A novel evaluation regarding the influence of surface emissivity on radiative and total heat transfer coefficients in radiant heating systems by means of theoretical and numerical methods

• Enclosure models for radiant heating are designed at different dimensions.
• The models have different surface emissivities as well as boundary conditions.
• Theoretical and computational methods are used to calculate coefficients.
• The ratio of the radiation phenomenon in the total heat transfer is found to be 65%.
• New correlations for convective and total heat transfer coefficients are derived.

In the present study, we investigate by means of theoretical calculations and the program Engineering Equation Solver (EES) total and radiative heat transfer coefficients in an enclosure heated from its one wall at several surface emissivities (ɛ = 0.90, 0.85, 0.80), with room dimensions (L × H × W = 1.8 × 2.85 × 1.8, 3 × 2.85 × 3, 3 × 2.85 × 4, 4 × 2.85 × 3, 6 × 2.85 × 6 m) and surface temperatures (Th = 20–40 °C, Tc = 5–15 °C, Tf = 14–31 °C and Tceil = 10–27 °C). To understand the influence of convection through computational methods in the aforementioned conditions, we performed numerical procedures and found a correlation including the aspect ratio influence (H/L). Afterward, through the tables and figures, we show that the average radiative coefficient lies within the range of 5.4–5.5 W/m2 K and varies very slightly with room dimensions and temperature differences at practical applications at the surface emissivity value of 0.9, which is a close value to a surface emissivity practically. Furthermore, we found the total heat transfer coefficient to be between 10.2 and 10.8 W/m2 K for the emissivity value of 0.9, and we observed that it did not significantly vary with room dimensions. Additionally, similar to the experimental literature results, we found that the average proportion of radiation to the total heat transfer was between 64% and 67%.