An Experimental analysis of heat transfer capability of nanofluids in single-phase tubular flows

In the present paper the results of an experimental investigation on the advantages of using nanofluids for heat transfer operations have been reported. The nanofluid systems varied both in terms of type of particles and their concentration, and of base fluid, for a total of 23 different system configurations. The experimentally derived heat transfer coefficients for these systems, for single-phase forced convection inside tubes, have been compared with those of water or of the corresponding base fluid. The trends identified have been reported as a function of different operating parameters (Re number and fluid average velocity) and the analysis showed that the advantage often claimed for nanofluids actually occurs only under a limited number of hydrodynamic conditions and at the expenses of a much higher pumping energy. At the same time, the most commonly adopted correlations for the prediction of the heat transfer coefficient of homogeneous mixtures, have been applied to the investigated systems, to check whether it is possible to predict the heat transfer capability of a nanofluid with the ordinary equations by simply introducing the average physical properties of the mixture. It has been found that with the exception of Al2O3 suspensions, in most of the cases the heat transfer coefficient can be actually predicted with a rather good level of accuracy.