Jet impingement heat transfer within a hemisphere
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ORIGINAL
Jet impingement heat transfer within a hemisphere Derwalt J. Erasmus1
¨ 1 · Matti Lubkoll1 · Theodor W. von Backstrom
Received: 15 February 2020 / Accepted: 29 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Jet impingement heat transfer finds applications where a large heat flux is required between a fluid and a surface. Impinging jets can be implemented in Concentrating Solar Power (CSP) thermal receivers and bayonet tube heat exchangers. A simultaneous outlook on the heat transfer and total pressure loss (performance) characteristics of several jets impinging on a concave hemispherical surface are investigated experimentally and using an axisymmetric Reynolds averaged Navier Stokes (RANS) Computational Fluid Dynamics (CFD) model. The four equation Transition SST RANS turbulence CFD model demonstrates to be most suitable for this domain with a mean absolute deviation from the experimental results of < 7% for the heat transfer coefficient and < 8% for the total pressure loss. Empirical correlations for the Nusselt number as a function of the nozzle outlet Reynolds number and Prandtl number are fitted. Relatively good agreement is found between the Nusselt correlation and existing literature. An empirical correlation is also presented for the total pressure loss factor for the jet impingement domain in general because it is found that the dominating total pressure loss occurs because of rapid expansion, which occurs in any impinging free jet. The developed empirical correlations and CFD model can be used to estimate the heat transfer and pressure loss characteristics of a bayonet tube heat exchanger, a solar thermal receiver employing impinging jets as well as other jet impingement domains. Keywords Jet impingement heat transfer · Concave surface · Conjugate heat transfer · Bayonet tube heat exchanger Nomenclature A Area (m2 ) d Nozzle diameter (m) D Impingement surface diameter (m) fd Darcy friction factor (-) h Heat transfer coefficient (W/(m2 K)) k Thermal conductivity (W/(m K)) k Turbulence kinetic energy (m2 /s2 ) L Jet to impingement surface distance (m) m ˙ Mass flow rate (kg/s) Nu Nusselt number (-) p Pressure (Pa) Pr Prandtl number (-) ˙ Q Heat rate (W) q˙ Heat flux (W/m2 ) r Surface radius from stagnation point (m) Re Reynolds number (-) Derwalt J. Erasmus
[email protected] 1
Solar Thermal Energy Research Group (STERG), Department of Mechanical and Mechatronic Engineering, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa
T TI u y+ ε μ ξ ρ ω
Temperature (◦ C) Turbulence intensity (-) Velocity (m/s) Dimensionless distance from a wall (-) Roughness constant (-) Dynamic viscosity (kg/(m s)) Loss coefficient (-) Density (kg/m3 ) Specific turbulence dissipation rate (1/s)
Subscripts al Aluminium cond Condensation dyn Dynamic exp Expansion es Exterior heat transfer surface fg Latent heat is Interior heat transfer surface l Liquid n Nozzle sat Saturation sph Sphere t Total
Heat Mass Transfer
tc v
Total, component Vapour
1 In
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