Example: Convection? Radiation? Or Both? Heat transfer takes place between objects with different temperatures and all three modes of heat transfer exist.

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Presentation transcript:

Example: Convection? Radiation? Or Both? Heat transfer takes place between objects with different temperatures and all three modes of heat transfer exist simultaneously. However, there are many situations when one mode dominates over the others. Question: how do we know which modes to neglect in order to simplify the calculation? The following is an example to provide a general guideline to determine the relative importance between convection and radiation. By neglecting the less important one can usually lead to a simpler solution without significant error. Example: An electronic chip can dissipation between 0.1 W to 200 W of power depending on its operating configuration. Determine the operating temperature of the chip under three different power settings: (a) 0.1 W, (b) 200 W, (c) 5 W. Assume the convection heat transfer coefficient (h) over the chip is 10 W/(m K), the ambient temperature surrounding the chip is 27°C, the surface emissivity (  ) of the chip is 0.3 and the chip has a surface area of m 2.

convectionradiation Question: what happens to conduction?

Question: what do you mean by saying high or low temperature? Unfortunately, there is no easy answer to this question. It will depend on your engineering judgement. Hope the following calculation can help to answer this question.