Document n9wV09mNGYzz2eEGXy8mb9wJw

50 CHAPTER 3 1949 Guide -data in Table 1 at temperatures below about 150 F, the volume v of moist air per.pound of,dry.air at any degree of saturation p may be computed from the, simple relation, v = + pXu (4) To obtain comparable accuracy at temperatures above about 150 F it is necessary to add a correction term as follows, Ml - MA 1 + oTV.p (4a) where a denotes the ratio of the apparent'molecular weight of dry air (28.966) to the molecular weight of water (18.016), namely, 1.6078. In Table 4are given, for each of several higher temperatures, the correspond ing value of the coefficient A, the value of p at which the correction term attains its maximum value, and the maximum value of the correction term there attained. At temperatures below about 150 F the enthalpy h of moist air per pound of dry air at any degree of saturation p may be computed from the simple relation, h = A, + phu (5) ,Tq.obtain comparable accuracy at temperatures above about 150 F it is necessary to add a correction term S as follows, ^ m(1 -- MB 1 + aW.fi (5a) In Table 4 are, listed values of the coefficient B and maximum values of the correction term H, the latter occurring at the same values of p as dp those of the correction term V. Unfortunately, values of the entropy s of moist air per pound of dry air computed from the simple relation, s = i 41 ptn ! ' !' /; '(6) do not approximate the true values as closely as might be desired except at temperatures, considerably lower than 150 F- Only a relatively small portion of the error is, contributed by the correction term ,. ; . i. .n-' \ . MO -- e)C 1 + aW.ii (6a) Table 4 lists values of the coefficient C and maximum values of the cor rection terms s, the latter occurring at the-same values of p as do those of the correction terms ti and H. The larger portion of the error is contributed by the so-called mixing entropy. It can be expressed as an additional correction term s.as follows, . . /-.0.1579 1(1 + paWJ logu(l + paty,.-- poW. logit Qt) .' . - Ml + aW,)logio(l + alV.] (6b) i' Maximum values of 3 and the values of p at which they occur are given :.in Table 4. In Equation 6b logTM denotes logarithm to the base 10, "-