Cooling channel efficiency

Cooling channel efficiency is a measure of how effectively a particular channel section extracts heat from the polymer during the entire cycle.

This measurement has no units and is calculated relative to the average performance of the whole cooling system: if there is no variation in the efficiency throughout the system, the efficiency should be equal to one throughout. The cooling channel efficiency of any channel is defined as:

where

• is the cycle time
• is the heat flux of each channel
• is the channel diameter
• is the total length of the cooling system
• is the total heat removed by the cooling system during the entire cycle time

From the above definition, it follows that if all channels have the same diameter and heat flux, then the cooling channel efficiency is equal to one (1) for all channel sections. If there is any variation in the amount of heat extracted by the sections, per unit length, then for that section, the cooling channel efficiency will be greater than or less than one. Cooling channel efficiency data helps identify which channels are extracting more heat than others.

Channels with a cooling efficiency that is close to zero are not participating in cooling. If these channels are located in a region where there is no heat load, they can be discarded. If they are located in a region where there is a significant heat load but they have a cooling channel efficiency close to zero, the performance of these channels should be improved by changing the cooling system design, or by changing the coolant process conditions.

Cooling channels with negative values of efficiency are, on cycle average, releasing heat instead of extracting heat. This can happen when the coolant temperature is higher than the ambient temperature and the cooling time is relatively long.