Showing papers by "Ralph L. Webb published in 1998"

A New Equivalent Reynolds Number Model for Condensation in Smooth Tubes

Abstract: In 1959, Akers et al. developed an in-tube condensation model, which defines the all-liquid flow rate that provides the same heat transfer coefficient as an annular condensing flow. This liquid flow rate was expressed by an equivalents Reynolds number and used in a single-phase, turbulent flow equation to predict the condensation coefficient. However, the assumptions on which the equivalent Reynolds number is based are shown in the present work to be faulty. This results in the underprediction of many researchers' data. A new equivalent Reynolds number model, based on the heat-momentum analogy, is developed in this study. This model is then shown to predict the experimental Nusselt number of 1197 data points from 18 sources with an average deviation of 13.64 percent. The data are for tube internal diameters between 3.14 and 20 mm.

A Parametric Study of Nucleate Boiling on Structured Surfaces, Part I: Effect of Tunnel Dimensions

Abstract: This two-part experimental work identifies the effect of geometric dimensions on the boiling performance of tunneled enhanced boiling surfaces. The surface is formed on an integral-fin tube having a copper foil wrapped over the fin tips. Pores of known diameter and pitch are pierced in the foil cover. Tests were performed on a 19.1-mm diameter horizontal tube using R-11 and R-123 at 26.7 C for heat fluxes from 2 to 70 kW/m{sup 2}. the first part of the study defines the effect of the tunnel dimensions. The data show that greater tunnel height and smaller tunnel pitch are preferred. Sharp tunnel corners provides greater enhancement.

Convective Condensation of Superheated Vapor

Abstract: This paper provides a rationally based method to calculate the condensation coefficient of superheated vapor for condensation inside tubes. The method is theoretically based, and is applicable to any pure vapor. The method may be easily extended to condensation inside enhanced tubes, or to shell-side condensation. This work is an extension of a theory previously presented by Lee et al. (1991).

A Parametric Study of Nucleate Boiling on Structured Surfaces, Part II: Effect of Pore Diameter and Pore Pitch

Abstract: This two-part experimental work identifies the effect of geometric dimensions on the boiling performance of tunneled' enhanced boiling surfaces, which is similar to the Hitachi Thermoexcel-E surface. Tests were performed on a horizontal tube using R-11 and R-123 at 26.7°C for heat fluxes from 2 to 70 kW/m 2 . This second part of the study defines the effect of the pore dimensions (pore diameter and pore pitch). The pore diameters are 0.12, 0.18, 0.23, and 0.28 mm and the pore pitches are 0.75, 1.5, and 3.0 mm. The results are interpreted to explain the relationship between pore diameter and pore pitch on the boiling performance.

Advanced heat exchange technology for thermoelectric cooling devices

Abstract: Thermoelectric coolers (TEC) are potentially ideal devices to cool electronic components or small electronic enclosures. However, practical heat exchange can limit the COP and restrict the range of useful applications. The TEC must reject heat from the hot-side to the ambient, which is typically air. The COP can be increased by reducing the hot-side temperature, which requires a high-performance heat exchanger. An understanding of the heat sources in the TEC is presented, and relations are presented to define the hot-side thermal resistance required to operate at desired operating conditions. A novel, air-cooled thermosyphon reboiler-condenser system has been developed that promises significantly higher COP for thermoelectric coolers than is possible with current heat exchange technology. This heat exchanger design concept is described and compared to conventional technology.