Discussion Thermo Air Cond

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NAME: MOHD SAPANE B TAHA UiTM ID: 2007127955 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. Process (A): (No Process) Data from process A Tdry Twet In = 25.3°C = 21.8°C Tdry Twet Out = 23.9°C = 21.5°C

At this moment, it can be assumed that there are no changes of temperature in this process because it does not have any process because it does not required the usage of any components that could change the temperature which can be the main factor contributes to the change of air property. Therefore, we assume all the values of readings obtained at stage in and out are all in the range of room temperature. Process (B): (Sensible Heating)

Heating Element

1 Q

2

Data from process B

NAME: MOHD SAPANE B TAHA UiTM ID: 2007127955 State1 Tdry = 25.9°C Twet = 22.5°C State Tdry = 36.2°C Twet = 25.4°C

From the Psychrometric Chart Ø1 = 76% Ø2 = 44%

Temperature rises at exit ∆Tdry = 36.2°C – 25.9 °C = 10.3°C ∆Twet = 25.4°C – 22.5°C = 2.9°C 1. 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 (ω i = ωe ). 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). The relative humidity of air will decrease from Ø1 = 76% to Ø2 = 44% during heating from T1 to T2 even the specific humidity is remain constant. This because the relative humidity is ratio of the moisture content to the moisture capacity of air at the same temperature. Ø=(mv/mg) and moisture capacity is increasing with temperature. The air in this heating process is heated by 2 stages of heating; first at 1KW and 0.5 KW. That factor contribute to the increasing of temperature of both wet bulb and dry bulb from 25.9°C to 36.2°C compared to those readings obtained in previous process (process A). Therefore, the changes that could be seen in the air property are that the air happens to be hotter at this stage. Related to this factor, 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.

2. 3.

4.

5.

NAME: MOHD SAPANE B TAHA UiTM ID: 2007127955

Process (C): steam Humidification

Heating Element Humidifier

From water tank

1 Q

2

3

From data for process C State 2 Tdry = 26.3°C Twet = 22.9°C ma= 0.1585kg/s 0.1585kg/s From the psychrometric chart: Ø2 ω2 Where,
• • • • • •

state 3 Tdry = 28.7°C Twet = 28.7°C ma=

= 74% = 15.3 x 10-3 kgv/kga

Ø3 ω3

= 100% = 24.6 x 10-3 kgv/kg

Dry air mass balance: ma1 = ma2 =ma3 =ma Water mass balance: ma1ω1 = ma2 ω2 ,ω1 = ω2 (heating section)
• • •

NAME: MOHD SAPANE B TAHA UiTM ID: 2007127955 section) • ma2ω2 + maw = m
a3ω3

( humidifying

Amount of steam mw = ma (ω3- ω2) = 0.145kg/s (24.6 x 10-3 – 15.3 x 10-3) kgv/kga = 1.3485 x 10-3 kg/s Temperature rises at exit ∆Tdry = 28.7°C – 26.3°C = 2.4°C ∆Twet = 28.7°C – 22.9°C = 5.8°C ∆Ø = 1.0 – 0.74 = 0.26 @ 26% = Ø3 – Ø2





1. Air is passed through a humidifying section where water is boiled to produce steam. When the steam is introduced in humidifier, this will resulting additional heat as we can see the temperature increase from T2 = 26.3°C to T3 = 28.7°C. 2. As can be seen from result data, relative humidity is increased from state 2 to 3. This is because the steam is introduced which the ability of air to hold maximum moisture is increase. 3. Therefore, the increasing of moisture capacity will associate with the temperature rise. That is why the temperature at state 2 increases as compared to state 1. 4. Simple heating processes produced low relative humidity (air is dry), because the moisture amount is constant (mv and ω constant) but the maximum moisture absorption capacity (mg) increases with temperature rise. 5. If the humidifying agent used is steam, this will result in additional heating (T3 > T2). 6. If water is sprayed, the stream will be partially cooled (T3 < T2) 7. Next, once the steam is produced, only 3 kW of heat is required to be used as for the reason to maintain the steam. Therefore, it can be assumed that the factor that contributes to the change of air property for this process is due to the usage of heat at a higher value (3 kW) to ensure that the level of steam is maintained as required and at the same time, the property of air is affected and change into the form of steam as part of it.

NAME: MOHD SAPANE B TAHA UiTM ID: 2007127955

Process (D): Cooling and Dehumidification

1

2

Data from process D at 5 minutes State 1 Tdry = 27.7°C Twet= 23.1°C ma1 = 0.1419 kg/s 0.1419 kg/s Tdry Twet

state 2 = 20.0°C = 19.1°C

m a2 =

From the psychrometric chart: Ø1 = 97% ω 1 = 15.3 x 10-3 kgv/kga h1 = 84 kJ/kg Ø2 = 68% ω2 = 1 6.0x 10-3 kgv/kga h2 = 80.8 kJ/kg

NAME: MOHD SAPANE B TAHA UiTM ID: 2007127955 Where;
• • • • • • • • • • • • •

Dry air mass balance: ma1 = ma2 = ma Water mass balance: ma1ω1 = ma2ω2 + mw mw = ma ( ω1 - ω2 ) Energy balance hw : ∑ m ihi = Qout + ∑ m ehe


Qout = ma ( h1 – h2 ) – mw

Where; mv2 mv3

ω1

= ω2

and

Ø2

= Ø3

= ω2 x ma = 1.6 x 10-3 kgv/kga x 0.1419 kg/s = 0.2270x10-3 kg/s = ω3 x ma = 15.3 x 10-3 kgv/kga x 0.1419 kg/s = 2.1711 x 10-3 kg/s



Amount of moisture mf = mv2 - mv3 = 2.1711 x 10-3 kg/s – 0.2270 x 10-3 kg/s = 1.9441 x 10-3 kg/s Amount of heat rate hw = hf @ T2=19°C from table A-4, therefore hw = Temperature(°C) 15 19 20



hf (kJ/kG) 62.982 hw 83.915

hw-62.982 = 19-15 83.915.62.982 20-15 =79.728 kJ/kg • Q out = ma (h1 – h2) + mfhf = 0.1419 (84 – 80.8) + (1.9441 x 10-3) (79.728)

NAME: MOHD SAPANE B TAHA UiTM ID: 2007127955 = 0.3087 kJ/kg 1. Dehumidification is process to remove excess water in the dry air by condensation. It is achieve by altering the cooling process. 2. The specific humidity of air remains constant during a simple cooling, but its relative humidity increases due to lower amount of maximum moisture (mg) that can be absorbed as the air temperature decreases. 3. The end result of this cooling process is the condensation of moisture in air. The water vapor that condensed is remove through separate channel while the air remain at it saturation condition. This is why the increasing of relative humidity to almost 100 %. The cool saturated air is routed to room so that it can make more comfortable level of temperature. 4. The air is allowed to cool at a longer period until it reaches its dew point (saturation state). Further cooling along the saturation state (100% relative humidity 0 will result in condensation of part of the moisture in the air. b) Find the schematic of a modern air-conditioning system with advanced air treatment processes and explain the function of the main devices.

Components and Devices 1 Air Inlet 2 Wet and Dry Temperature Stations 3 Steam Injector 4 Pre-Heaters 5 Evaporator 6 Pre-Heaters 7 Orifice

17 18 19 20 21 22 23

Solenoid Valve Water Inlet Sight Glass Vent Water Heaters Overflow to Drain Condensate Measurement

NAME: MOHD SAPANE B TAHA UiTM ID: 2007127955 8 9 10 11 12 13 14 15 16 Treated Air Fan Fan Speed Control Evaporator Pressure Thermostatic Expansion Valve Stop Valve Inclined Monometer Steam Generator Tank Water Level Control 24 25 26 27 28 29 30 31 Compressor Air Condenser Liquid Receiver Condenser Inlet Pressure Refrigerant Flow Meter Condenser Outlet Pressure Filter/Drier Steam Generator Tank Drain Valve

Temperature Upgrade Kit A000A 32 16 Way Selector Switch

33

Digital Temperature Indicator

Computer Linked Upgrade Kit A0000A 34 RS232 Serial link to PC 35 Datalogger 36 Transducer Inputs Air Recirculation Duct Kit A0006 40 Duct Section 41 Exhaust PID Control Upgrade Kit A0000 43 PID Controller – Humidity XRH 44 PID Controller – Temperature C 45 Combined XRH/Temperature Probe Environmental Chamber A0600 48 Environmental Chamber

37 38 39 42

Refrigerant Pressure Transducer Refrigerant Flow Transducer Differential Air Pressure Transducer Volume Control

46 47

Manual/PID Control Selector Switch RS485 Serial link to PC

In general, stated above are the devices used in a modern air conditioning system with advanced air treatment processes. In addition, in terms of the main devices used in a modern air conditioning are as listed and explained below: Compressor Otherwise known as the heart of the system, the compressor is a piston or vane type pump responsible for compressing refrigerant gas and transferring it through the air conditioning system. The compressor is a belt driven pump that is fastened to the engine. It is responsible for compressing and transferring refrigerant gas.

NAME: MOHD SAPANE B TAHA UiTM ID: 2007127955 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 The condenser acts as a heat exchanger radiating heat from refrigerant to the outside air. Refrigerant enters the top of the condenser as a hot compressed gas and is cooled within. As the refrigerant cools it condenses and changes from a high-pressure gas into a high-pressure liquid and exits the condenser through the bottom. The condenser is on the high side of the air conditioning system. This is the area in which heat dissipation occurs. 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. Humidifiers Usually reduces the humidity of the air processed by the system. The relatively cold (below the dew point) evaporator coil condenses water vapor from the processed air, (much like an ice cold drink will condense water on the outside of a glass), sending the water to a drain and removing water vapor from the cooled space and lowering the relative humidity. Since humans perspire to provide natural cooling by the evaporation of perspiration from the skin, drier air (up to a point) improves the comfort provided. The comfort air conditioner is designed to create a 40% to 60% relative humidity in the occupied space. In food retailing establishment’s large open chiller cabinets act as highly effective air dehumidifying units. Evaporator An air conditioning evaporator is a refrigeration coil mounted within cooling fins.The continuous flow of warm air over the coils causes the refrigerant flowing inside to boil and absorb large amounts of heat. The boiling refrigerant leaves the evaporator onto the condenser where it is dissipated into the atmosphere. The evaporator also acts as a dehumidifier and air purifier at the same time Fan Mainly the purpose of using fan concept in an air conditioning unit is to ensure that all the unwanted heat are rejected from the system into the atmosphere. At the same time, it ensures the cooling rate is maintained at its level

NAME: MOHD SAPANE B TAHA UiTM ID: 2007127955

c) Explain with the suitable diagrams the operation and arrangements in an automotive air-conditioning unit.

At 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. At 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. 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.

At 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. At thermal expansion valve 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. At 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 vaiations 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.

(At 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

CONCLUSION: The needs of the human body and the conditions of the environment are not quite compatible. Therefore, it often becomes necessary to change the condition of living space to make comfortable. Maintaining a living space or an industrial facility at the desired temperature and humidity may require simple heating (raising the temperature), simple cooling (lowering the temperature), humidifying (adding moisture), or dehumidifying (remove moisture). We can find the properties of atmospheric air at a specific total pressure are presented in the form of easily readable chart called psychometric charts. From this experiment, during a simple heating or cooling process we know that the specific humidity (ω) remains constant, but the temperature and the relative humidity change (Ø). We can change or add the process with include humidified or dehumidified, sometimes air is humidified after it is heated, and some cooling processes include dehumidification. In dry climates, air can be cooled via evaporative cooling by passing it through a section where it is sprayed with water. Most air conditioning processes can be modeled as steady flow processes, and therefore they can be analyzed by applying the steady flow mass (for both dry air and water) and energy balances. As a conclusion, the objective of the experiment has been achieved and successfully. The process will change the temperature of wet and dry if there have any other heater or reheated. We can see the result and the change of the temperature in process A, B, C and D where there have difference process. Else where, all the parameters involved in each and every process too have been calculated and solved wholly.

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