The energy and exergy characteristics of 3D-pinned heat sink (HS) designs have been computationally compared as the second part of a three-part investigation. Different pin profiles, such as circular, square, triangular, strip and elliptic pins, and without pin HS are conducted with three different types of nanofluids-Al2O3-water, SiO2-water, and CuO-water for laminar forced convection. The concentrations of nanofluids vary from 0 to 5vol% with different Reynolds numbers ranging between 100 and 1000. The finite volume method employing the SIMPLE algorithm for a computational solution is applied to solve the Navier-Stokes and energy equations. Four criterions studies are explained-energy efficiency, exergy loss, and exergy efficiency of HSs with pressure drop. The results showed that the highest energy and exergy efficiencies are nearly 76% and 57%, respectively, for elliptic-pinned HSs using pure water, while about 82% and 62% using 5vol% of SiO2-water nanofluids. Besides, the elliptic-pinned HSs have a favorable reduction in the exergy loss, nearly 17% using 5vol% of SiO2-water nanofluids. Subsequently, the elliptic-pinned HS is recommended to apply with pure water considering the development in pressure drop required. However, the elliptic-pinned HSs could be employed with 5vol% of SiO2-water nanofluids regardless of the development in pressure drop required for thermal energy dissipation applications with more exergy efficiency and reduction of exergy loss.
The hydraulic-thermal characteristics of 3D pinned heat sink designs have been numerically compared as the first part of a three-part investigation. Five different pin geometries (circular, square, triangular, strip, and elliptic pins) and an unpinned heat sink with three types of nanofluids (Al2O3-H2O, SiO2-H2O, and CuO-H2O) are considered for laminar forced convection. The range of Reynolds number is from 100 to 1000, and volume fractions vary between 0% and 5%. The finite volume method is employed to solve the Navier-Stokes and energy equations by employing a SIMPLE algorithm for a computational solution. Three parameters are presented-the Nusselt number, the bottom temperature, and the hydrothermal performance of the heat sink with pressure drop data. The findings indicated that the overall hydrothermal performance of elliptic-pinned (EP) heat sinks produces the most substantial value of 3.10 for pure water. For different nanofluids, the SiO2-water nanofluids with EPs have the most significant hydrothermal performance. Also, this factor is enhanced with an increase in nanofluid concentration up to nearly 3.34 for 5% of SiO2-water. Consequently, applying the elliptic-pinned heat sinks is recommended with pure water for considering an increase in the pressure drop, with 5% of SiO2-water nanofluids, regardless of an enlargement of pressure drop for heat-dissipation applications.
A vehicle radiator is used for cooling down the hot working fluid with airflow passing over its flow passages and fins. The proper design of the radiator is very important due to space and weight limitations in automobiles. In this study, a numerical investigation has been conducted on the improvements, which can be obtained by implementing different porous fins in the radiator channels. The effects of different porous fin configurations with the same porous media volume on the heat transfer rate and pressure drop were investigated. The coefficient of performance values were presented for evaluating the overall performance. The investigated geometries included horizontal, vertical, corrugated, and wavy-corrugated configurations. The results showed that the corrugated pattern had the best thermal performance among these geometries while the horizontal configuration presented the lowest pressure loss, even though the best overall performance belonged to wavy-corrugated configuration. After selecting this configuration, the influence of different porous materials on the radiator performance was studied. Finally, the radiator with the optimum porous media configuration and material was compared to a conventional radiator. It was found that implementing this porous media in the radiator channels improves its overall thermal performance factor up to 237%.
In a recent work Wahed M. Hasona have analyzed the effects of Hall currents and magnetic field through a horizontal and asymmetric channel with peristaltic waves for a synovial nanofluid. The author aim was to extend some previous works. These comments has been prepared from the perspective point of view that the readers of the above mentioned paper may not be aware of the several potentially serious flawed analysis and typographical errors throughout that work. In the next few pages we will focus on some of these mistakes/typos clarifying that the obtained results should be reported as fabricated results that no one can rely upon. For this reason we wrote these comments to elaborate on some of these errors with suggested corrections for these errors to correct the literature and ensure its integrity. We first show that the mathematical formulation for the model used in this paper is not satisfactory. As a result, the obtained analytical and numerical results are inappropriate and do not match with any results for the peristaltic flow models.
This study provides analysis of a cooled Ranque-Hilsch vortex tube (RHVT) with various specifications. It shows how cooling influences energy conversion inside the RHVT and improves performance of the device in separation of hot gas from the cold stream within the fluid by presenting the temperature detachment (the temperature diminution of cold air (Delta T-c = T-i - T-c), isentropic efficiency (eta(is)), and coefficient of performance (COP) of divergent, convergent, and straight VTs. Two key parameters including hot tube length and number of nozzles for cooling and insulated cases are investigated to find out how the performance of the VT is affected by different geometry configurations under cooling conditions. These influences were researched for straight, convergent, and divergent VT separators under different flow characteristics. The optimum geometrical conditions for the cooling cases were identified. Results are indicative of positive influence of cooling for energy separation inside a VT. The quantities of Delta T-c, eta(is), and COP for the cooled RHVT are greater than uncooled RHVT for various types of VTs. Cooling the VTs leads to an increase of 12.5% in Delta T-c, 14.4% in eta(is), and 15.1% in COP when the base case was an uncooled VT.
