tailieunhanh - Heat Transfer Handbook part 46

Heat Transfer Handbook part 46. The Heat Transfer Handbook provides succinct hard data, formulas, and specifications for the critical aspects of heat transfer, offering a reliable, hands-on resource for solving day-to-day issues across a variety of applications. | 442 FORCED CONVECTION EXTERNAL FLOWS A flat plate of large width w and small thickness t is often used to introduce the concept of boundary layer flow and heat transfer. An infinitely long cylinder d in cross flow is also a geometrically simple object but the flow develops complexity at high velocities due to separation on the curved surface. Flow passing an infinitely long rectangular body w h w also involves complexities caused by flow separation at the sharp corners. A sphere in uniform flow is also one of the basic configurations where axisymmetric flow prevails at low velocities. The orientation of the heated object relative to the fluid flow has a significant influence on heat transfer. Well-studied configurations are parallel flow along a flat plate as in Fig. flows impinging on a plane Fig. a wedge and a cone Fig. and the side of a cylinder Fig. . In many studies the impinging flow is assumed to be parallel to the symmetry axis of the object as illustrated by the sketches in Fig. . The study of impinging heat transfer has as one objective the understanding of heat transfer near the symmetry axis. For the plane and the cylinder the point on the symmetry axis is called the stagnation point. Figure illustrates flows through heated objects placed in regular geometric patterns. These arrays are commonly found in heat exchangers that transmit heat from the external surfaces of tubes or flat plates strips to the fluid. In heat exchanger applications the array of cylinders Fig. and b is called a tube bank. When the row of objects is deep the fluid flow develops a repeating pattern after a few rows that is a fully developed pattern. The fluid temperature increases toward the end of the row as the fluid absorbs heat from the objects in the upstream rows and the thermal environment for an individual object bears the characteristics of internal flow. The case of a stack of parallel plates Fig. and d involves an extra feature that is

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