# Process Variable Definitions :-

**What is ****Density** :-

Density is the mass per unit volume of any object. It is calculated by dividing the mass of an object by its volume. The volume of objects can be worked out by multiplying height by length by width.

The unit for density is kg/m^{3}. The density of water is approximately 1000 kg/m^{3} and the density of air is approximately 1.2 kg/m^{3}.

If solid objects are placed in water and they sink, they have a density greater than water (1000 kg/m^{3}).

**What is ****Viscosity :- **

The **viscosity** of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of “thickness”: for example, syrup has a higher viscosity than water.

Viscosity can be conceptualized as quantifying the internal frictional force that arises between adjacent layers of fluid that are in relative motion. For instance, when a fluid is forced through a tube, it flows more quickly near the tube’s axis than near its walls. In such a case, experiments show that some stress (such as a pressure difference between the two ends of the tube) is needed to sustain the flow through the tube. This is because a force is required to overcome the friction between the layers of the fluid which are in relative motion: the strength of this force is proportional to the viscosity.

**What is ****Temperature :- **

Temperature is an objective measurement of how hot or cold an object is. It can be measured with a thermometer or a calorimeter. It is a means of determining the internal energy contained within a given system.
When it is **54 degrees**outside,

**54 degrees**is an example of temperature. When your body is at

**98.6 degrees**, this is an example of a normal body temperature.

**What is ****Pressure :- **

Pressure is probably one of the most commonly measured variables in the power **plant**. It includes the measurement of **steam** pressure; feed water pressure, **condenser** pressure, lubricating oil pressure and many more. Pressure is actually the measurement of **force** acting on area of surface. We could represent this as

**What is Absolute pressure : **

Absolute pressure is a pressure that is relative to the zero pressure in the empty, air-free space of the universe. This reference pressure is the ideal or absolute vacuum.
**What is ****Gauge pressure:-**

The pressure of a system above the atmospheric pressure is called gauge pressure. Gauge pressure can calculated if the absolute and atmospheric **pressures**are known by using the

**Formula: Pgauge = Pabs – Patm**

**What is Steam :- **

Steam is a water in its gaseous state. It is invisible. It is a gas. It is formed by heating water under pressure.

**What is Vapour :**

Vapour is the product of evaporation. Evaporation is the process of change of liquid to gaseous phase not at saturated condition. During evaporation water at surface is converted into gaseous water molecules and diffuse into the air. This is the reason for humidity of air.

**What Is Specific Gravity?**

When we go out in the summer to enjoy the pools and the rivers, we always have to make sure that all of our equipment and safety measures are working and in place. When we go to the river and get on our boats, we make sure the boat has no leaks and we have our safety vests on. For young children who are still learning how to swim, we make sure they have their floaters on or we swim with them in a swim ring to make sure they do not sink. Why is it that boats and swim rings both float? There are many factors that determine if an object will sink or float in water, and one of these factors is what we call the specific gravity.
The **specific gravity**is the ratio between the density of an object, and a reference substance. The specific gravity can tell us, based on its value, if the object will sink or float in our reference substance. Usually our reference substance is

**water**which always has a density of 1 gram per milliliter or 1 gram per cubic centimeter.

**What is Density?**

So, what is density, anyway? An object’s **density**is a measure of how compact or heavy it is, in a given volume. We measure density in

**mass per unit volume**which is written using measures like grams per milliliter (g/mL), grams per cubic centimeter (g/cm^3), or kilograms per liter (kg/L). Here are two objects with different densities. On the left is an object highly packed with particles. That means it has a high density. On the right is an object with a low density. You can see that the particles are not packed tightly but that there are fewer particles occupying the same volume. To find the density of an object, we divide its mass by its volume. For example, take an object with a volume of four liters and a mass of one kilogram. We plug these numbers into the density formula and discover that its density is 0.25 kg/L.

**What is velocity:**

The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time. Velocity is equivalent to a specification of an object’s speed and direction of motion (e.g. 60 km/h to the north).
**What is Speed:**

The rate of change of position of an object in any direction. It is measured as the ratio of distance to the time in which the distance was covered. Speed is a scalar quantity as it has only direction and no magnitude.**What is Vapour pressure :**

Vapour pressure is a measure of the tendency of a material to change into the gaseous or vapour state, and it increases with temperature. The temperature at which the vapour pressure at the surface of a liquid becomes equal to the pressure exerted by the surroundings is called the boiling point of the liquid.

**What is pressure Drop :**

Process piping systems are subject to a phenomenon known as pressure drop. Simply put, *pressure drop is the difference in total pressure between two points in a fluid-carrying network.*When a liquid material enters one end of a piping system, and leaves the other, pressure drop, or pressure loss, will occur. Pressure drop in and of itself is not necessarily bad. Understanding how to calculate it in a specific pipeline allows engineers to properly design a system, and determine variables such as pipe diameter, pump specifications, and the types of valves to be used, among other things. However, there are also negative consequences associated with pressure drop if it is not well understood for a particular installation. These negatives, and the overall impact of pressure drop, are the focus of this article.

**What is Sound level** :

The logarithmic measurements of audible vibrations and may refer to: Sound exposure level, measure of the sound exposure of a sound relative to a reference value. Sound power level, measure of the rate at which sound energy is emitted, reflected, transmitted or received, per unit time.