The Impact of Reduced Gravity on Free Convective Heat Transfer from a Finite, Flat, Vertical Plate

• Published in: Microgravity science and technology Vol. 29; no. 5; pp. 371 - 379
• Main Authors: Lotto, Michael A., Johnson, Kirstyn M., Nie, Christopher W., Klaus, David M.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.10.2017; Springer Nature B.V
• Subjects: Advection; Aerodynamics; Aerospace Technology and Astronautics; Aircraft components; Classical and Continuum Physics; Control systems; Convection; Convective heat transfer; Engineering; Fluid dynamics; Fluid flow; Free convection; Gas cooling; Gravitation; Heat transfer; Mathematical analysis; Microgravity; Natural gas; Nusselt number; Original Article; Radiation; Reduction; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Spacecraft; Thermal control systems; Viscosity; Thermal control; Microgravity; Space habitat; Convection; Churchill-Chu
• ISSN: 0938-0108; 1875-0494
• DOI: 10.1007/s12217-017-9555-8

Convective heat transfer is governed by a number of factors including various fluid properties, the presence of a thermal gradient, geometric configuration, flow condition, and gravity. Empirically-derived analytical relationships can be used to estimate convection as a function of these governing parameters. Although it is relatively straightforward to experimentally quantify the contributions of the majority of these variables, it is logistically difficult to assess the influence of reduced-gravity due to practical limitations of establishing this environment. Therefore, in order to explore this regime, a series of tests was conducted to evaluate convection under reduced-gravity conditions averaging 0.45 m/sec 2 (0.05 g ) achieved aboard a parabolic aircraft. The results showed a reduction in net heat transfer of approximately 61% in flight relative to a 1 g terrestrial baseline using the same setup. The average experimental Nusselt Number of 19.05 ± 1.41 statistically correlated with the predicted value of 18.90 ± 0.63 (N = 13), estimated using the Churchill-Chu correlation for free convective heat transfer from a finite, flat, vertical plate. Extrapolating this to similar performance in true microgravity (10 −6 g ) indicates that these conditions should yield a Nusselt Number of 1.27, which is 2.6% the magnitude of free convection at 1 g , or a reduction of 97.4%. With advection essentially eliminated, heat transfer becomes limited to diffusion and radiation, which are gravity-independent and nearly equivalent in magnitude in this case. These results offer a general guideline for integrating components that utilize natural (free) convective gas cooling in a spacecraft habitat and properly sizing the thermal control system.