Refrigeration Fundamentals Terms and Concepts PDF

Refrigeration Fundamentals Concepts and Terminology Learning Outcomes: Demonstrate knowledge of the fundamental concepts of refrigeration Demonstrate knowledge of the refrigeration cycle What is refrigeration? Refrigeration is the process of removing heat from a space/an or objects and...

Refrigeration Fundamentals Concepts and Terminology Learning Outcomes: Demonstrate knowledge of the fundamental concepts of refrigeration Demonstrate knowledge of the refrigeration cycle What is refrigeration? Refrigeration is the process of removing heat from a space/an or objects and rejecting it where it makes little or no difference. Used to preserve food and transport food products. Aid in the manufacturing of commercial products. Aid in medical research. The first closed vapor compression system was developed in 1834 by Jacob Perkins. Willis Carrier pioneered modern air conditioning in 1902. States of Matter Matter is anything that has mass and occupies space. It is the substance that makes up all physical objects in the universe. The four states of matter are solid, liquid, gas, and plasma. Two states of matter are present in a refrigeration cycle, liquid and gas. The heat content and pressure are what determine the state of matter in a substance. Volume Volume is the amount of space a substance occupies. Volume in relation to gas is important to understand because it relates to the pressure, temperature, and number of molecules. Volume is three dimensional, it is calculated using 3 measurements. Volume of a square, rectangle: V = L x W x H Volume of a cylinder: V x h Mass and Weight Mass is a measure of the amount of matter in an object or substance. Mass is also the property of matter that responds to gravity Weight is the force that matter (solid, liquid or gas) applies to a surface while it is at rest. Ex. The earth has a stronger gravitational force than the moon, therefore a brick would weigh more on earth than it would on the moon. Density Density is used to describe the mass to volume relationship between an object or substance. Mass contained in a particular volume is the density of that substance. Comparing an objects weight per unit is finding the lbs. per cubic ft or lbs./ft3. Water for example, has a density of 62.4 lbs./ft3. Ex. Wood floats on water because it weighs less per cubic ft. Iron sinks because it weighs more per cubic ft. Specific Volume Specific volume is the volume that each pound of a specific gas occupies. Specific volume is different from total volume as the units are lb/ft³, not ft³. The specific volume of air at standard atmospheric conditions is 13.33 lbs/ft³. Specific volume and density are inverses of one another, which means that specific volume = 1 / the density and density = 1 / specific volume. As the pressure of a gas increases, the specific volume decreases, and the density increases. Compress = lower volume = packing more molecules = increased density = increased pressure Specific Volume Ex. The specific volume of air is 13.33 lbs/ft³. Density = 1/13.33 lbs./ft³ = 0.075 lbs/ft³. CFM = cubic feet per minute, picture a 1 ft x 1 ft x 1 ft box of air. If a blower moves 400 CFM, how many lbs. of air are being moved in 1 hour? 400 CFM x 0.075 lbs./ft³ = 30 lbs./min x 60 = 1800 lbs./hr. What weighs more, dry air or humid air? Dry air. H2O molecules weigh less than Oxygen, nitrogen and other molecules that make up air. Specific Gravity Specific gravity is the density of a substance divided by the density of water. This makes the specific gravity of water, simply 1. The density of water is 62.4 lb./ft³. 62.4 lb/ft³ / 62.4 lb./ft³ = 1. If the specific gravity is greater than 1, it will sink in water. If the density of red brass is 548 lb./ft³, what is the specific gravity? 548 lb/ft³ / 62.4 lb./ft³ = 8.78. 1 Ton of Refrigeration 1 ton of refrigeration is equal to 12,000 btu/hr. A ton of refrigeration is the amount of heat in btu’s required to melt 1 ton of ice (2000 lbs.) @ 32 F in a 24 hour period. Latent heat of fusion of ice = 144 btu. per pound. 2000 lbs. x 144 btu = 288,000 Btu. 288,000 btu/ 24 hrs. = 12,000 btu./hr. Since we added a period of time, this creates a rate of heat transfer rather than just a quantity of heat. Pressure Pressure is the force exerted by a gas or liquid per unit area on the surface of a container, cylinder, tubing, or other surfaces. PSI = pounds per square inch. Ex. 3/8” tube @ 50 PSIG compared to a ¾ “ tube @ 50 PSIG. Pressure = force/area Ex. Snowshoes, picture the weight of a person walking in snow with normal boots on, compared to with snowshoes. The weight of the person is the exact same, the snowshoes spread the weight out over a larger area, lowering the pressure. Pressure Calculations 1 cubic ft of water weighs 62.4 lbs. 1 cubic ft of water exerts a downward pressure of 62.4 lbs on a 1ft²(12” x 12 “). How much pressure per square inch in a 12” x 12” container? 62.4 lbs/144 in² = 0.433 PSI. How much PSI if we change the base of the container to 24 x 24 and keep the same volume of water? 62.4 lbs/576 in ² = 0.108 PSI Understanding Water Pressure And P.S.I. - A Quick Tutorial Vacuum Vacuum is a condition that exists in a closed system. It is a comparison to atmospheric pressure. Atmospheric pressure is 29.92 in. of mercury (inHg) at sea level. Lowering the pressure below this creates a vacuum condition. The industry measures vacuum typically in microns. 1 inHg = 25,400 microns. Atmospheric pressure is 759,168 microns. Vacuum applied Micron reading below 500 indicates a dry system. The final reading is taking with the pump turned off and a 30-minute decay test. Typically, you need to have a low micron reading with the pump on to achieve this. Ex. 200 microns. A way to look at it is, the system needs to hold a micron reading below 500 for at least 30 minutes. Most manufacturers inform you of this on start up reports. Critical Point Critical point is the highest temperature a gas can be and still be condensable by pressure. A point of the pressure/enthalpy diagram where critical temperature and critical pressure exist. No liquid refrigerant can be produced above a refrigerants critical point. Trans-critical Point Trans-critical refers to a process that occurs above a refrigerant's critical temperature. The refrigerant does have a distinct liquid- gas phase transition. Ex. CO2 system operating above 88 F Triple Point When a refrigerant can exist in all three phases, vapor, liquid and solid at the same time while being equalized. Ex. CO2 has a triple point of -70 F, equal to a pressure of 75 PSIA. CO2 operating below its triple point typically will change directly from a solid to gas, this is called sublimation. Enthalpy Enthalpy is referred to as ‘total heat’ content in a fluid. Reference point for refrigerant enthalpy charts is – 40 F. Ex. – 40 F on the example chart = 0 btu/lb. Energy Conservation of energy law states that energy cannot be created or destroyed. Energy can be transferred or converted from one form to another. Energy is a fundamental force that drives all physical processes and allows for ‘work’ to happen. Types of Energy Kinetic – the energy an object has due to its motion. Ex. A moving car. Potential – the energy stored due to an object position. Ex. Stretched spring or a book sitting on a shelf. Thermal – the total energy of particles in a substance, which is related to its temperature. Ex. Boiling water in a kettle. Chemical – the energy stored in the bonds of atoms. Ex. When natural gas is burned. Work Work is equal to force x distance. Ex. How much work is being done if a 180 lb. person climbs a 10-story building? Work(lb.-ft) = 180 lb. x 100 ft = 18,000 ft-lb. How to Calculate Work Done | Physics | Work = Force x Distance Power The rate at which work is being done. Typically expressed in horsepower. History of HP – 1 horse can lift 33,000 lbs. 1 ft. in 1 minute.