Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations MintJulep on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
Specific Heat of Steel
- Thread starter nornrich
- Start date
![[viking]](/data/assets/smilies/viking.gif "[viking] [viking]")
Rich,
The specific heat in the formula is intended to be the specific heat of the fluid, water (1.0 cal/g-C).
BTW, a good source for material properties is
ko (
The specific heat in the formula is intended to be the specific heat of the fluid, water (1.0 cal/g-C).
BTW, a good source for material properties is
ko (
To nornrich,
I'm not a metallurgist, but it seems to me logical to assume there are also latent heat releases resulting from microstructural phase transformations during quenching.
When considering these effects your formula with a constant Cp for steel taken over the whole cooling range doesn't appear right, and ko99's response is the correct one.
It would seem possible that by varying the Cp values over prescribed narrower temperature ranges, so as to include those enthalpy changes in this nonisothermal cooling process, one may help in assessing Q on the steel side.
CS has a specific heat around 500 j/kg/C at ambient temps.
How temperature dependant this is I dont know.
A good source for physical properties can be found at Best regards
Morten
How temperature dependant this is I dont know.
A good source for physical properties can be found at Best regards
Morten
sailoday28
Mechanical
An energy balance of the ingot yields
change internal energy=heat transfer - p*change in volume
dU =dQ -pdV
dU = M* (Cv* dT)
neglecting change in volume of ingot and integrating
The heat transfer is M* integralCvdT
and Cv approx =Cp
How accurately is the initial temp of the ingot known?
ko99 (Mechanical)has a better suggestion. However, If water bath is large enough, neglect its change in volume and measure delta T of water.
The heat transfer calculated to water will be dependent upon mean temp of ingot.
The real interesting part of the problem is that of the overall heat transfer, which is dependent upon temp of ingot and temp of water. When is temp of ingot = to temp of water?
change internal energy=heat transfer - p*change in volume
dU =dQ -pdV
dU = M* (Cv* dT)
neglecting change in volume of ingot and integrating
The heat transfer is M* integralCvdT
and Cv approx =Cp
How accurately is the initial temp of the ingot known?
ko99 (Mechanical)has a better suggestion. However, If water bath is large enough, neglect its change in volume and measure delta T of water.
The heat transfer calculated to water will be dependent upon mean temp of ingot.
The real interesting part of the problem is that of the overall heat transfer, which is dependent upon temp of ingot and temp of water. When is temp of ingot = to temp of water?
the equation you mention is the calorimetric equation as the heat released by the ingot is the same as the heat absorbed by the water Qw = Qi...
in Qw, Cp is for water
in Qi, Cp is for steel.
the problem resides in the temperatures.
the [Δ]T requires knowing the starting temperature of the ingot... it is easier to know the starting and ending temperature of the water.
also, you will need to evaluate the "equivalent in water of the calorimeter" in your case: the equivalent in water of the water bath.
there are a lot of sources of error for the calculation: sudden vaporization of water in contact with the steel (mass and heat lost to atmosphere)...
but if what you are looking for is a good approximation... using the water should be ok.
saludos.
a.
in Qw, Cp is for water
in Qi, Cp is for steel.
the problem resides in the temperatures.
the [Δ]T requires knowing the starting temperature of the ingot... it is easier to know the starting and ending temperature of the water.
also, you will need to evaluate the "equivalent in water of the calorimeter" in your case: the equivalent in water of the water bath.
there are a lot of sources of error for the calculation: sudden vaporization of water in contact with the steel (mass and heat lost to atmosphere)...
but if what you are looking for is a good approximation... using the water should be ok.
saludos.
a.
btrueblood
Mechanical
The CRC Handbook of Chemistry and Physics has a good tabular form list of formulas and data for sp. ht. of various materials over various temperatures. Another source (for metals) is MIL-HDBK-5; although I don't find a chart in there for "carbon steel", there are charts for low alloy steels (4140) etc. Look in the aero engineering forum on this site for pointers to MIL-HDBK-5 and its successor(?) document MMAPDS or some such acronym.
sailoday28
Mechanical
Original question relates to heat transfer from steel.
The rate of heat transfer is time dependent based on mean temp of water and steel. Neglecting changes in water volume, the overall heat transfer (not rate) will be time dependent.
A plot of the rise in temp of water vs. time will eventually tend to level off. When the rate of change of the rise in water temp is small, the overall heat transfer can be determined. Q=mass of water*specific heat*temp rise
The rate of heat transfer is time dependent based on mean temp of water and steel. Neglecting changes in water volume, the overall heat transfer (not rate) will be time dependent.
A plot of the rise in temp of water vs. time will eventually tend to level off. When the rate of change of the rise in water temp is small, the overall heat transfer can be determined. Q=mass of water*specific heat*temp rise
- Status
Similar threads
- Question
- Question
- Locked
- Question