Three-Dimensional, Numerical Investigation of Flow and Heat Transfer in Rectangular Channels Subject to Partial Blockage

Abstract

Numerical simulation of flow and heat transfer in two adjacent channels is conducted with one of the channels partially blocked. This system simulates typical channels of a material testing reactor. The blockage is assumed due to the buckling of one of the channel plates inward along its width. The blockage ratio considered in this work is defined as the ratio between the cross-sectional area of the blocked and the unblocked channel. In this work, we consider a blockage ratio of approximately 40%. However, the blockage is different along the width of the channel, ranging from 0% at the end of the channel to 90% in the middle. The channel walls are sandwiching volumetric heat sources that vary spatially as chopped cosine functions. Interesting patterns are highlighted and investigated. The reduction in the flow area of one channel results in the flow redistributing among the two channels according to the changes in their hydraulic conductivities. The results of the numerical simulations show that the maximum wall temperature in the blocked channel is well below the boiling temperature at the operating pressure. INTRODUCTIONThere is no doubt that materials used in the design and operations of nuclear reactors are subjected to a harsh environment that is very unusual. In addition to structural stresses resulting from the interaction of the different components of reactor systems and the thermal stresses associated with the generation of heat within the core, which may be common in several engineering applications, there are also induced stresses that are unique to nuclear reactor cores and may not be found in any other application. For example, the exposure of these material to continuous bombardment with neutrons and fission products (irradiation) results in new phenomena such as swelling of fuel elements and the wear of containment materials. It is therefore important that experimental studies on irradiation effects in fuel and reactor structural materials be conducted to accurately predict their Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/uhte. mechanical behavior and the possible changes in their nuclear chemistry. Unfortunately, it is not possible to mimic such an environment in a single isolated experiment. In other words, the only way to study such effects is within nuclear reactors themselves, which motivated the design of special types of nuclear reactors, called material testing reactors (MTR). These are designed to address in considerable detail the development and the qualification of materials and fuels under irradiation with sizes and environment conditions relevant for nuclear power plants in order to optimize safe operations of existing and future power reactors. MTR typically operate at low temperatures (coolant below 100 • C), the operating conditions are severe in a sense. That is, while power reactor fuel operates at power density of about 5 kW/cm 3 , a research reactor fuel may be at 17 kW/cm 3 in the fuel region. Furthermore, in MTR, bu...

CFD study on inlet flow blockage accidents in rectangular fuel assembly

“…However, there are many different empirical formulas that can be used for h(z) calculation, therefore different T cs (z) are predicted. For instance, in Salama (2011), the Dittus-Bolter equation (Winterton, 1998) provides consistent results with the CFD simulation on one channel, while in Salama et al (2015), the Sieder and Tate (1936) equation gives consistent predictions with the CFD calculation on more channels. Therefore, it is the choice of empirical equations that determines the T cs (z) calculation.…”

“…And the result indicates that, boiling may occur when the blockage ratio in the average channel is larger than 80%. Recently, Salama et al (2015) performed a three-dimensional CFD flow blockage investigation, and no boiling is predicted for the 90% blockage.…”