Question

3. CIN: A 50 m long section of a steam pipe at 15°C. The average temperature of the outer surface of combined heat transfer coefficient or the rate of heat loss from the steam plp generated in an natural gas furnance $0.52/therm (1 therm = 105, 0.035 W/mK) needed in order to say remain constant at 150°C. (10 marks) For a steam pipe whose outer diameter is 10 cm passes through an open space mperature of the outer surface of the pipe is measured to be 150°C. If the anster coefficient on the outer surface of the pipe is 20 W/mK, determine a) neat loss from the steam pipe: b) the annual cost of this energy lost If steam is an natural gas furnance that has an efficiency of 75% and the price of natural gas is mm (1 therm = 105.500 kl); and c) the thickness of fiberglass Insulation (k = I needed in order to save 90% of the heat lost. Assume the pipe temperature to 150°C Fiberglass insulation k = 0.035 W/mK To = 15°C h = 20 W/m2K

Answer 1

iven 3=20W/m2k ASETTDL < T7 (0-DI50)= 15708 m Sase- hoA -Tair)(20)(510150-15)-4241R W base 42412KN Sbase -42,4 u Rate o heat loss from pipes lost, is given by Anmal cost this erergy Q-At (42,412)(365)(24)9600) 8=1337x10lyr 81337x109 KJY¥ gas consumption at 757. ficienj gas= 337xXI09 0.15 Them i05,500 KJ KJ yr =16/897-3 therms/y

LAnmual cost l6s 1689T 3 therm cos2]therm) - 8186 6 819 0/yT To eave 90' heat loss and to Yeduce it to O.X42412-42412W The ic thickmess determined rom Bereulated ins ulation meeded TsTaix bnutl 2kL TSTair Ro t Rinsulation 424 150- 5 Lnlal003) Rnlo.035)(50) (20) IT Ut25o)) by tail ad CYor method Vt2-0.069m thickness o inscladion, tirsulation =0.069-8-05 t -0.019m |t =1-9cm