A chiller is a device that
transfers heat. It removes heat from one place and transfers it to another
using mechanical refrigeration. This removes heat from a process load and
transfers it to the surrounding environment. Plastics processors will employ
chillers if they need a lower process fluid temperature than a more straightforward
solution, such as a cooling tower, can deliver.
The purpose of Central Chillers for Plastics Processing Portable is
to provide a constant flow of coolant to the cold side of a process water
system at a "leaving water temperature" (LWT) of around 50 degrees
Fahrenheit (10 degrees Celsius) that the user predetermines. After that, the
coolant is circulated through the process, removing heat from the moulds and
equipment as it returns to the back of the process water system. The coolant
flow, which is now at a higher "entry water temperature" or EWT (five
to ten degrees warmer than LWT), then re-enters the chiller, which performs the
following three functions:
It does this by extracting heat
from the process coolant, then releasing the heat into the surrounding
environment, and finally bringing the temperature of the coolant down to the
LWT that is wanted, making it suitable for recirculation.
A chiller is a vapour compression
mechanical refrigeration system that is connected to the process water system
using a device known as an evaporator.
The evaporator is a heat
exchanger that transfers the heat that was picked up by the flow of the process
coolant to the flow of the fluid that is used in the refrigeration process. The
temperature of the process coolant is brought down to the level of
low-water-temperature that is needed while at the same time the refrigerant
evaporates, transforming from a low-pressure liquid into vapour.
The refrigerant then goes through
a compressor, which serves two purposes.
First, it eliminates the vapour
of the refrigerant in the evaporator. It ensures that the pressure in the
refrigerant line of the evaporator (the vapour pressure) stays low enough to
absorb the heat from the process at the appropriate rate.
Second, it increases the pressure
in the vapour of the refrigerant being released into the atmosphere. This is
done to ensure that the vapour's temperature is high enough to allow it to
release its heat when it reaches the condenser, where the vapour condenses back
into a liquid. A refrigerant transition from a vapour to a liquid state gives
off latent heat. This heat is transferred to the surrounding environment in a
cooling medium, such as water or air.
Because of this, most portable
and central chillers have a condenser that is either cooled by air or water.
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