ASTM D2890 Test Method for Calculation of Liquid Heat Capacity of Petroleum Distillate Fuels
6. Procedure
6.1 Calculate to the nearest 0.1 unit the slope of the Test Method D86 distillation curve, °F/volume %, as the difference between the 10 and 90 volume % distilled temperatures divided by 80.
6.2 Calculate to the nearest 1°F the volumetric average boiling point (VABP) as the sum of Test Method D86 10, 30, 50, 70, and 90 volume % distilled temperatures divided by 5.
6.3 Obtain a temperature correction to the nearest 1°F from Fig. 1, using the slope and VABP calculated in accordance with 6.1 and 6.2. Calculate the mean average boiling point (MeABP) as the VABP plus the correction.
6.4 Obtain to the nearest 0.1 unit the Watson characterization factor, K, from Fig. 2 using the determined API gravity and calculated MeABP.
6.5 Obtain the calculated heat capacity at each specified temperature, either graphically from Fig. 3 or by solving the following equation.
Cp = [0.6811 - 0.308 G + (0.000815 - 0.000306 G)T](0.055 K + 0.35)
where:
Cp = heat capacity, Btu/lb • °F,
G = specific gravity,
T = temperature, °F, and
K = Watson characterization factor
NOTE 2 - The broken lines in Fig. 3 illustrate the graphical procedure for the following example:
Calculate the heat capacity at atmospheric pressure and 190°F of a petroleum distillate fuel having an API gravity of 40 and Test Method D86 distillation temperatures of 239, 261, 288, 321, and 367 F at 10, 30, 50, 70, and 90 volume % distilled, respectively. The volumetric average boiling point (VABP) is 295°F, and the slope is 1.60. The temperature correction obtained from Fig. 1 is - 9°F, and the mean average boiling point is 286°F. The value of K obtained from Fig. 2 is 11.0. The heat capacity obtained as shown in Fig. 3 is 0.51 Btu/lb • °F.
