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Selecting a bath liquid that is suitable for the temperature range is critical for the safe and reliable operation of your thermostats.
The recommended temperature range, defined by the highest and lowest operating temperature, is the range in which a bath liquid in a thermostat can be used accurately and reliably over a long period of time. The indicated values result from extensive laboratory tests but must always be interpreted as a compromise between the requirements of the thermostat's tasks and possible undesirable side effects. Towards the lower value the bath liquid becomes more viscous, affecting temperature accuracy, pump output and cooling capacity. In the upper range there is an increased tendency to vaporisation and the production of smells. The values shown are realistic and honest and keep side effects within acceptable limits. Provided the other conditions are acceptable it is desirable to select a liquid which does not have to operate at the limits of the indicated temperature range.
Viscosity refers to the flow behaviour of a liquid which can range from thin to highly viscous. Viscosity depends very largely on temperature. It is a measure of the internal friction between adjacent liquid layers at different velocity. Viscosity affects the characteristics (temperature control, pimp power) of a thermostat and is therefore particularly important.
Density is understood to be the mass of a body per unit volume. In addiction to depending on the material, this value is essentially affected by temperature.
The volume change refers to the increase or decrease of liquid volume at a certain operating temperature with a reference to an initial temperature of 20°C. The liquid volume to be considered to includes both that inside the thermostat itself and also that in the external circulating system.
Specific heat capacity is the amount of thermal energy which is required for a temperature increase of 1°C in a mass of 1kg.
The pour point is understood to be the temperature at which a liquid becomes so viscous that it ceases to flow.
The boiling point identifies the temperature at which a liquid begins to boil. This temperature is dependent on atmospheric pressure, and the boiling point is therefore specified at a standard pressure of 1013 mbar.
The flash point on a flammable liquid indicates the lowest temperature at which the vapour produced can ignite for a short time, i.e. for less than 5 seconds. The limits of LAUDA bath liquids are mostly appreciably below the appropriate flash point in order to exclude any danger.
The fire point according to EN 61010 is the most important criterion for the upper limit of a bath liquid. According to ISO 2592 it is the temperature at which a liquid in an open crucible burns for at least 5 seconds. The fire point of a bath liquid is decisive for its maximum permitted temperature which must be not higher than 25°C below the fire point.
The ignition temperature is the lowest temperature at which a flammable substance in an air-liquid mixture ignites spontaneously and continues to burn without any addition of heat.
When changing from one bath liquid to another it is absolutely essential to clean the internal part of the thermostat, the connecting tubing and also the external system. For this reason suitable solvents are listed against each bath liquid. In order to protect the environment it has however proved satisfactory in most cases to empty the thermostat completely and then to fill it with water with the addition of a surfactant, e.g. a commercially available detergent, and to heat it to approx. 80°C followed by draining (not applicable with USH 400, Integra and WK). Ideally this operation should be repeated.
Breakdown of a liquid is produced by contact with oxygen at high temperatures or through high film temperatures on the heater. Cracking can be reduced by keeping the bath opening to a minimum. In addition the heaters of LAUDA thermostats are of optimal design so that unnecessary high film temperatures are avoided.