Natural convection horizontal pipe

Estimate the heat transfer coefficient for natural convection from a horizontal pipe 0.15 m diameter, with a surface temperature of 400 K to air at 294 K... 

For natural convection from a horizontal pipe to air, the simplified form of equation 9.102 may be used ... 

SOLUTION A horizontal hot-water pipe passes through a large room. The rate of heat loss from the pipe by natural convection is to be determined. Assumptions 1 Steady operating conditions exist. 2 Air is an ideal gas. 3 The... 

A 10-m-long section of a 6-cm diameter horizontal hot-water pipe passes through a large room whose temperature is 2TC. If the temperature and the emissivity of Ihe outer surface of the pipe are 73°C and 0,8, respectively, determine the rale of heal loss from the pipe by (a) natural convection and (b) radiation. 

The natural convection currents surrounding a hot, horizontal pipe are more complicated than those adjacent to a vertical heated plate, but the mechanism of the process is similar. The layers of air immediately next to the bottom and sides of the pipe are heated and tend to rise. The rising layers of hot air, one on each side of the pipe, separate from the pipe at points short of the top center of the pipe and form two independent rising currents with a zone of relatively stagnant and unheated air between them. 

A large tank of water is heated by natural convection from submerged horizontal steam pipes. The pipes are 3-in Schedule 40 steel. When the steam pressure is atmospheric and the water temperature is 80°F, what is the rate of heat transfer to the water in Btu per hour per foot of pipe length ... 

What heat-transfer coefficient would be expected for natural convection to water at 212°F and 1 atm, outside a 1-in. horizontal pipe with a surface temperature of 213°F Compare with Fig. 13.5 and comment on the difference. 

K. C. Cheng, M. Takeuchi, and R. R. Gilpin, Transient Natural Convection in Horizontal Water Pipes With Maximum Density Effect and Supercooling, Num. Heat Transfer (1) 101-115,1978. 

Natural convection from horizontal cylinders. For a horizontal cylinder with an outside diameter of D m, Eq. (4.7-4) is used with the constants being given in Table 4.7-1. The diameter D is used for L in the equation. Simplified equations are given in Table 4.7-2. The usual case for pipes is for the Afcr Pr range 10 to 10 (Ml). 

Perry and Green (P3, p. 10-14) give a convenient table of natural convection plus radiation coefficients (h + h ) from single horizontal oxidized steel pipes as a function of the outside diameter and temperature difference. The coefficients for insulated pipes are about the same as those for a bare pipe (except that lower surface temperatures are involved for the insulated pipes), since the emissivity of cloth insulation wrapping is about that of oxidized steel, approximately 0.8. A more detailed discussion of radiation will be given in Section 4.11. 

Dry vault storage may also be used. The fuel elements are stacked horizontally or vertically in concrete pipes which allows cooling of the fuel elements by air convection (forced or natural). 

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