SINGLE-PHASE CONVECTIVE HEAT TRANSFER IN A CIRCULAR MINICHANNEL WITH UNSTEADY THERMAL LOADS

Transient forced-convection heat transfer coefficients were measured for water flowing in a circular minichannel with exponentially increasing heat input. A stainless steel tube (SUS 304) with an inner diameter of 1.0 mm and a length of 47.4 mm, mounted vertically in the experimental water loop, was used as the experimental tube. In the experiment, the upward flow velocity ranged from 10 to 16 m/s and the inlet temperature ranged from 301 to 319 K. The heat generation rate increased exponentially. The e-folding time ranged from 39 ms to 15 s. The experimental results indicated that the turbulent heat transfer coefficients of the minichannel increased with decreasing e-folding time and increasing flow velocity. When the e-folding time was shorter than approximately 0.1 s, the heat transfer coefficients were significantly higher. Correlations of the steady and transient heat transfer for water flowing in a stainless steel tube were obtained from experimental data.