EXPERIMENTAL INVESTIGATION ON PULSATING HORIZONTAL HEATING OF A WATER-FILLED ENCLOSURE

Experimental results of the natural convection generated by the time p eriodic horizontal heating of a square cross-section enclosure filled with water are reported. A pulsating (on/off) heat flux is delivered t o the heating wall of the enclosure, with the opposite wall cooled by a high thermal capacitance system. All other surfaces are insulated He ating periods from 32 to 1600 seconds and cycle-averaged heat-flux bas ed Rayleigh numbers from 2.5 x 10(8) to 1.0 x 10(9) are considered. Re sults presented in terms of time series, phase-plane portraits, and cy clic evolution of surface-averaged cooling and heating wall temperatur es illustrate the main characteristics of the evolution to periodic re gime. Also presented are the cycle-averaged heat transfer coefficient versus heating period, and the corresponding average Nusselt number ve rsus Rayleigh number for various heating frequencies. These results, w hich support published theoretical and numerical analysis, indicate th at by tuning the heating period properly, the heat transfer across an enclosure can be enhanced The results also reveal that short heating p eriods hinder the convection within the enclosure, in general (e.g., f or Ra = 7.5 X 10(8) and a period of 32 s the heat transfer coefficient is 13 percent smaller than the steady heating value). The sensitivity of the transport phenomenon to pulsating heat is shown to depend stro ngly on Ra. Finally, a correlation for estimating the maximum heat tra nsfer coefficient derived from the experimental results, is presented.