How to calculate head?

There are many different formulas for calculating pump head, depending on the specific circumstances. Could you please specify the conditions? The basic principle is based on energy conservation: the pump head equals the sum of the potential energy, kinetic energy, pressure difference, and friction losses at both ends of the pump. For the general formula, refer to principles of chemical engineering; any version of such textbooks provides a detailed derivation for pump head.

It’s clearly explained in the principles of chemical engineering! Select the reference planes of the pump inlet and outlet vessels, apply Bernoulli’s equation, and calculate H. That is, the total of the increased static pressure energy, potential energy, kinetic energy, and the energy consumed to overcome frictional resistance during the fluid transport process.

Outlet pressure – inlet pressure + elevation + friction loss, that’s all

dP = rho x g x h; h = dP / (rho x g). dP represents the pressure at the pump outlet minus the pressure at the pump inlet (in Pa). h is the head (in m), g is 9.81, and rho is the density of the liquid (in kg/m3)

Head Head Head is the effective energy gained by a unit weight of liquid after passing through the pump. It is an important operational parameter of the pump, also known as head. It can be expressed as an increase in the pressure head, kinetic energy head, and potential energy head of the fluid, that is, H = (p2 – p1)/ρg + (c2 – c1)/2g + z2 – z1. Here, H represents the head, in meters ； 　　p1, p2 —— Pressure of the liquid at the pump inlet and outlet, Pa ； 　　c1, c2 —— flow velocity of the fluid at the inlet and outlet of the pump, m/s ； 　　z1, z2 —— inlet and outlet heights, m ； 　　ρ — liquid density, kg/m3 ； 　　g — gravitational acceleration, m/s2. 　　The head, flow rate, and power of a water pump are important parameters for evaluating its performance: 1. Flow rate: The flow rate of a water pump, also known as the water delivery volume, refers to the amount of water that the pump can transport in a unit of time. Denoted by Q, with units of m3/H or L/S. 　　2. Head: The head of a pump refers to the height to which the pump can lift water, usually denoted by H, with the unit being meters. The head of a centrifugal pump, measured with reference to the centerline of the impeller, consists of two parts. The vertical distance from the centerline of the water pump impeller to the water surface of the water source, that is, the height to which the water pump can draw water up, is called the suction lift, or simply the suction head ； The vertical height from the center line of the water pump impeller to the water surface of the outlet tank, that is, the height to which the water pump can lift water, is called the water lifting head, or simply the head. In other words, the pump head = suction head + discharge head. It should be noted that the head indicated on the nameplate refers to the head that the pump itself is capable of generating; it does not include the head loss caused by frictional resistance in the pipeline flow. This is something that cannot be ignored when selecting a water pump. Otherwise, water won’t be able to be pumped in. 　　3. Power: The amount of work done by a machine per unit of time is called power. It is usually denoted by the symbol N. Common units include: kilogram·meter/second, kilowatt, and horsepower. Typically, the power unit of motors is expressed in kilowatts ； The power unit of diesel or gasoline engines is expressed in horsepower. The power transmitted by the engine to the water pump shaft is called shaft power, which can be regarded as the input power of the water pump; generally, when referring to the power of a water pump, it is this shaft power that is meant. 　　Due to the frictional resistance of the bearings and fillers ； Friction between the impeller and water as it rotates ； Reasons such as swirls in the water flow inside the pump, backflow through gaps, inflow and outflow, and inlet shock. Some power is inevitably lost, so the water pump cannot convert all of the power supplied by the prime mover into useful power; there is always some power loss. In other words, the useful power of the water pump plus the power lost within the pump equals the shaft power of the pump. 　　4. For clean water pumps, the NPSH (M) parameter is extremely important, especially when used in suction-type water supply systems. For submersible pumps, the rated current parameter (A) is very important, especially when used in variable-frequency water supply systems.

Calculate using Bernoulli's equation

Learn the basics of chemical engineering; it’s clearly explained in \"Principles of Chemical Engineering.\" I hope this isn’t just a post made for the sake of posting :)

Any textbook on principles of chemical engineering provides detailed derivation processes. The people above also explained things very clearly. I’d like to add that the resistance loss includes the loss due to straight sections of pipe, as well as the loss caused by valves, elbows, etc. The resistance loss in straight sections can be calculated using Bernoulli’s equation, while the loss caused by valves and elbows can be calculated by converting them into equivalent straight sections or by using their K-values; these values are also easy to find.)

Many fellow travelers upstairs explained the energy requirement of the pipes for the pump. What the poster is asking about is the energy provided by the pump – the head. Head is the energy gained by a fluid as it passes through a pump. It is usually determined through experimental methods. There is specialized hydrodynamics research on this issue. It seems that there is no simple formula to calculate the head.

Simply put, the head of a pump is intended to compensate for factors such as the frictional losses in the pipes and the increase in the fluid’s potential energy. Based on the fluid flow rate that needs to be transmitted, one must find on the pump’s performance curve the head corresponding to that flow rate, to determine whether it is sufficient to overcome the frictional losses in the pipes and the increase in the fluid’s potential energy. :lol

\"Principles of Chemical Engineering\" is the best teacher

I’ve just started working in design; I understand the formulas, but when I encounter practical problems that I can’t solve on my own, I’m too embarrassed to ask my colleagues. Hehe, I assure you I’m not posting this just to post something...

Head – the increase in energy per unit mass of liquid as it is transported from the inlet to the outlet of the pump. Denoted by H. The units are: MPa, m. I. Cavitation in centrifugal pumps. Cavitation in centrifugal pumps occurs when the liquid being pumped vaporizes to some extent, as the saturated vapor pressure of that liquid at the pumping temperature is equal to or lower than the pressure at the pump inlet (actually at the inlet to the impellers). This leads to noise and vibration in the pump; in severe cases, it results in a significant decrease in the pump’s flow rate, head, and efficiency. Clearly, cavitation is not something that should occur during the normal operation of a centrifugal pump. The key to avoiding cavitation is to ensure the correct installation height of the pump, especially when transporting highly volatile liquids at high temperatures. II. The installation height Hg of the centrifugal pump: The allowable suction vacuum height Hs refers to the maximum degree of vacuum that can be achieved at the pump inlet pressure p1. The actual allowable suction vacuum height Hs is not calculated using a formula, but is determined through experiments by the pump manufacturer; this value is provided in the pump’s documentation for users’ reference. It should be noted that the Hs value given for the pump samples is based on clean water as the working medium, under operating conditions of 20°C and a pressure of 1.013×105 Pa; conversions are required when the operating conditions or the working medium differ. (1) For transporting clean water, but when the operating conditions differ from those in the experiment, the value of Hs1 can be calculated using the following formula: Hs1 = Hs + (Ha – 10.33) – (Hυ – 0.24). (2) When transporting other liquids, and when both the properties of the liquid being transported and the operating conditions differ from those in the experiment, two steps of calculation are required: in the first step, Hs1 is determined using the formula above based on values obtained from pump specifications ； In the second step, Hs1 is converted to H′s2 using the following formula. The net positive suction head Δh is used to calculate the installation height for oil pumps; that is, Δh is obtained from the specifications for the oil pump, and its value is also determined using clean water at 20°C. If other liquids are to be transported, calibration is also required; refer to relevant books for details. From a safety perspective, the actual installation height of the pump should be less than the calculated value. Furthermore, when the calculated Hg is negative, it indicates that the pump’s suction port should be located below the liquid level in the tank. Example 2-3: For a certain centrifugal pump, the allowable suction vacuum height Hs as determined from the specifications is 5.7 m. It is known that the total resistance of the suction pipeline is 1.5 mH2O, the local atmospheric pressure is 9.81×104 Pa, and the dynamic head of the liquid in the suction pipeline can be neglected. Try to calculate: (1) Pump installation for transporting water at 20°C ； (2) Changed to the pump installation height when conveying 80°C water. Solution: (1) Installation height of the pump when transporting water at 20°C. Given: Hs = 5.7 m, Hf0–1 = 1.5 m, and u12/2g ≈ 0. The local atmospheric pressure is 9.81×10^4 Pa, which is essentially consistent with the experimental conditions under which the pump was manufactured; therefore, the installation height of the pump is Hg = 5.7 – 0 – 1.5 = 4.2 m. (2) Installation height of the pump when transporting water at 80°C: When transporting water at 80°C, it is not possible to use the Hs value given in the pump specifications to calculate the installation height; instead, Hs must be adjusted using the following formula: Hs1 = Hs + (Ha – 10.33) – (Hυ – 0.24). Given that Ha = 9.81×10^4 Pa ≈ 10 mH2O, the saturated vapor pressure of water at 80°C is 47.4 kPa, as stated in the appendix. Hv=47.4×103 Pa＝4.83 mH2O. Hs1＝5.7+10－10.33－4.83+0.24=0.78 m. By substituting this value of Hs1 into the formula, the installation height is determined as Hg=Hs1－Hf0-1=0.78－1.5=－0.72 m. A negative value for Hg indicates that the pump should be installed below the water level of the tank, at least 0.72 m below it.

It’s very simple; to calculate it roughly, just find the pressure difference between the inlet and outlet, divide it by the fluid density, and then divide that result by g – and that gives you the head