FT36 Blast and Fluid Bed Freezer – Issue 1
The Armfield Blast and Fluid Bed Freezer combines these two important industrial processes into one scaled-down freezer cabinet.
Practical Training Exercises
- Detailed study of batch blast freezing process
- Study of fluid bed freezing
- Effect of air velocity
- Effect of air temperature
- Demonstration of the industrial process
The blast freezer and fluid bed sections are contained, along with the fan and evaporator, inside an insulated cabinet. Access doors to both sections are fitted with observation windows and an electrically heated surround to prevent the doors from freezing in the closed position. Inside the cabinet, a fan with adjustable impeller transports air from the interior of the cabinet into the freezer ducting and through the evaporator tube bank where it transfers heat to the refrigerant.
The air, now reduced in temperature, passes trought he tray section, which can be observed through a removeable perspex panel. It then changes direction and passes vertically up through the fluid bed section, back into the cabinet space where it is again circulated by the fan. The blast freezer section contains five trays onto which the food samples to be frozen are placed.
There is a facility for thermocouple sensor leads to pass into the ducting and through the cabinet wall so that freezing temperatures and rates can be monitored externally. There is a facility for a suitable anemometer to be inserted into the ducting to allow the air speed to be measured.
The compressor supplying the refrigerant to the evaporator is located externally on the same framework as the cabinet, as in the control system. Air flowrate is varied by external control of a damper system and required air temperature is set externally using a microprocessor based controller.
A floor standing, insulated freezer cabinet incorporating both blast and fluid bed freezer capabilities. Observation/access doors for both sections having heated perimeters to prevent freezing in closed position. Blast freezer section having five removeable stainless steel trays and a polycarbonate observation/loading section. A 1.1kW axial flow fan blows air from the cabinet interior through an evaporator tube bank where the air is chilled. Refrigerant (R 502) is circulated to the evaporator by an externally mounted 4kW compressor which is water cooled.
The chilled air is guided in an aluminium duct to the blast freezer section at velocities up to 10 m/s. This velocity can be varied by external adjustment of a 'damper' system in the ducting. After the blast freezer section, the ducting turns vertically upward and terminates with a 0.23m x 0.23m fluid bed section with adjustable surround. The chilled air then flows into the cabinet space to be recirculated by the fan. Cabinet temperature is controlled an external microprocessor controller down to a minimum of -35°C.
|Max air velocity:||10 m/s|
|Minimum cabinet temperature:||-35°C|
|Blast freezer section|
|Number of trays:||5|
|Cross-section of duct:||0.30m x 0.30m|
|Fluid bed section|
|Area of fluid bed:||0.05m2|
|Fluid bed surround height:||Adjustable to 100mm|
Water: The water supply must have a line pressure of not less than 3.0 bar and a flow capacity of more than 25 l/min @ 3 bar at 20°C