Head ratio, pump

Similitude for centrifugal devices volumetric flowrate ratios = (diameter of impeller ratio) times (impeller rpm ratio) head ratios = (diameter ratio) times (the impeller rpm ratio) power ratio = (diameter ratio) times (impeller speed ratio). Positive displacement reciprocating pumps head"-capacity curve is almost vertical flowrate decreases only slightly with higher discharge pressure. Although we usually consider head for centrifugal pumps, pressure is more appropriate for positive displacement. Suction velocity < 1 m/s. 

Concepts of Head Ratio and Efficiency Ratio When Pumping Solids... 

Heavy metal oxide slurry is to be pumped at a volumeUic concentration of 18%. The specific gravity of the solids is 5.0 and the rfso is 400 pim. The calculated head on slurry is 35 m. Determine the head ratio and the equivalent water head on the pump performance curve. 

To determine the effect of particle size on the pump performance perlite-A, perlite-B and perlite-C samples were chosen. To analyse the pump performance test results, the relative reduction in head developed and the efficiency of the pump for different concentrations of three perlites were computed in terms of the head ratio (Hr) and the efficiency ratio (r r) at various flow rates respectively. These ratios have been defined as follows ... 

To study the effect of particle size on pump performance, the average value of Hr and Tjr at any given concentration were calculated from the head ratio-flow rate and the efficiency ratio-flow rate characteristic curves. It has been observed that r r is almost equivalent to the corresponding Hr for a given operating condition of the pump. The variation of the average value of Hr with various concentrations of perlite-A, perlite-B and perlite-C slurries has been compared in Fig. 3. It is seen that, both Hr and Tjr decrease linearly with the increase in the concentration of the solids. For any concentration of the solids, both Hr and r r decrease with the increase in particle size of the perlite. This could be attributed to the reason that the energy required to maintain the solid in suspension and motion increases with the increase in the particle size. 

In order to investigate tip clearance effects on the pump performance, the values of Hr and r r at any given concentration were obtained from the head ratio-flow rate and the efficiency ratio-flow rate characteristic curves plotted for various tip clearances (x=1.25 mm, x=5.5 mm and x=8 mm) taking the best efficiency point as basis, [4]. The variation of the value of Hr and Pr with various relative tip clearances for two concentrations of perlite-A slurry is illustrated in Fig. 5. The value of Hr and r r for a=0 % was obtained from the closed impeller tests. In Fig. 5, the results show that, at first Hr and pr increase up to 5 % relative tip clearance, after that, tend to decrease until 22 % is reached... 

This correlation has been examined for a wide range of S (1.48-6.238), d, (0.105-26.7 mm) and up to 62.75 percent Cw, and gives sufficiently accurate predictions for slurries of all materials tested and those available in the literature. Since a wide range of test conditions considered in derivation of the correlation, such a comparison may be more favourable than the correction methods presented by some investigators and pump vendors. In Fig. 6, an error analysis for head ratio was conducted for the test results presented here, which shows... 

Figure 6. Efficiency ratio vs jet pump flow ratio for small values of jet pump head ratio...

Air from a cylinder at pressures up to about 10 bar (150 psi) is applied to a gas piston that has a relatively large surface area. The gas piston is attached to a hydraulic piston that has a smaller surface area. The pressure applied to the liquid = gas pressure x area of gas piston/area of hydraulic piston. With 10 bar inlet pressure and a 50 1 area ratio, the hydraulic pressure obtained is 500 bar (7500 psi). On the drive stroke, the outlet valve on the pump head is open to the column and the inlet valve closed to the mobile phase reservoir. At the end of the drive stroke, the air in the chamber is vented and air enters on the other side of the gas piston to start the return stroke. On the return stroke the outlet valve closes, the inlet valve opens and the pump head refills with mobile phase. The pump can be started and stopped by operation of a valve fitted between the cylinder regulator and the pump. 

That is, the net energy or work put into the fluid by the pump goes to increasing the fluid pressure or the equivalent pump head, Hp. However, because pumps are not 100% efficient, some of the energy delivered front the motor to the pump is dissipated or lost due to friction. It is very difficult to separately characterize this friction loss, so it is accounted for by the pump efficiency, rje, which is the ratio of the useful work (or hydraulic work) done by the pump on the fluid (—w) to the work put into the pump by the motor (—wm) ... 

The need for an air sampling pump can be eliminated by use of a diffusion tube having a set length to diameter (L/d) ratio in its geometry for introduction of a gas sample. Proper selection of the geometry and L/d ratio of the diffusion tube results in an electrochemical cell with a response which is independent of external gas flow rate. A schematic of a solid polymer electrolyte diffusion head sensor cell is shown in Figure 13. 

The basic requirement for a SFE pump is the ability to deliver constant flow (at least 2 mL/min) in the pressure range 3500 to 1000 psi. Reciprocating and syringe pumps are most common. To maintain C02 in a liquid state, the pump head is cooled by using a recirculating bath. There are several ways to add a modifier to the C02. One is to add it directly to the extraction cell, but the modifier is exhausted with the flow of extraction fluid. Another approach is to add the modifier to the C02 tank (i.e., it is premixed with C02). However, it has been reported that the ratio of modifier to C02 in the mixture changes with time [24], Moreover, the modifier may contaminate... 

The shape of the system curve determines the saving potentials of using variable-speed pumps. All system head curves are parabolas, but they differ in steepness and in the ratio of their static head to friction drop. The value of variable-speed pumping increases as the system head curve becomes steeper. Therefore, in mostly friction systems, the savings will be greater. 

Another so-called efficiency, known as hydraulic efficiency, is sometimes given for reciprocating pumps. This efficiency indicates losses due to velocity changes in the inlet and outlet of the pump, friction, and valves. It is defined as the ratio of the actual head across the pump to the sum of the actual head pumped and the losses in the suction and discharge lines. 

During the testing, the power to the motor or prime mover driving the pump is recorded. Multiplying this input power by the prime mover efficiency produces the brake or shaft power. In the figure, the powers are measured in terms of kilowatts (or kW). Call the head corresponding to the brake power as The brake efficiency of a pump is defined as the ratio of TDH to the brake input power to the pump. Therefore, brake efficiency q is... 

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. 

---