Conventional Impinging Jet Research Articles

Flow and Heat Transfer Characteristics of a Swirling Impinging Jet Issuing from a Threaded Nozzle of 45 Degrees

In order to achieve uniform and effective impingement cooling, a swirling jet with a swirling angle of 45° (SIJ 45°) is put forward in this paper. Namely, there are four 45° spiral grooves equipped on the inner wall of the circular hole. The difference in the flow field and heat transfer characteristics between the conventional impinging jet (CIJ) and SIJ 45° is compared and analyzed. The spiral channels can increase the heat transfer rate and cooling uniformity because of the action of superimposed airflow. In addition, the thread nozzle brings lower pressure loss, which can reduce the airflow friction while effectively ensuring high heat transfer in the center area of the jet. An experimental system is built to investigate the heat transfer and flow characteristics of the impingement surface. Smoke flow visualization technology is used to explore the complex flow field of the CIJ and SIJ 45°, and the heat transfer rate of the target surface is analyzed based on thermocouple data. When 6000≤Re≤30,000, and 1≤h/dj≤8, the averaged Nusselt number (Nu) correlation for SIJ 45° is established, which is in good agreement with the experimental results. SIJ 45° is an effective measure to replace the CIJ, and the research herein provides some reference for designing the structure of new jets.

Heat transfer enhancement on a surface of impinging jet by increasing entrainment using air-augmented duct

Flow and heat transfer characteristics of impinging jet from pipe nozzle with air-augmented duct were experimentally and numerically investigated. The effects of air-augmented duct geometry on heat transfer enhancement were concerned. The experimental parameters included a diameter (D) and a length (L) of air-augmented duct in the range of D = 2d, 3.3d, 6d, and L = 2d, 4d, 6d where d was the inner diameter of main pipe nozzle at 17.2 mm. The distance from air-augmented duct outlet to impingement surface (S) at S = 2d, 4d and 6d were considered. The conventional impinging jet was also studied to compare the results with the case of an air-augmented duct. The result comparison was based on constant jet mass flow rate by fixing the jet Reynolds number of conventional pipe at Re = 20,000. The temperature distributions on the impingement surface were measured by using a thermal infrared camera, and profiles of velocity and turbulence intensity of the jet were measured by using hot-wire anemometer. The 3-D numerical simulation with SST k-ω turbulence model was also applied to reveal the flow characteristics. The results show that the heat transfer rate on the impingement surface for the case of an air-augmented duct in conditions of 2d ≤ D ≤ 4d and L = 2d is noticeably higher than the case of conventional impinging jets due to increasing air entrainment. The heat transfer rate for the case of D = 6d, L = 2d at S = 2d, is the largest by getting 25.42% higher compared to a conventional impinging jet.

Numerical study of turbulent annular impinging jet flow and heat transfer from a flat surface

This paper presents the results of a numerical investigation of fluid flow and heat transfer due to a turbulent annular jet impingement on an isothermally heated flat surface. Annular impinging jets enhance the heat transfer and spread it more uniformly over the impingement surface compared to the round impinging jet, and have one noteworthy characteristic of forming a reverse stagnation flow. A parametric numerical study for turbulent annular jet impingement is conducted for various blockage ratios (0.4–0.8) and non-dimensional jet exit-to-target plate separation distances (0.5–4.0) at a wide range of jet exit Reynolds number (5000–25,000). The numerical computation on a highly refined mesh is performed using the ANSYS Fluent commercial code and the computational process is validated against other published experimental data on similar flow and geometric configuration. In order to choose an appropriate turbulence model for the computations, the performance of few different turbulence models is evaluated based on the comparison against experimental Nusselt number distribution on the flat surface. The Realizable k-ε model was chosen over the other turbulence model in this study. There are two different distinguished critical jet-to-target plate distance for a specific blockage ratio and jet exit Reynolds number, that generates three different flow patterns. When the separation distance is large, the impinging annular jet flow patterns, defined as flow pattern-1, is comparable/similar to the flow patterns of conventional impinging round jet. For intermediate separation distance, a doughnut-shaped recirculation region develops just downstream of the annular nozzle exit and a reverse stagnation flow occurs near the domain axis and the impingement surface, which is defined as the flow pattern-2. For small separation distance, the flow diverges more to the outer side of the annular slot and a reverse stagnation flow develops, which influences the heat transfer rate on the impingement plate. This is designated as flow pattern-3. The separation distances at which the transition from one flow pattern to the other occurs are designated as Hc1 and Hc2. These critical distances are determined for each combination of the blockage ratio and the Reynolds number considered. Additionally, the heat transfer processes are analyzed and the average Nusselt number as a function of the blockage ratio and Reynolds number is calculated and presented.

Numerical study on heat transfer by swirling impinging jets issuing from a screw-thread nozzle

To achieve uniform cooling at high heat transfer rates, a novel swirler with some circumferential screw grooves was developed to generate the swirling impinging jet (SIJ). Using the RNG k-ε turbulence model, the behavior of the flow field for the impinging jet in a confined cavity was analyzed, and the effects of jet spacing, swirl angle, and Reynolds number (Re) on the target wall heat transfer characteristics of the SIJ issuing from the screw-thread nozzle were studied. The numerical results showed that the designed swirler was effective to increase the radial uniformity of heat transfer compared to a multi-channel conventional impinging jet. A good result in terms of radial uniformity of local Nusselt number (Nu) was achieved in the case of θ=60° and a suitable Re in the turbulent status for a small jet spacing of h/dj≤3.0.

Heat transfer visualization of co/counter-dual swirling impinging jets by thermochromic liquid crystal method

The objective of the experimental study is to investigate heat transfer of co/counter-dual swirling impinging jets (Co-DSIJs/C-DSIJs) on the impingement surfaces under uniform wall heat flux boundary condition. Two twisted-tapes were inserted into pipe nozzles with different arrangements: (1) each tape was twisted in the same direction as the co-dual tapes for producing co dual swirls and (2) each tape was twisted in the different directions as the counter-dual tapes for inducing counter dual swirls. The effect of the Co-DSIJs/C-DSIJs with baffles placed between the tapes for jet confinement on heat transfer was also investigated. The effects of jet Reynolds number (5000⩽Re⩽20,000), jet-to-plate spacing (1<L/D<8) and tape twist ratio (y/W=3, 4, 5 and 6) were examined. In addition, the experiments using a single swirling impinging jet (SIJ) and a conventional impinging jet (CIJ) were also carried out, for comparison. The temperature distributions on impinged surfaces were recorded via a thermochromic liquid crystal (TLC) sheet and then Nusselt number distributions were obtained by a liquid crystal thermography technique. The experimental results revealed that for all Co-DSIJs and C-DSIJs, heat transfer increased with decreasing nozzle-to-plate spacing (L/D) and increasing Reynolds number. For the Co-DSIJs and C-DSIJs without baffle, heat transfer increased with increasing twist ratio (decreasing swirl number) while the opposite trend was found for the Co-DSIJs and C-DSIJs with baffle. At similar conditions, the Co-DSIJs and C-DSIJs with baffles offered higher heat transfer than the ones without baffle, owing to the combined effect of swirling flow and jet confinement. For small jet-to-plate spacings (L/D=1 and 2), all swirling jets possessed considerably higher average Nusselt numbers than the conventional jets, at similar conditions. At large jet-to-plate spacings (L/D=4, 6 and 8), the average Nusselt numbers of the conventional and swirling jets became comparable. For the studied range, the maximum average Nusselt number of 110 was achieved by using C-DSIJs with baffle at L/D=1, y/W=3 and Re=20,000.

Production of Norfloxacin Nanosuspensions Using Microfluidics Reaction Technology through Solvent/Antisolvent Crystallization

Hydrophobic active pharmaceutical ingredients (APIs) are often difficult to deliver effectively because of formulation limitations. Nanosuspensions of such drugs may be used to increase bioavailability and offer a variety of delivery options including injection, inhalation, oral, and transdermal. Microfluidics reaction technology (MRT) was used successfully to produce submicrometer API suspensions via a continuous process that involves solvent/antisolvent crystallization. As proof of concept, nanosuspensions of norfloxacin (NFN), an antibacterial agent, were produced varying the key parameters of the technology. The nanosuspensions had narrow particle size distributions and median particle sizes in the range of 170−350 nm. The particle size depends on the supersaturation ratio and energy dissipation expressed as processing pressure. However, the particle size was found to be insensitive to the presence of the surfactant used. The crystalline structure of NFN was not affected by the mixing intensity but by the solvent/antisolvent system. This “bottom up” process for creating nanosuspensions was compared to a “top down” process, in which NFN nanosuspensions were created as a result of particle size reduction. It was found that the “bottom up” process was substantially more efficient and resulted in smaller particles than the “top down” process. MRT is based on an impinging jet reactor design with jet velocities and energy dissipation that is orders of magnitude higher than those of conventional impinging jet reactors. The technology provides precise control of the feed rates and the subsequent location and intensity of mixing of the reactants. It may be the best choice economically due to its process intensification character that minimizes energy requirements and the proven scalability of the reactor.

Visualization of heat transfer for impinging swirl flow

The objective of the experimental study was to visualize the temperature distribution and evaluate heat transfer rate on the impingement surface kept at a constant wall temperature boundary condition for the swirling (SIJ), multi-channel (MCIJ) and conventional impinging jet (CIJ) using liquid crystal technique. The swirling jet assembly consisted of a housing tube and a solid swirl generator insert which had four narrow slots machined on its surface. The swirl angle, θ, was set as 0°, 22.5°, 41°, 50° to change the direction and strength of the swirl in the air flow exiting the housing tube. The local Nusselt numbers of the MCIJ ( θ = 0°) were generally much higher than those of CIJ and SIJs. As the swirl angle increased, the radial uniformity of the heat transfer was seen compared to MCIJ and SIJ; the best results were for θ = 50° and the jet-to-surface distance of H/ D = 14. The location of the distance of the maximum heat transfer for the swirl angles of θ = 41° and 50° was shifted away from the stagnation point in a radial distance of nearly r/ D = 2.5. Increasing Reynolds number for same swirler angle increased the heat transfer rate on the entire surface, and increased saddle shape heat transfer distribution on the surface, but had no significant effect on the position of the individual impingement regions, but increased saddle shape heat transfer distribution on the surface. The lower Reynolds number ( Re = 10 000) and the highest H/ D = 14 gave much more uniform local and average heat transfer distribution on the surface, but decreased their values on the entire surface.

A comparison of mass transfer between a plate and submerged conventional and multichannel impinging jets

This study presents a work on the comparison of mass transfer distribution on a plate subjected to impingement by a conventional impinging jet (CIJ) and multichannel conventional impinging jet (MCIJ). The local mass transfer coefficients were measured by the electrochemical limiting diffusion current technique (ELDCT). The jet Reynolds number varied in the range of 10,950–50,800 and jet-to-plate distance 2 d–10 d, where d is the nozzle diameter. The local mass transfer values were recorded beginning from the impingement point to a radial distance of approximately 15 d. The distribution of the local mass transfer coefficients (LMTC) was compared for both jet systems.

Heat transfer from a plate impinging swirl jet

Heat transfer and flow visualization experiments were conducted to investigate the performance of swirling and multi-channel impinging jets and compare the results with those of a multi-channel impinging jet (MCIJ) and conventional impinging jet (CIJ) for the present work at the same conditions. Swirling impinging jets (SIJs) employed the fixed blade lengths of 12.3 mm with four blades at the exit of the housing tube to divert the air flow through four narrow channels with a desired swirl angle (θ of 22.5, 41 and 50°). The MCIJ jet had the same dimensions as the SIJs, except that the narrow channels in the solid insert were vertical (θ=0°). The local and surface average Nusselt numbers of MCIJ were generally higher than those of the CIJ and SIJs. The SIJs, however, demonstrated significant improvement in radial uniformity of heat transfer compared to the MCIJ and CIJ. In the region of 2.7⩾X/D⩾0 for H/D=8 and Re=20 000, the average Nusselt number for the MCIJ was 11, 33, 72 and 98 per cent higher than that of the CIJ, θ=22.5, θ=41 and θ=50°, respectively. Copyright © 2002 John Wiley & Sons, Ltd.

Heat transfer and flow visualization experiments of swirling, multi-channel, and conventional impinging jets

Heat transfer and flow visualization experiments were conducted to investigate and compare the performance of swirling and multi-channel impinging jets with that of a conventional impinging jet (CIJ), having the same diameter at the same conditions. Swirling impinging jets (SIJs) employed a 25.4 mm long solid insert at the exit of housing tube to divert the air flow through four narrow channels along the surface of the insert, with the desired swirl angle (θ of 15, 30 and 45°). The multi-channel impinging jet (MCIJ) had same dimensions as SIJs, except that the narrow channels in the solid insert were vertical (θ = 0°). The local and surface average Nusselt numbers of MCIJ were generally much higher than those of CIJ. SIJs demonstrated large increases in both Nusselt numbers and significant enhancement in radial uniformity of heat transfer compared to MCIJ and CU; best results were for θ = 15° and jet spacing of 50.8 mm. Flow visualization experiments using smoke flow, smoke wires and water jet techniques revealed the mechanisms contributing to the higher and enhanced radial uniformity of heat transfer by SIJs. The smoke flow technique provided images of flow field between jet exit and impinged surface, while smoke wires showed details of flow field at and close to impinged surface. The water jet flow, seeded with tiny air bubbles as tracers, revealed details of flow field and induced mixing on the impinged surface.