What is a Thermal Vacuum Chamber?

What is a Thermal Vacuum Chamber and how does it work?

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- everything RF

Feb 20, 2022

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A Thermal Vacuum Chamber (TVC) system is a system that utilizes a metallic thermal vacuum chamber with supporting devices to simulate the real-world space conditions experienced by components in space. The system uses vacuum pumps (dry pumps & cryogenic pumps) to pump out the air & other gases from the chamber to establish low pressure below 10-6 mbar (high vacuum).

The external body of the vacuum chamber is usually made up of high-quality stainless steel to withstand the pressure difference between the internal & external atmosphere and to minimize the leak rates & outgassing for ensuring a deep vacuum inside the chamber.  

A thermoregulated stainless steel cylinder, called the shroud, acts as the inside of the TVC. The shroud of the system consists of two laminated sheets, which are separated by a few millimetres, through which a thermal fluid is circulated using a thermal power generation & circulation system. The shroud transfers heat to the DUT (device under test) using inner surface irradiation. To maximize thermal exchanges in high vacuum conditions, a special black paint layer is applied on the inner surface of the shroud that features high emissivity (> 0.9) and low RML (recovered mass loss <1% at 150°C).

In order to maintain a uniform temperature around the device under test, two disc-shaped heat shields cover the two ends of the cylinder.    

The thermal system of TVAC utilizes Liquid Nitrogen or other refrigerant liquid to maintain cold temperatures and radiant or conductive heaters to keep the temperature hot to conduct the test.  Depending upon the application type (i.e., the testing temperature needed by the DUT), the thermal system uses different types of thermal fluid.

For the temperature range from - 70 ° C up to + 150 ° C Mechanical Cooling with Intermediate Fluid:

In this temperature range, the thermal fluid is typically a diathermic oil that is cooled by refrigerant gas or heated electrically and is circulated by a magnetic coupling pump through the shroud in a closed loop. The benefit of the system is its low cost.

For the temperature range from - 180 ° C up to + 150 ° C Pressurised Gaseous Nitrogen: 

In this temperature range, a special fan is used to circulate the pressurized gaseous nitrogen via the shroud for ensuring good temperature uniformity over the entire radiating surface. The cooling mechanism is carried out by means of spaying the liquid nitrogen in the circuit, and heating is carried out by using the electrical heaters.  This system provides excellent temperature regulation over the whole range.

For the temperature range from - 196 ° C up to + 150 ° C Liquid Nitrogen + Irradiators:

In this temperature range, the liquid nitrogen is wholly or partially filled in the shroud that helps achieve a testing temperature range of -196°C and -185°C depending on the pressure in the circuit. This system creates a radiant cryogenic environment around the DUT. The circulation of thermal fluid LN2 can be natural or by a forced pump. The heating of the DUT or temperature control is done by means of heating elements (infrared lamps or emitters) placed on special structures in the test volume.

Other parts of the TVAC system include a decontamination system (to reduce contamination due to outgassing generated by compounds and materials inside the vacuum chamber during the test), venting system, supply system (manage water, air, electric etc.), and data acquisition and instrumentation control system.

Control and management system:

The TVC control & management system features a fully automated combination of hardware & software components such as PLC (the core of the control system), inter subsystem interlocks for ensuring the safety of operating personnel, test object & facility equipment, and HMI devices for providing local & remote control (via PC with dedicated software) of the PLC to maintain and control the required environmental conditions for TVAC Testing.