Sunday, February 22, 2009

Thermal Shock Chambers used in Test Laboratories

By Peter Brown

Thermal Shock Chambers are typically used to perform environmental stress screening of electronic components, aerospace parts or any other product that needs this type of test.

A Thermal Shock Chamber normally consists of two zones, hot and cold. The product being tested is moved between the two zones using a transfer mechanism. This transfer mechanism can be operated electrically or pneumatically (will require compressed air supply). The product is placed in a basket and moved using the transfer mechanism.

Thermal Shock Chambers are configured with two or three zones. If the chamber has a third zone, then this zone will be an ambient zone (same temperature as ambient since it is exposed to the ambient conditions around the chamber). Sometimes Thermal Shock Chambers are also configured to be of a double capacity type. If a double capacity style, then there will be two test baskets. As one of the baskets move into the hot chamber, the other basket moves into the cold chamber. This doubles up the capacity of the thermal shock chamber and therefore referred to as being a double capacity type.

The cold zone of a Thermal Shock Chamber needs to be made cold and the hot chamber needs to be made hot. Typically Thermal Shock Chambers have a temperature range of -70C to +170C. The temperature range is achieved by equipping the hot chamber with electric heating elements and the cold chamber with mechanical refrigeration, LN2 or Liquid CO2, or a combination of mechanical refrigeration and LN2 or CO2.

The compressors used in Thermal Shock Chambers need to be large enough to ensure that the product being tested recovers in a given time once it is transferred from the hot zone to the cold zone. The heating elements for the hot zone also need to be large enough to ensure that the product temperature recovers in a given time when it is moved from the cold zone to the hot zone. For example, a small thermal shock chamber with a test basket about 10x10x10 could have two 5hp compressors in a cascade configuration to accomplish this. Obviously there will be a limit to the size of the test load which can be tested using these size compressors.

Compressors for most Thermal Shock Chambers are water cooled (or remote air cooled) since they can become pretty large and the heat dissipated inside the test lab would become excessive otherwise. If the compressors are on the small size, LN2 or CO2 boost can be used together with mechanical refrigeration. In fact, many Thermal Shock Chambers can also run on LN2 or CO2 alone (without any compressors) - Although this can become costly if the chamber is used often.

Well known brands of Thermal Shock Chambers are Blue M, Thermotron, Ransco, Delta Design, Espec, Envirotronics and Associated Environmental.

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2 comments:

Suresh said...

Very informative article about the zones and configuration of Thernal Shock Chambers

ATT India said...

Thanks for sharing the information

For more info : Thermal Shock Chamber