Losses by Natural Convection from a Cylinder. A vertical cylinder 76.2 mm in diameter and 121.9 mm high is maintained at 397.1 K at its surface. It loses heat by natural convection to air at 294.3 K. Heat is lost from the cylindrical side and the flat circular end at the top. Calculate the heat loss neglecting radiation losses. Use the simplified equations of Table 4.7-2 and those equations for the lowest range of NG, NP.. The equivalent L to use for the top flat surface is 0.9 times the diameter. Gr Ans. 9 = 26.0 W

Transport Phenomena Question

A metallic sphere of radius R is heated in an oven to a temperature of 600 ° F throughout, and then removed from the oven and allowed to cool in ambient air to T∞ = 75 ° F, by convection and radiation (see attached figure). The thermal conductivity of the ball material is known to vary linearly with temperature. Assuming that the ball is uniformly cooled starting from the entire outer surface, obtain the differential equation that describes the change in temperature in the sphere during cooling. Note: In the image, the translation would be: metallic sphere

Solution the question in 15 mint

5

A fused-quartz sphere has a thermal diffusivity of 9.5×10−7 m2/s, a diameter of2.5 cm, and a thermal conductivity of 1.52 W/m· ◦C. The sphere is initially at auniform temperature of 25◦C and is suddenly subjected to a convection environmentat 200◦C. The convection heat-transfer coefficient is 110 W/m2 · ◦C. Calculate thetemperatures at the center and at a radius of 6.4 mm after a time of 3 min.

Estimate the natural convection heat transfer coefficient of the horizontal pipe. The temperature of the outer surface of the pipe is 120 ° C. The ambient air temperature is 25 ° C. The outer diameter of the pipe is 10 cm. Convection coefficient = Answer W / m² ° C.

Two identical 7.5-cm cubes of copper at 425 and 90°C are brought into contact. Assuming that the blocks exchange heat only with each other and that there is no resistance to heat flow as a result of the contact of the blocks, plot the temperature of each block as a function of time, using the lumped-capacity method of analysis. That is, assume the resistance to heat transfer is the conduction resistance of the two blocks. Assume that all surfaces are insulated except those in contact.

You can in handwritten also. A circular (annular) fin of radius r2 is attached to a pipe of radius r1. The fin is exposed to an ambient fluid at temperature T∞ having heat transfer coefficient h and the fin base is maintained at temperature Tb. The fin thickness (t) is small compared to the fin length and the heat loss from the fin tip can be considered negligible compared with that from the top and bottom surfaces of the fin. Derive the differential equation and the boundary conditions for this fin by writing an energy balance around a differential volume element. Write your assumptions in detail. Do not solve the differential equation.

The exposed surface (x = 0) of a planar wall of thermal conductivity k is subject to microwave radiation that causes the volumetric heating to vary as: q ̇ (x) = q ̇o (1-x / L) Where qo (W / m ^ 3) is a constant. The boundary of x = L is well insulated, while the exposed surface is kept at a constant temperature T0. Determine the temperature distribution T (x) in terms of x, L, k, q ̇o, and T0.     in the attached image it is in Spanish