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ISSN Online: 2377-424X

ISBN Print: 0-89116-130-9

International Heat Transfer Conference 6
August, 7-11, 1978, Toronto, Canada

DYNAMIC RESPONSE OF COUNTERCURRENT HEAT EXCHANGERS TO TEMPERATURE DISTURBANCES AND STEP FLOW VARIATIONS

Get access (open in a dialog) DOI: 10.1615/IHTC6.1730
pages 291-295

要約

We analyse three different models of a countercurrent heat exchanger; these models correspond to three different mathematical approximations of the same problem.
First, we treat of the model designated by two temperatures, or lumped parameter model, where at every transversal section of the exchanger, two temperatures are defined, one for each fluid, and the thermal capacity of the wall separating the two fluids is concentrated, in equal parts, in their thermal capacity.
The solution obtained for this model is extended to a second model characterized by three temperatures, since we take into account of a new variable, which is thought as the wall mean temperature. This second model is suiter than the first in order to examine the thermal resistence of the wall separating the fluids.
At last, we study the distributed parameter model to investigate the real temperature distribution into the solid wall: besides the equations, which govern the heat convection in the fluids, we consider the equations of heat diffusion into the wall of separation. The equations are linear, that is, the velocity of two fluids are kept constant and the parameters are independent from temperatures.
The two lumped parameter models are integrated using the Laplace transform, while the distributed parameter model is integrated by means of the Laplace transform for the time variable and a finite integral transform, purposely made, for the spatial axisymmetric variable. In this manner for the three models, we obtain explicit relations of input-output pattern, involving variables mesured in the same points of the system and to which correspond the same mathematical definition.
Then, it is calculated the Laplace transform of the transient due to step variations of the fluid flow and some approximations for short-time solution and asymptotic solution are evaluated.