Evaluation of candidate strategies for the estimation of local heat transfer coefficient from wall jets
TL;DR: In this article, the authors reported results of experimental investigations on planar and three-dimensional wall jets over a flat surface and the local heat transfer coefficient was estimated at transient conditions.
Abstract: This paper reports results of experimental investigations on planar and three-dimensional wall jets over a flat surface. The local heat transfer coefficient is estimated at transient conditions wit...
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TL;DR: In this article, the thermal and flow measurement of a multiple-orifice synthetic jet involving circular, square, and rectangular orifice shapes was performed using an infrared camera and consta...
Abstract: Present experimental study reports the thermal and flow measurement of multiple-orifice synthetic jet involving circular, square, and rectangular orifice shapes. Here, an infrared camera and consta...
15 citations
TL;DR: In this paper, the authors reported the results of experimental and numerical studies to understand the heat transfer characteristics of three-dimensional wall jets exiting from a single and a row of circular jet openings over an unheated flat plate.
15 citations
TL;DR: In this paper, fluid flow and heat transfer characteristics of 3D wall jets exiting from a circular and square opening are presented based on experimental investigations, and the effect of the jet diameter on the local and the spanwise-averaged Nusselt number is most pronounced near the jet exit.
Abstract:
In this work, fluid flow and heat transfer characteristics of three-dimensional (3D) wall jets exiting from a circular and square opening are presented based on experimental investigations. Two hydraulic diameters, namely, 2.5 and 7.5 mm and a Reynolds number range of 5000–20,000 have been considered. Mean velocity and turbulence intensity distribution in the walljet are quantified using a hot wire anemometry. Measurements are done both along the streamwise and spanwise directions. Transient infrared thermography is used for mapping the temperatures over the surface, and the heat transfer coefficients are estimated using a semi-infinite approximation methodology. Results show that, for circular jets, the effect of the jet diameter on the local and the spanwise-averaged Nusselt number is most pronounced near the jet exit. Further, it is also observed that circular jets have an edge over square jets. A correlation with a high correlation coefficient of 0.95 has been developed for spanwise average Nusselt number as a function of the Reynolds number and the dimensionless streamwise distance.
12 citations
TL;DR: In this article, steady-state experiments are conducted under the laminar forced convection heat transfer mode for cooling of seven asymmetric IC chips (heat sources) mounted at different positions on the substructure.
Abstract: Steady-state experiments are conducted under the laminar forced convection heat transfer mode for the cooling of seven asymmetric IC chips (heat sources) mounted at different positions on the subst...
11 citations
TL;DR: In this article, the effect of the sidewall on the thermal characteristics of a 3D turbulent wall jet with a square nozzle is explored experimentally and the mean and fluctuating quantities are presented through temperature decay, thermal half widths and temperature fluctuation.
8 citations
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TL;DR: In this article, a new technique is described for measuring the axial mass flow rate in the turbulent jet formed when a gas in injected into a reservoir of stagnant air at uniform pressure.
Abstract: A new technique is described for measuring the axial mass flow rate in the turbulent jet formed when a gas in injected into a reservoir of stagnant air at uniform pressure. The jet is surrounded by a porous-walled cylindrical chamber, and air is injected through the wall until the pressure in the chamber is uniform and atmospheric, a condition which is taken to signify that the ‘entrainment appetite’ of the jet is satisfied.Measurements made with the apparatus have allowed the deduction of an entrainment law relating mass flow rate, jet momentum, axial distance and air density, regardless of the injected gas, and including the effects of buoyancy. When the injected gas burns in the jet the entrainment rate is up to 30% lower than when it does not.
1,093 citations
"Evaluation of candidate strategies ..." refers background or methods in this paper
...Additionally, it can be observed that the peak turbulent intensity value is higher for lower Reynolds number and this phenomena is due to significance of the entrainment of ambient, which is higher for lowerReynolds numbers [38] (see Figure 14a)....
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...This is due to the increased entrained mass flow rate compared to the jet exit flow rate at lower Reynolds number [38, 39] resulting in higher turbulent intensity values for Re = 2000 as observed in Figure 14a....
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TL;DR: In this article, the authors considered the flow due to a jet spreading out over a plane surface, either radially or in two dimensions, and obtained a similarity solution for laminar flow.
Abstract: This paper considers the flow due to a jet spreading out over a plane surface, either radially or in two dimensions Solutions of the boundary layer equations are sought, according to which the form of the velocity distribution across the jet does not vary along its length For laminar flow, such a similarity solution is obtained explicitly For turbulent flow, an eddy viscosity is introduced, and it is eventually seen that complete similarity is not attainable, but that confident predictions can nevertheless be made about the nature of the velocity distribution and the rate of growth of the wall jet
899 citations
"Evaluation of candidate strategies ..." refers background in this paper
...Glauert [1] reported the results of a theoretical study on the hydrodynamic nature of a incompressible planar wall jet with constant physical properties in both laminar and turbulent flow conditions....
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02 Jan 1973
TL;DR: In this article, the first of several AGARDographs was used to deal with instrumentation techniques used in hypersonic short-duration facilities and with related topics, and a detailed analysis of the errors in the values of heat-transfer rate deduced from the observations was given.
Abstract: : This is the first of several AGARDographs commissioned by the Fluid Dynamics Panel to deal with instrumentation techniques used in hypersonic short-duration facilities and with related topics. Since one of the reasons for the development of such facilities was the need for experimental data on the extremely high heat-transfer rates that a body experiences in re-entry conditions, the measurement of heat transfer constitutes a particularly appropriate initial subject area; moreover, the methods to be described are also applicable to a variety of problems other than those of hypersonic flow. An important feature of this AGARDograph is the unified treatment that it accords to the theory underlying heat-transfer gauges of various types. In addition, a detailed analysis is given of the magnitude of the errors in the values of heat-transfer rate deduced from the observations. Constructional considerations are discussed fully; physical data and design charts are included.
478 citations
"Evaluation of candidate strategies ..." refers background in this paper
...In practice, semi-infinite assumption is valid only if the time (t) required for performing the experiments is less than the time (τ) at which the change in the temperature of the bottom surface is 10% of the (T(x,t)-Ti) [27, 28]....
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TL;DR: The turbulent wall jet, even limiting attention to the topologically simple cases beloved of academics, arguably provides more puzzles for those seeking an ordered set of rules to describe turbulence than any other class of turbulent shear layer as discussed by the authors.
Abstract: The turbulent wall jet, even limiting attention to the topographically simple cases beloved of academics, arguably provides more puzzles for those seeking an ordered set of rules to describe turbulence than any other class of turbulent shear layer. Formally, we can regard a wall jet as a boundary layer in which, by virtue of the initially supplied momentum, the velocity over some region in the shear layer exceeds that in the free stream. Wall jets are of great and diverse engineering importance. While some of the best known and most challenging applications lie in the field of advanced airfoil design, these aerodynamic roles are far outweighed in number and, probably, in economic importance by the use of wall jets in problems of heating, cooling or ventilating-areas where traditionally design has proceeded unfettered by any deep concern about the turbu lence structure of the flows in question. Two major industrial applications are the film-cooling of the lining walls of gas-turbine combustion chambers and of the leading stages of
438 citations
"Evaluation of candidate strategies ..." refers background in this paper
...Launder and Rodi [9, 10] reviewed various experimental and numerical studies on the flow behavior and free shear layer of planar wall jets....
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...In Figure 15a the rate of half jet growth is observed to be lower compared to the planar wall jet and the slope is found to be 0.046, which is similar to the value reported by Launder and Rodi [9]....
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TL;DR: There have been well over two hundred experimental studies published on the turbulent wall jet as mentioned in this paper, of which about one half have been prompted by heat transfer considerations and in most of these cases the flow field has been insufficiently well documented to merit close attention for the present purpose.
282 citations
"Evaluation of candidate strategies ..." refers background or result in this paper
...046, which is similar to the value reported by Launder and Rodi [9]....
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...075, respectively, and they are in good agreement with the value reported in previous studies [9, 14] for turbulent planar wall jets....
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...Launder and Rodi [9, 10] reviewed various experimental and numerical studies on the flow behavior and free shear layer of planar wall jets....
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...In Figure 15a the rate of half jet growth is observed to be lower compared to the planar wall jet and the slope is found to be 0.046, which is similar to the value reported by Launder and Rodi [9]....
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