RICERCA ITALIANA     

Research program

Innovative techniques for the enhancement of forced convection

University Co-ordinator

Università degli Studi di UDINE - ENERGETICA E MACCHINE - ()

Research Unit Leader

Gianni Comini

Description

The program is founded on the very large number of contributions to the technical literature published by us in the past (see Point 12), and on the already acquired knowledge of the international technical literature.

In the proposed research we mainly aim:
- to validate our numerical procedure for the evaluation of fin performance under dehumidifying conditions by a comparison with the most reliable experimental results available in the international literature;
- to demonstrate how our numerical model can be utilized in the design of compact heat exchangers of the tube-fin type.
Furthermore, we will use our know-how
- to optimize the geometric configuration of standard heat dissipators for the power electronic industry;
- to fill the informative gap concerning the design of electric air heaters which use banks of open-coil resistance wires;
- to formulate an innovative numerical model of the thermal behaviour of microscale heat dissipators.
Finally we will deal with two numerical modelling issues that concern, respectively
- the influence, on the heat transfer performances, of the temperature non-uniformity at the base of the fins utilized in tube-fin exchangers for the air-conditioning industry;
- the identification of suitable space-periodic boundary conditions for modelling coupled conduction-convection in cooling channels of pin-fin heat exchangers.

The research program covers a two-year period and, consequently, it is divided into two one-year stages. Synergies between the Udine unit and other units are expected, as outlined in the following:
- the simultaneous heat and mass convection in compact heat exchangers will be investigated also by the Bologna, Milan and Parma units;
- the use of pin fins in the heat dissipators for the electronic industry will be investigated also by the Ancona unit.

To obtain design data, the other units will mainly rely on experimental methodologies, while our unit will mainly rely on numerical simulations. In the first year we will focus on modelling issues and on the formulation of computational models. In the second year, we will concentrate on industrial applications both traditional and innovative.

FIRST YEAR TASK

COMPACT HEAT EXCHANGERS - We will validate our numerical procedure for the evaluation of fin performance under dehumidifying conditions by a comparison with the most reliable experimental results available in the international literature. For the validation purposes we will compare our numerical results with the most credited experimental results concerning rectangular and wavy fins operating under dehumidifying conditions.

HEAT DISSIPATORS FOR THE ELECTRONIC INDUSTRY - We will investigate forced convection in the fully developed region of coolant passages with staggered arrays of circular, square and elliptical pins made of nickel and copper. On the basis of overall (thermal and fluidodynamic) performances, the best shape-material combination will be identified.

ELECTRIC AIR HEATERS - We will correlate our experimental and numerical heat transfer results concerning open coil resistance wires in terms of Nusselt vs. Reynolds number in the air velocity interval which is of industrial interest. The correlation will be immediately utilized for the design of tumble dryer appliances.

MODELLING ISSUES - In the field of compact heat exchangers, we will investigate the influence, on the heat transfer performances, of the temperature non-uniformity at the base of the fins utilized in tube-fin exchangers for the air-conditioning industry. In the field of heat dissipators, we will identify suitable space-periodic boundary conditions for modelling coupled conduction-convection in cooling channels of pin-fin heat exchangers. These boundary conditions will account for the spreading of heat flow lines in the thick walls of cooling plates.


SECOND YEAR TASK

COMPACT HEAT EXCHANGERS - We will investigate the thermal performances for different Reynolds numbers, of two-row tube-fin exchangers, for both in-line and staggered arrangements of tubes. The aim will be to demonstrate the great importance that the ratio between latent and overall rates of heat transfer has in the design of compact heat exchangers operating in dehumidifying conditions. We will also attempt to modify a commercial code to enable the investigation of thermal performances, for different Reynolds numbers, of multi-row tube-fin exchangers operating in dehumidifying conditions.

HEAT DISSIPATORS FOR THE ELECTRONIC INDUSTRY - We will formulate an innovative numerical model of the thermal behaviour of microscale heat dissipators, utilizing the space-periodic boundary conditions for coupled conduction-convection problems.