Measurements of Developing and Fully Developed Heat Transfer Coefficients along a Periodically Interrupted Surface

The heat transfer and pressure drop characteristics for an array of colinear, equally spaced plates aligned parallel to the flow in a flat rectangular duct have been studied experimentally. The periodic interruptions (i.e., the gaps between the plates) preclude the attainment of hydrodynamic and thermal development of the type that is encountered in conventional duct flows, but a periodic fully developed regime can exist. Measurements of the heat transfer coefficients for the successive plates of the array affirmed the periodically developed regime and demonstrated the developmental pattern leading to its attainment. The thickness of the plates in the array was varied parametrically. In general, the Nusselt number increases with plate thickness. Thickness-related increases in the fully developed Nusselt number of up to 65 percent were encountered. The presence of the interruptions serves to augment the heat transfer coefficients. In the fully turbulent regime, the heat transfer coefficients are on the order of twice those for a conventional duct flow. The pressure drop also increases with the plate thickness.

Preliminary Report of Developments in Interrupted Surface Finishes

Expanding interest and investigation in the development of interrupted surface finishes indicates the current trend renascent as the result of experience during the 1939–45 war with various types of mechanical equipment. It is here attempted only to highlight the results of service use and laboratory tests in three generic types: mechanically, chemically, and electrolytically generated surface finishes and their combinations. Because of the innumerable variables involved by the wide range of functional use, only the most general conclusions are drawn to prompt further study and investigation of this promising development, and to emphasize the desirability of avoiding controversial interpretations and attempted correlations until more data are available.