I would like advice on choosing the formula for calculating steam pressure drop.

Steam is a compressible fluid; its flow is characterized by pressure drops due to friction along the pipe, which reduces the gas density and increases the gas flow velocity. For the calculation of pressure drop in steam pipelines, it is recommended to refer to Specification HG/T 20570.7, Section 2 on the Calculation of Pipeline Pressure Drop, particularly the contents related to single-phase flow (compressible fluids).

This post was last edited and replied to by zpg on 2011-1-11 at 21:41. Reply 1#: The Babcock formula is used for calculating the resistance in steam pipelines; it is applicable to conditions where the pressure drop is greater than 40% of the inlet pressure (this condition is not suitable for isothermal or adiabatic flow models). This formula yields good results when the inlet pressure is ≤ 3450 kPa, but when the pipe diameter is ≤ 100 mm, the calculated values may be too high. This is stated in the standard HG20570.7-95. However, the Babcock method yields significant errors in practical use. Many years ago, I personally measured data from a long-distance superheated steam pipeline; the total length of this pipeline was approximately 4 km, and aside from a few U-shaped expansion bends, it was essentially straight. After technical upgrades to the equipment, the amount of steam that needed to be transported doubled, necessitating modifications to the existing pipeline. Before these modifications, the pipeline was tested for a few days to collect actual data. Three pressure and temperature measurement points were taken at the starting point, the ending point, and 800 meters from the starting point. By comparing these values with those generated by the pressure and temperature transmitters on the DCS system, it was found that the formula in question produced large errors. Later, the design team organized tests, and the conclusion was that this formula indeed had significant calculation errors; therefore, its use is not recommended in future engineering designs, though its calculated values can serve as a reference. The table below shows a comparison between the measured values and the calculated values. Due to the long length of the pipes, the steam temperature drops; upon verification, there is no condensation of the superheated steam, and the steam flow rate is accurate. Steam pipeline Φ325×8, insulation layer 100 mm; steam flow rate ~40 t/h. Pipeline length (m), starting gauge pressure P1 MPa, starting temperature °C, ending gauge pressure P2 MPa, ending temperature °C. Measured ΔP MPa, calculated ΔP (Babcock method) MPa, calculated ΔP (actual flow) MPa, calculated ΔP (isothermal flow) MPa: 800, 1.401, 238.51, 1.303, 2290.098, 0.062, 30.095, 50.104. For 4000 m, the values are: 1.392, 2400.851, 11910.541, 10.379, 0.547, 0.635. If no modifications are made to this pipeline, the steam pressure drops from 1.4 MPa to only 0.85 MPa at the end, so modifications are necessary. The calculation errors are shown in the table below: for pipe lengths of 800 m and 4000 m, the Babcock method yields errors of 36.4% and 29.9%, respectively; actual flow (using an adiabatic flow model with account taken of heat loss) results in errors of 2.6% and 1.1%, respectively; isothermal flow gives errors of 6.1% and 17.4%, respectively. The calculation for actual flow is based on the adiabatic model, with consideration given to the drop in steam temperature caused by heat loss through the insulation layer. Compared to the measured values, the Babcock method yields the highest error, exceeding 30%. As long as the pipe length is not too great and the temperature drop is not severe, isothermal flow is actually easier to calculate – the error for a 800 m pipe length is 6.1%, a value that is acceptable in engineering terms. However, the Babcock error is too large, so it is not recommended. . In fact, in recent years, thanks to the advancement of simulation software and computational tools, some of the traditional empirical formulas can now be used as little as possible or even not at all. Today, technicians in design firms carry laptops with them, making it much more convenient to perform such calculations than before. .

Well, yes, it’s best to have software; otherwise, it’s just experience.