Each heat exchanger incorporates a Holding Tube between the final heating section
and the cooling section. The holding tube holds the product at the process temperature
for a defined time at the nominal process flow rate. A temperature sensor (T1)
measures the final product temperature at the end of the holding tube.
The sensor is used to control power to the hot water heater, by providing the control
input for a three-term controller. The output from the controller modulates the power
to the water heater via a solid state relay (SSR). In this way, the desired temperature
of product can be maintained.
The product is cooled in the cooling section of the heat exchanger, using a flow of
cold or chilled water. A combined flow meter and control valve is used to regulate
and measure the flow of cooling water.
A back-pressure valve at the product outlet from the heat exchanger is used to create a
pressure within the heat exchanger. This prevents the product boiling at the elevated
processing temperatures.
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