Channel heat transfer

Table 6.8 Two-phase flow boiling in micro-channels. Heat transfer coefficient. Reprinted from Lee and Mudawar (2005b) with permission...

Kandlikar SG, Balasubramanian P (2004) An extension of the flow boiling correlation to transition, laminar and deep laminar flows in mini-channels and micro-channels. Heat Transfer Eng 25 86-93... 

Lowry, B., and Kawaji, M. (1988) Adiabatic Vertical Two-Phase Flow in Narrow Flow Channels, Heat Transfer - Houston 1988, Papers Presented at the 25th National Heat Transfer Conference, Houston, TX, USA, Vol. 84, Publ by AIChE, New York, NY, USA, pp. 133-139. 

Apart from rectangular channels, heat transfer has also been studied in channels with different cross-sectional geometries. Along with their studies of friction factors, Shah [26] and Shah and London [25] also computed heat-transfer properties. Their results include both the Nusselt numbers for fixed-temperature and fixed-heat-flux wall boundary conditions and are given as tabulated values for different geometric parameters. 

Axial dispersion coefficient Activation energy Friction factor, tvv o-phase friction factor Gravitational acceleration Height of rectangular channel Heat transfer coefficient Molar flux ofjth component in ith phase... 

Smol skiy, B. M. and A. S. Chekol skiy, Investigation of Heat and Mass Transfer in Condensation of Water Vapor from Moist Air in Curved Channels, Heat Transfer—Sov. Res. (USA), 10, 162-169 (1978). 

Internal Cooling Channel Heat Transfer Coefficient Estimation... 

Existence of interaction from channel-to-channel heat transfer (through the connecting support material) and from the catalytic material to the reactor wall... 

Several wick stmctures are in common use. First is a fine-pore (0.14—0.25 mm (100-60 mesh) wire spacing) woven screen which is roUed into an annular stmcture consisting of one or more wraps inserted into the heat pipe bore. The mesh wick is a satisfactory compromise, in many cases, between cost and performance. Where high heat transfer in a given diameter is of paramount importance, a fine-pore screen is placed over longitudinal slots in the vessel wall. Such a composite stmcture provides low viscous drag for Hquid flow in the channels and a small pore size in the screen for maximum pumping pressure. 

The stainless steel plates are separated (ca 3 pm between) by nonabsorbent vulcanized gaskets. Various profiles and configurations, including raised knobs, crescents, channels, or diamonds, provide a rapid, uniform heat-transfer plate surface. During operation the plates must be pressed together to provide a seal, and mounted and coimected in such a manner that air is eliminated and that the product drains from the plates without opening. 

The final correlation for the overall boiling heat-transfer coefficient in pipes or channels (20) is a direct addition of the macroscopic (mac) and microscopic (mic) contributions to the coefficient ... 

For laminar flow of power law fluids in channels of noncircular cross section, see Schecter AIChE J., 7, 445 48 [1961]), Wheeler and Wissler (AJChE J., 11, 207-212 [1965]), Bird, Armstrong, and Hassager Dynamics of Polymeric Liquids, vol. 1 Fluid Mechanics, Wiley, New York, 1977), and Skelland Non-Newtonian Flow and Heat Transfer, Wiley, New York, 1967). 

Isothermal Gas Flow in Pipes and Channels Isothermal compressible flow is often encountered in long transport lines, where there is sufficient heat transfer to maintain constant temperature. Velocities and Mach numbers are usually small, yet compressibihty effects are important when the total pressure drop is a large fraction of the absolute pressure. For an ideal gas with p = pM. JKT, integration of the differential form of the momentum or mechanical energy balance equations, assuming a constant fric tion factor/over a length L of a channel of constant cross section and hydraulic diameter D, yields,... 

Spiral baffles, which are sometimes installed for hquid services to improve heat transfer and prevent channeling, can be designed to serve as reinforcements. A spiral-wound channel welded to the vessel wall is an alternative to the spiral baffle which is more predictable in performance, since cross-baffle leakage is eliminated, and is reportedly lower in cost [Feichtinger, Chem. Eng., 67, 197 (Sept. 5, I960)]. 

During filling, the catalyst is distributed uniformly to avoid the possibility of channeling that coiild lead to poor heat transfer, poor conversion, and harm to the catalyst because of hot spots. During startup, sudden surges of flow may disturb the bed and are to be avoided. For instance, in a study of a hydrodesulfuiizer by Murphree et al. (Ind. Eng. Chem. Proc. Des. size unit varied between 47 and 80 percent with different modes of loading and startup. 

Endurance Burn Under certain cou(itious, a successfully arrested flame may stabilize on the unprotected side of an arrester element. Should this condition not be corrected, the flame will eventually penetrate the arrester as the channels become hot. An endurance burn time can be determined by testing, which specifies that the arrester has withstood a stabilized flame without penetration for a given period. The test should address either the actual or worst-case geometry, since heat transfer to the element will depend on whether the flame stabilizes on the top, bottom, or horizontal face. In general, the endurance burn time identified by test should not be regarded as an accurate measure of the time available to take remedial action, since test conditions will not necessarily approximate the worst possible practical case. Temperature sensors may be incorporated at the arrester to indicate a stabilized flame condition and either alarm or initiate appropriate action, such as valve closure. 

This design has a number of tubes embedded inside the turbine blade to provide channels for the water (Figure 9-23). In most cases, these tubes are constructed from copper for good heat-transfer conditions. The water, which is converted to steam by the time it reaches the blade tips, is then... 

The dummy tubes do not pass through the tubesheets, and can be located close to the inside of the shell. The seating strips extend from baffle to baffle in a longitudinal direction and effectively channel the fluid across the tubes to minimize turbulence and heat transfer. On some fixed tubesheet designs, the outer tubes are in close proximity to the inside of the shell so that by-pass is minimal and no by-pass elimination is necessary. There are a number of... 

The simplest type of shell-and-tube heat exchanger is shown in Eigure 3-1. The essential parts are a shell (1), equipped with two nozzles and having tube sheets (2) at both ends, which also serve as flanges for the attachment of the two channels or beads ( 3) and their respective channel covers (4). The tubes are expanded into both tube sheets and are equipped w nil transverse baffles (5) on the shell side for support. The calculation of the effective heat transfer surface is based on the distance between the inside faces of the tube sheets instead of the overall tube length. 

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