1. Leonard Vasiliev, Alexander Zhuravlyov and Alexander Shapovalov
HEAT TRANSFER ENHANCEMENT IN MINI-CHANNELS WITH NANO-PARTICLES DEPOSIT ON THE HEAT LOADED WALL
Leonard Vasiliev, Alexander Zhuravlyov and Alexander Shapovalov
Porous Media Laboratory, Luikov Heat & Mass Transfer Institute, Minsk, Belarus
Abstract
The experimental data of the heat transfer at evaporation on a flooded and partially flooded horizontal tube with micro/nano porous coating disposed in the liquid pool or in confined space (annular mini-channels with the gap 0.1 to 2 mm) testify the phenomena of micro heat pipe, which ensures the temperature field uniformity inside the porous media. The mini-/micro porous coating on the heat loading wall is favorable to enhance the heat transfer (2-2.5 times) to compare with the heat transfer of the same tube in the liquid pool.
Cross section of the sample
1 – liquid surface, 2 – test sample, 3 – electrical heater, 4 – glass tube, z – height of liquid level z
20 1 2 4 3
Objectives
To investigate the mini-/microscale heat transfer of two-phase flow (propane) in mini-channels with micro-/nano-particles coating .
To extend knowledge about the mechanism of heat transfer at vaporization in capillary-porous bodies.
To investigate the influence of micro- and mini-effects combination on a heat transfer process enhancement in confined space at liquid evaporation in porous structures. 3 3
Test Rig
Test Sample
Material – copper tube
Diameter – 20 mm
Length – 100 mm
Porous Coating
Material – copper
Thickness – mm
Porosity – %
Particles dimension – m
Working fluid – Propane
Evaporation inside of Porous Body
1 – micro-pore, 2 – meniscus, 3 – vapor, 4 – macro-pore, 5 – liquid flow, 6 – two-phase flow d
Meniscus
Micro pore
Zone of evaporation (thickness of the liquid layer d)
Mini-channel
Liquid pool 2 1 3 4 Q
Heat transfer of porous tube placed in a liquid pool and annular mini-channel at different liquid level height: 1 – liquid pool, 2-5 – annular mini-channel, z=75, 20, 15 and 10 mm
Heat transfer of the horizontal porous tube (z=75 mm): 1-3 – copper sintered coating: 1 – liquid pool, 2 – annular mini-channel, 3 – flank mini-gaps; 4 – plane tube in the pool, 5 – tube with a sprayed stainless steel coating, 6 – flow boiling of R12 in mini-channel [Kuznetsov et al., 2004]
Liquid pool Transparent mini-channel
Direction of the convective two-phase flow initiated by bubbles generation in porous body without application of mechanical pump
Evaporating Element with Nano-Structural Coating Heat flux q = 34 кВт/м2
Vapor bubbles movement
in the pool
Schematic of the mini-evaporator with transparent walls heated by impulse laser beam
Fluid entrance
Fluid exit
Laser beam to heat the nano fluid
Schematic of two-phase loop (without and with the mechanical pump)
CONCLUSIONS
Thin copper sintered powder structure with micro heat pipe phenomena simulates the evaporative heat transfer near 8-10 times to compare with propane pool boiling heat transfer on the smooth horizontal tube. Reducing the size of cooling system we increase its efficiency, improve system performance by adding micro scale function (micro heat pipe effect) to macro scale engineering application.
Two-phase heat transfer in annular mini-channel with stable propane bubble generation on the thin (0.3 mm) porous surface of heat releasing tube stimulates Marangoni convection and 2-3 times enhance heat transfer to compare with the same tube heat transfer in the liquid pool without additional power supplying (no mechanical pumping).
Visualization of the micro heat pipe effect inside the porous structure  two-phase forced convection in the annular mini channel testify the availability of thermodynamically efficient mechanism of the semiconductor component cooling system, space thermal control, aircraft devices, traction drives and audio amplifiers. Cooling devices based on micro heat pipe effect inside the porous structure  two-phase forced convection in mini/micro channels are interesting to be applied in micro-and opto-electronics fields.