UNESCO-NIGERIA
NIGERIA TECHNICAL &
VOCATIONAL EDUCATION
REVITALISATION PROJECT-PHASE
PROJECT
II
NATIONAL DIPLOMA IN
MECHANICAL ENGINEERI
ENGINEERING
NG TECHNOLOGY
THERMODYNAMICS 1
(PRACTICALS)
COURSE CODE: MEC122
YEAR II SEMESTER 2
VERSION 1: DECEMBER 2008
TABLE OF CONTENT
Week1
Experiment1 :Temperature and Heat Transfer
Week2
Experiment 2 - use of constant pressure air thermometer
Week3
Experiment 3
Responses to measurements of thermometric substances
Week4
Experiment 4 : Use of resistance thermometer
Week5
Experiment 5: thermal conductivity of metals
Week6
Experiment 6 Newton’s law of cooling
Week7
Experiment 7 : Boyle's law
Week8
Experiment 8 : Charles’ law experiment
Week9
Experiment 9: Specific heat capacity of solids
Week10
Experiment 10: specific heat capacityof liquids
Week11
Experiment 11: Which fuel source has more heat energy?
Week12
Experiment12: Evaporation rate
Week13
Experiment 13: Finding dewpoint
Week14
Experiment 14: Supercooled water
Week15
Experiment15: Coefficient of performance of an air-conditioning unit
WEEK 1 THERMODYNAMICS I PRACTICAL
MEC I22
EXPERIMENT 1: Temperature and Heat Transfer
OBJECTIVE: To differentiate between temperature and heat
Supplies: mercury glass thermometer, glass cup, ice, water
Process: Record the air temperature of the room. Fill a glass half way with hot water.
Place the thermometer in the glass of water and wait 5 minutes. After the 5 minutes, Each
2 minutes thereafter record the temperature of the water. Continue recording the
temperature until the water is the same temperature as the air in the room. Next, pour ice
cubes into the water. Record the temperature each 2 minutes until the temperature of the
ice-water mixture stays the same.
Scientific principles: 1. Heat travels from warmer toward colder objects, 2. The freezingthawing point of water is 32 F (0 C), 3. It takes time for a system to come into thermal
equilibrium. It takes time for the thermometer to adjust to a new temperature. It takes time
for heat transfer between neighboring objects to produce the same temperature of those
objects, 4. The temperature of the water remains constant when latent heat absorption of
melting occurs (as the ice melts the temperature stays at 32 F).
WEEK 2 THERMODYNAMICS I PRACTICAL
MEC I22
EXPERIMENT 2 : USE OF CONSTANT PRESSURE AIR THERMOMETER
1.
2.
OBJECTIVE To understand the Principles of thermometry. And the use of a constant
pressure air thermometer and in particular to measure: (a) The room temperature (B) the
boiling point of a liquid
APPARATUS
A clean, dry thick-walled glass capillary tube sealed at one end, scale, mercury, ice, rubber
bands, long measuring jar, electrical steam heater, beaker.
Fig. 2.1
Fig. 2.3
THEORY
For the Kelvin gas scale of temperature
T = (pV)T/(pV)icex273.15K
Since in this experiment pressure
is constant
.-.
T = VT/V icex273.15K Neglecting the expansion of the glass,
T= length of air column at temperature T x 273.15K Length of air column at ice point
= lT/licex273.15K.
METHOD
Heat the capillary tube gently over a Bunsen flame and immersed beneath the surface of some clean
mercury in a clean beaker cool when a thread of mercury is drawn into the tube. Remove from the
beaker when the thread is about 20 mm long. Allow it to cool down to room temperature when the
mercury thread 01C approximately in the middle of the tube. If this has not been achieved the process
must be repeated until it has.
The tube is then fastened to the half-meter scale with rubber bands. Immerse the tube, with closed end
downwards, to just above the mercury level in a mixture of crushed ice and water in the measuring jar,
Allow plenty of tune, at least twenty minutes, for the enclosed air to assume the temperature of the ice
bath and then, when the air column has reached its minimum steady length, record the positions on the
scale of both ends of the enclosed air column. The thermometer is now calibrated and ready for use.
(a) Remove the tube from the ice bath, dry it and allow it plenty of time to assume the temperature
of the room. When the air column has reached its maximum steady length, record the
positions on the scale of both ends.
(b) Finally immerse the tube hi a liquid brought to boil in the measuring jar by means of an electric
heater (water will suffice) and allow plenty of time for the enclosed air to assume the
temperature of the boiling liquid, When the air column has reached its maximum steady
length again take the readings on the scale of both ends of the air column.
Tabulate the readings:
Ice point
Scale readings of air column
Temperature
Closed end
Mercury end Difference 1
...... mm
...... mm
lice =...... .mm 273.15K
Room
...... mm
...... mm
Lb.p.t= …mm
1.
It is extremely important that both the capillary tube and the mercury should be quite dry. If
necessary first clean the capillary tube with concentrated sulphuric acid, and use fresh, clean
mercury that has not been used in other experiments. Alternatively, the index itself may be
concentrated sulphuric acid instead of mercury.
2.
Ideally, drainage should be arranged for the ice bath but if this is difficult it may be
dispensed with.
3.
The experiment deals with the length of the enclosed column of air at constant pressure.
Hence the need for all measurements to be taken under the same conditions, i.e.
When the tube is vertical.
WEEK 3 THERMODYNAMICS I PRACTICAL
MEC I22
EXPERIMENT3
TITLE: Responses to measurements of thermometric substances
OBJECTIVES: To compare the characteristics responses and accuracy of the measuring
instruments incorporated in the measuring bench.
APPARATUS:
a.
b.
c.
d.
e.
f.
Temperature measuring bench
Beaker
Thermocouple
Thermometer
Flask
Heater
THEORY
Temperature is a manifestation of the average kinetic energy of the molecules of a
substance and is a measure of hotness or coldness of a substance. The concept of
temperature is based on the transfer of energy to and from the sensing body. The
temperature of the body is the thermometric property which is the measure of the ability
of the body to transfer thermal energy to another body. From the Zeroth law of
thermodynamics which states that when each of the two bodies has the same temperature
as a third body, the two bodies have equal temperatures.
To detect changes in temperature of a substance, certain physical properties that change
with temperature are used. Examples of such properties are length of rod, volume of
liquid and electrical resistance of a wire. The most common scales used in measuring
temperature are Celsius, Fahrenheit, Kelvin or absolute grade. The scales are based on the
primary reference point which represents the temperature at which sharp changes occur.
This temperature is assigned a number and serves as a starting point. A second reference
point is called ‘ice point’. Which is defined as the temperature at which pure microscopic
secondary points is divided in degrees and the number of them between two points is 100
celsius degree, and 100 kelvin degrees.
A and B are the two metals and T1 and T2 are the temperatures of the junctions. If T1 is
the colder junction and the thermoelectric current I flows in the direction indicated then
metal A is referred to as thermoelectrically positive to metal B. the thermal e.m.f. as
indicated in figure b is a measure of the difference in temperature between T2 and T1.
THERMOCOUPLE
Temperature measurements using thermocouples are based on the discovery by Seebeck,
that an electric current flows in a continuous circuit of two dissimilar metals if the two
junctions formed by the metals are kept at different temperatures.
The magnitude of the e.m.f. generated in the circuit depends on the temperature
difference between the two junctions.
RESISTANCE THERMOMETRY
Is the art of measuring temperature by utilizing the characteristic relationship of electrical
resistance to temperature of pure metals expressed as:
Rt = Ro(1 +at +bt2 +ctn )
Where:
Rt and Ro are the resistances of the platinum at temperature t and ice point respectively, a,
b and c are constants.
Platinum resistance thermometers
The properties that make platinum the best metal as sensing element for resistance
thermometers are:
a. Platinum is a noble metal, not subjected to corrosion and capable of being drawn
into very fine wire.
b. The melting point is high and the metal does not volatilize appreciably at
temperature below 1200C.
c. The metal can be obtained in a very pure state.
d. Platinum is used in highly precise measurement in the range 00C to 650C.
PROCEDURE:
The experiment is to be carried out with temperature measuring bench designed by
2 Fill both the heating flask and the cold junction flask with clean water and power the
setup by switching it on.
3 Heat the water in the heating flask for about 5 minutes to a reasonably high temperature
(below the boiling point of water). Then switch off the heater.
4 Insert the mercury-in-glass thermometer, the probes of the platinum resistance into the
hot water through some openings provided. Also insert one of the junctions of the
thermocouple into the hot water while the other junction into the cold water flask (ice
block).
5 take readings of the thermometers after an interval of one minute as the hot water cools
until a set of ten (10) readings are obtained.
6 switch off the power, disconnect the bench from the power supply, disconnect the
probes and disengage the thermocouple set-up.
RESULTS:
1 Tabulate the readings for the temperatures of platinum resistance thermometer in 0C the
temperature of liquid in glass thermometer in 0C and the e.m.f. of thermocouple in mv
2 using the tabulated readings plot a graph of temperature of platinum resistance
thermometer, liquid in glass thermometer and e.m.f. of the thermocouple against time.
s/no.
1
2
3
4
5
6
7
8
9
10
Time (min)
Temp in (0C)
for platinum
thermometer
Temp in (0C)
for liquid in
glass
thermometer
E.m.f. of
thermocouple
in mv
4 state the sources of error
WEEK 4 THERMODYNAMICS I PRACTICAL
MEC I22
EXPERIMENT 4 : USE OF RESISTANCE THERMOMETER
OBJECTIVE: TO DETERMINE TEMPERATURE WHEN A THERMOMETRIC
PROPERTY VALUE AT CERTAIN FIXED POINTS ARE GIVEN.
APPARATUS: Resistance thermometer, consisting of a test-tube containing a coil of wire
immersed in a paraffin or oil. The should be enamelled copper or iron wire of resistance
about 10Ω non-inductively wound on a suitable narrow former(e.g. a 1cm wide strip of
formica) and soldered onto thick copper leads which pass through holes bored in a cork.
Other apparatus: accumulator, rheostat capable of taking 1amp, ammeter0-1A,
voltmeter0-2V,, circuit key, large funnel, ice, beaker, steam heater.
THEORY:
Since gas thermometers on which the basic Kelvin scale is defined are inconvenient to
use, other thermometers, which can be calibrated against the Kelvin scale, are in common
use, of which the resistance thermometer is an example.
On the Kelvin scale the temperature of steam from water boiling under standard pressure
is found by experiment to be 373.15k, exactly 100k above the ice point. This enables a
Celsius scale of temperature to be defined on which the ice point is given the value
00Cand the steam point1000C, with the temperature interval.
The defining relationship between a Celsius temperature θ and the same temperature T on
the ideal gas scale is accordingly
θ= T-273.15K
Since temperatures on any particular scale are defined by linear relationship between
temperature and the magnitude of the property concerned, for the resistance thermometer
measuring temperatures in degrees Celsius, the resistances R0 and R100 of the
thermometer at the fixed points the ice points and the steam point are fixed determined.
The temperature t on a resistance temperature scale in degree Celsius is given by:
t=
Rt − R0
X 100 0 C
R100 − R0
Where: Rt is the resistance of the wire at temperature t; R100 is the resistance at steam
point
(t= 1000C); R0 is the resistance at ice point (t= 00C).
brought to the boil by heating with a Bunsen or electrical heater. Using the same
procedure as before (circuit key closed only for sufficient time to enable ammeter and
voltmeter readings to be taken), obtain the new constant am
ammeter
meter and voltmeter readings.
The thermometer is now calibrated and ready for use:
(a) Continue to boil the water but add sufficient salt to it until you notice that no more
salt will dissolve. Use the same procedure as before to obtain the constant ammeter
and voltmeter readings
(b) Finally, remove the resistance thermometer from the boiling brine and allow it to cool
down to room temperature, assisting it in doing so by immersing in cold water. Dry
the resistance thermometer and proceed to obtain the constant amm
ammeter
eter and voltmeter
readings when the thermometer has assumed the prevailing temperature of the
laboratory.
RESULTS: Tabulate your readings as follows:
Ammeter
reading I/A
Voltmeter
reading V/V
Ice point
Water boiling
point
Brine boiling
point
Room
temperature
Resistance =
V/I
(Ω)
Ro =
……….
R100 = …….
Temperature θ
00 C
1000C
Rbrine = …….
Rroom =
……..
θ
EXPERIMENTAL DETAILS
1 If preferred the resistance of the thermometer may be measured by the Wheatstone
bridge method.
2 Ideally the upper fixed point should be the steam point, i.e. the resistance of the coil
when immersed in steam, not boiling water, should be measured. The resistance in
boiling
ng water is, however, more convenient and sufficiently accurate for the purpose
of this experiment which is to illustrate the principle behind this method of measuring
temperature.
CONCLUSION:
1 Determine the brine boiling temperature
2 determine the room temperature
3 state the precautions you observed
4 how will you ensure better results in the experiments
WEEK 5 THERMODYNAMICS I PRACTICAL
MEC I22
Ingenhausz's apparatus, a steam boiler and wax.
Fig. 4.1 - Ingenhausz's apparatus
DESCRIPTION OF APPARATUS
The Ingenhausz's apparatus consists of a rectangular metal trough to one side
ide of which are soldered a
number of short metal tubes. Through one
one-bored
ed stoppers fitted into these tubes are inserted
ins
the
experimental rods of different
fferent materials, all having the same cross
cross-section and length.
PROCEDURE:
i)
To conduct the experiment, dip the rods in molten paraffin wax so that on solidification, each rod
will have a thin wax coating. Insert the rods in position. Pour boiling water into the trough and
keep it boiling by passing a continuous current of steam in
into
to it. The end of each rod is thus heated to a
constant temperature. Heat is conducted by each towards the other end and the wax coating
gradually melts along each rod. After some time, however, tthe
he line of demarcation between the
melted and the unmelted wax--remains
remains stationary. At these points all the rods have the same
temperature - the temperature at which the wax melts. Measure the distances of these points along
the rods when the steady state is reached. The conductivities of the rods are directly proportional
pr
to
the squares of these distances.
OBSERVATIONS
Length over which wax melts on copper rod, l1 =
cm.
Length over which wax melts on iron rod, 12
=
cm.
Length over which wax melts on brass rod, I3
=
cm.
2. Why?
WEEK 6 THERMODYNAMICS I PRACTICAL
MEC I22
EXPERIMENT 6 NEWTON’S LAW OF COOLING
INTRODUCTION
The purpose of this experiment is to measure the difference in temperature (∆T) between a cup of
cooling water and the room as a function of time. You will then see if the data are consistent with
Newton's law of cooling, which predicts ∆T to be an exponential function of the elapsed time.
THEORY
Newton suggested that the rate of heat flow from a hot body (that is, Q/∆t, where t represents
time) is roughly proportional to the difference in temperature between the body's temperature
(Twater, if that body is water) and the temperature of the surroundings, Troom. Since we often
recognize heat flow by a temperature change (Q/∆t is related to T/∆t), Newton's law of cooling
simply says that T/∆t = k(Twater - Troom), where k is a constant. Since Troom is constant, ∆T = (Twater Troom) so we can write:
 Twater − Troom 

 = k (Twater − Troom )
t


Thus the rate at which (Twater - Troom) changes is proportional to (Twater - Troom). When a quantity
varies in this way it is said to vary exponentially with time:
Or
(Twater − Troom ) = T0 e
−
t
τ
where To is the initial change in temperature, t is the elapsed time, and τ is called the time constant.
τ is the amount of time for the temperature to "decay" to 37% of the original To.
EXPERIMENT
1. You have two thermometers, one for measuring the temperature of the water and one for
measuring room temperature. A 10 milliliter beaker holding a small amount of hot water is
placed in a plastic box to protect it from drafts. Although the thermometer is marked in
whole degrees, try to read the temperature to the nearest 0.10°.
Set up the following data table in your notebook. The elapsed time is the time that has passed since
your first observation. Note that your first measurement occurs at t = 0!
Elapsed time, t
(min)
Twater
(°C)
Troom
(°C)
∆T = Twater – Troom
(°C)
0.0
—
—
—
0.5
—
—
—
…
—
—
—
20.0
—
—
—
2. Observe the temperature in the water and the room every 30 seconds for five minutes, then
every minute for the next 15 minutes.
ANALYSIS
3. During other experiments that we perform this semester, we typically will graph points as
the data is collected, to ensure that the experiment is behaving as expected. In this
experiment, care must be taken during the data collection, so you won't be able to graph as
you go along. After you have finished collecting your data, use Excel to create a graph of
∆T vs. t.
4. Fit an exponential curve to your Excel plot. From the equation Excel calculates, determine
the time constant, τ.
REPORT
•
State your value for the time constant. What are the units for τ?
•
When this experiment has been performed in the past, it was noted that the data deviates
from the (theoretical) exponential curve, especially during the first few readings. Does your
data exhibit this behavior? Compare your graph to those from other groups. Do they show
similar trends? What conclusions can you draw from this?
WEEK 7 THERMODYNAMICS I PRACTICAL
MEC I22
EXPERIMENT 7 : Boyle's Law
Apparatus and materials
Boyle's Law apparatus
Foot pump and adaptor
Kinetic theory model kit (transparent cylinder with small steel balls)
Theory
The apparatus has been specially designed to give quick, clear readings which the class can see.
A sample of dry air is confined in a tall, wide glass tube by a piston of oil. The volume is found
from the length of the air column, which should be clearly visible at the back of the class.
The pressure is read from a Bourdon gauge connected to the air over the oil reservoir. This is
calibrated to read absolute pressure and is also visible from the back of the class.
photo courtesy of J Kinchin
The foot pump is attached to the oil reservoir and is used to change the pressure. The gauge reads
up to 3 x 105 N m-2 and the pressure can safely be taken up to this value but must not be taken
beyond.
To fill the apparatus with oil, unscrew the Bourdon gauge with a spanner and fill the chamber
with a low vapour pressure oil. Tilt the apparatus in the final stage of filling in order to get
enough oil into the main tube. When refixing the gauge, tighten the nut to get a good seal, but not
so much that the thread is damaged.
Safety
It has been known for the glass tube to fly upwards when the gas is at maximum pressure. To
prevent this, check the compression joint holding the tube and any tube supports before use. (The
apparatus is filled and emptied by removing the pressure gauge.)
Procedure
a Give a quick demonstration to show that doubling the pressure halves the length of the air
column, and so its volume.
b Increase the pressure to its maximum value, and then record it and the (minimum) length of the
air column.
c Next, disconnect the pump and release a little air using the valve on the oil reservoir, so that the
oil level in the tube falls a few centimetres.
d Before taking the next pair of readings, wait a while so that the air temperature recovers and
the oil left behind has fallen down the wall of the tube.
e Keep repeating step c until the gauge returns to atmospheric pressure.
WEEK 8 THERMODYNAMICS I PRACTICAL
MEC I22
EXPERIMENT 8 : CHARLES’ LAW EXPERIMENT
INTRODUCTION
There is associated with all gases some common properties. For example a) gases are highly
compressible which means that between gas particles there exist significant amounts of space; b)
gases are quite expandable which means that gas particles will spread out and occupy the entire
volume of their containers; c) gases will exert pressure on the walls of their containers which
means that gas particles are in constant motion and must possess kinetic energy. This energy can
be decreased or increased by cooling or heating the gas.
About 1790, Jacques Charles began to investigate the relationship between a specific volume of
gas and its temperature while keeping its pressure constant. Charles discovered that each time he
would increase the temperature of the gas by 1 degree C, the volume of the gas would increase
by 1/273 of its original volume. On the other hand, each time he would decrease the temperature
of the gas by 1 degree C, the volume of the gas would decrease by 1/273 of its original volume.
This relationship can be expressed mathematically by the following equation:
V / T = k (1)
where T represents the temperature, V the volume, and k a constant. In short, it would seem that
if you were to decrease the temperature of a gas from O degrees C to -273 degrees C, the volume
would decrease by 273/273 of its original volume. This would mean that at –273 degrees C there
would be a O volume of gas, an impossibility since matter cannot be destroyed or created.
Obviously one must remember that Charles' Law concerns itself with gases, and that gases will
change from a gaseous state to a liquid state (condense) well before reaching -273 degrees C.
In this experiment, you will vary the temperature on a confined quantity of air 5 times, each time
RECORDING the temperature and volume. Finally, you will plot the data collected in order to
help you analyze your findings.
MATERIAL
CHEMICALS
•
15 Syringes (10 mL)
•
Ice
•
15 Rubber stoppers (#OO/modified)
•
Water
•
15 Plastic cups (10 oz/low)
•
15 Thermometers (-10 to 110 deg. C)
•
15 Beakers (256 mL)
•
15 Styrofoam cups medium (optional)
•
Microburners
•
1 Timer/class
•
15 Graph papers (sheet)
PROCEDURE
1. Setting up the Apparatus
Draw out the plunger of a small syringe so that the lower portion of its rubber ring is set at the 5
cc mark To contain this volume of air, connect a modified #00 rubber stopper to the syringe.
2. Measuring the Temperature and Volume
Place the syringe and a thermometer into an ice water bath and wait 5 minutes so that the gas and
thermometer will equilibrate to the temperature of the water bath. Now press the plunger
downward a little and release it. This will help reduce some friction there will be between the
plunger and the wall of the syringe. Alter releasing the plunger, wait 30 seconds. Then RECORD
the volume and temperature of the gas.
Repeat this process with water baths of approximately 20, 50, 80, and 95 degrees C. The water
baths greater
than 20 degrees C will require a heat source and thus you will need the use of a glass beaker for
your water bath. Be sure to RECORD your data after each measurement.
WEEK 9 THERMODYNAMICS I PRACTICALS MEC122
EXPERIMENT 9: SPECIFIC HEAT CAPACITY
AIM: TO DETERMINE THE SPECIFIC HEAT CAPACITY OF SOLIDS
APPRATUS: copper calorimeter, stirrer, weighing machine, water, thermometer
THEORY:
The specific heat capacity of a solid substance in block is determined by this method. When the
solid is heated and introduced in to water in a calorimeter, the heat loss by the solid is equal to
heat gain by the water and calorimeter.
Mathematically:
Heat loss by solid = heat gain by water and calorimeter …………………….(1)
Heat loss by solid = yx(ts2-t2)
Heat gain by water = mwCw (t2-t1)
Heat gain by calorimeter = mcCc(t2-t1)
From equation (1)
yx(ts2-t2) = mwCw (t2-t1) + mcCc(t2-t1) ……………………………………(3)
the specific heat capacity of the solid is equal to the heat capacity of the solid per unit mass of
solid
i.e
X = Y/Ms
……………………………………………………….(4)
Where:
y = the specific heat capacity of the solid J/k
ms =mass of the solid, g
ts2 = temperature of the solid, k
t1 = initial temperature of water, k
mw = mass of water, g
mc = mass of copper calorimeter, g
Cw = the specific heat capacity of water = 4.2 J/gk
Cc = the specific heat capacity of copper calorimeter = 0.4 J/gk
Cs = specific heat capacity of the solid, J/gk
PROCEDURE
1 Weigh the calorimeter empty
2 Partly fill the calorimeter by 2/3 with cold water and reweigh
3 Determine the mass of water
4 Record water initial temperature
5 Place the calorimeter in the lagged jacket
6 Measure the mass of the solid by weighing
7 Record initial solid temperature
8 Heat solid as shown above and record its temperature
9 Transfer the solid with of the string into the water in the calorimeter and stir
note the maximum temperature after stirring
RESULT:
Record your results as follows:
Mass of calorimeter =
Mass of water + calorimeter =
Mass of water =
Mass of substance =
Initial water temperature =
Final water temperature =
Temperature of hot solid =
CONCLUSION:
1 Determine solid heat capacity
2 Determine solid specific heat capacity
3 Why do you shake the solid on removal from the hot water?
4 Why do you cover the calorimeter with an insulating lid?
5 How is the calorimeter heat loss by radiation minimized?
6 How is heat loss by convection eliminated?
7 Compare your result with the generally accepted value for the specific heat capacity value of
the solid?
WEEK 10 THERMODYNAMICS I PRACTICAL
MEC I22
EXPERIMENT 10: SPECIFIC HEAT CAPACITY
AIM: TO DETERMINE THE SPECIFIC HEAT CAPACITY OF A LIQUID BY THE
METHOD OF COOLING.
APPRATUS: A blackened calorimeter with copper lid to fit, bored with two holes to take a
thermometer and a copper stirrer. The calorimeter should stand on insulating stand(wooden
cones or corks) inside an outer jacket which should be sufficiently large to ensure that the
calorimeter is surrounded by air at a reasonably constant temperature
THEORY:
The specific heat capacity of liquids is determined by this method.
Taking the specific heat capacities of copper, water and the given liquid as c0, cw and c
respectively, the average rate of cooling for the calorimeter and contents is
(m0c0 +m1-m0c)(θ2-θ1)/t1 and when the calorimeter contains water the average rate of cooling is
(m0c0 +m2-m0c)(θ2-θ1)/tw
The rate of heat loss of a liquid surrounded by a constant temperature enclosure depends at any
instance only on the temperature difference the liquid and the enclosure, and the nature of the
area of the cooling surface.
(m0 c0 + m1 − m0 c )(θ 2 − θ1 ) t1
=
(m0 c0 + m2 − m0 c )(θ 2 − θ1 ) t w
PROCEDURE
1 Weigh the calorimeter with the lid the stirrer
2 assemble the apparatus and heat up the water in the beaker to about 700C
3 Remove the calorimeter from the apparatus and fill it with the heated liquid to within
centimeters of the top
4 Replace the thermometer, stirrer and the lid ,and put the whole back into the cooling chamber.
5 keep the liquid well stirred, and when the liquid has fallen to about 600C record the
temperature at minute interval down to 400C.
RESULT:
Record your results as follows:
Mass of calorimeter =
Mass of water + calorimeter =
Mass of water =
Mass of substance =
Initial water temperature =
Final water temperature =
Temperature of hot solid =
CONCLUSION:
1 Determine heat capacity of the liquid
2 Determine specific heat capacity of the liquid
3 Why do you cover the calorimeter with an insulating lid?
5 How is the calorimeter heat loss by radiation minimized?
6 How is heat loss by convection eliminated?
7 Compare your result with the generally accepted value for the specific heat capacity
of the solid?
WEEK 11 THERMODYNAMICS I PRACTICAL
value
MEC I22
EXPERIMENT 11:Which Fuel Source Has More Heat Energy?
A Comparison Of The Amount Of Energy Given Off In A Combustion Reaction
Objective:
There are two objectives for this experiment. The first is to compare possible fuel sources for the
amount of energy they give off in the form of heat energy. The second is to tell which one(s) are
cleaner burning fuels than the others.
THEORY:
We are always looking for alternative energy sources since fossil fuels are nonrenewable
resources. There are two questions frequently asked when considering an alternative fuel. How
much energy will be released per unit of that resource, and what effects might burning it have on
the environment? When we use a resource, such as coal, oil, or natural gas to produce energy, we
are breaking the chemical bonds within the substance and rearranging them into more stable
bonds. This change results in the formation of different products, such as carbon dioxide and
water in the case of combustion, and a release of energy. How can we measure the amount of
energy?
If we tried to quantify it mechanically, we may never know just how much absolute energy is in
the resource itself. Therefore, we use the "heating value" of fuels: how using so much of a certain
resource (rearranging its bonds into a more stable state) converts to so much heat (motion of
molecules). We all hear every day about counting calories. What is a calorie? A calorie (cal) is
defined as the amount of heat needed to raise one gram of water 1o C. A food calorie actually
consists of one kilocalorie, or 1,000 calories. Why do we worry about calories in relation to our
weight? Energy conservation! If you feed your body more calories than it can use, it will store
the energy in a stable state like body fat for you to use and lose later.
For this lab, we will measure the amount of the temperature change and use that to indicate heat
energy. Temperature is defined as the average kinetic energy of all the molecules, and heat is the
movement of molecules.
Materials and Supplies:
•
goggles for each member of the group
•
1 piece of thick cord clothesline 3 cm long
•
1 large paper clip
•
1 soda can with tab still attached per group
•
one thermometer
•
teacher has matches - show set-up to get a light
•
ring stand with ring
•
stirring rod
•
400 ml beaker
•
100 ml graduated cylinder
•
cold tap water
•
eye dropper bottles pipette with assigned material in it
Procedure:
1. Bend the paper clip so that it looks like this:
2. Weave the paper clip in and out of the outer most layer of the
looks like this:
clothesline so it
3. Measure 100 ml of cold water with a graduated cylinder and pour it into a soda can.
4. Place the stir rod through the tab of the pop can.
5. Set the stir rod on top of the ring, letting the can hang beneath --see figure below.
6. Place the thermometer in the can so that
7. it can be easily read;
8. it is in the 100 ml of water in the can;
9. it is supported by a clamp on the ring stand.
10. Put 20 drops of your substance on the clothesline and place it below the can.
11. Adjust the height of the ring so the can is 5 cm above the paper clip apparatus.
12. Measure and record the initial temperature of the water in the data table.
The apparatus should look like this:
13. Have the teacher ignite the clothesline and observe the flame; record your observations.
14. Let the clothesline burn until the flame disappears and place the smoking remains in a
beaker of water.
15. Record the final temperature of the water in the data table.
Data and Calculations:
Substance
Initial Temperature
C
o
Final Temperature
o
C
Appearance of fumes from
burning
Methanol
Ethanol
Vegetable
oil
Peanut oil
Motor oil
Kerosene
1. Calculate the difference in the temperature for all the samples tested.
Methanol
Ethanol
Vegetable oil
Peanut oil
Motor oil
Kerosene
2. Which 'fuels' burnt the cleanest?
3. Which 'fuel' source had most heat energy?
4. Were you able to measure the total amount of energy released? Why or why not -explain your answer fully.
5. Does the fact that the clothesline may burn affect this comparison of 'fuel' sources?
Explain your answer fully.
6. What 'fuel' do we put in our bodies? How is what happens in your body with that 'fuel'
similar and dissimilar to how 'fuel' is used in your car?
WEEK 12 THERMODYNAMICS I PRACTICAL
MEC I22
EXPERIMENT12: Evaporation Rate
Supplies: White hand towel, clothes pins
Process: Determine a quantity of water that will wet a hand towel without any water dripping
away from it. Record the temperature, relative humidity and wind of outside air. Label wind as
light (5 mph or less), moderate ( 6 to 14 mph) or strong (greater than 14 mph). Wet the hand
towel with a specific quantity of water and hang it outside with clothes pins in the shade. Always
use the same amount of water on the towel and use the same towel on every trial. Check the
towel every 5 minutes until it is completely dry. Determine relationships between drying time
and the temperature, relative humidity and wind speed outside. It will take many trials to
determine these relationships.
Scientific principles: The following general relationships should be discovered:
a. At a similar temperature and relative humidity, drying time should be less as wind speed
increases. A stronger wind removes water vapor molecules away from the towel at a higher rate.
This keeps the vapor gradient between the towel and the air high and thus promotes a faster
evaporation rate as compared to lighter wind.
b. At a similar temperature and wind speed, drying time should be less as the relative humidity
decreases. When the relative humidity is 100% then the towel will not be able to dry since the air
is already saturated with water vapor. As the relative humidity decreases, the vapor gradient
between the saturated towel and air increases and thus evaporation increases.
c. At a similar relative humidity and wind speed, drying time should be less as the temperature
increases. Warmer air can evaporate more moisture into it than cooler air can. Thus, when the
relative humidity and wind speed is the same, warmer air will be able to evaporate moisture from
the towel at a faster rate.
WEEK 13 THERMODYNAMICS 1 PRACTICALS MEC 122
EXPERIMENT
13:
Finding
Dewpoint
Supplies: Cup, ice-water, warm-water, any type of syringe, mercury in glass thermometer
Note: For this experiment to work best the dewpoint needs to be well above freezing. If the
dewpoint is below freezing, salt water or a liquid that stays unfrozen below the freezing point of
water would need to be used in place of the ice-water and cold water would be used to start
instead of warm-water. If the dewpoint is below freezing, frost instead of condensation will
occur
on
the
cup
when
doing
the
experiment.
Process: Take a metal, hard plastic or glass cup (metal works best) and fill it up a third of the
way with warm water that is around 85 F. Place the thermometer into the warm water. Have
another cup with you that is filled with ice-water. Gradually place small amounts cold water into
the warm water with the syringe. Place enough cold water to drop the temperature of the water a
degree or 2 each time some cold water is added. Ice cubes may need to be added if the dewpoint
is near the freezing point. Do this until condensation starts to form on the outside of the cup.
When condensation on the outside of the cup starts to develop then the dewpoint temperature has
been
reached.
Scientific principles: 1. Dewpoint is the temperature that air needs to be cooled to in order for
condensation to occur. You have probably noticed that on warm/humid days that lots of
condensation will develop of the outside of a cup that has an icy cold beverage in it. If the cup
temperature is below the dewpoint temperature, moisture will condense out of the air since the
maximum amount of moisture that can be in the air decreases as temperature decreases. 2.
Dewpoint gives a meteorologist as assessment of the amount of moisture in the air. As dewpoint
increases, the amount of moisture in the air increases
WEEK 14 THERMODYNAMICS I PRACTICAL
EXPERIMENT
Supplies:
14:
Bowl,
salt,
MEC I22
Supercooled
ice,
small
plastic
Water
cup,
thermometer
Process: Fill a bowl half way with water. Dissolve as much salt as possible into the water. Next,
add ice and wait a few minutes. Measure the temperature of the ice/salt/water mixture. The
temperature should be below 32 F. Place a small amount of water into a plastic cup. Try to use as
pure of water as possible in the plastic cup and make sure the plastic cup in completely clean.
Float the plastic cup with the water in the bowl of ice/salt/water making sure not to touch the
experiment once the plastic cup is placed in the salty ice water. Wait about 10 minutes. The
water in the plastic cup will come into thermal equilibrium with the ice/salt/water and thus the
pure water will be supercooled. Next, drop a few grains of dust or other small matter into the
pure supercooled water. You should notice the water immediately turn to all or mostly ice.
Scientific principles: 1. Water will not freeze until it has a condensation nuclei to freeze on. The
plastic is not a good condensation nuclei but the small particles of matter dropped into the
supercooled water will be. Typically, liquid cloud drops in the troposphere that have
temperatures between 0 and -10 C will be supercooled. 2. Salt water has a lower freezing point
than pure water. 3. As the supercooled water turns to ice, the latent heat release will warm the
water back to 32 F (0 C).
EXPERIMENT 15
OBJECTIVE: To determine the coefficient of performance of the Air-conditioning test unit
when acting as:-
i.
A cooler
ii.
A heat pump
EQUIPMENT
Plint and partners versatemp air-conditioning TE/94/1902, flowmeter, cromption wattmeter,
thermometers.
Student to draw a schematic diagram of the arrangement.
PROCEDURE
Students to write this up as per instructed
THEORY
Conventionally, the air-conditioners is described as a cooler when it is extracting heat from the
surrounding air and rejecting it to the cooling water; and it is described as a heat pump when it is
extracting heat from the water and transferring it to air.
(i)
The coefficient of performance of the air-conditioning when acting as a cooler is given by
CPR
=
q1
W
Where q1 = heat extracted from air
= mass flow rate of air x Enthalpy drop of air in passing through air-conditioner.
Mass flow rate of air can be calculated from the pitot tube mounted in the discharge duct;
But
Pa
=
RT
P
Where R
=
287
Pa
=
atmospheric pressure in N/m2.
The velocity of the air U, corresponding to the velocity head H1 cm H2O as measured in the pitot
tube is given by
U2
=
98.1
H1
2
From these, it can be found that the mass flow rate of the air
m1
=
0.00332
H1 Pa kg/sec.
T2
Where T2 = temperature of the air leaving air – conditioner (0K)
∴ q1
=
m1 CP (T1 – T2)
Where T1 = temperature of air entering air-conditioner
CP = specific heat of air at constant pressure
= 1.005 kj/kg 0K.
W = Power input by fan + compressor + heat gained by water in cooling refrigerant.
Heat gained by cooling water
=
m2 CP (T5 – T4)
Where CP = 4.19 kj/kg 0K.
From the rotameter the volume of circulating water can be observed and hence the mass; take the
density of water as:(ii)
The coefficient of performance of the air-conditioner when acting as a heater.
CPH
=
q2
w
where q2 = energy gained by air in passing through air-conditioner.
W = power input to fan + compressor + heater
EXPERIMENTAL DATA
TEMPERATURE OF INCOMING AIR.
TEMPERATURE OF OUTGOING AIR
PITOT TUBE DEFLECTION
POWER INPUT TO FAN
POWER INPUT TO COMPRESSOR
POWER INPUT TO HEATER
TEMPERATURE OF WATER AT INLET
TEMPERATURE OF WATER AT OUTLET
RATE OF FLOW OF WATER
BAROMETRIC PRESSURE
CONCLUSION
i.
From standard calculations, the maximum coefficient of performance of the airconditioner as a cooler was found to be 6.2. Compare and contrast this with your
results.
ii.
The maximum coefficient of performance of this air-conditioner as a heater was also
found to be 4.78. Compare and contrast this with your results.