The SI unit of force in Newton (N), which is actually [kg * m/S2]. A man wearing skis can stand in deep snow without sinking deeply, but if it comes from his skis feet, probably sink deep into the snow. In the first case, a person's weight is distributed over a large surface (skis). In the second case, the same weight is distributed on the area of his Shoe soles - that a much smaller area than the area of the skis. The difference between these two cases is the pressure that man is having on the surface of the snow.
Pressure is defined as the force acting on the region divided by the size of the field. In the example skier force (gravity) is the same in both cases, but between different areas. In the first case the area is large and so the pressure becomes low. In the second case the area is small and so the pressure is high. In refrigeration pressure is mostly associated with liquids used as refrigerants. When a substance in a liquid or vapour form is stored in a closed container the pair will exert power on the inside walls of the container.
Steam power on the inner surface divided by its area is called the absolute pressure.
For practical reasons, the value of pressure sometimes as stated pressure above atmospheric pressure is atmospheric pressure (101.325 kPa = 1.013 bar)is deducted from the absolute pressure. Pressure above atmospheric pressure also often referred to as the (gauge pressure).
Units should reflect the choices absolute pressure or gauge pressure. The absolute pressure is displayed on the use of lowercase "a" and a gauge pressure denoted by a lower case letter "g". Example:
Absolute pressure : 10 bar(a), which is converted excessive pressure becomes (10 - 1.013 bar(g) to 9 bar(g). The combination of the international system of units (SI pressure [PA] and the term of the pressure sensor is not recommended. Other units, pressure that is still used today are mm Hg [century], and water-meter counter [mwg]. The latter is often used in connection with pumps to specify the height of the water column that the pump is capable of generating.
The vacuum is defined as the absolute pressure 0 Pa - but because it is almost impossible to get the term "vacuum" is usually used to describe the pressure is considerably lower than atmospheric pressure. Example: absolute pressure 0.1 bar (), which is converted excessive pressure becomes (0.1 - 1.013 bar(g) -0.9 bar(g). Vacuum also often described in Torr (1 Torr equal to 10 PA) and millibar (one thousandth of a bar)...
Chillers