KOTA DAMANSARA

B.ENG (Hons) MECHANICAL ENGINEERINGIn collaboration with

AIR CONDITIONING

Thermofluids and Engines EAT223LEVEL 2

STUDENT NAME : Mohammed Umer QureshiSTUDENT ID : SCM-028698LECTURER : Dr VinodDATE OF SUBMISSION : 5TH May 2014

Objective

Our main objective in this experiment is to study the cooling and heating effects in an air conditioning system by altering the speed of the blower. Additionally, the experiment was also carried out to determine the heating power of the heaters and the cooling power of the cooling coil in the evaporator. We will utilise a preheater in the system. The cooling process will be tested to analyse the temperature change of air at the outlet in the absence of a pre heater. Alongside the heating and cooling process, water vapour present in the air (humidify effect) will be analysed whenever there is a change in speed of the blower. For every change in the air pressure, the temperature of the refrigerant at every stage of the cycle will be noted recorded and analysed.

Introduction

In the broadest senseair conditioningcan refer to any form of cooling, heating, ventilation or disinfection that modifies the condition of air, typically for thermal comfort. The more common use ofair conditioningis to mean cooling and often dehumidification of indoor air, typically via refrigeration.

Figure: This is the Schematic Diagram of the Air-conditioning Module

Heat flows in direction of decreasing temperature, i.e., from high-temperature to low temperature regions. The transfer of heat from a low-temperature to high-temperature requires a refrigerator and/or heat pump. Refrigerators and heat pumps are essentially the same device; they only differ in their objectives,

Heating process

Heat transfer is the movement of heat from solid, liquid or gas materials to other solid, liquid and gas materials. According to the second law of thermodynamics, heat always flows from a material at a high temperature to a material at a low temperature. For heat to transfer there has to be a temperature difference between the two materials.In general the sensible heating process is carried out by passing the air over the heating coil. This coil may be heated by passing the refrigerant, the hot water, the steam The hot water and steam are used for the industrial applications.The sensible heating process is also represented by a straight horizontal line on the psychometric chart. The line starts from the initial DB temperature of air and ends at the final temperature extending towards the right (see the figure). The sensible heating line is also the constant DP temperature line.

Cooling processIn this Air-conditioning system the air is cooled by a direct evaporator. In large-scale systems so-called cold-water sets are frequently interposed, allowed for indirect cooling. From the compressor outlet the refrigerant flows into the condenser; the condenser is basically a heat exchanger that enables the heat transfer from the warm gaseous refrigerant to the surroundings at the outlet of the condenser the refrigerant is in a liquid phase at high pressure and from here it passes on to the expansion valve. Across the expansion there is a major pressure drop from the high pressure side to the low pressure side. This causes an expansion of the liquefied refrigerant from a high pressure small volume to a low pressure large volume. This abrupt change in pressure causes some of the refrigerant to evaporate, this phase change causes the temperature of the refrigerant to drop (the valve is insulated and cannot take up heat from the surroundings). At the outlet of the expansion valve the refrigerant is now partly liquid partly gas (in the two phase region) and has a low temperature and a low pressure. From the outlet of the expansion valve the refrigerant flows to the evaporator; the evaporator is basically a heat exchanger that enables heat transfer with the surroundings e.g. a cold storage room or any other industrial application.

The Reversed Carnot Cycle

The Reversed Carnot Cycle Reversing the Carnot cycle does reverse the directions of heat and work interactions. A refrigerator or heat pump that operates on the reversed Carnot cycle is called a Carnot refrigerator or a Carnot heat pump.

Diagram : T-s diagram and major components for Carnot refrigerator.The reversed Carnot cycle is the most efficient refrigeration cycle operating between two specified temperature levels.1-2: A reversible, adiabatic (isentropic) compression of the refrigerant. The saturated vapour at state 1 is superheated to state 2-3: An internally, reversible, constant pressure heat rejection in which the working substance is de-superheated and then condensed to a saturated liquid at 3. During this process, the working substance rejects most of its energy to the condenser cooling water 3-4: An irreversible throttling process in which the temperature and pressure decrease at constant enthalpy. The refrigerant enters the evaporator at state 4 as a low-quality saturated mixture. h3 = h4 4-1: An internally, reversible, constant pressure heat interaction in which the refrigerant (two-phase mixture) is evaporated to a saturated vapor at state point 1. The latent enthalpy necessary for evaporation is supplied by the refrigerated space surrounding the evaporator. The amount of heat transferred to the working fluid in the evaporator is called the refrigeration load

The Psychometric chart

It is used for detecting the changes of state of the air in air-conditioning systems. The changes of state of the air caused by heating and cooling can be plotted. The Psychometric chart shows the following constants as lines or curves:

tp: Relative air humidity in %t: Temperature in Ch: Enthalpy in kJ/kgx: Absolute humidity in kg/kg.

Apparatus Pressure gauge ManometerCompressorEvaporatorCondenserBlower

Complete Equipment Picture

The Blower and the Pressure Gauges

The Preheater and Evaporator

Base Condensing Unit, Contains all the probes and selectors for different selectionsPROCEDUREFor the heating process:1. The solenoid valve with the receiver was selected.2. Solenoid valve selector is set to expansion valve (SV3).3. The condensing unit is switched on.4. The blowers was switched on and regulated at a lower speed.5. The temperature and relative humidity at the inlet (AT1, AH1) and outlet (AT2, AH2) of the cooling coil was reached once steady state was reached. A steady state condition was reached when the digital readings for AT1 AND AH1 had stopped fluctuating.6. Reading for the pressure differential was recorded from the manometer.7. All four refrigerant temperatures were recorded by turning the nob each time (TT1, TT2, TT3, and TT4) followed by analogue readings from the pressure gauges (P1, P2).8. The blower speed regulator was rotated again to gradually increase the speed and step 5,6,7 and 8 were repeated 3 more times each time the blower speed was increased to acquire a total of 5 sets of readings of temperature, pressure and humidity while keeping the initial setting unchanged.9. All the switches were closed once the readings were acquired.For cooling process:1. The solenoid valve with receiver was selected.2. Solenoid valve selector was kept on expansion valve (SV3).3. The condensing unit was switched on.4. The preheater was switch on.5. The blower was switched on and the lowest speed was selected.6. The temperature and relative humidity at the inlet (AT1, AH1) and (AT2, AH2) of the preheater were recorded once the process was stabilized in approximately 15 minutes.7. The blower regulator speed was changed gradually (increasing it) and step 6 was repeated.8. Step 7 was repeated 2 more times to acquire 4 sets of reading in total, while waiting 15 minutes after each regulation to stabilize the system ResultCooling processManometerAir temperatureRefrigerant temperatureRelative humidity %Pressure gauge (psi)

P, N/AT1AT2TT1TT2TT3TT4AH1AH2P1P2

5028.715.111.438.139.28.750.781.2138.035.5

10029.015.813.239.140.09.848.589.9142.241.2

15029.216.613.438.939.79.945.792.2142.234.1

20029.316.213.739.139.910.445.093.0142.234.1

25029.316.413.939.240.510.645.193.6142.234.1

HEATING PROCESS

ManometerAir temperatureRelative humidity %

P, N/AT1AT2AH1AH2

5026.622.350.573.5

10026.422.250.670.4

15026.222.550.967.8

20026.122.851.266.7

25026.122.951.768.9

CalculationsDiameter of the air duct = 12cm .12mAir duct cross sectional area, A = x 0.01 h2 = 38h1 = 59.8

Simple calculation

WhenAT1 = 28.7 and AH1 = 50.7, the h1 = 59.8kJ/kg

When AT2 = 15.1 and AH12= 81.2, the h1 = 38kJ/kg

To calculate the velocity of the air across the orificev = 0.598 x = 0.598 x

= 329.90 ms-1By assuming the density of air at 1 atom pressure is equal to 1.1055/v = 0.598 = 5.687m/s

Area of the orifice A = =0.01Q = 329.90 x0.01= 3.299s-1M = 1.225 x 3.299 = 3.956 kgs-1

h2 = 51hh1 = 68

WhenAT1 = 26.6 and AH1 = 0.51he h1 = 53kJ/kgWhen AT2 = 22.3 and AH12= 0.74 the h2= 54kJ/kgAssuming the density of air at 1 atom pressure is equal to 1.1055/@ AT1 = 26.60 and AH1 = 0.51, H1 = 53 kJ/kg@ AT2 = 22.30 and AH2 = 0.74, H2 = 54 kJ/kg

Power in the heaterW = H2 H1 = 54 53= 1 kJ/kgPower = W x M= 1 x 3.956= 3.956 kJs-1Cooling Power of the cooling coil@ AT1 = 28.70 and AH1 = 0.51, H1 = kJ/kg@ AT2 = 15.10 and AH2 = 0.81, H2 = kJ/kg

Discussion

In this experiment we accomplished to study the heating and cooling effect and to determine the heating power of the heaters and the cooling power of the cooling coil. From the results of the experiment it can be seen that the air temperature decreases after undergoing i.e. thats the cooling process. The pressure decreases after exiting the expansion valve which helps the evaporator to change the state of the working fluid to vapour. However, the humidity is also increases in the re-heat process which controls and varies the humidity levels throughout the process.

From the Cooling Table at an air pressure of 50 N/, the entering temperature was 27.1. The air of this temperature passes through the cooling coil in the evaporator, and then the refrigerant takes in the heat from current air temperature reduces its temperature to 15.1. The humidity of air before reaching the evaporator was 0.57 whereas at the outlet it was found to be 0.81 as the air crosses the humidifier and means that the water vapour is reduced.

According to heating results at an air pressure of 50 N/, the entering air temperature was 26.6. As it passes through the preheater, the temperature of air was further raised by few degrees and allowed to pass through the evaporator. Evaporation occurs the hot air ,cools the air temperature to 22.2 and humidity level increases from 0.5 to0.73

Comparing the 2 processes and taking into account of the cooling process,, this experiment were had some acceptable errors which have affected the experiment but cannot be compensated such as human error. Overall it was successful, we established our aim, attained knowledge required to understand the processes.