Numerical analysis of cooling mechanisms in cylindroconical lager tanks.

Ishiguro, T., Mizutani, S. and Kuwahara, K.

Abstract
In general, cooling causes the density of the cooled substance to increase as its temperature decreases. In the case of water and of aqueous liquids such as beer, however, this rule only applies at temperatures above about 3 degrees C, at which the density reaches a maximum and then declines as the temperature is further reduced. Since most commercial beers undergo a temperature decrease from about 8 to about -1 degree C at the beginning of the cold conditioning phase of production, the physical effects of temperature differences within a tank of cooling beer, at the point where some of the beer has fallen below 3 degrees C and some is still above that temperature, can be rather peculiar compared to the normal behaviour of convection currents, etc., in a body of liquid in which there is variation in temperature. The development of a mathematical model of the movement of beer within a cylindro conical tank during such a cooling process, using an advanced computer, is described together with the experimental confirmation of the model's validity using a 20 hl pilot maturing tank. In a conventional (jacket cooled) tank, the cooled beer initially flows down the tank walls, but when it passes the point of maximum density, the coldest beer, being now less dense than that which is slightly less cold, begins to rise from the bottom, so that the flow in the centre of the tank, initially upwards, likewise reverses its direction. The change starts at the bottom, where the maximum density temperature is first reached, and an interface between cold beer with decreasing density (rising as it cools) and less cool beer with increasing density (descending as it cools) rises up through the tank until all the beer has been cooled below the point of maximum density. The use of the model to simulate the effects of changes in tank design (such as the use of baffles to change the flow patterns during cooling or the use of internal cooling equipment) is also described.
Keywords : beer cooling cylindro conical tank flow model simulation performance physics