Transfer In Air Research Articles

NUMERICAL STUDY OF TURBULENT NATURAL CONVECTION IN AN INNOVATIVE AIR COOLING SYSTEM

The process of buoyancy-induced turbulent convection in an asymmetrically heated vertical channel is studied numerically to simulate the situation of flow development and heat transfer in an innovative air cooling system. An upgraded two-equation closure model is employed to describe the turbulent motion, and the problem is formulated with proper account of the effects of property variations and surface radiation between the bounding watts. The governing system is solved by an implicit finite-difference method. Variable grid sizes are used in the numerical computation, and the velocity-pressure coupling is treated by a technique involving numerical iteration with underrelaxation. The accuracy of the present computational scheme is demonstrated by comparing the predicted results with available experimental data. Axial variations of watt temperatures and downstream evolution of local velocity and temperature fields are determined as functions of various controlling parameters of the system.

II–VI/III–V heterointerfaces: Epilayer-on-epilayer structures

The integration of several optoelectronic device functions onto a common substrate material is an area which is currently being actively pursued. In an effort to achieve this objective, experiments are under way to examine the epitaxial growth and material properties of a variety of both II–VI and III–V compounds grown on a substrate where the II–VI/III–V heterostructure can be utilized. This paper describes some recent developments involving the molecular beam epitaxial (MBE) growth and characterization of two important II–VI/III–V heterostructures, CdTe/InSb and ZnSe/GaAs. The structures are formed taking three approaches, by using (i) surface passivation techniques, combined with transfer in air from one chamber to the other, (ii) separate growth chambers connected by an ultrahigh vacuum transfer module, and (iii) both III–V and II–VI growth is performed in the same growth chamber. Multiple quantum wells of InSb have been grown at low temperatures of 300°C, using either Sb 4 or Sb 2 (the Sb 2 originates from an antimony cracker). Electrical characterization of metal/pseudomorphic ZnSe/p-GaAs capacitor structures illustrates accumulation, depletion and deep depletion; high frequency capacitance versus voltage data indicate interface state densities for the ZnSe/GaAs interface to be comparable to those reported for (Al,Ga)As/GaAs interfaces. The following paper represents a combined summary of two papers presented at the 5th International Conference on Molecular Beam Epitaxy.

Nanosecond air breakdown parameters for electron and microwave beam propagation

Air breakdown by avalanche ionization plays an important role in the electron beam and microwave propagations. For high electric fields and short pulse applications one needs avalanche ionization parameters for modeling and scaling of experimental devices. However, the breakdown parameters, i.e., the ionization frequency vs E/p (volt. cm−1. Torr−1) in air is uncertain for very high values of E/P. We review the experimental data for the electron drift velocity, the Townsend ionization coefficient in N2 and O2 and develop the ionization frequency and the collision frequency for momentum transfer in air. We construct the E/p vs Pτ diagram and show that our results are in better agreement with the most recent short pulse air breakdown experiments, compared to those predicted by the expression of Felsenthal & Proud (1965). This is because they extrapolate an expression for the drift velocity, linear in E/p, to high values of E/p. Experimentally the drift velocity varies as (E/p)½ in the region of E/p > 100.

THE EFFECT OF HEAT TRANSFER OF YARN PACKAGE DURING HEAT SET ON PROPERTIES OF HARD-TWIST YARN

As a factor affecting the hard-twist yarn's physical properties during heat set, the heat transfer of a yarn package was studied with a simple model.The simple model used regards the yarn package as the complex of yarn and air without radiation and convection, and implies the effect of barrel to the heat transfer coefficient of inner side.The results obtained are as follows:(1) Heat transfer of the yarn package in dry air is able to analyze with the simple model. On the other hand, heat transfer in humid air is difficult to analyze only with the simple model because of humid air's diffusion in the yarn package. But, this method is useful to predict the behavior of yarn that forms the yarn package.(2) Irregularity of hard-twist yarn's physical properties that appears during heat set is caused by obstruction of shrinking by barrel, difference in temperature rise and irregularity of relaxation of winding tension.

HEAT AND MASS TRANSFER AT AN UPSTREAM-FACING BLUNT FACE SITUATED IN A UNIFORM ONCOMING FLOW

A numerical investigation was performed to determine the heat /mass transfer from upstream-facing blunt faces of axisymmetric and plane two-dimensional bodies, which are situated such that a uniform flow approaches normal to the respective blunt faces. Face-average and stagnation-point Nusselt and Sherwood numbers, velocity and temperature profiles, and streamline maps are presented over the Reynolds number range from 5 × 103 to5 × 104. Average Nusselt number predictions for Pr = 0.7 (heat transfer in air) and average Sherwood numbers for Sc = 2.5 (naphthalene sublimation in air) agreed well with experiment. These results are well represented by a 0.5-power Reynolds number and 0.4-power Prandtl number fit. Stagnation-point Nusselt and Sherwood number predictions showed excellent agreement with boundary layer results using experimentally measured pressure distributions as input. Boundary layer results based on potential flow velocities as input overpredicted both the present numerical results and experimen...

The comparison of the surface properties of FeTi and Fe 2Ti 4O x in view of the different hydrogen sorption behaviours

FeTi and the oxygen-stabilized compound Fe 2Ti 4O x are known to form reversible metal hydrides. However, whereas samples of Fe 2Ti 4O x which have been exposed to air readily react with gaseous hydrogen at room temperature, FeTi samples have to be activated. We analysed the surface properties of Fe 2Ti 4O x and of FeTi before and after activation by means of photoelectron spectroscopy. A high pressure cell inside the spectrometer allowed us to analyse the samples immediately after the high pressure high temperature activation, thus avoiding a transfer in air. Elemental iron(0) and titanium(IV) are formed on the activation of FeTi; we have no evidence for the formation of TiH x , Fe 2Ti 4O x or FeTiO x . Significant differences between the oxidation behaviour of Fe 2Ti 4O x and that of FeTi fractured in an ultrahigh vacuum were found at room temperature.

Laminar mixed convection in an isothermal horizontal tube: Correlation of heat transfer data

A semi-analytical correlation for laminar mixed convection in an isothermal, horizontal tube is developed and found to describe all the available heat transfer data (excluding that of Kern and Othmer) with an RMS deviation of 11.7% based upon log-mean Nusselt number, 11.0% based on arithmetic-mean Nusselt number and 9.8% based on fractional bulk-temperature rise. The fact that the correlation does not describe the bulk of the Kern and Othmer data is attributed to the correspondingly large Rayleigh numbers, for which further investigations will be required. Although derived for a large-Prandtl-number fluid, the correlation is found to equally well describe available buoyancy-dominated heat transfer in air.

Natural convection heat transfer in air about a horizontal circular nonisothermal cylinder

Results are presented of a numerical investigation of laminar free convection heat transfer in air about a horizontal circular cylinder in the moderate Grashoff number range (104 ⩽ Grm ⩽ 109), for linear and quadratic laws of surface temperature variation.

Holographic interferometry measurement of convective heat transport beneath a heated horizontal circular plate in air

The technique of live-fringe holographic interferometry has been used in an investigation of convective heat transfer in air beneath a heated horizontal circular plate. Measurements were made beneath an 18.1 cm dia copper plate held at 16, 21 and 26 K above ambient temperature. This resulted in Rayleigh numbers of 1.07 × 10 6, 1.34 × 10 6 and 1.60 sx 10 6. The paper describes apparatus and procedures used in the holographic process as well as methods used in deriving temperature profiles from interferograms. Measured temperature profiles and Nusselt numbers agreed with predictions based on approximate analytical solutions to the heat transfer problem previously reported by others.

Specific antiserum staining of two‐dimensional electrophoretic patterns of human plasma proteins immobilized on nitrocellulose

AbstractHuman plasma proteins separated by high‐resolution two‐dimensional electrophoresis have been electrophoretically transferred to sheets of nitrocellulose using a modification of the method of Towbin, Staehelin, and Gordon [8]. Although the proteins have been denatured in sodium dodecyl sulfate and separated into subunits, the nitrocellulose‐bound molecules still react with appropriate specific antisera even after storage of the transfer in air at room temperature for 5 months. Of 25 proteins whose location in the pattern had been previously determined, 24 are specifically revealed on transfers of whole plasma patterns by appropriate antiserum. In addition, 6 previously unidentified proteins (prothrombin, C1s, C4γ, C1s inhibitor, Ig J‐chain, and a1AP glycoprotein) have been identified in the pattern for the first time using the transfer technique. It therefore seems likely that a large majority of proteins (> 96 % in this study) retain sufficient conformation throughout the analytical procedure (or can regain it easily afterwards) to be recognized immunologically. The transfer technique thus constitutes a generally useful immunological “third‐dimension” in the high‐resolution separation of proteins. Of three monoclonal antibodies similarly tested, none could detect antigen transferred to nitrocellulose from a two‐dimensional gel, while each bound specifically to the appropriate antigen absorbed in native form to the nitrocellulose.

A new theoretical formula for turbulent heat and mass transfer with gases or liquids in tube flow

AbstractA new theoretically‐based formula is presented for fully developed steady‐state forced convection heat or mass transfer in turbulent tube flow. This relationship, which is proposed for the frill range range of Prandtl or Schmidt numbers between 0.7 (gases) and 100 000 (liquids), is as follows: Coniparisons a with widely quotcd sets of data show very good agreement IFriend and metzner (heat transfer in liquids), Dcisser and Eian (heat transfer in air), Allen aid Eckert (heat transfer in water), Malina and Sparrow (heat trniisfcr in liquids), Harrott and Hamilton (mass transfcr in liquids)]. Absolute mean deviations vary from 3.6 to 8.1% over the range 0.73 + Pr or Sr ≤ 97 600.

Mechanical Augmentation of Convective Heat Transfer in Air

An experimental investigation was conducted into augmentation of forced convection heat transfer in air by mechanical removal of the boundary layer. A rotating blade element passing in close proximity to a flat plate convective surface was found to increase the rate of convective heat transfer by up to eleven times in certain situations. The blade element effectively scrapes away the boundary layer, thus reducing the resistance to heat flow. Parameters investigated include scraping frequency, scraper clearance, and type of boundary layer. Increased coefficients were found for higher scraping frequencies. Significant augmentation was obtained with clearance as large as 0.15 in. (0.0038 m) between the moving blade element and the convective surface. The technique appears most useful for laminar and transitional boundary layers, although some improvement was obtained for the turbulent boundary layers investigated. The simple surface renewal theory developed for scraped surface augmentation in liquids was found to approximately predict the coefficients obtained. A new relation is proposed which gives a better prediction and includes the effect of scraper clearance.

Thermal and ablative lag induced by a periodic heat input.

7 Wiese, W. L., Smith, M. W., and Glennon, B. M., Transition Probabilities, Vol. I. Hydrogen Though Neon, Rept. NSRDS-NBS4, May 1966, National Bureau of Standards. 8 Wilson, K. H. and Greif, R., Transport in Atomic Plasmas, Journal of Quantitative Spectroscopy & Transfer, Vol. 8, 1968, pp 1061-1086. 9 Armstrong, B. H., Apparent Positions of Photoelectric Edges and the Merging of Spectrum Lines, Journal of Quantitative Spectroscopy and Transfer, Vol. 4,1964, pp. 207-214. 10 Biberman, L. M. et al., Heating in Hypersonic Flow, Cosmic Research, Vol. 2, No. 3, 1964, pp. 376-387. 11 Alien, R. A., Radiation Graphs: Spectrally Integrated Fluxes Including Line Contributions and Self Absorption, AVCO Research Rept. 230, Sept. 1965, AVCO Everett Research Lab., Everett, Mass. 12 Hunt, B. L. and Sibulkin, M., Radiative Transfer in a Gas of Uniform Properties in Local Thermodynamic Equilibrium, Part I, II, and III, Rept. Nonr 562(35)/18, Dec. 1966, Brown University, Providence, R. I. 13 Page, W. A., private communication, Jan. 1968. 14 Hoshizaki, H. et al., Radiant Energy Transfer In Air, CR-585, Sept. 1966, NASA, Washington, D. C. 15 Wood, A. D. and Andrews, J. C., Fast-response Total Thermal Radiation Detectors, IEEE Transactions on Aerospace and Electrical Systems, Vol. AES-3, No. 2, March 1967, pp. 356-367. 16 Samson, J. A. R., Techniques of Vacuum Ultraviolet Spectroscopy, Wiley, New York, 1967, Chap. 8. 17 Gruszczynski, J. S. and Warren, W. R., Jr., Study of Equilibrium Air Total Radiation, AIAA Journal, Vol. 5, No. 3, March 1967, pp. 517-525. 18 Nerem, R. M., Stagnation Point Heat Transfer in High Enthalpy Gas Flows, Part II: Shock Layer Emission During Hypervelocity Reentry, FDL-TDR-64-41, Pt. II, March 1964, Air Force Systems Command, Wright-Patterson Air Force Base, Ohio. 19 Thomas, G. M. and Menard, W. A., Measurements of the Continuum and Atomic Line Radiation from High-Temperature Air, AIAA Journal, Vol. 5, No. 12, Dec. 1967, pp. 2214-2223. 20 Thomas, G. M., private communication, April 1968. 21 Page, W. A. et al., Radiative Transport in Inviscid Nonadiabatic Stagnation-Region Shock Layers, Paper 68-784, June 1968, AIAA. 22 Russell, L. D. and Beam, B. H., Thermodielectric Radiometer, Paper 68-403, April 1968, AIAA.

Optically thin stagnation-point flow.

Earth's Atmosphere, The High Temperature Aspects of Hypersonic Flow, Pergamon, Macmillan, New York, 1964, pp. 607-626. 10 Wilson, K. H. and Hoshizaki, H., Inviscid, Nonadiabatic Flow about Blunt Bodies, AIAA Journal, Vol. 3, No. 1, Jan. 1965, pp. 67-74. 11 Anderson, J. D., Jr., Nongray Radiative Transfer Effects on the Radiating Stagnation Region Layer and Stagnation Point Heat Transfer, NOLTR 67-104, July 1967, U.S. Naval Ordnance Lab., White Oak, Md. 12 Wood, A. D. et al., of the Total Radiant Intensity of Air, Paper 67-311, April 1967, AIAA. 13 Nerem, R. M., Atomic Line Radiation in Equilibrium Air, AIAA Journal, Vol. 4, No. 8, Aug. 1966, pp. 1485-1486. 14 Gruszczynski, J. S. and Warren, W. R., Jr., Study of Equilibrium Air Total Radiation, AIAA Journal, Vol. 5, No. 3, March 1967, pp. 517-525. 15 Nerem, R. M. and Golobic, R. A., Shock Tube Measurements of End-Wall Radiative Heat Transfer in Air, Paper 67695, 1967, AIAA; also AIAA Journal, Vol. 6, No. 9, Sept. 1968, pp. 1741-1747.

Shock-tube measurements of end-wall radiative heat transfer in air.

Measurements of radiative heat transfer to the end wall of a shock tube are presented for incident shock velocities from 6.5 to 9.5 mm/jusec and an initial driven tube pressure of 1-mm Hg. A thin film heat- transfer gage, mounted behind a sapphire window at the end of an arc driven shock tube, was used to measure the radiative flux behind reflected shock waves in air and in the wavelength region of 0.17 to 6 jit. Radiative heating rates in excess of 150 kw/cm2 were observed. For the conditions of the experiment, it is shown that equilibrium radiation dominates the end- wall heat transfer, and the experimental data are compared with equilibrium air radiation calculations for a transparent, homogeneous gas. For the higher shock velocities, the data are found to be factors of 2 or more lower than this prediction. Calculations are also presented to show the importance of radiative cooling and self- absorption. These calculations are compared with the data and the importance of these phenomena are discussed.

Effects of Ionization on Stagnation-Point Heat Transfer in Air and in Nitrogen

A study of the effect of ionization on the stagnation-point heat transfer to a noncatalytic wall is reported. The role of transport properties in heat-transfer calculations and a comparison of currently available results are made. The applicability of using a nitrogen model for heat transfer in the ionization regime is discussed and comparisons with available air results are made. Correlation formulas for heat transfer in air and in nitrogen are presented

Simultaneous heat and mass transfer in a fluidized bed of drying silica gel

AbstractThe determination of the partial coefficients of heat and mass transfer in air from and to a drying fluidized mass of silica gel is given. The analogy between the two methods of transport in the bed has been studied by an inspection of the relation between the two coefficients. A correlation of these coefficients with the void fraction, the superficial velocity, the particle size and the tube diameter of the bed has been derived. This correlation has been transformed into a correlation of dimensionless groups.

Heat Transfer in Humid Air (Cooling of Air)

As the heat and mass transfer problem of humid air cooling on finned pipe is necessary for air conditioning, the auther researches the heat transfer coefficient for finned pipe cooler. The cooler is set perpendicular to air flow and cooled by brine with temperature -5∼0°C. From the the results, it ts recognized that the analogy between heat and mass transfer exists and that the ratio of both coefficient α/k is about 0.21 kcal/kg°C. The ratio of heat transfer coefficient for wet and dry surface can be calculated from the experimental formula or nomograph of it.

Laminar free convection due to a line source of heat

Closed solutions are given in this paper for the velocity and temperature distributions in the fluid in free convection above a line source of heat embedded in an infinite horizontal plane for Prandtl numbers 2/3 and 7/3. Variations of the kinematic viscosity and of the thermal diffusivity with temperature, as well as the heat generated by viscous dissipation, are neglected. For heat transfer in air under normal conditions the Prandtl number is 0.73, so that the solution for Prandtl number 2/3 may be considered to furnish a fair approximation. Since the Prandtl number for diffusion of water vapor into air is approximately 0.6, the same solution can also be applied to the case of laminar evaporation from a line source of water into air.

Surface Heat-Transfer Coefficeints for Hydrogen-Cooled Rotating Electric Machines

A method is given for calculating the surface heat-transfer coefficients for hydrogen-cooled roating electric machinery from the values of these coefficients as determined from tests in air. The influence of hydrogen purity and of the velocity exponent on the ratio of heat transfer in hydrogen to heat transfer in air is evaluated; also, for gas flowing in ducts, the effect of the type of flow on this ratio is discussed. A method is also given for calculating the heat-transfer coefficients for ventilating ducts, in either air or hydrogen, on an inlet temperature basis, as an aid to simplifying the calculation of the surface temperature rise.