Numerical study on condensation heat transfer of trapezoid grooved surfaces

Abstract

This article presents a numerical analysis and experimental study on condensation heat transfer and fluid flow for filmwise condensation on trapezoid grooved surfaces. First, a physical model was properly simplified based on some reasonable assumptions. Then, the coupled non-linear governing equations for the mass transfer, fluid flow, and twodimensional thermal conduction were developed. The relationship between z-coordinate and heat transfer was obtained by solving the equations numerically. The influences of groove length and basic angle were discussed. The calculation results showed that the heat flux decreased with increase in groove length, and the decline range also decreased gradually. The calculation results also suggested that the heat flux through groove with a = 60°was lower than the groove with a = 75°at the top of the groove, while the opposite conclusion was obtained at the low parts. The distributions of wall temperature and heat flux on trapezoid groove were also studied systematically. The distribution of surface temperature and heat flux presents obvious lateral inhomogeneity, and the maximum wall temperature and heat flux were both obtained in region II. The thermal resistance of groove with a = 60°was lower but the liquid-discharged ability was better than that of groove with a = 75°. In order to validate the feasibility and reliability of the present analyses and to further investigate the heat transfer performance of trapezoid grooved surfaces, experiments were carried out with three condensing plates including two trapezoid grooved surfaces in different physical dimensions and one smooth surface. The experimental data obtained under various schooling were compared with the calculations, and the experimental results for different condensing plates are all in good agreement with the numerical model, with a maximum deviation less than 15%. Moreover, the trapezoid grooves can enhance the condensation heat transfer by 1.5-2.5 times higher than the smooth surface. The present analyses are feasible and can be used in the parameter design and heat transfer calculation of trapezoid grooved surfaces.

Enhancement of natural and forced convection condensation using three-dimensional extended structures

“…The use of extended surfaces to enhance external condensation of steam on vertical plates has been widely investigated. For instance, Qi et al [41,136] conducted experimental and theoretical studies on two-dimensional trapezoidal and involuted grooves whereas theoretical predictions of condensation on two-dimensional triangular grooves with and without drainage strips were reported by Maschmann and Ma [135]. In order to evaluate the thermal performances of the SLM fabricated pin fin structures, a comparison of the q'' values between specimen C2 and the enhanced surfaces reported in Refs.…”

“…In order to evaluate the thermal performances of the SLM fabricated pin fin structures, a comparison of the q'' values between specimen C2 and the enhanced surfaces reported in Refs. [41,135,136] at various ΔT is shown in Fig. 5-25.…”

“…For comparison against other enhanced surfaces, the grooved areas of the enhanced surfaces in Refs. [41,136] were estimated and their 2 values were converted to the condensation heat fluxes based on the specimen base area (q'') and presented in Fig. 5-25.…”

“…The better heat transfer performance of C2 as compared to Refs. [41,135,136] could likely be due to the larger surface tension forces induced by the conical geometry of the C2 fin. This is because the C2 fin is a three-dimensional structure which induces surface tension forces in two principal directions as compared to only one principal direction for the two-dimensional grooved surface.…”

“…On the other hand, the condensation heat fluxes of the enhanced surfaces ( 2 ) presented by Qi et al[41,136] …”