Method of continuously measuring the shear viscosity of a product paste
The present invention relates to a method of continuously determining the shear viscosity (η) of a product paste to be delivered to a spray nozzle for spray-drying applications wherein the continuous determination of the shear viscosity (η) of the product paste is carried out in a bypass to the product paste stream to the spray nozzle.
1. A method of continuously determining a shear viscosity of a product paste in a processing line, the method comprising:
continuously determining the shear viscosity of the product paste in a bypass to a stream of the product paste, the bypass comprising a pump, a flow meter, a differential pressure tube and a pulsation damper, and the shear viscosity is in a range of 20 to 1000 mPa·s, the shear rate is greater than 1000 s −1 , and the Reynolds number is less than 2300;
delivering the product paste to a spray nozzle for a spray-drying application; and
adjusting a droplet size of the product paste, the adjusting comprises a control device calculating an output control parameter based on the shear rate and the shear viscosity of the product paste and also based on spray nozzle geometry parameters stored in a memory of the control device, the output control parameter is delivered to the spray nozzle which adjusts a swirl chamber piston to a calculated position to obtain a desired swirl chamber volume.
2. The method according to claim 1 , wherein the determining the shear viscosity of the product paste comprising:
a) providing a constant feed-flow-rate of the product paste;
b) determining a mass flow of the product paste;
c) delivering the product paste to a pressure-drop-meter and determining a pressure drop;
d) calculating the shear viscosity of the product paste on the basis of the mass flow determined in step b), a known product density, as well as the pressure drop determined in step c).
3. The method according to claim 2 , wherein the calculation in step d) considers also the constant bypass-mass-flow-rate.
4. The method according to claim 2 , wherein the determination of the pressure drop in step c) is carried out according to a differential pressure drop method.
5. The method according to claim 2 , wherein the pressure drop meter comprises a tube having a fluid inlet section and a fluid outlet section and a first, second, and third pressure drop measuring sections provided between the inlet section and the outlet section.
6. The method according to claim 5 , wherein the second pressure drop measuring section is provided downstream of the first pressure drop measuring section, has a second internal diameter of the second pressure drop measuring section smaller than the first internal diameter of the first pressure drop measuring section, and has a second axial length shorter than the first axial length of the first pressure drop measuring section.
7. The method according to claim 6 , wherein the second pressure drop measuring section comprises a second differential pressure meter measuring a second pressure drop, a second axial distance between second two static pressure measuring openings in a second wall of the second pressure drop measuring section is shorter than the first axial distance of the first differential pressure meter.
8. The method according to claim 5 , wherein the third pressure drop measuring section is provided downstream of the second pressure drop measuring section opens into the outlet section, and the third pressure drop measuring section has a third internal diameter smaller than the second internal diameter of the second pressure drop measuring section and has a third axial length shorter than the second axial length of the second pressure drop measuring section.
9. The method according to claim 8 , wherein the third pressure drop measuring section comprises a third differential pressure meter measuring a third pressure drop, and a third axial distance between third two static pressure measuring openings in a third wall of the third pressure drop measuring section is shorter than the second axial distance of the second differential pressure meter.
10. The method according to claim 5 , wherein the first pressure drop measuring section is close to the inlet section, has a first internal diameter and a first axial length, and is connected to a first differential pressure meter measuring a first pressure drop.
11. The method according to claim 10 , wherein a first axial distance between first two static pressure measuring openings in a first wall of the first pressure drop measuring section is substantially equal to the first axial length of the first pressure drop measuring section.