Conditions needed for Natural Circulation

The Natural circulation will only take place when the right conditions exist. Still, after natural circulation has begun, elimination of any one of such conditions will cause the natural circulation to stop. The situations for natural circulation are as follows:

1. A temperature difference subsist (i.e., heat source and heat sink exists).

2. The heat source is at a lesser elevation than the heat sink.

3. The fluids should be in contact with each other.

There should be two bodies of fluid at various temperatures. This could also be one body of the fluid with regions of various temperatures. The difference in temperature is essential to cause a density difference in the fluid. The density disparity is the driving force for natural circulation flow.

The difference in temperature should be maintained for the natural circulation to carry on. Addition of heat by a heat source should exist at the high temperature region. The continuous elimination of heat by a heat sink should exist at the low temperature region. Or else the temperatures would ultimately equalize, and no further circulation would take place.

The heat source should be at a lower elevation than the heat sink. The illustration of the balloon explains, a warmer fluid is less dense and will tend to increase, and a cooler fluid is denser and will tend to sink. To take benefit of the natural movement of warm and cool fluids, the heat source and heat sink should be at the correct elevations.

The two regions should be in contact and hence flow among the areas is possible. When the flow path is hindered or blocked, then natural circulation cannot take place.