solid fraction at any direction and velocity of the throughflow. The thermal and vertical velocity profiles and the results obtained during the analysis have been presented graphically.

The quest for augmenting dropwise condensation heat transfer performance has been the driving force behind the exploration of innovative techniques and approaches to fulfill the desired objective. Mostly, earlier research on dropwise condensation was devoted to study condensation from horizontal tubes and plates but, rarely, addressed dropwise condensation from vertical tubes. An interesting topic of current research in dropwise condensation is to explore the application of Slippery Liquid Infused Porous Surfaces (SLIPSs) to improve the condensation performance. The aforesaid facts are the motivation behind the topics of interest in the present study. In this study, we explore the applicability of semisolid lubricant-impregnated porous surfaces in enhancing dropwise condensation performance of a vertical condenser tube. The experiments conducted over a wide range of subcooling (5°C ≤ ΔT ≤ 65°C) in saturated steam environment showed significant improvement in condensation heat transfer coefficient of a vertical condenser tube impregnated with semisolid lubricants when compared to bare vertical condenser tube. The highest enhancement is found to be 280% at a subcooling of 40°C. Furthermore, these surfaces proficiently sustain dropwise condensation over a period of 72 hours without compromising heat transfer performance. The devised fabrication method is simpler, more cost-effective, and less time-consuming than earlier techniques used for creating SLIPSs. Additionally, an approach based on numerical optimization by a stochastic global optimization technique, namely, Genetic Algorithm, is proposed to retrieve the coefficients and the exponent in the mathematical expression of overall resistance, that is being used to compute the tube-side dropwise convection heat transfer coefficient.

The two-dimensional mixed convective MHD flow with heat and mass transfer is investigated for its behavior with Dufour and Soret mechanisms over the porous sheet. The copper–alumina (Cu–Al₂O₃) hybrid nanoparticles are used in the base fluid water. The governing system of partial differential equations is converted into a system of ordinary differential equations via similarity transformations, obtaining the solution for velocity, temperature, and concentration fields in exponential form. The problem is demonstrated in the Darcy–Brinkman model, the impact of included parameters such as Richardson number, magnetic field, and Dufour numbers are studied for the obtained solution with the help of graphs. Increasing the magnetic field decreases both transverse and axial velocity profiles. Increasing the magnetic field and Richardson's number decreases the solution (Al₂O₃–H₂O). Increasing the values magnetic field and Richardson's number decreases both transverse and axial velocity profiles. Increasing the values of the Dufour effect increases the axial and transverse velocity boundary layer. The magnetohydrodynamic hybrid nanofluid flow over porous media works efficiently in liquid cooling and, therefore, has significant applications in industrial heating and cooling systems, solar energy, magnetohydrodynamic flow meters and pumps, manufacturing, regenerative heat exchange, thermal energy storage, solar power collectors, geothermal recovery, and chemical catalytic reactors.

This paper presents a technique to find the closed-form solution of the boundary-value problem representing free convection flow past a vertical cone. Partial differential equations that govern the flow are converted into nonlinear ordinary differential equations with the aid of similarity transformations. First, a numerical solution is obtained with the help of the bvp4c package of MATLAB, and then utilizing the numerical solution, the closed-form solution is obtained. The accuracy of the closed-form solution is analyzed by the residual technique. Graphs of the residuals of the governing equations indicate that our approximate closed-form solution closely matches the exact solution.

The present study aims to quantify the flow field, flow velocity, and heat transfer features over a horizontal flat plate under the influence of an applied magnetic field, with a particular emphasis on low Prandtl number fluids. Nonlinear partial differential expressions can be incorporated into the ordinary differential framework with the use of appropriate transformations. This research utilizes the variational iteration method (VIM) to approximate solutions for the system of nonlinear differential equations that define the problem. The objective is to demonstrate superior flexibility and broader application of the VIM in addressing heat transfer issues, compared to alternative approaches. The results obtained from the VIM are compared with numerical solutions, revealing a significant level of accuracy in the approximation. The numerical findings strongly suggest that the VIM is effective in providing precise numerical solutions for nonlinear differential equations. The analysis includes an examination of the flow field, velocity, and temperature distribution across various parameters. The study found that improving temperature patterns, velocity distribution, and flow dynamics were all positively impacted by increasing the Prandtl numbers. As a result, this leads to the thickness of the boundary layer to decrease and improves heat transfer at the moving surface. Thus, the convection process becomes more efficient. When the strength of the magnetic field is increased, the velocity of the fluid decreases. This observation aligns with expectations since the magnetic field hampers the natural flow of convection. Notably, the convection process can be precisely controlled by carefully applying magnetic force.

The current investigation focuses on examining viscous corrections for viscous potential flow (VCVPF) analysis concerning the Rayleigh–Taylor instability occurring at the interface of a Rivlin–Ericksen (R–E) viscoelastic fluid and a viscous fluid during the transfer of heat and mass between phases. The R–E model is a fundamental framework in the study of viscoelastic fluids, providing insights into their complex rheological behavior. It characterizes the material's response to both deformation and flow, offering valuable predictions for various industrial and biological applications. Within the framework of viscous potential flow (VPF) theory, viscosity is exclusively accounted for in the normal stress balance equation, disregarding the influence of shearing stress entirely. This study introduces a viscous pressure term into the normal stress balance equation alongside the irrotational pressure, presuming that this addition will improve the discontinuity of tangential stresses at the fluid interface. Through derivation of a dispersion relationship and subsequent theoretical and numerical stability analyses, the stability of the interface is investigated across various physical parameters. Multiple plots are generated using the dispersion relation, and a comparative analysis between VPF and VCVPF is conducted to establish improved stability criteria. The investigation highlights that the combined impact of heat/mass transport and shearing stress serves to delay the instability of the interface.

This study explores the effectiveness of periodically placed rotating blades in enhancing heat transfer in a channel. The channel consists of a cold top plate moving at a constant speed and a fixed hot plate at the bottom. Thin rotating blades are placed periodically along the channel's centerline, with the spacing between their axes equal to the channel's height. This paper analyzes a transient, two-dimensional, laminar flow problem using energy, momentum, and continuity equations. To address the challenges posed by moving blades, the Galerkin finite element method is implemented within an arbitrary Lagrangian–Eulerian framework, employing a triangular mesh discretization scheme. This study comprehensively explores thermal and hydrodynamic characteristics, including overall heat transfer, thermal frequency, and power consumption of the rotating blade for heat transfer in mixed convection scenarios with Richardson numbers (Ri) ranging from 0.1 to 10 at varying rotational frequency of the blade. Outcomes demonstrate that the inclusion of a rotating blade increases heat transfer up to 50% at lower Ri, after which the impact of the rotating blade diminishes and heat transfer reduces up to 20% at higher Ri. In addition, heat transfer enhances with increasing blade frequency up to Ri = 6.5, beyond which the effect of the frequency overturns. Examining thermal and hydrodynamic characteristics reveals that the blade achieves optimal performance when operating at f = 1 and Ri = 3. The study's insights into mixed convection heat transfer offer versatile applications, benefiting industries and equipment such as electronic cooling, chemical reactors, food processing, material fabrication, solar collectors, and nuclear reactor systems. Moreover, the findings are instrumental in the thermal ventilation of buildings and the development of micro-electromechanical systems.