Once the desired specific speed is known, basic dimensions of the unit's components can be easily calculated. It is this impeller's "shape" that predicts its flow and head characteristics so that the designer can then select a pump or turbine most appropriate for a particular application. it predicts the general shape of a pump's impeller. Specific speed is an index used to predict desired pump or turbine performance. The resulting figure would more descriptively be called the "ideal-reference-device-specific performance." This resulting unitless ratio may loosely be expressed as a "speed," only because the performance of the reference ideal pump is linearly dependent on its speed, so that the ratio of is also the increased speed at which the reference device would need to operate, in order to produce the performance, instead of its reference speed of "1 unit." Performance is defined as the ratio of the pump or turbine against a reference pump or turbine, which divides the actual performance figure to provide a unitless figure of merit. In metric units flow may be in l/s or m³/s and head in m, and care must be taken to state the units used. In Imperial units it is defined as the speed in revolutions per minute at which a geometrically similar impeller would operate if it were of such a size as to deliver one gallon per minute against one foot of hydraulic head. Specific speed is most commonly used in pump applications to define the suction specific speed -a quasi non-dimensional number that categorizes pump impellers as to their type and proportions. Common commercial and industrial practices use dimensioned versions which are of equal utility. Specific speed N s, is used to characterize turbomachinery speed.
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Please help improve this article by adding citations to reliable sources. When the most unfavorable loop is long, the K value is 0.2 to 0.3, and when the most unfavorable loop is short, the K value is 0.4 to 0.6.This article needs additional citations for verification. K is the sum of the local resistance equivalent length and the total length of the straight pipe in the most unfavorable loop. L is the length of the most unfavorable loop ΔP2 is the water pressure drop of each of the parallel connected air conditioners in the ring that has the largest water pressure loss. ΔP1 is the water pressure drop of the chiller evaporator. The flow rate of the water pump should be 1.1 to 1.2 times the rated flow rate of the chiller (1.1 for a single unit and 1.2 for two units in parallel).Īccording to the estimation, the loss along the pipe length per 100 meters can be roughly 5mH2O, and the pump head calculation formula (mH2O): Generally, a centrifugal clean water pump with a specific number of revolutions ns of 130 to 150 is used. The most commonly used pump head calculation formula is H = (p2-p1) / ρg + (c2-c1) / 2g + z2-z1.Īmong them, H - head, m p1, p2 - the pressure of the liquid at the inlet and outlet of the pump, Pa c1, c2 - the flow rate of the fluid at the inlet and outlet of the pump, m / s z1, z2 - the height of the inlet and outlet, m ρ - liquid density, kg / m3 g - gravity acceleration, m / s2. The head is usually the maximum height that the pump can lift, and is indicated by H. Below, the world factory pump valve network introduces the pump head calculation formula in detail. For the industry, the pump head calculation formula is a very common technical data. Pump head is an important working energy parameter of the pump. Generally speaking, hw occurs at the entrance, bend, valve, outlet, etc.
To check the relevant literature, v is the flow velocity in the tube. Hw=&*v^2/2g, & is called the local head loss coefficient. Hw is the head loss, including the Darcy formula or Xie Cai formula for calculating the head loss hf and the local head loss hw hf along the path. The pump head H=z+hw z is the height difference of the pumping height, that is, the water level from the inlet to the water surface at the exit. Other units: Pa (kPa), atm (1 engineering atmosphere) It is represented by the letter H and is usually expressed by the height m of the liquid column.
(1kg) The work done by the liquid, that is, the increase in energy of the unit weight of liquid after passing through the pump.
Specific speed ns calculator how to#
Pump head calculation formula, how to calculate pump head?
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