the liquid nitrogen , once inside the cryostream coldhead , passes through a heater called the evaporator heater , which evaporates most of the liquid into vapour at the boiling point of liquid nitrogen . this vapour then flows outward along one path of the heat exchanger , through the cryotream temperature controller , to arrive at the inlet of the diaphragm pump at approximately 10 K below room temperature . the nitrogen gas from the pump may then be dried with aline drier unit if appropriate . the flow rate of the gas from the pump is then regulated by a variable flow controller in the cryostream temperature controller . this gas flows back into the cryostream coldhead where it is re-cooled along the second path of the heat exchanger .