Rapid transient heat transfer of milli- or micro-second order has come to play an important role in advanced engineering, and the demand for active and direct control technology of heat transfer is growing. In this article, the recent needs for rapid transient heat transfer and its control are considered, and the conceptual differences between heat-transfer control and conventional temperature or thermal control is discussed. Then, the methods of heat-tranfer control are divided into passive and active methods. Active methods such as the variable physical property method, external-force method, boundary-layer control method, and phase change method are reviewed.
A number of papers had been published upon the subject of the formulas for calculation of the self-inductance of a circular coil of rectangular cross-section around the beginning of the 20th century. At that time, it was quite difficult to calculate those complicated formulas because the modern computer did not yet exist. Therefore, suitable tables or graphs had to be prepared for simplifying the numerical jobs. However, it must be much better to use the computer to calculate them today. In this paper, a numerical method to calculate the mutual-inductance between two coaxial circular coils of rectangular cross-section is presented. In this method, however, it takes a relatively long time because of calculating the total magnetic flux crossing the other coil. By this method, the self-inductance can also be obtained. Next, the more usable ranges of some expressions arranged by Hak for calculation of the self-inductance of a circular coil of rectangular cross-section are presented, and it is concluded that its maximum error is 0.23%.
Superconducting cable for power applications must have high stability against power system failures. The Nb3Sn superconductor is expected to be used for AC power machines from this point of view. It is very important to estimate the AC loss and stability margin under practical conditions. We have developed an Nb3Sn 400-kVA class AC coil composed of a six-stranded cable with a stainless steel center strand. The Nb3Sn cable was made by the React and Wind method. In fabricating the coil, we have given careful consideration to the stress of the reacted Nb3Sn. From the analysis of the results, the major component of AC loss was the coupling loss. The temperature margin was as high as 4.19K at the cable just before quenching. The reduced critical current due to the temperature rise was found to be consistent with the quench current. The Nb3Sn coil was proven to have a temperature margin large enough to be robust against power system failures.