SESSION 2

HEAT EXCHANGERS


EXPERIMENTAL STUDY OF TRANSIENT HEAT TRANSFER FOR TURBULENT FLOW WITH PERIODIC VARIATION OF INLET TEMPERATURE

K. Mansouri, B. Fourcher
Laboratoire de Thermodynamique, Facultť des Sciences et des Techniques de I'Universitť de Nantes
2, Rue de la Houssinière 44072 Nantes cedex 03

An experimental setup has been built to examine the thermal response of a water turbulent forced convection between two parallel plates subjected to a periodic inlet temperature. In practice, a rectangular duct which a cross sectional area of (300x20 mm2) is constructed with stainless steel plates of 5 mm thickness. The experimental results (amplitude and phase lag along the channel) are compared with the elementary quasi-steady approach which employs a classical heat transfer coefficient at interface liquid-solid and also with an usual turbulent model which introduces the thermal eddy diffusivity and the velocity profiles. For this two cases, we take into account the equation of diffusion in the thick wall. For example at Reynolds number ~ 12000 it was found that, for the smaller values of inlet frequency, the quasi-steady approach is sufficient, but for higher frequencies (>0.05 Hz), the turbulent model is necessary.

RESPONSE OF TEMPERATURE IN HEATED PIPE FLOW TO RAMP-TYPE EXCURSIONS OF FLOW RATE

O. BŁyŁkalaca* and J. D. Jackson**
*Department of Mechanical Engineering, University of «ukurova, Turkey
**School of Engineering, University of Manchester, UK

An experimental study is reported of turbulent heat transfer to water in a uniformly heated pipe during ramp-type excursions of flow rate in which it decreased linearly with time starting from a steady condition and finishing at another one. The variation with time of outer wall temperature and fluid temperature at a number of radial positions was measured. Some measurements were also made under conditions of steady flow. The experimental results revealed a very slow response of temperature to the imposed flow excursions and big differences between temperature measured during transient flow and under steady flow conditions.

SPATIAL VARIATION OF TRANSIENT BEHAVIOUR OF A COUNTER FLOW HEAT EXCHANGER: ANALYTICAL AND EXPERIMENTAL RESULTS

M. A. ABDELGHANI-IDRISSI*, F. BAGUI*, L. ESTEL* and C. THENARD**
*P.S.O.P.I.C. I.N.S.A. de Rouen**L.T.A.
B.P. 08 - Place Emile BlondelI.U.T. de Rouen
76131 Mont Saint Aignan Cedex76821 Mont Saint Aignan Cedex
FRANCEFRANCE

Spatial variation of transient behaviour of a counter current heat exchanger is studied while a flow rate step is applied. The linear evolution of time constants of both fluids, allows to obtain their analytic expressions by taking considerations on the boundaries of the heat exchanger. The confrontation of the theoretical results to experimental data allowed to validate the analytical relations which depend on initial and final steady states. The influence of flow rate step magnitude on transient behaviour is studied by maintaining initial steady state. In the same manner, effect of initial steady state is investigated with a constant flow rate step. Comparison between response time to positive and negative flow rate step is also presented.

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