Cylinders natural convection

Agrees with cylinder and oblate spheroid results, 15%. Assumes molecular (iffusion and natural convection are negligible. 

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 ... 

A. Mohoric, J. Stepisnik 2000, (Effect of natural convection in a horizontally oriented cylinder on NMR imaging of the distribution of diffiisivity), Phys. Rev. E 62, 6628. 

Equations (10-65) and (10-66) give a good fit to data of Takao (Tl) for heat transfer from a brass sphere to air with = 0.8. Natural convection at low pressures has been studied for cylinders and spheres (D9, K12). 

R.J. Kee and A.A. McKillop. A Numerical Method for Predicting Natural Convection in Horizontal Cylinders with Asymmetric Boundary Conditions. Comput. Fluids, 5 1-14,1977. 

Coefficients of heat transfer by natural convection from bodies of various shapes, chiefly plates and cylinders, are correlated in terms of Grashof, Prandtl, and Nusselt numbers. Table 8.9 covers the... 

For this value of the Grashof number, standard correlation equations for natural convection from a horizontal cylinder indicate that for a Prandtl number of 0.7 ... 

Oosthuizen. PH. and Naylor. D.. Natural Convective Heat Transfer from a Cylinder in an Enclosure Partly Filled w ith a Porous Medium, Ini. J. Sumer. L riiods Heat and Fluid Flow. Vol. 6, No. 6. pp. 51-63. 1996. 

A horizontal cylinder having a diameter of 5 cm and an emissivity of 0.5 is placed in a large room, the walls of which are maintained at 35°C. The cylinder loses heat by natural convection with an h of 6.5 W/m2 °C. A sensitive thermocouple placed on the surface of the cylinder measures the temperature as 30°C. What is the temperature of the air in the room ... 

Al-Arabi, M., and Y. K. Salman Laminar Natural Convection Heat Transfer from an Inclined Cylinder, Int. J. Heat Mass Transfer, vol. 23, pp. 45-51, 1980. Holman, J. P. "Heat Transfer," 4th ed., McGraw-Hill Book Co., New York, 1976. 

M. Other objects, including prisms, cubes, hemispheres, spheres, and cylinders forced convection jD=omzN ,NMr = -M- Terms same as in 5-20-J. [E] Used with arithmetic concentration difference. Agrees with cylinder and oblate spheroid results, 15%. Assumes molecular diffusion and natural convection are negligible. 500 < Nfo p < 5000. Turbulent. [88] p. 115 [141] p. 285 [111][112]... 

The final result of identification allows the estimation of a = 9.7+0.88 w/(m2 deg) and 2 = 49.8+2.35 w/(m deg). Considering the value of 2, we can appreciate that the cylinder is certainly made of a type of steel, whereas the value of a shows that the occurring heat transfer is the natural convection between the cylinder and the adjacent air. This last observation is in good agreement with the descriptive model of the process given at the beginning of this section. 

Natural Convection over Surfaces 510 Vertical Plates (Fj = constant) 512 Verbeal Plates (4 = constant) 512 Vertical Cylinders 512 Inclined Plates 512 Horizontal Plates 513 Horizontal Cylinders and Spheres 513... 

Mass How Rate ttirougn ttie Space beLV, een Plates 519 9-5 Natural Convection Inside Enclosures 521 effective Thermal Conductivity 522 Horizontal Rectangular Enclosures 523 Inclined Rectangular Enclosures 523 Vertical Rectangular Enclosures 524 Concentric Cylinders 524 Concentric Spheres 525 Combined Natural Convection and Radiation 525... 

Natural convection flow over a horizontal hoi cylinder. 

TTie temperature of the aluminum lube is determined in a similar manner using the natural convection relations (or two horizontal concentric cylinders. The characteristic length in this case is the distance betvreen the two cylinders, which is... 

For coMcewrrfc horizontal cylinders, the rate of heat transfer through the annular space between the cylinders by natural convection per unit length is... 

C Under what conditions can the outer surface of a vertical cylinder be treated as a vertical plate in natural convection calculations ... 

Coefficients of heat transfer by natural convection from bodies of various shapes, chiefly plates and cylinders, are correlated in terms of Grashof, Prandtl, and Nusselt numbers. Table 8.9 covers the most usual situations, of which heat losses to ambient air are the most common process. Simplified equations are shown for air. Transfer of heat by radiation is appreciable even at modest temperatures such data are presented in combination with convective coefficients in item 16 of this table. 

Previously, Durst and Stephan Q) observed some enhancement in heat transfer coefficients in natural convection in mixtures of n-heptane -- methane as the two-phase region was entered. We reported heat transfer results earlier ( ) for free convection and cross flow about a heated horizontal cylinder in a supercritical n-decane--C02 mixture. These also showed enhancement in the two-phase region relative to single phase. At that time, analysis was hindered by the unavailability of estimates or measurements of some crucial mixture properties. Happily, this situation has been remedied somewhat and we can now draw some conclusions. 

For the heated vertical plate and horizontal cylinder, the flow results from natural convection. The stagnation configuration is a forced flow. In each case the flow is of the boimdai7 Kiyer type. Simple analytical solutions can be obtained when the thickness of the du.st-free space is much smaller than that of the boundary layer. In this case the gas velocity distribution can be approximated by the first term in an expansion in the distance norroal to the surface. Expressions for the thickness of the dust-free space for a heated vertical surface and a plane stagnation flow are derived below. 

Under conditions of laminar flow, the usual natural convection equations can be used. Reference (K2) gives a table of heat transfer equations for spheres and cylinders recommended for use when molecular conduction is a factor, and a second table applicable to natural convection under laminar flow conditions. 

Consider the natural convection from a horizontal cylinder rotating with an angular frequency to (Fig. 5P-9). The peripheral surface temperature of the cylinder is Tm and the ambient temperature is To,. The diameter of the cylinder is D. Assuming that the natural convection resulting from rotation and that from gravity can be superimposed, express the Nusselt number in terras of the appropriate dimensionless numbers. 

Heat transfer between single horizontal cylinders and fluids in natural convection. 

The first section presents some fundamental ideas that are frequently referred to in the remainder of the chapter. The next three sections deal with the major topics in natural convection. The first of these addresses problems of heat exchange between a body and an extensive quiescent ambient fluid, such as that depicted in Fig. 4.1a. Open cavity problems, such as natural convection in fin arrays or through cooling slots (Fig. 4.1fe), are considered next. The last major section deals with natural convection in enclosures, such as in the annulus between cylinders (Fig. 4.1c). The remaining sections present results for special topics including transient convection, natural convection with internal heat generation, mixed convection, and natural convection in porous media. 

FIGURE 4.2 Measurements and predictions for a circular cylinder (a). (6) shows isotherms for natural convection around a horizontal cylinder. (Courtesy of ERG Eckert.)... 

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