A hot surface loses heat to its surroundings by the combined modes of convection and radiation. This module enables to analyze the combined effects of convection and radiation at different values of surface temperature and air velocity on the surface. The prevalence of convection at low surface temperatures and the prevalence of radiation at higher surface temperatures, as well as the increase of transferred heat due to forced convection, can be demonstrated. The equipment consists of a centrifugal fan with vertical outlet duct at the top of which a cross cylinder is mounted. This cylinder is heated by an electric heating element operating at low voltage. The power supplied to this heating element can be varied and measured. The surface of this cylinder is coated with heat-resisting mat black paint which ensures an emissivity close to one. A K-type thermocouple attached to the wall of the cylinder enables to measure the surface temperature under various operating conditions. An air lock at fan inlet enables to vary the air velocity through the outlet duct and an anemometer enables to measure the air velocity. A K-type thermocouple located in the outlet duct enables to measure the air temperature before the heated cylinder.
TRAINING PROGRAM
This unit enables to develop and analyze the following issues:
• combined heat transfer in conditions of natural convection
• determining the convection and radiation heat transfer coefficients and how they depend on temperature
• determining the effect of forced convection on the heat transfer from the cylinder at different values of air velocity
TECHNICAL CHARACTERISTICS:
• Centrifugal fan with vertical outlet duct
• Heated cylinder (100 W @ 24 Vdc) cross-mounted on the duct, with diameter of 10 mm, heated throughout its length of 70 mm and coated with low-emissivity paint
• K-type thermocouple for measuring cylinder surface temperature
• Housing for K-type thermocouple for measuring air temperature before the heated cylinder
• Air lock for varying air velocity
• Anemometer
