A heat pipe heat exchanger utilizing a working fluid such as water incorporates heating means for preventing the freezing of the working fluid when the heat exchanger is non-operational. These heating means are located at or near the heat pipe in the lower region of the heat exchanger so as to prevent the freezing of the working fluid. Trapped gases within the heat pipe caused by the reaction of the working fluid with the metallurgy of the pipe are released by heating the working fluid with the heating means in order to increase the gas pressure within the heat pipe until the pressure is greater than the external pressure of the heat pipe. A venting means is used to vent the trapped gases from the heat pipe due to the force of the pressure within the heat pipe.
An apparatus for the controlled heating of a process fluid has a heater, a process fluid vessel containing the process fluid, and a bundle of thermosyphons extending between a burner chamber of the heater and the process fluid inside the vessel for transferring heat from the heater to the process fluid. Burners in the burner chamber are controlled to maintain the bulk temperature of the process fluid T.sub.BULK substantially within an operating range defined by preset upper T.sub.HIGH and lower T.sub.LOW temperature setpoints. The burners can be turned on to maintain an outside metal temperature T.sub.EVAP of the evaporator ends of the thermosyphons above a preset dew point temperature T.sub.DEW to prevent corrosion. The burners can also be shut down if an outside surface temperature T.sub.OD of at least one of the condenser ends of the thermosyphons extending into the vessel exceeds a predetermined setpoint temperature T.sub.ALARM. Different configurations of condenser ends of the thermosyphons in the vessel may be utilized to enhance heating the process fluid. The vessel and heater are separated and sealed from each other by a sealed chamber encasing the thermosyphons, which may also be used to preheat incoming combustion air for the burners.
