The mass of a liquid substance passing per unit time is termed the mass flow rate. The mass of any object can be determined by its volume, density, and area it occupies. Hence, the mass is neither created nor destroyed, but it can modify from one form to another. According to physics the mass of the substance should always remain constant. The gases exit the nozzle, which has an area of 1.2 ft 2, into the atmosphere, which has a density of 0.763 lbm/ft 3.The conservation of mass is a part of thermodynamics and it is a fundamental concept of physics. At the nozzle entrance, the exhaust gases are flowing at a volumetric flow rate of 125 ft 3/s at a density of 20 lbm/ft 3. Example CalculationĪn example of applying the conservation of mass to the mass flow rate involves the flow of exhaust gases from a rocket engine. Another example is the flow of gases through a rocket nozzle, which is then used in the calculation of the rocket’s thrust. When calculating the mass flow rate at a specific point in a fluid flow, the fact that the mass in the system will not change can be used for further calculations, such as in the Bernoulli equation to calculate the lift on an aircraft wing. When evaluating the mass flow rate, this fundamental property of physics plays an important role. That is, the mass exiting a system will be equal to the mass entering the system.

In most practical engineering applications, mass will be conserved. The mass flow rate of a fluid with density 800 kg/m 3 through a pipe with an inlet area of 2 m 2, an outlet area of 1 m 2, an inlet pressure of 40 Pa, and an outlet pressure of 25 Pa can be calculated as follows: Mass Flow Rate And Conservation Of Mass P 2 is the outlet pressure, with units of lbf/ft 2.P 1 is the inlet pressure, with units of lbf/ft 2.A 2 is the outlet cross-sectional area, with units of ft 2.A 1 is the inlet cross-sectional area, with units of ft 2.To calculate the mass flow rate in a pipe with a changing cross-section using the pressure difference, the following equation is used: In such a scenario, Bernouli’s equation can be used to determine the flow rate from the pressure difference. Such a scenario is shown in the following figure: In some engineering scenarios where there is a pressure difference, such as flow through a pipe with a varying cross-sectional area, the mass flow rate can be calculated using that difference. This can be useful when applying the conservation of mass to a fluid flow calculation. It should be noted that the volumetric flow rate is equal to the area times the velocity. To calculate the mass flow rate using the area and velocity, assume a scenario where a fluid of density 62.71 lbm/ft 3 flows through a pipe with an area of 0.05 ft 2 at a velocity of 21 ft/s. The mass flow rate can also be calculated using the area through which the fluid flows and the velocity at which it flows, as follows: In this example, the mass flow rate is: Using The Area And Velocity To demonstrate calculating the mass flow rate using the volumetric flow rate, assume a scenario where a fluid of density 0.035 lbm/ft3 flows through a pipe with a volumetric flow rate of 50 ft3/s. V̇ is the volumetric flow rate, with units of ft 3/s.ρ is the density of the fluid, with units of lbm/ft 3.ṁ is the mass flow rate, with units of lbm/s.Using the volumetric flow rate, the mass flow rate can be calculated as follows: The volumetric flow rate is a measure of the volume of fluid passing a given point. In certain applications, pressure differences can be used in evaluating the mass flow rate.

Typically, the mass flow rate is calculated as a function of the volumetric flow rate or a function of the system area and fluid velocity. There are different ways to calculate the mass flow rate, depending on the overall situation and what information is known.

In fluid mechanics, the mass flow rate is the amount of mass that passes a given point in a given amount of time.

Mass Flow Rate And Conservation Of Mass.

Volume flow rate to mass flow rate