DIRECT MEASUREMENT OF THERMOSIPHON FLOW.

The rate of thermosiphon flow has been measured directly by the application of a simple and well-known laboratory technique, a constant level device. The measurements were performed on an open-cycle thermosiphon system. The thermosiphon flow rate was correlated both with the temperature difference across the solar collector ( DELTA T) and the global insolation rate for four different thermosiphon heights. The minimum DELTA T required to initiate thermosiphon flow in the morning was also determined.