There is some uncertainty regarding the definition of pump head
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In the principles of chemical engineering, the pump head (also known as pressure head) represents the energy gained per unit weight (1 N) of liquid as it passes through the pump; its unit is J/N = m (where m refers to the height of a liquid column). For centrifugal pumps, the pump head, flow rate, and efficiency do not change with variations in density – they are determined by the pump’s inherent characteristics. If 1 kg of water exerts a force of 9.8 N, then 1000 g ÷ 9.8 = 102 g corresponds to a force of 1 N. The density of water is 1000 kg/m3, and its volume is 0.001 m3. 1 kg of oil exerts a force of 9.8 N; therefore, 1000 g ÷ 9.8 = 102 g corresponds to a force of 1 N. With a density of 800 kg/m3, the volume of this amount of oil is 0.00125 m3. The volumes of water and oil are clearly different. Then why is it said that density has no effect on the volumetric flow rate of a pump? Where am I going wrong in my thinking?
After extensive verification and testing, it was concluded that the hydraulic model dimensions of the centrifugal pump impeller are the main factors affecting the overall performance of the impeller. The larger the outer diameter of the impeller, the higher the head generated. The outlet width of the impeller is also an important factor affecting performance; an increase in width leads to an increase in the flow area, which results in improved performance in terms of flow rate. A larger wrap angle corresponds to a higher head, and a larger outlet angle also results in a higher head. The head generated by centrifugal force is not related to the density of the medium, but rather to its viscosity, that is, its centipoise value. This centipoise value is proportional to that of water. Viscosity does affect the head generated, but when the viscosity is less than 20 centipoise, it generally has little impact on the head ； For the same pump pumping different media, the theoretical head generated is the same; however, due to differences in the density of the media, the pressure produced by the pump and the shaft power required vary. The greater the density of the medium, the higher the shaft power needed to achieve the designed head. Pumps of the same model should be equipped with motors of different power ratings when used to transport media of different densities.
The head is proportional to the square of the impeller diameter. The head is also proportional to the square of the motor speed. In centrifugal pumps, the motor speed remains almost constant as long as it operates within its rated capacity； At this point, the linear velocity of the medium remains constant; the kinetic energy acquired by the medium is proportional to its specific gravity. Therefore,
Viscosity: The property of a liquid that results in internal friction between its molecules as it flows, is known as the viscosity of the liquid. The degree of viscosity is expressed in terms of viscosity values, and it serves as a factor indicating the resistance associated with the properties of the liquid. Viscosity is further divided into dynamic viscosity, kinematic viscosity, and conditional viscosity. Density: In physics, the mass of a substance per unit volume is called the density of that substance; it is an attribute inherent to the substance itself.
The viscosity of the medium has a significant impact on the pump. As viscosity increases, the head performance curve of the pump declines; both the head and flow rate at the optimal operating conditions decrease as viscosity rises, while power increases with rising viscosity, resulting in a decrease in efficiency.
The last edit to this post was made by 0432108985 on 2015-8-16 at 23:13. Regarding pumps only: I believe that it is theoretically true that \"the head, flow rate, and efficiency of a pump with a characteristic curve do not change with variations in density.\" This is determined by the inherent properties of the pump itself, and it represents one of its characteristics. Different densities result in different power requirements; the power consumed for transporting water or oil is not the same. @Vegetable tea eggs: Although it is said that the characteristic curve does not change with density, it certainly changes with \"viscosity\"! The concept of extreme magnification: water and asphalt. @zhangya*ong I think the conditions mentioned by LZ refer to performance under conditions of constant rotational speed and viscosity. -- These are purely personal opinions for reference only
OP, why did you set both water and oil at 1kg? The flow rate of a centrifugal pump isn’t a constant mass