Institute of Fluid-Flow Machinery
Polish Academy of Sciences

Work was continued in 2010 to develop an effective cooling method using single-phase flow in free-flows.

The aim of the work is to develop an effective method of cooling the solid surface, which can be used in micro heat exchangers using microstrings. Liquid structures are also used in steel and plastic production processes to maintain proper temperature during the process. This method is also used for cooling lasers, high-loaded computer processors and other electronic components, machine components and internal combustion engines.

The studies concern heat exchange in planks and liquid films, and in particular surface cooling by a single-phase spray. The aim of the work is to learn about the problem of taking over heat in the individual areas of the flow of the stream on a flat surface, with particular emphasis on the impact of the hydraulic fault arising at the transition of supercritical flow into subcritical on the heat transfer factor.

This issue was experimentally studied at the research station constructed for this purpose at IMP PAN, and analytically and numerically using the CFD code. In 2010, the work focused mainly on numerical analysis of the phenomenon.

Numeric calculations of flow and heat exchange issues of impacting fluid streams were continued using Fluent to simulate fluid mechanics issues. A numerical model was created, which takes into account the surface voltages and allows to determine the basic parameters of the liquid film resulting from the impact of the strug to the surface of the plate. For the calculation it was assumed that the liquid is water moving in a gas centre (air). It was also assumed that the issue is axial and stationary, the flow is inaccurate and the fluids do not mix. The fluid viscosity is consistent. The starting point for numerical calculations is the arrangement of mass, momentum and energy balance equations for two-phase flow using the VOF model, supplemented by equations for the evolution of k-÷ turbulence and taking into account surface voltage forces.

For given initial and coastal conditions and specific geometry of the area, basic parameters of liquid film were defined. The following results were obtained: thickness of liquid film in the subcritical zone (Fr1) and supercritical zone (Fr>1) and in the hydraulic fault area, distribution of tangential stresses on the wall in radial direction and speed profiles in the liquid film section.