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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-474-8

ISBN Online: 978-1-56700-473-1

International Heat Transfer Conference 16
August, 10-15, 2018, Beijing, China

TRANSIENT CHARACTERIZATION OF A HEAT EXCHANGER THROUGH IDENTIFICATION OF ITS TRANSFER FUNCTIONS

Get access (open in a dialog) DOI: 10.1615/IHTC16.her.021381
pages 4473-4480

Abstract

We show here that a transient temperature perturbation at the inlet of any fluid can be used for characterizing the behavior of a heat exchanger, in terms of performance or presence of fouling. This requires that the system of equations modeling the exchanger remains linear with time invariant (LTI) coefficients (negligible thermodependence of the thermophysical coefficients, possible space but not time dependant internal velocity field, with an exchange of sensible heat only). Under these conditions, the temperature response at any point of the system (inlet/outlet fluid or even in walls) is a convolution product between this temperature perturbation and the corresponding impulse response (a time transfer function that is called "transmittance" here). This transmittance can be identified using measurements of both the perturbation and its response. In practice, such a deconvolution is an ill-posed problem, because of presence of noise in both measured temperatures. It requires some regularization in order to recover a correct time distribution of the corresponding transmittance. Once this transfer function estimated, its integral in time allows to calculate the steady state behavior of the exchanger, in terms of effectiveness. If this experimental identification is repeated in time, a significative change of its transmittance, that is a non LTI behavior, allows to detect the occurrence of some change, such as fouling, in a time earlier than its detection in the corresponding output points in a steady state regime. This can give rise to a new non destructive technique for the maintenance of heat exchangers.