Convection

OLYMPUS DIGITAL CAMERA

Demo 1

convection20setup

Demo 2

 

 

convection20jar

 

 

Equipment: 

  • Chimney apparatus
  • Candle
  • Smoke source
  • Lighter
  • Cylindrical heater and L shaped tube
  • Glass tank
  • Water and ice
  • Rheoscopic fluid
  • Lab jack
  • Lamp with shade
  • 2 Variac transformers

Demo:

  1. Convection Box: When a lit candle is placed under one clear chimney and a source of smoke (incense or punk) is placed above the other clear chimney, convection currents can be seen. See top photo.
  2. Convection in Liquids: This setup (middle photo) is based on a small cylindrical heater attached to the tip of an L-shaped tube and immersed into a square glass tank with a mixture of water and rheoscopic fluid (bottom photo). The tank is resting on the lab jack and illuminated by the table lamp with a deep plastic shade. The heater temperature and lamp brightness can be regulated by variacs.
    Adding ice to the tank enhances downflow of the liquid. Switching the heater on (70-80V) forces bulk movement of the liquid up. Ice and heat together cause interesting convection patterns (watch this video to see demonstration).

Explanation:

Convection is heat transfer by mass motion in a fluid. When the fluid it heated and moves away from the heat source it carries heat energy with it. When the fluid heats up it expands and becomes less dense. It then moves towards the more dense and colder fluid, creating convection currents.

  1. Convection Box: The candle in the right chimney causes hot air to rise. To keep the pressure equalized cold denser air flows in from the left chimney creating a suction that brings smoke with it.
  2. Convection in Liquids: In this demo you will be able to see convection currents in liquid. The less dense (hot) liquid will rise and the denser (cold) liquid will fall creating circular currents that you will be able to observe.