Thermal Hydraulics & Heat Transfer

[IMAGE: Large industrial stainless-steel pipe with multiple sensor penetrations, cable trays, and insulation lagging, running along a concrete wall]

Figure 1: Instrumented DN 300 test section of the Building 6 primary loop. Thermocouple arrays (visible as wire bundles entering the pipe wall at regular intervals), absolute and differential pressure transducers, and a clamp-on ultrasonic flow meter are installed. The test section is viewed from the operating gallery, looking east.

Overview

The Thermal Hydraulics programme leverages the Building 6 Central Thermal Facility as a uniquely capable experimental platform for heat transfer and fluid flow research at industrially relevant scales. The facility provides access to steady-state steam-water conditions at temperatures and flow rates that cannot be achieved in bench-scale laboratory rigs.

The programme is conducted jointly by the Plasma & Thermal Sciences Division and the Operations Directorate under Prof. Sigrid Lindqvist. It is closely integrated with the Thermal Systems Research Group, which maintains a more detailed page on the Building 6 research platform.

Active Research Areas

Two-Phase Flow in Large-Diameter Pipes

Measurement of void fraction, flow regime boundaries, and two-phase pressure drop in horizontal and inclined pipes of DN 200 to DN 400 under steam-water conditions at pressures up to 1.2 MPa. The work addresses a recognised gap in two-phase flow databases, which are overwhelmingly dominated by small-diameter (<50 mm) data at laboratory scale.

Key findings to date include the identification of a previously under-reported transitional flow regime in the stratified-to-slug transition region at large pipe diameters, with implications for system analysis codes used in power plant safety assessment. [Lindqvist & Okonkwo, Nucl. Eng. Des. 2002]

[IMAGE: Two-dimensional plot with superficial velocity axes and coloured regions indicating different flow patterns, with data points overlaid]

Figure 2: Flow regime map for horizontal DN 300 pipe under saturated steam-water conditions at 0.8 MPa, showing the observed stratified, slug, and annular regimes as a function of superficial gas and liquid velocities. The newly identified transitional regime is highlighted.

Heat Exchanger Fouling Under Extended Operation

Long-duration monitoring of shell-and-tube heat exchanger thermal performance in the Building 6 primary and secondary loops. The primary loop exchangers have now accumulated over 2,400 hours of continuous operation (as of March 2004), with fouling resistance approaching an asymptotic value. Results inform maintenance scheduling and heat exchanger over-design margins for comparable systems.

Transient Thermal Response

Experimental characterisation and computational modelling of the thermal response of coupled multi-loop systems under load-following, partial-load, and transient conditions. Step-change and ramp-change experiments on the Building 6 loops provide validation data for a custom thermal-hydraulic model developed in MATLAB/Simulink. The work has direct application to the design of thermal management systems requiring high reliability under variable load.

Instrumentation

Measurement	Instrument	Accuracy
Fluid temperature	Type-K thermocouple arrays (in-stream)	±0.5 K
Pipe wall temperature	Surface-mounted Type-K thermocouples	±0.8 K
Absolute pressure	Strain-gauge transducers (0–2 MPa)	±0.1% FS
Differential pressure	Variable-capacitance DP cells	±0.5% reading
Flow rate (single-phase)	Clamp-on ultrasonic (transit-time)	±1% reading
Void fraction	Multi-beam gamma densitometer (Cs-137)	±3% (absolute)

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