Pergamon Int. Comm. HeatMass Transfer, Vol. 23, No. 1, pp. 55-68, 1996 Copyright © 1996 Elsevier Science Ltd Printed in the USA. All rights reserved 0735-1933/96 $12.00 + .{30 0735-1933(95)00084-4 AN IMPROVED MODEL FOR THE SINGLE-BLOW MEASUREMENT INCLUDING THE NON-ADIABATIC SIDE WALL EFFECT Ping-Hei Chert and Zei-Chi Chang National Taiwan University Department of Mechanical Engineering Taipei, Taiwan Republic of China (Communicated by J.P. Hartnett and W.J. Minkowycz) ABSTRACT The present study proposes an improved model for the single-blow technique which is commonly used to measure the thermal performance of a cryocooler's regenerator matrix. The improvements in the present model include the heat flux from the fluid into the side wall and the axial conduction of the wire-screen matrix and side wall as a suddenly heated fluid passes through the wire-screen matrix. Numerical results obtained from the present model are compared with both the analytic results that exclude the axial conduction and the predicted results of a prior study that neglect the heat flux into the side waU. Results are also presented to illustrate the effect of the heat capacity of the side wall, the heat flux into the side wall and the axial conduction on both the exit fluid temperature response and the NTUvalue. Introduction A transient single-blow technique has been commonly used for determining the NTU value of a compact heat exchanger [I-6] and the regenerator of cryocooler [7-8]. The single-blow technique requires a steady fluid flow passing through the test heat exchanger. In addition, both the fluid flow and test heat exchanger are in thermal equilibrium before the sudden change in the inlet fluid temperature. Once the inlet fluid temperature is suddenly heated up or cooled down, the 55