Discharge Head, hd

The discharge head of a pump is the head measured at the discharge nozzle (gauge or absolute), and is composed of the same basic factors previously summarized 1. static head 2. friction losses through pipe, fittings, contractions, expansions, entrances and exits 3. terminal system pressure. 

Velocity head is the kinetic energy of a liquid as a result of its motion at some velocity, v. It is the equivalent head 

Note For a system evaluation, including suction and discharge, the units of P must be the some, either gage or absolute. expressed as feet of fluid. 

The friction losses from the pump to the vessel include any entrance or exit losses.Unless velocities are high,these losses are usually negligible. 

Applied Process Design for Chemical and Petrochemical Plants 

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The suction head hs decreases and the discharge head hd increases with increasing liquid flow rate because of the increasing value of the friction head loss terms hfs and hfd. Thus the total head Ah which the pump is required to impart to the flowing liquid increases with the liquid pumping rate. 

Hs0 = Head at no flow, or shutoff, ft I4ms = Head of viscous fluid, ft Hw = Water equivalent head, ft hd = Discharge head on a pump, ft of fluid hs = Suction head (or suction lift) on a pump, ft of fluid hSL, hDL = Friction losses in pipe and fittings , subscript SL for suction line and DL for discharge line, ft of fluid hv = Velocity head, ft of fluid L = S = Static head, suction side, ft (Figure 3-38)... 

Example 6.12 Flow Rate of LDPE in a CDP with Fixed Head Pressure Calculate the flow rate of a 2MI LDPE (m = 4.31 x 103 N s"/m2, n = 0.5) in a 7.5-in-diameter CDP, with a — 0.5 and wedged channel with Hd = 0.25 in, rotating at 75 rpm with a discharge pressure of 1200psi. Assume that entrance and exit parts occupy 90° of the circumference. 

This equation shows that for 5 percent maldistribution, the pressure drop across the holes should be about 10 times the pressure drop over the length of the pipe. For discharge manifolds with K = 0.5 in Eq. (6-147), and with 4fL/HD 1, the pressure drop across the holes should be 10 times the inlet velocity head, pYf 2 for 5 percent maldistribution. This leads to a simple design equation. 

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