Measurement of Temperature & Heat Flux Dr. Md. Zahurul Haq Professor Department of Mechanical Engineering Bangladesh University of Engineering & Technology (BUET) Dhaka-1000, Bangladesh http://zahurul.buet.ac.bd/ ME 361: Instrumentation and Measuremen http://zahurul.buet.ac.bd/ME361/ c Dr. Md. Zahurul Haq (BUET) Measurement of Temperature ME 361 (2019) 1 / 32 Temperature Measurement by Mechanical Effects Liquid-in-glass Thermometer T832 Inexpensive, simple, portable, no need for additional indicator. High heat capacity = ⇒ time lag exists. Not suitable for distant reading. Not suitable for surface temperature measurement. Alcohol is limited to low-temperature measurements. Its high coefficient of expansion makes it more sensitive. Mercury cannot be used below its freezing point of -37.8 o C. Its upper limit is usually 315 o C, but it may be extended to 540 o C by filling gas filling above the mercury. c Dr. Md. Zahurul Haq (BUET) Measurement of Temperature ME 361 (2019) 2 / 32 Temperature Measurement by Mechanical Effects T806 T808 c Dr. Md. Zahurul Haq (BUET) Measurement of Temperature ME 361 (2019) 3 / 32 Temperature Measurement by Mechanical Effects Reading in Liquid-in-Glass Thermometer T833 T834 c Dr. Md. Zahurul Haq (BUET) Measurement of Temperature ME 361 (2019) 4 / 32
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Measurement of Temperature & Heat Flux
Dr. Md. Zahurul Haq
ProfessorDepartment of Mechanical Engineering
Bangladesh University of Engineering & Technology (BUET)Dhaka-1000, Bangladesh
http://zahurul.buet.ac.bd/
ME 361: Instrumentation and Measuremen
http://zahurul.buet.ac.bd/ME361/
c
Dr. Md. Zahurul Haq (BUET) Measurement of Temperature ME 361 (2019) 1 / 32
Temperature Measurement by Mechanical Effects
Liquid-in-glass Thermometer
T832
� Inexpensive, simple, portable, no need for additional indicator.
� High heat capacity =⇒ time lag exists.
� Not suitable for distant reading.
� Not suitable for surface temperature measurement.
� Alcohol is limited to low-temperature measurements. Its high
coefficient of expansion makes it more sensitive.
� Mercury cannot be used below its freezing point of -37.8oC. Its
upper limit is usually 315oC, but it may be extended to 540oC by
filling gas filling above the mercury.c
Dr. Md. Zahurul Haq (BUET) Measurement of Temperature ME 361 (2019) 2 / 32
Temperature Measurement by Mechanical Effects
T806 T808
c
Dr. Md. Zahurul Haq (BUET) Measurement of Temperature ME 361 (2019) 3 / 32
Temperature Measurement by Mechanical Effects
Reading in Liquid-in-Glass Thermometer
T833
T834
c
Dr. Md. Zahurul Haq (BUET) Measurement of Temperature ME 361 (2019) 4 / 32
Temperature Measurement by Mechanical Effects
Fluid-expansion Thermometer
T828
� Economical, versatile, and widely used devices for industrial
applications.
� Long capillary tubes (60 m) may be used.
� Low cost, stable operation, and accurate within ± 1oC.
c
Dr. Md. Zahurul Haq (BUET) Measurement of Temperature ME 361 (2019) 5 / 32
Temperature Measurement by Mechanical Effects
Bimetallic Strip Thermometer
T809
◦ Widely used as on-off temperature-control device, thermostat. Also
used for measuring ambient and oven temperatures.c
Dr. Md. Zahurul Haq (BUET) Measurement of Temperature ME 361 (2019) 6 / 32