1-19
1.7
HEAT TRANSFER FLUID SYSTEM
1.7.1 General Description
Reference Drawing 91S25917
The Model 2500 Benchtop Humidity Generator incorporates a unique test chamber, in that it
has a fluid shell surrounding the test space (figure 1-4). Temperature controlled fluid,
consisting of approximately 30-40% water and 60-70% propylene glycol, is circulated at a
rate of nearly 10 gallons per minute through the fluid shell by a magnetically coupled
centrifugal pump (FP1). The fluid mass and fast circulation rate result in inherent
temperature stability allowing a very stable and precise humidity to be generated. The
chamber interior and fluid shell are constructed of 300 series stainless steel assuring rustproof
quality. All seams are heliarc welded for hermetic sealing of the liner and shell.
In this closed loop, non-pressurized system, conditioned fluid flows from the pump outlet to
the saturation temperature/control sensor (RTD0). From this point, the fluid circuit splits;
one path flowing through the test chamber fluid shell and the other path flowing through the
saturator assembly:
Path 1) Temperature conditioned heat transfer fluid flows through the test chamber fluid
shell, exits at the upper left of the fluid shell and enters the refrigeration evaporator
(EX1). The refrigeration evaporator is a single pass, tube in shell type, heat
exchanger allowing fluid cooling. After cooling, fluid enters the immersion heater
housing, flows over the immersion heater (H3), and exits to the circulation pump
intake, completing the chamber fluid circuit.
Path 2) Temperature conditioned heat transfer fluid enters the saturator assembly (SAT) at
the opposite end from the airstream and flows through the saturator to the expansion
tank (located on top of the test chamber). The saturator fluid circuit then merges
with the chamber fluid circuit at the exit of the chamber fluid shell.
Figure 1-4
FLUID FILL PORT.
(SAT)
REFRIGERANT
OUT
IN
(H3)
(EX1)
TEST
CHAMBER
(FP1)
(RTDØ)
