World Leaders in Ultra-Pure Heating
Revision 10
www.heateflex.com
01/17/13
405 E. Santa Clara St.
Arcadia, CA 91006-7218
Tel: (626) 599-8566 Fax: (626) 599-9567
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2.2 How the Process is Heated
The heating system receives its heating power from <15 psig regulated steam supply. This
steam comprises the shellside-heating medium and completely surrounds the tube bundle
inside the pressure vessel. The steam flow into the vessel is not throttled as it is "self-
controlling". As the flow of process water inside the exchanger tubing increases or decreases,
the rate of condensation of the steam on the outside of the tubing also increases and decreases
proportionally. In the case where the flow of process water stops completely, the tubing and
process water equilibrate to the same temperature as the steam, condensation ceases, and steam
flow into the vessel ceases.
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2.3 How the Temperature is Controlled
The PC series D.I. water heating system utilizes a "mixing-valve" temperature-control system
which can deliver unmatched accuracy in output temperature, independent of the most extreme
variations in D.I. water flow rate.
D.I. water is heated in the Fluidix PFA heat exchanger to above the set point temperature and is
continuously blended in varying ratios with ambient-temperature D.I. water by means of two
PVDF mettering valves to yield the desired set point temperature. The two mixing valves are
positioned 90° from one another (one is fully open when the other is fully closed) and are
driven by a common actuator such that a 90° rotation of the actuator can produce output
temperatures anywhere from ambient to near the steam inlet temperature.
The control system uses a look-up table, which is calibrated initially at start-up, to give the
proper actuator position as a function of set point temperature and flow rate. This type of
control provides immediate adjustment in the hot / cold blending ratio over the fast changes in
flow rate associated with many semiconductor- process tools. Once the flow rate re-stabilizes,
the control system also provides a “trimmer” function to make small adjustments in the
actuator position to fine tune.
The following figure shows the basic schematic of the process components. The exchanger is
actually broken down into two or more parallel tube bundles each fitted with isolation valves
and two pressure relief valve systems (steam and D.I.), which are not shown in this simplified
diagram.
