Question

Heat transfer. I just need the right choice

Qu Choose the correct answer was The handle of a saucepan, 30 (6 cm long and 2 cm in diameter is partially immersed in boling water at 100°C. The average unit conductance over the handle surface is 735 Wim2K in the kitchen air at 24C. The cook is likely to grasp the last 10 cm of the handle and hence, the temperature of this portion should not exceed 32C. What should be the material conductivity of handle? The handle may be treated as a fin of insulated tip 5 A hollow sphere of inside radius (5 30 mm and outside radius 50 mm is electrically heated at its inner surface at a constant rate of 10 KWm2. The outer surface is exposed to a fluid at 30°C, with heat transfer coefficient of 170 Wilm2K. The thermal conductivity of the materialis 20 Wim.K. Calculate inner and outer surface temperatures 57.14°C Not all the above 301.5°C 30.19°C 60.14°C O The handle of a saucepan, 30 (6 cm long and 2 cm in diameter is partially immersed in boiling water at 100°C. The average unit conductance over the handle surface is 735 Wim2K in the Kitchen air 24.The cook is likely to grasp the last 10 cm of the handle and hence, the temperature of this portion should not exceed 37°C. What should be the material conductivity of handle? The handle may be treated as a fin of insulated tip 10.4 W/mK 10.0 W/mK. 10.5 W/mK 10.72 WMKO Not the above

Answer 1

Quassi- Griven, L=30 cm = 0.3m D = 2 cm = 0.02m To = 100°c h = 7.35 W/m2K "To=24°c Tatxo 2m = 32° c

rolun For insulated tip Cosh m (2-x) The Top To-Top IT ဆီ 0. Cosh mL 32-24 cash in (0.3-0.2) coshm (0.3) P100-24 0.105- Cosh (alm) Cosh (0.3m) Cosh (0.3m) x 0.105= cosh (0.1m) ott from het & trial method we get m= 11.71 hp KA 11.71 7.35XFXD K & A 2² = 11.71 7.35 x 4 KX 0.02 11.71 ving 80 K= 10.72 W/mk

(Arka, n,) + tom Take Ti-To # q. Ai = > 10 x 0.011309 - T-30 0.053054 0.18724 so T, = 301.7°C Take - 201T-T2) 2 q.A;= ข้ารา, 47KO, D2 S 301.7 _T2 10 x8.01130g = 0.05305 => T2 = 241.7°C