TED-AJ03-402 DYNAMIC BEHAVIOUR OF THREE-FLUID CROSSFLOW HEAT EXCHANGER WITH LARGE CORE CAPACITY
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概要
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Transient behaviour of heat exchangers needs to be known for designing the control strategy during start-up, shut down, failure and accidents. Though a few papers in the literature are available on steady state performance of three-fluid heat exchangers, no work has been reported on the dynamic behaviour of three-fluid crossflow heat exchangers to the best of the knowledge of the authors. A typical example of co-current crossflow heat exchangers with two-thermal communications has been investigated in the absence of axial dispersion in fluids and longitudinal conduction in separating sheets. Due to the introduction of a third fluid the process of energy exchange in a three-fluid heat exchanger is more complex compared to that in a conventional two-fluid heat exchanger. The central fluid stream exchanges heat simultaneously with two adjacent streams. The exact distribution of this thermal energy plays an important role in steady state as well as in dynamic behaviour of heat exchanger. The behaviour of the mean exit temperature of the three fluids is obtained numerically as a function of NTU, conductance ratios, capacitance ratios and a specified inlet temperature of the central fluid stream for the large core capacity. Though the conductance ratio is not having any effect on the steady state performance of the heat exchanger, its effect should not be neglected during the transients. It may be noted that a lower value of conductance ratio increases the time to reach the steady state and the effect is more pronounced in the central fluid stream In case of sinusoidal excitation the exit temperatures show unsteady periodic behaviour to start with. Gradually this becomes steady while the frequency ultimately reaches the frequency of the input excitation. It has been shown that the functional dependence of exit temperatures with the inlet excitation can be depicted with the help of Lissajous plots under steady state. Though the numerical solution considered above applies to a typical example, with suitable modification of formulation and boundary conditions, different other cases of transient heat transfer in three-fluid heat exchangers can be analysed. The study will be helpful in calculating thermal stresses in separating sheets and hence in detailed thermal and mechanical design of such heat exchangers.
著者
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Das P.
Mechanical Engineering Department Indian Institute Of Technology
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Mishra Manish
Mechanical Engineering Department Indian Institute Of Technology
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SARANGI SUNIL
Cryogenic Engineering Centre Indian Institute of Technology