Medium Of Capillary Thermostat
The liquid expansion type thermostat must contain liquid inside. The switch of the thermostat contact is controlled by the principle of thermal expansion and contraction of the liquid, and the setting circuit starts to work.
The liquid medium of the liquid expansion thermostat should have the following requirements:
(1) The liquid expansion coefficient should be large and sensitive to temperature changes.
(2) The liquid does not corrode the temperature bulb, capillary tube and measuring bellows.
(3) The liquid has small viscosity and specific heat, but has high thermal conductivity.
The liquid expansion type thermostat should choose different working media according to the different measurement range. The lower limit of temperature measurement cannot be lower than the freezing point of the working liquid, but the upper limit of temperature measurement can be higher than the boiling point of the working liquid under normal pressure. As the measured temperature rises, the pressure in the closed container will rise, and the boiling point of the working liquid will rise accordingly.
Commonly used liquid media in liquid expansion thermostats include mercury, xylene, methanol, ether, glycerin, water and ethanol. Among these media, the expansion coefficients of methanol and ether are relatively large, while the expansion coefficients of water and mercury are relatively small.
