Conditions of Onset of Boiling in a Vertical Thermosiphon Reboiler

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An analysis of the incipience of nucleate boiling for a vertical thermosiphon reboiler was developed as a modification and extension of earlier analysis. The maximum superheat attained around the onset of boiling was taken from the wall-temperature distributions and correlated with heat flux, submergence, and physical properties of the test liquids. The results predicted from theoretical analysis are consistent with the experimental data that are available in the literature. All of the data for the eight fluids tested, each having different thermophysical properties, were correlated with a single correlation having an average absolute relative error of 21.35%. Nomenclature a1, b 1= constant used in equation of Agrawal 13 a2, b 2= constant used in equation of Ali and Alam 15 a3, b 3= constant used in equation of Kamil et al. 17 C1 = constant used in equation of Davis and Anderson 5 (C1 = 1, θ = 90 deg) C P = heat capacity, kJ/kg K hfg = latent heat of vaporization, J/(kgK) k = thermal conductivity, W/m K N = number of experimental data P = pressure, psia PrL = Prandtl number of fluid q = heat flux, W/m 2 R =g as constant, Nm/kg K r = radius, m rmax = maximum cavity radius, m rtan =c avity radius based on the tangency criterion, m S = submergence, % T = temperature, ◦ C � Ts =d egree of superheat (Tw − Ts), ◦ C � Tsub =d egree of subcooling (Ts − TL ), ◦ C y = distance perpendicular to the heated wall, m Z = distance along the test section, m δ ∗ = superheated layer thickness, m µ = viscosity, Ns/m 2 ρ = density, kg/m 3 σ = surface tension, N/m ψ =e xponent used in Eq. (11) Subscripts av g= average B = boiling b =b ubble