Thermodynamics Flashcards
What is saturated steam
Saturated steam is steam at a temperature corresponding to its pressure
What is superheated steam
Superheated steam is steam at a temperature higher than the temperature corresponding to its pressure
What is meant by the term “degree of superheat’’
The number of degrees higher than the saturation temperature corresponding to its pressure
Steam exists in three (3) forms. What are they
Steam can be wet, dry or superheated
What is sensible heat
Sensible heat is heat added to a substance that causes a change in temperature that can be measured with a thermometer
What is latent heat
Latent heat is heat added to a substance that causes a change of state without a change in temperature
What is the definition of a BTU
A British thermal unit is the amount of heat required to raise one pound of water 1℉
What is the definition of specific heat
Specific heat is the heat required to raise one pound of any substance 1℉
What is specific gravity
Specific gravity is the weight of any substance when compared to the weight of water. Also known as density
How many BTU’s are required to change 1 pound of water at 212℉ to one pound of steam at 212℉
970.3 btu’s per pound are required to change one pound of water at 212℉ into one pound of steam at 212℉
How many BTU’s are required to change 1 pound of ice at 32℉ into one pound of water at 32℉
144 btu’s
How much does 10,000 gallons of water weigh
10,000 X 8.33 lbs/gallon = 83,300 lbs
How many BTU’s are required to raise the temperature of 100 gallons of water from 50℉ to 150℉
100 gallons X 8.33 lbs/gallon = 833 lbs.
833 lbs X 100 btu’s per pound = 83,300 btu’s
What are the 5 headings on the steam table
- absolute pressure
- absolute temperature
- specific volume
- enthalpy btu’s/lb
- entropy
Describe saturated and superheated steam
Saturated is steam at a temperature corresponding to its temperature. Super-heated steam is steam above the temperature corresponding to its pressure and contains no moisture
How many BTU’s does it take to raise one pound of water at 32®F to the boiling point at 14.7 psia and then to steam
180 BTU’s to raise one pound of water at 32®F to the boiling point and an additional 970 BTU’s to create steam for a total of 1150 BTU’s.
What is meant by heat being transmitted by radiation? By conduction? By convection
Radiant- heat transferred by light waves without a material carrier
Convection- heat transferred by currents in a fluid
Conduction- heat transferred molecule to molecule
What is meant by the saturated steam temperature? What is heat of vaporization
Saturated steam temperature is the temperature corresponding to its pressure and contains no moisture. Heat of evaporation is the amount of heat energy which changes from liquid to gas (latent heat)
What is wet steam, and how is the enthalpy of wet steam calculated?
Wet steam is a mix of steam and water which can be found in values in steam table.
What is superheated steam, and what does degrees of superheat mean
Superheated steam is steam at a temperature above that of dry saturated steam at the same pressure. Degrees of superheat would be the number of degrees higher the steam is to the temperature corresponding to its pressure
What are the advantages of using superheated steam
Travels long distance with no condensate, no moisture, and higher heat content and more efficient.
What device measures absolute pressure
Barometer
What is a pyrometer used for
Temperature measurement
What is a manometer used for
Measure draft
TON OF REFRIGERATION
IS THE MELTING OF ONE TON OF
ICE (2,000 LBS.) IN 24 HOURS
2,000 X 144 = 288,000 BTU/DAY
144 = LATENT HEAT OF FUSION
288,000 = 12,000 BTU/HR
What is enthalpy
The total heat content of a substance expressed as btu/lb
Hf = enthalpy of fluid Hfg = enthalpy of latent heat Hg = enthalpy of gas/vapor
formula
Hf+Hfg = Hg
What is the first law of thermodynamics
Energy can not be created or destroyed but may be converted from one form to another
What is the 2nd law of thermodynamics
No machine actual or ideal can both continuously and completely transfer heat into mechanical energy. nothing is 100% efficient
What is latent heat of fusion
heat that is added to a solid that causes a change of state to a liquid. ( one lb of ice @ 32 deg f becomes one lb of water at 32 deg f when 144 btu’s are added)
What is latent heat of evaporation
Heat added to a liquid that causes a change of state to a gas/vapor. ( one lb of water at 212 deg f becomes one lb of steam at 212 deg f when 970.3 btu’s are added
What is specific gravity
The weight of any substance when compared to water
What is specific volume
the volume of any substance when compared to water cu ft/lb
Fuel oil with a specific gravity of 0.89, what is the weight
Multiply 8.33 by .89 to get the weight.
8.33 x .89 = 7.41
What are the 7 lines on a mollier chart
Lines of constant enthalpy Lines of constant entropy lines of constant temperature Lines of constant pressure Lines of constant quality Saturation line Degree of superheat Standard atmosphere
What is a mollier chart
The steam tables in graph form plotted in XY coordinates
