Fluid parallel flow channels

The fluid flow through the core, through the SG and the PRHRS HEX, is characterized by flow through parallel channels. The channels in the core are formed by the fuel rods and those in the SG and PRHRS by closed flow-tube channels. Such flow configurations, parallel flow channels, are susceptible to instabilities for single-and two-phase flows. Under long-term safe shut-down conditions the PRHRS is expected to be a two-phase flow system. 

A numerical study of the effect of area ratio on the flow distribution in parallel flow manifolds used in a Hquid cooling module for electronic packaging demonstrate the useflilness of such a computational fluid dynamic code. The manifolds have rectangular headers and channels divided with thin baffles, as shown in Figure 12. Because the flow is laminar in small heat exchangers designed for electronic packaging or biochemical process, the inlet Reynolds numbers of 5, 50, and 250 were used for three different area ratio cases, ie, AR = 4, 8, and 16. 

Sobhan CB, Garimella SV (2001) A comparative analysis of studies on heat transfer and fluid flow in micro-channels. Microscale Thermophys Eng 5 293-311 Steinke M, Kandlikar SG (2003) Flow boiling and pressure drop in parallel flow micro-channels. In Kandlikar SG (ed) Proceedings of 1st International Conference on Micro-channels and Mini-channels, Rochester, 24-25 April 2003, pp 567-579 Thome JR (2006) State-of-the-art overview of boiling and two-phase flows in microchannels. Heat Transfer Eng 27(9) 4-19... 

Warrier et al. (2002) conducted experiments of forced convection in small rectangular channels using FC-84 as the test fluid. The test section consisted of five parallel channels with hydraulic diameter = 0.75 mm and length-to-diameter ratio Lh/r/h = 433.5 (Fig. 4.5d and Table 4.4). The experiments were performed with uniform heat fluxes applied to the top and bottom surfaces. The wall heat flux was calculated using the total surface area of the flow channels. Variation of single-phase Nusselt number with dimensionless axial distance is shown in Fig. 4.6b. The numerical results presented by Kays and Crawford (1993) are also shown in Fig. 4.6b. The measured values agree quite well with the numerical results. 

Two-dimensional compressible momentum and energy equations were solved by Asako and Toriyama (2005) to obtain the heat transfer characteristics of gaseous flows in parallel-plate micro-channels. The problem is modeled as a parallel-plate channel, as shown in Fig. 4.19, with a chamber at the stagnation temperature Tstg and the stagnation pressure T stg attached to its upstream section. The flow is assumed to be steady, two-dimensional, and laminar. The fluid is assumed to be an ideal gas. The computations were performed to obtain the adiabatic wall temperature and also to obtain the total temperature of channels with the isothermal walls. The governing equations can be expressed as... 

Hetsroni G, Mosyak A, Segal Z (2001) Nonuniform temperature distribution in electronic devices cooled by flow in parallel micro-channels. IEEE Trans Comp Packag Technol 24(1) 16-23 Ho CM, Tai Y-C (1998) Micro-electronic mechanic systems (MEMS) and fluid flows. Ann Rev Fluid Mech 30 5-33... 

The experimental investigations of boiling instability in parallel micro-channels have been carried out by simultaneous measurements of temporal variations of pressure drop, fluid and heater temperatures. The channel-to-channel interactions may affect pressure drop between the inlet and the outlet manifold as well as associated temperature of the fluid in the outlet manifold and heater temperature. Figure 6.37 illustrates this phenomenon for pressure drop in the heat sink that contains 13 micro-channels of d = 220 pm at mass flux G = 93.3kg/m s and heat flux q = 200kW/m. The temporal behavior of the pressure drop in the whole boiling system is shown in Fig. 6.37a. The considerable oscillations were caused by the flow pattern alternation, that is, by the liquid/two-phase alternating flow in the micro-channels. The pressure drop FFT is presented in Fig. 6.37b. Under... 

The platelets comprise an array of parallel micro channels with microstructured triangular-shaped headers at both ends. In the headers holes form conducts to the external feed fluid supply. Optimization of the shape of the header with respect to flow equalization was the topic of various simulation studies [52, 53]. 

Natinal convection flow through a channel foimned by two parallel plates as shown in Fig. 9-16 is commonly encountered in practice. When the plates arc hot (Tj > r,), the ambient fluid at enters the channel from the lower end, rises as it is healed under the effect of buoyancy, and the heated fluid leaves the channel from the upper end. The plates could be the fins of a finned heat sink, or the PCBs (printed circuit boards) of an electronic device. The plates can be approximated as being isothermal (Tj = constant) in the first case, and isoflu.x = constant) in the second case. 

In all these fields the traditional cross-flow reactor is represented. This reactor consists of a great number of parallel porous plates separated from each other by corrugated planes or by a similar regular structure, giving rise to a compact system of parallel closed channels, with only entrance and exit openings perpendicular to the main flow direction (cf. Fig. 3). The parallel-channel system of this traditional cross-flow reactor is arranged so that the inflows of the two fluids are separated 90°. This means that the two fluids will not be mixed in the same channels and the fluids will penetrate the plane plates from different sides. The fluids can meet only inside the porous catalytic plates where the reactions proceed. 

Al-Nimr, M.A., and Alkam, M.K. (1998) Unsteady non-darcian fluid flow in parallel-plates channels filled with porous materials, Heat and Mass Transfer 33,315-318. 

A number of analytical results are available for fully developed Nusselt values for the laminar flow of power law fluids in rectangular channels having aspect ratios ranging from 0 (i.e., plane parallel plates) to 1.0 (i.e., a square duct). Newtonian results (n = 1) are available for the T, HI, and H2 boundary conditions for the complete range of aspect ratios. Another limiting case for which many results are available is the slug or plug flow condition, which corresponds to n = 0. At other values of n, results are available for plane parallel plates and for the square duct. 

Flow rate The volumetric rate of flow of fluid parallel to the membrane surface. This is expressed in terms of volume/time (e.g. 1/min or gal/min). Flow rate is velocity (f) X cross-sectional area of the feed channel. Also sometimes termed recychng rate or recirculation rate. This is the major determinant of the state of turbulence in a membrane module. 

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