310201a Temperature Measurement Flashcards
Define temperature
Temperature is a measure of the average kinetic energy of the particles in an object.
Define boiling
Boiling is the process where molecules transition from the liquid phase to the gas phase. This process results in the formation of vapor bubbles within the liquid
Define boiling point
Boiling point is the temperature at which the vapor pressure of the liquid equals the environmental pressure that surrounds the liquid. At boiling point, the vapor pressure of the liquid becomes sufficient to overcome atmospheric pressure and lift the liquid to form bubbles inside the bulk of the liquid.
Define latent heat of vaporization
Latent heat of vaporization is the amount of energy a substance requires to convert from liquid to gas or from gas to liquid, without a change in the external temperature.
The temperature stays constant during these phase changes.
Define triple point.
Triple point is the temperature and pressure at which 3 phases (for example, gas liquid and solid) of a substance coexist in thermodynamic equilibrium
The triple point of water is 0.01°C and 610 PA.
Define absolute zero
Absolute zero is the theoretical temperature at which all substances have 0 thermal energy or zero kinetic energy
Kinetic energy increases as temperature increases
Absolute zero is represented by the different temperature units as follows:
-273.15°C
-459.67°F
0 K (Kelvin)
0 R (Rankine)
Define condensation
Condensation is the change of the physical state of matter from the gas phase into the liquid phase
What is the formula for the Combined Gas Law?
What is the formula for these Ideal Gas Law?
Define Charles’ Gas Law.
According to Charles’ Gas Law, volume and absolute temperature are directly proportional: The higher the temperature is, the larger the gas volume is when the pressure remains unchanged
What is the equation for charles’s gas law
Define Boyles’ Gas Law
Boyles’ Gas Law describes the inversely proportional relationship between the absolute pressure and the volume of a gas if the temperature remains constant within a closed system.
This law requires pressure to be stated in absolute pressure units. You must convert any gauge pressure measurements to absolute pressure to make your calculations correct
What are the 4 common temperature scales used to measure temperature?
The metric system uses Kelvin and Celsius scales, the Imperial system uses Rankine and Fahrenheit scales.
Define the coefficient of linear expansion.
The coefficient of linear expansion relates to the change in the linear dimensions of a material to a change in temperature.
It is the fractional change in length per degree of temperature change.
True, or false? The coefficient of area expansion is equal to twice the coefficient of linear expansion.
True.
True, or false? You can estimate the volume expansion coefficient for a solid from its linear expansion coefficient because the volume coefficient is approximately 3 times the linear coefficient
True
In physics, thermal contact conductance is the study of heat conduction between solid bodies and thermal contact.
When 2 solid bodies make contact the following 4 things occur:
- Heat flows from the hotter body to the colder body.
- The temperature gradient along the 2 bodies varies
- A temperature drop occurs at the interface of the 2 surfaces.
- Heat flow directly relates to the conductivities of the bodies, the surface area and the contact resistance.
What are three parasitic thermal connections?
- Heat conduction and sensor wires
- Conduction to air
- Radiant energy transfers.
If the temperature is changing more quickly than a sensor can track, the measurement is likely to be in error.
What are the 3 best solutions to improve sensor accuracy?
- Use a more responsive sensor
- Improve thermal contact
- Reduce the sensor thermal mass by minimizing how much material in contact with the sensing element is not associated with improving thermal contact.
What are the 4 classifications for thermowells?
- Threaded
- Flanged
- Vanstone
- Welded
True, or false
Authoritues require that manufacturers of Thermowells used for pressure applications in Alberta must stamp or tag these fittings with the Canadian Registration Number (CRN) to ensure traceability
True
What are 4 considerations for selecting a thermowell?
- Process pressure
- Process composition
- Flow velocity
- Immersion length
For a Therma, couple and a resistance temperature detector what is the recommended minimum immersion length for a thermowell/protecting tube?
The recommended minimum immersion length is ten times the outside diameter of the protecting tube or thermowell
In flowing liquids, what is the minimum recommended immersion length for a protecting tube or thermowell?
In flowing liquids, you should have a minimum immersion length of six times the outside diameter of the protecting tube or thermowell
What additive can you add to a sensor thermowell assembly to improve the performance of the sensor?
You can add a heat transfer compound to fill the air space between the sensor and the bore of the thermowell
Ex. Thermal conductive grease
List five devices used for indirect temperature measurement
- Liquid filled thermometer
- Bimetallic thermometer
- Thermocouple
- Resistance temperature detector.(RTD)
- Radiation pyrometry thermometer
What is a thermal time constant?
A thermal time constant is the time required for the element output signal to change by 63.2% of the total difference between its initial and final output values when subjected to a step change
List the 3 purposes that a thermowell serves
- Protects the temperature sensor from harmful atmospheres
- Prevent mechanical damage to the sensor
- Permit access to the sensor for replacement over repair without having to isolate the process
Which responds more quickly to a change in temperature, a small or large mass sensor?
A small mass sensor
When you require a thermowell in a small pipe, what are the 2 mounting options that you can use?
- Mount at a forty five degree angle with the tip pointing towards the flow
- Mount on an elbow with a tip pointing towards the flow.
