Heat Transfer During Pulsating Liquid Jet Impingement onto a Vertical Wall

Abstract

Liquid jet impingement is used in industry when surfaces must be cooled or cleaned, since this process is characterized by high heat or mass transport rates. One of the methods suggested for heat transfer optimization is using pulsating jets. Zumbrunnen and Aziz investigated pulsating water jets impinging on a heated horizontal wall. The pulsation with frequencies up to $140\mathrm{ Hz}$ leads to an enhancement of the heat transfer in the stagnation flow area of up to 100% [1]. The influence of pulsation on heat transfer by jet impingement onto a vertical wall has not been studied so far. The impingement of an initially circular liquid jet onto a vertical wall is—as for the horizontal wall—accompanied by a stagnation flow and the development of a radial thin liquid film bounded by a hydraulic jump, but the latter is not circular as in the case of normal impingement onto horizontal surfaces, but has an arc shape. The impingement of a pulsating jet (consisting of successive jet sections) leads to development of complex periodic wall flow patterns, which typically can be subdivided into several phases: (i) the spreading phase directly after impingement, eventually leading into (ii) the quasi-stationary phase lasting until the end of the jet section impingement phase, followed by (iii) the drainage of the wall film. The latter is dominated by the drainage of water accumulated in the arc-shaped hydraulic jump during the stationary phase. This flow contributes to convective heat transport without ongoing inflow of cooling liquid, which leads to improvement of resource efficiency.