The presence of tube supports in PWR steam generator tube bundles creates regions of restricted flow which may result in altered heat transfer effects and increased pressure drop. One heat transfer effect which can occur is localized vaporization or “dry out”. At higher heat flux levels this may result in a stable vapor blanket or an alternate wetting and drying occurring with an accompanying increase in the local tubewall surface temperature. A test program was conducted to determine the thermal/hydraulic conditions at the inception of the tubewall temperature excursion for selected tube support designs and to measure the pressure drop across the supports using a multitube steam generator model. Tests were performed on each of four tube supports over a broad range of shellside quality/subcooling conditions and pressures, temperatures, and mass flow rates that are prototypical of PWR steam generator operating conditions. Photographs and high-speed movies were taken of the flow both above and below the test piece.

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