Condensation of steam on the underside of a horizontal surface in the presence of air and helium

Abstract

Experinonts and data analysis for the condensation of steam on the underside of a horizontal surface in a closed vessel are described. Previously reported results for fflrs condense lion with <tir as a noncondensable gas are reviewed and compared with new data with helium .is the noncondensable in the sane apparatus. Observations, including photographs of the condensate configurations, related to the occurrence of drop-vise condensation are also discussed. It is noter? that data reproducthiiiiy over long periods of time wore possible only with film, rondeir-ation and that with rfrepwise condensation condensing surface temperatures exhibited large nonunffornities and randcrc fluctuations with titsn. The well known mass transfer calculatJonal node! for accounting for the presence of noncondensable f;ases had been shown previously to be successful with air. The sane nodci when applied to the helium data was not successful except for small gas contents. It appears that the suppression of convection that would be expected to occur with the less dense gas is counteracted by convection induced by fog or mist formation.

Theoretical and experimental analysis of a horizontal planar Liquid-Vapour Thermal Diode (PLVTD)

“…For sensible convective heat transfer through vapour within a horizontal PLVTD of the form shown in Figure 2 ( Stein et al (1985) and Peterson (1996). Equations 18 to 20 can be used in cases where all non-condensable gases have been removed such that the PLVTD cavity exists at the working fluid saturation pressure (PLV) corresponding to the average temperature T12 = (T1+T2)/2.…”

“…In the case of vapour flowing due to phase changes, the effective thermal conductivity (k of Equation 11) has both sensible vapour (kv) and latent (kLv) components which can be quantified using Equation 19 and 20. Heat transfer due to condensation on the underside of the top plate during forward mode operation (relevant to evaluation of Rc) can be evaluated using Equations 21 and 22 which are based on expressions given by Gerstmann & Griffith (1967) and by Stein et al (1985). The difference in the liquid and vapour densities (L and v) plays an important role in both expressions alongside the liquid kinematic viscosity (vL), surface tension (L), and thermal conductivity (kL).…”

“…An inherent bias is apparent in the data causing the model to consistently overpredict the heat transfer coefficients by +20% relative to the measured data. There are a number of possible reasons for this bias but the most likely explanation is the presence of non-condensable gasses (air) in the PLVTD which increases thermal resistances associated with vapour mass transfer (Rec) and condensation (Rc) as described by Stein et al (1985) and Peterson (1996). This explanation is consistent with the fact that measured pressures (Pmeas) were in some cases up to 25% higher than the estimated saturation pressures (PLv(HCCH)) as apparent in results towards the right of Figure 8.…”

Vertical Planar Liquid-Vapour Thermal Diodes (PLVTD) and their application in building façade energy systems

“…Condensation occurring on the surface of a flat plate will create a downward flowing film of condensate. Equations describing condensate flows across vertical and tilted plates are based on expressions given by Cengel & Boles (2006) whereas equations relevant to droplet flows from downwards-facing horizontal surfaces are based on expressions given by Stein et al (1985) and Gerstmann & Griffith (1967). Key parameters include the saturated fluid-to-plate temperature difference (TLv-T2), gravitational acceleration (g), plate tilt angle (), plate height dimension (z), condensate film Rayleigh and Reynolds numbers (Rac and Rec), and various temperature dependent working fluid thermodynamic properties including latent heat of evaporation (hLv) and saturated vapour pressure (PLv).…”

“…The latent component (kLv) is determined using Equation 18based upon the latent heat of phase change (hLv), thermal diffusivity (ϑ), working fluid molar mass (ℳ), and universal gas constant (ℛ). Equations 16 to 18 are based upon expressions proposed by Pugsley (2017) drawing upon the work of Stein et al (1985) and Peterson (1996) and can be used in cases where all non-condensable gases have been removed from the PLVTD cavity to enable the working fluid to exist in a mixed phase state close to the saturation pressure (PLv) corresponding to the saturation temperature (TLv) which can be evaluated using the iterative procedure proposed in Section 2.6. All working fluid thermodynamic properties (k, v, Pr, ϑ, , )…”