Experiments on the drying power of a hot jet, issued from commercial hairdryers, are reported in the paper. A dedicated experimental apparatus was built and operated: measurements included the air flow rate, and the input electrical power, while the jet average outlet temperature was derived from the energy balance. The drying power was estimated by weighing a thin fabric patch before the test and after a prescribed amount of time. Results were compared with available models of jet drying, showing considerable discrepancy especially for high values of input power; the reasons for this discrepancy are at present not fully understood, but can likely be found in a distribution of the temperature of the surface to be dried different from the expected one, that is the adiabatic saturation. Finally, the energetic balance of the system was introduced, and an attempt was made to define an energetic efficiency of the appliance, on the basis of the energy actually spent for evaporation over the input electrical power. The measured efficiency resulted to be strongly dependent on outlet temperature and weakly dependent on flow rate, in agreement with the theoretical models.
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