EMISSIVITY - NATURAL CONVECTION AND RADIATION

The Natural Convection and Radiation equipment allows the study of heat transfer at different pressures and vacuum. It shows the differences between radiation and natural 'free' convection. It allows students to find the emissivity of a surface and verify the Stefan-Boltzman equation. It also gives students an understanding of the non-dimensional characteristics using Nusselt, Grasof, Prandtl and Knudsen numbers.

A small heated element hangs in the centre of a pressure vessel. The heater has a matt black surface. Attached to its surface is a thermocouple to measure the temperature. The vessel’s inside is also black, and it has a thermocouple fitted to its wall to measure the temperature in the vessel. The vessel may be charged with compressed air up to 1 bar (gauge) or evacuated down to about 5 Pa (absolute). Students can extrapolate the results down to a total vacuum (no convection). This allows them to isolate the heat transfer by radiation.

Instruments and a digital display measure and display the temperatures, pressures and power to the element. To give accurate measurements of pressure and vacuum, the equipment has two different pressure transducers - one for pressures above atmospheric and one for pressures below atmospheric.

Included is a vacuum pump, and a regulator for an external compressed air supply (up to 10 bar). The system includes a pressure relief valve to protect the equipment and the user.

Students can do tests with or without a computer connected. However, for quicker tests with easier recording of results, TecQuipment supply their Versatile Data Acquisition System (VDAS®) with this product. This gives accurate real-time data capture, monitoring and display, calculation and charting of all the important readings on a computer (computer not included).