Chimney Trip Structures for Downcomer Mixing
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Solution Overview
Problem
In natural circulation type boiling water nuclear reactors, the lack of mixing in the downcomer region leads to non-uniform water temperature and power generation due to the smooth exterior surface of the chimney, resulting in increasing downward velocity with little axial or radial mixing, which affects the core inlet enthalpy and power distribution.
Innovation Solution
The introduction of trip structures on the exterior surface of the chimney, such as ribs, fins, and flow interrupters, to disrupt the downward water flow and create mixing micro-zones, enhancing axial and radial mixing by breaking thermal and hydrodynamic boundary layers, thereby improving core inlet conditions and power distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the chimney exterior surface is kept smooth, then frictional losses are minimized and flow is maintained, but mixing in the downcomer region is insufficient leading to non-uniform water temperature
Solution Approach 1:
The patent applies local quality by introducing trip structures (ribs, fins, or protrusions) at specific locations on the chimney exterior surface. These localized features create turbulence and mixing zones only in the downcomer region where temperature uniformity is needed, while keeping the rest of the surface smooth to minimize overall frictional losses.
Solution Approach 2:
The patent transitions from a two-dimensional smooth surface to a three-dimensional structured surface by adding trip structures that protrude into the flow. This dimensional change creates flow disruption and mixing micro-zones that enhance thermal homogenization without significantly increasing frictional losses across the entire surface.
2Stability of the object's composition
If trip structures are added to the chimney exterior surface, then mixing and temperature uniformity are improved, but device complexity increases
Solution Approach 1:
The trip structures are applied locally to specific portions of the chimney exterior surface rather than the entire surface. This localized application achieves the desired mixing effect in the downcomer region while minimizing the overall structural complexity and maintaining simplicity in other areas of the chimney.
Solution Approach 2:
The patent modifies the surface parameters of the chimney by adding small-scale geometric features (ribs, fins, or protrusions) with specific dimensions and spacing. These parameter changes enhance mixing efficiency without fundamentally altering the overall chimney structure, thus limiting the increase in device complexity.
3Speed
If the chimney height is increased to enhance natural circulation, then steam flow is improved, but velocity gradient increases and mixing decreases
Solution Approach 1:
The patent addresses the velocity gradient issue by adding trip structures that create three-dimensional flow disruption. This transforms the predominantly axial flow into a more complex flow pattern with radial and tangential components, enhancing mixing despite the increased velocity gradient from greater chimney height.
Solution Approach 2:
The trip structures act as intermediary elements between the steam flow and the downcomer water flow. These structures facilitate momentum transfer and mixing by creating turbulence and flow disruption, mediating the interaction between the high-velocity steam flow and the cooler downcomer water to achieve temperature uniformity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The implementation of trip structures on the chimney surface leads to uniform core inlet conditions, increased mixing efficiency, and reduced temperature variations, allowing the reactor to achieve rated core thermal power more consistently and facilitating better refueling processes.
Implementation Method 1
enhancing axial and radial mixing by breaking thermal and hydrodynamic boundary layers
Implementation Method 2
The water flows vertically upward due to the decreasing density above the core 112 as a result of steam formation and the water flow in the downcomer region 106
Implementation Method 3
The water flows vertically upward due to the decreasing density above the core 112 as a result of steam formation
Data Source
AI summary
A chimney of a nuclear reactor may include a hollow body with an interior surface and an opposing exterior surface; and a plurality of trip structures on the exterior surface of the hollow body. The chimney may be used in a method of improving a core inlet enthalpy of a nuclear reactor. The method may include interrupting a downward flow of water within a downcomer region of a reactor pressure vessel with a plurality of first trip structures. The downcomer region is an annular space defined by the reactor pressure vessel and a chimney within the reactor pressure vessel. The plurality of first trip structures are disposed on an exterior surface of the chimney.