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Abstract
An experiment was performed to explore the effects of inclination, aperture ratio, and heat flux on heat losses of a fully or partially open cylindrical cavity, where only the bottom wall (opposite to the aperture) was heated at constant heat flux. Temperature distributions on cavity bottom and side walls are presented. The empirical correlations of free convection and radiation heat losses in terms of Nusselt number are proposed. The credibility of the experiments was checked by detailed uncertainty analysis. It confirmed that the present experimental results are credible and can be used to validate the relevant numerical codes. In addition, the cavity inclination, aperture ratio, and heat flux significantly affect the combined heat losses characteristics, and the influence of these factors, which is intercoupled to some extent, should be considered at the same time.
NOMENCLATURE
| A1 | = | total inner wall area of cavity, m2 |
| A2 | = | aperture area, m2 |
| A3 | = | inner wall area of bottom wall, m2 |
| A4 | = | outer wall area of bottom wall, m2 |
| AR | = | aperture ratio, d/d2 |
| b | = | systematic standard uncertainty |
| cp | = | specific heat at constant pressure of air, J/(kg-K) |
| d | = | inner diameter of cavity, m |
| d1 | = | outer diameter of cavity, m |
| d2 | = | aperture diameter, m |
| g | = | gravitation acceleration, m/s2 |
| hc | = | free convection coefficient between the cavity and ambient air, W/(m2-K) |
| H | = | inner height of cavity, m |
| I2 | = | current, A |
| Nu | = | Nusselt number |
| P | = | heat loss, W |
| q | = | heat flux, W/m2 |
| Ra | = | Rayleigh number |
| s | = | random standard uncertainty |
| t | = | average temperature of insulation layer, °C |
| t1 | = | average temperature of the side wall, °C |
| t2 | = | outer wall average temperature of side wall insulation material, °C |
| t3 | = | average temperature of the bottom wall, °C |
| t4 | = | outer wall average temperature of bottom wall insulation material, °C |
| tw | = | average temperature of cavity walls, °C |
| t∞ | = | ambient temperature, °C |
| T∞ | = | ambient temperature, T∞ = t∞ + 273, K |
| U | = | expanded standard uncertainty |
| U2 | = | voltage, V |
| X | = | radiative view factor |
| xi | = | influencing parameter |
Greek Symbols
| αV | = | thermal expansion coefficient, K−1 |
| δ1 | = | thickness of side wall insulation material, m |
| δ2 | = | thickness of bottom wall insulation material, m |
| ϵw | = | emissivity of cavity wall |
| ϵα | = | effective emissivity of cavity |
| λa | = | thermal conductivity of air, W/(m-K) |
| λi | = | thermal conductivity of insulation, W/(m-K) |
| θ | = | sensitivity |
| ν | = | kinematic viscosity of air, m2/s |
| σ | = | Stefan-Boltzmann constant, W/(m2-K4) |
| ϕ | = | inclination of cavity, ° |
| ρ | = | density of air, kg/m3 |
Subscripts
| c | = | free convection heat loss |
| cond | = | conduction heat loss |
| r | = | radiation heat loss |
Additional information
Funding
Notes on contributors
Shuang-Ying Wu
Shuang-Ying Wu received his M.S. from the College of Power Engineering, Chongqing University, Chongqing, China, in 1994 and his Ph.D. in engineering thermophysics from Chongqing University in 2004. He worked as a visiting scholar from June 2008 to June 2009 in the Department of Mechanical and Materials Engineering, Florida International University, Miami, FL. Currently, he is a professor at Chongqing University. His major interests are heat transfer, thermodynamics and its engineering application, and energy conversion and saving. He has co-authored more than 100 refereed journal and conference publications.
Zu-Guo Shen
Zu-Guo Shen received his B.S. from the College of Power Engineering, Chongqing University, China, in 2012. Currently, he is doing his Ph.D. at Chongqing University. His major interests are heat transfer and heat exchangers.
Lan Xiao
Lan Xiao received her B.S. from the College of Power Engineering, Chongqing University, Chongqing, China, in 2006, and her Ph.D. in engineering thermophysics from Chongqing University in 2012. She studied as a joint Ph.D. student from November 2008 to November 2009 in the Department of Mechanical and Materials Engineering, Florida International University, Miami, FL. Currently, she is a lecturer at Chongqing University. Her major interests are heat transfer and energy conversion and utilization.