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Pumps and Fans

2 tools in the Fluids and Heat Transfer area.

Pump and Fan Performance

Operating point and scaling of a centrifugal pump or fan. A pasted performance curve (flow, head or total pressure, optional efficiency and power at a reference speed and impeller diameter) is fitted by least squares (quadratic or cubic, printed with its coefficients and residuals) and crossed with the system curve H = H_st + K Q² (static head plus a loss term from a design point or an entered coefficient) for the operating point, its efficiency, fluid power and shaft power; the best-efficiency point, shut-off head, specific speed in the Hydraulic Institute US and metric forms and the dimensionless type number (ANSI/HI 14.1-14.2) follow. The affinity laws (Q ∝ N D³, H ∝ N² D², P ∝ N³ D⁵) give the curve and the new operating point after a speed or diameter change and the speed that puts the curve through the design point; two identical machines can be combined in parallel or series. For a pump the NPSH available, (p_s − p_v)/(ρ g) + z_s − h_fs, is compared with the NPSH required as a plain margin; for a fan the curve is corrected to the actual air density. The default is an illustrative textbook-style pump (0 to 1,500 gpm, head 150 to 90 ft, efficiency peaking at 80 % at 1,000 gpm, 1,750 rpm) against a system with 40 ft of static head and 100 ft at 1,000 gpm; its numbers are checked against numpy least squares and the published affinity-law and specific-speed values.

1 worked example reproduced, listed on the tool page.

Compressed Air System Sizing

Sizes an industrial compressed air system from a list of tools and processes: the average, peak and connected demand with the duty cycles and the units running at the peak, the leak allowance as an entered share of the supply or from a load / unload or pressure-decay test (the DOE / Compressed Air Challenge Sourcebook methods), the compressor capacity at the site altitude, temperature and humidity (the standard-to-actual flow conversion of UFC 3-420-02 Appendix A), the base-load / trim split of the compressors listed with a straight-line part-load power model for the control type, the receiver volume for a demand event (V = T C p_a / (p_1 − p_2)) with the pump-up time by the ideal-gas mass balance and the gallons-per-cfm rule, the header and branch pressure drops by the isothermal Darcy–Weisbach solution with the Colebrook friction factor beside Harris's 1917 formula and Fritzsche's, the line velocities against entered limits, the condensate at the aftercooler and the dryer with the pressure dew point by the psychrometric relations, and the energy and cost for the year with the leak cost and the saving of a pressure reduction. The default is an illustrative 100 hp two-compressor shop at 100 psig with about 400 scfm of average demand.

1 worked example reproduced, listed on the tool page.

Other Fluids and Heat Transfer sections

Pipe Flow · Compressible Flow · Conduction · Convection · Radiation · Heat Exchangers · Thermodynamic Cycles · Fluid Properties