DESCRIPTION

The Armfield Free and Forced Convection unit has been specifically designed to demonstrate the phenomena of natural (free) and forced convection. Temperature profiles and heat flux over three different heat transfer surfaces can be easily studied.

The HT19X is designed for use with the Armfield HT10X Heat Transfer Service Unit.

This unit consists of a bench mounted vertical air duct positioned on the top of a centrifugal fan. The air duct incorporates an aperture positioned at the rear wall of the duct, into which three different types of heat-transfer surfaces can be inserted. The three types of heat exchangers supplied are; flat plate, cylindrical pins and finned surface.

Incorporating an electrical heating element, with positive thermal cut-out, and thermocouples for precise temperature measurement. The clamping mechanism ensures accurate alignment of the surface inside the duct. The front wall of the duct is acrylic to allow viewing of the heated surface and measurement sensors.

For forced convection, the centrifugal fan draws ambient air upward through a flow straightener and over the heated surface. A manually variable throttle controls the air flow.

An air-velocity sensor measures the air velocity inside the duct upstream of the heat exchanger.

Thermocouples measure the air temperature before and after the heated surface, together with the surface temperature at three positions along the extended surface exchangers.

EXPERIMENTAL CAPABILITIES

• Relationship between surface temperature and power input in free convection
• Relationship between surface temperature and power input in forced convection
• Understanding of the use of extended surfaces to improve heat transfer from the surface
• Determining the temperature distribution along an extended surface
• Comparing characteristics of a vertical and horizontal flat plate in free convection
• Determining the characteristic velocity, the Reynolds, Grashof and Rayleigh numbers for a flat plate in free convection
• Calculation of the average heat-transfer coefficient of the pinned heater in forced convection
• Comparing horizontal and vertical configurations for a finned exchanger in free convection

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