Investigation of flow reversal in a vertical channel with a cyclic heater

Abstract

A numerical study of airflow in a vertical channel between parallel plates with a channel heater has been conducted. The numerical model parallels a typical home fireplace. The primary objective of the study is to verify the existence of flow reversal due to a cyclic heater in the channel. Both steady state (isothermal heater) and transient (cyclic heater) analyses were performed for dimensionless heater temperatures of Theater = 1.0 , 1.5, and 2.0 and with heated inlet air at Tinlet = 1.0. The steady state runs were completed for Grashof numbers between 0 and 105 and the transient runs were for Grashof numbers of 104 and 105. Three cyclic heater operating times were also analyzed. The results conclude that reversed flow occurs for each heater temperature and cyclic heater operating time studied for Gr = 104. The reversed flow was independent of cyclic heater operating time for a fixed heater temperature at Gr = 104. The rate of flow reversal is successively faster as the cyclic heater temperature approaches the inlet temperature. Reversed flow did not exist for a fixed heater temperature over the range of cyclic heater operating times considered at Gr = 105. However, the flow did exhibit perturbations with slowly decreasing flow rates followed by slowly increasing flow rates as the heater cycled. The present study concludes that, for the given geometry and thermal boundary conditions, the cyclic nature of a channel heater will cause reversed flow for Gr = 104.