Glossary of Terms

Here you will find a glossary of specialised terms commonly used in thermostating and metrology.

R

Radial pumps

Radial pumps are centrifugal pumps with a running wheel that has a so-called 'radial' shape. The non-linear characteristics of a radial wheel differ fundamentally from the characteristics of a peripheral wheel. At lowest feed pressure and highest feed flow rate the highest drive energy is required with the radial shape. Standard pumps for the chemical industry are radial pumps. Radial pumps are especially suited for small feed pressures and high flow rates.

Recommended temperature range

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 thermostating tasks and possible undesirable side effects. Towards the lower value the bath liquid becomes more viscous, affecting temperature stability, 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 other conditions are acceptable it is desirable to select a liquid that is not used at the limits of its indicated temperature range.

Reduced viscosity (viscosity coefficient)

The specific viscosity based on the concentration C of the dissolved substance.

Refrigerant

Operating material of the cooling process that is located in the closed refrigeration system. The compressor sucks it from the evaporator, where it changes to gaseous condition under heat absorption. On the warmer side of the evaporator the medium cools down through heat absorption. On the high pressure side of the compressor the cooling medium is liquefied in the condenser/heat exchanger under heat transfer. The condenser/heat exchanger is water- or air-cooled.

Refrigerant

This is used in the circuit of the cooling unit and extracts the heat of the thermostating liquid when the compressed gas expands in the evaporator. LAUDA exclusively uses refrigerants with ODP = 0 that cannot cause any harm at all to the ozone layer (ODP = Ozone Depletion Potential).

Refrigeration system

See refrigerant.

Relative viscosity

The ratio of the dynamic viscosity ç of the solvent to that of the solvent çs. In the case of severely diluted solvents, this corresponds almost to the ratio of the kinematic viscosities:

Resolution of indication

This mostly relates to the actual value of the digital temperature display and gives the temperature difference between two consecutive figures. In the case of thermostats with the E 100 control head it is 0.1 °C, and for thermostats with the E 200 and E 300 control heads it is 0.05 °C. For the C/K and Ultra the resolution of indication can be adjusted to 0.01 °C or 0.001 °C.

Reverse CMC

Reverse CMC is the determination of CMC by automatically reducing surfactant concentration. This measuring method is based on a LAUDA patent. It is faster and offers significant advantages in handling compared to other methods.

Reverse flow protection

Used when thermostating open external baths with a pressure/suction pump or Duplex pump and prevents overflowing after switching off the thermostat. The reverse flow protection is screwed instead of the metal tube connections onto the pump outlets and is electrically connected to the control head of the C/K series or the Ultra series. The liquid circuit is ventilated by means of a solenoid valve when the thermostat is switched off, the liquid column breaks and cannot flow back.

Ring/Plate tensiometers

Measure the force with which a lamella attacks a Du Noüy ring or Wilhelmy plate. This is used to calculate the surface/ interfacial tension between liquid phases. Ring/plate tensiometers are also used for dynamic contact angle measuring and CMC measuring with software controlled burettes.

Risk analysis

The risk analysis has to be generated by the manufacturer of the temperature control unit. The analysis serves to determine the dangers in connection with the unit with reference to the provided operating conditions. Lay-out and construction of the temperature control unit take place in consideration of the risk analysis. As to the remaining dangers which cannot be covered through technical solutions, as well as measures required from the operator, the manufacturer has to inform the operator through indications in the operating manual, and if necessary through mounting alert labels on the temperature control unit.

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