Temperature distribution and mass transfer of flow by free convection in enclosures

Natural convection in shallow rectangular enclosures with horizontal gradients of temperature and/or concentration is investigated experimentally. The experimental electrochemical cell has four plexiglass walls and two opposite Cu walls (one electrically heated and one water cooled) and is filled with a mixture of 1.5 M H2SO4 and 0.05-0.08 M CuSO4; the setup provides for electrolytic deposition of Cu and total current and potential measurements. The techniques used to determine the mass-transfer rates are explained, and the results for conditions with gradients favoring or opposing the flow are presented graphically. In all cases, a three-layer flow structure is observed, with lower temperature in the upper layer than in the middle layer; after some time, the temperature gradient becomes unstable. The implications of the results for the design of crystal-growth chambers are considered.