The number of molecules in a flowing gas is measured by mass flow. Volumetric flow quantifies the amount of space occupied by such molecules. Because gases are compressible, changes in pressure or temperature can produce significant variations in volumetric flow rates. Mass flow rates are usually expressed in grams per second (g/s). Volumetric flows are usually given in liters per minute (l/min) or gallons per hour (gph). However, mass and volume measurements need to be considered together when calculating efficiency values for heat transfer devices operating with gases.
What is the distinction between mass and volumetric flow? Mass flow meters cannot be used to measure volumes of gases.
Mass flow meters count the number of molecules entering or leaving some known area. This may seem obvious, but there are several types of mass flow meters: magnetic, mechanical, thermal. Each type has its own special advantages and disadvantages. For example, thermal mass flow meters are very accurate but they need constant heating which makes them difficult to use in mobile applications.
The most common type of mass flow meter is the turbine meter. It works on the same principle as a windmill. When air flows across the blades of the turbine, it spins a rotor which is connected to an electrical generator. The faster the air flows, the more rapidly the rotor turns. Thus, the speed at which the rotor turns is directly proportional to the air flow rate.
Another common type of mass flow meter is the hot-wire anemometer. It consists of two wires attached to a resistive heater. One wire goes up into the flow stream while the other stays outside the flow path. The amount of heat lost by the heater depends on the resistance of the two wires.
The link between mass flow and nonstandard volumetric flow may be demonstrated using simple mathematics. The greater the distance between molecules, the less mass there is in a particular volume. If mass flow remains constant as temperature rises, volume flow rises in order to pass the same quantity of mass (molecules) over the sensor. Therefore, the linearity of the relationship between mass flow and volume flow holds for temperatures from -273 to +473 Celsius.
The movement of substances in bulk or in masses down a pressure gradient (in plants, a pressure gradient is visible owing to changes in solute concentration) or a temperature gradient is known as mass flow or bulk flow. For example, blood circulation and water transfer in vascular plants. The term "bulk" here means large quantities of material rather than the meaning of "general." That is, any small particle of matter can be considered part of a bulk flow system.
Bulk flows are often distinguished from fine flows, which are flows of very small particles. For example, dust flows in air and water flows around obstacles such as rocks. Bulk flows usually occur over distances larger than fine flows. For example, a river's bulk flow is that which carries sediment far away from its source area while a drop of water may travel only a few feet before falling out of suspension due to friction with the surrounding medium.
Bulk flows can be divided into two main types: gravitational and non-gravitational. Gravitational bulk flows include all forms of liquid flow, except capillary action. These include falls, rivulets, and streams. Non-gravitational bulk flows include waves, currents, jets, and explosions.
All forms of fluid flow involve bulk movements of some kind. However, not all bulk movements are fl ows.
What is flow? The movement of liquids and gases is generally referred to as "flow," a concept that describes how fluids behave and how they interact with their surrounding environment--for example, water moving through a channel or pipe, or over a surface. Flow can also be either laminar or turbulent. In engineering applications, we are often interested in the rate at which fluid flows. This is called its "flow rate." The word "flow" is used here to describe the movement of fluid within a vessel or conduit, regardless of the speed with which it moves.
The flow of liquid depends on the relative strength of the forces acting on it. These forces include gravity, which acts on all objects weighing more than 2.5 grams per cubic centimeter of liquid; the force of viscosity, which tends to keep particles of one type of liquid separated from those of another type (such as oil and water) unless there is some physical barrier between them; and the force of pressure, which pushes liquids forward. All other forces are weaker than these three.
If you release your grip on a glass of water, it will continue to flow until the forces acting on it are no longer greater than its weight. At this point, the water will stop flowing unless something else gives it new energy. For example, if you poured the water into a vacuum bottle and then released the cap, the water would now flow because the force of pressure is stronger than gravity.
Flow is a volume per unit time measurement of air production. Pressure is a unit of measurement for the amount of force delivered to a certain region. Pressure is commonly measured in pounds per square inch (PSI), Pascals (Newtons per square metre), and other units. Flow is usually measured in cubic feet or milliliters.
The term "pressure differential" is used to describe the difference in pressure between two points. The word "differential" here means "difference." Therefore, a pressure differential is the measure of the difference in pressure between two points.
Differential pressure is the pressure difference between two points. It is often represented by p1 - p2, where p1 and p2 are the pressures at those two points. If point 1 has a pressure of 10 inches of water and point 2 has a pressure of 5 inches of water, then the differential pressure is 5 - 10 = -5 inches of water.
Pressure can also be described as the force per unit area that is applied perpendicular to a surface. This means that pressure can be thought of as the product of force and area. For example, if there is a force of 100 newtons being applied over an area of 12 square meters, then the pressure is 100 newtons per square meter or 1000 Pa.
Pressure can also be described as the rate of push or pull on a surface.
When the line pressure is doubled, the volumetric flow rate is cut in half, and vice versa. However, the quantity of air molecules that flow per unit of time (mass flow rate) remains constant. In Motion: The Ideal Gas Law Volumetric flow rates vary with pressure, while mass flow rates do not.