Sorensen's bubble pump

US Patent 5,351,488

Sorensen's heat powered  bubble pump has a history of successful deployment in the Sol Perpetua solar water heater manufactured by
Bubble Action Pumps Ltd. in Kingston, Ontario. Pictures of the pump may be seen at

Excerpt from the patent:Sorensen's bubble pump, US patent 5,351,488

... reference will be made to the bubble pump shown in FIG. 2. The bubble pump 1 comprises, preferably but not essentially, a dome shaped container 2, preferably but not essentially, made of glass or transparent plastics material for ease of viewing the operation therein. Container 2 is divided into two separate chambers 3, and 6 by an impervious divider 5. Chamber 3 is defined as the separator and chamber 6 is defined as the condenser. Cold condensate working fluid 4 from condenser chamber 6 passes through a conduit 7 to the bottom of a solar array 8 where it is heated by solar energy. The working fluid 4 may be water, or where there is a risk of freezing, a mixture of ethylene glycol and water or another fluid having a suitable boiling point and vapour pressure. Solar energy causes the liquid 4 to boil and form a gas/liquid mixture containing a large number of vapour bubbles 9 which rise up tube 10 and splash out of the top thereof, in the manner of a coffee percolator. The vapour rises into dome 2 and passes into tube 11 which carries the vapour to the condenser chamber 6 where it condenses in cold working fluid 4. The hot working liquid thus separated from the vapour falls to the bottom of the separator chamber 3 from whence it passes via tube 12 to a heat exchanger (not shown), as described in more detail hereinafter, or to the external turbine 13 from which the liquid returns to the condenser chamber of the downstream bubble pump via conduit 14. The pressure in the condenser chamber 6 is controlled by air purge tube 15 and a hand operated vacuum pump 16, in conjunction with valve 19, so as to balance the flow of working fluid in the system and prevent flooding of the separator or condenser.

End of excerpt from the patent.

The pump generates a pressure difference between the outlet 12 and inlet 14 due to the  difference in the heights of  the surfaces of the working fluids in the separator 3 and the condenser 6.  

There is an interesting study of the performance of Sorensen's pump: Thermal modelling of a bubble pumped solar domestic hot water system, T.O. Bahomed and S.J. Harrison Solar Calorimetry Laboratory, Queen’s University, Kingston, Ontario, Canada, K7L 3N6.$File/BAHO0250.pdf

The bubble pump produces a pressure difference of approximately  3 feet of water. Since this pressure difference is produced between the tops of a pair of pipes whose fluid contents balance each other,  the heat exchanger and storage tank may be located a greater distance below the solar water heater.