Pumps throughputs

Equation (2.6) shows that the cooling power decreases exponentially when temperature decreases, because pvap and the pump throughput vanish. 

The concept of pump throughput is of major significance in practice and should not be confused with the pumping speed The pump throughput is the quantity of gas moved by the pump over a unit of time, expressed in mbar /s the pumping speed is the transportation capacity which the pump makes available within a specific unit of time, measured in m /h or l/s. 

Figure 9.2. Line diagram showing variables for the production of fat spreads TP Pump throughput...

Gas flow can be measured in standard cubic centimeters per minute (seem) or standard cubic centimeters per second (sees), where the standard cubic centimeter of gas is the gas at standard atmospheric pressure and 0°C. The flow can also be measured in Torr-liters/sec. For a standard atmosphere (760Torr, 0°C), there are 2.69 X 10 molecules per cubic centimeter and a Torr-liter/sec of flow is equivalent to 3.5 X 10 molecules per sec. In vacuum pumping, the gas flow through the pump is called the pump throughput (Torr-l/s, ft (STP)/h, cm (STP)/s). 

Pump throughput (vacuum technology) The mass of gas (or number of molecules of gas) that pass through a pump per unit time (Torr-Uters/sec). Also called Mass throughput. 

Pumping speed The volume flow rate through a vacuum pump in liters per second. Also called pump speed. See also Mass throughput Pump throughput. 

Vacuum flow is usually described with flow variables different from those used for normal pressures, which often leads to confusion. Pumping speed S is the actual volumetric flow rate of gas through a flow cross section. Throughput Q is the product of pumping speed and absolute pressure. In the SI system, Q has units of Pa m vs. 

The large variety of displacement-type flmd-transport devices makes it difficult to list characteristics common to each. However, for most types it is correct to state that (1) they are adaptable to high-pressure operation, (2) the flow rate through the pump is variable (auxiliary damping systems may be employed to reduce the magnitude of pressure pulsation and flow variation), (3) mechanical considerations limit maximum throughputs, and (4) the devices are capable of efficient performance at extremely low-volume throughput rates. 

The nature of the liquid to be pumped. For a given throughput, the viscosity largely determines the friction losses and hence the power required. The corrosive nature will determine the material of construction both for the pump and the packing. With suspensions, the clearances in the pump must be large compared with the size of the particles. 

The size of the suction and deli very valves is determined by the throughput of the pump. Where the rate of flow is high, two or more valves may be used in parallel. 

It is apparent, therefore, that the required vane angle in the diffuser is dependent on the throughput, the speed of rotation, and the angle of the impeller blades. The pump will therefore operate at maximum efficiency only over a narrow range of conditions,... 

For a given speed of rotation, there is a linear relation between the head developed and the rate of flow. If the tips of the blades of the impeller are inclined backwards. ft is less than tt/2, tan ft is positive, and therefore the head decreases as the throughput increases. If ft is greater than jt/2 (i.e. the tips of the blades are inclined forwards), the head increases as the delivery increases. The angle of the blade tips therefore profoundly affects the performance and characteristics of the pump. For radial blades the head should be independent of the throughput. 

In laminar flow, the pressure drop is constant when scaleup is carried out by geometric similarity. In turbulent flow, it increases as the square root of throughput. There is extra pumping energy per unit volume of throughput, which gives... 

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