Instantaneous Measurement of Heat Transfer From an Oscillating Wire in Free Convection

Abstract

The instantaneous heat transfer properties are measured as a function of time for an oscillating wire (20 to 40 Hz) in still air. The wire is oscillated by thermal contractions and expansions which match the natural frequency based on wire mass and tension. The temperature variation results from the internal resistance heating of an alternating current. The wire temperature and velocity are measured as a function of time by photocells. This eliminates any instrumentation interference with the heat transfer. The results are plotted as a function of instantaneous and average Reynolds’ number. The oscillatory heat transfer data are divided into two regimes of free and forced convection by the critical Reynolds number. Oscillatory heat transfer rates are smaller for forced convection and greater for free convection than those for steady state conditions recommended by McAdams [2] for the respective regimes. No significant difference is found in the heat transfer for oscillations in the vertical and horizontal planes. Due to the time variation of the variables an appreciable amount of emphasis is placed on the experimental apparatus and the recording of data. The recorded data is basically corrected by assuming first order linear systems.