Device for measuring the amount of gas dissolved in a liquid

Beer fermentation apparatus comprises a main pipe for transporting a water-entrained mixture of wort, yeast and gas to a fermentation tank. A measuring device is mounted in a by-pass circuit of the main pipe for measuring the amount of gas dissolved in the water, the device comprising a vertically disposed measuring chamber having an inlet at its lower end and an outlet at its upper end which are connected to upstream and downstream portions of the main pipe for flowing the mixture through the measuring chamber. The chamber inlet is located a sufficient distance above the lowermost end of the chamber so as to effect formation of a relatively stagnant flow region which is substantially free of gas bubbles in the measuring chamber beneath the level of the inlet during flow of the water-entrained mixture through the measuring chamber. A gas-sensitive element extends downwardly in the measuring chamber into the stagnant flow region for measuring the amount of gas dissolved in the mixture and due to the relative locations of the chamber inlet and outlet and the location of the gas-sensitive element, the gas bubbles and lighter mixture particles entrained in the water flow in the inlet upwardly through the measuring chamber and out the outlet while the heavier mixture particles entrained in the water tend to flow downwardly and settle in the stagnant flow region thereby minimizing erroneous measurements which would otherwise occur due to the presence of gas bubbles in the vicinity of the gas-sensitive element.

This invention relates to a device for measuring the amount of a gas, in 
particular oxygen, dissolved in a liquid, and in particular for measuring 
the degree of oxygenation in a wort before or after its inoculation with 
yeast, that is before or during its fermentation phase, in the production 
of beer. 
Up to the present time this procedure has been carried out in a continuous 
manner after the inoculation, or on a tapping or off-take, by inserting an 
electrode of the Clark measuring electrode type in the wort flow pipe. The 
procedure is carried out after the wort oxygenation phase, that is to say 
after the injection of a certain amount of oxygen or a gaseous mixture 
containing oxygen. 
Experience shows that under these conditions there still exists a large and 
continuous flow of gas bubbles which cause random perturbations at the 
level of the measuring electrodes, producing quite false readings which 
are, of course, not a true indication of dissolved the actual amount of 
gas, in particular oxygen. 
The number and variety of technical embodiments and size modifications for 
the pipe make it impossible to form a satisfactory mathematical model for 
the transfer of a gas in a liquid, especially in the case of a beer 
brewing plant. Corrections to the measurements using a mathematical 
approximation of the system are therefore not possible. 
It has been observed that the dynamic pressure affects the measurements, 
this effect being greater the higher the pressure and the greater the 
number of bubbles. In order to restrict these perturbations it is thus 
necessary to reduce simultaneously the velocity of the fluid and the 
number of bubbles. 
It has also not proved practical to carry out measurements in a local 
enlargement or widening in the pipe, since although such an enlargement 
reduces the dynamic pressure at the level of the measuring electrode, the 
large number of bubbles following the amount of air injected does not 
allow a stratified flow to take place and leads to the same measuring 
difficulties. 
The present invention comprises a device for measuring the amount of gas 
dissolved in a liquid, the device being mounted in an off-take circuit 
from a main pipe which supplies wort to a fermentation tank, an upstream 
tapping being effected at the low point of the pipe. The device comprises 
a rectilinear closed body defining an internal measuring chamber having a 
side inlet branch in its lower or middle part, the chamber housing a 
central measuring electrode having a length such that a sensitive element 
for effecting the measurement is situated close to the bottom of the 
chamber and at a level lower than that of the said inlet. The chamber 
includes in its upper part an outlet branch, means for measuring the 
temperature, and various checking, safety and calibrating instruments. 
By means of the invention it is possible to measure the degree of 
oxygenation of a wort by polarography under satisfactory measuring 
conditions within a device inserted in a circuit arranged as a tapping of 
the main flow pipe of the wort and which, by virtue of its location, the 
arrangement of its constituent elements, its internal technical structure 
and its volume, enables meaningful measurements to be made. 
The device is placed in series in an off-take circuit and comprises a 
chamber having a low or central side inlet and an upper outlet, the 
chamber housing in its internal volume a central electrode whose measuring 
cell is at a level lower than that of the inlet, the device further 
comprising various safety and checking means. 
The mounting of the device in an off-take circuit enables the number of 
bubbles at the level of the measuring cell to be reduced. Furthermore, the 
upstream tapping at the low point of the pipe further reduces the velocity 
and number of bubbles. 
Finally, the device itself, without reducing the velocity of the fluid too 
much yet while preserving an advantageous response time, makes the 
disturbing effect of the bubbles negligible since their minimal number in 
the apparatus and their favoured path directly from the inlet to the 
outlet no longer causes them to flush the measuring cell.

The device is attached to the wort feed pipe of a fermentation tank after 
its inoculation and aeration, or to any other recirculation pipe conveying 
the wort during fermentation. In the arrangement shown, air and yeast are 
injected simultaneously into a mixing chamber 1 for the simultaneous 
inoculation and oxygenation of the wort. The chamber is placed in a wort 
supply pipe 2 and comprises a monoblock structure with a double nozzle 
arrangement comprising a converging nozzle 3 and then a diverging nozzle 
4, and two lateral inlets 5 and 6 for air and yeast respectively, which 
enables a good dynamic mixing effect to be achieved by virtue of the 
venturi effect. The water-entrained mixture obtained after the inoculation 
and oxygenation is conveyed by the main pipe 2 to the fermentation tank. 
The device itself is placed in a circuit 7 mounted as an off-take of the 
main pipe 2 supplying the wort mixture. Its upstream connection is 
effected by a tapping at the lower part of the pipe 2 and its downstream 
connection is effected after an angle joint. This low-level arrangement, 
in addition to the tapping, reduces the number of bubbles passing through 
the measuring device to a minimum. The off-take circuit 7 is isolated from 
the main pipe 2 by two valves 8 and 8a placed at the inlet and outlet 
respectively. A flow meter 9 having a direct reading or a digital display 
system is also provided in the off-take circuit, and is connected in 
series. 
The device per se comprises an elongate, preferably rectilinear, closed 
body 10 defining an internal measuring chamber 11 having a single lateral 
inlet branch 12 in its lower or middle part, opposite a cylindrical 
measuring electrode 13 located centrally and occupying practically the 
whole length of the body 10 and terminating at its lower end in a gas 
sentitive element 14 of the cell type at least 1 cm from the bottom of the 
chamber. 
It is estimated that the distance between the inlet and the cell should not 
be less than 2 cm in order to obtain a good measurement independent of the 
effect of the bubbles, and an adequate response time. 
The measuring electrode 13 is secured to the upper part of the body 10 and 
emerges from the latter via an end provided with electrical connecting 
leads 15 which transmit the signal or measurement current to a processing 
and display circuit box 16. 
The body 10 contains, in the vicinity of its upper part and in the same 
plane as the inlet 12, an outlet branch 17 directly connected to the flow 
meter 9. Experiments show that the distance between the inlet and outlet 
branches should exceed 2 cm. 
The chamber 11 also contains in its upper part, opposite the outlet 17, a 
temperature detector in the form of a glove finger 18 for detecting the 
temperature, and also various checking, safety, calibrating and operating 
devices such as a manometer 19 and upper and lower air stopcocks 20 and 21 
respectively. The two air stopcocks enable the sampling device to be 
recalibrated at any instant without having to remove the device from the 
arrangement. The temperature detector is connected to an indicator unit 22 
and, as mentioned above, the electrode is connected to a box 16 for 
processing the display information. 
By virtue of the position of the sensitive cell 14 and the inlet branch 12 
situated in the vicinity of the base of the chamber 11, and also the 
position of the outlet branch 17, a low turbulence zone or stagnant flow 
region which is substantially free from bubbles is formed beneath the 
inlet at the level of the measuring cell. Furthermore, the off-take 
circuit 7 is closed through the device by a direct path going from the 
inlet branch 12 to the outlet branch 17. 
Thus, by means of this device, it becomes possible to carry out meaningful 
and stable measurements of constant accuracy without the random 
disturbances in the direct measurement systems previously employed. 
Furthermore, if the temperature is known it is a simple matter to 
determine the actual value of the amount of dissolved oxygen.