Cylinder heat transfer

The drag coefficients for disks (flat side perpendicular to the direction of motion) and for cylinders (infinite length with axis perpendicular to the direclion of motion) are given in Fig. 6-57 as a Function of Reynolds number. The effect of length-to-diameter ratio for cylinders in the Newton s law region is reported by Knudsen and Katz Fluid Mechanics and Heat Transfer, McGraw-Hill, New York, 1958). 

Cylinder Heat-Transfer Units Sometimes called can dryers or drying rolls, these devices are differentiated from drum diyers in that they are used for solids in flexible continuous-sheet form, whereas drum dryers are used for liquid or paste forms. The construction of the individual cyhnders, or drums, is similar in most respec ts to that of drum diyers. Special designs are used to obtain uniform distribution of steam within large drums when uniform heating across the drum surface is critical. 

The heat-transfer performance capacity of cylinder diyers is not easy to estimate without a knowledge of the sheet tenmerature, which, in turn, is difficult to predict. According to published data, steam temperature is the largest single factor affecting capacity. Overall evaporation rates based on the total surface area of the diyers cover a range of 3.4 to 23 kg water/(h m ) [0.7 to 4.8 lb water/(h fF)]. 

Even the good heat transfer conditions turned out to be false, however, if the correlation derived for single cylinders by McAdams (1954) were extrapolated to Rep < 100. Nelson and Galloway (1975) pointed out that at low Reynolds numbers the real heat transfer coefficient could be four... 

Why use an adiabatic relationship with a compressor whose cylinder is almost always cooled An assumption made in Chapter 2 on adiabatic isentropic relationships was that heat transfer was zero. In practical applications, however, the cooling generally offsets the effect of efficiency. As a side note, cylinder cooling is as much cylinder stabilization for the various load points as it is heat removal. 

A widely used correlation for heat transfer from a cylinder in a perpendicular flow is ... 

The sum includes concentric cylinder layers, such as the layer between the outer and inner diameters of the pipe or a possible thermal insulation layer. For each layer the corresponding heat conductivity Aj is used. The outer heat transfer fac-ror is the sum of the proportions of convection and radiation. Note Very thin pipes or wires should not be insulated. Because the outer diameter of the insulation is smaller than A/a , the resistance is less than that without the insulation.)... 

In some cases, particularly for the radial flow of heat through a thick pipe wall or cylinder, the area for heat transfer is a function of position. Thus the area for transfer applicable to each of the three media could differ and may be A, A2 and A3. Equation 9.3 then becomes ... 

Analytical solutions of equation 9.44 in the form of infinite series are available for some simple regular shapes of particles, such as rectangular slabs, long cylinders and spheres, for conditions where there is heat transfer by conduction or convection to or from the surrounding fluid. These solutions tend to be quite complex, even for simple shapes. The heat transfer process may be characterised by the value of the Biot number Bi where ... 

Temperatures at off-centre locations within the solid body can then be obtained from a further series of charts given by Heisler (Figures 9.17-9.19) which link the desired temperature to the centre-temperature as a function of Biot number, with location within the particle as parameter (that is the distance x from the centre plane in the slab or radius in the cylinder or sphere). Additional charts are given by Heisler for the quantity of heat transferred from the particle in a given time in terms of the initial heat content of the particle. 

Figure 9.26. Distribution of the film heat transfer coefficient round a cylinder with flow normal to the axis for...

The differential equation describing the temperature distribution as a function of time and space is subject to several constraints that control the final temperature function. Heat loss from the exterior of the barrel was by natural convection, so a heat transfer coefficient correlation (2) was used for convection from horizontal cylinders. The ends of the cylinder were assumed to be insulated. The equations describing these conditions are ... 

Addoms, J. N., 1948, Heat Transfer at High Rates to Water Boiling Outside Cylinders, D.Sc. thesis, Massachusetts Institute of Technology, Cambridge, MA. (2)... 

Elkassabgi, Y., and J. H. Licnhard, 1988, The Peak Pool Boiling Heat Fluxes from Horizontal Cylinders in Subcooled Liquids, Trans. ASME, J. Heat Transfer /70 479—496. (2)... 

SK Friedlander. Mass and heat transfer to single spheres and cylinders at low Reynolds numbers. AIChE J 3 43-48, 1957. 

The lack of hydrodynamic definition was recognized by Eucken (E7), who considered convective diffusion transverse to a parallel flow, and obtained an expression analogous to the Leveque equation of heat transfer (L5b, B4c, p. 404). Experiments with Couette flow between a rotating inner cylinder and a stationary outer cylinder did not confirm his predictions (see also Section VI,D). At very low rotation rates laminar flow is stable, and does not contribute to the diffusion process since there is no velocity component in the radial direction. At higher rotation rates, secondary flow patterns form (Taylor vortices), and finally the flow becomes turbulent. Neither of the two flow regimes satisfies the conditions of the Leveque equation. 

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