Many processes in power plants involve the storage and transfer of fluids including water in outdoor pipelines. Under extreme cold weather conditions, water can freeze if allowed to cool down to the freezing temperature. Installing insulation and maintaining adequate flow rate can sometimes prevent problems. However, during extended non-processing times, there are circumstances where cool down cannot be avoided and heat tracing along the piping becomes a necessity.
In many instances, the need for the installation of heat tracing is simply determined based on pipe size. However, by performing accurate calculations, it is possible to determine if the need for heat tracing is real or not, thus saving on installation and maintenance costs. Correlations for the estimation of the heat transfer coefficient in horizontal cavities are not sufficiently documented in literature. In the present work, two-dimensional CFD models are used to investigate the natural convection in water-filled horizontal pipes of different diameters. The analysis has been carried out based on the assumption of a uniform pipe surface temperature. The Nusselt number is estimated as a function of the Rayleigh number and shown not to be strongly dependent on the Prandtl number.
The analysis and the results of the numerical investigation are presented and compared to experimental data and other correlations available in literature. The documented correlation has an expanded range of applicability to high and low Rayleigh numbers, is supported by numerical and experimental results and is expressed in a simple form.
Cooling towers are widely used across a range of industries and represent the largest reuse of water in industrial and commercial applications. While continually recycling water, cooling towers loose significant inventory through evaporation and blowdown.
The local climate strongly affects the efficiency of a cooling tower and its water consumption. This paper discusses the performance of cooling towers in different climatic zone of the U.S. considering the seasonal variations of outdoor air temperature, wind speed and solar radiation. The analyses are carried out with the Sargent & Lundy’s software suite UHS which simulates the transient heat and mass transfers occurring in cooling tower/basin systems.
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