Activity responsible: Dr. Giuseppe ZUMMO
Address: ENEA C.R. Casaccia, Institute of Thermal Fluid Dynamics, Via Anguillarese 301 (S.P. 092), 00060 S. M. di Galeria RM, Italy 
Phone: +39 06 3048 4567 Fax: +39 06 3048 3026 

Email: zummo@casaccia.enea.it


Activity description

In order to increase heat transfer efficiency in many industrial applications, cooling systems for computer cpu, heat exchangers for advanced space components, compact heat exchangers (with enhanced surfaces), the use of microchannels, with hydraulic diameter less than 1 mm, is becoming widespread. Although the advantages offered by microchannels, there is a complete lack of detailed information about their heat transfer and hydraulic performance. This experimental research is devoted to highlight the heat transfer (with and without phase change) and the hydraulic (pressure drop) characteristics of micro tubes (with diameter less than 0.5 mm) cooled with refrigerants. Refrigerant such as FC-72, R134A and new refrigerant mixtures will be tested.

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Objectives

1. Geometry: capillary tubes with inner diameter in the range 30 - 500 mm
2. Fluids: water, FC-72, R134A
3. Study of hydraulic characteristic in laminar and turbulent single phase flow
4. Study of two-phase flow pattern in microtubes
5. Study of heat transfer in Single Phase convection and Two-Phase flow boiling
6. Verification of heat transfer correlations in microgeometries
7. Verification of pressure drop correlations in microgeometries

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Results

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Publications

G.P. CELATA, M. CUMO, M. GUGLIELMI and G. ZUMMO, Experimental Investigation of Hydraulic and Single Phase Heat Transfer in 0.130 mm Capillary Tube
Microscale Thermophysical Engineering, Vol. 6, n. 2, pp. 85-97, 200
G.P. CELATA, M. CUMO and G. ZUMMO, Thermal-Hydraulic Characterization of Single-Phase Flow in Capillary Tubes
International Symposium on Compact Heat Exchangers, Keynote lecture, pp. 43-49, Grenoble, 24 August 2002

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Activity responsible: Dr. Giuseppe ZUMMO
Address: ENEA C.R. Casaccia, Institute of Thermal Fluid Dynamics, Via Anguillarese 301 (S.P. 092), 00060 S. M. di Galeria RM, Italy 
Phone: +39 06 3048 4567 Fax: +39 06 3048 3026 

Email: zummo@casaccia.enea.it


Activity description

The main objective of this experimental campaign is to study two-phase flow cooling systems in microgravity environment. Two-phase flow heat transfer is the most appropriate cooling method for those components characterised by high heat fluxes, which are expected to be used in space systems. Experimental activity will cover the main aspects of two-phase flow: heat transfer, pressure drop, CHF, and flow pattern visualisation, in subcooled and saturated flow boiling.
In flow boiling systems (subcooled and saturated flow boiling), microgravity affects vapour bubble size, coalescence and formation as well as flow pattern. These influences tend to disappear for increasing values of liquid velocity and for decreasing flow channel diameter.
The aim of the experimental campaign is to study the effect of tube diameter and flow velocity on flow boiling systems in low gravity conditions in order to define the limit conditions at which the gravitational forces do not have any influence on the physical mechanisms of flow boiling. The results of the experimental campaign will be useful in defining the design tools for two-phase flow components in low gravity environment. The design tools are defined in terms of heat transfer correlations, pressure drop correlations, CHF correlations.


Results

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Activity responsible: Dr. Giuseppe ZUMMO
Address: ENEA C.R. Casaccia, Institute of Thermal Fluid Dynamics, Via Anguillarese 301 (S.P. 092), 00060 S. M. di Galeria RM, Italy 
Phone: +39 06 3048 4567 Fax: +39 06 3048 3026 

Email: zummo@casaccia.enea.it


Activity description

This activity is aimed to the development of a new type of micro heat exchanger made by polymeric material. The new heat exchanger should be obtained from a sheet of polymeric microtubes (with a overall thickness of some tenths of millimeter), with the capability to be adapted to several surfaces.
One of the main problems of the micro-heat-exchangers, given the minimum internal diameter of the microtubes, is represented by high pressure-drops. The high dissipation leads to an inadequate equipment size for the pumping system. The use of polymeric additives or of surfactants can have relevant effects on the reduction of the friction coefficient. Particular properties of flow channel material could decrease the pressure drop, making their employment even more efficient.
During the space missions, the problems related to the thermal conditioning of devices, to the personnel comfort and to the thermomechanical stresses are known and important. Furthermore for a space mission certain priorities are stressed, such as the small dimension and the lightness of thermal equipments. Due to the presence of high temperature gradients, which straightforwardly implies significant heating/cooling powers, these characteristics are sometimes difficult to obtain. Besides miniaturized heat exchangers will have a terrestrial large industrial diffusion for integrated circuit cooling, in propulsion and in the power production of microsatellites and spacecrafts and in many biomedical applications, among the others, in the cloth conditioning in harsh environmental conditions. Given the great value of the ratio between exchanging surface and volume of these systems, the specific thermal power per volume unit can reach extremely high values (100 W/cm2).