Showing papers on "Convection published in 1972"

Extended surface heat transfer

Abstract: Preface. Convection with Simplified Constraints. Convection with Real Constraints. Convective Optimizations. Convection Coefficients. Linear Transformations. Elements of Linear Transformations. Algorithms for Finned Array Assembly. Advanced Array Methods and Array Optimization. Finned Passages. Compact Heat Exchangers. Longitudinal Fin Double-Pipe Exchangers. Transverse High-Fin Exchangers. Fins with Radiation. Optimum Design of Radiating and Convecting-Radiating Fins. Multidimensional Heat Transfer in Fins and Fin Assemblies. Transient Heat Transfer in Extended Surfaces. Periodic Heat Flow in Fins. Boiling From Finned Surfaces. Condensation on Finned Surfaces. Augmentation and Additional Studies. Appendix A: Gamma and Bessel Functions. Appendix B: Matrices and Determinants. References. Author Index. Subject Index.

Parameterization of the Planetary Boundary layer for Use in General Circulation Models1

Abstract: The surface stress and fluxes of heat and moisture are parameterized for use in numerical models of the general circulation of the atmosphere. The parameterization is designed to be consistent with recent advances in knowledge of both the planetary boundary layer and the surface layer. A key quantity throughout is the height, h, of the planetary boundary layer, which appears in the governing stability parameter, a bulk Richardson number. With upward heat flux, a time-dependent prediction equation is proposed for h that incorporates penetrative convection and vertical motion. Under stable conditions, h is assumed to depart from the neutral value and to become nearly proportional to the Monin-Obukhov length. The roughness length, Zo, is incorporated in the combination h/zo, and the parameterization is consistent with h/zo affecting only the wind component in the direction of the surface velocity. The direction of the surface wind and stress is derived in a manner consistent with the known value of ...

Atmosphere-ocean interaction

Abstract: Preface 1. Basic Concepts 1.1. Notation 1.2. Conservation equations 1.2.1. Conservation of matter 1.2.2. Conservation of momentum 1.2.3. Conservation of energy 1.3. Turbulence and turbulent transport 1.4. Statistical description of fluctuating quantities 1.4.1. Correlation functions and spectra 1.4.2. Isotropic turbulence 1.5. Scaling techniques and similarity relations 2. The State of Matter Near the Interface 2.1. Sea water 2.1.1. The equation of state 2.1.2. Latent heat and saturation vapour pressure of pure water 2.1.3. Colligative properties 2.1.4. Atmospheric gases in solution 2.1.5. Molecular transport coefficients 2.2 Moist air 2.2.1. The equation of state 2.2.2. Molecular transport coefficients 2.2.3. Isobaric mixing and fog formation 2.2.4. Adiabatic and pseudo-adiabatic changes of state 2.3. The liquid-gas interface 2.3.1. Laminar sublayers 2.3.2. Surface tension 2.3.3. Contamination 2.4. Bubbles and spray 2.4.1. Generation of bubbles and spray droplets 2.4.2. Equilibrium pressure in air bubbles and spray droplets 2.4.3. Terminal velocities of gas bubbles and spray droplets 2.4.4. The size and flux spectra of air bubbles in bubble clouds 2.4.5. Sea surface bubble spectra and whitecap coverage as a function of wind speed 2.4.6. The size and flux spectra of spray droplets 2.4.7. Environmental effects of bubbles and spray 2.5 Sea ice 2.5.1. Formation and growth 2.5.2. Physical properties of sea ice 3. Radiation 3.1. Definitions 3.2. Solar radiation 3.2.1. The net short-wave irradiance at the sea surface 3.2.2. Reflection at the sea surface 3.2.3. Absorption of solar radiation in the ocean 3.3. Terrestrial radiation 3.3.1. Long-wave emission from the sea surface 3.3.2. Radiative transfer in the lower atmosphere 3.4. Empirical formulas for estimating the surface radiation budget 3.4.1. Short-wave irradiance 3.4.2. Short-wave exitance 3.4.3. Long-wave irradiance and exitance 4. Surface Wind Waves 4.1. Basic dynamics of harmonic waves in fluids 4.2. Small amplitude waves at the air-sea interface 4.3. Second-order quantities and approximations 4.4. Sources and sinks of surface wave energy 4.4.1. Transfer of energy between waves 4.4.2. Dissipation and breaking 4.4.3. The generation of waves by the wind 4.5. The evolution and parameterization of surface wave spectra 5. Turbulent Transfer Near the Interface 5.1. The structure of the interface and adjacent layers 5.1.1. The profiles in the molecular sublayers 5.1.2. The matching of surface layers to molecular sublayers 5.1.3. Transition from smooth to rough flow 5.2. The effect of stratification 5.3. Dynamic interactions between wind and sea surface 5.3.1. Surface drift 5.3.2. Wind-wave interactions 5.4. Transport of trace gases across the interface 5.4.1. Application of the surface renewal model 5.4.2. The stagnant water film model 5.4.3. Experimental methods and results 5.5. The sea surface temperature (SST) and the energy budget 5.6. Methods to observe the fluxes in the atmospheric surface layer 5.6.1. The eddy correlation method 5.6.2. The eddy accumulation method and the conditional sampling method 5.6.3. The gradient method 5.6.4. The dissipation and inertial dissipation methods 5.6.5. Fluxes obtained with remote sensing techniques 5.6.6. The ageostrophic transport or momentum budget method 5.6.7. Bulk parameterizations 6. The Planetary Boundary Layer 6.1. The Ekman boundary layer 6.1.1. The stationary laminar Ekman layer 6.1.2. Transient Ekman layers and Ekman transports 6.1.3. The depth of the turbulent Ekman layer surface-waves effects 6.2. Coherent structures in the planetary boundary layer 6.2.1. Observations of oceanic longitudinal rolls 6.2.2. Observations of atmospheric longitudinal rolls 6.2.3. Laboratory experiments 6.2.4. Numerical simulations 6.2.5. Energetics of longitudinal rolls 6.2.6. Physical concepts and theories 6.3. Parametric representation of PBL fluxes and profiles 6.3.1. Diffusive models 6.3.2. The transilient scheme 6.3.3. Parametric representation of PBL profiles 6.4. Mixed-layer models 6.4.1. The oceanic mixed layer 6.4.2. The cloud-free atmospheric mixed layer 6.4.3. The cloud-topped convective marine boundary layer 6.5. Discussion and evaluation 7. Atmospherically-forced Perturbations in the Oceans 7.1. Perturbations of a shallow, homogeneous ocean 7.1.1. The different types of atmospheric forcing 7.1.2. The forced shallow water equation 7.1.3. Perturbations of different extent and duration 7.2. The two-layer ocean model 7.2.1. The governing equations 7.2.2. Gravity waves at an internal density discontinuity 7.2.3. The rigid-lid approximation 7.2.4. Ekman pumping 7.3. Internal inertio-gravity waves 7.3.1. Internal waves in a continuously-stratified ocean 7.3.2. Long-waves normal modes 7.3.3. Atmospheric forcing of inertio-gravity waves 7.4. The response of the open ocean to moving cyclonic storms 7.4.1. Observations 7.4.2. The simulated short-term oceanic response to moving storms 7.4.3. The long-term oceanic response to moving storms 7.5. The effect of lateral boundaries on wind-forced perturbations 7.5.1. Wind-forced upwelling and downwelling along a straight coast 7.5.2. Coastal Kelvin waves 7.5.3. Shelf waves 7.5.4. Storm surges 7.6. Rossby or planetary waves 7.6.1. Free planetary waves 7.6.2. Forced plantary waves 7.7. Equatorial currents and perturbations 7.7.1. Balanced equatorial currents 7.7.2. Equatorial perturbations 8. Large Scale Forcing by Sea Surface Buoyancy Fluxes 8.1. The predominant direction and variability of air-sea interactions 8.2. Deep convection 8.2.1. The general character and organization of deep convection 8.2.2. Laboratory experiments and dimensional analysis 8.2.3. Deep convection and bottom-water formation in the oceans 8.3. The tropical atmosphere 8.3.1. Deep convection in the presence of clouds and precipitation 8.3.2. The Inter-Tropical Convergence Zone (ITCZ) and the Hadley circulation 8.3.3. Hurricanes 8.4. Some low-frequency ocean-atmosphere feedback processes 8.4.1. El Nino and the Southern Oscillation (ENSO) 8.4.2. The Somali current and the Indian monsoon 8.4.3. Interactions between the hydrological cycle and the thermo-haline circulation

Natural Convection in Enclosures

Abstract: Publisher Summary This chapter discusses the complex nature of the natural convection phenomena in enclosures. It discusses the two basic configurations of natural convection— that is, a rectangular cavity and a horizontal circular cylinder. In rectangular cavities, consideration is given to the two-dimensional convective motion generated by the buoyancy force on the fluid in a rectangle and to the associated heat transfer. The two long sides are vertical boundaries held at different temperatures and the short sides can either be heat conducting or insulated. Particular attention is given to the different flow regimes that can occur and the heat transfer across the fluid space between the two plane parallel vertical boundaries. Although heat transfer by radiation may not be negligible it is independent of the other types of heat transfer and can be fairly accurately calculated separately. To formulate the boundary value problem that describes this phenomena it is assumed that: (a) the motion is two-dimensional and steady, (b) the fluid is incompressible and frictional heating is negligible, and (c) the difference between the hot wall and cold wall temperatures is small relative to the absolute temperatures of the cold wall. In horizontal circular cylinder, consideration is given to the large Rayleigh number flow with the Prandtl number large and the Grashof number of unit order of the magnitude.

The stress of hot environments

Abstract: Preface 1. Heat exchange with the environment 2. Convection and evaporation 3. Radiation 4. The heat balance of sweating skin 5. Clothing 6. Respiration and insensible water loss 7. Physiological responses 8. Equivalent environments - steady state 9. Indices of heat stress - steady state 10. Heat stress and time Appendices References Index.

The oscillatory instability of convection rolls in a low Prandtl number fluid

Abstract: The instability of convection rolls in a fluid layer heated from below is investigated for stress-free boundaries in the limit of small Prandtl number. It is shown that the two-dimensional rolls become unstable to oscillatory three-dimensional disturbances when the amplitude of the convective motion exceeds a finite critical value. The instability corresponds to the generation of vertical vorticity, a mechanism which is likely to operate in the case of a variety of roll-like motions. In all aspects in which the theory can be related to experiments, reasonable agreement with the observations is found.

The propagation and transfer properties of steady convective overturning in shear

Abstract: A conservative quantity is found as an integral of a component of the vorticity equation and used to formulate a non-linear theory of steady, two-dimensional convection in shear. The steering-level and propagation speed are determined in terms of a Richardson number and a density-scaling parameter. Case studies indicate a favourable agreement between theory and observation, especially where the Richardson number is of order unity. The parcel theory of convection is extended and the importance of the horizontal pressure gradient as a control on the updraught intensity is discussed quantitatively. Heat and momentum transfer laws are obtained in terms of the mean flow parameters, and define a non-Fickian transfer.

Convection electric fields and polar thermospheric winds

Abstract: Use of the qualitative ideas of convection electric fields over the earth's polar regions to demonstrate the importance of ion drag in establishing a thermospheric wind system. Recent measurements indicate that uniform electric fields of 10 to 40 mV/m are a regular feature of the polar-cap ionosphere. Calculations of the neutral thermospheric wind, using these measured fields in a simple ionospheric model, have been made. The time scale for motion of the neutral gas ranges from less than 1 hour at F-region heights to about 2 hours in the dynamo region of the ionosphere. It has been found that the viscosity of the atmosphere is important in determining the winds in the dynamo region. Results are given that show ion-temperature enhancements of hundreds of degrees that are due to ion-neutral frictional effects. In addition, the total deposition rate of convection energy in the polar thermosphere is shown to be of the same order of magnitude as that due to absorption of solar EUV radiation. The implications of these results for the dynamics and energetics of the thermosphere are discussed.

On steady convection in a porous medium

Abstract: For convection in a porous medium the dependence of the Nusselt number on the Rayleigh number is examined to sixth order using an expansion for the Rayleigh number proposed by Kuo (1961). The results show very good agreement with experiment. Additionally, the abrupt change which is observed in the heat transport at a supercritical Rayleigh number may be explained by a breakdown of Darcy's law.

Convection in boxes: experiments

Abstract: Convective motions in rectangular boxes with one side horizontal have been studied. The critical Rayleigh numbers were determined. In most cases cell patterns with rolls parallel to the shorter side wall of the rectangular box were observed. The results have been compared with the known theoretical results of Davis (1967). In general, good agreement has been found.

Mantle Convection and the New Global Tectonics

Abstract: Within the last five years new unifying concepts in geology and geo­ physics have won general acceptance. These concepts explain the origin of earthquakes, volcanism, and mountain building as well as the evolution of oceanic and continental crust. It is postulated that the surface of the earth is divided into a series of plates that are in relative motion with respect to each other. Earthquakes, volcanism, and mountain building occur on plate margins. Most geophysicists accept that some form of thermal convection drives the motion of the plates. The hot crystalline upper mantle behaves like a highly viscous fluid, owing to solid-state creep processes. Heating from the decay of radioactive elements drives thermal convection cells. Observations of surface heat flux, surface topography, and variations in the surface gravitational field may be compared with predictions of convection theories. Seismic observations and surface measurements of variations of magnetic and electric fields yield information on the properties of the earth's interior that must be consistent with the predicted convective flows.

Field experiment study on the convective heat transfer coefficient on exterior surface of a building

Abstract: Two identical units of heat flow meter panels were used for the experiment and were mounted side by side on the exterior surface of the building. They were maintained at slightly different temperatures and the heat flux conducted toward the surface from inside was measured. The two panels received exactly the same incident radiation so the difference in the measured heat conduction was equal to the difference in heat loss by convection and long wave emission. The convective heat transfer coefficient was calculated from the temperature of the two surfaces and the emissivity.

Thermohaline Instability and Salt Fingers in a Porous Medium

Abstract: An extension of the analysis of Nield is made to more completely characterize the onset of convection in an infinite horizontal porous medium stratified by temperature and concentration. Comparisons are made with thermohaline convection in Newtonian fluids. Major differences lie in the concentration Rayleigh number dependence of the wavenumber at the marginal state of overstability and the dependence of the horizontal wavenumber in the “salt finger” region of stationary convection on both temperature and concentration Rayleigh numbers. Suggestions of geological applications and laboratory verification using a Hele‐Shaw cell are presented.

Roll-diameter dependence in Rayleigh convection and its effect upon the heat flux

Abstract: The average roll diameter in Rayleigh convection for 2000 < R < 31000, where R is the Rayleigh number, has been measured from photographs of three convecting fluids: air, water and a silicone oil with a Prandtl number σ of 450. For air the average dimensionless roll diameter was found to depend uniquely upon R and to increase especially rapidly in the range 2000 < R < 8000. The fluids of larger σ exhibited strong hysteresis but also had average roll diameters tending to increase with R. The increase in average roll diameter with R tended to decrease with σ. Through use of two-dimensional numerical integrations for the case of air it was found that the increase in average roll diameter with R provides an explanation for the usual discrepancy in heat flux observed between experiment and two-dimensional numerical calculations which prescribe a fixed wavelength.

Heat Flow and Convection Demonstration Experiments Aboard Apollo 14

Abstract: A group of experiments was conducted by Apollo 14 astronaut Stuart A. Roosa during the lunar flyback on 7 Fehruary 1971 to obtain information on heat flow and convection in gases and liquids in an environment of less than 10-(6)g gravity. Flow observations and thermal data have shown that: (i) there are, as expected, convective motions caused by surface tension gradients in a plane liquid layer with a free upper surface; (ii) heat flow in enclosed liquids and gases occurs mainly by diffusive heat conduction; and (iii) some convective processes, whose characteristics are not fully known, add to the heat transfer.

Thermal Diffusion and Convective Stability

Abstract: The stability of a two‐component fluid layer subjected to a temperature gradient has been studied, and the associated thermal diffusion separation has been found to exert a large influence even when the separations are small. The most unexpected and perhaps important result is that an instability has been found which can give rise to convection currents even though the density gradient is not adverse. Thus, a system heated from above can become unstable even when the fluid is less dense at the top of the system provided the more dense substance rises to the upper plate. Many measurements of the Soret coefficient could be subject to this instabilitity.

Plume Convection with an Upper-Mantle Temperature Inversion

Abstract: Convection driven by temperature differences at phase transitions would be accompanied by a temperature inversion below the asthenosphere. The inversion explains the asthenosphere's low viscosity and low velocity.

Gas Flow Pattern and Mass Transfer Analysis in a Horizontal Flow Reactor for Chemical Vapor Deposition

Abstract: To study mass transfer characteristics in a vapor deposition reactor, gas flow patterns in a horizontal tube were investigated. Combined free and forced convection spiral flow and pure forced convection laminar flow were observed depending on experimental conditions of various flow rates and pressures. Further, local deposition rates under two flow behaviors were numerically obtained by solving a three‐dimensional mass conservation equation. It was estimated on the basis of calculated results that forced convection laminar flow in a rectangular reactor produced better uniformity on the deposition rate distribution across the width than did combined convection spiral flow.

Electric fields in the magnetosphere

Abstract: Two techniques, tracking the motions of Ba(+) clouds and measuring the differences in floating potential between symmetric double probes, were successful in: (1) demonstrating the basic convective nature of magnetospheric electric fields, (2) mapping global patterns of convection at upper ionosphere levels, and (3) revealing the physics of electric currents in the ionosphere and the importance of magnetosphere-ionosphere feedback in altering the imposed convection.

Thermal history of the moon.

Abstract: The thermal history of the lunar interior has been investigated for many sets of parameters and initial conditions by the construction of mathematical models. These models have been extended to include the effects of melting and redistribution of radioactive heat sources with time. The models considered include the possibility of heat transfer by lattice conduction, radiative transfer, removal of radioactive heat sources and, in a molten zone, fluid convection. The energy sources are divided into initial temperature sources that operate during the formation of the moon or shortly thereafter, and long-lived radioactive heat sources.

Thermal Diffusion and Convective Stability. II. An Analysis of the Convected Fluxes

Abstract: The stability of a horizontal, two‐component fluid layer subjected to a positive vertical temperature gradient (heating from above) is investigated taking advantage of the fact that the time scales for thermal relaxation and concentration relaxation are widely separated. Based on this hypothesis a buoyancy driven instability owing to the separation by thermal diffusion is found even when the density gradient favors stability. This is in agreement with the previous findings of Schechter, Prigogine, and Hamm thus verifying that the difference in time scales is the essential feature giving rise to this unexpected instability. A convective state in which rolls are assumed to be stable is then studied by solving the nonlinear problem. The analysis shows that the contribution of the convective heat flux to the total heat flux vanishes to the approximation studied here, but that the convective mass flux is an important part of the total. Thus, the separation by thermal diffusion tends to be destroyed by the instability.

Physical and numerical experiments on layered convection in a density-Stratified fluid

Abstract: The formation and growth of horizontal layered convection cells in a density stratified solution of salt water subject to an impulsively applied lateral temperature gradient is investigated with physical and numerical experiments. Results indicate that lyers are induced by two mechanisms. One is the successive formation of layers due to the presence of the top and bottom boundaries. The other is the spontaneous occurrence of layers when a suitably defined Rayleigh number exceeds a critical value. It is found that well established layers are homogeneous in temperature and salinity and are separated by sharp gradients in density. Lateral heat transfer is of a periodic nature. Numerical experiments were carried out for finite and infinite geometry cases. For the finite geometry case, convection cells are generated successively inward from the horizontal boundaries. For the infinite geometry case, periodic conditions in the vertical direction are assumed. With continuous input of small perturbations,...