2

where the first term is the centrifugal effect of essentially solid body rotation of the fluid confined within the impeller; and the second term is the pitot effect of the recirculating fluid from the impeller that impinges against the volute or diffuser throats which in turn are connected through stagnant fluid to the exit port of the pump. While the factors kimp and kex associated with these effects vary with the hydraulic configuration, the values involved can be estimated as follows: kimp « 1, as the radial equation of motion3 would indicate for fluid rotating at Q,r everywhere within the blades, i.e., for rh1 < r < rt,2 (Fig. 8). Thus, as indicated by Eqs. 65 and 66, increasing the minimum radius of the blades at inlet rh1 tends to reduce the shut-off head. However, the presence or absence of fluid swirl in the region upstream of the impeller blades at shut-off has been found experimentally to affect the value of kimp in surprising ways—sometimes increasing it above unity in such a way as to minimize the effect on shut-off head of any non-zero value of rh1. The value of kex depends on (r3 — r2)/r2, or "Gap B" and other features of the impeller exit and collector geometry. It is usually in the range 0.2 ± 0.1, any change in the geometry that increases the shut-off power coefficient (see below) raising kex by driving more recirculating flow from the impeller against the volute or diffuser throats. Thus the shut-off head coefficient Cs/o (Eq. 66) for typical radial-flow pumps generally exceeds 2, the value of 0.585 being advanced by Stepanoff4. Estimates for Cs/o are also indicated in Fig. 22b.

Shut-off power consumption P^ includes disk, bearing, and seal drag power PD and that which drives the recirculation Precirc. The latter is generally dominant by far. From similarity arguments (Eq. 33), the shut-off power coefficient

Survival Treasure

Survival Treasure

This is a collection of 3 guides all about survival. Within this collection you find the following titles: Outdoor Survival Skills, Survival Basics and The Wilderness Survival Guide.

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