Question

Air at 30 c dbt and 18.5 c wbt is passed through a cooling coil maintained at 4.5 c

Answer 1

Answer:

Pressure is the force exerted per unit area. It may be described as the measure of intensity of a force exerted on any given point on the contact surface. Whenever a force is evenly distributed over a given area the pressure at any point on the surface is the same. It can be calculated by dividing the total force exerted by the area (on which the force is exerted).

Atmospheric pressure

The Earth is surrounded by an envelope of air called the atmosphere, which extends upward from the surface of the earth. Air has mass and due to gravity exerts a force called weight. The force per unit area is called pressure. This pressure exerted on the Earth’s surface is known as atmospheric pressure.

Gauge pressure

Most pressure measuring instruments measure the difference between the pressure of a fluid and the atmospheric pressure. This is referred to as gauge pressure.

Absolute pressure

Absolute pressure is the sum of gauge pressure and atmospheric pressure.

Vacuum

If the pressure is lower than the atmospheric pressure, its gauge pressure is negative and the term vacuum is applied to the magnitude of the gauge pressure when the absolute pressure is zero (i.e. there is no air present whatsoever).

The relationships among absolute pressure, gauge pressure, atmospheric pressure and vacuum are shown graphically in the Figure 1.1.

Figure 1.1

Relationship between absolute, gauge and vacuum pressures

In the above figure

Pa is the atmospheric pressure

Pgauge is the gauge pressure

Pab is the absolute pressure

Pvacuum is the vacuum pressure

1.2.3 Density

It is defined as the mass of a substance divided by its volume or the mass per unit volume.

ρ = mass/volume

Specific Volume is defined as the reciprocal of density or volume per unit mass.

v = V/m

Specific Weight (Ws) is

Explanation: