02 part1 thermo laws zeroth law

1. Thermodynamics - Laws
S.Gunabalan
Associate Professor
Mechanical Engineering Department
Bharathiyar College of Engineering & Technology
Karaikal - 609 609.
e-mail : gunabalans@yahoo.com
1. Zeroth law of Thermodynamics
a) Temperature Measurement
b) Thermal Equilibrium

2. Temperature
• Thermodynamics – science of temperature
• Temperature – is associated with ability to
differentiate the hot from cold.
• Thermal equilibrium – When two bodies at
deferent temperature are brought into
contact, some time later they attain a
common temperature – now they are in
thermal equilibrium.

3. Zeroth law of Thermodynamics
• Base for all temperature measurement.
• Thermal equilibrium is the key word for zeroth law
Definition:
When a body A is in thermal equilibrium with a
body B, and also separately with a body C, then
B and C will be in thermal equilibrium with each
other.

4. Zeroth law of Thermodynamics
• Temperature measurement procedure
– A reference body is used, and a certain physical
characteristic of this body which changes with
temperature is selected.
– The changes in the selected characteristic may be
taken as an indication of change in temperature. The
selected characteristic is called the thermometric
property,
• expansion of the mercury in the tube is used as the
thermometric property
– The reference body which is used in the determination
of temperature is called the thermometer

5. Zeroth law of Thermodynamics

6. Zeroth law of Thermodynamics

7. Zeroth law of Thermodynamics
• An easily reproducible state of an arbitrarily
chosen standard system is called a fixed point
– (a) The ice point, the temperature at which pure ice
coexisted in equilibrium with air-saturated water at
one atmosphere pressure.
– (b) the steam point, the temperature of equilibrium
between pure water and pure steam at one
atmosphere pressure.
– (c) the triple point of water, the state at which ice,
liquid water and water vapour coexist in equilibrium
(273.16Kelvin).

8. Zeroth law of Thermodynamics
• The use of two fixed points was found
unsatisfactory and later abandoned,
– (a) the difficulty of achieving equilibrium between
pure ice and air- saturated water (since when ice
melts, it surrounds itself only with pure water and
prevents intimate contact with air-saturated
water).
– (b) extreme sensitiveness of the steam point to
the change in pressure

9. Zeroth law of Thermodynamics
• The temperature of the triple point of water,
which is an easily reproducible state, is now
the standard fixed point of thermometry.
Considerable difference in temperature measurement between
thermometers, the smallest difference observed in different gas
thermometers. So gas is chosen as standard thermometric
substance.

10. Zeroth law of Thermodynamics

11. Zeroth law of Thermodynamics

12. Questions
1. Fixed point ?
An easily reproducible state of an arbitrarily chosen
standard system is called a fixed point.
Before 1954, there were two fixed points:
(a) the ice point
(b) the steam point
• Method in Use After 1954
Triple point of water is the only one fixed
point used after 1954.

13. Questions
2. Why gas is chosen as standard thermometic
substance?
There is considerable difference in temperature
measurement between thermometers, the smallest
difference observed in different gas thermometers. So gas
is chosen as standard thermometric substance.
3. Celsius Temperature Scale?
= − 273.15
4. Applications of zeroth law of thermodynamics?
temperature measurement.

14. Reference
• Rajput, R. K. 2010. Engineering thermodynamics. Jones and Bartlett
Publishers, Sudbury, Mass.
• Nag, P. K. 2002. Basic and applied thermodynamics. Tata McGraw-Hill, New
Delhi.
• http://www.grc.nasa.gov/WWW/BGH/thermo0.html