Functionality and historical development of our contact cooling system
As early as the 1970s, Eisvoigt developed systems for the special requirements of bakery cooling and refrigeration technology. They were equipped with so-called silent cooling. This technology achieved the best results for unbaked doughs and cream cakes. Due to large cooling surfaces, with respect to the individual cooling capacity, the dehumidification of the product could be significantly reduced. In addition, there were no fans in the room: the main cause of dough dehumidification is air movement above the product and a large difference between the room temperature and the temperature of the cooler surface. Thermodynamically, a temperature difference is required. It is therefore a matter of minimizing them by means of heat exchanger surfaces that are as large as possible.
In modern plants, it is no longer possible to achieve an optimum temperature difference with silent coolers, as the quantity of cooled products to be produced and the resulting cooling capacities have risen to such an extent that the necessary cooler surfaces cannot be accommodated.
The following findings can be derived:
1) The larger the cooler surfaces are in relation to the cooling capacity, the lower the dehumidification (small temperature difference).
2) The lower the air velocity above the object, the lower the dehumidification (moisture removal).
3) A small difference between room humidity and dough humidity reduces the dehumidification of the dough.
4) Humidity is always separated on the coldest surfaces.
Today, very good results can be achieved with large radiator surfaces, speed-controlled fans, humidification equipment and air ducting systems. However, the quality of the goods has never been achieved through the use of silent cooling.
Our plate cooling with suitable dough conveying systems offers an optimal approach. The dough conveyor belt is guided directly over cooled surfaces, which is why we also speak of contact cooling. A small temperature difference between the dough and the cooler surface can be achieved by precisely controlling the individual plate temperatures. The movement of air over the object is only created by pure thermal action. The heat transfer from the product to the plate is optimal. The penetration speed of the cold is much higher than with conventional dough coolers. The large cooling surfaces mounted under the conveyor belts and the additional coolers for cooling the room air, which are controlled separately, bring the optimum of silent cooling very close.
Especially with so-called layer doughs, such as for the production of croissants, an exact separation of the individual layers (dough and fat) is a quality feature. Here, rapid cooling down to the product core ensures that the individual layers do not mix with each other. Comparative measurements have shown that the core temperature is reached approx. 25 % faster than in conventional refrigeration systems.
With the first system we implemented in 2010, the quality improvements compared to the existing technology were immediately noticeable, but also the vulnerability to over-humidification during standstill. According to measurements, the room humidity during operation was around 90% RH. After switching off the system at the weekend and through open doors, the incoming, relatively warm air from the production area very quickly leads to dew point undershoots in the cooling tunnel. The conveyor belt frame, the cooling plates and also the room embracing surfaces were correspondingly wet. To solve this problem, a dehumidification circuit was programmed via the software, which dries the room for downtimes or after cleaning the tunnel. In the meantime, by optimizing the hydraulic systems, a maximum humidity can be set and maintained even during normal operation. In addition, an adjustable overpressure for the room has been integrated into the system to prevent the inflow of external air.
Our plate cooling is the perfect technology for customers with high quality demands.