The influence of wall temperature distribution on the mixed convective losses from a heated cavity

• Published in: Applied thermal engineering 2019-06, Vol.155, p.157-165
• Main Authors: Lee, Ka Lok, Chinnici, Alfonso, Jafarian, Mehdi, Arjomandi, Maziar, Dally, Bassam, Nathan, Graham
• Format: Article
• Language: English
• Subjects: Air flow; Concentrated solar thermal; Convective heat loss; Dependence; Effects; Heat exchangers; Rangefinding; Solar cavity receiver; Temperature distribution; Wall temperature; Wind; Wind effects; Wind speed; Wind tunnels; Yaw
• ISSN: 1359-4311; 1873-5606
• DOI: 10.1016/j.applthermaleng.2019.03.052

•Measurements of mixed convection from a cavity with various temperature distributions.•Internal wall temperature distribution strongly influences heat losses from a cavity.•Measured heat losses varied up to 50% by varying wall temperature distribution.•Heat losses from downward tilted cavities were ∼3 times larger than upward cases. An experimental investigation is presented of the effects of wind speed (0–9 m/s), yaw angle (0° and 90°), and tilt angle (15° and −90°) on the mixed convective heat losses from a cylindrical cavity heated with different internal wall temperature distributions. The internal wall comprised 16 individually controlled heating elements to allow the distribution of the surface temperature to be well controlled, while the air flow was controlled with a wind tunnel. It is found that temperature distribution has a strong influence on the convective heat losses, with a joint dependence on the wind speed and its direction. For the no-wind and side-on wind conditions, the measured range of the heat losses varied by up to 50% with a change in the wall temperature distribution. However, for high head-on wind speeds, this variation reduced down to ∼20%. In addition, the heat losses from downward tilted were ∼3 times larger than the upward facing heated cavity for high wind speeds (typical of tower-mounted and beam-down configurations, respectively). Also, the measured heat losses were found to be only slightly dependent on wind speed and direction in contrast with the downward tilted cases.