1.1 Here are the main temperature related variables to consider when using thermal covers or liners. In approximate order of priority they are:
(i) Products
Core product temperature
Surface product temperature
Specific Heat Capacity
Product Weight
(ii) Thermal Cover/Liner construction
Material
Foundation material
Weave
Thermal Conductivity
Thickness
Dimensions i.e. is it a good fit?
(iii) Roll cage fill
(iv) Outside air temperature
(v) Operation
Timings within different air temperatures
Total incidence and total time that cover/liner has been opened
Amount by which it has been opened
How well the cover/liner has been sealed?
Compression of thermal cover/liner
Movement (usually a negligible effect)
1.2 The thermal cover/liner has a measurable intrinsic thermal conductivity. When producing a product that is designed to slow down temperature degradation we use filling that is designed
to minimise this conductivity. However, this attribute is only a theoretical value. Actual thermal transmittance in real operations depends on the other variables mentioned above.
1.3 Because of this, we recommend that our customers carry out trials prior to purchase.
2. Mathematical Modelling:
2.1 The mathematical relationship between variables is complex. A vital issue is the gap between the allowed temperature range and the ambient temperature. The greater this gap the more
rapid will be the temperature movement (whether this is up or down).
2.2 The potential change in a product’s temperature up until it reaches its limit can be translated into energy (Joules). Thus, if we know the starting temperature and the product’s
weight, the product’s specific heat capacity as well as the temperature limit, we know how much energy would be required to move the temperature to the limit.
2.3 Our aim, of course, is to avoid this limit being reached.
2.4 The heat transference is the product of the thermal cover/liner’s intrinsic thermal conductivity multiplied by its surface area.
By converting this transfer of heat to Joules, we can compare, like-for-like, the upper limit of the product temperature with the performance of the thermal cover/liner, to arrive at the
maximum amount of time the product can be left out of temperature in the protection of the thermal cover or liner.
