Heat and Mass Transfer between Impinging Gas Jets and Solid Surfaces
TL;DR: In this article, the authors present a comprehensive survey emphasizing the engineering applications and empirical equations, presented for the prediction of heat and mass transfer coefficients within a large and technologically important range of variables.
Abstract: Publisher Summary Heating or cooling of large surface area products is often carried out in devices consisting of arrays of round or slot nozzles, through which air impinges vertically upon the product surface. This chapter presents a comprehensive survey emphasizing the engineering applications and empirical equations, presented for the prediction of heat and mass transfer coefficients within a large and technologically important range of variables. The local variations of the transfer coefficients are based on the experimental data for single round nozzles (SRN), arrays of round nozzles (ARN), single slot nozzles (SSN), and arrays of slot nozzles (ASN). The variation of local transfer coefficients is graphically represented. It also explores how to apply these equations in heat exchanger and dryer design as well as in optimization. The flow field of impinging flow is diagrammatically represented. External variables influencing heat and mass transfer in impinging flow depends on mass flow rate, kind and state of the gas and on the shape, size, and position of the nozzles relative to each other and to the solid surface. The design of high-performance arrays of nozzles is also discussed.
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TL;DR: In this article, the authors derived a correlation for the Nusselt number of the form suggested by this evidence using a selection of the data and showed that this exponent should be a function of nozzle-to-plate spacing and of the radial displacement from the stagnation point.
1,030 citations
TL;DR: In this paper, heat transfer characteristics of single and multiple isothermal turbulent air and flame jets impinging on surfaces are reviewed, and the effect of crossflow on impingement heat transfer is included.
935 citations
TL;DR: In this article, a review of recent impinging jet research publications identified a series of engineering research tasks that are important for improving the design and resulting performance of impinging jets: (1) clearly resolve the physical mechanisms by which multiple peaks occur in the transfer coefficient profiles, and clarify which mechanism(s) dominate in various geometries and Reynolds number regimes.
Abstract: Publisher Summary This chapter presents a discussion on jet impingement heat transfer. The chapter describes the applications and physics of the flow and heat transfer phenomena, available empirical correlations and values they predict, and numerical simulation techniques and results of impinging jet devices for heat transfer. The relative strengths and drawbacks of the Reynolds stress model, algebraic stress models, shear stress transport, and v 2 f turbulence models for impinging jet flow and heat transfer are compared in the chapter. The chapter provides select model equations as well as quantitative assessments of model errors and judgments of model suitability. The review of recent impinging jet research publications identified a series of engineering research tasks that are important for improving the design and resulting performance of impinging jets: (1) clearly resolve the physical mechanisms by which multiple peaks occur in the transfer coefficient profiles, and clarify which mechanism(s) dominate in various geometries and Reynolds number regimes, (2) develop a turbulence model, and associated wall treatment if necessary, that reliably and efficiently provides time-averaged transfer coefficients, (3) develop alternate nozzle and installation geometries that provide higher efficiency, meaning improved Nu profiles at either a set flow or set blower power, and (4) further explore the effects of jet interference in jet array geometries, both experimentally and numerically. This includes improved design of exit pathways for spent flow in array installations.
693 citations
Cites background or methods from "Heat and Mass Transfer between Impi..."
...Martin [2] Single slot nozzle, orifice or pipe Nuavg 3,000pRep 90,000 2pH/(2B)p10...
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...7, H/D 1⁄4 6 will deliver an average Nu of 19 over a circular target spanning six jet diameters, while at Re 1⁄4 100,000 the average Nu on the same target will reach 212 [2]....
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...First, simple correlations such as those supplied by Martin [2] (with a summary in [1]) predict Nu as a function of the governing parameters in cases where the fluid has a continuously laminar flow (Rejeto1,000, Rewallo10,000) over the entire fluid and target region of interest....
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...Martin [2] Array of slot nozzles, orifice or pipe Nuavg 1,500pRep 40,000 1pH/(2B)p40...
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...The boundary layer within the wall jet begins in the stagnation region, where it has a typical thickness of no more than 1% of the jet diameter [2]....
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TL;DR: In this article, the authors examined the local heat transfer characteristics of air jet impingement at nozzle-plate spacings of less than one nozzle diameter using an infrared thermal imaging technique.
553 citations
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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
TL;DR: In this paper, it was shown that some seemingly anomalous heat transfer phenomena can be explained as effects of the intense and spatially varying turbulence inherent in jets, which can be used to explain the heat transfer properties of impinging jets.
608 citations
395 citations
TL;DR: In this paper, the mean velocity distribution of the incompressible, turbulent, plane wall-jet has been examined in some detail with the aid of a hot-wire anemometer.
Abstract: With the aid of a hot-wire anemometer, the mean velocity distribution of the incompressible, turbulent, plane wall-jet has been examined in some detail. As previously reported, this fully developed boundary layer belongs to the class of self-preserving flows. Over the entire range of experimental conditions, a single velocity scale , the Boussinesq exchange coefficient e, and the shear stress at the wall have been evaluated. The Reynolds number based on the maximum velocity and the thickness of the boundary layer varied from 22,000 to 106,000.
250 citations