Search Results (7)

Particle-reinforced metals are being developed for advanced heat dissipation applications. However, an irregularly shaped void develops during eutectic solidification and enhances interfacial stress induced by visco-plastic deformation in temperature gradient conditions. An analytical solution to an irregularly shaped coated hole embedded in an infinite substrate under an arbitrarily located heat source or sink is presented. For a coated polygonal hole with any number of edges, a rapidly convergent series solution of the temperature and stress functions is expressed in an elegant form using conformal mapping, the analytic continuation theorem, and the alternation method. The iterations of the trial-and-error method are utilized to obtain the solution for the correction terms. First, temperature contours are obtained to provide an optimal suggestion that a larger thermal conductivity of the coating layer exhibits better heat absorption capacity. Furthermore, interfacial stresses between a coating layer and substrate increase if the strength of a point thermal singularity and thermal mismatch increases. This study provides a detailed explanation for the growth of an irregular void at an ambient temperature gradient. Full article

The current investigation aims to analyze the nanofluid flow between two infinite rotating horizontal channels. The lower plate is porous and stretchable. The impact of physical parameters such as Hall current, thermal characteristics, heat source/sink, chemical reaction on velocity, temperature, and concentration profiles are discussed through graphs. The governing equations are transformed to ordinary differential equations using suitable transformations and then solved numerically using the RK4 approach along with the shooting technique. For varying values of the Schmidt number (SN) and the chemical reaction factor (CRF), the concentration profile declines, but decreases for the activation energy. It is observed that the velocity profile declines with the increasing values of the suction factor. The velocity profile increases when the values of the rotation factors are increased. The temperature field exhibits a rising behavior with increasing values of the thermophoresis factor, Brownian motion, and the thermal radiation factor. It is also observed that the heat transfer rate is significant at the lower wall with the increasing values of the Prandtl number (PN). For the numerical solution, the error estimation and the residue error are calculated for the stability and confirmation of the mathematical model. The novelty of the present work is to investigate the irregular heat source and chemical reaction over the porous rotating channel. A growing performance is revealed by the temperature field, with the increase in the Brownian motion (BM), thermophoresis factor (TF), thermal conductivity factor (TCF), and the radiation factor (RF). Full article

Heat and mass transfer due to a magneto micropolar fluid flow along a semi-infinite vertical plate bounded by a porous medium are investigated in presence of induced magnetic field. In case of cooling flow, heat and mass fluxes from the plate are subjected to be constant under the action of a constant heat sink. Mathematical model related to the problem is developed from the basis of studying magnetohydrodynamics (MHD) for both lighter and heavier particles. Dimensionless model of momentum, microrotation, induction, energy and concentration equations are solved simultaneously by the explicit scheme of finite difference technique. According to the obtained stability and convergence criteria of this transient flow, very negligible time step (Δt = 0.002) compared to the existing works has been taken to perform the numerical computation. Quantities of chief physical interest of the flow as shear stress, couple stress, current density, Nusselt number and Sherwood number are also studied here. The numerically computed results are compared with published results of available research works. Interestingly an excellent agreement is found with finite difference solutions in both explicit and implicit schemes. In order to discuss the physical aspects of the problem, the flow variables for different values of associated parameters are illustrated in graphs. Finally, important findings of the study are listed as concluding remarks. Full article

Waste heat recovery is an actual goal. The best way to valorize waste heat is to use it directly with the appropriate level of temperature. If the temperature level is insufficient, many reverse machine configurations are available in order to obtain the appropriate conditions (the most known are heat pumps and heat transformers). Finally, the remaining unused heat could be converted to any noble form of energy (mechanical, electrical essentially). We propose here to examine, with a new point of view, the thermomechanical conversion limit of waste heat. This limit corresponds to adiabatic conversion for an endo-reversible Carnot engine, with a perfect thermal contact at the atmospheric sink (supposed infinite). The Carnot–Chambadal model version is applied to latent and sensible heat recovery cases. The results associated with these two cases differ fundamentally. Comments are provided on the two studied cases, and new criteria to characterize the corresponding waste heat recovery are proposed. Full article

The aim of this current contribution is to examine the rheological significance of Maxwell fluid configured between two isothermal stretching disks. The energy equation is also extended by evaluating the heat source and sink features. The governing partial differential equations (PDEs) are converted into the ordinary differential equations (ODEs) by using appropriate variables. An analytically-based technique is adopted to compute the series solution of the dimensionless flow problem. The convergence of this series solution is carefully ensured. The physical interpretation of important physical parameters like the Hartmann number, Prandtl number, Archimedes number, Eckert number, heat source/sink parameter and the activation energy parameter are presented for velocity, pressure and temperature profiles. The numerical values of different involved parameters for skin friction coefficient and local Nusselt number are expressed in tabular and graphical forms. Moreover, the significance of an important parameter, namely Frank-Kamenetskii, is presented both in tabular and graphical form. This particular study reveals that both axial and radial velocity components decrease by increasing the Frank–Kamenetskii number and stretching the ratio parameter. The pressure distribution is enhanced with an increasing Frank–Kamenetskii number and stretching ratio parameter. It is also observed that thetemperature distribution increases with the increasing Hartmann number, Eckert number and Archimedes number. Full article

Energy consumption for heating and cooling constitute the majority of the energy use for building loads. Using passive cooling systems to reduce the energy consumption or to make the process more efficient can be very beneficial. Ground coupled heat exchangers and night sky radiative cooling systems have been used for centuries to achieve cooling and ice making. Ground coupled heat exchangers use the temperature difference between underground soil and ambient air or water for heat transfer between the soil and the fluid passing through buried pipes. Night sky radiative cooling takes advantage of the night sky as the coldest heat sink available for heat transfer with any surface. Use of these simple designs with the modern cooling/heating systems has the potential for a major impact on the heating and cooling needs. This review paper describes the various designs, configurations and applications of these systems as well as determining the parameters that impact their performance. Full article

The purpose of this work is to precise and complete one recently proposed in the literature and relative to a general criterion to maximize the first law efficiency of irreversible heat engines. It is shown that the previous proposal seems to be a particular case. A new proposal has been developed for a Carnot irreversible thermomechanical heat engine at steady state associated to two infinite heat reservoirs (hot source, and cold sink): this constitutes the studied system. The presence of heat leak is accounted for, with the most simple form, as is done generally in the literature. Irreversibility is modeled through , created internal entropy rate in the converter (engine), and , total created entropy rate in the system. Heat transfer laws are represented as general functions of temperatures. These concepts are particularized to the most common heat transfer law (linear one). Consequences of the proposal are examined; some new analytical results are proposed for efficiencies. Full article