Armfield Engineering Education
HEAT TRANSFER AND THERMODYNAMICS
HT14 Combined Convection and Radiation
HT14 Computer Controlled Combined Convection and Radiation - Issue 1
A hot surface loses heat (heat is transferred) to its surroundings by the combined modes of convection and radiation. In practice these modes are difficult to isolate and therefore an analysis of the combined effects at varying surface temperature and air velocity past the surface provides a meaningful teaching exercise.
The heated surface studied is a horizontal cylinder which can be operated in free convection or forced convection when located in the stream of moving air. Measurement of the surface temperature of the uniformly heated cylinder and the electrical power supplied to it allows the combined effects of radiation and convection to be compared with theoretical values. The dominance of convection at lower surface temperatures and the dominance of radiation at higher surface temperatures can be demonstrated as can the increase in heat transfer due to forced convection.
On the HT14C, the heater power and the air flow are controlled via the HT10XC, either from the front panel, or from the computer software. On HT14 these are controlled manually.
Right: HT14C Computer Controlled Radial Heat Conduction Accessory
shown with the HT10XC - Service Unit
Ordering Specification
• A small scale accessory designed to demonstrate combined convection (free and forced) and radiation from a horizontal heated cylinder. It consists of a centrifugal fan with vertical outlet duct at the top of which is mounted the heated cylinder.
• Comprises a heated cylinder mounted in a vertical air duct, with a fan at the base of the duct which can be used to provide a variable air flow over the cylinder.
• Heater rating 100 Watt at 24V DC.
• K-type thermocouples measure the air temperature upstream and the surface temperature of the cylinder.
• On HT14C the air flow is electronically adjustable over the range 0 - 7 m/s by an variable speed fan.
• On HT14 the air flow is manually adjustable
• The air flow rate is measured by a vane type anemometer in the outlet duct.
• The accessory is mounted on a PVC baseplate which is designed to stand on the bench top and connect to the Heat Transfer Service Unit without the need for tools.
• A comprehensive instruction manual describing how to carry out the laboratory teaching exercises in combined radiation and convection (free and forced) and their analysis as well as assembly, installation and commissioning is included.
Experimental Capabilities
> Determining the combined heat transfer (Q radiation + Q convection ) from a horizontal cylinder in natural convection over a wide range of power inputs and corresponding surface temperatures.
> Measuring the domination of the convective heat transfer coefficient Hc at low surface temperatures and the domination of the radiation heat transfer coefficient Hr at high surface temperatures
> Determining the effect of forced convection on the heat transfer from the cylinder at varying air velocities
Technical Details
The equipment consists of a centrifugal fan with a vertical outlet duct at the top of which is mounted a heated cylinder. The mounting arrangement for the cylinder in the duct is designed to minimise loss of heat by conduction to the wall of the duct.
The surface of the cylinder is coated with heat resistant paint which provides a consistent emissivity close to unity. A K-type thermocouple (T10) attached to the wall of the cylinder, at mid position, allows the surface temperature to be measured under the varying operating conditions.
A variable fan blows air through the outlet duct and a vane type anemometer within the fan outlet duct allows the air velocity in the duct to be measured. On the HT14C the fan is a variable speed fan with electronic control. On HT14 a manually adjustable throttle plate allows the air velocity to be varied.
A K-type thermocouple (T9) located in the outlet duct allows the ambient air temperature to be measured upstream of the heated cylinder.
Accessories
Essential Armfield Accessories
HT14C requires HT10XC Computer Controlled Heat Transfer Service Unit
HT14 requires either HT10XC or HT10X Heat Transfer service units
Requirements
All electrical requirements are obtained from the service unit.
NOTE: the supply rating of the HT14/HT14C must
be the same as
that of the HT10X/HT10XC that it is used with, i.e.
HT14-A, HT14C-A: 230V/1ph/50Hz
HT14-B, HT14C-B: 115V/1ph/60Hz
HT14-G, HT14C-G: 230V/1ph/60Hz
Shipping Specification
HT14
Volume: 0.1 m3³
Gross Weight: 9 kg
HT14C
Volume: 0.2 m³
Gross Weight: 13 kg
Overall dimensions
HT14
Height: 1.20 m
Width: 0.35 m
Depth: 0.30 m
HT14C
Height: 1.20 m
Width: 0.49 m
Depth: 0.44 m
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