Experimental study of the effects of flow inserts on heat transfer and critical heat flux
- Atomic Energy of Canada Ltd., Chalk River, Ontario (Canada). Chalk River Labs.
The effects of flow inserts in a tube on heat transfer in single-phase flow, and on the critical heat flux (CHF), were investigated at Chalk River Laboratories using Freon-134a as a coolant. The test section was a vertical 8 mm ID directly heated tube, made of inconel 600. Two ring-shaped flow obstructions were tested, which reduced the flow area by 17.8% and 30%. The presence of these flow inserts enhanced the heat-transfer coefficient up to 38% and 61%, respectively. The enhancement in heat transfer was observed over a very short distance (L/D < 7) downstream of the obstruction. Subsequently, CHF tests were performed in the same facility with one to four rings, with a 30% flow obstruction, evenly distributed along the test section. The impact on CHF of changing the axial spacing between these flow obstructions was found to be very significant: compared to a test section without flow obstructions, the CHF was increased by up to 110% for spacing of 12.5 cm, and up to 30--50% for spacings in excess of 25 cm. These tests were performed at pressures of 1.13 and 1.66 MPa, mass flux from 2 to 4 Mg/m{sup 2}s and critical quality from 0.05 to 0.25. These effects of the flow obstruction on heat transfer and CHF were determined using a novel technique that allowed a change of flow-obstruction location by externally moving the obstructions with magnets, without changing the local flow conditions. The primary objective of the CHF study was to determine the dependence of CHF on the axial spacing of adjacent flow obstructions for conditions simulating PWR as well as CANDU reactor conditions.
- OSTI ID:
- 234262
- Report Number(s):
- CONF-960306--; ISBN 0-7918-1226-X
- Country of Publication:
- United States
- Language:
- English
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