Experimental assessment of a new heat flux sensor for measuring convective heat transfer coefficients

A new steady-state method for measuring convective heat transfer coefficients is illustrated and tested. The proposed technique can be applied to thermally thin sensors, such as slabs made of relatively high thermal conductivity material. Unlike the heated-thin-foil method, demanding a given uniform heating of the slab, the sample is externally heated, and the heat input is not even to be known. In the energy balance, the tangential conduction and the convective heat fluxes are the predominant contributions. Currently available InfraRed (IR) thermography allows to measure the two-dimensional temperature distribution with relatively high resolution, enabling the evaluation of the tangential conduction by numerical computation of the temperature distribution Laplacian value. Spatial filtering with a Gaussian window and computation of the numerical derivatives with a relatively large step are proposed to deal with the unavoidable noise presence in the acquired data. An experimental assessment of the technique, concerning the measurement of the convective heat transfer coefficient distribution over a thermally thin aluminium slab, subjected to a jet issuing from a nozzle and normally impinging onto it, is performed. Tests are carried out by varying the nozzle-to-plate distance (from 2 to 6 nozzle diameters) and the heating configuration. They prove the feasibility of the technique even if a small dependence of the latter on the result values is observed.