Coolant-single phase, heat transfer

The assumptions for the heat balance along the channel are (1) steady-state flow (2) constant properties (3) closed channel analysis, no cross-flow between channels (4) channel flow area is constant in the axial direction (5) no boiling in the coolant, single-phase flow (6) constant heat transfer coefficient between the coolant and the heated surface (7) the channel is vertical channel and (8) the volumetric heat generation rate is independent of radial position in the fuel pellet. 

Single-component condensation. Figure 15.12 shows the resistances to heat transfer in filmwise condensation. When a single component is condensed (Fig. 15.12a), the entire heat transfer resistance on the condensing side is in the liquid phase. This heat transfer resistance is usually small, and the heat transfer resistance on the coolant side almost always controls the heat transfer rate. 

Within the assembly subchannels, the gravity-dominated, churn-turbulent coolant and air flows are sensitive to perturbations caused by air heatup and coolant cross flow to adjacent subchannels through the variable (0-40 mils) rib gaps. As a consequence, it is difficult to quantify local heat transfer conditions. A semi-empirical approach, based on separate effects (single heated wall) experiments, is being taken to establish the T/H criteria for the ECS phase. For restart, a conservative T/H precursor criterion to potential fuel damage conditions for the ECS phase power limit have been adopted. The criterion is as follows ... 

For single-phase flow, the heat transfer equation from the fuel cladding surface to the coolant is given by... 

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