SOLTEQ ®
EQUIPMENT FOR ENGINEERING EDUCATION
EXPERIMENTAL MANUAL
WATER COOLING TOWER
Table of Contents Page List of Figures............................................................................................................................... i 1.0. INTRODUCTION ……………………………………………………………….……………………1 2.0. GENERAL DESCRIPTIONS DESCRIPTIONS 2.1 Components of the HE152 Basic Cooling Cooling Tower Tower Unit Unit …………………..… ..….... ........................ 2 2.2 The Proces Process s Invol Involved ved in in the the Operat Operatiion ………………………………………………... …... 5 2.3 Over Overall all Dimen Dimensi sion ons……… s……………………………………………………………………….. 5 2.4 Gener General al Requi Requirrement ements……… s…………………………………………………………………….5 …. 5 3.0 SUMMARY OF THEORY 3.1 Basic Basic Princi Principl ple e ………………………………………………………………............... 6 3.2 Evaporati Evaporation on from a Wet Surface Surface …………………………….... ............................... ...................... ........... 6 3.3 Cooli Cooling Tower Tower Perf Performanc ormance…… e………………………………………………………….. 6 3.4 Ther Thermod modyn ynami amic c Prope Properrty……………………………………………………………… 7 3.4.1 Dalt Dalton’ on’s and and Gibbs Laws…… Laws…………………………………………………….. 7 3.4.2 Psyc Psycho homet metrric Char Chart…………………………………………………………… 8 3.5 Ori Orifice Cali Calibrat bratiion…… on…………………………………………………………………………. 9 3.6 A .6 Ap pplic licatio tion of Steady Flow low Energy Equatio tion………………………………………….. 10 3.7 Charac Charactteri eristi stics Column Column Study Study…… ………………………………………………………….. 13 3.8 Usef Useful Infor nformat matiion …… 16 16
APPENDIX A
Experi Exp erimen mental tal Data Sheets Sheet s
APPENDIX B
Sample Samp le Resul Res ults ts and Calcul Calc ulati ation on
APPENDIX C
Compo Com ponen nents ts Pro Proper pertities es and Diagram Diag ram
APPENDIX D Pro Proces cesss Flow Fl ow Diagram Diag ram
List of Figures Figures
Page Figure 1
Parts Identifi Identificati cation on and Equipment Equipment Set-up of Bench Top Cooli Cooling ng Tower Tower
4
Figure 2
System A
10
Figure 3
System B
12
Figure 4
Schemati Schematic c Representations Representations of the Air and Water Streams entering entering and leaving leaving a Block of Packing
13
Graphical Representation of Tower Tower Characteristi Characteristics cs
15
Figure 5
SOLTEQ® BENCH TOP COOLING TOWER UNIT UNIT (MODEL: HE152)
1.0
INTRODUCTION The SOLTEQ® Basic Cooling Tower Unit (Model: HE152) has been designed to demonstrate students the construction, design and operational characteristics of a modern cooling system. The unit resembles a full size forced draught cooling tower and it is actually an "open system" through which two streams of fluid (in this case air and water) pass and in which there is a mass transfer from one stream to the other. The unit is selfcontained supplied with a heating load and a circulating pump. Once energy and mass balances are done, students will then be able to determine the effects on the performance of the cooling tower by the following parameters: a) Temperature and flow rate of water b) Relative Humidity and flow rate of air c) Cooling load Ad Additio ition nally lly, a Packing ing Charac racter teristi istic cs Colum lumn (op (optio tional) is is av availa ilable for for SOLTEQ® Basic Cooling Tower Unit (Model: HE152). This column is designed to facilitate study of water and air conditions at three additional stations (I, II and III) within the column. This enables driving force diagrams to be constructed and the determination of the Characteristic Equation for the Tower.
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
2.0
GENERAL DESCRIPTIONS 2.1
Components of the HE152 Basic Cooling Tower Unit The unit comes complete with the following main components: i)
Load Tank The load tank is made of stainless steel having a capacity of approximately 9 liters. The tank is fitted with two cartridge heaters, 0.5 kW and 1.0 kW each, to provide a total of 1.5 kW cooling load. A make-up tank is fixed on top of the load tank. A float type valve at the bottom of the make-up tank is to control the amount of water flowing into the load tank. A centrifugal type pump is supplied for circulating the water from the load tank through a flowmeter to the top of the column, into the basin and back to the load tank. A temperature sensor and temperature controller is fitted to load tank to prevent overheating. A level switch is fitted to the load tank so that when a low level condition occurs, the heater and the pump will be switched off.
ii) Air Distribution Chamber The stainless steel air distribution chamber comes with a water collecting basin and a one-side inlet centrifugal fan. The fan has a capacity of approximately 251 CFM of air flow. The air flowrate is adjustable by means of
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
iv) Measurements Temperature sensors are provided to measure the inlet and outlet water temperatures as well as the make-up tank water temperature. In addition, temperature sensors have been installed to measure the dry bulb and wet bulb temperatures of inlet and outlet of the air. The followings show the list of codes assigned to each temperature sensors. T1 T2 T3 T4 T5 T6 T7 T8
Dry Bulb Temperature of the Inlet Air Wet Bulb Temperature of the Inlet Air Dry Bulb Temperature of the Outlet Air Wet Bulb Temperature of the Outlet Air Inlet Water Temperature Outlet Water Temperature Make up Tank Temperature Hot Water Tank Temperature
A differential pressure transmitter is provided for the measurement of pressure drop across the packed column. On the other hand, the differential pressure transmitter and the orifice are also used to determine the air flowrate. A flowmeter is provided for the measurement of water flowrate. The flowmeter is ranged at 0.4 to 4 LPM.
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
1 2
3 4 5
7 8 9
6 10
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
2.2
The Process Involved in the Operation i)
Water Circuit Water temperature in the load tank will be increased before the water is pumped through a control valve and flow meter to the column cap. Before entering the column cap, the inlet temperature of the water is measured and then the water is uniformly distributed over the top packing deck. This creates a large thin film of water, which is exposed to the air stream. The water gets cooled down, while passing downward through the packing, due to the evaporation process. The cooled water falls into the basin below the lowest deck and return to the load tank where it is re-heated before re-circulation. The outlet temperature is measured at a point just before the water flows back into the load tank. Evaporation causes the water level in the load tank to fall. The amount of water lost by evaporation will be automatically compensated by equal amount from the make-up tank. At steady state, this compensation rate equals the rate of evaporation plus any small airborne droplets discharged with the air.
ii) Air Circuit A one-side inlet centrifugal fan draws the air from the atmosphere into the distribution chamber. The air flow rate is varied by means of an intake damper. The air passes a dry bulb temperature sensor and wet bulb temperature
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
3.0
SUMMARY OF THEORY 3.1
Basic Principle First consider an air stream passing over the surface of a warm water droplet or film. If we assume that the water is hotter than the air, then the water temperature will be cooled down by radiation, conduction and convection, and evaporation. The radiation effect is normally very small and may be neglected. Conduction and convection depend on the temperature difference, the surface area, air velocity, etc. The effect of evaporation is the most significant where cooling takes place as water molecules diffuse from the surface into the surrounding air. During the evaporation process, the water molecules are replaced by others in the liquid from which the required energy is taken.
3.2
Evaporation from a Wet Surface When considering evaporation from a wet surface into the surrounding air, the rate is determined by the difference between the vapour pressure at the liquid surface and the vapour pressure in the surrounding air. The vapour pressure at the liquid surface is basically the saturation pressure corresponding with the surface temperature, whereas the total pressure of the air and its absolute humidity determines the vapour pressure in the surrounding air. Such evaporation process in an enclosed space shall continue until the two vapour pressures are equal. In other words, until the air is saturated and its temperature equals the surface.
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
The effect of these factors will be studied in depth by varying it. In this way, students will gain an overall view of the operation of cooling tower. 3.4
Thermodyn amic Property In order to understand the working principle and performance of a cooling tower, a basic knowledge of thermodynamic is essential to all students. A brief review on some of the thermodynamic properties is presented below. At the triple point (i.e. 0.00602 atm and 0.01°C), the specific enthalpy of saturated water is assumed to be zero, which is taken as datum. The specific enthalpy of saturated water (h f ) at a range of temperatures above the datum condition can be obtained from thermodynamic tables. The specific enthalpy of compressed liquid is given by h = h f + v f (p − p sat )
(1)
The correction for pressure is negligible for the operating condition of the cooling tower; therefore we can see that h ≈ h f at a given temperature. Specific heat capacity (C p ) is defined as the rate of change of enthalpy with respect to temperature (often called the specific heat at constant pressure). For the purpose of experiment using bench top cooling tower, we may use the following
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
same temperature. The Absolute or Specific Humidity is defined as follows: Specific Humidity ω = ,
Mass of Water Vapour Mass of Dry Air
(4)
The Relative Humidity is defined as follows: Re lative Humidity , φ =
Partial Pr essure of Water Vapour in the Air
(5)
Saturation Pr essure of Water Vapour at the same temperatur e
The Percentage Saturation is defined as follows: Percentage Saturation =
Mass of Water Vapour in a given Volume of Air
(6)
Mass of same vol of Sat Water Vapour at the same Temp
At high humidity conditions, it can be shown that there is not much difference between the "Relative Humidity" and the "Percentage Saturation" and thus we shall regard as the same.
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
3.5
Orific e Calibr ation As mentioned above, the psychometric chart can be used to determine the value of the specific volume. However, the values given in the chart are for 1 kg of dry air at the stated total pressure. However, for every 1 kg of dry air, there is w kg of water vapour, yielding the total mass of 1 + w kg. Therefore, the actual specific volume of the air/vapor mixture is given by: va =
v ab 1 + ϖ
(7)
The mass flow rate of air and steam mixture through the orifice is given by m = 0 0137 .
x va
Where, m = Mass flow rate of air/vapor mixture v a = Actual specific volume and x = Orifice differential in mmH20.
(8)
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
3.6
Application of Steady Flow Energy Equation Consider System A for the cooling tower defined as in Figure 2. It can be seen that for this system, indicated by the dotted line, a) b) c) d) e)
Heat transfer at the load tank and possibly a small quantity to surroundings Work transfer at the pump Low humidity air enters at point A High humidity air leaves at point B Make-up enters at point E, the same amount as the moisture increase in the air stream
B
a m
E
E m m
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
Note:
a ) through a cooling tower is a constant, a) The mass flow rate of dry air ( m whereas the mass flow rate of moist air increases as the result of evaporation process. E h E can usually be neglected since its value is relatively small. b) The term m Under steady state conditions, by conservation of mass, the mass flow rate of dry air and of water (as liquid or vapour) must be the same at inlet and outlet to any system. Therefore,
(m a ) A = (m a ) B
(13)
and
(m s ) A + m E = (m s ) B E = (m s ) B − (m s ) A m
or (14)
The ratio of steam to air (ϖ ) is known for the initial and final state points on the psychrometric charts. Therefore,
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
Say, we re-define the cooling tower system to be as in Figure 3 where the process heat and pump work does not cross the boundary of the system. In this case warm water enters the system at point C and cool water leaves at point D.
B
a m
C
w m E
E m a m A D
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
3.7
Characteristics Column Study In order to study the packing characteristics, we define a finite element of the tower (dz) as shown in Figure 4, the energy balances of the water and air streams in the tower are related to the mass transfer by the following equation: C pW m W dT = K a dV (∆h )
(20)
where C pW = Specific heat capacity of water m W = Mass flow rate of water per unit plan area of packing
= Water Temperature = Mass Transfer Coefficient = Area of contact between air and water per unit volume of packing = Volume occupied by packing per unit plan area ∆h = Difference in specific enthalpy between the saturated boundary layer and the bulk air
T K a V
T2
t2
WATER
H2
INLET
m
h2 AIR m OUTLET
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
Integrating Equation 21, Ka V m W
T2
= C pW
∫h
T1
dT w
− ha
(22)
The numerical solution to the integral expression Equation 22 using Chebyshev numerical method gives, Ka V m W
T2
= C pW
∫h
T1
dT w
− ha
=
T2 − T1
1 1 1 1 + + + h h h h ∆ ∆ ∆ ∆ 2 3 4 1
4
(23)
Where Ka V = Tower Characteristic m W
∆h1 = value of h w − h a at T 2 + 0.1(T 1 − T 2 ) ∆h 2 = value of h w − h a at T2 + 0 4(T1 − T2 ) .
(T − T ) = value of h w − h a at T − 0.1(T − T )
∆h 3 = value of h w − h a at T 1 ∆h 4
1
− 0.4
1
2
1
2
Thermodynamics state that the heat removed from the water must be equal to the
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
hw2 (Hot water Temp) Enthalpy
Enthalpy Water Operating Line C
ha2 (Air out) hw1 (Cold water Temp)
Air Operating Line A
L/G
Approach Twb (In)
(hw-ha)
D
B
Saturation Curve ha1 (Air in)
Driving Force
Range T1
Twb (Out)
T2
Temperature
Figure 5: Graphical Representation of Tower Characteristics
The following represents a key to Figure 5:
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
3.8
Useful Information 1.
Orifice Calibration Formula: Mass flow rate of air and vapor mixture,
= 0.0137 m
x(1 + ϖ ) v ab
The mass flow rate of dry air,
a = 0.0137 m
x v ab (1 + ϖ )
Where, x v a B
= orifice differential in mmH20, = specific volume of air at the outlet
ϖ
= humidity ratio of the mixture
2.
Pump Work Input = 80W (0.08kW)
3.
Column Inner Dimension = 150 mm x 150 mm x 600 mm
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
4.0
EXPERIMENTAL PROCEDURES 4.1
General Operating Procedures 4.1.1
General Start-up Procedures 1. Check to ensure that valves V1 to V6 are closed and valve V7 is partially opened. 2. Fill the load tank with distilled or deionised water. It is done by first removing the make-up tank and then pouring the water through the opening at the top of the load tank. Replace the make-up tank onto the load tank and lightly tighten the nuts. Fill the tank with distilled or deionised water up to the zero mark on the scale. 3. Add distilled/deionised water to the wet bulb sensor reservoir to the fullest. 4. Connect all appropriate tubing to the differential pressure sensor. 5. Install the appropriate cooling tower packing for the experiment. 6. Then, set the temperature set point of temperature controller to 50°C. Switch on the 1.0 kW water heater and heat up the water until approximately 40°C. 7. Switch on the pump and slowly open the control valve V1 and set the water flowrate to 2.0 LPM. Obtain a steady operation where the water is distributed and flowing uniformly through the packing. 8 Fully open the fan damper, and then switch on the fan. Check that the
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
4.1.2
General Shut-Down Procedure 1. Switch off heaters and let the water to circulate through the cooling tower system for 3-5 minutes until the water cooled down. 2. Switch of the fan and fully close the fan damper. 3. Switch off the pump and power supply. 4. Retain the water in reservoir tank for the following experiment. 5. Completely drain off the water from the unit if it is not in used.
4.2
Experiment 1: General Observation of the Forced Draught Cooling Tower Objective:
To observe the processes within a forced draught cooling tower 1. Perform the general start-up procedures and observe the forced draught cooling tower proves. 2. As the warm water enters the top of the tower, it is fed into channels from which it flows via water distribution system onto the packing. The channels are designed to distribute the water uniformly over the packing with minimum splashing. 3. The packing surfaces are easily wetted and the water spreads over the surfaces to expose a large area to the air stream. 4 The cooled water falls from the lowest packing into the basin and then is
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
4.3
Experiment 2: End State Properties of Air and Steady Flow Equations Objective:
To determine the “end state” properties of air and water from tables or charts To determine Energy and mass balances using the steady flow equation on the selected systems Procedure:
1. Prepare and start the cooling tower with according to Section 4.1.1. 2. Set the system under the following conditions and allow stabilizing for about 15 minutes. Water flow rate : 2.0 LPM Air Flow : Maximum Cooling load : 1.0 kW Column installed : A 3. Fill up the make-up tank with distilled water up to zero mark at the level scale, and then start the stop watch. 4. Determine the make-up water supply in an interval of 10 minutes. 5. In this 10 minutes interval, record a few sets of the measurements (i.e. temperatures (T1–T7), orifice differential pressure (DP1), water flowrate (FT1) and Heater Power (Q1)), then obtain the mean value for calculation and analysis. 6. Determine the quantity of make up water that has been supplied during the time interval by noting the height reduction in the make-up tank.
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
4.4
Experiment 3: Investigation of the Effect of Cooling Load on Wet Bulb Approach Objective:
To investigate the effect of cooling load on “Wet Bulb Approach” Procedure:
1. Prepare and start the cooling tower with according to Section 4.1.1. 2. Set the system under the following conditions and allow stabilizing for about 15 minutes. Water flow rate : 2.0 LPM Air Flow : Maximum Cooling load : 0 kW Column installed : A 3. After the system stabilizes, record a few sets of measurements (i.e. air inlet dry bulb and wet bulb temperature (T1 and T2), water outlet temperature (T6), orifice differential pressure (DP1), water flowrate (FT1) and Heater Power (Q1)), then obtain the mean value for calculation and analysis. 4. Without changes in the conditions, increase the cooling load to 0.5 kW. When the system stabilized, record all data. 5. Similarly, repeat the experiment at 1.0kW and 1.5kW. 6. Finally, measure the cross sectional area of the column. 7. The four tests may be repeated at another constant airflow. 8 The observation may also be repeated at different conditions, i.e. at different
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
4.5
Experiment 4: Investigation of the Effect of Air Velocity on Wet bulb Approach and Pressure Drop through the Packing Objective:
To investigate the effect of air velocity on: (a) Wet Bulb Approach (b) The pressure drop through the packing Procedure:
1. Prepare and start the cooling tower with according to Section 4.1.1. 2. Set the system under the following conditions and allow stabilizing for about 15 minutes. Water flow rate : 2.0 LPM Air flow rate : Maximum Cooling load : 1.0 kW Column installed : A 3. After the system stabilizes, record a few sets of measurements (i.e. temperature (T1-T6), orifice differential pressure (DP1), water flowrate (FT1). heater power (Q1) and pressure drop across packing (DP2)), then obtain the mean value for calculation and analysis. 4. Repeat the test with 3 different sets of orifice pressure drop values (75%, 50% and 25% of the maximum value) without changing the water flow rate and cooling loads. 5 Finally, measure the cross sectional area of the column.
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
4.6
Experiment 5: Investigation of the Relationship between Cooling Load and Cooling Range Objective:
To investigate the relationship between cooling load and cooling range Procedure:
1. Prepare and start the cooling tower with according to Section 4.1.1. 2. Set the system under the following conditions and allow stabilizing for about 15 minutes: Water flow rate : 2.0 LPM Air flow rate : Maximum Cooling load : 0.0 kW Column installed : A 3. After the system stabilized, record a few sets of measurements (i.e. temperature (T1-T6), orifice differential pressure (DP1), water flowrate (FT1) and heater power (Q1)), then obtain the mean value for calculation and analysis 9. Without changes in the conditions, increase the cooling load to 0.5 kW. When the system stabilized, record all data. 4. Similarly, repeat the experiment at 1.0kW and 1.5kW. 5. The tests may be repeated: i.At other water flow rates ii.At other air flow rate
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
4.7
Experiment 6: Investigation of the Effect of Packing Density on the Performance of the Cooling Tower Objective:
To investigate the effect of packing density on the performance of the cooling tower Procedure:
1. Prepare and start the cooling tower with according to Section 4.1.1. 2. Set the system under the following conditions and allow stabilizing for about 15 minutes: Water flow rate : 2.0 LPM Orifice differential : Maximum Cooling load : 1.0kW Column installed : A 3. After the system stabilizes, record a few sets of measurements (i.e. temperature (T1-T6), orifice differential pressure (DP1), water flowrate (FT1). heater power (Q1) and pressure drop across packing (DP2)), then obtain the mean value for calculation and analysis. 4. Without changing condition, change the column packing to column B. When stability is achieved, repeat the observation. 5. Repeat step 4 with column B and C. 6. The tests may be repeated: i. At other water flow rates
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
4.8
Experiment 7: Determination of Characteristic Equation of the Packing Characteristic Column Objectives:
To determine the Characteristic Equation of the cooling tower using Packing Characteristic Column Procedures:
1. Install the Packing Characteristic Column (Column E) properly. 2. Prepare and start the cooling tower with according to Section 4.1.1. 3. Set the system under the following conditions and allow stabilizing for about 15 minutes: Water flow rate : 1.5 LPM Orifice differential : Maximum Cooling load : 1.0kW Column installed : E 4. After the system stabilizes, record a few sets of measurements (i.e. temperature (T1-T6 and T8-T15), orifice differential pressure (DP1), water flowrate (FT1) and heater power (Q1)), then obtain the mean value for calculation and analysis. 5. Without changing the air flow rate, and cooling load, change the water flow rate to 2.0 LPM. When stability is achieved, repeat the observation.
SOLTEQ® BENCH TOP COOLING TOWER UNIT (MODEL: HE152)
5.0
REFERENCES
Perry, R.H., Green, D.W. and Maloney, J.O., “Perry’s Chemical Engineering Handbook”, 6th Edition, McGraw Hill, 1984.
Experiment 2: End State Properties of Air and Steady Flow Equations Results: Column Installed
: _______
Initial water level
:
cm
Final water level
:
cm
Time Interval
:
minutes
Packing Density Air Inlet Dry Bulb, T1 Air Inlet Wet Bulb, T2 Air Outlet Dry Bulb, T3 Air Outlet Wet Bulb, T4
m-1 C
˚
C
˚
C
˚
C
˚
Experiment 3: Investigation of the Effect of Cooling Load on Wet Bulb Approach Results: Column Installed
:
_________
Descriptio n
Unit
Packing Density
m-1
Air Inlet Dry Bulb, T1 Air Inlet Wet Bulb, T2 Water Outlet Temperature, T6 Orifice Differential, DP1
C
˚
C
˚
C
˚
Pa
0.0kW
0.5kW
1.0kW
1.5kW
Experiment 4: Investigation of the Effect of Ai r Velocity on Wet bul b Appr oach and Pressure Drop through the Packing Results: Column Installed
:
_____ Air Flow
Description
Unit 100 %
Packing Density Air Inlet Dry Bulb, T1 Air Inlet Wet Bulb, T2 Air Outlet Dry Bulb, T3 Air O tl W B lb T4
m-1 C
˚
C
˚
C
˚
C
˚
75 %
50 %
25 %
Experiment 5: Investigation of the Relationship between Cooling Load and Cooling Range
Results: Column Installed
: Descriptio n
Packing Density Air Inlet Dry Bulb, T1 Air Inlet Wet Bulb, T2 Air Outlet Dry Bulb, T3 Air Outlet Wet Bulb, T4
____ Unit m-1 C
˚
C
˚
C
˚
C
˚
0.0kW
0.5kW
1.0kW
1.5kW
Experiment 6: Investigation of the Effect of Packing Density on the Performance of th e Cooling Tower
Results: Column Description
Unit A
Packing Density Air Inlet Dry Bulb, T1 Air Inlet Wet Bulb, T2 Air Outlet Dry Bulb, T3 Air Outlet Wet Bulb, T4
m-1 C
˚
C
˚
C
˚
C
˚
B
C
Experiment 7: Determination of Characteristic Equation of the Packing Characteristic Column Result: Water Flowrate (LPM) Description
Unit 1.5
Top Air Outlet Dry Bulb, T3 Air Outlet Wet Bulb, T4 Water Inlet Temperature, T5
C
˚
C
˚
C
˚
Station III Air Dry Bulb, T8 Air Inlet Wet Bulb, T9 Water Temperature, T14 Station II
C
˚
C
˚
C
˚
2.0
2.5
Experiment 2: End State Properties of Air and Steady Flow Equations Results: Column Installed
:
A
.
Initial water level
:
0
cm
Final water level
:
4.0
cm
Time Interval
:
10
minutes
Description
Unit
Value
Packing Density
m-1
110
Air Inlet Dry Bulb, T1
˚C
31.6
Air Inlet Wet Bulb, T2
˚C
27.1
Air Outlet Dry Bulb, T3
˚C
30.2
Calculation: By plotting the air inlet dry bulb and air inlet wet bulb (point A) and air outlet dry bulb and air outlet wet bulb (point B) on the Psychrometric chart, the enthalpy and humidity of air mixture is obtained and the result is showed as below: h A
= 88.0 kJ/kg
w A
= 0.023 kg water/kg dry air
hB
= 96.0kJ/kg
wB
= 0.0268 kg water/kg dry air
vaB
= 0.950 m3/(kg dry air)
From the orifice calibration,
a = 0.0137 m
x
x v aB (1 + wb )
= 88Pa x 1mm H2O / 10.13Pa = 8.69 mmH2O
=
0.172 600
kg .s −1
= 2.867 x 10-4 kg.s-1 Specific enthalpy of make-up, hE = 126.586kJ/kg (at T7) Applying the Steady Flow Equation to the system indicated by the chain the (System A)
−P Q
− ∆K E = ∆H
Now, solving the left side, Q − P = 883W − (− 65W )
= 948W (Work by pump is estimate –65W) On the right side of the equation,
(change of air velocity is negligible)
Experiment 3: Investigation of the Effect of Cooling Load on Wet Bulb Approach Results: Column Installed
:
A
.
Descriptio n
Unit
0.0kW
0.5kW
1.0kW
1.5kW
Packing Density
m-1
-
110
110
110
Air Inlet Dry Bulb, T1
˚C
-
31.5
31.7
31.8
Air Inlet Wet Bulb, T2
˚C
-
27.1
27.2
27.3
Water Outlet Temperature, T6
˚C
-
29
30.6
32.1
Orifice Differential, DP1
Pa
-
89
89
89
Specific volume at outlet = 0.950 m3/kg ( x = 89 Pa x 1mm H2O / 10.13 Pa = 8.786mm H2O )
a = 0.0137 m = 0.0137
x v B 8.786 0.950
= 0.0417 kg/s Cross sectional area of column (A) = 0.15 x 0.15 m2 = 0.0225m2
Air mass flow per unit area = =
a m A
0.0417 0.0225
kgs −1m − 2
= 1.853kg s-1 m-2
Water flow rate per unit area =
W m
Results: Description
1
2
3
110
110
110
Air Flow per Unit Area, kgs-1m-2
1.853
1.853
1.853
Total Cooling Load, kW
0.536
0.964
1.424
Approach to Wet Bulb, K
1.9
3.6
4.8
Packing Density, m-1
Experiment 4: Investigation of the Effect of Ai r Velocity on Wet bul b Appr oach and Pressure Drop through the Packing Results: Column Installed
:
A
. Air Flow
Description
Unit 100 %
75 %
50 %
25 %
m-1
110
110
110
110
Air Inlet Dry Bulb, T1
˚C
29.5
29.9
30.2
31.0
Air Inlet Wet Bulb, T2
˚C
26.3
26.5
26.8
27.2
Air Outlet Dry Bulb, T3
˚C
29.4
29.8
30.4
31.8
Air O tl W B lb T4
˚C
28.4
28.7
29.5
30.7
Packing Density
Calculation: By taking the data obtained when 100% of air flow was employed, Inlet wet bulb temperature
= 26.3oC
Outlet water temperature
= 30.6 oC
“Approach to wet bulb”
= 30.6 – 26.3 K = 4.3K
Specific volume of air at outlet (by plotting Air Outlet Dry bulb and Air Outlet Wet bulb on the Psychometric Chart)
= 0.890m 3kg-1
Air mass flow rate =0.0137
x v B
(x = 89 Pa x 1mm H2O / 10.13 Pa = 8.786 mm H2O) = 0.0137
8.786 0.890
= 0.04049 kgs-1 Air volume flow rate
vB =m 0.04049 0.893
3 -1
Results:
Nominal Velocity of Air, ms-1 Approach to Wet Bulb, K Pressure, mm H2O
1
2
3
4
1.7027
1.609
1.2387
0.9064
4.3
3.6
4.5
5.5
0.3949
0.8885
1.4808
1.7769
Experiment 5: Investigation of the Relationship between Cooling Load and Cooling Range
Results: Column Installed
: Descriptio n
A
. Unit
0.0kW
0.5kW
1.0kW
1.5kW
m-1
-
110
110
110
Air Inlet Dry Bulb, T1
˚C
-
30.5
30.8
30.9
Air Inlet Wet Bulb, T2
˚C
-
27.2
27.3
27.4
Air Outlet Dry Bulb, T3
˚C
-
28.6
29.3
30.9
Air Outlet Wet Bulb, T4
˚C
-
28.3
28.7
29.9
Packing Density
Experiment 6: Investigation of the Effect of Packing Density on the Performance of th e Cooling Tower
Results: Column Description
Unit A
B
C
m-1
110
77
200
Air Inlet Dry Bulb, T1
˚C
30.1
30.2
31.0
Air Inlet Wet Bulb, T2
˚C
27.4
27.3
27.5
Air Outlet Dry Bulb, T3
˚C
29.7
30.1
30.4
Air Outlet Wet Bulb, T4
˚C
29.4
29.6
29.7
Packing Density
Results:
1
2
3
Packing Density, m-1
77
110
200
Approach to Wet Bulb, K
5
4.2
3.8
Experiment 7: Determination of Characteristic Equation of the Packing Characteristic Column Results: Water Flowrate (LPM) Description
Unit 1.5
2.0
2.5
Top Air Outlet Dry Bulb, T3
˚C
29.9
30.3
30.3
Air Outlet Wet Bulb, T4
˚C
29.1
29.8
29.7
˚C
39.3
38.5
36.2
Air Dry Bulb, T8
˚C
31.6
32.1
31.7
Air Inlet Wet Bulb, T9
˚C
29.6
30.0
29.8
˚C
35.5
35.6
34.2
Water Inlet Temperature, T5 Station III
Water Temperature, T14 Station II
Calculation: By taking the data obtained when 2.50 LPM of water was used,
w m
=
2.50 LPM
×
1kg L
×
min 60 s
= 0.04167 kg s-1 vaB
=
0.8980 m3/(kg dry air)
wb
=
0.0266 kg water/kg dry air
a = 0.0137 m
x v aB (1 + wb )
x = 49 Pa x 1mmH2O / 10.13Pa = 4.84 mmH2O
a = 0.0314 kgs m
−1
For Air Operating Line, T1 = Water Outlet temperature, T6 (31.5°C) T2 = Water Inlet temperature, T5 (36.2°C)
T 2 + 0.1(T 1 − T 2 ) = 35.73˚C
(
T2 + 0.4 T1 − T2
)
= 34.32˚C
T 1 − 0.4(T 1 − T 2 )
= 33.38˚C
T 1 − 0.1(T 1 − T 2 )
= 31.97˚C
Therefore, from the graph, ∆h1
= 15.92 kJ/kg
∆h 2
= 14.23 kJ/kg
∆h 3
= 12.93 kJ/kg
∆h 4
= 10.09 kJ/kg
L G
=
(h 2 − h 1 ) (T2 − T1 ) a
a
Referring to the Driving Force Diagram Plotted 110 84 93 96
Appendix C Components Properties and Diagrams
Appendix D Process Flow Diagram