Questions_ _Responses_N68335-16-R-0172_7-26-2016.doc

Questions / Concerns for CET Chambers Solicitation N68335-16-R-0172

1) The temperature change rate is listed as 10C/Minute from +80C to -65C with a load of 500 pounds of aluminum and a live load of 2,000 watts. Previous discussions had the change rate at 10C/Minute from +71C to -54C with an empty chamber (3.1.2.4.3.1 and 3.1.2.5.1). What is the minimum change rate that is acceptable with the load?

A) 10 °C/minute with the 500 lb of aluminum and 2000 W of heat load is the minimum. This simulates the vibration fixture and the test item generating heat within the chamber.

2) For previous revisions the change rate had been at ambient pressure. This new specification calls out that the change rate is applicable while at altitudes of up to 65,000 feet (3.1.2.4.1). Even with motors that can automatically adjust (3.2.5.6.1) there is not enough air moving to allow this type of transition at altitude. Is the change rate at ambient altitude?

A) The change rate applies only at site pressure.

3) Previously the maximum blast air into the chamber at an altitude of 65,000 feet had been 2 pounds/minute. The spec now calls out 5 pounds/minute (3.1.3.2). This will have a large impact on the pump sizing. What has driven this change? Is the maximum blast air 2 pounds/minute?

A) 2 pounds/minute would be the most for 1 test item. Often these chambers are used for reliability testing where multiple test items are often run simultaneously. 5 pounds allows us to be able to feed multiple test items as required.

4) The blast air transition requirement has been increased to +85C to -65C at a change rate of 82C/minute (3.1.5.4.3.2)? What has driven this change? Is this the correct blast air transition rate?

A) This is the correct blast air transition rate. That is why a split system is defined in the SOW where we can have a capacity of hot air and a capacity of cold air at the ready and available to be mixed or independently shut off with a valve allowing fast transitions of the blast air.

5) The spec requires the window to be heated (3.2.6.3). Glass that is the appropriate thickness for altitudes of up to 80,000 feet cannot be heated due to the conductivity of the glass. Is the glass window a requirement?

A) A window is required. Oftentimes only the outermost glass pane is heated which will prevent fogging allowing for visual inspections into the chamber.

6) The specification has asked for a manual wiper for the window (3.2.6.4.1). A manual wiper will require maintenance as the seal of the feedthrough will wear and leak. Is the wiper required?

A) A manual wiper is required.

7) The space for these units and the power packs is very small and the heat rejection could be an issue. The specification calls out that the ambient is non-conditioned in the summer and has limited heat in the winter (3.4.8.1). An ambient of up to +46.1 will lead to excessive condensation at the shaker to chamber interface when running cold, and could lead to reliability issues for the compressors. Are the space dimensions correctly stated in the solicitation?

A) The available space for the chambers/support equipment is properly defined in the site drawing; with an available footprint of approximately 26’ square plus some available space adjacent for ancillary equipment. There are two 10-ton spot coolers in the high bay lab used during the summer to reduce the temperature/humidity in the lab though it is possible they may fail.

8) The specification says the vacuum exhaust should be clear of oil before it is rejected into the government supplied exhaust pipe (3.4.11.2.2). It will be nearly impossible to prevent oil mist out of the pump, especially if there is oil in the air stream into the pump from a leak in the chamber. Is there a minimum amount of oil that is acceptable in the vacuum exhaust?

A) If oil is present in the pump outlet pump, a filter may be required to remove oil mist before exiting the pipe which exhausts outside.

9) This chamber will require temperature limited sheath heaters due to the potential exposure to flammable materials (3.4.9.1). This will make the required heat up transition of 11.5C/minute with the load (3.1.2.4.3.1 and 3.1.2.5.1) nearly impossible due to the space available for heaters. Can the 11.5 deg C/minute be reduced based on the performance of temperature limited sheath heaters?

A) If sheathed heaters are used the minimum transition rate of 10 °C/minute from +80 to -65 °C will still apply. Additional heaters or heaters with a higher density may be required.