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Water Coolant Loop System

The WCLS provides thermal conditioning of the crew cabin by collecting heat at the cabin-air-to-water-coolant-loop heat exchanger and transfers heat to the water coolant loops. The water coolant loops transfer the heat at the water and Freon-21 coolant loop interchanger. The WCLS also provides thermal conditioning for the three avionics bays by an air-to-water heat exchanger in each avionics bay, the cabin heat exchanger, liquid-cooled garament and water chiller, which transfers heat to the water coolant loops. The IMU air-to-water heat exchanger also transfers heat to the water coolant loops.

There are two complete and separate water coolant loops that flow side by side and can operate at the same time. The only difference between water coolant loops 1 and 2 is that loop 1 has two water pumps and loop 2 has one pump.

Some electronic units in each of the avionics equipment bays are mounted on cold plates. The water coolant loops flow through the cold plates, and the heat generated by the electronics unit is transferred to the cold plate and then to the water coolant loop, which carries heat from the electronic unit. The cold plates mounted on the shelves in each avionics equipment bay are connected in a series-parallel arrangement with respect to the water coolant loop flow.

The water pumps in coolant loop 1 are controlled by the H2O pump loop 1 A and B switch on panel L1 in conjunction with the H 2 O pump loop 1 GPC off and on switch on panel L1. The GPC position enables the general-purpose computer to command the loop 1 pump, which is selected by the H2O pump loop 1 A or B switch, to circulate water through water coolant loop 1. The on position energizes the loop 1 pump. A ball-type check valve downstream of each water pump prevents reverse flow through the non-operating pump. The off position removes electrical power from both the A and B pumps of loop 1.

Water pump 2 is controlled by the H 2 O pump loop 2 GPC on, off switch on panel L1. When the switch is positioned to GPC , water pump 2 is commanded by the GPC to circulate water through water coolant loop 2. The on position energizes the water pump 2 to circulate water through water coolant loop 2. The off position removes electrical power from water coolant loop 2 pump.

Water loops 1 and 2 flow side by side through the same areas when both loop pumps are in operation. Downstream of the water pump in each loop, water flow splits into three parallel paths: one through the avionics bay 1 heat exchanger and cold plates; another through the avionics bay 2 heat exchanger and cold plates, payload bay floodlight cold plates and thermal conditioning of the crew cabin windows; and the third through the crew cabin multiplexer/demultiplexer flight deck cold plates, the avionics bay 3A heat exchanger and cold plates and avionics bay 3B cold plates. The three parallel paths in each coolant loop then rejoin.

The water coolant loops 1 and 2 flow toward the Freon-21 coolant loops 1 and 2 and water heat exchanger and split into two parallel paths. One parallel path in each water coolant loop flows through the Freon-21 coolant loops 1 and 2 and water interchanger, liquid-cooled garment heat exchanger, potable water chiller, cabin heat exchanger and IMU heat exchanger to the respective water coolant loop 1 and 2 pump. The other parallel path in each water coolant loop flows to a water coolant loop bypass in that loop.

The bypass controller in each water coolant loop is enabled by its corresponding H2O loop 1 and 2 bypass mode auto/man switch on panel L1. When a coolant loop's H 2 O loop bypass mode auto/man switch is positioned to auto , the water bypass controller and bypass valve automatically control the amount of water in the coolant loop that bypasses the water/Freon-21 coolant loop interchanger. When the bypass controller's outlet temperature is 65.5 F, the loop's bypass valve is fully closed, and the excess heat in the loop is transferred to the corresponding Freon-21 coolant loop at the coolant water interchanger. Cooled water flows through the LCG heat exchanger, cabin heat exchanger and IMU heat exchanger, which joins with the bypass flow parallel path. When the bypass controller senses that the coolant loop water pump's outlet temperature is 60.5 F, the controller bypasses a maximum amount of water around the Freon-21 coolant loop/water interchanger and allows the water at that coolant loop pump to be warmed from the parallel path of water flowing from the interchanger and corresponding LCG heat exchanger, cabin heat exchanger and IMU heat exchanger. When the H2O loop bypass mode auto/man switch for the coolant loop is positioned to man , the flight crew sets the corresponding H2O loop man incr/decr switch on panel L1 to manually control the bypass valve in that water coolant loop.

Because of changes in heat loads from the initial design, the water bypass controllers are not able to control temperatures automatically as originally intended. As a result, the water bypass control valve is manually controlled by the flight crew by positioning the H 2 O loop bypass mode auto/man switch in man and the H 2 O loop bypass man incr/decr switch for that water coolant loop on panel L1. The bypass valve is adjusted before launch to provide a flow of 900 to 1,000 pounds per hour through the Freon-21 coolant loop/water interchanger, and the control system remains in the manual mode for the entire flight.

The accumulator in each water coolant loop provides a positive pressure on the corresponding water pump inlet and accommodates thermal expansion and dampening pressure surges in that water coolant loop when the pump is turned on or off. Each accumulator is pressurized with gaseous nitrogen at 19 to 35 psi.

The pressure at the outlet of the water pump in each water coolant loop is monitored and transmitted to the H 2 O pump out press loop 1 and loop 2 switches on panel O1. When the switch is positioned to loop 1 or loop 2, the corresponding water coolant loop's pressure is monitored on the H 2 O pump out press meter on panel O1 in psia.

The yellow H2O loop C/W light on panel F7 will be illuminated if the outlet pressure of the water coolant loop 1 pump is below 45 psi or above 79.5 psi or if the outlet pressure of the loop 2 pump is below 45 psi or above 81 psi. The pump inlet and outlet pressure of each coolant loop is monitored and transmitted to the systems management GPC for CRT readout.

In summary, with the crew cabin's structural thermal capacity, its temperature will not exceed 95 F during entry or until flight crew egress.


Curator: Kim Dismukes | Responsible NASA Official: John Ira Petty | Updated: 04/07/2002
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