2013 1(12)

EFFECT OF THE MICROSTRUCTURE OF THE WALL ON THE FLOW OF THE SUBMERGED JET IN THE NARROW SLOT

Perepelitsa B.V., Ovchinnikov V.V.

Institute of Thermophysics SB RAS, Novosibirsk, Russia

Introduction

Hydrodynamics research in mini and micro channels is very important for development of various new compact devices. The special attention last years is given to the structured solid surfaces with various micro channels which provide heat and mass transfer intensification. Various methods of visualization are used widely for the purpose of direct observation of complex transient turbulent flows in the micro channels. The flows in narrow channels are especially difficult for theory and numerical simulation. Presence of horizontally oriented micro texture of the solid wall leads to occurrence of more complex structure of flow. Experimental investigation of the submerged jet in the narrow slot is necessary for correct prediction of processes of heat transfer in apparatuses with micro textured wall surface.

Purpose

The purpose of this study is experimental research of structure of the submerged jet in the narrow slot with one micro textured wall.

Method

The slot channel is formed by two vertical rectangular plates 220õ260 mm placed in a vessel with distilled water. The gap is 1.05 mm. One of plates has surface with horizontally oriented microstructure having triangular profile. A step of a profile is 1.75 mm, depth of a profile is 0.175 mm. Nozzle was length 50 mm and external diameter of 1.05 mm, interior diameter of 0.65 mm. The water flow rate through a nozzle was constant. Average speed of a jet on an exit from a nozzle varied from 0.2 to 7.5 m/s. Current visualization was carried out by light-scattering corpuscles, and also by means of coloring agent. A current flow pattern was recorded by camcorder (speed of a video is 50 fps).

Results

Various flow regimes of the submerged jet in the slot channel have been investigated. The following flow regimes were revealed: the laminar, the laminar with two-dimensional vortex structures, transient regime and a turbulent regime. It is shown, that different instabilities appear above Reynolds number 450. Development of sinusoidal instability leads to formation of vortex structures. Feature of a flow of a jet in the narrow slot is the long laminar initial sector. With increase of number of Reynolds the length of a laminar sector of a jet decreases and of a jet breakup point come nearer to a nozzle. It is shown that micro textured presence on a wall of slot leads to anisotropy of a flow concerning an axis of jet. It is observe that the liquid symmetrically extends on periphery; except for a small zone near a nozzle (the perimeter has the circle form).

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