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Fluid-induced vibration in heat exchanger tube bundles

Project coordinator(s)

Dr. Craig Meskell
Email: cmeskell@tcd.ie
Tel: +353 1 896 1455

Research Student(s)

Mr. Daniel Keogh

YouTube
Description

Watch an Innovation Academy video about this research on www.youtube.com/watch?v=QOQdROO4nPI

A key feature of the Pressurized Water Reactor is that water is heated under pressure to ~300˚C in the core. The pressurization prevents the water boiling. This is called the “primary coolant”. Typically the reactor core transfers 5GW of heat power to the coolant. This energy is then transferred to the secondary coolant which is also water, but this is allowed to boil. This heat transfer occurs in very large heat exchangers called Steam Generators (SG). The SG consists of literally hundreds of long, slender tubes, typical ~19mm diameter, with a length of the order of 10m. The hot primary coolant flows inside the tubes, while the secondary coolant flows across the bundle of tubes. The combination of flexible tubes (the tubes have an aspect ratio larger than a guitar string), and highly turbulent, energetic cross flow means that the structure is prone to flow induced vibration. As the primary and secondary coolant must be kept separate, the tubes must not rupture. Thus, the flow induced vibration represents a major operational and design constraint. For example, a particular type of flow induced vibration called fluidelastic instability places an upper limit on the flow velocity, and hence heat exchange rates and hence electricity generating capacity of the entire plant. In terms of designing for life extensions or uprating, or for longer design life in new build of 60 years, the long term fretting wear damage associated with flow-induced vibration is the key limiting factor. The critical nature of the problem means that a very conservative engineering approach to predicting and managing flow-induced vibration in nuclear steam generators has been adopted. However, as in any engineering system, an overly conservative approach embeds large inefficiencies.

In both CCGT and coal plant, the heat exchanger is a steam generator, similar to the nuclear steam generators discussed above, but with combustion gas on the hot side. Concentrating solar plant, which are currently under ongoing development will use a combination of molten slat and pressurized water to raise steam for the generating turbines. The performance and reliability of the heat exchanger is important to the overall efficiency, reliability and economics of these facilities, and so this work will have wide applicability in energy systems.

Dan is currently on a 6-month research visit in École Polytechnique de Montréal, Canada working with Professor Njuki Mureithi, studying two-phase flow in nuclear steam generators with the intention of improving theoretical models of flow-induced vibration.

Funding Body

HEA PTRLI GREP