Numerical Heat Transfer, Part A: Applications is an international vehicle for the publication of numerically based, results-oriented papers dealing with problems in heat transfer, mass transfer, and fluid flow. The journal will consider for publication the following types of material: contributed papers, technical notes, invited papers, letters to the editor, and book reviews, the latter by invitation of the editor. All contributions will be evaluated by referees and the editor. Submission of Manuscripts. Three copies of the manuscript in final form should be sent with a cover letter to Professor W. J. Minkowycz, Editor-in-Chief, Numerical Heal Transfer, Department of Mechanical Engineering (MC 251), The University of Illinois at Chicago, 842 West Taylor Street, Room 2049, Chicago, IL 60607-7022. Authors will be asked to submit the final accepted manuscript on a disk. 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Abstract Until recently, computer simulation of filling flows in die casting have been focused on the determination of the free surfaces of injected liquid and has had difficulties to relate the flows with the formation of casting porosity. Flow visualization in scaled experiments indicates that the liquid has very complicated surfaces and that, in many cases, the surfaces break up and create a mixture zone with liquid droplets and air. This is especially true in pressure die casting where liquid metal is injected at a speed in order of 100 m/s and at a pressure up to 100 atm. The Reynolds number in the process could be above 105 and the Weber number above 102. Surface tension is far from sufficiently strong to sustain disturbance growth due to various instabilities. It is hard to keep the liquid as a separate continuous phase. Based on flow visualization experiments, a mathematical model is proposed as an alternative and effective simplification to the traditional tracing methods. Instead of determining the continuous free surfaces, the model tries to predict distributions of mass fraction of the injected liquid by solving a partial differential equation of mass transport together with the Navier-Stokes equations. Appropriate unsteady schemes of a finite difference analysis have been developed and are described in the paper. Results with an uniform straight injection into a die cavity are presented, which have re-created the filling patterns of the flows in experiments.

A visualization of the flow on the suction side and end-wall of a passage between two neighboring turbine blades is compared with mass (heat) transfer measurements on the same surfaces. Besides the horseshoe and passage vortices, there are several smaller vortices formed near the junction of blade and end-wall whose origins are discussed. The vortices detach from the end-wall and move up the blade's span. These vortices, sometimes in counter rotating pairs, are responsible for substantial local variations of heat transfer.

This report investigates our present ability to predict the thermal performance of film cooling arrangements used to protect the hot components of gas turbines. The required information is usually obtained by model experiments carried out at near room temperature as opposed to the high temperature encountered in the gas turbines. Dimensional or similarity analysis is used to develope the functional relationships for film effectiveness and convective heat transfer and the use of mass transfer experiments with foreign gas injection and naphthalene sublimation based on the heat-mass transfer analogy is discussed. The law of superposition is used to describe the combined effects of film cooling, surface convection or radiation and frictional heating. An order of magnitude estimate indicates to what extent local temperature gradients are alleviated in the cooled walls by internal heat conduction.

Detailed studies of the filling process of the die with liquid metal and the solidification are necessary to put this technology on a firm scientific basis. An experimental study of the fluid flow, heat transfer, and solidification encounters, however, enormous difficulties. It is extremely fast [in order of milliseconds], the small scale of the die makes local measurements difficult, and the temperature range and the nature of the liquid metal does not lend itself readily to experimentation. This paper explores whether similarity analysis is useful for the design of model experiments which reduce these difficulties and which reproduce the actual occurrence faithfully. The study is carried out in two steps. During the initial period, the whole cavity of the die is available for the fluid. Reynolds and Weber numbers which have to have the same value for the model experiment and for the die casting process permit the use of any fluid and of a large scale model which decreases the injection velocity and increases the filling time. During the later period of the filling process the cavity available for the liquid is reduced by the solidified metal. The energy conservation equation results in two more dimensionless numbers, the Prandtl and Jakob numbers which prescribe that model experiments have now to use a liquid metal but use of a metal with a low melting point and of a large scale decrease again the required injection velocity and increase the filling time by orders of magnitude, conditions beneficial for detailed and accurate experiments.

Porous and granular materials often defy an accurate description which would identify them. Property values for such media reported in the literature can then serve as guides only and a user of such material who needs accurate property values has to obtain them by measurement on a sample of the specific material with which he is concerned. It is the purpose of the present paper to describe a device by which specific heat, heat conductivity, and thermal diffusivity of particulate materials can be measured rapidly and accurately. The sample has an annular cylindrical shape, and is heated with a uniform heat flux on its inside and outside surfaces. The analysis performed has resulted in closed form expressions for the properties in terms of the measured variables in the quasi-steady state regime. An apparatus was designed and manufactured to verify the analysis. The conductivity of dry sand obtained by this method agrees with that measured in a steady state test within 2.17%.

Fluids flowing over an unheated cylinder with its axis normal to the flow separate in their wake into a central stream with a total enthalpy lower than the one in the upstream and two outer streams with higher total enthalpies provided the Reynolds number is such that alternate separation of vortices and the formation of a Karmán vortex street occur. Evidence of this was observed in 1940 by low values of the recovery temperature on the downstream side of a cylinder normal to a high velocity air stream. A number of experimental studies by various investigators confirmed the energy separation, established that it was connected with the unsteady character of the vortex formation, and that it was enhanced by the presence of sound waves. Various explanations have been proposed for the mechanisms which lead to this energy separation. The present paper surveys the significant experimental findings and attempts to describe the energy separation effect in physical terms starting with the unsteady energy equation and drawing on recent computer solutions.

The Ranque-Hilsch vortex tube (RHVT) is a compact thermo-fluidic device primarily used to split a highly pressurized gaseous fluid into two different temperature streams. Vortex tubes are mainly known for their energy separation characteristic. But the interesting fact is that the vortex tube can also separate constituents of the fluid mixture into various phases. In some instances, the highly swirling fluid inside the RHVT gets split into distinct species at the outlets. This paper reviews previous vortex tube studies on energy, phases, and species separation to analyze the mechanism and their influencing parameters. The paper also includes a brief CFD study conducted on five working gases to show the nature of thermal separation. The effect of nozzle number and nozzle geometry, L/D ratio and divergent angle of the main tube, and conical valve geometry are discussed for each separation behavior. Operating parameters such as inlet pressure, temperature, and thermo-physical properties of working fluids are discussed for the efficient and optimized operation of RHVT. Reviewing the previous literature supported exploring more novel ideas in optimizing separation techniques, such as the appropriate selection of tube material, cooling of the hot tube, and insulation near the cold end. The analysis presented a broad application of RHVT utilizing its energy and mass separation behavior in several mechanical processes. The study also led to an understanding of the utility of RHVT in trans-critical refrigeration systems, water droplet separation, and liquid oxygen collection systems.