Techshore Inspection Services-Kochi-official blog of Techshore Kerala: TECHSHORE INSPECTION SERVICES : Flow

Measurement of flow rate and quantity is the oldest of all measurement of process variable in the field of instrumentation. It is made for determining the proportions and quantity of materials flowing in and out of a process. These values are necessary for plant material balancing, quality control, operation of the process and for cost accounting. But flow is the most difficult parameter to measure. In process pressure level temperature are controlled by controlling the flow itself. Flow measurements are made for gases, liquids and solids.

Definition: the displacement of any volumetric quantity of fluids from higher potential to lower potential in a particular time period is called flow.

Units of flow: gallon/min, litre/hour, tons/hour, pound/minute, kg/sec, cubic foot/hour.

PHYSICAL PROPERTIES OF FLOWING FLUIDS.

DENSITY

All substances have density. Density is a measure of closeness to one another of the molecules that makeup the substance in the simplest terms. Density is defined as the mass/unit volume.

SPECIFIC GRAVITY

Another term commonly used to express density of fluid is specific gravity. Specific gravity of a liquid is equal to the density of the liquid / density of water at standard conditions.

VISCOSITY

Viscosity is the property that determines how freely fluid flows. Viscosity can be further defined as the property of the fluid that contributes to laminar or turbulent flow characteristics fluids have various degrees of viscosity such variations results from internal friction between particles of the substance .a substance with a higher viscosity has a high resistance to flow. Two substances with different viscosities are oil and water; water pours freely while oil pours more slowly. Laminar flow is highly affected by viscosity than turbulent flow. Viscosity is reducing with the increase in temperature.

PRESSURE

The flow of fluids which is caused by a force which shall be a change or difference in pressure. There are many types of pressure in flow we consider static pressure, dynamic pressure and differential pressure. Pressure is defined as the force acting per unit area.

Pressure = Force / Area.

VELOCITY

Velocity of a flowing fluid is the speed in the direction of flow.

Velocity = Displacement / Time ( m/s ).

REYNOLDS NUMBER

In flow metering the nature of flow can be determined by a number called Reynolds number. Reynolds number is a very important reference number in the accurate determination of flow. It is used to determine the point at which the flow goes from laminar to turbulent stage.

RD =pVD / n

Where, p = density of fluid.

V =velocity of the flowing fluid.

D = inner diameter of pipe line

n = viscosity of fluid.

LAMINAR FLOW

When the average velocity of the flowing fluid is slow the flow is said to be laminar. This means that the fluid flows in layers which the fastest moving layers towards the centre and slowest moving layers on the outer edges of stream. In laminar flow fluid particles moving along parallel paths. If a particular flow is having its Reynolds number value below 2000 it will be a laminar flow.

TURBULENT FLOW

As the velocity increases the flow becomes turbulent with the layers start disappearing and the velocity across the stream becomes more uniform. If a particular flow is having its Reynolds number greater than 4000 mean it will be called as turbulent flow.

TRANSITIONAL FLOW

It exhibits the characteristics of both laminar flow and turbulent patterns. In some cases transitional flow will oscillate between laminar and turbulent flow. If a particular flow is having its Reynolds number in between 2000 and 4000 means it will be called as transitional flow.

Wednesday, February 22, 2017

TECHSHORE INSPECTION SERVICES : Flow

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