density pi. to a solar collector is essentially the same as the density out from a collector, can be taken outside the summation sign in (A-6) and assigned the appropriate value. If a chemical reaction occurs in the collector, then both and p. may differ in the entrance and exit lines. The pipe lengths must be predetermined for the considered system. A criterion is needed to select the pipe I.D. distribution. Dp and is now developed. The cost of pipe material may be small compared to installation costs, and so the total installed pipe cost is of interest. Let Bn _• (D.) be the cost of installed pipe as a function of diameter only, neglecting variations in costs due to pipe thicknesses. Thus, Bp = [$/ft]. Then This is not a restrictive assumption since any real Bp versus D curve can be represented by a series of straight line segments. Thus, for a cost curve
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