Experimental evaluation of flow boiling incipience of subcooled fluid in a narrow channel

Experimental investigations dealt with heat transfer of R123 flowing through a narrow vertical channel of 1 mm height with one wall heated uniformly and others approximately adiabatic. Particular attention was paid to boiling incipience conditions and nucleate hysteresis phenomena. An inverse problem was dealt with as, on the basis of temperature measurement on external side of the heating foil (with thermography technique) and the measurement of the electric power supplied to this foil, it was possible to determine local heat transfer coefficients on the contact surface of the heating wall and the fluid flowing along the narrow channel. Two models of heat transfer through the heating foil and the isolating glass into the boiling liquid were proposed and discussed: one- and two-dimensional. In order to solve the two-dimensional inverse heat conduction problem the method of thermal polynomials was used with application of the least square and Trefftz computational techniques. Some exemplary results of numerical calculations on the basis of experimental data were presented for both models. The correlations concerning Nusselt number determination for R123 boiling incipience in vertical narrow channel were developed.