Temperature body surface

At high environmental temperatures, food intake and oxygen consumption will fall, as will voluntary activity. Thus a reversal of the effect secondary to food intake noted for cold exposure may be expected. Whether or not adrenal activation occurs is of interest, since one tends to consider environmental temperatures other than those normally found in the individual s natural habitat to constitute a stress, but all environmental temperatures below body surface temperature will impose an obligatory heat loss on the animal, and may thus be considered stressful. 

Body surface temperature in the rat is about 34°C, depending on skin blood flow, environmental temperature, and the interpretation of surface. The results of Hale et al. (H2) that adrenal weight is lowest at 34°-35°C would support the above, insofar as adrenal weight may or may not reflect adrenal activity. 

This is known as the Planck radiation law. Figure A2.2.3 shows this spectral density fiinction. The surface temperature of a hot body such as a star can be estimated by approximating it by a black body and measuring the frequency at which the maximum emission of radiant energy occurs. It can be shown that the maximum of the Planck spectral density occurs at 2.82. So a measurement of yields an estimate of the... 

Since each ratio is dimensionless, any consistent units may be employed in any ratio. The significance of the symbols is as follows t = temperature of the surroundings tb = initial uniform temperature of the body t = temperature at a given point in the body at the time 0 measured from the start of the heating or coohng operations k = uniform thermal conductivity of the body p = uniform density of the boc c = specific heat of the body hf = coefficient of total heat transfer between the surroundings and the surface of the body expressed as heat transferred per unit time per unit area of the surface per unit difference in temperature between surroundings and surface r = distance, in the direction of heat conduction, from the midpoint or midplane of the body to the point under consideration / = radius of... 

The thermal parameters for comfort should be relatively uniform both spatially and temporally. Variations in heat flow from the body make the physiological temperature regulation more difficult. Nonuniform thermal conditions can lead to nonuniform skin temperatures. The active elements of the regulatory system may need to make more adjustments and work harder in order to keep thermal skin and body temperatures stable. To avoid discomfort from environmental nonuniformities, the temperature difference between feet and head should be less than about 3 °C (Fig. 5.9) and the mean surface temperature or radiant difference from one side of the body to the other should not he greater then about 10 °C. 

In buildings away from outside perimeter walls, air and surface temperatures are usually approximately equal. The heat losses from a person by radiation (q ) and convection (q ) are then flowing to the same temperature level. In such uniform spaces, the radiant and convective losses are about equal and together account for about 80-90% of the total heat loss of a sedentary comfortable individual. In the presence of hot or cold surfaces, as may occur in perimeter or other locations in a building, the average surface temperature of the surroundings (called mean radiant temperature) as seen by the person s body may be substantially different from air temperature. If the mean radiant temperature (MRT) is greater or less than air temperature (T,) the person will feel warmer or colder than in a thermally uniform space where MRT =. ... 

Body temperature The temperature of a human body, either the body core temperature, the mean temperature of the body, or the temperature at some point on the skin.. lso, the temperature of a surface which is radiating, conducting, or convecting heat. 

Nucleate boiling is boiling at the tube surfece at a temperature difference between outside tube surface temperature and the fluid body, less than the critical temperature difference. At and beyond the critical temperature difference, metastable and film boiling take place. These produce lower transfer coefficients as the temperature difference increases. 

Temperature measurement is a case in point. A large transducer in close contact with the body whose temperature is being measured will act as a heat sink and consequently produce a localized reduction at the point where the temperature is being measured. On the other hand, if an air gap exists between the transducer and the hot surface then the air (rather than the surface) temperature will be measured. 

The heat flux radiated from a real surface is less than that from an ideal black body surface at the same temperature. The ratio of real to black body flux is the normal total emissivity. Emissivity, like thermal conductivity, is a property which must be determined experimentally. 

Intermediate values ofBi. In this case the resistances to heat transfer within the solid body and the fluid are of comparable magnitude. Neither will the temperature within the solid be uniform (case 1), nor will the surface temperature be equal to that in the bulk of the fluid (case 2). 

If the emissive power E of a radiation source-that is the energy emitted per unit area per unit time-is expressed in terms of the radiation of a single wavelength X, then this is known as the monochromatic or spectral emissive power E, defined as that rate at which radiation of a particular wavelength X is emitted per unit surface area, per unit wavelength in all directions. For a black body at temperature T, the spectral emissive power of a wavelength X is given by Planck s Distribution Law ... 

Electrically-heated carbide elements, JO mm in diameter and 0.5 m long, radiating essentially as black bodies, are to be used in the construction of a heater in which thermal radiation from the surroundings is negligible. If the surface temperature of the carbide is limited to 1750 K, how many elements are required to provide a radiated thermal output of 500 kW7... 

A flat-bottomed cylindrical vessel, 2 m in diameter, containing boiling water at 373 K, is mounted on a cylindrical section of insulating material, l m deep and 2 m ID at the base of which is a radiant heater, also 2 m in diameter, with a surface temperature of 1500 K. If the vessel base and the heater surfaces may be regarded as black bodies and conduction though the insulation is negligible, what is the rate of radiant heat transfer to the vessel How would this be affected if the insulation were removed so that the system was open to the surroundings at 290 K ... 

SOLUTION We can use Wien s law in the form T = constant/ max to determine the surface temperature of stars treated as hot black bodies ... 

If the heat flux from friction or viscous shear is properly estimated, the surface temperature, which is of interest in most engineering problems, can be determined through integrating an analytical solution of temperature rise caused by a moving point heat source, without having to solve the energy equation. For two solid bodies with velocity u j and Ui in dry contacts, the temperature rises at the surfaces can be predicted by the formula presented in Ref. [22],... 

Temperature influences skin permeability in both physical and physiological ways. For instance, activation energies for diffusion of small nonelectrolytes across the stratum corneum have been shown to lie between 8 and 15 kcal/mole [4,32]. Thus thermal activation alone can double the rate skin permeability when there is a 10°C change in the surface temperature of the skin [33], Additionally, blood perfusion through the skin in terms of amount and closeness of approach to the skin s surface is regulated by its temperature and also by an individual s need to maintain the body s 37° C isothermal state. Since clearance of percuta-neously absorbed drug to the systemic circulation is sensitive to blood flow, a fluctuation in blood flow might be expected to alter the uptake of chemicals. No clear-cut evidence exists that this is so, however, which seems to teach us that even the reduced blood flow of chilled skin is adequate to efficiently clear compounds from the underside of the epidermis. 

The planet does not have a real surface instead, there is a gradual transition from the H2/He mixture to the central body, which consists of molecular hydrogen. Since there is no actual surface, temperatures can only be expressed in terms of their corresponding pressures. 

Jupiter s moon Europa has only been the subject of intense scientific investigation in recent years it is considered to be a member of that small group of heavenly bodies which could perhaps accommodate life (or a precursor of life). About 20 years ago, the Voyager passes afforded sensational pictures of Europa. These showed a network of linear bands, of differing breadths, on a very bright surface. The mean density was calculated as 3,018 35 kg/m3, and the surface temperature measured was 90-95 K. Circumstantial evidence points to either a surface consisting of water ice, or the presence of liquid water or warm ice under the surface. Three models were proposed (Oro et al., 1992) ... 

Body Radius (km) Surface pressure (bar) Albedo Effective temperature (K) Surface temperature (K) Surface g (m s-2)... 

The preceding calculation of the thermal energy balance of a planet neglected any absorption of radiation by molecules within the atmosphere. Radiation trapping in the infrared by molecules such as CO2 and H20 provides an additional mechanism for raising the surface temperature - the greenhouse effect. The local temperature of a planet can then be enhanced over its black body temperature by the atmosphere. 

An average of temperature records on the earth s surface over a year indicates that the earth s average surface temperature is about 14°C (57°F). But, the earth s 240 watts per square meter of thermal infrared radiation as measured by satellite is equivalent to the radiation emitted by a black body whose temperature is about -19°C (-3°F), not the 14°C (57°F) average measured at the earth s surface. The 33°C (60°F) difference between the apparent temperature of the earth as seen in space and the actual temperature of the earth s surface is attributed to the greenhouse effect. 

Variation of temperature is usually not an issue for solid oral dosage forms, since experiments are always conducted at body temperature (37°C). For dosage forms applied on the skin, this can be a further consideration e.g., drug-release testing of transdermal products is typically performed at the average temperature of body surface 32°C (5). 

Disregarding for a moment the bright and dark bands that decorate the spectrum of a heavenly body at specific wavelengths, the overall hue of that spectrum can tell us the surface temperature of the object. A blue star is thus hotter than a yellow one, and a yellow star is hotter than a red one. The Sun is hotter at the surface than the red star Antares, which in turn stands as a torrid desert before the brown dwarfs or interstellar clouds. The stars go red with cold. 

In contrast to line and band emissions, the emissivity of a hot body can be a function of temperature only. Hence, after absorbing incident radiation, the hot body re-emits a spectrum dependent on its surface temperature, which is known as black body radiation. 

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