Two-pass vacuum coolers are a very clean design in preventing bacteria growth within the cooler. By utilizing the center air plenum (as shown) there is a reduction of corners, which are the cause of stagnate airflow areas where product builds-up and bacteria grows. Airflow on each bed can be adjusted to set the rate of cooling. It is important not to shock the hottest product with the cool airflow.

Heat and moisture is release from the product when it is cooled. In some cases the heat in the product is enough to properly dry it. Other cases require additional heat to further dry or compensate for poor ambient conditions. A vacuum dryer model is selected when a small amount of heat is required in addition to cooling. These units generally incorporate steam coils above the upper pass of a two-pass vacuum model. In effect the upper pass dries and performs some cooling. The bottom pass finishes the cooling to the desired degree.

With both models product is loaded by various spreading mechanisms at the beginning of the conveyor and discharged at the end of the conveyor. Multiple-pass models with an even number of conveyors discharge at the same end the product is loaded. Airflow velocity, resident time, and air temperature can be set to a wide range of adjustments. Air velocity through the bed can be set from 25 fpm to 200 fpm. Normal operating range is 100 to 150 fpm. Generally, most applications call for 500 to 1000 cfm per ton of material being cooled.

These models are sold as all cool or dryer/cooler. Cooler units can be fitted to dryer models when necessary. Standard widths are 2', 6', and 8' and standard lengths are in increments of 12'. Custom widths and lengths are available. These models are usually selected for drying of various feed and food products. Vacuum coolers are especially economical over the pressure coolers when a cyclone or dust collector is required.