High prandtl number natural convection in a low-aspect ratio rectangular enclosure

종횡비 가 낮은 직각밀폐용기내 의 Prandtl 수 가 큰 유체 의 자연대류 에 관한 실험적 연구

Experimental investigation was carried out to study the natural convection of water and silicon oil due to end temperature differences in a horizontally insulated rectangular enclosure of aspect ratio 0.1 with a special attention on the core configuration in the laminar boundary-layer flow regime. Rayleigh number ranges covered herein are Ra=4.40 * 10$^{6}$ -9.64 * 10$^{7}$ for water and Ra=1.69*10$^{5}$ -3.80*10$^{6}$ for silicon oil, respectively. In the case of water, for Ra.geq.2.21 * 10$^{7}$ there appeared distinct horizontal thermal layers adjacent to the horizontal boundaries in the core and the temperature distribution outside the horizontal thermal layers, i.e., in the mid-core region, is vertically stratified. The core flow pattern was shown to be nonparallel with a weak back flow in the mid-core for Ra.geq.3.63 *10$^{7}$ . In the case of silicon oil, distinct horizontal thermal layers appeared along the core horizontal boundaries for Ra.geq.1.27 * 10$^{6}$ with a stratified temperature distribution in the mid-core, but the core flow pattern in this case was shown to be parallel. In addition, secondary flow appeared near the hot wall for Ra.geq.3.80 * 10$^{6}$ . Nusselt number, Nu, was found to be proportional to R $a^{0.3}$ for water and R $a^{0.28}$ for silicon oil in the boundary-layer flow regime. There also in an indication from the comparison with other results that Nu is independent of aspect ratio for water in the boundary-layer flow regime in low aspect ratio enclosures.res.

본 연구에서는 종횡비 0.1이고 상.하 수평경계면이 단열된 직각밀폐용기내에 서 Pr수가 1보다 큰 물(Pr=6.97, 20.deg. C) 및 실리콘 오일(Pr=1086.42, 20.deg. C)의 양단의 온도차에 의한 자연대류에서 아직 충분히 연구되지 않은 코어형상에 주안점을 두고 실 험적으로 관찰, 조사하였으며 그 결과를 Lee의 이론적인 예측과도 비교, 검토해 보았 다.