enclosure.pdf - Thermal Management Heat Dissipation in Electrical Enclosures Technical Information Thermal Management Heat Dissipation in Electrical

enclosure.pdf - Thermal Management Heat Dissipation in...

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Spec-00488 E THERMAL MANAGEMENT HEAT DISSIPATION IN ELECTRICAL ENCLOSURES EQUIPMENT PROTECTION SOLUTIONS SUBJECT TO CHANGE WITHOUT NOTICE TECHNICAL INFORMATION 1 TECHNICAL INFORMATION THERMAL MANAGEMENT HEAT DISSIPATION IN ELECTRICAL ENCLOSURES HEAT DISSIPATION IN SEALED ELECTRICAL ENCLOSURES The accumulation of heat in an enclosure is potentially damaging to electrical and electronic devices. Overheating can shorten the life expectancy of costly electrical components or lead to catastrophic failure. ENCLOSURE MATERIALS The following discussion applies to gasketed and unventilated enclosures. Higher temperature rises can be expected with unfinished aluminum and unfinished stainless steel enclosures due to their material’s less efficient radiant heat transfer. Non-metallic enclosures have similar heat transfer characteristics to painted metallic enclosures, so the graph can be used directly despite the difference in material. ENCLOSURE SURFACE AREA The physical size of the enclosure is the primary factor in determining its ability to dissipate heat. The larger the surface area of the enclosure, the lower the temperature rise due to the heat generated within it. To determine the surface area of an enclosure in square feet, use the following equation: Surface Area = 2[(A x B) + (A x C) + (B x C)] ÷ 144 where the enclosure size is A x B x C in inches. This equation includes all six surfaces of the enclosure. If any surface is not available for transferring heat (for example, an enclosure surface mounted against a wall), that surface’s area should be subtracted. Note: Enclosure volume cannot be used in place of surface area. ENCLOSURE HEAT INPUT For any temperature rise calculation, the heat generated within the enclosure must be known. This information can be obtained from the supplier of the components mounted in the enclosure. ENCLOSURE TEMPERATURE RISE (ΔT) Research has shown for every 18 F (10 C) rise above normal room temperature 72 - 75 F (22 - 24 C), the reliability of electronic components is cut in half. The temperature rise illustrated by the curves in the Sealed Enclosure Temperature Rise graph is the temperature difference between the air inside a non-ventilated and non-cooled enclosure and the ambient air outside the enclosure. This value is described in the graph as a function of input power in watts per square foot. In order to predict the temperature inside the enclosure, the temperature rise indicated in the graph must be added to the ambient temperature where the enclosure is located. Sealed Enclosure Temperature Rise 0 20 40 60 80 100 120 2 4 6 8 10 12 14 16 11.1 22.2 33.3 44.4 55.5 66.6 Input Power (Watts/Square Foot) Temperature Rise Above Painted Metallic and Non-metallic Enclosures Unfinished Aluminum and Stainless Steel Enclosures Temperature Rise Above Ambient (ºC) Ambient (ºF) DETERMINING TEMPERATURE RISE The temperature rise inside a sealed cabinet without forced ventilation can be approximated as follows.
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