Mean Internal Temperature Research Articles

Heat transport by variable viscosity convection II: pressure influence, non-Newtonian rheology and decaying heat sources

This study is an extension of previous work on the heat transport properties of convection with Newtonian temperature-dependent viscosity. There it has been found that the Nusselt number ( Nu) only weakly depends on the Rayleigh number defined with the viscosity at the mean internal temperature ( Ra T ) when the temperature at the top boundary is fixed. Here the cases are considered where the viscosity depends not only on temperature, but additionally on pressure, or on stress according to a third-power law. Numerical solutions for bottom-heated steady state cells with free boundaries are calculated. The weak dependence of Nu on Ra T is also found with pressure influence on the viscosity, provided only that the temperature dependence is stronger. On the other hand, the pressure dependence can reduce the internal temperature of the cell below the mean of the top and bottom temperature, even when the temperature effect is much stronger. With power-law rheology and strong temperature influence a sharp transition between convective regimes with active and stagnant lid is found. In the region of the NuRa-space where present-day whole mantle convection may be located, the heat transport becomes insensitive to the internal Rayleigh number also with power-law creep. Finally, two numerical experiments of time-dependent convection with a decaying rate of bottom or internal heating and variable Newtonian viscosity were performed. The bottom heated cases is found in good agreement with the parameterization derived from steady state results. For internal heating the exponent in the Nu Ra T -relationship is ∼0.10, thus slightly larger than with bottom heating but still much lower than the value for constant viscosity convection. These results strengthen the view that the parameterized models for the thermal evolution of a cooling planet, based on results of constant viscosity convection, need a revision.

Planetary shape: internal constraints for small bodies

Summary. This paper describes the attainment of sphericity, or equivalent isopotential forms, for the surface of small Solar System objects (linear dimensions - 300 km) as a consequence of viscous relaxation (creep). The viscous relaxation time is shown to be directly proportional to the viscosity and proportional to the inverse square of the linear dimensions of the object. Since the effective viscosity varies very rapidly with temperature the detailed internal temperature distribution will in most cases significantly affect the rate of relaxation. If this temperature is sufficiently high during any phase of the object’s history, virtually complete relaxation will have occurred. Because the thermal relaxation time is usually less than the age of the objects considered, and because differentiation and convection are unlikely to occur, a simple model for the thermal regime within the object is easy to develop from which the viscosity is determined at various depths. It is shown that a body is more likely to relax if it is composed of a mixture of ice and silicate rock rather than either pure substance. The relaxed shape of Phoebe and the irregular shape of Hyperion may be accounted for by a lower radiogenic content in Hyperion, a hypothesis supported by albedo observations. The assumption that the object can be treated throughout as having a viscosity corresponding to the mean internal temperature is of course far from exact. It is shown that a plastic core may be formed which can eventually cause fracture of the outer harder shell and consequent sudden relaxation to an approximately spherical shape.

Fate of Bacillus cereus in Whipped Potatoes During Pre-Service Holding as Could Occur in a Conventional Foodservice System

Dehydrated potatoes were reconstituted (50 1/2-cup servings), mixed, transferred to a pan and the surface was inoculated with spores of Bacillus cereus to give ≥40 colony forming units (CFU) per 20.3 cm2. Survival of the organism was determined following pre-service holding, (52°C; 32% relative humidity; 1 h) as could occur in a conventional foodservice system. No statistically significant differences were found in numbers of B. cereus before and after pre-service holding. Although the mean surface temperature (56°C) of whipped potatoes was below the maximum germination temperature of B. cereus (59°C), mean internal temperature (63°C) and surface temperature (56°C) of whipped potatoes were never low enough for growth of vegetative cells to occur.

Energy use in dwellings: An exercise to investigate the validity of a simple calculation method

This note presents the results of an exercise carried out to investigate the validity of a method of predicting seasonal energy consumption in occupied dwellings. The calculation method and the ranges of values of parameters suggested in the original presentation were used to predict the fuel consumptions in a total of 42 dwellings, ranging from small flats to large detached houses. The information required to select, from the ranges available, values for the parameters used in the energy calculation equations was obtained from only a simple questionnaire and the external dimensions of each dwelling. The results obtained from studying this group of dwellings indicated that on average, the predicted fuel consumption was 14 per cent higher than the actual consumption. A discrepancy of this magnitude is considered to be consistent with the uncertainties associated with the various parameters used and the simplicity of the method. The most likely reasons for the over-estimates are discussed and an indication given of the research required to permit revision of the appropriate parameters. It is concluded that the accuracy of the method to predict actual fuel consumptions would be improved if in particular realised values of mean internal temperature and precise records of actual fuel consumption were available.

Effect of microwave heating in cook/chill food service system

In the microwave-heating subsystem of the simulated cook/chill food service, 100-gm. portions of precooked beef loaf were heated 80 sec. (2,450 mHz; 237 V.; 3,003 W. input power; 1,407 W. output power) to a mean internal end temperature of 82 +/- 9 degrees C. Mean input power to the microwave oven during heating, controlled by a transformer, was 240 kJ. per 80 sec. Fifty-three percent of the input power to the microwave oven was used to operate the oven. Of the 47 percent output power available to heat the beef loaf, 12 percent of the total input power was estimated to heat beef loaf, 17 percent was estimated to evaporate water from beef loaf, and 18 percent was attributed to miscellaneous energy losses.

Some aspects of core formation in Mercury

Evidence for a large metallic core in Mercury is all indirect; the internal magnetic field may imply a convective dynamo; the surface geology is suggestive of large-scale differentiation; and thermal history calculations based on cosmochemical models for Mercury predict core formation. The presence of a core will not be confirmed by an accurate measure of J 2, probably two orders of magnitude larger than the hydrostatic value. Core infall on Mercury would be accompanied by an increase in planetary radius of 17 km, an increase in the mean internal temperature of 700°K, and substantial melting of the mantle. If Mercury's core differentiated from an originally homogeneous planet, such an event must predate most of the present surface. Subsequent to core formation, Mercury's radius has decreased by about 2km due primarily to cooling of the lithosphere, in agreement with the estimate by Strom and others of the amount of planetary contraction based on photogeologic measurements of length, dip and throw on the global system of lobate scarps. A convective dynamo mechanism for Mercury's magnetic field is in apparent conflict with cosmochemical models that do not predict a substantial source of heat, most probably radiogenic, in Mercury's core. Without such a heat source, the core would solidify within about 1 b.y. after core infall, producing an unacceptably large contraction in Mercury's radius.

Thermo-Physical Characteristics of Glaciers — Toward a Rational Classification

Thermo-Physical Characteristics of Glaciers — Toward a Rational Classification

Thermo-Physical Characteristics of Glaciers — Toward a Rational Classification

Thermo-Physical Characteristics of Glaciers — Toward a Rational Classification

A Theory of the Permanent Magnetic Fields of the Sun and Earth

The motion of ions, executing short free paths under the influence of thermal agitation in an inhomogeneous magnetic field, in crossed magnetic and gravitational fields or in crossed magnetic and electric fields are shown to produce drift currents. The ion drifts are found to be opposite in direction to the drifts produced in the analogous cases of long free path. Under the condition of radial symmetry and a closed circuit the magnetic gradient gives rise to circular currents which flow in such a direction that magnetic regeneration takes place. Regeneration is limited by demagnetizing currents arising from the thermal motions of the ions interacting with the resultant magnetic field and an internal electric or gravitational field. The magnetic moments of the sun and earth are calculated from data which are approximately known and the correct magnitudes obtained. The permanent fields arise from the thermal energy of the body and would be maintained if the bodies ceased their rotation. The asymmetry of the earth's magnetic field indicates that the hemisphere embraced by the Pacific Ocean is at a higher mean internal temperature than the rest of the earth.