Transient heat transfer due to exponentially increasing heat inputs for turbulent flow of FC-72 in small diameter tubes

•Transient heat transfer due to exponential heat input is studied for miniscale tubes.•Flow velocity (u) and inner diameter (d) affect transient turbulent heat transfer.•Fourier number (Fo) is introduced to describe transient turbulent heat transfer.•Transient heat transfer correlation is proposed based on the effects of u, d and Fo. The transient heat transfer process due to exponentially increasing heat inputs for turbulent flow of FC-72 was schematically investigated for different combinations of parameters such as flow velocity, inlet liquid temperature and period of exponentially increasing heat inputs. The ranges of Reynolds number, Red, and Prandtl number, Pr, were 23,400–81,800 and 8.4–10.8, respectively. The test heaters used in this study were circular SUS304 tubes with small inner diameters of 1, 1.8 and 2.8mm, wall thickness of 0.5mm, and heated lengths around 30, 40 and 50mm. The effects of flow velocity, exponential period and tube inner diameter on transient turbulent heat transfer process were discussed in detail. It was clarified that the transient turbulent heat transfer due to exponentially increasing heat inputs could be analyzed by introducing a dimensionless time, Fourier number, Fo. An empirical correlation for transient turbulent heat transfer caused by exponentially increasing heat inputs on small diameter tubes was developed based on the effects of Fo, flow velocity and tube inner diameter. The empirical correlation presents the experimental data within ±25%.