Coolant channels

The multiplicity of phenomena characteristic of flow in heated micro-channels determined the content of the book. We consider a number of fundamental problems related to drag and heat transfer in flow of a pure liquid and a two-phase mixture in micro-channels, coolant boiling in restricted space, bubble dynamics, etc. Also considered are capillary flows with distinct interfaces developing under interaction of inertia, pressure, gravity, viscous and capillary forces. 

The reflector above the active core is composed of two layers, a layer of full-height elements over a layer of half-height elements. The top reflector elements channel coolant flow to the active core and provide for the insertion by gravity, of reseirve shutdown material into the active core. They have the same array of coolant holes as the fuel element and the same holes for the insertion of reactivity control devices. 

Small tabs on the outside of the canisters center the control assembly string in the control rod channel. Coolant flows down the outside and down the center hole to remove heat generated in the canisters. The string of canisters is designed with mechanical flexibility to articulate any postulated offset between elements during a seismic event. Thus, full insertion is ensured for any operating condition. The control rod drive... 

During steady state operation process channel coolant outlet teisperature shall not exceed 1 0 C. 

Process channel coolant adequacy 1 of 1 Manual No. 1 Variable 6... 

Maxim mi channel coolant mass velocity Ib/ft h (g/cm2s) 2.23x10 (305) 2.65x10 (362) 2.05x10 (278)... 

Once the boundary conditions are fixed (i.e., local decay heat generation rate, inlet coolant temperature, channel coolant flow rate, plenum pressure, assembly pressure drop and inlet air void fraction), FLOWTRAN-TF iterates between cells/nodes to obtain an axial temperature distribution for the fuel assembly subchannel surfaces as a function of time. In the calculation for power limits, the assembly power is progressively increased in increments until one of the subchannel surface nodes equals or exceeds the ECS T/H criterion (i. e., the fuel surface temperature exceeds the coolant saturation/boiling temperature for the static pressure conditions at that axial location (T... 

In this model, the heat transfer between fuel channel coolant and water rod moderator through the water rod wall structure is ctMisidered. Axial heat conductitm in the water rod is assumed to be negligible. Since the water rod wall structure is relatively thin, heat conduction in the water rod structure is also neglected. The governing equations for this model are given below. 

The coolant temperature distribution, the moderator temperature distribution, and the heat transfer coefficients between fuel channels and water rods are used in this model to generate the rate of heat transfer between fuel channel coolant and water rod moderator to the two thermal-hydraulics models. 

Next, the axial profile of the hot-channel coolant temperature can be computed using the axial power profile and the engineering hot-channel factor. The former can be estimated with sufficient accuracy for design since the analysis is relatively insensitive to the uncertainty involved. However, the hot-channel factor is of considerable importance and represents a design challenge. The subject will be discussed separately later. 

Euel assembhes became much more sophisticated, eventually consisting of concentric tubes made from an outer sheath, three fuel tubes, and an inner lithium-target tube, thus having four coolant channels. Locally developed extmsion techniques were used. 

The fuel for the Peach Bottom reactor consisted of a uranium-thorium dicarbide kernel, overcoated with pyrolytic carbon and silicon carbide which were dispersed in carbon compacts (see Section 5), and encased in graphite sleeves [37]. There were 804 fuel elements oriented vertically in the reactor core. Helium coolant flowed upward through the tricusp-shaped coolant channels between the fuel elements. A small helium purge stream was diverted through the top of each element and flowed downward through the element to purge any fission products leaking from the fuel compacts to the helium purification system. The Peach... 

The reactor core was made up of stacks of hexagonal graphite blocks. Each fuel element block had 210 axial fuel holes and 108 axial coolant holes (Section 5, Fig. 14). The fuel particles were formed into a fuel compact (Section 5.3) and sealed into the fuel channels. 

Productivity is directly related to cycle time. There usually is considerable common knowledge about a geometry and process conditions that will provide a minimum cycle time. Practices such as using thinner wall sections, cold or hot runners for TPs or hot or cold ones for TSs narrow sprues and runners, the optimal size and location of coolant (or heat) channels, and lower melt or mold heat, will decrease the solidification time reducing the cycle time. 

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-... 

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... 

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