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The essential ideas of investigations of turbulent flow in a straight rectangular duct are chronologically presented. Fundamentally significant experimental and theoretical studies for mathematical modeling and numerical computations of this flow configuration are analyzed. An important physical aspect of this type of flow is presence of secondary motion in the plane perpendicular to the streamwise direction, which is of interest from both the engineering and the scientific viewpoints. The key facts for a task of turbulence modeling and optimal choice of the turbulence model are obtained through careful examination of physical mechanisms that generate secondary flows. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no.TR-33018: Increase in Energy and Ecology Efficiency of Processes in Pulverized Coal-Fired Furnace and Optimization of Utility Steam Boiler Air Pre-heater by Using In-House Developed Software Tools]

In this paper three-dimensional numerical simulation of the atmospheric saturated pool boiling was performed. The applied modelling and numerical methods enable full representation of the two-phase mixture behaviour on the heating surface with the inclusion of the swell level prediction. The three-dimensional investigation presented here was performed in order to take into account a convective heat transfer on the heated surface, as well as spatial effects of the vapour generation and a twophase flow such as phase dispersion within the two-phase mixture. The results are presented for a short period of time after the initiation of the heat supply and vapor generation on the heating surface. The replenishment of the heating surface with water and partial surface wetting for lower heat fluxes is shown. The influence of the density of nucleation sites and the bubble residence time on the wall on the pool boiling dynamics is discussed. Also, the influence of the heat flux intensity on the pool boiling dynamics is investigated. The applied numerical and modelling method showed robustness by allowing stable calculations for wide ranges of applied modelling boiling parameters.

Understanding nucleate pool boiling heat transfer and, in particular the accurate prediction of conditions that can lead to critical heat flux, is of the utmost importance in many industries. Due to the safety issues related to the nuclear power plants, and for the efficient operation of many heat transfer units including fossil fuel boilers, fusion reactors, electronic chips, etc., it is important to understand this kind of heat transfer. In this paper, a comprehensive review of analytical and numerical work on nucleate pool boiling heat transfer is presented. In order to understand this phenomenon, existing studies on boiling heat transfer coefficient and boiling heat flux are also discussed, as well as characteristics of boiling phenomena such as bubble departure diameter, bubble departure frequency, active nucleation site density, bubble waiting and growth period and their impact on pool boiling heat transfer.

In this paper, influence of the temperature fluctuations, (as a version of turbulence-radiation interaction), on the flame temperature and radiative heat exchange inside the pulverized coal-fired furnace was investigated. The radiative heat exchange was solved by the Hottel zonal model. The influence of the temperature fluctuation was studied for three values of the extinction coefficient of the flame: 0.3, 1.0, and 2.0 m-1. The investigation was conducted for the relative temperature fluctuations obtained by solving the transport equation for the temperature variance, and for four constant values of the relative temperature fluctuations (0.0, 0.1, 0.15, and 0.2). The maximal values of the mean temperature fluctuations and relative temperature fluctuations were obtained in the region close to the burners. The decrease of the flame temperature of about 100 K was obtained in the hottest region, for every extinction coefficient. An increase in the mean wall flux was found to be on the order of several percents, compared to the case without the temperature fluctuations. When the temperature variance was calculated, the mean relative temperature fluctuations were approximately 15%, for every extinction coefficient. The mean wall fluxes increased and flame temperature at the furnace exit plane decreased with the increase in the relative temperature fluctuations. The selected indicators of the furnace operation, such as the mean wall flux and mean flame temperature at the furnace exit plane, obtained for the calculated temperature variance, were close to the values predicted for the constant relative temperature fluctuation of 15%.