these are equations from section 3.11 (20) Consider the evacuated tube collector
ID: 1843623 • Letter: T
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these are equations from section 3.11
(20) Consider the evacuated tube collector that I passed around in class. It is an annular space with an inner diameter of 40 mm and an outer diameter of 47 mm (ignore the thickness of the glass). Assume that there is air in the space between the walls. The inner tube is 85 C and the outer tube wall is 25 C, and assume that they have an accommodation coefficient with air of 0.9. Plot the effective thermal conductivity keff vs. pressure in the annular region for 10-2 Pa < P < 105 Pa. Read Section 3.11, the part about heat transfer between concentric cylinders. Also plot the heat lost per unit meter vs. the pressure in this situation. How low a pressure is needed to effectively stop conduction heat loss? Please give the answer in Pa and mTorr, since mTorr is the commonly used unit on vacuum gauges.
The Nusselt, Rayleigh, and Prandtl numbers are given by HL gB' AT LL Ra Where h at transfer coefficient [W/m2 K] L plate spacing [ml k thermal conductivity [W/m K] g gravitational constant [m/s B' volumetric coefficient of expansion (for an ideal gas, B' 1/T) [1/K] AT temperature difference between plates [K] v kinematic viscosity [m2/sl a thermal diffusivity [m2/s]Explanation / Answer
The answer of the following question is as follows
48 Pa pressure is needed to effectively stop conduction heat loss.
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