Abstract
A series of experimental investigations with a new modified transient liquid crystal method on the studies related to the fluid flow and heat transfer characteristics in a channel installed without and with a heat sink have been successfully performed. The parametric studies on the local and average effective heat transfer characteristics for confined heat sinks have been explored. The influencing parameters and conditions include air preheating temperature at channel inlet(ΔT), flow velocity (V) and heat sink types.From the thermal aspect, the effect of the air preheating temperature on local and average effective heat transfer coefficients of confined heat sinks is not significant. The local and average effective heat transfer coefficients increase with increasing flow velocity. The average effective heat transfer coefficient increases with decreasing channel porosity; the highest and lowest average effective heat transfer coefficients can be found for fully-confined and unconfined heat sinks at a specific channel inlet velocity, respectively. A new empirical correlation of average effective heat transfer coefficient for confined heat sinks with various flow velocities is proposed. In addition, two correction factors of K1 and K2 representing average heat transfer enhancement due the confinement effect of confined heat sinks are proposed. The local heat transfer coefficient gradually decreases along the streamwise direction for unconfined heat sinks; and the maximum heat transfer is generally existed around the entrance region of unconfined heat sinks; while, for partially-confined and fully-confined heat sinks, the heat transfer coefficient increases from the entrance region of the confined heat sink to X=0.1-0.15 and then gradually decreases along the streamwise direction. A maximum heat transfer is generally existed around X=0.10-0.15 for confined cases.From the frictional aspect, the overall channel pressure drop increases with increasing flow velocity or decreasing channel porosity; the highest and lowest pressure drops can be found for fully-confined and unconfined heat sinks at a specific channel inlet velocity, respectively.Finally, a concept of the amount of enhanced heat transfer (AEHT) is introduced and defined as the ratio of j/f. The j/f ratio is almost independent of Reynolds number for a specific confined heat sink. The maximum and minimum j/f ratios are 0.0603 and 0.0124 for fully-confined and unconfined heat sinks, respectively.