1. Engineering
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  3. a section of underground cable shown on back side generates...

Question: a section of underground cable shown on back side generates...

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2. A section of underground cable (shown on back side) generates 1200 W/m at peak load. In order to prevent the cable from melting, this heat is removed by pumping light oil in a concentric annulus around the cable. The oil temperature must not exceed 90°C, so there is a cooling station every 1500 m which cools the oil back to 20°C. The outer surface of the annulus can be considered adiabatic (a) Determine the minimum mass flow rate of oil required to satisfy the given conditions. (b) Given the minimum flow rate, determine the surface temperature of the cable just before the cooling station. HINT: You will need to calculate the heat transfer coefficient for the flowing oil. (c) Determine the pumping power at the minimum flow rate. v 2.3 x 10-5 m2/s at 20°C, v 1.18 x 10-6 m2/s at 90°C Pr 3292.5 at 20°C, Pr 15.5 at 90°C, p 860 kg/mt cp 2090 J/kg. K, k 0.14 W/m K, adiabatic Oil out Oil in: 90°C Electrical Cable T- 20°C L-1500m Answers 12.3 kg/s 1. a) m b) T 90.93 OC c) W F5.31 kW

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