FREE CONVECTION 1
QUALITATIVE ESTIMATES OF CONVECTIVE HEAT TRANSFER IN A VOLUMETRICALLY HEATED FLUID
L. A. Bolshov, P. S. Kondratenko, V. F. Strizhov
Nuclear Safety Institute, Russian Academy of Sciences,
Bolshaya Tul'skaya 52, Moscow 113191, Russia
Qualitative correlations of heat transfer and characteristic transient times in a volumetrically heated fluid in a closed volume are obtained. The basis of the analysis are the relations deduced from the condition of energy balance and modern physical concepts on heat transfer processes in an energetically neutral fluid. Four main and one asymptotic regime of heat transfer, which differ from each other by exponents of power dependence of Nu number on RaI number is distinguished. Dependences Nuup ~ RaI7/32 and Nudn ~ RaI1/4 take place in asymptotic limit when RaI-1/32<<1 for heat transfer to the upper horizontal and faced down curved parts of the boundary respectively. In the range of values RaI, which is of interest to the nuclear safety problem, the obtained theoretical correlations are in good agreement with the experiment.
TRANSIENT NATURAL CONVECTION AND ORIENTATION OPTIMIZATION IN A DIFFERENTIALLY HEATED INCLINED SQUARE ENCLOSURE WITH INTERNAL HEAT SOURCES
A. Cihat Baytaž
Istanbul Technical University, Institute For Nuclear Energy
A computational study is carried out to investigate the thermodynamic orientation optimization of the enclosure for different inclined angles and for minimum entropy generation in laminar natural convection heat transfer. The entropy generation number v.s. inclined angle and different Ra numbers and the local entropy generation maps over the entire cross section of the enclosure are presented as figures. It is shown how the inclination angles of enclosure may be selected in order to minimize the irreversibility associated with a transient natural convection in an inclined enclosure.
CONVECTIVE WAVE DRIVEN HEAT TRANSFER PROCESSES IN A TRANSITIONAL PLASMA PLUME
Ludek Krejcí*, Vladimir Dolínek*, Ludek Sára*, Jirí Vogel*,
Václav Nenicka**, Jan Hlína**
*Institute of Thermomechanics, Academy of Sciences of the Czech Republic, Prague, Czech
**Institute of Electrotechnical Engineering, Academy of Sciences of the Czech Republic, Prague, Czech Republic
In the paper, some striking events characterising the unsteady convective heat transfer processes in a transitional thermal plasma plume are described and their mechanisms is analysed. The analysis shows that both the plume thermal energy transport metamorphoses as well as the thermal energy generation itself are controlled by distinct resonance processes determined by simultaneous wave process produced by the plume mixing layer and plume core instabilities. The consecutive energy transport as well as the energy transport generation changes are the products of different energy exchange between them; their limits - the maximum and minimum plume core heat flux and the maximum arc heater exit average enthalpy - are the results of complex changes in the character of the wave energy distribution.