Search

Purpose: The purpose of this study is to study the simultaneous effect of embedded reverting microchannels on the cooling performance and mechanical strength of the electronic pieces. Design/methodology/approach: In this study, a new configuration of the microchannel heat sink was proposed based on the constructal theory to examine mechanical and thermal aspects. Initially, the thermal-mechanical behavior in the radial arrangement was analyzed, and then, by designing the first reverting channel, maximum temperature and maximum stress on the disk were decreased. After that, by creating second reverting channels, it has been shown that the piece is improved in terms of heat and mechanical strength. Findings: Having placed the second reverting channel on the optimum location, the effect of creating the third reverting channel has been investigated. The study has shown that there is a close relationship between the maximum temperature and maximum stress in the disk as maximum temperature and maximum stress decrease in pieces with more uniform distribution channels. Originality/value: The proposed structure has decreased the maximum temperature and maximum thermal stresses close to 35 and 50%, respectively, and also improved the mechanical strength, with and without thermal stresses, about 40 and 24%, respectively. [ABSTRACT FROM AUTHOR]

Purpose: In the present research, a numerical investigation is carried out to study the fluid flow and heat transfer in a double-pipe, counter-flow heat exchanger exploiting metal foam inserts partially in both pipes. The purpose of this study is to achieve the optimal distribution of a fixed volume of metal foam throughout the pipes which provides the maximum heat transfer rate with the minimum pressure drop increase. Design/methodology/approach: The governing equations are solved using the finite volume method. The metal foams are divided into different number of parts and positioned at different locations. The number of metal foam parts, their placements and their volume ratios in each pipe are sought to reach the optimal conditions. The four-piece metal foam with optimized placement and partitioning volume ratios is selected as the best layout. The effects of the permeability of metal foam on the Nusselt number, the performance evaluation criteria (PEC) and the overall heat transfer coefficient are investigated. Findings: It was observed that the heat transfer rate, the overall heat transfer coefficient and the effectiveness of the heat exchanger can be improved as high as 69, 124 and 9 per cent, respectively, while the highest value of PEC is 1.36. Practical implications: Porous materials are widely used in thermo-fluid systems such as regenerators, heat sinks, solar collectors and heat exchangers. Originality/value: Having less pressure drop than fully filled heat exchangers, partially filled heat exchangers with partitioned metal foams distributed optimally enhance heat transfer rate more economically. [ABSTRACT FROM AUTHOR]

Reduced drag, increased lift and, consequently, increased vital ratio and lift-to-drag coefficients are crucial in almost all efficient micro air vehicles. Riblet geometries use a variety of air vehicles. Further investigation on micro air vehicles is, however, necessary for enhanced development. Rectangular riblets on a rectangular micro air vehicle are computationally investigated. In this study, the governing equation of fluid flow is solved numerically; the turbulent model around the NACA S5020 airfoil section is covered by riblets either on both sides or on the upper side of the wings. Results show a difference of behavior in drag reduction due to the angle of attack on the airfoil. When the lift-to-drag coefficient of an angle of attack is at its maximum, an improvement can be observed, where lift-to-drag ratio increases, and drag decreases. Results for the two-side riblets show an increase in the lift-to-drag ratio as well; although the lift-to-drag coefficient and the drag reduction of riblets on both sides were comparatively less than that for riblets on the upside.