As a conclusion, the Recirculating Air conditioning unit may used to demonstrate and evaluate most of the processes found in practical air conditioning plant, such as heating, cooling, humidification, dehumidification air stream. Sometime two or more of these process are needed to bring air to adesired temperature and humidity level. Various air conditioning processes in psychrometric chart. Notice that simple heating and cooling processes appear as horizontal line on this chart since moisture content of the air remains constant (ω = constant) during this processes. Air is commonly heated and humidified in winter and cooled and dehumidified in summer. Notice how these processes appear on the psychrometric.
Saturday, January 10, 2009
Friday, January 9, 2009
DiSCUSSION 4
ORIFICE TUBE
The orifice tube, probably the most commonly used, can be found in most GM and Ford models. It is located in the inlet tube of the evaporator, or in the liquid line, somewhere between the outlet of the condenser and the inlet of the evaporator. This point can be found in a properly functioning system by locating the area between the outlet of the condenser and the inlet of the evaporator that suddenly makes the change from hot to cold. You should then see small dimples placed in the line that keep the orifice tube from moving. Most of the orifice tubes in use today measure approximately three inches in length and consist of a small brass tube, surrounded by plastic, and covered with a filter screen at each end. It is not uncommon for these tubes to become clogged with small debris. While inexpensive, usually between three to five dollars, the labor to replace one involves recovering the refrigerant, opening the system up, replacing the orifice tube, evacuating and then recharging. With this in mind, it might make sense to install a larger pre filter in front of the orifice tube to minimize the risk of of this problem reoccurring. Some Ford models have a permanently affixed orifice tube in the liquid line. These can be cut out and replaced with a combination filter/orifice assembly.
THERMAL EXPANSION VALVE
Another common refrigerant regulator is the thermal expansion valve, or TXV. Commonly used on import and aftermarket systems. This type of valve can sense both temperature and pressure, and is very efficient at regulating refrigerant flow to the evaporator. Several variations of this valve are commonly found. Another example of a thermal expansion valve is Chrysler's "H block" type. This type of valve is usually located at the firewall, between the evaporator inlet and outlet tubes and the liquid and suction lines. These types of valves, although efficient, have some disadvantages over orifice tube systems. Like orifice tubes these valves can become clogged with debris, but also have small moving parts that may stick and malfunction due to corrosion.
RECEIVER-DRIER
The receiver-drier is used on the high side of systems that use a thermal expansion valve. This type of metering valve requires liquid refrigerant. To ensure that the valve gets liquid refrigerant, a receiver is used. The primary function of the receiver-drier is to separate gas and liquid. The secondary purpose is to remove moisture and filter out dirt. The receiver-drier usually has a sight glass in the top. This sight glass is often used to charge the system. Under normal operating conditions, vapor bubbles should not be visible in the sight glass. The use of the sight glass to charge the system is not recommended in R-134a systems as cloudiness and oil that has separated from the refrigerant can be mistaken for bubbles. This type of mistake can lead to a dangerous overcharged condition. There are variations of receiver-driers and several different desiccant materials are in use. Some of the moisture removing desiccants found within are not compatible with R-134a. The desiccant type is usually identified on a sticker that is affixed to the receiver-drier. Newer receiver-driers use desiccant type XH-7 and are compatible with both R-12 and R-134a refrigerants.
ACCUMULATOR
Accumulators are used on systems that accommodate an orifice tube to meter refrigerants into the evaporator. It is connected directly to the evaporator outlet and stores excess liquid refrigerant. Introduction of liquid refrigerant into a compressor can do serious damage. Compressors are designed to compress gas not liquid. The chief role of the accumulator is to isolate the compressor from any damaging liquid refrigerant. Accumulators, like receiver-driers, also remove debris and moisture from a system. It is a good idea to replace the accumulator each time the system is opened up for major repair and anytime moisture and/or debris is of concern. Moisture is enemy number one for your A/C system. Moisture in a system mixes with refrigerant and forms a corrosive acid. When in doubt, it may be to your advantage to change the Accumulator or receiver in your system. While this may be a temporary discomfort for your wallet, it is of long term benefit to your air conditioning system
Thursday, January 8, 2009
DiSCUSSION 3
. Explain with suitable diagrams the operatio and arrangements in an automotive air-conditioning unit.
COMPRESSOR
Commonly referred to as the heart of the system, the compressor is a belt driven pump that is fastened to the engine. It is responsible for compressing and transferring refrigerant gas.
The A/C system is split into two sides, a high pressure side and a low pressure side; defined as discharge and suction. Since the compressor is basically a pump, it must have an intake side and a discharge side. The intake, or suction side, draws in refrigerant gas from the outlet of the evaporator. In some cases it does this via the accumulator.
Once the refrigerant is drawn into the suction side, it is compressed and sent to the condenser, where it can then transfer the heat that is absorbed from the inside of the vehicle.
CONDENSER
This is the area in which heat dissipation occurs. The condenser, in many cases, will have much the same appearance as the radiator in you car as the two have very similar functions. The condenser is designed to radiate heat. Its location is usually in front of the radiator, but in some cases, due to aerodynamic improvements to the body of a vehicle, its location may differ. Condensers must have good air flow anytime the system is in operation. On rear wheel drive vehicles, this is usually accomplished by taking advantage of your existing engine's cooling fan. On front wheel drive vehicles, condenser air flow is supplemented with one or more electric cooling fan(s).
As hot compressed gasses are introduced into the top of the condenser, they are cooled off. As the gas cools, it condenses and exits the bottom of the condenser as a high pressure liquid.
EVAPORATOR
Located inside the vehicle, the evaporator serves as the heat absorption component. The evaporator provides several functions. Its primary duty is to remove heat from the inside of your vehicle. A secondary benefit is dehumidification. As warmer air travels through the aluminum fins of the cooler evaporator coil, the moisture contained in the air condenses on its surface. Dust and pollen passing through stick to its wet surfaces and drain off to the outside. On humid days you may have seen this as water dripping from the bottom of your vehicle. Rest assured this is perfectly normal.
The ideal temperature of the evaporator is 32° Fahrenheit or 0° Celsius. Refrigerant enters the bottom of the evaporator as a low pressure liquid. The warm air passing through the evaporator fins causes the refrigerant to boil (refrigerants have very low boiling points). As the refrigerant begins to boil, it can absorb large amounts of heat. This heat is then carried off with the refrigerant to the outside of the vehicle. Several other components work in conjunction with the evaporator. As mentioned above, the ideal temperature for an evaporator coil is 32° F. Temperature and pressure regulating devices must be used to control its temperature. While there are many variations of devices used, their main functions are the same; keeping pressure in the evaporator low and keeping the evaporator from freezing; A frozen evaporator coil will not absorb as much heat.
PRESSURE REGULATING DEVICES
Controlling the evaporator temperature can be accomplished by controlling refrigerant pressure and flow into the evaporator. Many variations of pressure regulators have been introduced since the 1940's. Listed below, are the most commonly found.
Wednesday, January 7, 2009
DISCUSSION 2
Legal action
There have been many cases of legal action being taken against businesses due to illness or damage caused through the lack of air filtration and providing cleaner fresher air, as it is the company’s responsibility to look after the working atmosphere.
Air conditioning is also important in an indoor atmosphere as the right temperature creates a comfortable working environment. There are systems that incorporate the two different features.
Deodorizing VOC and Odor Remediation
On the deodorizing application, the hydroxyl radicals accelerate the breakdown of any Volatile Organic Compounds or VOCs by destroying the molecular bonds. This will help combine the organic gases to form a single molecule that is not harmful to humans thus enhance the air cleaning efficiency. Some of the examples of odor molecules are: Tobacco odor, formaldehyde, nitrogen dioxide, urine and fecal odor, gasoline, and many other hydro carbon molecules in the atmosphere.
Sterilizing Anti-Bacterial and Mold Prevention
Titanium dioxide has strong oxidation affects to single-celled organism that includes all bacteria and fungus. The very strong oxidizing power of Titanium Dioxide can destroy bacteria's cell membrane, causing leakage of the cytoplasm, which inhibits bacteria’s activity and ultimately results in the death and decomposition of bacteria. Generally speaking, disinfections by titanium oxide is three times stronger than chlorination, and 1.5 times stronger than ozonation.
Self-Cleaning, Anti-Soiling and Anti-Fogging
The hydrophilic nature of titanium dioxide, coupled with the gravity, will enable the dust particles to be swept away following the water stream, thus making the product self-cleaning.
When the surface of photocatalytic film is exposed to light, the contact angle of the phtocatalyst surface with water is reduced gradually. After enough exposure to light, the surface reaches super-hydrophilicity. In other words, it does not repel water at all, so water cannot exist in the shape of a drop, but spreads flatly on the surface of the substrate. And the water took the form of a highly uniform thin film, which behaves optically like a clear sheet of glass.Tuesday, January 6, 2009
DISCUSSION
2.find the schematic of a modern air –conditioning system with advanced air threatment proseses and explain the function of the main devices
Air-conditioning units that only cool the air are only addressing part of the equation. Air filtration to remove and neutralise bacteria is just as important, as STUART MADDOCK explains.
Air filtration is essentially the insurance of a higher quality of air in indoor spaces. It is the procedure in which the harmful aspects of the atmosphere, such as bacteria, are withheld and the non harmful aspects are released.
Bacteria and viruses are not easy to remove from the air, due to their miniscule size and the fact that they reproduce so quickly.
The usual size of bacteria is smaller than that of a pin head so filtration is difficult through normal methods. The speed at which they reproduce creates danger. and as so much of our lives is in an indoor atmosphere it is obvious that the air has to be filtered.
Filtration methods
There are various methods of filtration; these vary depending on size, efficiency, and cost. These can be divided into various categories. Usually the filter is inactive and consists of paper or cloth that is pleated and disposable, or a plastic type mesh that is washable.
Active filters are smaller than inactive types but have better efficiency. These air filters generally use electric fields to attract and then kill bacteria. The plasma filter is based on the technology of electric attraction.
Air filtration is important for indoor atmospheres because the work place is becoming increasingly dangerous due to either smoking or illnesses. As many illnesses are passed through air, it is sensible to filter air to sustain a healthy workforce. Filtration reduces allergies and the threat of asthma attacks to sufferers.
Monday, January 5, 2009
EXPERIMENTAL 4
- cooling and dehumidification- switch on the compressor of the refrigeration system. Cool the air until 18°C to 20°C (stable temperature), and then print the data and chart. Calculate the heat rate amount of moisture removed from the air.
Schematic diagram psychrometric chart
Cooling and Dehumidification w1= w2
Tdry = 31.1 Tdry = 19.9
Twet = 25.8 Twet = 18.9
From Psychrometric Chart
ω1 = 0.01925 kg/kga 3= 0.01336 kg/kga
Ø1= 66% Ø3= 92%
h1 = 80 h2= 74 h3 = 54
Qout = ma( h1- h2) + mfhf
mv2 = ω2 ma = 0.01925( 91.7x 10-3) = 1.765 x 10-3
mv3 = ω3 ma = 0.01336( 91.7x 10-3)= 1.225 x 10-3
mf = mv2 – mv1
= (1.765 – 1.225) x 10-3
= 5.4 x 10 -4
hf = h2- h3 = 74 – 54 = 20 kJ/kg
☼ Qout = 91.7x 10-3( 80 – 74) + (5.4 x 10 -4 )(20)
= 0.561 kJ
Sunday, January 4, 2009
EXPERIMENTAL 3
- Steam humidification-switch all water heaters to boil the water. When steam is produced, switch only 3 kW of heat to maintain the steam. Print the data and chart when the conditions are stable. Then, calculate the amount of steam introduced, the change in relative humidity, and the corresponding rise of temperature
Schematic diagram psychrometric chart
Steam Humidification
TAd = 30.2 TBd = 35
To value Ø, ω, extend the psychrometric chart to find the value
TAw = 26.4 TBw = 35
From Psychrometric Chart
ω1 = 20.5 x 10-3 ω2 = 36.85 x 10-3
Ø1= 25% Ø2= 93.4%
1) amount of steam = mv2 – mv1
= ( w2 • ma ) – (w1 • ma)
= ( 36.85 • 94.1) x 10-3 – ( 20.5 • 94.1) x 10-3
= 3.468 – 1.9291
= 1.539 kg
2) ∆ Ø = Ø2 – Ø1 = 93.4 – 75
= 18.4%
3) ∆Tdry = 35 – 30.2 = 4.8 oC
∆Twet = 35 – 26.4 = 8.6 oC
Saturday, January 3, 2009
EXPERIMENTAL 2
- Sensible heating-switch on 1 kW pre-heater and print the data. Then, switch on the 0.5kW re-heater and print the data and chart. For this process, calculate the temperature rise of the air at the exit.
Schematic diagram psychrometric chart
Sensible heat – temperature rise
TAd = 30.3 TBd = 42.2
TAw = 25.4 TBw = 29.9
Temperature rise, Td = 42.2- 30.3 = 11.9oC
Tw = 29.9- 25.4 = 4.5oC
Friday, January 2, 2009
EXPERIMENTAL 1
Start the unit by having te suction fan running and the screen displaying the master menu. Programme 1 shows the process data displayed on a schematic layout of the system. Programme 2 displays the properties of the treated air on the psychometric chart.
- No process- print the data and psychometric chart to read the initial properties of the air as it enters the air-conditioning unit.
Schematic diagram psychrometric chart
No process occur so initial condition are TAd 29.0 and TAw 25.5
Thursday, January 1, 2009
Analysis of air conditioning process
OBJECTIVE:
To observe and understand the changes in air properties as it is treated in a basic air-conditioning unit.
EQUIPMENT:
Computer Linked Air Conditioning Laboratory Unit ( P.A. Hilton)
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