Thermal Hood: A Low Cost Thermal Chamber
Original Publication Date: 2004-Mar-19
Included in the Prior Art Database: 2004-Mar-19
An alternative to a stand-alone Thermal Chamber is the Low Cost, Light Weight, Thermal Hood that allows a thermally controlled environment for thermal (heat) stressing any object that generates heat in some fashion. The achieved goal is to elevate the machine to a temperature above ambient for extended periods of time enabling thermal stress to be added to the normal test cycles. Our specific application is to create a device which would allow a machine (in this case, a 2105 Storage Subsystem - 'Shark Box') to be tested at an elevated temperature by re-circulation of its own hot air exhaust, and controlled by regulating the escape of that exhaust air into the surrounding room. This is an inexpensive, yet effective, way to perform an elevated temperature test without an additional exterior heat source e.g. running the machine in a thermal chamber. In fact, no extra power is required to thermally stress the product, and there is little to no additional floor space required.
Thermal Hood: A Low Cost Thermal Chamber
Last year the Manufacturing Engineering Team in San Jose developed a Thermal Hood that could be used as an alternative to costly, bulky, stand-alone thermal chambers for thermal (heat) stressing. Our existing, fully operational 'dual' thermal chambers cost over 115 thousand dollars each, and can separately test two machines at a time, in hot, cold, or ambient temperatures. The basis for developing the Thermal Hood, which can be purchased for around 3 thousand dollars for a large application, was to do testing at just elevated temperatures at a fraction of the cost. An expansion of this design could apply to all types of testing at elevated temperatures given that the system has its own internal heat generation. Systems with internal heat generation can be strictly electrical, electromechanical or chemical. This article will explain the thermal hood application in each category.
High tech electrical components, such as computer processors, are generally very heat sensitive making them a challenging component of a larger subsystem. The ability to test processors at elevated temperatures would give engineers the ability to assess the quality of production and sustainable life of the product under high use. The thermal hood in this application could simply redirect the hot rising air from the top of the processor to the bottom. The circulation would be controlled by the expansion of the hot gasses, similar to the way in which gas turbines use expanding gasses to turn large turbine wheels. The hot air would rise up the draft tube, as seen in Figure 1, and create a temperature increase by circulating back down as it cools. Temperature control is achieved by exhausting hot air out the top and letting cool make up air enter at the bottom. A simple feed back controller could automate the process.
Hot Air Outlets
Processor setting on central mounted grate in cylindrical draft tube.
Cool air Inlets
Figure1: Cross-section of thermal hood tester for increasing temperature of processor. As heat rises natural air circulation created. Controlled by exhaust flaps and cool air inlets.
Electromechanical systems because of size and heat load pose a complex situation. The benefit of testing a machine or any electrical unit above ambient temperature is to flush out any early life defects that could be present before delivering the machine to a customer. The idea was to elevate the temperature of a given system by use of its internal heat generation. If elevated temperature testing is to happen during part of the normal manufacturing process, where quality and quantity are the objectives, the stakes are even higher, and the following guidelines must be observed. Moving a large system in and out of a thermal chamber for testing depletes time and manpower. Therefore the chamber has to come to the machine. A moveable chamber would have to be very light weight so a single operator could move it. The cos...