AL-Qadisiyah University College of Engineering
Department of Mechanical Engineering
Laboratory brochure SINCE 2016
Air Conditioning and Refrigeration Laboratory By Ahmed Thabit Abed AL-Rubaye Assistant Lecturer in Department of Mechanical - AL-Qadisiyah University
https://sites.google.com/site/engahmedalrubaye/ Mail:
[email protected]
College of Engineering Department of Mechanical Engineering
AL-Qadisiyah University
Air Conditioning and Refrigeration Laboratory For students of the fourth stage by MSc.Ahmed Thabit Abed AL-Rubaye Time: Two hours every week Contains (Exp.1 to Exp.10)
Exp.No.1 Psychometric processes (Heating and Humidification) Psychrometric is the study of air and water vapor mixtures. Air is amixture of five main gases. Nitrogen 78.03%, Oxygen 20.99%, Argon 0.94%, Carbon Dioxide 0.03%, and Hydrogen 0.01% by volume. The Ideal Gas Laws are used to determine psychrometric data for air so that the engineer can carry out calculations. easier a chart has been compiled with all the relevant psychrometric data indicated. This is called the Psychrometric Chart. A typical chart is shown below. Relative Humidity RH %
Air at any state point can be plotted on the psychrometric chart. The information that can be obtained from a Psychrometric Chart as follows: Dry bulb temperature ( DBT) oC . Wet bulb temperature ( WBT) oC . Moisture content (humidity ratio or specific humidity)(w) Relative humidity (RH) ( ϕ=100 %) . Specific enthalpy (h) kJ/kg . Specific volume (v) m3/kg 1
If any two properties of air are known then the other four can be found from the psychrometric chart. This chart is designed for a barometric pressure of 1.01325 Bar which is a figure for a standard atmosphere at sea level. However, under extreme weather conditions or at very high or very low (below sea level) altitudes the effect of barometric pressure will become significant. Note: 1 mbar = 0.001 bar = 100 N/m2 = 102 Pa = 0.749mm Mercury Bar= 105 Pa= 102 kPa
practice: Find the specific volume, wet-bulb temperature, moisture content(W) and specific enthalpy of air at 35oC dry-bulb temperature and 30% Relative Humidity. Sol: A vertical line is drawn upwards from 35oC dry-bulb temperature until it intersects with the 30% RH This intersection is the state point. Where: specific volume = 0.88775 m3/kg wet-bulb temperature =21.55oC dew-point temperature=14.87 oC ( horizontal line to the lift) moisture content =0.0105 kg w.v /kg dry air ( horizontal line to the right) specific enthalpy =62.25 kJ/kg vapor pressure =1.68835 bar ( horizontal line to the right)
Basic Air Conditioning Processes
O
2
1.Sensible Cooling and Heating When air is heated or cooled sensibly, that is, when no moisture is added or removed, this process is represented by a horizontal line on a psychrometric chart. For sensible heating:
(OC)
2.humidification and dehumidification: (latent heat) Is the process in which the moisture or water vapor or humidity is added to the air without changing its dry bulb (DB) temperature. This process is represented by a straight vertical line on the psychrometric chart starting from the initial value of relative humidity, extending upwards and ending at the final value of the relative humidity. Humidification (OA) Dehumidification (OE) In actual practice the pure humidification process is not possible, since the humidification is always accompanied by cooling or heating of the air. Heating and Humidification (OB) Add some moisture to the supply air by injecting steam into the air stream. Cooling and Humidification (OH) The moisture is added to the air by passing it over the stream or spray of water which is at temperature lower than the dry bulb temperature of the air (evaporative cooler ), ( adiabatic cooling). Heating and Dehumidification (OD) Same chemical industry needs heating with dehumidification process. Cooling and Dehumidification (OF) The most commonly used method of removing water vapour from air (dehumidification) is to cool the air below its dew point. 3
Exp.No.2 Psychometric Processes (Cooling with Adiabatic Humidification) 1. Object . To study the psychometric Processes of the air . To estimate the average heat transfer to the air. 2. Apparatus The apparatus consist of the following part as shown in Fig (1). . Centrifugal air fan. · Electric heaters. . Humidifier · Electrical control panel. . Thermometers . Air duct. . Grille. . Digital Flow meter.
Figure (1)
4
3. Theory The four main psychometric processes are : Cooling with Adiabatic Humidification
4. Procedure a. Fill the container with water b. Operate the water-pump. c. Operate the Air fan. d. Read the inlet and outlet temperature of the humidifier at points (A)&(C). e. State the process on the psychometric chart. g. After few-minutes read the temperature in points (A) & (C). h. State the process on the psychometric chart. 5.Readings B
6.Calculations a. State the processes on the psychometric chart. b. Sketch the psychometric chart. c. Calculate the heat transfer QAc. 7.Results QAc. kw
9.discussion · Discuss your results. 5
Exp.No.3 Air Conditioning Cooling 1.Introduction Many recent air conditioning units use the technology of reversing vapour compression cycle in cooling and heating processes ,as it is more veliable ,less danger and high performance ,by means of using a reverse valve (Two way valve) ,this way of cooling and heating is so called (mechanical heat pump). 2.Object Study the performance of heat pump / cooling at different loads of condenser (different mass flow rates of air passing over the condenser). 3.Theory a- condenser Heat rejected by Freon to air passing through condenser , or the heat absorbed by air from Freon across the condenser.
Q = m ⋅ a Cp a (Ta 2 − Ta1 ) OR Q air = m⋅air (h − h ) out in ⋅
air mass flow rate (Kg/sec)= m a = specific heat at constant pressure (kJ/kg.K) Cp a
( C) inlet and outlet air temperature Ta 2 = and Ta1 Where =air mass flow rate passing through evaporator (kg/s) m⋅air ⋅ = p.V.A m air
6
b-Evaporator Heat absorbed by Freon from air ,or heat absorbed by atmospheric air from Freon in evaporator
Q air = m⋅air (h 1 − h 2 ) Where =air mass flow rate passing through evaporator (kg/s) m⋅air ⋅ = p.V.A m air Where P=air density (kg/m3) V=air velocity (m/s) (m2) A = area of outlet section = h1 & h2 =inlet and outlet air enthalpies which can be found from psychometric chart.
c-compressor Input power (Compressor work ) can be estimated directly from Kilo Watt meter at the apparatus.
Wcomp = Wtotal − Wfan Where Wfan=work of fan (kW) Wtotal=work of fan and compressor(kW) 7
D-Coefficient of performance
C.O.P ]cooling = Q e / Wcomp Where Qe=Refrigeration effect = Qair assuming zero By pass factor
C.O.P ]cooling = Q air / Wcomp
E-Psychometric chart Use psychometric chart to explain the processes which carried on the atmospheric air in evaporator and to estimate the inlet and outlet enthalpies of air (h1 & h2 ) by using dry and wet bult temperatures.
8
4.Apparatus Schematic drawing of the apparatus used in the experiment shown Below
5.procedure: a. Connect the power to the device . b- Operate the unit (fan only )and measure Wfan then operate compressor and reversing valve . c- Adjust the air flow rate in Rotometer . e- Wait for (5)minutes to take readings . d- Read the total power supply ( Wcomp÷fan ) . f- Read the inlet and outlet temperature of air (dry and wet temperature ) and velocity of air at the air side . g- Read the inlet and outlet temperatures, and the flow rate of air at air side. h- Repeat the procedure for further readings. 6.Readings: Condenser
Inlet air
No
Td1
C
Evaporator
Inlet air
Outlet air
Outlet air
Tw1
Td2
Tw2
Td1
Tw1
Td2
Tw2
C
C
C
C
C
C
1 2
9
C
Fan Work kW
Total Work kW
Air Velocity y u m/s
7.Calculations: Calculate: a-Heat absorbed by air in evaporator (Qair kW) b- Heat rejected in the condenser ( Qair kW ) . c-Compressor work. d-C.O.P of cooling.
8.Results: Use the table below for your calculation:
No
Vw 1/m
Qair kW
Qair kW
Wcomp kW
C.O.P cooling
9.Graphics Plot the following relationship
10.Discussion: Discuss the effect of air flow rate on Qair condenser , Qair Evaporator , Wcomp , and C.O.P cooling.
10
Exp No.4 Thermo-Electric Heat Pump Performance 1-Introduction Thermo electric cooling uses the Peltier effect to creat a heat flux between the junctions of two different type of material. Apeltier cooler, heater or thermo electric heat pump is a solid -state active heat pump which transfer heat from one side of the device to the other with consumption of electric energy, depending on the direction of the current. They can be used either for heating or cooling (Refrigeration), although in practice the main application is cooling. A peltier cooler can also be used as a thermo electric generator .when operate as a cooler, a voltage is applied across the device, and as a result in difference in temperature will build up between the two side .when operating as generator, one side of the device is heated to a temperature greater than the other side, and as a result a difference in voltage will build up between the two side (the see beck effect). 2-Object of experiment To study the performance of the thermo electric, heat pump by calculation: 1- peltier effect 2-Thomson 3-effectseebeck 4-effect C.O.P 3-Semi Conductors The material that used in the thermo electric heat pump are 36 semiconductors which have the following properties . 1-High convesion factor with respect to flowing current 2-High electric conductivity = I2R 3-Low thermal conductivity. there semiconductors are an alloy made of Biz mouth chloride (Sb2te3 b12te3) represent the P type as it is poor in electrons and the other alloy is 11
(bi2se3 - b12te3) which represent the N type and it is rich with electrons .the two unique semiconductors one N type and one P type are used because they need to have different electron densities .the semiconductors are placed thermally in parallel to each other and electrically in series and then joined with thermally conducting plate on each side. when a voltage is applied to the free end of the two semiconductors there is a flow of DC current across the junction of the semi-conductors causing temperature different .the side with the cooling plate a bsorbit heat which is then moved to the other side end of the device where the heat sink is TEHP are typically connected side by side and sandwiched between two ceramic plate. the device is equiped with a variable resistance(loud) ,voltmeter ,a meter ,wattmeter ,fan , thermometer ,for cold and hot side and two away switch and electrical heater (loud).
12
Exp.No.5 Mixing Of Outdoor Air and Recalculated Air Introduction: Mixing of several streams is the process which very frequently used in air conditioning. The mixing normally takes place without edition or rejection of heat or moisture i.e adiabatically at constant total moisture constant. The mixing process are used in determines a confortable climate inside occupation zones and supply the required amount of fresh air to the space in order to maintain human comfort and energy conservation purposes. Object Of Experiment To obtain the properties of air after mixing of specified quantities of return air fresh [outside] air. The mixing is obtained by adjusting the return air control damper from 0 to 100% . the required mixing properties include [DBT, WBT, RH, h, … etc] Apparatus Figure [1] shows the apparatus used in the mixing. The locations of points A to F are as follows: Point A is before the fan. Point B is after Pre- heater. Point C is after the cooling coil . Point D is after Re-heater. Point E is at the return duct, near and before the exhaust outlet . Point F is the fresh air inlet section. At Point E there is internal orifice plate to allow for measuring air flow rate . after the orifice plate there is a T- section with an exhaust and gravity operated flap valve on discharge. There is a main volume flow damper and mixing box at the end of return bend duct. Fresh air is brought into the system through an orifice plate at measuring Station F. This orifice plate is retained from the discharge of the basic Air Conditioning Laboratory unit A660. By comparing the total flow through the internal orifice plate at Station E and the 13
fresh air at Station F, the volume of recirculated air may be adjusted as required. After mixing, the air continues to the fan inlet measuring Station A. Adjustment of the volume control damper allows the recirculation to be varied from 0 to approximately 100%. However, the maximum sustainable degree of recirculation will depend upon the local ambient conditions and the amount of steam or heating that is applied, assuming that the refrigeration plant is also running.
Figure(3)
14
Exp.No 6 Refrigeration System 1-Object: To demonstration the refrigeration cycle components and to determint the coefficient of performance of the cycle. 2-Apparatus: The electric refrigeration training unit work with R 134a and consists of compressor, condenser, expansion valve and evaporator. There are also measurement device for temperature, pressure, voltage, current and mass flow rate of the system show in figure.
Figure (2) The P-H diagram for the refrigeration cycle Figure (1)
15
Exp. No 7 Refrigeration Unit Performance 1.Object: To demonstration the refrigeration cycle components and to determine the coefficient of performance of the cycle experimental. 2.Apparatus: The electric refrigeration training unit work with R134a and consists of compressor,condenser, expansion valve and evaporatoras show in figure (2). There are also measurement devices for temperature, pressure and mass flow rate of the refrigeration.
Figure (1)
16
Ideal refrigeration cycle schematic arrangement of mechanical equipment
Ideal refrigeration cycle plotted on P-h diagram
Figure (2)
Figure (3)
17
Exp. No.8 Cooling Coil Capacity Calculation 1:Introduction: For an air conditioning system to operate continsety, the refrigerant must be used repeatedly. For this reason, all air conditioners use the same cycle of compression, condensation, expansion, and evaporation in a closed circuit. The same refrigerant is used to move the heat from one area, to cool this area, and to expel this heat to another area evaporator represent and cooling coil in A/C system. 2-Object: Calculating the cooling coil capacity.
Figure (1) Unit Refrigeration Laboratory 3-Basic Refrigeration Cycle • The refrigerant anther the compressor at a low-pressure and temperature gas, it is compressed and then discharge out of the compressor as a high-pressure and temperature gas. • The gas then flows to the condenser. Here the gas condenses to a liquid, and gives off its heat to the outside air. • The liquid then moves to the expansion valve under high pressure. This valve restricts the flow of the fluid, and reduuse its pressure and then leaves the expansion valve. • then The low-pressure liquid and gas moves to the evaporator, where is absorbed from room air and the refrigeration changes from a liquid to a gas. • The low-pressure gas, of refrigerant moves to the compressor and the cycle is repeated. 18
Refrigeration in side the evaporator and condenser charge Liquids absorb heat when changed from liquid to gas.(ie.Latent heat for vaporation) Gases give off heat when changed from gas to liquid. (ie.Latent heat for condensation). The four-part of cycle can be divided a high pressure side and a low pressure side refers to the pressures of the refrigerant in each side of the system The pressures recorded from the system are in gauge relative to atmosphere. In order to convert these to absolute pressure the local atmospheric pressure must be added. The atmospheric pressure was 1010 mBar=101 kN/m2 Pabs = Pg + Patm A measurable pressure drop exists in the condenser due to friction effects. The condenser is a commercial unit and as such is designed by the manufacturers with minimum cost as a prime consideration. The evaporator, designed for the unit was oversize diameter tube to reduce the pressure drop to a negligible value. 4-Experiment Apparates: The air condition unit is shown in figure (1) is Unit Refrigeration Laboratory. The detail of its component is give.
5-P-h Diagram of the basic Refrigerant cycle: Using the absolute pressures and temperatures recorded around the refrigeration system, a full cycle diagram may be drawn on a refrigerant R134a pressure-enthalpy diagram. The state points may be determined as follows. Refer to Figure (2) where the state points are shown diagrammatically.
19
Figure (2) P-h diagram for the experimental refrigeration cycle.
Figure (3) Refrigeration cycle processes on a P-h diagram of R 134 a . Vapor compression Refrigeration Cycle Processes: 1. Evaporator Outlet/Compressor Inlet (State Point 1) Locate pressure P1 on the chart a horizontal line and its intersection with a superheated temperature of(t13). The vertical Enthalpy line h1and the specific volume 1at this point can be found. 20
2. Condenser Inlet (State Point 2) Locate the pressure P2at Condenser inlet as a horizontal pressure line and its intersection with a superheated temperature of (t14). The vertical Enthalpy line h2at this point can be found. 3. Condenser Outlet (State Point 3) Locate the pressure P3 at Condenser outlet as a horizontal pressure line and its intersection with the vertical sub-cooled liquid line from (t15) saturated liquid condition. If this point (3)found on the saturated liquid line. This indicates that the liquid is not sub-cooled. The Enthalpy h3at this point can be found. After leaving the condenser the liquid enters the receiver and passes to the expansion valve where it is assumed to expand adiabatically from P3 to P4. Hence a vertical line is drawn from State point 3 to State Point 4. Thehorizontal pressure P4 line also corresponds to a line of constant enthalpy between the saturated liquid and saturated vapour conditions at P4 . The temperaturet16 of saturation at P4 can be found from tables. The state points are shown on a real R134a Pressure-Enthalpy Diagram for reference in Figure (3). The conditions may also be determined from the R134a tables provided. The following conditions may be determined for the refrigeration system: h1, h2 , h3 , h4 , v1( from P-h diagram) and t16 ( temperature saturation from tables at P4)
21
Exp. No 9 Automobile Air Conditioner 1 .General : Refrigeration is defined as “the transfer of heat from a lower temperature region to a higher temperature one”. Some examples of refrigeration devices are refrigerators, automotive air-conditioners, and residential / commercial air-conditioners. All of these devices have one thing in common, to reduce the temperature of an enclosed environment. 2.Object : a)Demonstration on refrigeration cycle configuration and apparatus. b) study: 1- Effect of variable load on c.o.p 2-Effect of variable compressor speed on c.o.p 3.Apparatus : The automobile air conditioner training unit is shown in figure 5.1 and Figure 5.2. It is consist of three phase induction motor , compressor , condenser ,evaporator , dehydrating filter , pressure gauges ,digital thermometers ,expansion valve and electrical resistances (is simulate the human body heat rejection ) . The unit works with R134a and the charge is 0.6 kg.
22
Control board
Evaporator Cooled room
Receiver
Motor
Wheeled steel frame
Figure 5.1 Automobile training Air Conditioner
23
Exp. No.10 Refrigeration Cycle Performance at Variable Speeds of Compressor 1. Introduction: Issue in brief statement about variable speeds compressor systems. 2. Objects: a. To study & draw the cycle at variable speeds b. To calculate refrigeration effect and C.O.P for each case. 3.Theory: a. Write more details about variable speeds systems. b. Equations used in experiment are: o 1: Q evaporator (R.E.) : m R12 (h1-h4) 2: Compressor work: o -Theoretical = m R (h2-h1) (Output) - Actual = 2πrN × 2 F (input) 3- Heat rejected from condenser: o Q(cond.) = m R (h2-h3) o
Q(cond.) = m water Cpw∆tw 4- Mechanical Efficiency: o
m R12( h2 − h1 ) ηm = 2πrN × 2 F 5- C.O.P coefficient of performance: h1 − h4 Q .Evaporator = - Theoretical = h2 − h1 Wcomp .( theoretical ) o
o
m ( h1 − h4 ) m ( h1 − h4 ) -Actual = = Wcomp( Actual ) 2πrN × 2 F
Where: R.E= Refrigeration effect (Kw) or (Q. Evaporator ) o Wcomp=Compressor R12 mass flowrate = ρ 12 V R12 (kg/s) 24
h1,h2,h3,h4 specific enthalpies as shown . N= Revoultions per second r=torque.radius = 15 cm F= motor. motive force 4. Apparatus: a. Draw the apparatus & point the parts b. write about the apparatus in brief c. Draw schematic drawing showing the parts and points of the cycle
5.Procedure: Write the steps followed to do the experiment 6.Readings: Take the following readings shows in this table T1
T2 T 3
T
T
T
T
T
T
P
4
5
6
7
8
9
1
o
o
o
o
o
o
o
o
o
C
C
C
C
C
C
C
C
C
P1′
P 2
b ba b ar r ar
R W
Rr1 2
N Ic I F h A A N
T1: R12 temp compressor delivery , T2:R12 condenser inlet temp T3: Water inlet temp to condenser , T4: Water out of condenser T5: R12 out of condenser , T6: Glycol solution temperature T7: R12 temperature after expansion, T8: R12 temp after evaporator T9: R12 temp inlet of compressor , P1: Evaporator pressure (Lp)[bar] P1′ =compressor suction pressure (P) , P2 : compressor delivery (HP)[bar] RW: water flow rate through condenser ( ) , RR12:R12 flow rate ( ) N: compressor no. of revolution per second (RPS) , Ic: motor current Ih: Heater current (A) , F: motor motive force.
25
7. Calculatations & results: a. Calculate (one sample) 1. Refrigeration EffecERE (the conditions of T7, T8,P1 should be used) 2. Compressor work (using the conditions of ( P1′ , T9) (P2, T1) 3. Q condenser (Freon, Eater) using inlet & outlet for both 4. C.O.P theoretical and actual 5. State the actual and the theoretical cycle on Ph diagram of R12 6. Plot the curves showing the relationship between N (revolution/sec) and the following: a: RE , b: C.O.P theoretical, c: C.O.P actual d: of compressor , e: Q(condenser) 8: Discussion: a. b. c. d.
Show the aim of experiment Express your idea about readings Discuss the results with explanations Write about similar systems , (cars , automobiles)
26
