Apparatus and method for regulating temperature in a cryogenic test chamber

In cryogenic apparatus of the kind including a cryogenic vessel adapted to contain a fluid in a liquid phase at a cryogenic temperature, means defining a test chamber in the cryogenic vessel, test chamber heater means in thermal communication with the test chamber, an opening to admit fluid from the cryogenic vessel to the test chamber, evacuation means operative to partially evacuate the test chamber to draw fluid from the cryogenic vessel through the opening into the test chamber, and a test vessel adapted to receive and enclose a test specimen and located in the test chamber to maintain the temperature of the specimen approximately equal to the temperature in the test chamber, an improvement for regulating the temperature in the test chamber by maintaining the fluid therein at a desired temperature, the improvement comprising:

• an impedance capsule located in the cryogenic vessel in spaced apart relation to the test chamber and defining an elongated impedance chamber;
• a capillary tube located in the impedance chamber;
• capillary heater means in thermal communication with the capillary tube;
• and
• a coupling tube having a diameter larger than that of the capillary tube and in fluid communication with the capillary tube and extending out of the impedance chamber and in fluid communication with the opening to the test chamber,
• operable in a high temperature mode wherein the capillary heater means is operative to warm the capillary tube sufficiently to boil any liquid flowing therein and thereby to change the phase of the fluid from liquid to gas as the fluid is drawn through the capillary tube into the test chamber and wherein the test chamber heater means is operative to warm any gas in the test chamber to a desired temperature and thereafter to maintain the gas at said temperature,
• operable in a medium temperature mode wherein the fluid remains in its liquid phase without undergoing any net change in temperature as it is drawn through the capillary tube into the test chamber and is thereby maintained at the cryogenic temperature in the test chamber, and
• operable in a low temperature mode wherein the fluid remains in its liquid phase as it is drawn through the capillary tube into the test chamber until a reservoir of liquid has accumulated in the test chamber, the capillary heater means thereupon being operative to warm the capillary tube sufficiently to substantially prevent the flow of any more fluid through the capillary tube, and the evacuation means thereupon being operative to reduce the pressure in the test chamber sufficiently to lower the boiling temperature of the liquid in the chamber to a desired temperature and thereafter to evacuate any gas produced as the liquid boils and thereby to maintain the liquid at said temperature.

In cryogenic apparatus of the kind including a cryogenic vessel adapted to contain a fluid in a liquid phase at a cryogenic temperature, means defining a test chamber in the cryogenic vessel, and a test vessel adapted to receive and enclose a test specimen and located in the test chamber to maintain the temperature of the specimen approximately equal to the temperature in the test chamber, a method of regulating the temperature in the test chamber by drawing fluid into the test chamber and maintaining the fluid at a desired temperature, the method comprising:

• selecting a mode of operation;
• drawing fluid from the cryogenic vessel into the test chamber through a fluid flow path having a capillary tube by partially evacuating the test chamber;
• if a high temperature mode has been selected, applying sufficient heat to the capillary tube to boil any liquid flowing therein and thereby to change the phase of the fluid from liquid to gas as the fluid is drawn through the capillary tube into the test chamber, and applying sufficient heat to the gas in the test chamber to warm the gas to the desired temperature and thereafter to maintain the gas at said temperature;
• if a medium temperature mode has been selected, maintaining the fluid in its liquid phase without any net change of temperature as the fluid is drawn through the capillary tube into the test chamber and thereby maintaining the fluid in the test chamber at the cryogenic temperature;
• and
• if a low temperature mode has been selected, maintaining the fluid in its liquid phase as the fluid is drawn through the capillary tube into the test chamber until a reservoir of liquid has accumulated in the test chamber, applying sufficient heat to the capillary tube to substantially prevent the flow of any more fluid through the capillary tube, reducing the pressure in the test chamber sufficiently to lower the boiling temperature of the liquid in the test chamber to a desired temperature, and evacuating any gas produced as the liquid boils to maintain the liquid at said temperature.