Randall F. Barron

The Graetz problem extended to slip-flow

Abstract The original problem for thermally developing heat transfer in laminar flow through a circular tube, as formulated by Graetz, did not consider the ‘slip-flow’ condition. This paper extends the original work of Graetz to include the effect of slip-flow, which occurs in gases at low pressures or in microtubes at ordinary pressures. A special technique was developed to evaluate the eigenvalues for the problem. Eigenvalues were evaluated for Knudsen numbers ranging between 0 and 0.12. Simplified relationships were developed to describe the effect of slip-flow on the convection heat transfer coefficient.

Evaluation of the eigenvalues for the graetz problem in slip-flow

Abstract A technique was developed for evaluation of the eigenvalues for the Graetz problem extended to slip-flow. The first four eigenvalues for Knudsen numbers of 0.02, 0.04, …, 0.12 were found. By using a least square curve-fit method, simplified relationships between the eigenvalues and Knudsen number were obtained. The efficient and accurate determination of the eigenvalues will lead to better predictions of heat transfer in rarefied gas flows and for gas flows in microtubes.

Effect of Heat Transfer from Ambient on Cryogenic Heat Exchanger Performance

Heat exchangers used in cryogenic applications operate at significantly different temperatures from ambient and, as a result of this temperature difference, there is always some heat exchange between the heat exchanger and the environment. This heat transfer can result in serious deterioration of the heat exchanger performance. The effect must be considered in the design of liquefaction systems and cryogenic refrigeration systems, because the heat exchanger effectiveness must be greater than approximately 95 percent for these systems to achieve reasonable liquid yields or refrigeration effects1.

Film Boiling Under an Impinging Cryogenic Jet

Jet impingement cooling has found application in spot cooling of electronic components, cryosurgery, cryogenic freezing of food and other areas in which a relatively high heat flux is required. In this paper, the film boiling heat transfer process for a jet of liquid nitrogen impinging on a heated flat plate was examined analytically and the analytical correlation was verified by experiment. The analytical solution involved the application of the von Karman integral analysis for both the saturated liquid layer and the vapor film. The film boiling heat transfer coefficients were measured using both a transient method and a steady-state method.

Resonant Pressure Transmission To The Inner Ear

Engineering analysis of pressures in fluid-filled ducts and cavities is applied to the vertebrate inner ear. The human endolymphatic duct and combined utricle and saccule exhibit resonance in the auditory frequency range. The analysis can be used to develop more complex models of pressure transmission in inner ear ducts and cavites.

Film Boiling to a Plate Facing Downward

An experimental study was conducted to verify an analytical model developed to predict the film boiling heat transfer coefficient from a circular plate facing downward in liquid nitrogen. The film boiling coefficients were measured using a transient technique, in which the entire boiling curve was generated in a single experimental run. The analytical solution was of the form, Nu = f(Ra) Ra1/5, where Ra is the film boiling Rayleigh number, and the function f(Ra) involved the effect of the finite thickness of the vapor layer at the edge of the plate. The agreement between the analytical model and the experimental results was good for the range of Rayleigh number between 1010 and 5 × 1012 for plate diameters ranging from 50 mm to 150 mm and temperature differences between 50 K and 210 K.

Boiling Enhancement by Microgrooves

Several techniques have been proposed to improve the boiling heat transfer process, including surfaces with re-entrant holes, porous sintered metal coatings, etc. The purpose of this work was to examine the effect of circumferential microgrooves, produced by diamond-bit machining, on the film boiling heat transfer from a horizontal cylinder immersed in liquid nitrogen. The depth of the grooves was varied from 25 to 75 micrometers, and the width of the grooves was varied from 25 to 50 micrometers. Auxiliary tests were run using a cylinder with a smooth (polished) surface and one run was conducted with a cylinder having both circumferential microgrooves and longitudinal microgrooves. The boiling heat transfer coefficients were measured using a transient cool-down method.