Head coefficient

For adiabatic head, the head coefficient is defined as ia and Equation 2.70 is recalled. The geometric and the thermodynamic head relationships for a stage may be equated. 

Similarly, for polytropic head, the head coefficient is defined as Pp and Equation 2.73 is recalled, the geometric and thermodynamic head relationships, on a per-stage basis, may be equated as above. 

Step 4. Use the geometric form of Equation 5.12 to calculate a tip speed to produce the head per stage just calculated. Also, use the recommended head coefficient i =. 48 in the equation. 

Head coefficient, 156 Head equation, adiabatic, 3 t Head equation, poly tropic, I Head, centrifugal, 156 Head, reciprocating, 58 Heat run test (dry), 413 Helical compressor, 5, 7 adiabatic efficiency, Itil applicalion mnge, 7. ly asymmetric profile, 96 bearings, 116 capacity control, 95 casings, 114 circular profile, 95 cooling, I i 1 discharge temperature (dry), I 17... 

The pressure coefficient or head coefficient is dimensionless and is expressed ... 

F = pressure or head coefficient p. = pressure or head coefficient... 

Term (3) similarly can be shown to be gH/U and is usually known as a head coefficient (or specific energy coefficient)... 

Figure 7.25. Efficiency and head coefficient qad as functions of specific speeds and specific diameters of various kinds of impellers (Evans, 1979). Example An axial propeller has an efficiency of 70% at A, = 200 and Ds = 1.5 and 85% at Ns = 400 and Ds = 0.8. See Table 7.4 for definitions of qad, Ns, and Ds.

HgKo D ) is called the head coefficient, Ch, while QKcoD ) is called the jiow coefficient, Cq. Because no one pump was chosen in the derivation, the equation is general. For any number of pumps a, b, c,...,n and using Equations (4.28) and (4.29), the relationships next follow ... 

Raisin the flow coefficient Cq = Q/ a)D ) to the power i, the head coefficient Ch = gH/(a) D ) to the power and forming the ratio of the former to that of the latter, D will be eliminated. Calling this ratio as produces the expression... 

Dynamically similar pumps—Pumps with head coefficients that are eqnal. 

Specific speed—A ratio obtained by manipulating the ratio of the flow coefficient to the head coefficient of a pump. Values obtained are values applying at the best operating efficiency. 

Head coefficient Flow coefficient Power coefficient... 

Jacob, C.E. (1946). Slope-area measurements and the proper velocity-head coefficient. Water Resources Bulletin (Feb.lO) 34-46 (May 10) 124-125 (Aug.lO) 172-181. 

Two-phase friction loss in valves and fittings can be estimated using the no-slip velocity, v s, the single-phase head Coefficients. K, and the no-slip density ... 

Dimensionless parameters are also used to characterize compressor performance. The impeller work eoeffieient r is defined as the total enthalpy change across the impeller (per unit mass) divided by the tip speed squared. The polytropic efficiency tjp is defined as shown in Eq. (3) below. The polytropic head coefficient fx is calculated by multiplying the polytropic efficiency with the impeller work coefficient... 

Because it is difficult to measure slip, an experimental head coefficient is defined as ... 

Addle and Hehnly (1989) measured the head coefficient (as defined in the United States) and the efficiency of a number of slurry and dredge pumps. Their results are shown in Figures 8-13 and 8-14. They pointed out that the slurry and dredge pumps were on the average between 5% and 9% less efficient than their water counterparts. 

A slurry pump is to be designed for a head at best efficiency of 150 ft at a flow rate of 1200 gpm. Assuming a head coefficient of 0.5 (by U.S. definition), determine the diameter and the speed of rotation if the specific speed is 1100 (in U.S. units). 

FIGURE 8-13 Head coefficient versus specific speed from Addie and Helmly (1989) (reproduced by permission of Central Dredging Association, Delft, Netherlands). This plot is somewhat confusing as it uses the U.S. definition of the head coefficient (as per Equation 8-15) against the specific speed in SI units. The reader should multiply the head coefficient by a factor of 2 to use the SI definition of head coefficient as per Equation 8-14. 

Ujnip Rotational velocity of the impeller or expeller si Head coefficient to SI convention... 

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