H Q2Pd PsQxPi Ps hN

These two other definitions assume that the primary/power stream pressure falls to Ps, not Pd, as shown in Figure 2. Efficiency conversions are possible only if all three pressures and two flow rates involved are given. Comparisons of efficiencies reported in the literature should be made with caution.

Combining Eqs. 1, 11—14, the theoretical pressure characteristic N for the LJL pump is a ^b(1 + Ken)

1 + Kn - 2b - —SmT + b2( 1 + K,d + a2)(1 + M)( 1 + SM) + (1 - j)(SM-J(1 + KJ

1 + Kn - 2b - —SmT + b2( 1 + K,d + a2)(1 + M)( 1 + SM) + (1 - j)(SM-J(1 + KJ

FIGURE 2 LJL jet pump and installation

where Ktd = Kth + K^. The term j = 0 for the normal (jet loss) case, and J = 1 for no jet loss. Jet pumps normally are designed with a finite nozzle-throat spacing, typically sp/flth = 1; jet loss is experienced, and thus j = 0 for this (usual) case. Eq. (15) becomes

2b + - b2( 1 + Kd + a2)(1 + M)(1 + SM) — (SM2)(1 + Ken)

In terms of pressure,

Two simplifications of Eq. (16) are often appropriate: 1) The area ratio term a2 = 0 for the usual 5°-8° included-angle diffuser (a = At/Ad is small). 2) The density ratio S = 1 for similar primary and secondary liquids, for example, a water primary jet pumping water as the secondary fluid. With these simplifications, Eq. (16) for the normal (jet loss) case becomes

And pump efficiency is

For the LJL jet pump, note also that

Computer Programs for LJL Models It is convenient to use Eqs. (17) and (18) in spreadsheet form to generate tables of "N(b, M, Kn, Ktd, Ken);" that is, the LJL jet pump pressure characteristic N as a function of the bracketed variables. Typically the Ks and the area ratio b are held constant and a table is generated using step increases in M to show resultant N values. Table 1 shows N(M) for b = .25; and Kn = .05, Ktd = .2, and Ken = 0. The performance of this pump is shown in Figure 3 as N(M) and h(M).

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