Pipe length 100ft

• Fuel data: Natural gas, burned to heat the fluid in the pipe at $3/MCF. Efficiency of combustion is approximately 80%

STEP 1. Determine present heat loss. From Table 15.8 (4-in. pipe, temperature difference = ts - ta = 700 - 85 = 615°F), heat loss = 4,356 Btu/hr-lin.ft. Then, QTpres = (heat loss/lin.ft)(length)

STEP 2. Determine insulation thickness. In this example, the surface temperature has to be below 140°F, which is accomplished with an insulation thickness = tk = 3.5-in.

STEP 3. Determine heat losses with insulation. For this example, we need to calculate the heat losses for tk = 3.5-in following the procedure outlined in Section 15.4.5.

1) From the example in Section 15.4.3, ts = 140 °F, k = 0.49 and Rs = 0.85.

2) From Table 15.2, Eq tk for 3-1/2-in insulation n a 4-in. pipe = 5.396 in. Then,

3) Calculate heat loss QF:

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