Application of the periodic temperature variation technique to the measurement of heat transfer coefficients in high-NTU matrices

The existing periodic temperature variation technique for determining heat transfer characteristics of heat exchanger surfaces is extended to the high NTU (over 50) ranges. The initial formulation of the problem considers the effects of axial conduction in both fluid and matrix and the effects of the regenerator casing. The model is solved analytically by using the complex temperature technique. This solution is used in conjunction with experimental measurements to obtain the regenerator NTU at the given conditions. Results from experiments conducted on regenerators consisting of packed lead spheres and stainless steel screen under varying Reynolds numbers are presented. Very good agreement is observed between the results obtained and those from established correlations for the heat transfer coefficient.