In this study, thermal-hydraulic performance of a confined slot jet impingement with Al2O3-water nanofluid has been numerically investigated over Reynolds number ranges of 100-1000. Two triangular ribs are mounted at a heated target wall; one rib located on the right side of the stagnation point and another one located on left side of the stagnation point. The governing momentum, continuity and energy equations in the body-fitted coordinates terms are solved using the finite volume method and determined iteratively based on SIMPLE algorithm. In this study, effects of Reynolds number, rib height and rib location on the thermal and flow characteristics have been displayed and discussed. Numerical results show an increase in the average Nusselt number and pressure drop when Reynolds number and rib height increases. In addition, the pressure drop and average Nusselt number increases with decrease the space between the stagnation point and rib. The maximum enhancement of the average Nusselt number is up to 39 % at Reynolds number of 1000, the rib height of 0.3, rib location of 2 and nanoparticles volume fraction of 4%. The best thermal-hydraulic performance of the impinging jet can be obtained when the rib height of 0.2 and rib location of 2 from the stagnation point with 4% nanoparticles volume fraction.
Enhancing the hydrothermal performance of plate-fin microchannels heat sink (PFMCHS) promises smaller size and lighter weight, and then improve the heat removal in consequently increase the speed of electronic devices. In this numerical study, an innovative hydrothermal design of PFMCHS is suggested by inserting elliptic pins inside microchannels in different; aspect ratio (AR) of pin, pin number ratio (ψ) in order to optimize the hydrothermal design of this kind of heat sinks. The main objectives of this study are; investigating the effect of pins on the performance of PFMCHS by investigating the best geometry in the pinned-fin MCHS and which is higher, thermal or hydraulic performance of this kind of heat sinks and what is the optimal number of pins numerically and what about the pressure drop penalty in the proposed design, little, modest or high increase. It is seen that the thermal resistance of the pinned fin MCHS is about 50% lower, and pressure drop of it is much higher than that of the (PFMCHS) under the condition of equal wind velocity. Maximum mechanical fan power reduction obtained is about 57% for the pinned fin MCHS with ψ = 1 and Dh = 1 ×10-3 m compared to the corresponding original channel heat sink. To show the overall performance of the two parameters; aspect ratio (AR), pin number ratio (ψ), the overall JF factor is estimated and the concrete findings shows that the best hydrothermal performance is obtained at the greater aspect ratio which is around overall JF = 1.2. In addition, the trend of overall JF is going down with the pin number ratio, starting from 1.2 to 1.15. And the concrete findings show that pinned fin MCHS provides thermal performance of 1.42 times greater than the smooth one under the corresponding conditions when one pin is used in each channel
In this paper, the hydraulic-thermal performance of a double-pipe heat exchanger equipped with 45°-helical ribs is numerically studied. The ribbed double-pipe heat exchanger is modelled using three heights (H = 0, 2.5, 3.75, 5 mm) of 45°-helical ribs. Two numbers (4-ribs and 8-ribs) of 45°-helical ribs are attached on the outer surface of the inner pipe of the counter-flow double-pipe heat exchanger and compared with a smooth double-pipe heat exchanger. Three-Dimensional computational fluid dynamics (CFD) model for a laminar forced annular flow is performed in order to study the characteristics of pressure drop and convective heat transfer. In addition, the influence of rib geometries and hydraulic flow behaviour on the thermal performance is system-atically considered in the evaluations. The annular cold flow is investigated with the range of Reynolds numbers from 100 to 1000, with three heights of ribs at the same width (W = 2 mm) and inclined angles of (θ = 45°).The results illustrate that the average Nusselt number and pressure drop increase with an in-creasing number of ribs, the height of ribs and Reynold number, while the friction factor decreas-es with increasing Reynolds numbers. The percentage of averaged Nusselt number enhancement for three rib heights (H = 2.5, 3.75 and 5 mm) at 4-ribs is (34%, 65% and 71%), respectively, While for 8-ribs the enhancement percentage is (48%, 87% and 133%) as compared with the smooth double-pipe heat exchanger at Re = 100. The best performance evaluation criteria of (PEC) at (8-ribs, and H = 5 mm) is 2.8 at Re = 750. The attached 45-helical ribs in the annulus path can generate kind of secondary flows, which enhance the fluid mixing operation between the hot surface of the annular gap and the cold fluid in the mid of the annulus, which lead to a high-temperature distribution. Increasing the height of 45°-helical ribs lead to an increase in the sur-face area subjecting to convective heat transfer.
In this paper, turbulent convective heat transfer in a triangular-ribbed chan-nel has been numerically investigated. SiO2-water with nanoparticles volume fraction of 4% and nanoparticles diameters of 30 nm is employed with Reyn-olds number ranging from 2000 to 8000. The governing continuity, momen-tum and energy equations in addition to low Reynolds number k-ε model have been transformed into body-fitted coordinates system and then solved using finite volume method. The effects of Reynolds number and rib heights on Nusselt number, pressure drop, thermal-hydraulic performance factor and entropy generation are presented and discussed. It is observed that the Nusselt number, pressure drop and thermal performance increase with in-creasing of Reynolds number and rib height. In addition, the highest perfor-mance factor can be obtained at Reynolds number of 6500 and rib height of 1.5 mm.
Numerous inserts types are employed in different heat transfer improvement application devices. In this review study is forced on various types of twisted tape inserts in heat exchanger pipe. Geometrical configurations of twisted tape for example twist direction; length, width, space, twist ratio etc. were highly effect on flow pattern, hydrodynamic flow and heat transfer performance. In this review study observed that using different types of twisted tapes can improve thermal performance and hydrodynamic as compared to smooth pipe (without twisted tape). The review investigations found that improvement of thermal performance happens owing to decrease in pipe cross area, leads to rise in mixing flow, turbulence flow intensity flow and rise in swirl flow established through different kinds of twisted tapes. This article dealt with investigations pub-lished in corrugated pipes with varying field applications to provide good information for engi-neers and designers whom dealing and concerning with improvement of heat performance in heat exchanger corrugated pipes.
Flow of crude oil in pipelines suffers from a problem of fluid flow pressure drop and high energy consumption for fluid pumping. Flow can be enhanced using either viscosity reduction or drag reduction techniques. Drag reduction (DR) is considered as a most effective and most applicable method. The technique contributes in reducing the frictional energy losses during the flow by addition of little amounts from drag reducing agents. The present work focuses on preparation and application of a new natural and low cost material derived from palm fiber (PF) that has been tested as a drag reducing agent (DRA) for crude oil flow enhancement. This objective has been achieved through designing and constructing of an experimental rig consisting of: a crude oil pipe, oil pump, pressure sensors, solenoid valve and programmable logic control. The additive material (PF) is prepared with different diameters (75µm, 125µm, 140µm) and tested with different concentrations as: 100, 200, 300, 400, and 500 mg/L for reducing the drag inside the oil pipe. The experimental results showed that the fiber with 125µm diameter and 100ppm is the best where the percentage of drag reduction reached 43%. Furthermore, the results of this work proved that PF is an efficient and low cost DRA that can be applied successfully in crude oil pipelines as well as its contribution in the waste management.
This article presents a numerical study on forced convection of nanofluid flow in a two-dimensional channel with trapezoidal baffles. One baffle mounted on the top wall of channel and another mounted on the bottom wall of channel. The governing continuity, momentum and energy equations in body-fitted coordinates are iteratively solved using finite volume method and SIMPLE technique. In the current study, SiO2-water nanofluid with nanoparticles volume fraction range of 0- 0.04 and nanoparticles diameters of 30 nm is considered for Reynolds number ranging from 100 to 1000. The effect of baffles height and location, nanopar-ticles volume fraction and Reynolds number on the flow and thermal fields are investigated. It is found that the average Nusselt number as well as thermal hydraulic performance increases with increasing nanopartiles volume fraction and baffle height but accompanied by increases the pressure drop. The results also show that the best thermal- hydraulic performance is obtained at baffle height of 0.3 mm, locations of baffles at upper and lower walls of 10 and 15 mm, respectively, and nanoparticles volume fraction of 0.04 over the ranges of Reynolds number.
Heat exchangers are considered essential parts in many industrial applications. The construction process for heat exchangers is completely complex because accurate measurements of the penalty of pressure-drop and the rate of heat transfer are needed. Designing a compact heat exchanger with a high heat transfer rate, while utilizing the least amount of pumping power, is the main design challenge. The most recent investigations (including experimental results, numerical models, and analytical solutions) in the field of circular tube heat exchangers in general, and twisted tapes and wire coils in particular, are covered in this review article, which has more than 90 references. The enhancement techniques in heat exchangers tubes can generally be separated into three groups: active, passive, and hybrid (compound) approaches. This article reviews the literature on advancements made in passive enhancement approaches, with a specific focus on two types of passive promoters that employ twisted tapes and wire coils. The main contribution of this research is to highlight the behavior and structure of fluid flow and the heat transfer features for the twisted tapes and the wire coils. It also explains how these passive promoters can be used in circular tube heat exchangers to improve hydrothermal performance. Where, the installation of wire coils and twisted tapes considerably alters the flow pattern and aids in the improvement of heat transfer. Where, comprehending the behavior of fluid flow is crucial and contributes to the enhancement of heat transfer. Twisted tapes are less effective in turbulent flow than wire coils because they obstruct the flow, which results in a significant pressure reduction. When it comes to turbulent flow, the thermohydraulic performance of twisted tapes is lower to that of wire coils.