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hw8 - (D(3 ME 114 Homework Set 8 Fall 2008 Consider a 25-mm...

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Unformatted text preview: (D (3 ME 114 Homework Set 8 Fall 2008 Consider a 25-mm diameter circular tube duough which liquid mercury, water, or engine oil at 27‘?C .. may flow at a rate of 0.03 kgls. Determine the ve- locity. the hydrodynamic entry length. and the thermal entry length for each of the fluids. Engine oil flows through a 25-min diameter. 10-min; long tube at a rate of. 0.5 kgls. The oil enters th tube at 25"C, while the tube surface is maintaine at?100°C. (a) Determine the total heat transfer to the oil an the oil outlet temperature. ' Cb) Repeat part (a). subject to the assumption 95:4 fully developed conditions throughout the tuber-3gj Due October 30 _ An electrical power transformer of diameter 300 mm and height 500 mm dissipates 1000 W. It is desired to maintain its surface temperature at 47°C 1 by supplying glycerin at 24°C through thin-walled tubing of 20-mm diameter welded to the lateral surface of the transformer. All the heat dissipated by the transformer is assumed to be transferred to the‘ glycerin. 10mg: a) ”T; $30.4”C @ :§\QO W (amswws mag Wag 6t bf“?— wt‘l’k Fmeéffies) (a) Assuming the maximum allowable temperature rise of the coolant to be 6°C and fully devel- oped flow throughout the tube, determine the required coolant flow rate, the total length of tubing, and the lateral spacing S between turns of the tubing. .For a prescribed tube length of 15 m and a maximum allowable transformer surface tem- perati'ire of 47°C. compute and plot the maxi- mum allowable transformer power and the out— let temperature of the glycerin as a function of flow rate for 0.05 s n'i S 0.25 kgls. Account for the fact that the flow is not fully developed. lib/a1 a) L-‘IS‘J :th 14:) :(a.€i?fmhz{c§[5 (Z? [/flms‘. Water flowing at 2 lrg/s through a 40-mm diameter tube is to be heated from 25 to 75°C by maintain- Jng the tube surface temperature at 100°C. What is the required tube length for these con- dittons? L— : )0-(91’1'7 ...
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