Channel micro

The front opening of such a microchannel element has a diameter of only a few microns, but it is only one element of a whole multichannel array (Figure 31.2). Whereas the orifice to one micro-channel element covers an area of only a few square microns, an array of several thousand parallel elements covers a much larger area. In particular, the area covered by the array must be larger than... 

Unlike the array collector, with a microchannel plate all ions of only one m/z value are detected simultaneously, and instrument resolution does not depend on the number of elements in the micro-channel array or on the separation of one element from another. For a microchannel plate, resolution of m/z values in an ion beam depends on their being separated in time by the analyzer so that their times of arrival at the plate differ. 

Photomultiplier, or Electron multiplier, or Micro-channel plate... 

L.P. Yarin, Fluid Flow, Heat Transfer and Boiling in Micro-Channels Springer 2009... 

The first part of this book deals with the characteristics of flow and heat transfer in the channels and comparison between conventional size and micro-channels, which are important to understanding micro-processes in cooling systems of electronic devices with high power density and many other applications in engineering and technology. 

Chapter 2 presents general schemes of these systems, as well as the characteristics of the micro-channels used. 

In Chap. 3 the problems of single-phase flow are considered. Detailed data on flows of incompressible fluid and gas in smooth and rough micro-channels are presented. The chapter focuses on the transition from laminar to turbulent flow, and the thermal effects that cause oscillatory regimes. 

Chapter 4 is devoted to single-phase heat transfer. Data on heat transfer in circular micro-tubes and in rectangular, trapezoidal and triangular ducts are presented. Attention is drawn to the effect of energy dissipation, axial conduction and wall roughness on the thermal characteristics of flow. Specific problems connected with electro-osmotic heat transfer in micro-channels, three-dimensional heat transfer in micro-channel heat sinks and optimization of micro-heat exchangers are also discussed. 

The concepts of boiling in micro-channels and comparison to conventional size channels are considered in Chap. 6. The mechanism of the onset of nucleate boiling is treated. Specific problems such as explosive boiling in parallel micro-channels, drag reduction and heat transfer in surfactant solutions are also considered. 

Chapter 7 deals with the practical problems. It contains the results of the general hydrodynamical and thermal characteristics corresponding to laminar flows in micro-channels of different geometry. The overall correlations for drag and heat transfer coefficients in micro-channels at single- and two-phase flows, as well as data on physical properties of selected working fluids are presented. The correlation for boiling heat transfer is also considered. 

We attempt here to describe the fundamental equations of fluid mechanics and heat transfer. The main emphasis, however, is on understanding the physical principles and on application of the theory to realistic problems. The state of the art in high-heat flux management schemes, pressure and temperature measurement, pressure drop and heat transfer in single-phase and two-phase micro-channels, design and fabrication of micro-channel heat sinks are discussed. 

For flow at a given rate, the only way to significantly increase the heat transfer coefficient is to reduce the channel size, whose optimum can be calculated assuming a practical limit on the available pressure. Recourse to multiple channels, instead of continuous coolant flow over the entire back substrate surface, enables one to multiply the substrate area by a factor (jp, representing the total surface area of the channel walls which are in contact with fluid. Single-row micro-channels etched dir-... 

Fig. 2.10 High-performance micro-channel heat sink. Reprinted from Tuckerman and Pease (1981) with permission...

The definition of mini-channels and micro-channels has not been clearly and strictly established in the literature although many related studies have been done. For example, for compact heat exchangers, Mehendale et al. (1999) gave a relatively... 

Conventional channels Mini-channels Micro-channels Transitional channels Molecular nanochannels... 

The overall performance of micro-channel heat sinks... 

A micro-channel heat sink can be classified as single-phase or two-phase according to the state of the coolant inside it. For single-phase fluid flow in smooth... 

Fig. 2.12 Pictures from IBM paper showing high-performance liquid cooling technology using micro-channels. Reprinted from Colgan et al. (2005) with permission...

Poor flow distributions may result in localized dry hotspots which, absent control of the temperature fluctuations, may cause rapid overheating. Temperature and pressure fluctuations, and poor flow distribution, are the main problems that accompany the use of two-phase micro-channels. 

The lower chip contains the micro-channel test section with inlet and exit plenums, eight static pressure tap lines intersecting the micro-channel at equally spaced intervals, and one tap line per plenum. The tap line to the micro-channel... 

The IR technique also yielded temperature distributions (Fig. 2.17) in the symmetry plane at Re = 30 and g = 19 x lO W/m. The wall temperature decreases by axial conduction through the solid walls in the last part of the micro-channel (x/L > 0.75) since this part is not heated. Neither the wall nor the fluid bulk temperature distribution can be approximated as linear. 

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