RICERCA ITALIANA     

Experiments on Heat Transfer and Two Phase Flow for Innovative Industrial Applications

Università degli Studi di Genova

Abstract

The project deals with the study of fluid flow and convective heat transfer in single and two-component two-phase flow systems.
Notwithstanding the large amount of research carried out on this subject, there are many situations in which prediction, essentially empirically based, may carry with it high uncertainty owing to the large number of variables encountered in two-phase flow that play a definite role in determining flow pattern, pressure drop and heat transfer. To reduce uncertainty, further work is needed in order to improve our understanding of the phenomena and to obtain data in specific operating conditions.
The study is to be divided into the following main categories:

1) heat transfer and two-phase flow during evaporation and condensation in channels;
2) fluid-dynamics of two-phase flow systems: flow structure and pressure drop in channels and singularities.

Each subject is subdivided into a number of specific topics on the basis of heat transfer mechanisms and operating conditions. Moreover, both subjects are correlated by means of transferring the data obtained from studies on flow structure to the conditions in which two-phase flow and heat transfer simultaneously develop.
The project will involve intense experimental activity jointly performed by the Research Units. Such activity constitutes an indispensable basis on which to construct proper simulations and draw up novel calculation procedures for >>>

Principal Investigator

Giovanni GUGLIELMINI Università degli Studi di GENOVA

Research Objectives

Heat transfer during phase change and the flow features of two-phase mixtures play an important role in many industrial applications. A number of energy conversion systems and plants, technological applications and industrial processes are affected both by phase changes of fluids and by the flow characteristics of two-phase fluids. In such applications, the performance of thermal devices and the quality of products in industrial processes can be influenced by heat transfer and thermal efficiency.
The design of thermal systems that use very small, complex components is an emerging industrial sector which finds application in refrigeration and air conditioning. Heat pipes, fuel cells and new-generation compact evaporators make use of the vaporisation of refrigerant fluids in mini-channels with hydraulic diameters in the order of one millimetre or less.
Condensation inside mini-channels can also be found in such applications as heat pipes in electronic equipment cooling and automotive air-conditioning condensers. Automotive condensers use flat, extruded aluminium channels, which reduce the air-side pressure drop and the refrigerant charge in the equipment.
Another very interesting aspect concerns the replacement of traditional refrigerants with novel fluids, on account of the environmental problems caused by the use of CFC and HCFC refrigerants (ozone layer damage and greenhouse anthropic effect).
The literature on thermal and fluid-dynamic >>>

First Results

1. HEAT TRANSFER AND TWO-PHASE FLOW DURING EVAPORATION AND CONDENSATION IN CHANNELS

1.1. Experimental data on condensation of HFC refrigerants in multi-port mini-channels and analysis of data. Experimental data on pressure drop for adiabatic flow of HFC. Change in the experimental test rig for study on vaporisation.

1.2. Overhaul and setting up of both single-phase and two-phase test facilities and construction of the test sections. Preliminary measurements.

1.3. Experimental data on vaporization of halogenated dielectric fluids, for natural circulation, in plain and ribbed channels. Experimental data of pressure drop and flow patterns in two phase flow of dielectric fluids in horizontal mini channel with circular and non circular cross section.

1.4. Set up of experimental apparatus. Data on phenomenology of heat transfer in periodically operating two-phase thermosyphons.Comparison between experimental data and numerical ones obtained by numerical code.

2. FLUID-DYNAMICS OF TWO-PHASE FLOW SYSTEMS: FLOW STRUCTURE AND PRESSURE DROP IN CHANNELS AND SINGULARITIES.

2.1. Development of a new electronic device able to record two phase impedance by means of several void fraction probes. Data on pressure drops and flow structure through singularities of various configurations.

2.2. Experimental data on core-annular flow in ducts of various diameter and orientation >>>

Timescale

24 months

National and international background

The research form part of experimental two phase flow and heat transfer, with specific reference to the heat transfer during vaporization and condensation in channels and adiabatic two-phase flow analysis. This broad field of research, which has many applications, has attracted numerous researchers, as is witnessed by the growing number of papers published on these topics every year. The main body of the research project follows on from programmes previously funded on two-phase flow and heat transfer. The researchers involved in this project are part of a national scientific network for the study of Applied Thermal Fluid Dynamics, co-ordinated by the Italian Union of Thermal Fluid Dynamics.

The project is divided into two main themes:

1. Heat transfer and two-phase flow during evaporation and condensation in channels

2. Fluid-dynamics of two-phase flow systems: flow structure and pressure drop in channels and singularities.

Each theme is subdivided into a number of more specific topics. Researches will involve prevailingly experimental approaches, performed by means of traditional and novel techniques, will develop empirical relationships and validate physical-mathematical models and computational codes, will develop innovative components and systems for applications in thermal control, air-conditioning and refrigeration.

1. HEAT TRANSFER AND TWO-PHASE FLOW DURING EVAPORATION AND CONDENSATION IN >>>