Heating Solutions

Electric heating solutions are an irreplaceable accessory for many vacuum systems. The operating conditions of the vacuum system can be optimized by adapting the temperature and time of bakeout to the application. In generating very low pressures, the continuous desorption of gases, especially water vapour, limits the achievable final pressure. By heating, the desorption rate can be reduced to such an extent that pressures of <10-10 mbar can be achieved. To reduce the water vapour of your chamber a minimum bakeout temperature of 120 °C is recommended. It is optimal to monitor the pressure during this process. The bakeout with the selected temperature has been successful if the pressure drops or no longer decreases in the chamber during the bakeout process. Only higher temperatures would enable further effects by splitting up longer-chain molecules. It is difficult to recommend a bakeout temperature regarding hydrocarbons, because it depends on the length of the hydrocarbon compounds. In principle the following rule applies: the more long-chained the compound the higher the temperature needs to be. Usually bakeout temperatures of about 200 °C are used.

Another advantage of baking out is to extend the life of the measuring instruments which are directly connected with the vacuum chamber. This can be made by selective heating which ensures that the measuring instruments will become less dirty or rather trying to remove deposits from the measuring instruments by supply of energy. In addition, a possible drift of the measured values can be avoided or reduced. By baking-out your plants regularly, you can create equal conditions in your process or experiment. It is important that the temperature distribution is homogeneous because otherwise the particles condense on the cold spots, where in most instances the measurement technique is installed. This can be compensated only by longer baking-out. In summary, there are three parameters for an optimal bakeout process which have to be considered:

1. Bakeout temperature
2. Duration of bakeout
3. Homogenous temperature distribution

In principle, temperature compensation during heating can be made by heat conduction, heat radiation and convection.
During heat conduction temperature compensation takes place inside solids or between solids which touch each other directly and between which a temperature gradient exists. The time needed for temperature compensation basically depends on the heat conductivity of the material or materials, their masses and their temperature gradients.

The convection also takes place according to the principle of heat conduction. The heat transfer within a gas, as far as still existing in vacuum, happens from a zone of high temperature to a low temperature zone. This is done by buoyancy. As this effect lessens with decreasing pressure, it is irrelevant in vacuum technology and is no longer observable below 10 mbar.
During thermal radiation, heat energy is transferred by emission and absorption of electromagnetic waves. Every object with a temperature of > 0 K emits radiation. And every object hit by this radiation absorbs a part of it and reflects or allows the rest of the radiation to pass through. For this reason, it is the only mechanism to heat constructional systems located in the vacuum and having small contact surfaces to heated recipient areas, without heating a sample heater.

There are the following options for a controlled heating of the vacuum system from atmosphere side:

You are here: Home Products Heating Solutions