IDENTIFICATION OF THE HEAT-TRANSFER COEFF ICIENT OVER THE EXTERNAL AREA OF A FINNED TUBES HEAT-EXCHANGER WITH RESPECT TO THE MOISTURE-CONTENT OF THE AIR WITHOUT CONDENSATION

The following study, which is rather oriented towards experimentation, shows the influence of the humidity content of air on heat transfer. This first article concerns heat transfer between the external fluid ( moist air) and the internal fluid (water containing glycol, whose ther mal behavior inside circular tubes is well-known) in a heat exchanger of the same type as those used in automotive air conditioning (horizon tal copper tubes and plane aluminium fins), in the absence of condensa tion. The most difficult part of this experimental work is the measure ment and control of the air humidity, since one has to make sure that the measurement incertainties are not significant compared to the prec ision of the calculation of the heat transfer coefficient. The conclus ion is that, for this type of exchanger, the heat transfer coefficient decreases with air humidity in the absence of condensation (dry wall) . Some correlations have been developed with respect to the relative a ir humidity. An analog experimental investigation, but this time carri ed out in the presence of condensation (partially or completely wetted wall), is about to be completed; the obtained results will be communi cated later on.