Micro conduits

STEADY STATE AND PERIODIC HEAT TRANSFER IN MICRO CONDUITS... 

The modem microstmcture applications led to increased interest in convection heat transfer in micro conduits. Huid transport in micro channels has found applications in a number of technologies such as biomedical diagnostic techniques, thermal control of electronic devices, chemical separation processes, etc. 

Experimental results have been published for micro tubes [1], micro channels [2], and micro heat pipe [3]. The micro scale experimental results differ from the prediction of conventional models. Some neglected phenomena must be taken into account in micro scale convection. One of them is the Knudsen number defined as the ratio of the molecular mean free path to characteristic length of the micro conduit. 

The conventional laminar forced convection in conduits at periodic inlet temperature is investigated mainly by Kaka9 and coworkers [23, 24, 25, 26, 27]. The periodic heat transfer in micro conduits, to the our knowledge, is not investigated. 

According to reference [1] four flow regimes for gases exist continuum flow (0iKn<0.001), slip flow (0.00l Kn<0.1), transition flow (0.l SKn<10), and free molecular flow (lOsKn). Continuum equations are valid for Kn- >0, while kinetic theory is applicable for Kn>8. Slip flow occurs when gases are at low pressure or in micro conduits. The gas slip at the surface, while in continuum flow at the surface it is immobilized. 

Steady State Heat Transfer in Micro Conduits... 

Consider steady-state heat transfer in thermally developing, hydrodynamically developed forced laminar flow inside a micro conduits (parallel plate micro channel or micro mbe) under following assumptions o The fluid is incompressible with constant physical properties, o The free heat convection is negligible, o The energy generation is negligible, o The entrance temperature is uniform, o The surface temperature is uniform. 

The surface temperature of the micro conduits is Ts. As result of the temperature jump on the surface the boundary condition at rl becomes ... 

Consider the heat transfer in thermally and hydrodynamically developed electro-osmotic flow inside a micro conduits under following assumptions ... 

C. Kleinstreuer and J. Koo, Computational analysis of wall roughness effect for liquid flow in micro-conduits, Journal of Fluids Engineering 126, 1-9... 

J. Koo and C. Kleinstreuer, Analysis of surface roughness effects on heat transfer in micro-conduits, International Journal of Heat and Mass Transfer 48, 2625-2634 (2005). 

Handbook). Nevertheless, a number of phenomena unique to micro-conduits still prevail, causing pressure drops, flow rates, and/or friction factors to differ from results obtained for macrochannels [2]. Examples include dominant entrance effects because the conduits are very short, significant surface roughness effects due to the closeness of the channel walls, earlier onset of turbulence because of induced instabilities, measurable viscous dissipation effects resulting from steep velocity gradients, possible fluid-slip on channel walls depending upon the physical-chemical characteristics of the (coated) surfaces, and significant effects of low-level forces usually not relevant in macro-devices, such as surface tension and electrostatics. 

M. Yi, H. H. Bau, The Kinematics of Bend-Induced Mixing in Micro-Conduits. Int.f Heat Fluid Flow, 2003, 24, 645-656. 

Miniature heat-removal devices Micro-heat exchangers MicroChannel heat sinks (MCHS) Row of coolants in micro-conduits Nanofluid flow in microcharmels... 

Bau HH, Pfahler JN (2001) Experimental observations of liquid flow in micro conduits, 39th AIAA Aerospace Sciences Meeting and Exhibit (2001-1), AlAA 2001-0722... 

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