THERMAL SCIENCE

International Scientific Journal

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Heat transfer crisis in the capillary-porous cooling system of elements of heat and power installations

ABSTRACT
It was shown that liquid boiling processes occur in the porous cooling systems of the elements of the heat and power installations and crisis situation of heat exchange wall overheating may occur at high thermal conditions. Experimental installation was assembled whose schematic and conditions of experimentation were represented in the paper studying the crisis. A crisis mechanism was developed. The gravitational potential aids in the destruction of steam conglomerates in a porous structure, facilitating the transport of an underheated liquid. A surplus of liquid in the porous system creates a directional movement of the flow, which leads to deformation of steam bubbles in the structure, a decrease in diameter, an increase in the frequency of the formation of bubbles. As the flow velocity increases, the energy consumed for displacement of liquid from the wall boundary layer increases, and, consequently, the rate of steam generation and the value of the critical flow increases. An increase of critical load will be achieved at a high flow velocity of the liquid, which will lead to an increase of consumption of energy that is used to power the pressure units. Equations are proposed for computing the hydrodynamic crisis, taking into account the combined actions of gravitational and capillary forces, creating surplus of liquid, underheating and additional velocity to the flow. Theoretical models are confirmed by experiments for a wide range of pressure changes in the system, the parameters of the capillary-porous structure and its orientation in a gravitational field.
KEYWORDS
PAPER SUBMITTED: 2017-10-16
PAPER REVISED: 2018-04-11
PAPER ACCEPTED: 2018-04-13
PUBLISHED ONLINE: 2018-05-12
DOI REFERENCE: https://doi.org/10.2298/TSCI171016139G
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