The Unsteady Characteristics of a Laminar Flow and Heat Transfer of a Pair of Confined Impinging Air Jets

The unsteady laminar flow and heat transfer characteristics for a pair of confined impinging air jets centered in a channel were studied numerically. The time-averaged heat transfer coefficient for a pair of heat sources centered in the channel was determined as well as the oscillating jet frequency for the unsteady cases. The present study continues the authors’ previous investigation [1], which emphasized how the small spacing between the heat sources leads to a reduction in heat transfer when increasing the flow Reynolds (Re) number, particularly in the unsteady regime. It depends on the proximity of the jet inlets, the channel dimensions and the jet Reynolds number. The jet unsteadiness causes the stagnation point locations to sweep back and forth over the impingement region, and the jets “wash” a larger surface area on the target wall. The results indicate that the dual jets become unsteady between a Renumber of 200 and 300. Prior study indicated that in this Re range, a fixed stagnation “bubble” forms on the target wall between the two jets, reducing the local heat transfer and leading to its quasi-independence on flow conditions. In this study, due to the larger space between the heat sources, the “bubble” occurring between the jets is not having a detrimental impact on heat transfer. The oscillating frequency of the flow increases with Re number for the unsteady cases, leading to significant heat transfer enhancement. The time-averaged heat transfer coefficient on the heat sources rises with Re number increase for both steady and unsteady cases. By varying the distance between the heat sources, the “bubble” region does not impact the cooling of the heat sources, as the increase in flow rate leads to increased heat transfer coefficients. Alternative designs and their impact on the heat source thermal performance are further investigated.