Glossary of Terms

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

D

Delivery head

The delivery head is a theoretical value which is used within the pump characteristics (see pump characteristic) instead of the feed pressure (see feed pressure). The advantage is that the delivery head is valid for any given liquid. The feed pressure is then calculated for the respective feed medium by multiplying the density with the delivery head (see feed pressure).

Density

Density is understood to be the mass of a body per unit volume. In addition to depending on the material, this value is essentially affected by temperature.

Diffusion coefficient

characterizes the thermal migration movements of molecules in the material examined. In tensiometry, the diffusion coefficient refers to the migration of molecules in the liquid measured.

Discharge pressure

The over-pressure of the circulating pump of a thermostat directly at the pressure nozzle, measured with water. If only one value is given in the table, this is the maximum delivery pressure at flow rate zero. In the diagrams the delivery pressure is given in relation to the flow rate.

Discharge suction

is the suction of the circulating pump (pressure/suction or Duplex pump) directly at the suction nozzle, measured with water. If only one value is given in the table, this is the maximum suction at flow rate zero. In the diagrams the discharge suction is given in connection with the flow rate.

Drop Volume Tensiometers

Determine the surface/interfacial tension of liquids at the moment of drop separation, from the volume of the drop that is formed in air or in an immiscible second liquid. The densities of the phases concerned must be known in order to calculate the surface/interfacial tension from the measured drop volume.

Du Noüy ring

A measuring body made of a platinum-iridium alloy to determine surface/interfacial tension from the tensile force of a lamella produced by this body using a ring/plate tensiometer.

Du Noüy ring method

Used to measure the surface/interfacial tension using a standardized ring with a ring/plate tensiometer. The ring is immersed into the liquid and then drawn out. This forms a liquid lamella that is stretched to its maximum. The surface/interfacial tension is calculated from the resulting force. The calculated value must be corrected.

Duplex pump

The LAUDA Duplex pump is a pressure/suction pump with built-in constant level controller in the thermostat. It is suitable for connection to open and closed circuits in the same way as the pressure/suction pump. The Duplex pump is offered as an option exclusively for the Ultras.

Dynamic interface or surface tension

The measurable reduction in interfacial/surface tension with time due to adsorption of surface active substances.

Dynamic measuring process (tensiometry)

Used to calculate the surface/interfacial tension dependent on the surface age.

Dynamic viscosity

Is essential to the shear flows, viscosity coefficient, between shearing strength τ and speed gradient D in τ = η D, and has the unit mPas (formerly centipoise, cps).

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