Pumps velocity head

Pumping, Velocity Head, and Power. Mechanical mixers can be compared with pumps (1) because they produce circulating capacity and velocity head H. The analogy between a pump and mixer can be appreciated by comparing a pumping loop with a mixing tank (Fig. 2). Power input P to a pump is represented by... 

The term pump head represents the net work performed on the liquid by the pump. It is eomposed of four parts. They are the statie head (Hs), or elevation the pre.ssure head (Hp) or the pre.ssures to be overcome the friction head (Hf) and velocity head (Hf), which are frictions and other resistances in the piping system. These heads are discussed in Chapter 8. The head formula is the following ... 

When vapor bubbles eollapse inside the pump the liquid strikes the metal parts at the speed of sound. This is the elicking and popping noise we hear from outside the pump when we say that eavitation sounds like pumping marbles and roeks. Sound travels at 4,800 ft per second in water. The velocity head formula gives a elose approximation of the energy contained in an imploding cavitation bubble. Remember that implosion is an explosion in the opposite direction. 

Howe er, most conventional pump impellers receive the fluid into the impeller eye, at the center or inside diameter of the impeller. There are single suction impellers, and dual or double suction impellers with two eyes, one on each side. Dual suction impellers are mostly specified for low NPSH applications because the eye area is doubled (it ean reeeive twice as much fluid at a lower velocity head). Dual suction impellers arc mostly found on split case pumps where the shaft passes completely through the impeller. But they can afso be found mounted onto the end of the shaft in some special pump designs. 

F = Factor for fractionation allowable velocity or packed column packing factor or pump developed head, ft. 

From Table 2-10, a 6-inch pipe has a velocity of 5.55 fps at 500 gpm and a head loss of 0.720 psi/100 ft. The 5-inch pipe has a velocity of 8.02 fps and might be considered however 5-inch pipe is not commonly stocked in many plants, and the velocity is above usual economical pumping velocities. Use the 6-inch pipe (rough estimate). 

The total head developed by a pump is composed of the difference between the static, pressure and velocity heads plus the friction entrance and exit head losses for... 

These are not velocity heads at pump connections, but are related to the piping connections. See earlier note in this regard. 

The total suction head. Figure 3-41, is the difference in elevation between the liquid on the pump suction side and the centerline of the pump (plus the velocity head). Note that the suction head is positive when above the... 

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)... 

Formation of vapor bubbles in rapidly flowing or turbulent water causing risk of pumping failure and erosion and/or corrosion. Due to an increase in velocity at the pump head resulting in a localized pressure reduction and the subsequent collapse of the vapor into voids or cavities. Where FW temperatures are high (over perhaps 195-205 °F) the pump velocity can reduce FW vapor pressure below that corresponding to the temperature of the liquid and cavitation can occur accompanied by some noise. Warning of severe pump cavitation is often indicated by a heavy noise. 

It is required to pump cooling water from a storage pond to a condenser in a process plant situated 10 m above the level of the pond. 200 m of 74.2 mm i.d. pipe is available and the pump has the characteristics given below. The head lost in the condenser is equivalent to 16 velocity heads based on the flow in the 74.2 mm pipe. 

If the maximum flow-rate required is 20,000 kg/h, calculate the pump motor rating (power) needed. Take the pump efficiency as 70 per cent and allow for a pressure drop of 0.5 bar across the control valve and a loss of 10 velocity heads across the orifice. 

Fanning friction factor, [—] acceleration due to gravity, [L/t2] energy dissipated per unit mass of fluid, [FL/M = L2/t2] force component in the x direction, [F = ML/t2] enthalpy per unit mass, [FL/M = L2/t2] friction loss head, [L] pressure head, [L] work (pump) head, [L] velocity head, [L] static head, [L]... 

The following equations relate velocity head, pumping rate, and power under turbulent-flow conditions ... 

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