Time-dependent buoyant convection in an enclosure with discrete heat sources

Abstract

A numerical study is performed for the time-dependent laminar natural convection air cooling in a vertical rectangular enclosure with three discrete flush-mounted heaters. The lowest-elevation heater changes the thermal condition between the 'on' and 'off' modes. In Case I (Case 2), the lowest-elevation heater is abruptly switched on (off) from the 'off' ('on') state. In Case 3, the 'on' and 'off' modes are repeated periodically. Numerical simulations were conducted for a range of non-dimensional period and for the Rayleigh number based on the cavity width between 10(5) and 10(7) with given heater size and locations. The results show the influence of the time-dependent thermal condition of the lowest-elevation heater on the temperatures of the other heaters. At low Rayleigh number, the cycle-averaged temperatures of all heaters are little affected by the periodic change. At high Rayleigh number, the temperatures of the heaters reach peak values when the non-dimensional period of the change in thermal condition takes intermediate values. The evolutions of global flow and temperature fields are exemplified to provide physical interpretations. The study emphasizes that the transient-stage temperatures at the heaters can exceed the corresponding steady-state values. This is relevant to practical design of electronic devices. (C) 2003 Elsevier SAS. All rights reserved.