HEAT TRANSFER IN COLD BOXES

There are two keys to long cold life and efficient use of cold source in a cold box.

1.Restrict the flow of energy from outside the Cold Box to the Payload

2.Do not restrict the flow of energy from the Payload to the Cold Source

Efficient Cold Life performance depends on

1.Thermal Conductivity, Thickness, Surface Area and Construction of the Insulation System.

2.Number and Area of convective surfaces

3.Number and Area of reflective surfaces.

For Plain Surfaces

1. Transfer of Heat by Conduction;

2. The use of insulation materials with the lowest Thermal Conductivity (K); and

3. Maintain thermal integrity by closely fitting and sealing lids, joints & corners.

Convection that occurs in the Cold Space where Heat is transferred by air through direct contact with the Payload and the Refrigerant Surface, and is swept away by the small air currents created by warmer air rising.

For Reflective surfaces

1. Transfer heat to air by convection;

2. Reflect 95 -98% incoming infra-red radiation.

This makes them an excellent barrier to Heat particularly when combined with a plain surface.

Cold Life depends on how effective the insulation system restricts the flow of heat energy from outside into the Cold Space. Cold life also depends on the LID SEAL, the LID CLOSING CATCHES, and the proper sealing of PENETRATIONS through the sides or lid of the box (ie after fitting digital thermometers or data loggers).

First task for the Insulation is to restrict the flow of heat energy from outside, into the Cold Space;Second task is to increase the structural strength of the Cold Box.

If a liner is being used, the first task for the Insulation in the liner is to increase restriction to the flow of heat energy from outside into the Cold Space to give a longer cold life;

Second task is to provide pockets for holding the Refrigerant Packs.

Thermal Energy can be stored either as Specific Heat or as Latent Heat, and both Thermal Energy processes are reversible. HTIceGels and HTIceBricks are good examples of Refrigerants that store Thermal Energy as Specific Heat (Specific Heat Storage Materials).

Insulation System is feasible for a Vaccine Carrier. You can choose different insulation material and cold source to achieve different cold life performance.