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TRANSIENT NATURAL CONVECTION BETWEEN TWO VERTICAL WALLS HEATED/COOLED ASYMMETRICALLY
The present paper analyses a closed form solution for the transient free convective flow of a viscous and incompressible fluid between two vertical walls as a result of asymmetric heating or cooling of the walls. The convection currents between the walls occur due to a change in the temperature of the walls to that of the temperature of the fluid. The La place transform method has been used to find the solutions for the velocity and temperature fields by solving the governing partial differential equations. The numerical values obtained from the analytical solution show that the flow is initially in the downward direction near the cooled wall for negative values of the buoyancy force distribution parameter. The temperature field of both the air and water gradually decreases and becomes negative near the cooled wall for all negative values of the buoyancy force distribution parameter. The transient solution approaches a steady state when the non-dimensional time becomes comparable with the actual Prandtl number.
WHITE CEMENT - PROPERTIES, MANUFACTURE, PROSPECTS
KARTEŘINA MORESOVÁ, FRANTI.EK .KVÁRA
Special cements differ from conventional Portland cements in their chemical and phase composition as well as in their properties. Their properties can be achieved by using a modified raw material mix, a grinding admixture or by adjusting the grinding fineness of the cement. Special cements include a number of cements whose production volumes are considerably lower compared to those of conventional cements (max.5 to 10 %). However, they constitute a significant part of the assortment supplementing the conventional cement. These materials include cements with high early strengths, sulphate-resistant Portland cements, road cements, white cement and coloured cements, expanding cements, Portland cement with a low heat of hydration, Portland cement with a higher MgO content,insulating Portland cement, plasticized Portland cement, strontium and fungistatic cements.
MODELING OF CLINKER COOLERS
Puneet Mundhara, Surendra Sharma
Grate coolers are extensively used in cement industry to recover heat from hot clinkers coming out of rotary kilns. Heat transfer in coolers indirectly controls the performance of the rotary kiln and is therefore crucial in a cement industry. In this report, we present a computational model to capture heat transfer in grate coolers. The schematic of grate cooler considered in the present study is shown in Figure 2. The solids of uniform particle size and constant porosity were assumed to move in a plug flow with constant grate speed. Air was assumed to enter in a cross flow mode with respect to solids as shown in Figure 1a. To get the temperature profiles of solid bed and air, the length and the height of clinker bed in the cooler were subdivided into individual balance segments. The energy balance was solved for individual segments. Conductive heat transfer was considered for solids in both x and y directions. Convective heat transfer coefficient between air and solids was calculated from empirical correlation assuming solids as packed bed. The boundary conditions used are shown in Figure 1a. The model equations obtained from energy balances were solved using TDMA Technique. Several numerical simulations were carried to understand the influence of operational parameters like grate speed, solids inlet temperature and particle size, and airflow rate on the performance of the cooler. The presented computational model and the simulation results will be helpful in developing better understanding of heat transfer in grate coolers and to improve the cooler efficiency by choosing optimized operating parameters.