Surface condensers work indirectly, steam gives up heat to one surface of the condenser gives while a
coolant such as water or air absorbs that heat from the other. “Direct contact condensers” have no
intermediary surfaces; the steam and coolant (usually water) directly contact each other although a heat
exchanger may eventually cool the resulting mixture.
Direct Contact Condensers
Jet condensers are direct contact
condensers which spray a jet of
cooling water into the steam to be
condensed. One of the earliest types
(to right) is little more than a
perforated horizontal pan inside the
upper portion of a metal box.
Pumping water into the pan causes a
shower, condensing steam admitted
to the space below. This
condensation causes a vacuum which
is maintained by a vacuum pump
that removes air and other non-
condensable gasses liberated from
the steam, a water pump removes the
condensate against the resulting
vacuum
Possibly the most common jet condenser is the ejector condenser, ejectors being a type of “jet pump”. A
nozzle accelerates a moving stream of water, directing it through an enclosed cavity through which the
exhaust steam is admitted. The moving water entraps the steam, and any resident air, carrying them out
the discharge nozzle. Ejector condensers are compact and need no air or vacuum pump, the fluid flow
itself removing entrained air. Ejector condensers may reduce engine output because the engine must
supply the power to pump the fluid flow.
SACA member John Wetz took the unusual
step of converting an automotive radiator
into a direct contact, rather than a surface
condenser. While his radiator is not suitable
for vacuum condensing, it is affordable and
apparently effective. A hose connecting the
upper and lower radiator manifolds
facilitates circulation by serving as a
downcomer, a tee in the hose supplies water
to the boiler feed pump. Steam is admitted
evenly across the lower manifold from within
a perforated pipe. The steam bubbles rise
through the water columns in the finned
radiator tubes and condense on contact with
the surrounding water. The cooled
condensate spills over into the upper
manifold into the downcomer hose, some of
the condensate being drawn back to the
boiler by the feed water pump and the rest
free to sink to the lower manifold and
establish a natural circulation.