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Heat loss convective

To simplify the effects of radiation and convection on dry heat transfer, the concept of operative temperature is often used. By definition operative temperature is the temperature of a uniform environment (= MRT) that has the same total dry heat loss (convection + radiation) as the actual environment where MRT. [Pg.188]

In order to account for the heat loss through the metallic body of the cone, a heat conduction equation, obtained by the elimination of the convection and source terms in Equation (5.25), should also be incorporated in the governing equations. [Pg.163]

One design for a low temperature convection furnace shown in Figure 4 utilizes an external circulating fan, heating chamber, and duct system. The fan draws air (or a protective atmosphere) from the furnace and passes through the external heating chamber and back into the furnace past the work. This system minimizes the chance that the work receives any direct heat radiation. In theory it is less efficient because the external blower, heating chamber, and ductwork add external surfaces that are subject to heat losses. [Pg.135]

The maximum velocity at the axis is twice the average, whereas the velocity at the wall is zero. The effect of the burner wall is to cool the flame locally and decrease the burning velocity of the mixture. This results in flame stabilization. However, if the heat-transfer processes (conduction, convection, and radiation) involved in cooling the flame are somehow impeded, the rate of heat loss is decreased and the local reduction in burning velocity may no longer take place. This could result in upstream propagation of the flame. [Pg.523]

Radiation differs from conduction and convection not only in mathematical structure but in its much higher sensitivity to temperature. It is of dominating importance in furnaces because of their temperature, and in ciyogenic insulation because of the vacuum existing between particles. The temperature at which it accounts for roughly half of the total heat loss from a surface in air depends on such factors as surface emissivity and the convection coefficient. For pipes in free convection, this is room temperature for fine wires of low emissivity it is above red heat. Gases at combustion-chamber temperatures lose more than 90 percent of their energy by radiation from the carbon dioxide, water vapor, and particulate matter. [Pg.569]

There will also be heat loss from tire substrate due to convection cuiTents caused by the teirrperamre differential in the suiTounding gas phase, but this will usually be less than the radiation loss, because of the low value of the heat transfer coefficient, / , of gases. The heat loss by this mechanism, Qc, can be calculated, approximately, by using tire Richardson-Coulson equation... [Pg.82]

In all of these systems, the rate of generation at the gas-solid interface is so rapid that only a small fraction is canied away from the particle surface by convective heat uansfer. The major source of heat loss from the particles is radiation loss to tire suiTounding atmosphere, and the loss per particle may be estimated using unity for both the view factor and the emissivity as an upper limit from tlris source. The practical observation is that the solids in all of these methods of roasting reach temperatures of about 1200-1800 K. [Pg.283]

Now, the heat conducted from the cell will be considered to be controlled by the radial conductivity of the total cell contents and not by the cell walls alone. Furthermore, the axial conductivity of the cell will be ignored as its contribution to heat loss will be several orders of magnitude less than that lost by radial convection. [Pg.223]

It is advantageous to use a low-retentivity carbon to enable the adsorbate to be stripped out easily. When empirical data are not available, the following heat requirements have to be taken into consideration (1) heat to the adsorbent and vessel, (2) heat of adsorption and specific heat of adsorbate leaving the adsorbent, (3) latent and specific heat of water vapor accompanying the adsorbate, (4) heat in condensed, indirect steam, (5) radiation and convection heat losses. [Pg.294]

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 =. ... [Pg.188]

Ar higher air speeds > h convective heat loss becomes greater than radiation and approaches Tj. For such conditions Eq. (5.20) is recommended... [Pg.189]

TABLE 10.7 Heat Loss Coefficients (h by Natural Convection ... [Pg.871]

Heat loss, dry The heat exchange that fakes place from the human body to the surroundings by convection, radiation, and conduction but not by evaporation. [Pg.1447]

Thermal discomfort Discomfort experienced due to excessive heat loss or gain from or to the human body due to radiation, convection, conduction, evaporation, or air movement. [Pg.1482]

To measure the efficiency of a whole window, special testing takes into account all heat transfer from conduction, convection, and radiation. Certain values are used to represent the thermal and solar efficiency of high-performance windows by measuring reduced thermal heat loss (measured by the U-... [Pg.1227]

Btu/(hr) (ft2)(°F/ft) i = inside wall pipe o = outside wall surface of pipe Heat loss from fluid inside pipe through exterior insulation to outside air. Combined convection and radiation ... [Pg.245]

Heat transfer from the surface of an insulated or uninsulated pipe in air involves convection and radiation. In still air more heat is lost by radiation than convection. The heat loss from an insulated or bare pipe is, in Btu/hr ... [Pg.246]

In calculating heat loss from surfaces freely exposed to air it is necessary to deal separately with both radiant and convective losses. [Pg.112]

It is not proposed to deal with forced convection here. Experimental work has yielded considerably differing results for ostensibly similar conditions. It is sufficient to note that forced convection affects small-bore pipes to a greater extent than large-bore and is dependent on temperature differences. While the heat loss from non-insulated surfaces may increase by a factor of up to 200-300 per cent, the increase in heat loss from the insulated surface would be considerably less (of the order of 10 per cent). [Pg.112]

As with all convective systems, warm air heating installations produce large temperature gradients in the spaces they serve. This results in the inefficient use of heat and high heat losses from roofs and upper wall areas. To improve the energy efficiency of warm air systems, pendant-type punkah fans or similar devices may be installed at roof level in the heated space. During the operational hours of the heating system, these fans work either continuously or under the control of a roof-level thermostat and return the stratified warm air down to occupied levels. [Pg.412]

A little of this is lost by radiation if the surrounding surfaces are cold and some as sensible heat, by convection from the skin. The remainder is taken up as latent heat of moisture from the respiratory tissues and perspiration from the skin (see Table 23.2). Radiant loss will be very small if the subject is clothed, and is ignored in this table. [Pg.234]

Convective heat loss will depend on the area of skin exposed, the air speed, and the temperature difference between the skin and the... [Pg.234]

Thus
forced convection currents to be absent, and the heat loss is probably higher than this value,... [Pg.557]

Calculate the total heat loss by radiation and convection from an unlagged horizontal steam pipe of 50 mm outside diameter at 415 K to air at 290 K. [Pg.844]

The heat loss through a firebrick furnace wall 0.2 in thick is to be reduced by addition of a layer of insulating brick to the outside. What is the thickness of insulating brick necessary to reduce the heat loss to 400 W/m2 The inside furnace wall temperature, is 1573 K. the ambient air adjacent to the furnace exterior is at 293 K and the natural convection heat transfer coefficient at the exterior surface is given by h S.OAT11 23 W/in2 K, where AT is the temperature difference between the surface and the ambient air,... [Pg.850]

The asbestos packing served two advantages first, it reduced heat losses and hence improved accuracy and second, it replaced the vapor gap between the liner and reactor wall. This minimized the convective heat transfer of the vapor, which is also difficult to calculate. [Pg.345]


See other pages where Heat loss convective is mentioned: [Pg.558]    [Pg.558]    [Pg.502]    [Pg.154]    [Pg.460]    [Pg.334]    [Pg.529]    [Pg.240]    [Pg.764]    [Pg.1171]    [Pg.408]    [Pg.82]    [Pg.218]    [Pg.357]    [Pg.374]    [Pg.374]    [Pg.871]    [Pg.1232]    [Pg.696]    [Pg.112]    [Pg.161]    [Pg.165]    [Pg.555]    [Pg.846]    [Pg.187]   
See also in sourсe #XX -- [ Pg.281 , Pg.282 , Pg.283 ]

See also in sourсe #XX -- [ Pg.281 , Pg.282 , Pg.283 ]




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