G.L. Wedekind

An experimental investigation into forced, natural and combined forced and natural convective heat transfer from stationary isothermal circular disks

Experimental heat transfer data are presented and dimensionless correlations developed for forced, natural and combined assisting forced and natural convection for heated stationary isothermal circular disks over wide ranges of the Reynolds, Rayleigh and modified Reynolds numbers, respectively. Experiments with air were performed for a variety of disks ranging in diameter and thickness-to-diameter aspect ratio. The correlation for combined forced and natural convection was developed utilizing the concept of a modified Reynolds number which accounts for a buoyancy-induced velocity. Utilizing this concept, the experimental data and respective empirical correlations for all three convection modes can be collapsed and plotted on the same continuous curve.

An experimental investigation into natural convection heat transfer from horizontal isothermal circular disks

Abstract Experimental heat transfer data are presented and a dimensionless correlation developed for natural convection from heated horizontal stationary isothermal circular disks over a wide range of the Rayleigh numbers. Experiments with air were performed for a variety of disks of different diameters and thickness-to-diameter aspect ratios. The significant volume of data is consistent with the single set of data available in the archival literature, and is correlated with a classical Nusselt–Rayleigh correlation.

Modeling the local and average heat transfer coefficient for an isothermal vertical flat plate with assisting and opposing combined forced and natural convection

Abstract A theoretical model is formulated, utilizing an integral technique, to describe the thermal boundary layer development. Special case closed-form solutions are obtained for 0.72 ⩽ Pr ⩽ 10 to predict the local and average heat transfer coefficient for combined forced and natural convection from an isothermal vertical flat plate, for both assisting and opposing flows. No opposing flow closed-form solutions are known to exist in the current literature. Assisting and opposing flow experiments were performed to measure the average heat transfer coefficient with air for two flat plate heat transfer models of different lengths. The predictive capability of the present theoretical model was compared to this experimental data with excellent agreement. Excellent agreement is also found to exist with the experimental data and numerical solutions of other researchers.

Predicting the Influence of Compressibility and Thermal and Flow Distribution Asymmetry on the Frequency-Response Characteristics of Multitube Two-Phase Condensing Flow Systems

An equivalent single-tube model concept was extended to predict the frequency-response characteristics of multitube two-phase condensing flow systems, complete with the ability to predict the influence of compressibility and thermal and flow distribution asymmetry. The predictive capability of the equivalent single-tube model was verified experimentally with extensive data that encompassed a three-order-of-magnitude range of frequencies, and a wide range of operating parameters.

Predicting the average heat transfer coefficient for an isothermal vertical circular disk with assisting and opposing combined forced and natural convection

Circular disks are an important geometry when considering electronic component cooling, such as the cooling of disktype resistors and power transistors, or other related applications, such as the use of commercially available disk-type thermistors [1] for temperature and air flow measurements. Empirical correlations exist in the literature [1] for combined forced and natural convection from vertical circular disks for assisting flows, but not opposing flows. Also, to the best knowledge of the authors, there is no theoretical model currently available for predicting the convective heat transfer coefficient for assisting and opposing flows. Therefore, a conversion scheme is developed in the present research that utilizes a previously developed theoretical model [2], which was successful in predicting the average convective heat transfer coefficient for vertical flat plates experiencing combined forced and natural convection, to predict heat transfer coefficients for circular disks. The conversion scheme involves the concept of an effective flat plate length for a circular disk. The following flat plate solutions [2] may be used to predict the average heat transfer coefficient for circular disks by using this effective length, L* :

Predicting the Onset of a Low-Frequency, Limit-Cycle Type of Oscillatory Flow Instability in Multitube Condensing Flow Systems

A means was developed for extending the predictive capability of the Equivalent Single-Tube Model (ESTM) to accurately predict the onset of a self-sustained oscillatory flow instability for a multitube condensing flow system. The model includes the effects of compressibility, subcooled liquid inertia, and thermal and flow distribution asymmetry. Previously, liquid inertia, a necessary mechanism for the instability, had not been modeled for a multitube system. Extensive experimental data was obtained for a two-tube system that verifies not only the predictive capability of the ESTM, but also its accuracy and its wide range of applicability.

Analysis for the optimal performance of three-channel split-flow heat exchangers

Governing equations for describing the axial variation of temperature differences of fluids flowing in a three-channel single-pass heat exchanger are formulated by adopting similar assumptions as those used in the classical log-mean-temperature-difference (LMTD) method for two-channel heat exchangers. A special-case solution and a generalized solution of these governing differential equations are obtained for designing exchangers with split-flow channels in both parallel-flow and counterflow configurations. The special-case solution can be obtained under the condition of having identical axial-temperature distributions in the split-shell-flow channels and is similar to the classical formulation for two-channel heat exchangers, but with some parameter modifications. Solutions of this general model confirm that the special-case model represents the optimum design of such heat exchangers. These results are also verified experimentally using a concentric-tube heat exchanger. Theoretically predicted heat-exchanger effectivenesses are found on the average to be within ±5% of the experimental measurements.