Turbulent flow and heat transfer in rod bundles.
|Title:||Turbulent flow and heat transfer in rod bundles.|
|Authors:||Guellouz, Mohamed Sadok.|
|Abstract:||Presented in this study is an investigation of turbulent flow and heat transfer near narrow gaps of rod bundles. At first, practical empirical correlations for the subchannel average and the gap local heat transfer coefficients were fitted to experimental results available in the literature. Then, the thesis presents a new technique, using a pendulum, for the calibration of hot-wire anemometers over low velocity ranges, a signal analysis procedure for three-sensor hot-wire probes, and a method for the enhancement of the results of the Variable Interval Time Average (VITA) conditional sampling technique, all used in the main experimental study. The experimental investigation was conducted in a rectangular channel with an aspect ratio of 2/3, containing a suspended rod, having a diameter equal to half the channel height. The rod was positioned so that it would form a narrow rod-wall gap with the channel base. The flow Reynolds number, based on bulk velocity and hydraulic diameter, was 140,000. Two-point correlations and conditional sampling measurements, using hot-wire anemometry, as well as flow visualization were employed in this study. The experimental investigation substantiated the occurrence of large-scale coherent structures in the gap region, documented their properties and proposed a physical model for them. An explanation for their formation and spatial configuration was also offered. The insensitivity of the intersubchannel mixing and the local heat transfer coefficient to the gap size was explained as a result of the presence of these coherent structures in the gap region. The turbulence structure in the gap region was also investigated. Measurements of the coherent, incoherent and Reynolds averaged statistical properties of the flow were presented and compared to those in turbulent pipe flow.|
|Collection||Thèses, 1910 - 2010 // Theses, 1910 - 2010|