ABOUT THE 2ND-ORDER INSTABILITY ON AN ELECTRICALLY HEATED TEMPERATURE-CONTROLLED TEST SECTION UNDER FORCED CONVECTIVE BOILING CONDITIONS

During boiling experiments with electrically heated temperature-controlled test sections it was observed by many researchers that although stability conditions can be satisfied in the ordinary sense, wall temperature distribution may tilt over from one form to another quite different form near the CHF and the minimum film boiling conditions. The measured local boiling curves appeared to be discontinuous. By solving the heat conduction problem of the test section with a simplified continuous boiling topography as one of its boundary conditions it is shown that the discontinuous phenomena may be caused by the experimental construction rather than by boiling characteristics. Using an unsteady-state measurement system the two types of second-order instability are observed. Possible ways of getting a fully stable operation of the test section are proposed.