AEROSPACE ENGINEERING
LAB 1
(MEC 2700)
LABORATORY
MANUAL
JULY 2007
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
Table of Contents
Experiment 1: Heat Capacity of Gases
Experiment 2: Thermal and Electrical Conductivity of Metals
Experiment 3: Heat Pump
Experiment 4: Heat Conduction
Experiment 5: Free and Forced Convection
Experiment 6: Thermal Radiation
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
Experiment 1: Heat Capacity of Gases
1. BACKGROUND
The first law of thermodynamics can be illustrated particularly well with an ideal gas.
This law describes the relationship between the change in internal intrinsic energy
ΔUi the heat exchanged with the surroundings ΔQ and the constant-pressure change
pdV.
dQ = dUi + pdV
(1)
The molar heat capacity C of a substance results from the amount of absorbed heat
and the temperature change per mole:
(2)
n = number of moles
One differentiates between the molar heat capacity at constant volume CV and the
molar heat capacity at constant pressure Cp.
According to equations (1) and (2) and under isochoric conditions (V const., dV = 0),
the following is true:
(3)
and under isobaric conditions (p = const., dp = 0):
(4)
Taking the equation of state for ideal gases into consideration:
pV = n R T
(5)
it follows that the difference between Cp and CV for ideal gases is equal to the
universal gas constant R.
Cp – CV = R
(6)
It is obvious from equation (3) that the molar heat capacity CV is a function of the
internal intrinsic energy of the gas. The internal energy can be calculated with the aid
of the kinetic gas theory from the number of degrees of freedom f:
(7)
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
where
kB = 1.38 · 10-23 J/K (Boltzmann Constant)
NA = 6.02 · 1023 mol-1 (Avogadro's number)
Through substitution of
R = kB NA
(8)
it follows that
(9)
and taking equation (6) into consideration:
(10)
The number of degrees of freedom of a molecule is a function of its structure. All
particles have 3 degrees of translational freedom. Diatomic molecules have an
additional two degrees of rotational freedom around the principal axes of inertia.
Triatomic molecules have three degrees of rotational freedom. Air consists primarily
of oxygen (approximately 20%) and nitrogen (circa 80%). As a first approximation,
the following can be assumed to be true for air:
f=5
CV = 2.5 R
CV = 20.8 J · K-1 · mol-1
and
Cp = 3.5 R
Cp = 29.1 J · K-1 · mol-1.
2. OBJECTIVE
The experiment aims to determine the molar heat capacities of air at constant volume
Cv and at constant pressure Cp.
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
3. EQUIPMENT
Precision manometer
Barometer/Manometer
Digital counter
Digital multimeter
Aspirator bottle (10000 ml)
Gas syringe (100 ml)
Stopcock, 1-way and 3-way
Rubber stopper, d = 32/26 mm, 3 holes
Rubber stopper, d = 59.5/50.5 mm, 1 hole
Rubber tubing, d = 6 mm
Nickel electrode
Chrome-nickel wire
Push-button switch
4. PROCEDURE
Part A – Determining the Constant Value Cv
i)
ii)
iii)
iv)
v)
vi)
The setup is as shown in Figure 1.
To determine Cv, connect the precision manometer to the bottle with a piece
of tubing. The manometer should be positioned exactly horizontally.
Pressure increase has to be read immediately after the heating process.
Begin the measuring procedure by pressing the push button switch. The
measuring period should be less than a second.
Take readings of the pressure (from the manometer), the current and voltage.
Remove the air from the aspirator bottle after each measurement.
Repeat steps iii) to v) in order to obtain 10 sets of results. Vary Δt within the
given range.
Part B – Determining the Constant Value Cp
i)
ii)
iii)
iv)
v)
vi)
vii)
The setup is as shown in Figure 2.
Replace the precision manometer with two syringes which are connected to
the aspirator bottle with the 3-way stopcock. One syringe is mounted
horizontally, whereas the other syringe is mounted vertically with the
plunger facing downwards.
The vertical plunger is rotated before each measurement in order to
minimize static friction.
The air pressure is determined with help of the syringe scale. Take note of
the initial volume of the syringe before performing the experiment.
Begin the measuring procedure by pressing the push button switch. The
measuring period should be less than a second but longer than 300ms.
Take readings of the final volume (from the syringe), the current and voltage.
Take readings up to 1 decimal point if possible as the difference is too small.
Remove the air from the aspirator bottle after each measurement and rotate
the vertical plunger.
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
viii) Repeat steps iv) to vii) in order to obtain 10 sets of results. Vary Δt within
the range 300ms to 1s.
5. REPORT
Part A – Determining the Constant Value Cv
a)
Plot a graph of pressure versus time. Calculate the slope of the graph.
b) Given that, the indicator tube in the manometer has a radius of r = 2 mm and a
pressure change of p = 0.147 hPa causes an alteration of 1 cm in length,
calculate a.
ΔV = a · Δp
c) Calculate Cv.
where
po = 1013 hPa
T0 = 273.2 K
V0 = 22.414 l/mol
p = atmospheric pressure
Part B – Determining the Constant Value Cp
a)
Plot a graph of volume versus time. Calculate the slope of the graph.
b) Calculate Cp, given the following information.
where
po = 1013hPa
T0 = 273.2K
V0 = 22.414 l/mol
p = pa – pk
pa = atmospheric pressure in hPa
pk = pressure reduction due to weight of plunger
pk 
Where
mk  g
FK
mk = 0.1139 kg = mass of the plunger
g = acceleration of gravity
FK = 7.55 x 10-4 m2 = area of the plunger
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
c) Calculate R.
R = Cp – Cv
d) Compare the calculated R to literature.
Figure 1: Experimental setup for Part A
Figure 2: Experimental setup for Part B
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
DATA COLLECTION
Part A – Determining the Constant Value Cv
Time (ms)
Pressure (Bar)
Current (A)
Voltage (V)
Part B – Determining the Constant Value Cp
Volume
Time (ms)
Initial
Final
Difference
(by calculation)
Current (A)
Voltage (V)
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
Experiment 2 – Thermal and Electrical Conductivity of Metals
1. BACKGROUND
If a temperature difference exists between different locations of a body, heat
conduction occurs. In this experiment there is a one-dimensional temperature
gradient along a rod. The quantity of heat dQ transported with time dt is a
function of the cross-sectional area a and the temperature gradient dT/dx
perpendicular to the surface.
(1)
λ is the heat conductivity of the substance.
The temperature distribution in a body is generally a function of location and
time and is in accordance with the Boltzmann transport equation
(2)
Where r is the density and c is the specific heat capacity of the substance.
After a time, a steady state
(3)
is achieved if the two ends of the metal rod having a length l are maintained at
constant temperatures T1 and T2, respectively, by two heat reservoirs.
Substituting equation (3) in equation (2), the following equation is obtained:
(4)
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
2. OBJECTIVE


To determine the thermal conductivity of copper and aluminium is
determined in a constant temperature gradient from the calorimetrically
measured heat flow.
The electrical conductivity of copper and aluminium is determined, and
the Wiedmann-Franz law is tested.
3. EQUIPMENT
Calorimeter vessel, 500 ml
Calor. vessel w. heat conduct. conn.
Heat conductivity rod, Cu
Heat conductivity rod, Al
Magn. stirrer, mini, controlable
Heat conductive paste, 50 g
Gauze bag
Rheostat, 10 Ohm , 5.7 A
Immers.heater, 300 W, 220-250VDC/AC
Temperature meter digital
Temperature probe, immers. type
Surface temperature probe
Stopwatch, digital, 1/100 sec.
Tripod base -PASSBench clamp -PASSSupport rod -PASS-, square, l 630 mm
Support rod -PASS-, square, l 1000 mm
Universal clamp
Right angle clamp -PASSSupporting block 1053105357 mm
Glass beaker, short, 400 ml
Multitap transf., 14VAC/12VDC, 5A
Digital multimeter
Universal measuring amplifier
Connecting cord, 500 mm, red
Connecting cord, 500 mm, blue
4. PROCEDURE
Part A – Heat Capacity of the Calorimeter
i)
ii)
iii)
iv)
Weigh the lower calorimeter at room temperature
Measure and record the room temperature.
Prepare hot water and record its temperature.
Pour the hot water into the lower calorimeter.
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
v)
vi)
Immediately take the temperature readings of the hot water in the
calorimeter every 10 seconds for 5 minutes.
Reweigh the calorimeter to determine the mass of water.
Part B – Ambient Heat
i)
ii)
iii)
iv)
The calorimeter is then put under running tap water in order to get it
back to room temperature.
The calorimeter is then filled with ice water. With the assistance of ice,
obtain water with a temperature of 0oC.
When a temperature of 0oC is obtained, remove all the pieces of ice
and record the temperature every minute for 30 minutes.
Reweigh the calorimeter to determine the mass of water.
Part C – Thermal Conductivity
i)
ii)
iii)
iv)
v)
vi)
The setup is as shown in Figure 1. In this experiment, the difference in
temperature between the upper and lower mediums are monitored, as
well as the temperature of the water in the lower calorimeter.
The empty lower calorimeter is weighed.
Fill the lower calorimeter with ice water. With the aid of ice, obtain a
temperature of 0oC.
When a temperature of 0oC is obtained, pour hot water in the upper
calorimeter. Ensure that the upper calorimeter is well filled with hot
water.
Keep the temperature of water in lower calorimeter water at 0oC with
the help of ice, until the difference in temperature between two points
on the rod, is steady.
When a constant temperature gradient is obtained, remove all the ice in
the lower calorimeter and begin taking readings of the difference in
temperature and the temperature of the water in the lower calorimeter.
Readings should be taken every 30 seconds for 5 minutes.
Part D – Electrical Conductivity
i)
ii)
iii)
The setup is as shown in Figure 2. The metal rod in the setup is
aluminium.
Ensure that the voltage on the variable transformer is set to 6V.
The amplifier must be calibrated to 0 in a voltage-free state to avoid a
collapse on the output voltage. Select the following amplifier settings:
Input
Amplification
Time Constant
iv)
Low Drift
104
0
Set the rheostat to its maximum value and slowly decrease the value
during the experiment.
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
v)
vi)
Collect readings of current and voltage for six rheostat settings.
Repeat steps i) to v) with the copper rod from the Part B.
Figure 1: Experimental Set-up for Thermal Conductivity
Figure 2: Experimental Set-up for Electrical Conductivity
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
5. REPORT
Part A – Heat Capacity of the Calorimeter
i) From the results obtained, plot a graph of temperature vs. time.
ii) The temperature of the mixture, m , is determined from extrapolating the
plotted curve, as sketched in figure below. The straight line parallel to
temperature axis was drawn such that the shaded parts are equal in area.
 u = Temperature of the surrounding atmosphere
1 = Initial temperature
m = Temperature of mixture
iii)
Calculate the heat capacity of the calorimeter using the following
equation:
  M
C  c w  mw  w
M   R
where
cW = Specific heat capacity of water
mW = Mass of the water
W = Temperature of the hot water
M = Mixing temperature
R = Room temperature
Part B – Ambient Heat
i)
Calculate the addition of heat from the surroundings.
Q  (cW  mW  C )  T
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
where
ΔT = T – T0
T0 = Temperature at time t = 0
ii)
iii)
iv)
Draw a graph of temperature vs time for the cold water.
Draw a graph of heat from surroundings vs time.
Calculate the slope for the graph which will give you dQ/dtambient.
Part C – Thermal Conductivity
i)
ii)
Calculate Q and draw the graph of Q vs t. Find the slope of this graph,
dQ
which will give you
ambient.+ metal.
dt
dQ
Calculate
metal, given that:
dt
dQ
dt
iii)
metal
=
dQ
dt
ambient.+ metal
-
dQ
dt
ambient
Given the length of the rod as 31.5 cm and the area as 4.91x10-4 m2,
calculate the heat conductivity of the rod, λ.
dQ
T
 A 
dt
x
Part C – Electrical Conductivity
i)
Calculate the electrical conductivity using the following equation:
ii)
The Wiedmann-Franz Law is as stated below:

l
A R

 LT

Calculate the Lorenz number in each case.
iii)
Given that the value of L is as follows, calculate the error in each case.
L
 2 k2

3 e
2
 2.4 10 8
W
K2
k – Universal gas constant = 1.38 · 10-23 J/K
e – Elementary unit charge = 1.602 · 10-19 AS
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
DATA COLLECTION
Part A – Heat Capacity of the Calorimeter
Hot water temperature before poured into calorimeter = ____________
Calorimeter Temperature (assume same to Room Temperature) = ___________
Time (seconds)
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
Hot Water
Temperature (oC)
Time (seconds)
160
170
180
190
200
210
220
230
240
250
260
270
280
290
300
Temperature (oC)
Part B – Ambient Heat
Time (mins)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Cold water
Temperature (oC)
Time (mins)
0
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Temperature (oC)
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
Part C – Thermal Conductivity
Time (seconds)
0
30
60
90
120
150
180
210
240
270
300
Water Temperature (oC)
0
ΔT (oC)
Part C – Electrical Conductivity
Reading
1
2
3
4
5
6
Reading
1
2
3
4
5
6
Aluminium
Current (A)
Voltage (V)
Copper
Current (A)
Voltage (V)
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
Experiment 3 - Heat Pump
1. BACKGROUND
Pressures and temperatures in the circulation of the electrical compression heat
pump are measured as a function of time when it is operated as a water-water heat
pump. The energy taken up and released is calculated from the heating and
cooling of the two water baths. When it is operated as an air-water heat pump, the
coefficient of performance at different vaporizer temperatures is determined.
The Mollier (h, log p) diagram, in which p is the pressure and h the specific
enthalpy of the working substance, is used to describe the cyclic process in heat
technology. Fig. 1 shows an idealised representation of the heat pump circuit. The
curve running through the critical point K delineates the wet vapour zone in which
the liquid phase and gas phase coexist. In this zone the isotherms run parallel to
the h axis. Starting from point 1, the compressor compresses the working
substance up to point 2; in the ideal case this action proceeds without an exchange
of heat with the environment, i.e. isentropically (S = const.). On the way from
point 3 useful heat is released and the working substance condenses. Then the
working substance flows through the restrictor valve and reaches point 4. In an
ideal restricting action the enthalpy remains constant. As it passes from point 4 to
point 1, the working substance takes up energy from the environment and
vaporises. The specific amounts of energy q0 and q taken up and released per kg
and the specific compressor work w required can be read off directly as line
segments on the graph.
q0 = h1 – h3
q = h2 – h3
w = h2 – h1
For evaluation purposes the data for the working substance R 134a in the wet
vapour zone are set out in Table 1.
Figure 1: h, log p diagram of a heat pump, ideal curve.
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
2. OBJECTIVE
i) Water heat pump: To measure pressure and temperature in the circuit and in
the water reservoirs on the condenser side and the vaporizer side alternately.
To calculate energy taken up and released, also the volume concentration in
the circuit and the volumetric efficiency of the compressor.
ii) Air-water heat pump: To measure vaporizer temperature and water bath
temperature on the condenser side under different operating conditions on
the vaporizer side, ie. Natural air, cold blower and hot blower.
iii) To determine the electric power consumed by the compressor and calculate
the coefficient of performance.
3. EQUIPMENT
Heat pump, compressor principle
Lab thermometer, -10…+100C
Lab thermometer, w. stem, -10…+110C
Heat conductive paste, 50 g
Hot-/Cold air blower, 1000 W
Stopwatch, digital, 1/100 sec
Tripod base -PASSSupport rod -PASS-, square, l 250 mm
Universal clamp with joint
Glass beaker
Glass rod
4. PROCEDURE
Part A – Water-water Heat Pump
i.
ii.
iii.
Pour 4.5L of water into the two water reservoirs.
Record all the initial pressures and temperatures before switching on the
heat pump.
Start the stopwatch at the same time the heat pump is switched on. Record
the power reading and the pressure and temperatures on both the vaporizer
and condenser side every minute for approximately 30 minutes.
Part B – Air-water Heat Pump
i.
ii.
iii.
iv.
Remove the water reservoir on the vaporizer side and dry the heat
exchanger coils.
Obtain a temperature of 20oC for the 4.5L water on the condenser side.
Record all the initial pressures and temperatures before switching on the
heat pump.
Start the stopwatch at the same time the heat pump is switched on. Record
the power reading, and the temperatures at the vaporizer outlet and
condenser water temperature, every minute for approximately 20 minutes.
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
v.
Repeat steps ii to iv but with a hot blower and a cold blower approximately
30cm away.
5. REPORT
Part A – Water-water Heat Pump
i)
Mass of water:
a) condenser = ____________
b) vaporizer = _____________
ii)
Plot a graph of temperature vs time for all inlet and outlet.
iii)
Calculations at t = 10mins:
Q2
o
T
  c  mw  Q
b) Condenser heat flow, Q
T
c) Average compressor power, P
a) Vaporizer heat flow,
Q
 c  mw 
d) Performance at the condenser side,  
Q
P
Q 0
e) Volume flow at the vaporizer side, V  v 
h1  h3
(v = specific volume of the vapour)
f) Geometrical volume flow, Vg  Vg  f
Given
Vg = 5.08 cm3
f = 1450 min-1
g) Volumetric efficiency of the compressor,  
V
Vg
Part B – Air-water Heat Pump
i)
ii)
iii)
iv)
v)
Plot a graph of temperature versus time for all the results.
Calculate the average vaporizer temperature.
Calculate the condenser heat flow.
Calculate the performance.
Compare the results for all the conditions and discuss.
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
DATA COLLECTION
Part A – Water-water Heat Pump
Time
(min)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Power
(W)
P1
Condenser
θ1
θci
θco
P2
Vaporiser
θ2
θvi
θvo
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
Part B – Air-water Heat Pump
Time
(min)
Natural Air
Power
θ1
θvo
(W)
Hot Blower
Power
θ1
θvo
(W)
Cold Blower
Power
θ1
(W)
θvo
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
Experiment 4 – Heat Conduction
1. BACKGROUND
Thermal conduction is a mode of heat transfer which occurs in a material due to
the presence of temperature gradient. It is a transfer of energy from the more
energetic particles to the adjacent less energetic particles.
Generally, heat is defined as energy transfer due to the temperature gradients or
difference between two points. Heat energy can be transferred in three modes,
which are conduction, convection, and radiation. One of the most common heat
transfer modes, which is conduction heat transfer, is defined as heat transferred by
molecules that travel a very short distance (~0.65m) before colliding with
another molecule and exchanging energy.
In this experiment, both linear and radial conduction heat transfer methods are
studied. The entire system (insulated heater/specimen, air and laboratory
enclosure) are at room temperature initially (t = 0). The heater generates uniform
heat flux as switched on.
For linear conduction, an electrical heating element is bonded to one end of a
metal rod (heat source). Another end of the rod is exposed to heat discharge (heat
sink). The outer surface of the cylindrical rod is well insulated; thus yielding onedimensional linear heat conduction in the rod once the heating element is switched
on. Thermocouples are embedded in the rod, along its centerline, at x = 0, 12, and
24 mm from the heating element. A simple mimic diagram for heat conduction
along an well-insulated cylindrical rod is shown as below:
Insulation
Imposed Hot Th
Temperature
(Heat Source)
Ac
qx
dx
Tc, Imposed Cold
Temperature
(Heat Sink)
x
L
For radial conduction, the electrical heating element is bonded to the center
part of a circular brass plate (heat source). The cooling water flows through
the edge of the plate that acts as a heat sink for heat discharge. The other
surfaces of the plate are well insulated to simulate radial heat conduction from
the plate center to its edge when the heating element is switched on. The brass
plate has a radius, rplate = 60 mm and thickness, t = 3.2 mm. Thermocouples
are embedded in the circular plate, at r = 0, 12, 24, 36, 48, and 60 mm. A
simple mimic diagram for heat conduction along an well-insulated cylindrical
rod is shown as below:
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
y
Imposed cold temperature
(Heat Sink)
r
t
Imposed hot temperature (Heat
Source)
2. OBJECTIVE
The aim of the experiment is to study the Fourier’s Law on linear and radial
conduction heat transfer, as well as to illustrate the transfer of heat by conduction
in solid materials while varying the parameters affecting conduction.
3. EQUIPMENT
The Heat Conduction Study Bench Model FF105 will be used in this experiment.
4. PROCEDURE
Part A – Linear Conduction along a Homogeneous and Composite Bar
1. Clamp the 25mm diameter brass specimen into the intermediate section of the
linear module.
2. Insert the probes into the holes provided along the Homogeneous Bar, making
sure that each one is touching the rod. Remember to take note of the distance
between each thermocouple on the linear module (these are the x-values).
3. Ensure that the cooling water tubes are connected (supply and drain).
4. Turn on the cooling water.
5. Switch on the heater by turning the knob.
6. Set the heater power control knob to 10W (refer to the display, not the knob
settings).
7. By using the selector switch, take the temperature readings from T1 to T9.
This is done after time is allowed for the steady state to occur. This is after
about 20 to 30 minutes. Also, record the corresponding heater power input.
8. Repeat steps 1 to 7 using the 25mm diameter stainless steel and 13mm
diameter brass specimen.
* Note : During the assembly of the intermediate sections, ensure that the contact
surfaces are properly mated. Use the heat transfer compound provided to ensure
good contact.
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
Part B – Radial Conduction along Circular Metal Plate
1. Insert the thermocouples in the holes provided on the specimen, making sure
that each one is operating properly. Take note of the distance for each
thermocouple (r-values).
2. Ensure that there is water supply to the unit for simulating heat sink is turned
on.
3. Turn on the heater and set the power to 10W.
4. Record the temperatures after a steady state is obtained, which is after about
20 to 30 minutes. Also, record the corresponding heater power input.
5. Repeat steps 1 to 4 for power settings of 20 W, 30 W and 40 W.
5. REPORT
1. Plot the temperature profile for both models as a function of distance and obtain
the slope dT/dx for linear conduction and dT/dr for radial conduction.
2. By using the slope of the graph plotted, calculate the thermal conductivity for each
specimen used.
3. Compare and discuss the thermal conductivity obtained from the two methods and
the typical values contained in tables of published data.
4. Compare and discuss the effect of changing the radius of the cylindrical rod for
the brass specimen.
5. Discuss all the results obtained, the graphs plotted and the problems faced.
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
DATA COLLECTION
Linear Conduction
Power (W)
Specimen
T1 (oC)
T2 (oC)
T3 (oC)
T4 (oC)
T5 (oC)
T6 (oC)
T7 (oC)
T8 (oC)
T9 (oC)
10
25 mm diameter Brass
10
13 mm diameter Brass
Power (W)
Specimen
T1 (oC)
T2 (oC)
T3 (oC)
T4 (oC)
T5 (oC)
T6 (oC)
T7 (oC)
T8 (oC)
T9 (oC)
10
25 mm diameter Stainless Steel
Radial Conduction
Power (W)
R1 (oC)
R2 (oC)
R3 (oC)
R4 (oC)
R5 (oC)
R6 (oC)
10
20
30
40
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
Experiment 5 – Free and Forced Convection
5. BACKGROUND
Convection is a mode of energy transfer between a solid surface and the adjacent fluid in
motion. Convection heat transfer involves the combined effects of conduction and fluid
motion.
The transfer of heat by convection plays an important role in many areas of our daily life
as well as of industry.
Heat transfer by convection between a surface and the surrounding fluid can be increased,
by attaching thin strips of metal fins to the surface. When heat transfer takes place by
convection from both interior and exterior surfaces of a tube or a plate, generally fins are
used on the surfaces where the heat transfer coefficients are low.
Heat transfer by simultaneous conduction and convection, whether free or forced, forms
the basis of most industrial heat exchangers and related equipment. The measurement and
prediction of heat transfer coefficients for such circumstances is achieved in the free and
forced convection heat transfer apparatus by studying the temperature profiles and heat
flux in an air duct with associated flat and extended transfer surfaces.
In this experiment, students are required to perform free and force convection heat
transfer using different type extended surface plate.
A heated surface dissipates heat to the surrounding fluid primarily through a process
called convection. Heat is also dissipated by conduction and radiation, however these
effects are not considered in this experiment. Air in contact with the hot surface is heated
by the surface and rises due to reduction in density. The heated air is replaced by cooler
air, which is in turn heated by the surface, and rises. This process is called free convection.
In free convection small movements of air generated by this heat limit the heat transfer
rate from the surface. Therefore more heat is transfer if the velocity is increase over the
heated surface. This process of assisting the movement of air over the heated surface is
called forced convection. A heated surface experiencing forced convection will have a
lower surface temperature than that of the same surface in free convection, for the same
power input.
Convection heat transfer from an object can be improved by increasing the surface area in
contact with the air. In practical it may be difficult to increase the size of the body to suit.
In these circumstances the surface area in contact with the air may be increased by adding
fins or pins normal to the surface. These features are called extended surfaces. A typical
example is the use of fins on the cylinder and head on an air-cooled petrol engine. The
effect of extended surfaces can be demonstrated by comparing finned and pinned surfaces
with a flat under the same conditions of power input and airflow
6. OBJECTIVE
The experiment aims to illustrate the transfer of heat by convection both naturally and by
force. The parameters that affect the heat transfer are also explored and comparisons
between different types of solid surfaces are made.
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
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To demonstrate the use of extended surfaces to improve heat transfer from a surface.
To demonstrate convection heat transfer by using different type of extended surface.
To see the effect of different flow velocity on the convection heat transfer.
To determine the temperature distribution along an extended surface.
7. EQUIPMENT
1.
2.
3.
4.
G.U.N.T. WL350 TEST UNIT, FREE AND FORCED CONVECTION
Heater inserts – flat plate, cylinder and fin
Thermocouple
Air measurement probe
Sketch diagram of Convention Heat Transfer Rig
8. PROCEDURE
PART A – Natural Convection (Fin and Cylinder Heater Insert)
1. Insert the fin heater insert. (Make sure that the heater power supply is first switched
off before replacing the heater insert. Beware of hot surfaces!!!)
2. Switch on the equipment. Ensure that the fan is switched off.
3. Set the heater to no. 7.
4. Allow sufficient time to achieve a steady state condition before taking the readings of
velocity and temperature as shown below:
a. Inlet flow rate, νin and the inlet temperature, Tin at TP1 (using a probe)
b. Outlet air flow rate, νout and the air temperature, Tout at TP12 (using a probe)
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
c. Temperatures T2, T3, T4 and T5 (using a thermocouple)
5. Repeat steps 1 to 4 for the pinned heater insert.
6. Remember to measure the distance of the access holes from the back plate of the
heater inserts.
PART B – Forced Convection (Fin and Pin Heater Insert)
1. Switch on the fan to no. 8 (do not run at a lower setting).
2. When steady state is achieved, take the readings as in the recent experiments.
3. Carry out this experiment for both the pinned and finned heater inserts.
PART C - Forced Convection (Fin and Pin Heater Insert) at Varying Flow Rates
1. Carry out the experiment the same way as in Part B, only, vary the fan speed to no. 7,
9 and 10.
2. Obtain steady state condition and note down the respective velocity and temperatures.
9. REPORT
1. Plot graphs of temperature against distance for each plate. Explain on the graphs
plotted.
2. Plot graphs of velocity against temperature for each of the plates. Explain on the
graphs plotted.
3. Plot graphs of extended surface temperature against distance from the back plate for
both heat exchangers at all the various air velocities.
4. Comments on the correlation between total surface area of the heat exchanger and the
temperature achieved. Which of the extended surfaces has greater surface area?
5. For a heat exchanger with 100 % efficiency, the whole of the extended surface should
be at the same temperature as the backplane, why this is not achievable in the
experiment?
6. Discuss the results and the graphs obtained.
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
DATA COLLECTION
Pin Heater Insert
Fan speed
7
8
9
10
7
8
9
10
νin (m/s)
Tin (oC)
νout (m/s)
Tout (oC)
T2 (oC)
T3 (oC)
T4 (oC)
T5 (oC)
Cylinder Heater Insert
Fan speed
νin (m/s)
Tin (oC)
νout (m/s)
Tout (oC)
T2 (oC)
T3 (oC)
T4 (oC)
T5 (oC)
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
Experiment 6 – Thermal Radiation
1. BACKGROUND
Thermal radiation is a transfer of heat by electromagnetic waves with its related laws
being different to those for conduction and convection. No medium of transfer is required
as exemplified by the energy of the sun reaching the earth and all bodies at temperatures
above absolute zero emit thermal radiation.
Two most important physical laws on thermal and optical radiation are Stefan
Boltzmann’s and Lambert’s distance laws.
As commonly known heat transfer due to a temperature difference. Heat can be
transferred in three different ways, which are known as conduction, convection and
radiation.
Any object that is hot gives off light known as Thermal Radiation. The hotter an object is,
the more light it emits. And, as the temperature of the object increase, it emits most of its
light at higher and higher energies. (Higher energy light means shorter wavelength light.)
In general, the net rate of energy transfer by thermal radiation between two surfaces
involves complicated relationships among the properties of the surface, their orientations
with respect to each other, the extent to which the intervening medium scatters, emits and
absorbs thermal radiation and other factors
In these experiments, we will prove some fundamental law relating to radiation.
Inverse square law of heat
The total energy dQ from an element dA can be imagined to flow through a hemisphere
of radius r. A surface element on this hemisphere dA1 lies on a line making an angle
with the normal and the solid angle subtended by dA1 at dA is dw = dA1/r2
If the rate of flow of energy through dA1 is dQthen dQ= idwdA where iis the
intensity of radiation in the direction
Figure 3.1 Solid Angle
The Stefan-Boltzmann Law states that :
q b= (Ts4 –Ta4)
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
Where
qb = energy emitted by unit area of a black body surface (Wm-2)
(Note: Energy emitted by surface =3.040 X reading from radiometer
R – refer to Radiometer Data sheet for explanation)
 = Stefan-Boltzmann constant equal to 5.67 x 10-8 (Wm-2K-4)
Ts = Source temperature and surrounding = black plate temp. (K)
Ta = Temperature of radiometer and surrounding = room temp.(K)
2. OBJECTIVE
The experiment aims to demonstrate the most important physical laws on thermal and
optical radiation.
3. EQUIPMENT
Thermal Radiation Study Unit WL360
4. PROCEDURE
Part A - Inverse Square Law of Heat
1. Place the radiometer at a distance of 1000mm from the heat source.
2. Switch on the radiometer and observe and record the background readings i.e.
radiation and temperature. (Ensure that the load is switched off)
3. Switch on the load switch and set the power regulator to 5.
4. Wait for a steady temperature. Record the radiometer reading and the distance from
the heat source of the radiometer along the horizontal track for ten radiometer
positions.
Part B – Stefan-Boltzmann Law
1. Place the radiometer 150mm and the black plate 50mm from the heat source.
2. Record the black plate temperature and the radiometer reading at room temperature.
3. Then record the readings for selected increments of increasing temperature up to
100oC. Both readings should be calculated simultaneously at any given point.
Part C – Lambert’s Direct Law (Cosine Law)
1. Mount the luxmeter at a separation of L = 400mm from the light source. Ensure that
the luxmeter is connected to the measuring amplifier.
2. Switch on the measuring amplifier and note the background readings.
3. Mount the light source in position φ = 0o, switch it on and turn the power regulator to
setting no. 9.
4. Record the illuminance, E in Lux and repeat the procedure with increasing angle of
incidence, φ in steps of 10o (0o to 900).
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
5. REPORT
Part A - Inverse Square Law of Heat
1. Calculate the logarithm values (log10) of the data taken.
2. Plot a graph of radiometer reading vs. distance.
3. Plot a graph of Log10 R versus log10 X.
4. Determine the gradient of the slope for the graph of Log10 R versus log10 X.
5. What does the gradient of slope determined indicate?
6. Discuss the results and graphs plotted.
Part B – Stefan-Boltzmann Law
1. Compare the emissivity of the black plate and Stefan Boltzmann Law. Discuss and
explain the trend and the discrepancy between both results.
2. Error analysis
3. Sample calculations.
Part C – Lambert’s Direct Law (Cosine Law)
1. Tabulate the values of background illuminance, measured illuminance, corrected
illuminance (measured – background) and normalized illuminance (corrected /
illuminance at φ = 0o) for every angle taken.
2. State the relation of Lambert’s Direct Law, Eφ = En . cos φ where En = normal
irradiance.
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics
DATA COLLECTION
Part A - Inverse Square Law of Heat
Distance
Radiometer Reading
Part B – Stefan-Boltzmann Law
Temperature
Radiometer Reading
Blackplate Reading
Part C – Lambert’s Direct Law (Cosine Law)
Angle
0
10
20
30
40
50
60
70
80
90
Luxmeter Reading
Aerospace Engineering Lab 1 (MEC 2700)
Thermodynamics