Augmented Heat Transfer in a Triangular Duct by Using Multiple Swirling Jets

1999 ◽  
Vol 121 (3) ◽  
pp. 683-690 ◽  
Author(s):  
J.-J. Hwang ◽  
C.-S. Cheng
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Swirling Flow ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Wall Jets ◽  
Flow Reynolds Number ◽  
Flow Phenomena ◽  
Target Wall ◽  
Inlet Angle

Measurements of detailed heat transfer coefficients on two principal walls of a triangular duct with a swirling flow are undertaken by using a transient liquid crystal technique. The vertex corners of the triangular duct are 45, 45, and 90 deg. The swirl-motioned airflow is induced by an array of tangential jets on the side entries. The effects of flow Reynolds number (8600 ≦ Re ≦ 21000) and the jet inlet angle (α = 75, 45, and 30 deg) are examined. Flow visualization by using smoke injection is conducted for better understanding the complicated flow phenomena in the swirling-flow channel. Results show that the heat transfer for α = 75 deg is enhanced mainly by the wall jets as well as the impinging jets; while the mechanisms of heat transfer enhancement for α = 45 and 30 deg could be characterized as the swirling-flow cooling. On the bottom wall, jets at α = 75 deg produce the best wall-averaged heat transfer due to the strongest wall-jet effect among the three angles (α) investigated. On the target wall, however, the heat transfer enhancements by swirling flow (α = 45 and 30 deg) are slightly higher than those by impinging jets (α = 75 deg). Correlations for wall-averaged Nusselt number for the bottom and target walls of the triangular duct are developed in terms of the flow Reynolds number for different jet inlet angles.

Experimental Investigation of Local Heat Transfer Distribution on Smooth and Roughened Surfaces Under an Array of Angled Impinging Jets

2001 ◽  
Author(s):  
Lamyaa A. El-Gabry ◽  
Deborah A. Kaminski
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Cross Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Roughened Surface

Abstract Measurements of the local heat transfer distribution on smooth and roughened surfaces under an array of angled impinging jets are presented. The test rig is designed to simulate impingement with cross-flow in one direction which is a common method for cooling gas turbine components such as the combustion liner. Jet angle is varied between 30, 60, and 90 degrees as measured from the impingement surface, which is either smooth or randomly roughened. Liquid crystal video thermography is used to capture surface temperature data at five different jet Reynolds numbers ranging between 15,000 and 35,000. The effect of jet angle, Reynolds number, gap, and surface roughness on heat transfer efficiency and pressure loss is determined along with the various interactions among these parameters. Peak heat transfer coefficients for the range of Reynolds number from 15,000 to 35,000 are highest for orthogonal jets impinging on roughened surface; peak Nu values for this configuration ranged from 88 to 165 depending on Reynolds number. The ratio of peak to average Nu is lowest for 30-degree jets impinging on roughened surfaces. It is often desirable to minimize this ratio in order to decrease thermal gradients, which could lead to thermal fatigue. High thermal stress can significantly reduce the useful life of engineering components and machinery. Peak heat transfer coefficients decay in the cross-flow direction by close to 24% over a dimensionless length of 20. The decrease of spanwise average Nu in the crossflow direction is lowest for the case of 30-degree jets impinging on a roughened surface where the decrease was less than 3%. The decrease is greatest for 30-degree jet impingement on a smooth surface where the stagnation point Nu decreased by more than 23% for some Reynolds numbers.

Experimental Investigation of the Effects of Fluid Properties and Geometry on Forced Convection in Finned Ducts With Flow Pulsation

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
B. O. Olayiwola ◽  
P. Walzel
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Pulsation ◽  
Transfer Coefficients ◽  
Glycerol Water ◽  
Heat Transfer Intensification ◽  
Heat Transfer Coefficients ◽  
Flow Reynolds Number ◽  
Fluid Properties ◽  
Convective Heat Transfer Coefficients

An experimental study was conducted on the effects of flow pulsation on the convective heat transfer coefficients in a flat channel with series of regular spaced fins. Glycerol-water mixtures with dynamic viscosities in the range of 0.001–0.01 kg/ms were used as working fluids. The device contains fins fixed to the insulated wall opposite to the flat and smooth heat transfer surface to avoid any heat transfer enhancement by conduction of the fins. Pulsation amplitude xo=0.37 mm and pulsation frequencies f in the range of 10 Hz<f<47 Hz were applied, and a steady-flow Reynolds number in the laminar range of 10<Re<1100 was studied. The heat transfer coefficient was found to increase with increasing Prandtl number Pr at a constant oscillation Reynolds number Reosc. The effect of the dh/L ratio was found to be insignificant for the system with series of fins and flow pulsation due to proper fluid mixing in contrast to a steady finned flow. A decrease in heat transfer intensification was obtained at very low and high flow rates. The heat transfer was concluded to be dynamically controlled by the oscillation.

Condensation of R134a Flowing Inside Horizontal and Vertical Helicoidal Pipe

1999 ◽  
Author(s):  
H. J. Kang ◽  
C. X. Lin ◽  
M. A. Ebadian
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Water Flow ◽  
Heat Transfer Characteristic ◽  
Cooling Water ◽  
Transfer Characteristic ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Mass Fluxes ◽  
Flow Reynolds Number

Abstract Condensing heat transfer characteristic of an ozone-friendly refrigerant HFC-R134a (Hydrofluorocarbon R134a) flowing inside a 12.7mm helicoidal tube was investigated experimentally to obtain heat transfer data and correlations. For this long helicoidal pipe at horizontal and vertical helicoidal positions, heat transfer measurements were performed for the refrigerant flow mass fluxes from 100 to 400 kg/m2/s, in the cooling water flow Reynolds number range of 1500 &lt; Rew &lt; 9000 at fixed system temperature (33°C) and cooling tube wall temperature (12°C and 22°C). Experimental results show that, with the increase of mass flux, the overall condensing heat transfer coefficients of R134a increase. However, with the increase of mass flux (or the cooling water flow Reynolds number), the refrigerant side heat transfer coefficients decrease. The effects of cooling wall temperature on heat transfer coefficients were considered. Predictive correlations valid over the above water flow Reynolds number ranges and refrigerant flow mass fluxes were proposed. Helicoidal pipe heat transfer characteristics were compared with data from literature reports for horizontal straight tube. Experimental results show that helicoidal pipe, especially at horizontal position, conducts a much better heat transfer characteristic than that of horizontal tube even it was grooved. The helicoidal pipe’s position plays a very great role on heat transfer characteristic with 100 percent higher results at a horizontal position than that of vertical position.

scholarly journals Effect of Integrating Metal Wire Mesh with Spray Injection for Liquid Piston Gas Compression

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3723
Author(s):  
Barah Ahn ◽  
Vikram C. Patil ◽  
Paul I. Ro
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Metal Wire ◽  
Wire Mesh ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Gas Compression ◽  
Liquid Piston

Heat transfer enhancement techniques used in liquid piston gas compression can contribute to improving the efficiency of compressed air energy storage systems by achieving a near-isothermal compression process. This work examines the effectiveness of a simultaneous use of two proven heat transfer enhancement techniques, metal wire mesh inserts and spray injection methods, in liquid piston gas compression. By varying the dimension of the inserts and the pressure of the spray, a comparative study was performed to explore the plausibility of additional improvement. The addition of an insert can help abating the temperature rise when the insert does not take much space or when the spray flowrate is low. At higher pressure, however, the addition of spacious inserts can lead to less efficient temperature abatement. This is because inserts can distract the free-fall of droplets and hinder their speed. In order to analytically account for the compromised cooling effects of droplets, Reynolds number, Nusselt number, and heat transfer coefficients of droplets are estimated under the test conditions. Reynolds number of a free-falling droplet can be more than 1000 times that of a stationary droplet, which results in 3.95 to 4.22 times differences in heat transfer coefficients.

A computational analysis on convective heat transfer for impinging slot nanojets onto a moving hot body

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Hakan Coşanay ◽  
Hakan F. Oztop ◽  
Fatih Selimefendigil
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Unsteady Flow ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Computational Analysis ◽  
Impinging Jets ◽  
Content Type ◽  
Moving Body ◽  
Flow Effects

Purpose The purpose of this study is to perform computational analysis on the steady flow and heat transfer due to a slot nanojet impingement onto a heated moving body. The object is moving at constant speed and nanoparticle is included in the heat transfer fluid. The unsteady flow effects and interactions of multiple impinging jets are also considered. Design/methodology/approach The finite volume method was used as the solver in the numerical simulation. The movement of the hot body in the channel is also considered. Influence of various pertinent parameters such as Reynolds number, jet to target surface spacing and solid nanoparticle volume fraction on the convective heat transfer characteristics are numerically studied in the transient regime. Findings It is found that the flow field and heat transfer becomes very complicated due to the interaction of multiple impinging jets with the movement of the hot body in the channel. Higher heat transfer rates are achieved with higher values of Reynolds number while the inclusion of nanoparticles resulted in a small impact on flow friction. The middle jet was found to play an important role in the heat transfer behavior while jet and moving body temperatures become equal after t = 80. Originality/value Even though some studies exist for the application of jet impingement heat transfer for a moving plate, the configuration with a solid moving hot body on a moving belt under the impacts of unsteady flow effects and interactions of multiple impinging jets have never been considered. The results of the present study will be helpful in the design and optimization of various systems related to convective drying of products, metal processing industry, thermal management in electronic cooling and many other systems.

An Experimental Study of Heat Transfer on an Outlet Guide Vane

2014 ◽  
Author(s):  
Chenglong Wang ◽  
Lei Wang ◽  
Bengt Sundén ◽  
Valery Chernoray ◽  
Hans Abrahamsson
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Guide Vane ◽  
Incidence Angle ◽  
Boundary Layer Transition ◽  
Transfer Coefficients ◽  
Suction Surface ◽  
Layer Transition

In the present study, the heat transfer characteristics on the suction and pressure sides of an outlet guide vane (OGV) are investigated by using liquid crystal thermography (LCT) method in a linear cascade. Because the OGV has a complex curved surface, it is necessary to calibrate the LCT by taking into account the effect of viewing angles of the camera. Based on the calibration results, heat transfer measurements of the OGV were conducted. Both on- and off-design conditions were tested, where the incidence angles of the OGV were 25 degrees and −25 degrees, respectively. The Reynolds numbers, based on the axial flow velocity and the chord length, were 300,000 and 450,000. In addition, heat transfer on suction side of the OGV with +40 degrees incidence angle was measured. The results indicate that the Reynolds number and incidence angle have considerable influences upon the heat transfer on both pressure and suction surfaces. For on-design conditions, laminar-turbulent boundary layer transitions are on both sides, but no flow separation occurs; on the contrary, for off-design conditions, the position of laminar-turbulent boundary layer transition is significantly displaced downstream on the suction surface, and a separation occurs from the leading edge on the pressure surface. As expected, larger Reynolds number gives higher heat transfer coefficients on both sides of the OGV.

Cooling of a Finned Cylinder by a Jet Flow of Air

2002 ◽  
Author(s):  
F. Gori ◽  
F. De Nigris ◽  
E. Pippione ◽  
G. Scavarda
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Jet Flow ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Electric System ◽  
Heavy Trucks ◽  
Turbo Compressor ◽  
University Of Rome ◽  
The University

The paper describes a patented proposal to use jets of air in the cooling system of heavy trucks. Preliminary tests have been carried out, in the Heat Transfer Laboratory of the University of Rome “Tor Vergata”, to evaluate the heat transfer characteristics of a jet flow of air, impinging onto an externally finned cylinder. The cylinder is internally heated with an electric system. Thermocouples, located inside the cylinder, allow to measure the wall temperatures, in order to calculate the local and average convective heat transfer coefficients. A preliminary design of the practical apparatus, applied to heavy trucks, has been done in cooperation with Iveco. Nozzles are designed to be put after the fan of heavy trucks to converge air, in the form of jets, onto the tube where the charged air is flowing from the outlet of the turbo-compressor. The efficiency of the jet flow increases the cooling performances but, due to the high temperature at the outlet of the turbo-compressor, it may not be enough. The heat transfer cooling performances are enhanced if the tube to be cooled is externally finned. Some preliminary experiments have been carried out in a real scale bank test of an heavy truck engine at the Engineering Testing Laboratories Department of Iveco. Comparisons are done between the experiments and a simple theoretical model. Some conclusions are drawn about the cooling at different fluid dynamics conditions of the impinging jets.

scholarly journals Aerodynamics and Heat Transfer Investigations on a High Reynolds Number Turbine Cascade

1991 ◽  
Author(s):  
Taher Schobeiri ◽  
Eric McFarland ◽  
Frederick Yeh
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
High Reynolds Number ◽  
Test Facility ◽  
Experimental Investigations ◽  
Turbine Cascade ◽  
Calculation Methods ◽  
Transfer Coefficients ◽  
Pressure Distributions ◽  
High Reynolds

In this report the results of aerodynamic and heat transfer experimental investigations performed in a high Reynolds number turbine cascade test facility are analyzed. The experimental facility simulates the high Reynolds number flow conditions similar to those encountered in the space shuttle main engine. In order to determine the influence of Reynolds number on aerodynamic and thermal behavior of the blades, heat transfer coefficients were measured at various Reynolds numbers using liquid crystal temperature measurement technique. Potential flow calculation methods were used to predict the cascade pressure distributions. Boundary layer and heat transfer calculation methods were used with these pressure distributions to verify the experimental results.

scholarly journals Highly Resolved Distribution of Heat Transfer for Turbine Leading Edge Film Cooling Including Reynolds Number and Blowing Rate Effects

1998 ◽  
Author(s):  
K. Jung ◽  
D. K. Hennecke
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Heat Mass Transfer ◽  
Leading Edge ◽  
Transfer Coefficients ◽  
Complex Flow ◽  
Long Distance ◽  
Naphthalene Sublimation Technique

The effect of leading edge film cooling on heat transfer was experimentally investigated using the naphthalene sublimation technique. The experiments were performed on a symmetrical model of the leading edge suction side region of a high pressure turbine blade with one row of film cooling holes on each side. Two different lateral inclinations of the injection holes were studied: 0° and 45°. In order to build a data base for the validation and improvement of numerical computations, highly resolved distributions of the heat/mass transfer coefficients were measured. Reynolds numbers (based on hole diameter) were varied from 4000 to 8000 and blowing rate from 0.0 to 1.5. For better interpretation, the results were compared with injection-flow visualizations. Increasing the blowing rate causes more interaction between the jets and the mainstream, which creates higher jet turbulence at the exit of the holes resulting in a higher relative heat transfer. This increase remains constant over quite a long distance dependent on the Reynolds number. Increasing the Reynolds number keeps the jets closer to the wall resulting in higher relative heat transfer. The highly resolved heat/mass transfer distribution shows the influence of the complex flow field in the near hole region on the heat transfer values along the surface.

MEMS Impinging-Jet Cooling

2000 ◽  
Author(s):  
Qiao Lin ◽  
Shuyun Wu ◽  
Yin Yuen ◽  
Yu-Chong Tai ◽  
Chin-Ming Ho
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Jet Impingement ◽  
Impinging Jet ◽  
Impinging Jets ◽  
Measured Temperature ◽  
Transfer Coefficients ◽  
Element Analysis ◽  
Heat Transfer Coefficients ◽  
Jet Cooling

Abstract This paper presents an experimental investigation on MEMS impinging jets as applied to micro heat exchangers. We have fabricated MEMS single and array jet nozzles using DRIE technology, as well as a MEMS quartz chip providing a simulated hot surface for jet impingement. The quartz chip, with an integrated polysilicon thin-film heater and distributed temperature sensors, offers high spatial resolution in temperature measurement due to the low thermal conductivity of quartz. From measured temperature distributions, heat transfer coefficients are computed for single and array micro impinging jets using finite element analysis. The results from this study for the first time provide extensive data on spatial distributions of micro impinging-jet heat transfer coefficients, and demonstrate the viability of MEMS heat exchangers that use micro impinging jets.

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