Manometer Equations
General Manometer Equation
The formula that relates the pressure difference P1 – P2 to the
difference in manometer fluid levels is based on the principle that
the fluid pressure must be the same at any two points at the same
height in a continuous fluid.
In particular, the pressure at the height of the lower surface of a
manometer fluid is the same in both arms of the manometer.
the general manometer equation
In a differential manometer, fluids
1 and 2 are the same, and
consequently p1 = p2 = p.
Differential Manometer Equation
• If either fluid 1 or 2 is a gas at a moderate
pressure (e.g., if one arm is open to the
atmosphere), the density of this fluid is 100
to 1000 times lower than the density of the
manometer fluid, so that the corresponding
pgd term may be neglected.
• If both fluids are gases, then the equation
becomes P1 – P2 = pfgh
Manometer Formula for Gases:
• If P2 is atmospheric pressure, then the
gauge pressure at point 1 is simply the
difference in the levels of the manometer
fluid.
Temperature and its Scales
What is Temperature?
•Temperature is a physical property of a system that underlies the
common notions of hot and cold;
•Temperature is a property of matter.
•One of the principal parameters of thermodynamics.
•The unique physical property that determines the direction of heat flow
between two objects placed in thermal contact. If no heat flow occurs,
the two objects have the same temperature; otherwise heat flows from
the hotter object to the colder object.
Definitions
• It is the measurement of the AVERAGE kinetic
energy of the particles of matter.
• The temperature of a substance in a particular state
of aggregation (solid, liquid. or gas) is a measure
of the average kinetic energy possessed by the
substance molecules.
• A measure of its thermal state considered in
reference to its power to transfer heat to other
bodies. (Maxwell Definition)
Measurement
• Must be determined indirectly by measuring some physical
property of the substance whose value depends on temperature in
a known manner.
• Volume of a Fluid (thermometer)
• Resistance of a metal(Resistance thermometer)
• Voltage at the junction of two dissimilar metals(thermocouples)
• Spectra of emitted radiations(pyrometer)
Temperature Scales
Comparison of temperature scales
Can be defined in terms of any of these properties, or in terms of
physical phenomena, such as freezing and boiling, that take
place at fixed temperatures and pressures.
• Relative Scales
– Fahrenheit (°F)
– Celsius (°C)
• Absolute Scales
– Rankine (°R)
– Kelvin (K)
Physical Scales Vs Numerical
Scales
• "the temperature at which the resistivity of a
copper wire is 1.92 x 10-6 ohms/cm3 “
• "the temperature two-thirds of the way from
the boiling point of water.“
• A defined temperature scale is obtained by
arbitrarily assigning numerical values to
two reproducibly measurable temperatures;
Temperature Scales
• To construct a thermometer scale:
• Select Two naturally occurring fixed
events
• Freezing and Boiling Point of water
are normally chosen.
• Then numbers are assigned to
these points
• Then the space in-between is
divided into a fixed number of
equal degrees.
• Main temperature scales
• Celsius
• Fahrenheit
• Kelvin
• Rankine
Uses of the Scales
• Fahrenheit scale is used
for engineering and
Household purposes.
• Celsius scale is
universally used for all
scientific measurements
The Fahrenheit Scale
• The fixed points on which the Fahrenheit
scale were created:
A mixture of ice water and salt
as the low
AND
The human body temperature as
the high.
°F Scale
• Boiling point
212 0F
became = ________
• Freezing point
32 0F
became = _________
Absolute zero
falls at -459.67°F.
Celsius Scale
Boiling Point = 100 0C
Freezing Point = 0 0C
• The original name was the
• CENTIGRADE scale
– In 1948 it was renamed in honor of
the original creator, Anders Celsius
Absolute zero
(theoretically the lowest temperature attainable in nature) on this
scale falls at -273.15°e.
Absolute Scales
• The Kelvin and Rankine scales are defined
such that absolute zero has a value of 0 and
the size of a degree is the same as a Celsius
degree (Kelvin scale) or a Fahrenheit degree
(Rankine scale ).
Kelvin Scale
• Named for William Thomson
• Who became Lord Kelvin of
Largs.
• His scale is based on the
temperature at which all
molecular movement STOPS.
KE=0
Kelvin Scale and
•This temperature is known as
•ABSOLUTE ZERO
• Absolute Zero = 0
• Boiling point of water = 373 K=100C
• Freezing point of water = 273 K=0C
Rankine Scale
• KE=0
• Incerements=Farenhite
• 459.67R=0F
Converting Temperatures
Conversion Factors
A degree is both temperature and temp interval
Conversion Equations
Temperature Conversions
• Fahrenheit to Celsius
C = (F-32) x 5
9
• Celsius to Fahrenheit
F=
(
Cx9
5
) + 32
Temperature Conversions
Cont.
Celsius to Kelvin:
K = C + 273
Kelvin to Celsius:
C = K - 273
Quick Conversion
Celsius to Fahrenheit:
Double the Celsius
then
Add 30.
Find the number of Celsius
degrees between 32°F and 212°F