Question

1. A ¾ inch (nominal), Schedule 40, mild steel pipe carries 40 psia steam through a room having an air temperature of 80°F. The pipe is covered with a 0.125 ft thick layer of fiberglass insulation having a thermal conductivity of 0.037 Btu/(h ft ‘F). The hi value on the steam side of the pipe is 1000 Btu/h ft2 °F. The ho value on the outside of the insulation is 2.0 Btu/(h ft2 ’F).

For the mild steel, k=26Btu/(ft H F)

Pipe dimensions =.133" thickness of metal ID= .824" OD=1.050" Steam temperature = 267 degrees F A. Calculate the thermal resistance (units of h °F/Btu) per foot of pipe length for each of the following layers: inner film on the steam side, the pipe wall, the insulation, and the outer film on the air side.

B. Calculate the area-normalized thermal resistance values in units of ft2 h °F/Btu for the same three layers.

C. Use your results from Part A to calculate the total resistance contributed by all the layers and the fraction of the total resistance due to each of the layers. Would you consider any of the resistances to be negligible? Justify your answer.

D. Calculate the overall heat transfer coefficient based on the inner surface area of the tube (Ui) and the corresponding inner surface area (Ai) in units of Btu/(h ft2 ‘F).

E. Calculate the total amount of energy lost to the air per day if the pipe were 10 ft long

Answer 1

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W W aTThi L Rs Rx3.Lu 1000 aTk ( L n(0.95 2*314 к26 Ln 2T k 0.VA x31y 0.03 - TTho Undewand th uon. 4 didn't reione? thormal Apua-nomalzed

R 5 0060 5.0060 C.0060 4.24 O S419 0060 0.0 006 nghet the amabve frectans Can We gtaam Alm anido h pipe offendy ta! ertoni by mild as wll

aLea innu wtoue Uo A T (T RgtRtRtRa Ui an ak TkL aTih 2TTYiL 2YLho 0.0686 (0900-S E 0.46328 L10 ft € E Total anount Ena lon (Q): uiAt T- Ta) 10 Q (0-.06e )x (2-x0) X 76-848 Btu 3.202 Btu. ft