Date of Award

Spring 1968

Degree Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

First Advisor

Bush, John E.

Second Advisor

Richardson, B. L.

Third Advisor

Lewis, James L.

Abstract

The transient technique of testing the heat transfer performance of heat exchanger cores is frequently being used because of certain advantages for highly compact surfaces over the more conventional steady-state technique. There are two methods of employing the transient technique, the single blow method and the periodic (or cyclic) method. The single blow method has been used the most and it is reasonably well refined in the test range 5 < Ntu < 30 where the maximum slope evaluation can be used. The periodic method, which has received very limited attention in the past, is the object of study in this report. The equations governing the transient behavior of an ideal heat exchanger are developed and solved for the periodic case. These solutions are used to provide data reduction relations based on the amplitude attenuation and phase shift of the fluid temperature at the core outlet. These relations are then examined to determine when the heat transfer data is least sensitive to temperature measurement uncertainties. The results of this study, which are verified in tests using air as the working fluid, are summarized in the following paragraph. For Ntu < 1, the amplitude attenuation method of processing data should be used with "formula" (a nondimensional period) < 0.2. For 1 < Ntu < 5, the phase shift method of processing data should be used with 1 < "formula"< 3 (Fig . 5 should be used for more precise values of "formula"). It appears that the amplitude attenuation method could be used for Ntu > 5 but this has not been verified. Future work should involve making direct comparisons between the "single blow" and periodic methods particularly for Ntu < 5 and also investigating the use of transient techniques for measuring local heat transfer coefficients.

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