Unsteady Convective Heat Transfer in Micro Ducts
The classification between steady and unsteady convective boiling in internal flows refers only to the controlled parameters such as heat flux or mass flow rate. Single-phase heat convection flows under steady boundary conditions are expected to be steady, especially in microsystems as discussed in Chapter 6, in the sense that all flow properties are constant in time and may vary only in space. However, some properties of two-phase forced convection flow, under steady heating, may not be steady such as the oscillations of the liquid-vapour interface discussed in Chapter 7. Then, even if all boundary conditions are steady, some flow properties may vary in space and time due to flow instabilities that develop within the system. In this context, unsteady convective heat transfer to be discussed hereafter refers to controlled variations of certain parameters with respect to time. In particular, the response of the microsystem to a step or a periodic change of one of the input parameters is of interest as in control theory. Experimental and analytical studies of unsteady heat convection in microducts have just begun and some preliminary results are discussed [84,176].
KeywordsHeat Transfer Natural Convection Input Power Forced Convection Forced Convection Heat Transfer
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