In determining the heat transfer characteristics of a heat exchanger, it is important to have a clear picture of the physical exchanger prior to calculations. For example, in a pipe heat exchanger, it is common to determine the UA for a unit length of pipe. An exchanger can then be sized to meet the heat transfer requirements. Consider a heat exchanger of stainless steel tubes with the cross section shown in Figure 4. Each tube is 1-in. OD with the following dimensions:

D1 = inside diameter = 0.782 in. (0.0199 m) D0 = outside diameter = 1.000 in. (0.0254 m) xw = wall thickness = 0.109 in. (0.00277)

The heat transfer coefficients are inside: h{ = 120 Btu/(h)(ft2)(°F) or 681 W/m2 • K inside fouling: = 660 Btu/(h)(ft2)(°F) or 3748 W/m2 • K outside fouling: h„s = 1000 Btu/(h)(ft2)(°F) or 5678 W/m2 • K outside: h0 = 1500 Btu/(h)(ft2)(°F) or 8517 W/m2 • K

and the conductivity of the stainless steel tube is k = 9.4 (Btu)(ft)/(h)(ft2)(°F) or 16.3 W-m/m2-K

Determine UA for the tubes in this heat exchanger. Basis:

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