TABLES OF CONTENTS
NO TITLES
PAGE
1.0
Objectives
2
2.0
Introduction
2
3.0
Theory
2
4.0
Apparatus
6
5.0
Procedure
7
6.0
Results and Calculation
8
7.0
Discussion and Conclusion
15
8.0
References
40
9.0
Appendix
41
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1.0 OBJECTIVE
To observe and understand the changes in air properties as it is treated in a basic airconditioning unit 2.0 INTRODUCTION
Air-conditioning is a process of treating air for the comfort requirements of the occupants in the conditioned space. The properties of air can be modified by undergoing certain thermodynamic processes. The most basic of processes involved in an air-conditioning system are sensible heating (raising the temperature), steam humidification (adding moisture), cooling and dehumidification (lowering the temperature and removing moisture). But, there are some cases where we need two or more of the processes in order to make the air is a desired tempereture t empereture and humidity level. All the equipment was set a nd we just need to follow and understand the experimental procedure for every process that need to be done as we are conducting the analysis of air-conditioning process by using Computer Linked Air Conditioning Laboratory Unit (P.A. Hilton). The properties of treated air can be determined through the psychometrics chart 3.0 THEORY
Air conditioning can be defined as a treatment of a ir to simultaneously control its temperature, humidity, cleanliness and distribution to achieve the requireme nts of a conditional space. The term “air conditioning” applies it to the cooling of air. air. Every air conditioning system uses an assembly of equipment to treat air. Commonly, the assembly consists of a heating system for modifying winter indoor temperature and humidity. Most of air conditioning system utilize a vapour-compression refrigeration system to shift the indoor heat to a suitable heat sink such as the outdoors. Vapour compression refrigeration systems occupy a cycle in which the refrigerant, is 2|Page
1.0 OBJECTIVE
To observe and understand the changes in air properties as it is treated in a basic airconditioning unit 2.0 INTRODUCTION
Air-conditioning is a process of treating air for the comfort requirements of the occupants in the conditioned space. The properties of air can be modified by undergoing certain thermodynamic processes. The most basic of processes involved in an air-conditioning system are sensible heating (raising the temperature), steam humidification (adding moisture), cooling and dehumidification (lowering the temperature and removing moisture). But, there are some cases where we need two or more of the processes in order to make the air is a desired tempereture t empereture and humidity level. All the equipment was set a nd we just need to follow and understand the experimental procedure for every process that need to be done as we are conducting the analysis of air-conditioning process by using Computer Linked Air Conditioning Laboratory Unit (P.A. Hilton). The properties of treated air can be determined through the psychometrics chart 3.0 THEORY
Air conditioning can be defined as a treatment of a ir to simultaneously control its temperature, humidity, cleanliness and distribution to achieve the requireme nts of a conditional space. The term “air conditioning” applies it to the cooling of air. air. Every air conditioning system uses an assembly of equipment to treat air. Commonly, the assembly consists of a heating system for modifying winter indoor temperature and humidity. Most of air conditioning system utilize a vapour-compression refrigeration system to shift the indoor heat to a suitable heat sink such as the outdoors. Vapour compression refrigeration systems occupy a cycle in which the refrigerant, is 2|Page
vaporized, compressed, liquefied, and expanded continuously in an enclosed system. A compressor serves as a pump, pressurizing pressurizi ng the refrigerant and circulating it through the system. In the condenser, the pressurized refrigerant is liquefied, liberating heat. Refrigerant passes through an expansion device into an evaporator evaporator where it boils and expands into a vapour, absorbing heat in the process. Air conditioning processes can be demonstrated as steady flow processes:
Ma M ass cons conse er vation: ion: Dry air : Water
:
ma,i = mw,i=
mw,e mw,e or
maii = ma,ee
E ner ner gy conser conser vation: vation: Disregard kinetic and potential energy changes
Stea Steady F low low E nerg nergy y B alanc lance e Ei = Eo Qi + W i +
mihi = Qe + W e +
mehe
Simple heating and cooling: The amount of moisture for simple heating and cooling remains constant
because no moisture is added or removed into the air stream. Therefore, the specific humidity at the inlet and the exit remains equal ( i= e). Heating method : the air stream flow inside a duct and passes resistance
wires (heaters). Heat is added to the air stream, so the dry bulb temperature increases (Te>Ti). Heating Element
1
2 Q
Cooling method: the air stream passes pass es through cooling coil (evaporator
tubes of a refrigeration system). Heat transfer occurs from the hotter air stream to the cooler refrigerant refri gerant of chilled water flow, and the dry dr y bulb temperatures decreases (Te< Ti)
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Cooling Element
1
2 Q
Conservation of mass: ma,1 = mw,2
and
(
1 =
2)
Conservation of energy : Q = ma (h2 - h1) q = h2 - h1 Steam humidification Steam humidification processes : produced low relative humidity (air is dry),
because the moisture amount is constant (mv and constant) but the maximum moisture absorption capacity (mg) increases with temperature rise. If the humidifying agent used is steam, this will result in additional heating (T 3 > T2). If water is sprayed, the stream will be partially cooled (T3 < T2)
Heating Element
From water tank
Humidifier
1
2
3
Q
Mass conservation
D r y ai ai r mass ba balance: ma1 = ma2 =ma3 =m =ma Water mass balance: ma11 = ma2 2 , ( 1 = 2) (heating section) ma2 2 + mw = ma3 3 mw =ma( 3 -
E ner ner gy B alance lance::
2
( humidifying section)
)
Qin + mah1= ma h2 (heating section) Qin= ma (h2 - h1)
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Cooling and dehumidification:
Dehumidification is process to remove excess water in the dry air by condensation. It is achieved by altering the cooling process. The air i s allowed to cool at a longer period until it reaches its dew point (saturation state). Further cooling along the saturati on state (100% relative humidity 0 will result in condensation of part of the moisture in the air.
Heating Element
1
2
\
Q
Dry air mass balance: ma1 = ma2 = ma
ma2 2 + mw =ma3 mw =ma( 1 -
E nergy B alance:
2
)
mhin= Qout +
mhout
Qout = m (h2 - h1) - mwhw
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4.0 APPARATUS
Computer Linked Air Conditioning Laboratory Unit (P.A. Hilton)
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5.0 PROCEDURE
The unit was started by having the suction fan running and master Menu was displayed by the screen. The process data displayed on a schematic layout of the system was showed by Programme 1. The properties of the treated air on t he psychrometric chart were displayed on Programme 2. a) No Process – The data and psychrometric chart were printed as to read the initial properties of the air when it enters the air-conditioning unit. b) Sensible Heating I. II. III.
1kW pre-heater was switched on and 5 minutes was allowed. The data and psychrometric chart were printed. Then, the 0.5kW re-heater was switched on and 5 minutes was allowed. The data and psychrometric chart were printed. For this process, the temperature rise of the air at the exit was calculated.
c) Steam Humidification – All the water heaters were switched on to boiled the water. When steam was produced, only 3kW of heated was switched to maintain the steam and 5 minute was allowed. The data and psychrometric chart were printed. Then, the amount of steam introduced, the change in relative humidity, and the corresponding rise of temperature were calculated. d) Cooling and Dehumidification – The compressor of the refrigeration system was switched on. The air was cooled until 18ºC to 20 ºC (stable temperature). Then 5 minutes was allowed when the temperature was stable. The data and psychrometric chart were printed. The heat rated and amount of moisture r emoved from the air were calculated. During experiment, the time and the rated of condensation (100ml) from the beginning of the cooling process (stable temperature) were measured. The analysis was compared.
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6.0 RESULTS AND CALCULATION
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SAMPLE OF CALCULATIONS No Process:
1. Data obtained from the experiment, T1 (TAd) = 26.4°C T2 (TAw) = 23.3°C Ma1 = 0.0591 kg/s
2. Calculation of Pg: Pg @ T1=24.925oc calculated by interpolation of Table A-4. (P – 3.1698) / (24.925 – 25) = (2.3392 – 3.1678) / (20 – 25) P = 3.157 kPa
3. Data from psychometric chart (Plot T 1 and T2 and find its relative humidity) Relative Humidity, Ø1 = 73% = 0.73
4. Analysis by calculation: Ø1 = pv1/pg Pv = 0.73 x 3.157kPa = 2.3046 kPa 5. Specific Humidity, ω1 = 0.622P v1 / Patm – Pv1 (where Patm = 101.325 kPa) =
(0.622)(2.3046) (101.325−2.3046)
=0.0145 kg v/kga 6. Enthalpy, h1 = C pT1+ ω1hg (where hg=2501.3+1.82T1) = (1.005x26.4) + 0.0145(2501.3+1.82(26.4)) = 63.4975 kJ/kg a
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Sensible Heating:
1. Data obtained from the experiment, T3 (TBd) = 39.5°C T4 (TBw) = 29.0°C Ma2 = 0.0586 kg/s
2. Calculation of Pg: Pg @T3=39.5oC calculated by interpolation of Table A-4 (P – 7.3851) / (39.5 – 40) = (5.6291 – 7.3851) / (35 – 40) P = 7.2095 kPa 3. Data from psychometric chart (Plot T 3 and T4 and find its relative humidity) Relative Humidity, Ø2= 46% = 0.46
4. Analysis by calculation: Ø2 = pv2/pg Pv2 = 0.46 x 7.2095kPa = 3.316 kPa
5. Specific Humidity, ω2 = 0.622P v2 / Patm – Pv2 (where Patm = 101.325 kPa) =
(0.622)(3.316k) (101.325k−3.316k)
= 0.021 kg v/kga 6. Enthalpy, h2=C pT2+ ω2hg (where hg=2501.3+1.82T2) = (1.005x39.5) + 0.021 (2501.3+1.82(39.5)) = 93.73 kJ/kg a
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Steam Humidification:
1. Data obtained from the experiment, T5 (TCd) = 35.8°C T6 (TCw) = 36.2°C Ma3 = 0.2065 kg/s
2. Calculation of Pg: Pg @ T5=35.8 calculated by interpolation of Table A-4. (P – 7.3851) / (35.8 – 40) = (5.6291 – 7.3851) / (35 – 40) P = 5.91 kPa
3. Data from psychometric chart (Plot T 5 and T6 and find its relative humidity) Relative Humidity,Ø3= 98% = 0.98
4. Analysis by calculation: Ø3 = pv3/pg Pv3= 0.98 x 5.91k = 5.79 kPa 5. Specific Humidity, ω3= 0.622P v3 / Patm – Pv3 (where Patm = 101.325 kPa) =
(0.622)(5.79k) (101.325k−5.79k)
= 0.0377 kg v/kga 6. Enthalpy, h3=C pT3+ ω3hg (where hg=2501.3+1.82T3) = (1.005x35.8) + 0.0377(2501.3+1.82(35.8)) = 132.73 kJ/kg a 7. From conservation of mass,Ma Dry air, ṁa1= ṁa2= ṁa3=ṁa Water vapour, ṁv2+ ṁf 3= ṁv3 Mass flow rate of steam injector, ṁf 3 = ṁa3 (ω3-ω2) = 0.2065(0.0377 -0.0210) = 3.44855 x 10 -5 kg/s 12 | P a g e
Cooling and dehumidification:
1. Data obtained from the experiment, T7 (TDd) = 16.5°C T8 (TDw)= 17.0°C Ma4 = 0.2183 kg/s
2. Calculation of Pg: Pg @T7=17.2 calculated by interpolation of Table A-4. (P – 2.3392) / (16.5 – 20) = (1.7057 – 2.3392) / (15 – 20) P = 1.89575 kPa
3. Data from psychometric chart (Plot T 7 and T8 and find its relative humidity) Relative Humidity, Ø4=100% = 1
4. Analysis by calculation: Ø4 = pv4/pg Pv4= 1 x 1.89575 =1.89575 kPa 5. Specific Humidity, ω4= 0.622P v4 / Patm – Pv4 (where Patm = 101.325 kPa) =
(0.622)(1.89575k) (101.325k−1.89575k)
= 0.01186 kg v/kga 6. Enthalpy, h4=C pT4+ ω4hg (where hg=2501.3+1.82T4) = (1.005x16.5) + 0.01186(2501.3+1.82(16.5)) = 46.604 kJ/kg a
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7. Conservation of mass, Σṁin = Σṁout Water vapor, ṁv4+ ṁf 4= ṁv1 mω = ṁf 4 = ṁa3 (ω1-ω4) =0.2065 (0.0145-0.01186) = 5.4516 x 10 -4 kg/s
Conservation of energy,ṁa1h1=Qout+ṁa4h4+mωhω (where ṁa1 = ṁa4 = ṁa) Qout = ṁa (h1- h4) – mω (hf ) Qout = 0.2065(63.4975-46.604)-(5.4516 x 10 -4)(69.2619) = 3.451 kW
Before substitute hf into Q out formula, we have to interpolate the hf value. (hf – 83.915) / (16.5 -20) = (62.982 – 83.915) / (15 – 20) hf = 69.2619
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7.0 DISCUSSION AND CONCLUSION
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MOHAMED ZARIF IMRAN BIN MOHAMED SHAHRIN 2015116451
DISCUSSION
a) Answer all the problems in the experimental, and discuss the results obtained by explaining the factors that contributes to the air property changes for each process problems No Process Based on the data, we can see that there are no changes in the temperature because it does not involve with any variable. Even though, there is still a value for the first data but the value is just a reading taken from the surrounding condition. So, at this moment we cannot make any assumption and we still need more data from other variable to see clearly the relation between all the variables
Sensible Heating
During sensible heating process, we investigated that the temperature raises reading for both wet bulb and dry increased compare to no process experiment. The different between these two experiments is because in sensible heating experiment we use the pre-heat and reheat to heat the air while in no process experiment there is nothing particular changes had been made. The usage of 1 kW pre-heater as well as 0.5 kW re-heater is the factor of temperature increasingly. Theoretically, the preheat and reheat both of them is actually increasing the temperature of the air since both of them is provide heat to the air. Unfortunately, there is still some temperature drop during the air flow to the outlet. In order to solve this problem the air must be reheat to a certain temperature so that we can get the temperature that we want. Therefore, the changes that could be seen in the air property are that the air happens to be hotter at this stage. That is why once the air conditioning system is switched on, the hot air will first flow out from the system followed by the cooled air accordingly.
Steam Humidification
During the process, the air that passed through the section of water boiling to produce steam will caused an increase in temperature because the steam has the ability to hold 16 | P a g e
maximum moisture of air. Moreover, the increasing of moisture capacity will respond with the temperature rise. That is the reason for the temperature at state 2 increases as compared to state 1. 3kw of heat switched on to maintain the steam after the steam is produced. This is because, the factor that contributes to the change of air property for this process is the present of heat at higher value to ensure that the level of steam is maintained and at the same time, the property of air is change into the form of ste am.
Cooling and dehumidification
Based on our result, it can be noted that all of the value of readings obtained for both dry bulb as well as wet bulb temperature are totally lower compared to the previous processes. At this stage the compressor of the refrigeration system is switched on and by the way, the air is cooled until 18°C to 20°C (stable temperature). As for that, that is why all of the temperatures reading are at a lower value since the process of cooling and dehumidification are both involved. The cooled air starts to flow and the room temperature will cold down. In terms of the factor that contributes to the change in air property for this process is due to the reason of compressor usage which in a way it changes the temperature of the air to become lower and producing a cooled air to flow out of the system.
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b) Find the schematic of a modem air-conditioning system with advanced air treatment processes and explain the function of the main devices.
The function of main devices The three main parts of an air conditioner unit are the compressor, the condenser and the evaporator. The compressor and condenser are located on the outside of the air conditioner and the evaporator is located on the inside. The basic functioning of the air conditioner is based on the principle of successive heating and cooling of a highly volatile liquid, such as a Freon. The liquid first will enters the compressor, where its function is to compress into a gas. This reaction will releases heat and makes the liquid cooler. After that, the dissipated heat is radiated outwards with the help of a fan. The liquid then enters the condenser, where its function is to absorb heat from the surroundings to reconvert into a gas. Hence, the surroundings temperature will become cool. The entire process continues and eventually causes of the cooling of the room. Besides the three main air conditioner parts, an air conditioner also has a hot coil on the outside to dissipate heat, a cool coil on the inside to absorb heat, two fans (one outside and one inside) and a control circuit to modify the temperature. This is done by changing the rotation speeds of the fans using a potentiometer. 18 | P a g e
c) Explain with suitable diagrams the operation and arrangements in an automotive airconditioning unit.
COMPRESSOR
The compressor is a belt driven pump that is fastened to the engine used for compressing and transferring refrigerant gas. A/C system has been separate into two sides. There are high pressure side and low pressure side that 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 by 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.
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CONDENSER
The condenser serves as the heat dissipation component. The condenser will have similar appearance as the radiator in car as both have very similar functions. The main function of condenser is to radiate heat. Basically it is located in front of the radiator. Its location may differ due to aerodynamic improvements to the body of a vehicle. 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. 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.
ORIFICE TUBE
The orifice tube 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. Small dimples placed in the line that keeps the orifice tube from moving. Most of the orifice tubes in use today measure approximately 3inch 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 labour 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 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.
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EVAPORATOR
The evaporator serves as the heat absorption component. Its primary function is to remove heat from the inside of your vehicle. A secondary benefit is dehumidification. As warmer air travels through the aluminium 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 moist 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 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 as 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 0 Celcius. 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
A pressure regulating devices is a control valve that reduces the input pressure of a fluid to a desired value at its output. Regulators are used for gases and liquids, and can be an integral device with an output pressure setting, a restrictor and a sensor all in the one body, or consist of a separate pressure sensor, controller and flow valve.
THERMAL EXPANSION VALVE
Thermal expansion valve is another common refrigerant regulator. 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.
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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 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 main function of the receiver-drier is to separate gas and liquid. The secondary function 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, vapour 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. 22 | P a g e
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.
CONCLUSION
In conclusion, we can say that the experiment is a success because at the end of the experiment we are able to observe and understand the changes in air properties as it is treated in a basic air-conditioning unit. We are now understand that the air properties varies depends on the relative humidity, specific humidity, temperature, heat transfer, and air motion whereas it changes causes a different results
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HAIZATUL SYAHIRAH BINTI HAIRUDDIN 2015125707
DISCUSSION
1)
Answer all the problems in the experimental and discuss the results obtained by explaining the factors that contributes to the air property changes for each process problems
1- No process It had been seen that the value of dry temperature was higher compared with wet temperature. Dry temperature higher because it was located nearest to blower speed control which there has no steam produced at dry temperature. But at the wet temperature, it located nearest to the steam injector. The dry temperature, t1 produced in no process experiment was 26.4˚c and wet temperature, t2 produced was 23.3˚c. The temperature increases up to 26.7˚c at t3 and then decrease back at t5, 26.4˚c and finally increase at t7; 26.5˚c. Same for the wet temperature, the values increases at t4; 23.8˚c, then decrease at t6; 23.0˚c and finally increase back at t8; 23.3˚c. No process in air conditioning gives the meaning of no heat produced in the air conditioning and all the properties produced same as it in the room temperature.
2- Sensible heating a) 1kW For the value of dry and wet temperature, it had been showed that t he dry temperatures gave higher value compared with wet temperatures. The value for dry temperature, t1 was 26.7 ˚c and wet temperature, t2 was 23.6 ˚c. Then the values obtained from this process were not constant. For the dry temperature, it had been increased at the t3 but then the value had been decreased until t7. The values obtained in wet temperature also same pattern as dry temperature. Temperature increased at t4, and then decreased linearly to t8. b) 1.5kW For the value of dry and wet temperature, it had been showed that t he dry temperatures gave higher value compared with wet temperatures. The value for dry temperature, t1 was 27.1 ˚c and wet temperature, t2 was 23.7 ˚c. Then the values obtained from this process were not constant. For the dry temperature, it had been increased at the t3 but then the value had been decreased until t7. The values obtained in wet temperature also same pattern as dry temperature. Temperature increased at t4, and then decreased linearly to t8.
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Theoretically, the preheat and reheat both of them is actually increasing the temperature of the air since both of them is provide heat to the air. Unfortunately, there is still some temperature drop during the air flow to the outlet. In order to solve this proble the air must be reheat to a certain temperature so that we can get the temperature that we want. 3- Steam humidification Based on the data we can see that after we switch the water heater to boil the water the output temperature started to increase for both dry and wet bulb temperature. Is obvious that the cause of the temperature to increase is because of the steam that had been produced from the water that had been boiled. It seem that the steam make the wet bulb temperature to increase more than the other processes. By using these reactions, we can take advantages from it which is by adding the air we can increase the humidity of the air whereas for the steam we can use it to increase the tempearture of the air.
4- Cooling and dehumidification The value obtained for the both dry and wet temperatures were fluctuated which increase at t3 and t4, decrease at the t5 and t6 and finally increased back at t7 and t8. But, this process produced the temperatures values up to t12. As for that, that is why all of the temperatures reading are at a lower value since the process of cooling and dehumidification are both involved. The cooled air has start to flow and the room temperature will cold down. All in all, in terms of the factor that contributes to the change in air property for this process i s due to the reason of compressor usage which in a way it changes the temperature of the air to become lower and producing a cooled air to flow out of the system.
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2)
Find the schematic of a modern air-conditioning system with advanced air treatment processes and explain the function of the main devices
Device
Compressor
Condenser
Expension Valve
Evaporator
3)
Function To compress the refrigerant refrigerant from the low pressure at low temperature to high pressure at high temperature. Used to liquify the high presure refrigerant from the compressor. In air, cooled condensers, metallic surface cools the gas and changed to form liquid. In the watercooled condenser, water had been circulated to produce the same cooling effect. It removes pressure from the liquid refrigerant to allow expansion or change the state from liquid to a vapour in evaporator. The high-pressure liquid refrigerant enters in quite situation and leaves it in cold situation. Orifice within the valve does not remove heat but only reduces the pressure. It absorbed heat from the surrounding air and had been produced cooled air.
Explain with the suitable diagrams the operation and arrangements in an automotive air-conditioning unit.
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Components Condenser
Drier
Evaporator
Expansion valve
Compressor
Operations Like a miniature radiator, usually mounted at the front of the car right next to the big radiator. Sometimes the condenser will have its own electric cooling fan, too. The hot, compressed air passes through the condenser and gets lots cooler. As it cools, it becomes a liquid. Also known as the receiver-drier. The drier catches refrigerant that could make it back to the compressor. Before it can damage it. Since even the tiniest leak or careless installation can introduce water moisture to the system, the drier absorbs this chemically, using what's called desiccants. The drier also has a filter that catches any gunk that might be in there. Another little radiator that does just the opposite task as the condenser. When the super-cool liquid is passed through its tubes, air is forced through and gets really cold, right before it hits your face. As it warms up again, the refrigerant starts turning back into a gas. Control the flow of super cool refrigerant to the evaporator. With this we can regulate how cold the air blowing on us. Even though, there are a few types of valves in use these days, but they all do the same thing.
Takes the refrigerant (the gas) and pressurizes it so it will cool the air surrounding. It's run by an engine belt. The compressor also has an electrically operated clutch that turns the compressor on and off as you demand more cool air.
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CONCLUSION
Along this experiment, we can conclude that the experiment is success since we manage to achieved our goal which is to observe and understand the changes in air properties as it is treated in a basic air-conditioning. We knew that the air properties is changes based on what types of process that we running it. Each types of process which is the no process, sensible heating, steam humudification, also cooling and dehudification have their own result and reason why it is occur like that. With that data and result we can study throughout about the air-conditioning. But still an error must be avoided in order to get the pr ecise data.
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AZMI BIN A.MATALI 2015110295 DISCUSSION
a) Answer all the problems in the experimental, and discuss t he results obtained by explaining the factors that contributes to the air property changes for each process problems. 1) No process The value of dry temperature is higher compared to the wet temperature. Dry temperature is higher because it is located near to the blower speed control which steam is not produced at dry temperature. While, wet temperature is located near to the steam injector. At the point A, the dry temperature is 26.4ºC while wet temperature is 23.3 ºC. At the point B, the temperature is slightly increases compared at the point A. The dry temperature obtain at point B is 26.7 ºC while wet temperature is 23.8 ºC. At point C, the dry temperature is 26.4 ºC and wet temperature is 23.0 ºC. It is found that at the point D, the dry temperature is 26.5 ºC while wet temperature is 23.3 ºC. In no process condition, heat is not produced in the system and all the properties is same in the room temperature. 2) Sensible Heating a) 1kW The dry temperature is higher than wet temperature in this process. The value of dry temperature at point A is 26.7ºC and wet temperature is23.6 ºC. At point B, the temperature is increases in both dry and wet temperature. The dry temperature is 39.5 ºC and wet temperature is 29.0 ºC. At point C, the dry temperature and wet temperature is decreased. The value of dry temperature is 37.6 ºC and wet temperature is 26.9 ºC. At the point D, dry and wet temperature is decreased again. The value of dry temperature is36.4 ºC while the value for wet temperature is 26.6 ºC. b) 1.5kW It is shown that the dry temperature is higher than wet temperature. The value of dry temperature at point A is 27.1 ºC while for wet temperature is 23.7 ºC. The values obtained from this experiment is not constant. It is f ound that dry and wet temperature is increase at the point B, but these temperatures keep droppings until it reaches point D. Theoretically, the preheat and reheat process is to increase the temperature of air since the process is to transfer heat into air.
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3) Steam humidification Based on the data obtain from experiment, the dry and wet temperature is increasing after the water heater is switch on to boil the water. It is found that the steam produced from boiled water increase the wet and dry temperature. The wet temperature is increase more than other process. At this process, the humidit y of air is increase because of the steam. 4) Cooling dehumidification The data obtained from this process from both wet and dry temperature we re fluctuated which increase at point B, then the both temperature decrease at point C, and finally increased back at point D. In this p rocess, all temperature at the lower value because both cooling and dehumidification occurs. The cooled air starts flowing and the room temperature will be decrease. The factor that contributes to the change of air properties is because of the compressor usage which in a way it changes the air temperature to decrease and produced cooled to flow out of the system. b) Find the schematic of a modem air-conditioning system with advanced air treatment processes and explain the function of the main devices.
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The main function for air-conditioning system is to treat an air for human comfort. The air-conditioning system is used system which transfer heat from the inside to the outside. It is because heat is a type of energy which cannot be destroyed or created. There are four main devices in an air-conditioning system which are evaporator, compressor, condenser, and expansion valve. First device is called compressor which main functions is to compresses the refrigerant. The refrigerant will compress into a high pressure gas state and its temperature is increased because of compression. It is to increase the temperature of refrigerant higher the outside surrounding temperature. The refrigerant then flows into a condenser which the t emperature of refrigerant will transfer to the air. Blower fan is function to blow ambient air to the condenser units to increase the cooling rate of re frigerant. The gas state refrigerant will change into a liquid state in this process. expansion valve which is to decrease the pressure of refrigerant. The temperature of refrigerant will decrease because change of pressure in refrigerant. This process is important in order the refrigerant can change into gas state in the evaporator units and to change the properties of refrigerant so it can absorb more heat in the next process. Last device is called evaporator is to absorb heat in surrounding area. The heat is absorbing by using refrigerant. In this process, the refrigerant will change into gas state because it low melting point thus this device is called evaporator. c) Explain with suitable diagrams the operation and arrangements in an automotive air conditioning unit.
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Compressor
Compressor is important in the system. The compressor is driven by belt which fastened to the engine. Main function of compressor is to compress the refrigerant gas into high pressure gas refrigerant then transfer it to the condenser. It is important to compress the refrigerant into a high pressure gas state. The temperature of high pressure refrigerant gas is increases above the ambient temperature at the outside at the condenser unit. Condenser
This unit is the area which heat from refrigerant is dissipated. The condenser usually has a same appearance as the radiator and located at the front of radiator. The condenser is designed to radiate heat from the ref rigerant. In some cases, the location of condenser may differ due to the aerodynamic improvements to the body of car. The condenser must have a good air flow through its units at any time t he system is operates. When the high pressure refrigerant gas is introduced into a condenser, the h eat is transferred to the outside and cooled off. It i s condensed and at the exit of condenser, the refrigerant will change its state into a high pressure refrigerant liquid. Evaporator
Evaporator is located at the inside of the vehicle. The main function of evaporator is to absorb heat from surrounding. A secondary function of the evaporator as a dehumidification device. As a warmer air flow to the aluminum fins of the cooler evaporator coil, the moisture of air is condensed into its surface thus dust and pollen passing will be stick to the wet surface and drain out to the outside. The ideal for condenser temperature is 0 degree Celsius. Refrigerant that flow to the evaporator is in low pressure liquid state. The warm air which pass through the evaporator will boil the refrigerant. It is because the melting point of refrigerant very low thus warm heat transfer to the refrigerant is enough to boil the refrigerant to the gas state. Low pressure of liquid refrigerant can absorb large amount of heat. It is important to keep an evaporator from freezing as a frozen evaporator coil will not absorb large amount of heat.
Expansion valve
An expansion valve is to control the temperature of refrigerant before its enter an evaporator. It is important to control the temperature of refrigerant flow to the evaporator because to determined how much of heat will be absorb from inside of the vehicle. There are many types of valve but its main function still same.
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Receiver-drier
The primary function of drier is to separates gas and liquid. It is to ensure the valve will get a liquid refrigerant. Other purpose of drier is to remove moisture and filter out dirt. The drier usually have a sight glass at the top. This sight is used to charge the system. in a normal condition, bubbles should not be visible in the sight glass. However, it is not recommended to charge the s ystem in R-134a systems. But, newer receiver-drier are compatible with both R-12 and R-134a refrigerant. Conclusion
From this experiment, we concluded the experiment is successfully conducted since the objective to observe and understand the change in air properties in an air-conditioning system. Different process which have been done has a different air property. With data and result obtain from experiment, we can study about air-conditioning system.
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MOHD SOLEH BIN MOHD JALI 2015102845 DISCUSSIONS:
A. Answer all the problems in the experimental, and discuss the results obtained by explaining the factors that can contributes to the air property changes for each process problems. No Process:
Since there is no process running on this test, it is clearly can be seen in the data obtained. Firstly, we can see there are no big changes of temperature recorded in this process, all the value of temperature readings obtained at this stage is all in the range of room temperature. This is because no main factors contributes to the increasing or decreasing of air temperature value and air properties. The factors that may can contributes to the air temperature and properties may include all of the components on the air conditioning system such as heater, compressor and others. There are no components running on this process except the air blower. The relative humidity on this process is quite high, which mean the moisture content in the air is high because temperature is inversely proportional to the humidity. The condensation rate on this process also low, so that the moisture trapped in the air, so that no big temperature increase occur. This can be prove by the enthalpy value in this process is quite low; the enthalpy value is directly proportional to the condensation rate. Sensible Heating:
For this sensible heating process, we have two conditions, which is on the first test, we used 1kW pre-heater and allow for 5 minutes before we print the data, and on the next test, we continue the first process by 0.5kW re-heater and allow for 5 minutes and the data was printed. The usage of the 1kW and 0.5kW heater is clearly contributes to the changes of air property in this test. As we can see on the data, the air temperature value on this process is greater compared to the previous process which i s no process. The temperature in this process began to exceed the room temperature as on 1kW pre-heater, the highest temperature recorded is 39.5 and on the 0.5kW re-heater is 45.6. The relative humidity in this process is obviously lower than in the previous process, the increasing of the temperature influence the moisture content in the air on this process. The condensation rate in this process is quite high since the enthalpy value is quite high. Lastly, the most obvious observation that can be made from this experiment is the value of Qr where Qr for 1kW is 0 and Qr for next 0.5kW reheater is 526.1.
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Steam Humidification:
For steam humidification process, all water heater switched on to boil the water in order to produce steam. When the steam produced, only 3kW of heat switched to maintain the steam produced before. As we can see on the data obtained, the temperature value for both dry and wet bulb is in constant range. The constant value of the temperature recorded prove that the 3kW heater is perfectly running, in other word, the steam is successfully maintain. The maintains of steam is very important in order to achieve the process goal which is to humidify the air. The steam has to be maintain to ensure the moisture content in the air is high, so that the humidity also high. The relative humidity obtained from psychometric chart is very high which is 98%, so it is prove that the air was successfully humidified. Lastly, the temperature value in this process is quite higher compare to previous processes. The steam produced before may influence the value of the temperature. Cooling and dehumidification:
Compared to all of the previous processes, the temperature dif ference from stage 1 to 4 is very high. The temperature for this process is also very low among all of the previous processes. The temperature drop massively in this process. The relative humidity is very high which is 100 %. Its mean that the moisture content in the air of this process is very high. The enthalpy value also quite low, so that the condensation rate is also low. The time taken to condense 100ml water is 14.56. The condensation rate in this process is 5.4516 x 10 -4 kg/s. So that, it proved that the low value of enthalpy is logical since the condensation rate value is also low. Lastly, the heat transfer obtained aft er some calculations is 3.451 kW.
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B. Find the schematic of a modem air-conditioning system with advanced air treatment processes and explain the function of the main devices.
There are four main component in modem air-conditioning system, which is compressor, condenser, evaporator and expansion valve. At the evaporator, heat from the ambient air evaporates the liquid refrigerant, thus make the air temperature decrease. The compressor circulates the refrigerant gas and compresses it increasing its pressure and making the gas hot. Next, the condenser, ambient air cools and liquefies the hot refrigerant gas, which then reenters the refrigerant cycle. Lastly at the expansion valve, removes pres sure from the liquid refrigerant to allow expansion or change the state from liquid to a vapour in evaporator. The high-pressure liquid refrigerant enters in quite situation and leaves it in cold situation. The expansion valve does not remove the heat, the valve just remove the pressure. The refrigerant is at the coolest state when it leave the expansion valve before it enter the evaporator.
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C. Explain with suitable diagrams the operation and arrangements in an automotive airconditioning unit.
1. Compressor Commonly referred to as the heart of the s ystem, 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. 2. 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 locat ion 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 an ytime 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 electr ic cooling fan(s). As hot compressed gasses are introduced into the top of t he condenser, they are cooled off. As the gas cools, it condenses and exits the bottom of the condenser as a high pressure liquid. 37 | P a g e
3. 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. Se veral 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. 4. 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. 5. Expansion Valve Expansion valves are devices used to control the refrigerant flow in a refrigeration system. They help to facilitate the change of higher pressure of liquid refrigerant in the condensing unit to lower pressure gas refrigerant in t he evaporator.The term "low side" is used to indicate the part of the system that operates under low pressure, in this case the evaporator. The "high side" is used to indicate the part of the system that operates under high pressure, in this case the condenser. 6. Drier The receiver-drier’s primary function is to receive and store some liquid refrigerant from the condenser.
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CONCLUSIONS:
In the conclusions, after conducting this experiment, we can conclude that the objective of this experiment, which is to observe and understand the changes in air properties as it is treated in a basic air conditioning unit, was successfully achieved. Besides that, we also can understand the modem air-conditioning system with advanced air treatment processes and we also can understand the operation and arrangements in an automotive airconditioning unit. By conducting this experiment, we also learn how to manage the Computer Linked Air Conditioning Laboratory Unit (P.A Hilton). Lastly, we hope that, this experiment will help us to understand more about the air-conditioning in the future.
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8.0 REFERENCES:
1. Lab Sheet No:1, Heating Ventilation and Cooling Sheet (HVAC), Analysis of Airconditioning, MEC 554, Thermodynamics Lab, UiTM Shah Alam, 2017. 2. Third Edition Heat And Mass Transfer (A Practical Approach)By Yunus A. Cengel 3. Thermodynamics an Engineering Approach 3rd Edition. 4. https://global.britannica.com/science/specific-humidity 5. https://macsworldwide.wordpress.com/2010/10/13/what-is-a-receiver-drier/ 6. MEC 551, Thermal Engineering, UiTM, Faculty of Mechanical Engineering, McGraw Hill Education (Asia).
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9.0 APPENDIX
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