Download THERMODYNAMICS LAB 4 – Thermal Conductivity

EPT 201 Thermodynamics
Experiment 1 : Temperature Measurement Method
Laboratory Module
EXPERIMENT 1
Temperature Measurement Method
1. OBJECTIVE
2. INTRODUCTION
3. COMPONENT AND EQUIPMENT
4. PROCEDURE
5. RESULTS
6. DISCUSSION / EVALUATION AND QUESTION
7. CONCLUSION
1
EPT 201 Thermodynamics
Experiment 1 : Temperature Measurement Method
Laboratory Module
EXPERIMENT 1
Temperature Measurement Method
1. OBJECTIVE
1.1
1.2
To learn fundamental temperature measuring techniques using
i.
Mercury-glass thermometer
ii.
Thermocouple (type K)
iii.
Thermistor
iv.
Resistance Temperature Detector (RTD)
v.
Bi-metal thermometer
To compare the accuracy of the various temperature measurement devices.
2. INTRODUCTION
2.1 Background
Temperatures measure of the relative warmness or coolness of an object.
Temperature is measured by means of a thermometer or other instrument having a scale
calibrated in units called degrees. The size of a degree depends on the particular
temperature scale being used. A temperature scale is determined by choosing two
reference temperatures and dividing the temperature difference between these two points
into a certain number of degrees. The two reference temperatures used for most common
scales are the melting point of ice and the boiling point of water. On the Celsius
temperature scale, or centigrade scale, the melting point is taken as 0°C and the boiling
point as 100°C, and the difference between them is divided into 100 degrees. On the
Fahrenheit temperature scale, the melting point is taken as 32°F and the boiling point as
212°F, with the difference between them equal to 180 degrees.
The temperature of a substance does not measure its heat content but rather the
average kinetic energy of its molecules resulting from their motions. A one-pound block of
iron and a two-pound block of iron at the same temperature do not have the same heat
content. Because they are at the same temperature the average kinetic energy of the
2
EPT 201 Thermodynamics
Experiment 1 : Temperature Measurement Method
Laboratory Module
molecules is the same; however, the two-pound block has more molecules than the onepound block and thus has greater heat energy.
The scale we use to measure temperature is "degrees" (°). There are three
temperature scales that are used today.
i. The Kelvin (K) scale is used by scientists and for astronomical temperatures.
ii. The Celsius scale (°C) is used in most of the world to measure air temperatures.
iii. The Fahrenheit scale(°F) is used to measure temperatures at or near the surface.
All three temperature scales are related to each other through the "triple point of
water". The triple point of water is the temperature at which water vapor, liquid water, and
ice can coexist simultaneously. The triple point occurs at 0.01 °C (273.16 K or 32.02 °F).
To convert from one temperature scale to another, we need to use the equations as below:
1) Convert Celsius to Kelvin: K = °C + 273
2) Convert Celsius to Fahrenheit: °F = 1.8(°C) + 32
2.2
Mercury in Glass Thermometer
The mercury in glass thermometer (figure 1) is a thermometer consisting of
mercury in a glass tube. Calibrated marks on the tube allow the temperature to be read by
the height of the mercury column in the capillary tube which varies according to the
temperature. Glass thermometer is accurate, economical instrument that measures
temperature of liquids or gases. All of the glass thermometers conform to the International
Temperature Scale of
1990 (ITS-90). ASTM (American Society for Testing
Materials) thermometers
vary from 5.5 mm to 8 mm in diameter;
most
and
other
thermometers have a 6 mm to 7 mm diameter. Glass thermometer temperature ranges are
around -199.8°C until 499.5°C.
3
EPT 201 Thermodynamics
Experiment 1 : Temperature Measurement Method
2.1.1
Laboratory Module
Types of Glass Thermometer
a) Partial Immersion
Partial immersion thermometer is immersed in the fluid to a specified immersion
depth. The remaining (emergent) portion of the stem is exposed to the air.
b) Total Immersion
Total immersion thermometer need to be immersed up to the liquid
temperature mark on the thermometer. Since the thermometer column is
fully immersed, this thermometer is the most accurate.
Figure 1 : Glass Thermometer
2.3
Thermocouple
Thermocouple as shows in figure 2, is a temperature measurement sensor that
consists of two dissimilar metals that joined together at one end (a junction) that produces
a small thermoelectric voltage when the junction is heated. Thermocouple thermometers
interpret the change in thermoelectric voltage as a change in temperature.
Figure 2 : Thermocouple with probe
4
EPT 201 Thermodynamics
Experiment 1 : Temperature Measurement Method
Laboratory Module
Thermocouple is available in various types with different combinations of dissimilar
metals. The most common types are: Type J, K, T and E. For example, Type K
Thermocouple is ranged between -249.75°C to 1373.625°C and Type J Thermocouple is
ranged between -189.81 °C to 999°C.
Exposed junction thermocouple is fast responding but the thermocouple itself is
unprotected and subject to corrosion from the environment. Also, the smaller the probe
sheath diameter, the faster the response. Often the thermocouple is located inside a metal
or ceramic shield that protects it from a variety of environments. Metal-sheathed
thermocouple is also available with many types of outer coating, such as polytetrafluoro
ethylene for trouble-free use in corrosive mediums.
2.4
Thermistor
Thermistor as shows in figure 3 is a thermally sensitive resistor and has, according
to type, a negative (NIC) or positive (PTC) resistance/temperature coefficient. Thermistor
thermometry is based on the principle that metal oxides change resistance with a change
in temperature. Resistance decreases as the temperature decreases. The meter where it
is converted and displayed as a temperature reading detects this resistance change.
Thermistor has excellent accuracy over biological or ambient temperature ranges when
compared to RTDs or Thermocouples. Response time is generally faster than RTDs.
Figure 3 : Thermistor with probe
Thermistor is generally composed of semiconductor materials. Most thermistors
have negative temperature coefficient (TC) which means resistance decreases with
increasing temperature. The negative TC can be as large as several percents per degree
Celsius (%/°C), allowing the thermistor circuit to detect minute changes in temperature,
which could not be observed with an RTD, or thermocouple circuit.
5
EPT 201 Thermodynamics
Experiment 1 : Temperature Measurement Method
Laboratory Module
Thermistor has a semiconductor material which changes its electrical resistance as
a function of temperature. Extension wires used with thermistor can be plain copper wire.
Thermistor offers accuracy similar to RTD within narrow temperature ranges near to
ambient temperature. It is generally responses faster comparatively. Since thermistor
standards vary, care must be taken to match the instrumentation to the sensor. The
resistance-temperature relationship of a thermistor is negative and highly nonlinear.
Thermistor is usually designated in accordance with it's resistance at 25°C.
2.5
Resistance Temperature Detector (RTD)
A typical RTD as shows in figure 4 consists of a fine platinum wire wrapped around
a mandrel and covered with a protective coating. Usually, the mandrel and coating is glass
or ceramic. Depositing can also make the platinum as a film on a substitute and then
encapsulating it. RTD is wire wound and thin film device that work on the physical principle
of the temperature coefficient or electrical resistance of metals.
Figure 4 : RTD with probe
The electrical resistance of the RTD changes as a function of temperature. Circuitry
similar to Wheat stone bridge is built into control designed for use with RTD. Constant
current into the bridge produces an output voltage that varies with temperature. Lead wire
resistance can significantly affect the RTD measurement. This is typically corrected using
a third (compensating) lead wire.
6
EPT 201 Thermodynamics
Experiment 1 : Temperature Measurement Method
Laboratory Module
RTD is nearly linear over a wide range of temperatures and can be made small
enough to have response times of a fraction of a second. The classical resistance
temperature detector (RTD) construction using platinum was proposed by C.H.Meyers in
1932. This requires an electrical current to produce a voltage drop across the sensor that
can be then measured by a calibrated read-out device.
2.6
The Bimetallic Thermometer
The bimetallic thermometer as shows in figure 5
uses a bimetal, which is
composed of two types of metals with different thermal coefficients of expansion and they
are wound into a helical form, change according to temperature is transmitted to the
indicator. This thermometer is simple in construction and reasonably priced.
Figure 5 : Bimetallic Thermometer
7
EPT 201 Thermodynamics
Experiment 1 : Temperature Measurement Method
3.
Laboratory Module
COMPONENT AND EQUIPMENT
Figure 6: Temperature Measurement Bench
Equipment apparatus :
qty
 Vacuum flask.
1
 Water heater jug
1
 Digital resistance /mV indicator
1
 Direct reading digital
1
temperature indicator for use
1
with thermocouple
Equipment apparatus :
 Thermocouples Type K & lead
qty
1
wires
 Mercury in glass thermometers:-5
1
to 105 Deg C
 Mercury in glass thermometers:- -
1
5 to 360 Deg C
 Thermistor
 Vapor pressure thermometer
1
 Wet and dry bulb thermometer
1
 Platinum resistance thermometer
1
 Bimetallic temperature indicator:
1
0-400 Deg C.
Equipment Note
This Temperature Measurement Bench (Model: HE 151) has been designed to
demonstrate the fundamental temperature measuring techniques using thermocouples,
mercury in glass thermometer, resistance temperature detector (RTD), thermistor,
bimetallic temperature indicator and etc. Temperature measurement is used to measure
air temperature, boiling water temperature, ice-point temperature and wet or dry bulb
temperature. Temperature can be measured via a various ranges of sensors. All of these
sensors infer temperature by sensing changes in physical characteristics.
8
EPT 201 Thermodynamics
Experiment 1 : Temperature Measurement Method
Laboratory Module
4. PROCEDURE
PART 1 : Ambient air temperature measurement
No.
Procedure
1.
Take out the mercury-glass thermometer, close inspection will reveal a column of
mercury protrude from the bulb. Temperature measurement is achieved by
relating the length of this column to an engraved scale on the glass.
Read the
temperature indicated by the column at ambient air temperature.
2.
Take out the bi-metal thermometer, close inspection will reveal a metal rod at the
end of the indicator. Temperature measurement is achieved by transferring heat to
the metal rod.
3.
Take out a Type K thermocouple. Connect the blue and yellow plugs to the
corresponding sockets of the Type K thermocouple temperature indicator. Place
the thermocouple on the baseboard and allow the readings to stabilize at the
ambient air temperature. Read the temperature indicated on the temperature
indicator.
4.
Take out a resistance temperature detector (RTD). Connect the RTD plugs to the
corresponding sockets of the RTD indicator. Place the RTD on the baseboard
and allow the readings to stabilize at the ambient air temperature. Read the
temperature indicated on the RTD temperature indicator.
5.
Take out a thermistor. Connect the thermistor plugs to the corresponding sockets
of the thermistor indicator. Place the thermistor on the baseboard and allow the
readings to stabilize at the ambient air temperature. Read the temperature
indicated on the thermistor indicator.
6.
Take out the vapor pressure thermometer. Place the vapor pressure thermometer
on the baseboard and allow the readings to stabilize at the ambient air
temperature. Read the temperature indicated on the indicator
9
EPT 201 Thermodynamics
Experiment 1 : Temperature Measurement Method
Laboratory Module
PART 2 : Ice-point temperature measurement
No.
Procedure
1.
Half fill the vacuum flask with a mixture of crushed ice and pure water
2.
Insert the bulb of the thermometer into the water-ice mixture; stir gently to ensure
intimate contact with the mixture. Observe the reading on the thermometer.
3.
Insert the metal rod of the bi-metal thermometer into the water-ice mixture; stir
gently to ensure intimate contact with the mixture. Observe the reading on the
bimetallic temperature indicator.
4.
Insert the thermocouple probe into the water-ice mixture; stir gently to ensure
intimate contact with the mixture. Observe the reading on the thermocouple
temperature indicator
5.
Insert the RTD probe into the water-ice mixture; stir gently to ensure intimate
contact with the mixture. Observe the reading on the RTD temperature indicator.
6.
Insert the thermistor probe into the water-ice mixture; stir gently to ensure intimate
contact with the mixture. Observe the reading on the thermistor temperature
indicator.
7.
Insert the metal rod of the vapor pressure indicator into the water- ice mixture; stir
gently to ensure intimate contact with the mixture. Observe the reading on the
indicator.
10
EPT 201 Thermodynamics
Experiment 1 : Temperature Measurement Method
Laboratory Module
PART 3 : Boiling-point temperature measurement
No.
Procedure
1.
Half fill the water heater jug with clean water and connect the power cord.
2.
Swicth ‘ON’ the water heater jug. wait until water is boil .
Be careful to the hot water.
3.
Insert the bulb of the thermometer into boiling water. Observe the reading on the
thermometer.
4.
Insert the metal rod of the bimetalic indicator into boiling water. Observe the
reading on the bimetallic indicator.
5.
Insert the thermocouple probe into boiling water. Observe the reading on the
temperature indicator.
6.
Insert the RTD probe into boiling water. Observe the reading on the resistance
indicator.
7.
Insert the thermistor probe into boiling water. Observe the reading on the
thermistor indicator.
8.
Insert the metal rod of the vapor pressure indicator into boiling water. Observe the
reading on the thermometer.
11
EPT 201 Thermodynamics
Experiment 1 : Temperature Measurement Method
Name
:____________________________________
Matrix No.
: ____________________________________
Date
:____________________________________
Laboratory Module
5. RESULTS
PART 1 : Ambient air temperature measurement
No.
Temperature device
1.
Mercury-glass thermometer
2.
Bi-metal thermometer
3.
Thermocouple Probe (type K)
4.
RTD probe
5.
Thermistor probe
6.
Vapor pressure indicator rod
ºC
PART 2 : Ice-point temperature measurement
No.
Temperature device
1.
Mercury-glass thermometer
2.
Bi-metal thermometer
3.
Thermocouple probe (type K)
4.
RTD probe
5.
Thermistor probe
6.
Vapor pressure indicator rod
ºC
PART 3 : Boiling-point temperature measurement
No.
Temperature device
1.
Mercury-glass thermometer
2.
Bi-metal thermometer
3.
Thermocouple probe (type K)
4.
RTD probe
5.
Thermistor probe
6.
Vapor pressure indicator rod
ºC
12
EPT 201 Thermodynamics
Experiment 1 : Temperature Measurement Method
Laboratory Module
6. DISCUSSION/ EVALUATION AND QUESTIONS
6.1
Discuss experimental results. You may use below guidelines:
(Include a discussion on the result noting trends in measured data, and comparing measurements
with theoretical
predictions when possible. Include the physical interpretation of the results and graphs, the reasons on deviations of your
findings from expected results, your recommendations on further experimentation for verifying your results, and your
findings)
13
EPT 201 Thermodynamics
Experiment 1 : Temperature Measurement Method
Laboratory Module
6.2
Why there are differences in temperature readings among measurement devices?.
6.3
Which device gives the fast response during taken measurement?
6.4
To continuously measure temperature in 24 hours within 200 meter distance
which device could you propose and why?
6.5
From you own reading, give the temperature measurement device that could
be use to measure melted aluminium which having temperature > 400°C.
14
EPT 201 Thermodynamics
Experiment 1 : Temperature Measurement Method
6.6
7.
Laboratory Module
Convert the below data (show you calculations)
i.
89 ºC
to
Kelvin
ii.
321° Kelvin to Fahrenheit
iii.
Water standard boiling temperature in ºC , ºK
iv.
Water standard ice temperature in
and ºF
ºC , ºK and ºF
CONCLUSION
Based on data and discussion, make your overall conclusion by referring to experiment objective.
15