Heat transfer forced convective

The kind of convective heat transfer—forced convection or natural (at floor, wall, or ceiling)—must be considered and taken into account by selecting appropriate values for the convective heat transfer coefficient see Eq. (11.14)). Thus, the heat transfer coefficient implicitly assumes the flow situation at the surface. Normally, coefficients for convective heat transfer are considered as a preset constant parameter (the coefficient may be defined as variable, however, depending on other parameters). Therefore, the selection of appropriate values is crucial. Values for heat transfer coefficients can be found in several references a comprehensive summary is given in Daskalaki. ... 

Regulation of the aeration rate to fulfill the requirement for both oxygen mass transfer and heat transfer. Forced convection should be performed if necessary and... 

Ratio of the fluid stream thermal capacity to convective heat transfer Forced convection... 

Peclet number, Pe (heat transfer) LupCp Lu k a u liquid velocity Cp specific heat a thermal diffusivity heat transfer by bulk motion conductive heat transfer Forced convection... 

Convection. Heat transfer by convection arises from the mixing of elements of fluid. If this mixing occurs as a result of density differences as, for example, when a pool of liquid is heated from below, the process is known as natural convection. If the mixing results from eddy movement in the fluid, for example when a fluid flows through a pipe heated on the outside, it is called forced convection. It is important to note that convection requires mixing of fluid elements, and is not governed by temperature difference alone as is the case in conduction and radiation. 

HEAT TRANSFER BY CONVECTION 9.4.1. Natural and forced convection... 

Conductive and Convective Heat Transfer, Thermo Explosion by. There are three fundamental types of heat transfer conduction, convection radiation. All three types may occur at the same time, but it is advisable to consider the heat thransfer by each type in any particular case. Conduction is the transfer of heat from one part of a body to another part of the same body, or from one body to another in physical contact with it, without appreciable displacement of the particles of either body. Convection is the transfer of heat from one point to another within a fluid, gas or liquid, by the mixing of one portion of the fluid with another. In natural convection, the motion of the fluid is entirely the result of differences in density resulting from temp differences in forced convection, the motion is produced by mechanical means. Radiation is the transfer of heat from one body to another, not in contact with it, by means of wave motion thru space (Ref 5)... 

Transfer of heat by physical mixing of the hot and cold portions of a fluid is known as heat transfer by convection The mixing can occur as a result of density differences alone, as in natural convection, or as a result of mechanically induced agitation, as in forced convection. 

Convection is the transfer of energy by conduction and radiation in moving, fluid media. The motion of the fluid is an essential part of convective heat transfer. A key step in calculating the rate of heat transfer by convection is the calculation of the heat-transfer coefficient. This section focuses on the estimation of heat-transfer coefficients for natural and forced convection. The conservation equations for mass, momentum, and energy, as presented in Sec. 6, can be used to calculate the rate of convective heat transfer. Our approach in this section is to rely on correlations. 

P clet number Fe Re Fr = p CpVL k Dimensionless independent heat transfer parameter (ratio of heat transfer by convection to conduction) Forced convection... 

Dimensionless mass transfer coefficient Ratio of sensible heat absorbed by the liquid to the latent heat absorbed Forced convection (heat, mass, and momentum transfer analogy) Boiling... 

Continuous metal hand (heated by forced convection air, IR, direct steam or direct hot water) Heat transfer coefficient from impinging hot air. U = 0.06-0.09 kW/m K air velocity 15-25 m/s 5-50 kg water evaporated/m drying surface 1.5-2 kg steam/kg water evaporated power required is 20-30 kW with values relatively independent of the size. 

During the manufacture of many polymer-containing materials, and particularly solid state lithium ion battery separators and electrodes, it is desirable to include plasticizers so that the components will be rendered porous after the plasticizer was removed. Many porous membranes and other similar porous rrraterials are produced using this method. Plasticizer is continuously reused in such processes. Plasticizers are frequently removed by extraction with suitable solvents but they rrray evaporate under low heat and low pressure conditions as described in the preserrt inverrtioa Plasticizer is removed by conductive heat transfer, forced air convection, or radiative heating, all conpled with application of the vacuum. 

Heat transfer by convection occurs in liquids and gases where there is a velocity field caused by extorted fluid motion or by natural fluid motion caused by a difference in density. The former case involves forced convection, and the latter case free convection. Combined convection occurs when both forced and free convection are present. The convection coefficient of surface heat transfer, a, defining the heat exchange in the contact boundary layer between fluid and soUd, is determined. Coefficient or is often expressed by equations containing criteria numbers, such as those of Nusselt (Nu), Prandtl (Pr), Reynolds (Re) and Grashof(Gr) ... 

Q is the amount of heat in Joules that is transferred from surroundings into the system. Although the temperature difference is the driving force, the energy transfer is Q in Joules of energy. The heat transfer is transient in nature. The study of heat transfer is a separate subject in itself and is discussed in detail elsewhere [7] and in Chapter 11. The modes of heat transfer, conduction, convection, and radiation and of late microscale mechanisms such as wave heat conduction is discussed in Chapter 9. 

Heat conduction, convection, boiling heat transfer, radiation, transient heat transfer, forced flow in pipes and packed beds, mass transfer by diffusion, and diffusion in porous solids. 

Steady-state heat transfer Unsteady-state heat transfer Convective heat transfer (heat transfer coefficient) Convective heat transfer (heat transfer coefficient) Radiative heat transfer (not analogous with other transfer processes) Steady-state molecular diffusion Unsteady-state molecular diffusion Convective mass transfer (mass transfer coefficients) Equilibrium staged operations (convective mass transfer using departure from equilibrium as a driving force) Mechanical separations (not analogous with other transfer processes) ... 

Convective heat transfer is classified as forced convection and natural (or free) convection. The former results from the forced flow of fluid caused by an external means such as a pump, fan, blower, agitator, mixer, etc. In the natural convection, flow is caused by density difference resulting from a temperature gradient within the fluid. An example of the principle of natural convection is illustrated by a heated vertical plate in quiescent air. 

In the forced convection heat transfer, the heat-transfer coefficient, mainly depends on the fluid velocity because the contribution from natural convection is negligibly small. The dependence of the heat-transfer coefficient, on fluid velocity, which has been observed empirically (1—3), for laminar flow inside tubes, is h for turbulent flow inside tubes, h and for flow outside tubes, h. Flow may be classified as laminar or... 

DropletHea.tup, A relation for the time required for droplet heatup, T can be derived based on the assumption that forced convection is the primary heat-transfer mechanism, and that the Ran2-MarshaH equation for heat transfer to submerged spheres holds (34). The result is... 

The mathematical formulation of forced convection heat transfer from fuel rods is well described in the Hterature. Notable are the Dittus-Boelter correlation (26,31) for pressurized water reactors (PWRs) and gases, and the Jens-Lottes correlation (32) for boiling water reactors (BWRs) in nucleate boiling. 

Likewise, the microscopic heat-transfer term takes accepted empirical correlations for pure-component pool boiling and adds corrections for mass-transfer and convection effects on the driving forces present in pool boiling. In addition to dependence on the usual physical properties, the extent of superheat, the saturation pressure change related to the superheat, and a suppression factor relating mixture behavior to equivalent pure-component heat-transfer coefficients are correlating functions. 

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