What is so typical about low flows?
How is a low liquid flow of less than 100 g/h different from 'normal' or high flows? Well, (ultra) low flow applications involve some phenomena which are not observed in or are not relevant to larger flows. Due to the (very) small amount of liquid that is being moved, (ultra) low flows are so sensitive that even the tiniest disturbances in process or ambient conditions can have a massive effect on flow stability. The influence of external conditions on flow stability is therefore key here - as well as the means to control these external conditions.
For example, even small leaks of gases or liquids into or out of the process have a considerable influence on the intended liquid flow. Furthermore, any obstruction caused by solid particles or contaminations in the small liquid flow lines will obviously reduce the flow in an undesired way. For low liquid flow dosing in particular, unstable pressures will lead to unstable flows. Variations in pre-pressure, pulsation due to excessive pump stroke volumes compared to the flow rate, and dissolution of gas (pressurised air) when pressurising the liquid to be dosed will all result in an unstable flow.
Knowledge of the application as well as the physical transport phenomena of the process are essential to deal with this complex matter of low flow handling. Optimising flow stability and performance of fluid systems requires in-depth knowledge of fluid characteristics and system components in a wide range of circumstances. Every component used in a fluid system can affect the behaviour of a fluid or interact with other components, especially when it comes to low flows.