Thermal design cross-flow

Entrance andExit SpanXireas. The thermal design methods presented assume that the temperature of the sheUside fluid at the entrance end of aU tubes is uniform and the same as the inlet temperature, except for cross-flow heat exchangers. This phenomenon results from the one-dimensional analysis method used in the development of the design equations. In reaUty, the temperature of the sheUside fluid away from the bundle entrance is different from the inlet temperature because heat transfer takes place between the sheUside and tubeside fluids, as the sheUside fluid flows over the tubes to reach the region away from the bundle entrance in the entrance span of the tube bundle. A similar effect takes place in the exit span of the tube bundle (12). 

There are various WT and FT boiler economizer designs, classified as either steaming economizer and nonsteaming economizer types according to thermal performance. These economizers are constructed in either bare tube or finned tube (extended surface) patterns. They may be positioned horizontally or vertically within the boiler system, in either cross-flow or counterflow arrangements. 

The Boral curtains, in addition to serving as a neutron absorber, act also as coolant flow isolators preventing cross flow of the water between adjacent assemblies. The effect is such that each of the bundles becomes isolated and sits, therefore, in its own thermal chimney. Relap-4 (Ref. 8) models previously reported were used to ensure that local boiling would not take place with the current design. 

Fig. 12.25. The principal characteristics of such beds include cross flow of solid and drying gas, a solids residence time controllable from seconds to hours, and suitability for any gas temperature. It is necessary that the solids be free-flowing, of a size range 0.1 to 36 mm (59]. Since the mass flow rate of gas for thermal requirements is substantially less than that required for fluidization, the bed is most economically operated at the minimum velocity for fluidization. Multistage, cross-flow operation (fresh air for each stage) is a possibility [2], as is a two-stage countercurrent arrangement, as in Fig. 11.28 (58]. A tentative design procedure has been proposed (40].

Velocity meters measure the velocity v of fluid flow in a pipe of known cross section, thus yielding a signal linearly proportional to the volume flow rate Q. Mass meters provide signals directly proportional to the mass flow rate m = pQ, where p is the mass density. Coriolis meters, which are true mass meters, can be used only for liquids. Thermal-type flow meters use a heating element and determine the rate of heat transfer, which is proportional to the mass flow rate. This type of device is used mostly for gas measurements, but liquid flow designs are also available. 

Countercurrent flow can always be assumed, if thermally possible, regardless of the range of the temperature cross as long as the temperature approaches (e.g., hot outlet and cold inlet temperatures) are greater than 5°F. Also, only TEMA E and F -type shells should be used for countercurrent flow designs, provided that the number of shell and tube passes are the same. 

Tlie core-internal thermal-hydraulic performance of fuel temperature, core-internal structure, and core-internal coolant distribution were confirmed to be appropriate to their design during the full power operation. Tlie maximum temperature of the core support-plate measured at the upper surface of the centre core support-plate was 450°C that was sufficiently below its limited value of 530°C. Also, it was confirmed that other core-internal structure temperatures were well below their design criteria. From the result tliat no core-internal structure temperature measurement showed an abnormal value, it was confinned tliat there was no abnormal leak flow of coolant such as cross and bypass flows between fuel blocks, replaceable reflector blocks, permanent reflector blocks, etc. The maximum fuel temperature was evaluated to be 1 463°C prior to the high-temperature test operation. It was re-evaluated using the measured temperature data i.e. core-inlet and -outlet coolant temperatures and the calculated value of 1478°C does not exceed the normal operation hmit of 1 495°C. 

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