Temperature Measurement Method 4b6iu

ENT 211 ThermoFluid

Laboratory Module

EXPERIMENT 3A TEMPERATURE MEASUREMENT METHOD 1.0 OBJECTIVES 1.1 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 2.1 To compare the accuracy of the various temperature measurement devices.

2.0

EQUIPMENTS / APPARATUS

Figure 7: Temperature Measurement Bench Equipment apparatus :  Vacuum flask.  Water heater jug  Digital resistance /mV indicator  Direct reading digital temperature indicator for use with thermocouple  Thermistor  Vapor pressure thermometer  Wet and dry bulb thermometer

qty 1 1 1 1 1 1 1

Equipment apparatus : qty  Thermocouples Type K & lead 1 wires 1  Mercury in glass thermomerters:5 to 105 Deg C 1  Mercury in glass thermomerters:-5 to 360 Deg C 1  Platinum resistance thermometer 1  Bimetallic temperature indicator : 0-400 Deg C.

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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. Thermocouples consist essentially of two wires made of different metals that ed at one end. Resistance temperature detector devices capitalize on the fact that the electrical resistance of a metal changes as a result of temperature change. Thermistors are based on resistance change in ceramic semiconductor where the resistance drops nonlinearly with temperature rise. Bimetallic devices take advantage of the difference in rate of thermal expansion between different metals.

3.0 INTRODUCTION AND THEORY Temperature, 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 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

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3.1

Laboratory Module

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 and Materials) thermometers vary from 5.5 mm to 8 mm in diameter; most other thermometers have a 6 mm to 7 mm diameter. Glass thermometer temperature ranges are around -199.8°C until 499.5°C. 3.1.1

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

3.2

Thermocouples Thermocouple (figure 2) is a temperature measurement sensor that consists of two dissimilar metals that ed 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. 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.

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Figure 2 : Thermocouple with probe

3.3

Thermistor Thermistor (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. 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.

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3.4

Laboratory Module

Resistance Temperature Detector (RTD) A typical RTD (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 a Wheatstone 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. 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.

3.5

The Bimetallic Thermometer The bimetallic thermometer (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.

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Figure 5 : Bimetallic Thermometer

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4.0 EXPERIMENTAL PROCEDURE No. 1.

2. 3.

4.

5.

6.

1. 2. 3. 4. 5. 6. 7.

1. 2. 3. 4.

Procedure PART 1 : Ambient air temperature measurement 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. 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. 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. 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. 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. 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 PART 2 : Ice-point temperature measurement Half fill the vacuum flask with a mixture of crushed ice and pure water Insert the bulb of the thermometer into the water-ice mixture; stir gently to ensure intimate with the mixture. Observe the reading on the thermometer. Insert the metal rod of the bi-metal thermometer into the water-ice mixture; stir gently to ensure intimate with the mixture. Observe the reading on the bimetallic temperature indicator. Insert the thermocouple probe into the water-ice mixture; stir gently to ensure intimate with the mixture. Observe the reading on the thermocouple temperature indicator Insert the RTD probe into the water-ice mixture; stir gently to ensure intimate with the mixture. Observe the reading on the RTD temperature indicator. Insert the thermistor probe into the water-ice mixture; stir gently to ensure intimate with the mixture. Observe the reading on the thermistor temperature indicator. Insert the metal rod of the vapor pressure indicator into the water- ice mixture; stir gently to ensure intimate with the mixture. Observe the reading on the indicator. PART 3 : Boiling-point temperature measurement Half fill the water heater jug with clean water and connect the power cord. Swicth ‘ON’ the water heater jug. wait until water is boil . Be careful to the hot water. Insert the bulb of the thermometer into boiling water. Observe the reading on the thermometer. Insert the metal rod of the bimetalic indicator into boiling water. Observe the reading on the bimetallic indicator.

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ENT 211 ThermoFluid

5. 6. 7. 8.

Name :

Laboratory Module

Insert the thermocouple probe into boiling water. Observe the reading on the temperature indicator. Insert the RTD probe into boiling water. Observe the reading on the resistance indicator. Insert the thermistor probe into boiling water. Observe the reading on the thermistor indicator. Insert the metal rod of the vapor pressure indicator into boiling water. Observe the reading on the thermometer.

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Date : ______________

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ENT 211 ThermoFluid

Matrix No :

Laboratory Module

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5.0 DATA & RESULT PART 1 : Ambient air temperature measurement No. 1. 2. 3. 4. 5. 6.

Temperature device Mercury-glass thermometer Bi-metal thermometer Thermocouple Probe (type K) RTD probe Thermistor probe Vapor pressure indicator rod

ºC

PART 2 : Ice-point temperature measurement No. 1. 2. 3. 4. 5. 6.

Temperature device Mercury-glass thermometer Bi-metal thermometer Thermocouple probe (type K) RTD probe Thermistor probe Vapor pressure indicator rod

ºC

PART 3 : Boiling-point temperature measurement No. 1. 2. 3. 4. 5. 6.

Temperature device Mercury-glass thermometer Bi-metal thermometer Thermocouple probe (type K) RTD probe Thermistor probe Vapor pressure indicator rod

Name : Matrix No :

______________________________ ______________________________

ºC

Date : ______________

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ENT 211 ThermoFluid

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7.0

DISCUSSION / EVALUATION & QUESTION

7.1.

Briefly summarize the key results of experiment (5%) - Discuss about the trends and the nature of your results

7.2.

Explain the significance of your findings (5%) - First tell about the experiment objective - Explain the significance about your results and why is it of interest to you

7.3.

Explain any unusual difficulties or problems which may have led to poor results (5%) - Gives 3 problems in your experiment

7.4.

Offer suggestions for how the experimental procedure or design could be improved. (5%) - Give 3 suggestion how to improves your results

7.5.

Compare your experimental results with theoretical results.

7.6 Why there are differences in temperature readings among measurement devices?.

7.7 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

and ºF

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iii)

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Water standard ice temperature in

Name :______________________________

ºC , ºK and ºF

Date : ______________

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Matrix No :______________________________

8.0

CONCLUSION - Make an intelligent conclusion of your experiment base on data and discussion - Give examples in industrial application - Is this result a kind of contribution to knowledge?

8.0

REFERENCE (2%) - Gives at least 2 reference

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