Multichannel Systems PH01 Manual - Manual (Page 10)

PH01 Manual
8
2.6 Flow Stream
A titanium wire inserted into the cannula ensures a turbulent flow. In turbulent flow, there
are no discrete layers of flowing liquid. The momentum of the fluid overcomes the viscous
shear forces, and there is extensive and continual mixing across the flow stream. This ensures
that the temperature of the liquid is constant across the flow stream. Especially flow rates
higher than 2500 μl/min would be critical without the wire, because the heat transmission to
the inner layers is impaired by the laminar flow.
The titanium wire can be removed by the user to increase the inner diameter and thus the
maximum flow speed through the cannula. This is not recommended, as removal of the wire
results in a laminar fluid flow. In laminar flow, the fluid moves in layers, with one layer sliding
smoothly over the other. There is no mixing of fluid from layer to layer, since viscous shear
forces damp out relative motions between layers. As a result, the separate layers show
different temperatures. The inner layers move much faster than the outer layers. As the
temperature sensor is on the outside of the flow stream, the controller will stop the heating if
the actual temperature of the outer layer reaches the setpoint temperature. In other words,
the inner layers will be considerably colder than the setpoint temperature.
3 Appendix
3.1 Pin Assignment
Pin 1, 6 Heating
Pin 2, 5 Temperature sensor power supply
Pin 3, 4 Temperature sensor probe