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What is the Significance of Specific Heat?

02/02/2018 11:26 AM

So I'm a student, and I recently had a lab that dealt with the specific heat of metals. At the end of the lab, we were supposed to determine which material would be best for underground piping conduits for a steam heating system. I know that if a material has a higher specific heat value, then it takes more energy to heat that material up...I just don't know if a high heat value would be better when compared to one that's lower. In my head, having a lower heat value would be good, as it would get into thermal equilibrium faster than higher heat values, but I'm not sure if the purpose of the pipes is to keep as much steam as possible or to turn as much steam into liquid. If anyone can help me understand this, it would be much appreciated!

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#1

Re: What is the Significance of Specific Heat?

02/02/2018 12:06 PM

You have now discovered the problem of an inexact question. When you leave academia you will find more inexact questions in your career so it is good to learn how one can answer an inexact question. I find that it is best to first stipulate what you are assuming to produce an answer and only then should one proceed to answer the question. Some people don't take an implied or direct correction kindly.

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#2

Re: What is the Significance of Specific Heat?

02/02/2018 12:12 PM

Alright, thank you! This helps a lot for answering this question.

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#3

Re: What is the Significance of Specific Heat?

02/02/2018 12:47 PM

Materials with high specific heat values are better insulators.

But you already knew that. Steam lines usually run all the time, so you'd like the lowest possible thermal conductivity in the piping material (and surrounding backfill) to keep as much heat in the steam as possible.

The less heat you lose in transmission the more heat you have to do the work it was intended to do.

Good luck.

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#5

Re: What is the Significance of Specific Heat?

02/02/2018 12:53 PM

Thank you very much!

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#7

Re: What is the Significance of Specific Heat?

02/02/2018 2:46 PM

"Materials with high specific heat values are better insulators."

I don't think that is correct.

For example, aluminum has a much higher specific heat value than stainless steel, and it is also a much better thermal conductor.

I don't think there is a good correlation between specific heat values and thermal conductivity.

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#9

Re: What is the Significance of Specific Heat?

02/02/2018 4:10 PM

Specific heat is the amount of heat needed to raise the temperature of one kilogram of mass by 1 kelvin. ... The molar heat capacity is the heat capacity per unit amount (SI unit: mole) of a pure substance, and the specific heat capacity, often called simply specific heat, is the heat capacity per unit mass of a material.

Heat capacity

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#12

Re: What is the Significance of Specific Heat?

02/02/2018 11:26 PM

Troy36 is correct. Specific heat capacity and thermal conductivity are not well correlated across varying material types.

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#14

Re: What is the Significance of Specific Heat?

02/03/2018 12:57 PM

That’s doesn’t sound right, it sounds very similar to BTU’s the amount of energy to raise pound of water 1 degree F.

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#16

Re: What is the Significance of Specific Heat?

02/03/2018 2:11 PM

You really are a contrarian at times, aren't you. You even disagree when a reference is provided.

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#17

Re: What is the Significance of Specific Heat?

02/03/2018 3:22 PM

Oh, I thought this was a conference room,... I’m sorry, how’s this...

The British thermal unit is a traditional unit of heat; it is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. It is part of the United States customary units.

.. feel better buttercup?...

Since your abstract understanding capacity appears inferior or at least limited, I’ll spell it out for you...

Do you see the relationship between the two?... that was the point I was making.

I can see why you don’t like BTU’s.... so be careful, we don’t what you wetting yourself.

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#21

Re: What is the Significance of Specific Heat?

02/03/2018 6:13 PM

Wow, you really are a contrarian. You will even disagree with the meaning of your own words:

That’s doesn’t sound right, it sounds very similar to BTU’s the amount of energy to raise pound of water 1 degree F.

You are trying to disagree with Lyn's simplified yet accurate description of Specific Heat by citing the obsolete heat definition of a BTU. Ironically your memory accurately assumes the British relative Specific Heat of one. Units matter!

You do prove my point though. Some people don't take an implied or direct correction kindly.

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#22

Re: What is the Significance of Specific Heat?

02/03/2018 6:24 PM

Your confusing disagreement with challenge, but I understand.

It appears to me you’re nothing but an analysis, well, good for you..., hope you feel better that maybe next time, you’ll try to set higher goals...

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#24

Re: What is the Significance of Specific Heat?

02/03/2018 10:34 PM

"I thought this was a conference room." " we don’t what you wetting yourself."

With remarks like that one, you would NOT be allowed in any conference room I had anything to do with.

You are rude and condescending, and should apologize to those whom you have offended!

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#26

Re: What is the Significance of Specific Heat?

02/04/2018 1:59 AM

Is it causal or merely coincidental that the most vigilant of the 'rudeness-condescention-offensiveness' police appear completely unaware of their own transgressions....or have none of the type of remorse for their actions that they demand of others?

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#28

Re: What is the Significance of Specific Heat?

02/04/2018 2:37 AM

Interesting...

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#30

Re: What is the Significance of Specific Heat?

02/04/2018 8:14 AM

Some of us self mark OT when their own response are Off Topic from the original post, in an act of courtesy.

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#31

Re: What is the Significance of Specific Heat?

02/05/2018 6:04 AM

And when the same some of us that don’t mark off topic from the original post, you can count on others for the correction to mark it Off Topic. So what?

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#32

Re: What is the Significance of Specific Heat?

02/05/2018 7:18 AM

This is just as I thought. You're actually proud that you are incapable of self correction.

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#33

Re: What is the Significance of Specific Heat?

02/05/2018 7:34 AM

Proud?, I do it when I can... FYI, not having a point is not a point in itself.

but thanks for sharing your,... thought.

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#27

Re: What is the Significance of Specific Heat?

02/04/2018 2:30 AM

and only now your responding, interesting,... not surprising, just amusingly interesting

As far this comment;

You are rude and condescending,...

Lyn, I said this before, if it’s not political you are an asset for this site, for the most part that is, if not, I’ll stand toe to toe with you or anyone else on my position until one backs down leave or proceeds to deliever their argument to change my own position.

But, when your are challenged on something other then your beliefs, you (, oppsie, that came out of no where) display the hypocrite you are with repeated psychological projection disorder, like I said before... maybe that’s why your so reserved in your response to me, who knows

you can talk smart, but just can’t take the heat. Because you know what happens to to you when challenge with someone that doesn’t back down, then please refer to the the video on post 17.

As far as redfred is concerned... he’s also a smart man, yet I feel there’s something else that’s bothering him other then just critiquing me, IMO, that’s just an excuse for an exchange for redfred looking for something else. So I’ll humor him and give him what I believe is what his real motive is.

as far as wetting himself other then from a snowflake melting.,... there’s always depends.

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#34

Re: What is the Significance of Specific Heat?

02/05/2018 11:47 AM

Lyn,

You are confusing specific heat with thermal conductivity. They are not the same property.

The specific heat of aluminum is .21 BTU/lbm-deg F

compared to copper, which is .09 BTU/lbm-deg F

The thermal conductivity of aluminum is 118 BTU/HR-deg F-ft

compared to copper, which is 223 BTU/HR-deg F-ft.

The aluminum will condense more than twice as much steam compared to copper to heat the same weight of pipe to the same temperature. (Specific heat)

The outer wall of the copper pipe will heat up faster than the aluminum. (Conductivity)

Not the same thing.

The students answer needs to be a typical engineering answer: The material you pick depends on what you are trying to achieve. If the object is to transmit as much steam as possible, you want a material that has the lowest specific heat times the mass of the pipe. A low specific heat for a very heavy pipe might give a worse result than a very light pipe with a high specific heat. Best answer is a light pipe with low specific heat.

If the object of the project is to condense as much steam as possible, then the opposite choice is best.

It's important that the mass of the material is just as important as the specific heat.

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#35

Re: What is the Significance of Specific Heat?

02/05/2018 1:07 PM

For the record, I never mentioned Aluminum. Troy36 introduced the subject of Aluminum in his post #7.

I did say, "Steam lines usually run all the time, so you'd like the lowest possible thermal conductivity in the piping material (and surrounding backfill) to keep as much heat in the steam as possible. The less heat you lose in transmission the more heat you have to do the work it was intended to do."

Troy36 introduced the subject of Aluminum in his post #7.

I attempted, unsuccessfully it seems, to differentiate between specific heat and specific heat capacity in #9.

I'll be gone now, and leave you all to continue.

I

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#36

Re: What is the Significance of Specific Heat?

02/05/2018 1:39 PM

to keep as much heat in the steam as possible.

To digress further, to do that is to keep the steam as dry as possible,... by incorporating steam traps in the lines.

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#37

Re: What is the Significance of Specific Heat?

02/05/2018 1:44 PM

IMO we're going way beyond what Tess 43 was asking about. My guess is she (?) had all she needed after the first few posts.

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#38

Re: What is the Significance of Specific Heat?

02/05/2018 1:47 PM

True... but that never stopped CR4 before on a topic digression.

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#40

Re: What is the Significance of Specific Heat?

02/05/2018 2:11 PM

Also, if they want to recoup savings, they could think about recouping and sending the condensate back to the boiler.

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#42

Re: What is the Significance of Specific Heat?

02/05/2018 3:47 PM

I suspect her(?) teacher mistakenly used the wrong attribute. Then again the teacher might be clever enough to have deliberately used the wrong attribute to see who is actually thinking and understanding the subject.

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#41

Re: What is the Significance of Specific Heat?

02/05/2018 3:06 PM

Lyn, concern over who did or didn't mentioned aluminum first is a distraction. More important is the (unless I missed a retraction) over a claim made about a general trend of a fundamental material property. Namely:

"... Materials with high specific heat values are better insulators...."

A multitude of counterexamples make disproving this claim trivial. The only thing missing is your acquiescence/retraction, as the esteemed member of CR4 who originally made the claim.

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#45

Re: What is the Significance of Specific Heat?

02/09/2018 12:00 AM

Perhaps it is not so trivial for some....

Consider two groups of substances.

Group A: Aluminum, magnesium, lithium, sodium, beryllium, helium, and hydrogen.

Group B: asbestos, mica, sandstone, perlite, Pyrex, quartz, dry soil, fire brick, pyroceram, argon, slate and dry bone.

Group B substances do not conduct heat as well as Group A materials. As such, Group B substances are better insulators.

...yet Group A substances have higher specific heat values than Group B materials.

.

This should put to be the erroneous assertion that materials with higher specific heat make better insulators.

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#4

Re: What is the Significance of Specific Heat?

02/02/2018 12:49 PM

Steam pipes are usually run in black iron, and then insulated with fiberglass, if that helps...

https://sciencing.com/thermal-properties-black-iron-pipe-8043410.html

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#10

Re: What is the Significance of Specific Heat?

02/02/2018 4:11 PM

You would have to know the details of the application to make anything more than a general recommendation...such as pressure, length of run,, creep allowance, pipe size and velocity, these are mostly covered by codes(ASTM A106) such as those established by the American Society of Mechanical Engineers (ASME) and the American Petroleum Institute (API)...

http://www.wermac.org/steam/steam_part9.html

https://www.thefabricator.com/article/tubepipefabrication/comparing-materials-for-high-temperature-steam-piping

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#6

Re: What is the Significance of Specific Heat?

02/02/2018 2:19 PM

It's not just the specific heat, joule/kg/K, it's the total heat capacity of the pipe, joule/K (specific heat x mass). If the material has lower tensile strength so needs greater wall thickness the heat capacity might be higher even if the specific heat is lower. In any case it's likely to be negligible compared with the enthalpy of the steam, and as it's likely to run at fairly steady temperature it's only an issue during start-up.

You want thermal conductivity to be low to minimise heat loss, but the pipe should be insulated and most of the resistance to heat flow is due to the insulation, not the pipe wall.

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#8

Re: What is the Significance of Specific Heat?

02/02/2018 4:00 PM

Your goal is to deliver as much heat as possible to the end user. The most important factor is how well the piping is insulated.

I agree with you, the lower heat capacity pipe is preferable. It takes less heat out of the steam to get up to temperature and there is less thermal energy stored in the pipe to leak through the thermal insulation to the outside world.

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#13

Re: What is the Significance of Specific Heat?

02/03/2018 4:44 AM

<...goal is to deliver as much heat as possible to the end user...> Quite.

What is important is:

• the quality and quantity of insulation, which has to have a low thermal conductivity, and
• the diameter and length of the pipe, which represents a restriction to flow, and
• the quality of the steam, which is where specific heat comes in, and
• the effectiveness of condensate removal at intervals along the pipe and at user end of it downstream of the equipment

The thermal conductivity and capacity of the of the pipe material is of rather less relevance than its ability to withstand corrosion in whatever environment it finds itself, given that raising the temperature is an accelerating factor in most chemical reactions, including those of corrosion. So the piping material has to be considered carefully, using a client-preselected standard if one is applicable.

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#11

Re: What is the Significance of Specific Heat?

02/02/2018 8:34 PM

It's always interesting to consider the ideal material vs the economical material. What material would you use in the dream castle vs what is standard in the production world. Insulation is also a fact of life, how does it factor into the choice. If you know the specific heat of your pipe materials and insulative value of your insulation choices, what will you calculate as optimal? And how far from optimal is the most economical.

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#15

Re: What is the Significance of Specific Heat?

02/03/2018 2:05 PM

I guess ideal would be a plastic pipe which was cheap, easy to work with, and needed no, or very little insulation, due to low heat transfer characteristics....anybody who has run pvc in place of copper or conduit, knows what an improvement this was...but plastic tends to melt and pvc won't work...so it would probably have to be developed, a new kind of composite with the same attributes as pvc, except it can withstand high temperatures...

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#18

Re: What is the Significance of Specific Heat?

02/03/2018 3:28 PM

I did an expansion at one of our facilities and I looked into that... AQUA-Therm I believe was the manufacture, the problems is that it was going outside, and had issues with UV...

it was light weight, installation time could have been reduced by 75%, if I recall, I believe it was twice expensive

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#20

Re: What is the Significance of Specific Heat?

02/03/2018 5:37 PM

Yeah there are a few options that are not quite there...Aquatherm blue pipe is good for 200° F and Thermoflex has some high pressure pipe that's good for 180° F but a whopping 1500 psi, probably not cheap either...haha

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#23

Re: What is the Significance of Specific Heat?

02/03/2018 6:31 PM

To digress further, For UV protection, there was an option to put on a UV sheeting... which also deteriorated.

but for installing it inside a building. It’s taking off pretty good in our area. Even though it’s more expensive... the shorter installation time more then makes up for it.

A lot of schools and hospitals are using it.

and the cutting and welding equipment can be rented from the supplier.

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#19

Re: What is the Significance of Specific Heat?

02/03/2018 3:34 PM

What is the maximum temperature and the maximum pressure of the steam, please?

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#25

Re: What is the Significance of Specific Heat?

02/03/2018 11:10 PM

..."A common question that every person involved with steam systems must address at some point is what is the correct steam pressure for the application. Selecting higher than required steam pressure to a process application will result in a number of negative effects. High steam pressures have a higher steam temperature, but the negative; is a lower usable (latent) energy. This is often an overlooked fact in the more steam pressure is better world.

A review of the steam tables shows us that as we increase the steam pressure, the latent energy decreases as the sensible energy increases. Typical steam process applications utilize only the latent energy in the steam. The sensible energy is removed from the system with the condensate. By contrast, one should select the lowest effective steam pressure and temperature that permits operational process success. Using the lowest effective steam pressure to achieve the process objective will result in the following:

• Lower steam consumption

• Lower thermal expansion of components

• Lower flash steam volume, particularly at the discharge of the trap.

• Better temperature control, due to the closer proximity to the process heat sink.

• Longer equipment life

Unfortunately, history has shown that the steam process plant accepts the recommendation of the steam equipment manufacturers to designate the required steam pressure. In true practice, the plant should be the designator of the steam pressure to the equipment manufacturer."...

..."Process applications typically require high process temperatures, therefore higher steam pressures are needed to meet the process requirements. How does a process person find the correct steam pressure? An example in the Steps to find the correct steam pressure:

1. Assume a process requires 280°F temperatures

2. Review the steam tables and find 280°F

3. The equivalent “steam” pressure at 280°F is 35 psi

4. Add 45 psi to the required pressure

5. Add 45 psi to 35 psi = 80 psi steam pressure

Steam 80 psi pressure that is provided to the equipment manufacturer for design of the process heat transfer. 80 psi shall be the pressure after the steam control valve or the steam pressure that can be delivered to the process."...

https://www.swagelok.com/~/media/Distributor%20Media/C-G/Chicago/Services/ES%20-%20Steam%20Pressure%20for%20Process%20Applications_BP_15.ashx

So let's say 80 psi....and 280° F , For a typical application...

http://www.jgbhose.com/technical-reference-literature/steam-temperature-pressure-conversion-guide.asp

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#29

Re: What is the Significance of Specific Heat?

02/04/2018 3:51 AM

Interesting treated purely at face value.

A steam pipe in the ground would usually be a composite arrangement.

You have first to address safety in operation because of the relatively high operating pressures and the energy in transmission.

The second factor to address is heat loss. Normally we use an insulated backing selected to suit the operating environment and to meet the financial balance for cost against operating losses.

Thus far you can select a rapid transmission low C coefficient if the insulation can economically balance out the higher conductance of the safety material.

Then we look at other constraints:

1. Cost.
2. Expansion coefficient.
3. Jointing methods.
4. Possible issues caused by condensation through over-cooling.
5. Pipe size.

• A material with low c coeff. will be a higher conductor
• A material with higher c coeff will be a lower conductor

Just concentrate on the temperature of the pipes exposed outer surface and the impact of any resultant conduction.

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#39

Re: What is the Significance of Specific Heat?

02/05/2018 1:50 PM

Tess,

If the object is to minimize steam condensation, then you need the lowest number for specific heat times the mass of the pipe. Both terms contribute to the mass of steam that will condense to heat up the pipe and both are equally important.

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#43

Re: What is the Significance of Specific Heat?

02/05/2018 5:19 PM

In a steam heat system you have three sections: Steam makers (boiler) Steam transport (piping) and steam condensation (radiators).

For transport of steam, you want to minimize condensation. During startup, you want to spend as little heat as possible to warm up the pipes. That is where low specific heat and low mass works for you. Once you hit steady state operation, you are no longer warming up the pipe and specific heat is not an issue. Then things like insulation become most important to conserve heat.

At the radiator end, it's a mixed bag. A high specific heat radiator of large mass will take a long time to reach steady state. It will be slow to reach the comfort level on startup. However, if the system on/off cycles, a low specific heat, low mass radiator will always seem to be either too warm or too cold, but a high specific heat, high mass radiator will take longer to heat and cool and will be in the comfort range longer, but will continue to give off heat after it is shut off. Tuning the thermal mass of the radiators with the control system will determine what specific heat and mass of radiator you want.

I design electrically heated radiant tile floors that take about 30 minutes to do a major temperature change. The control system cycles on/off on a 7 to 10 minute cycle, so the floor temperature rarely swings more than about three degrees and the end user doesn't have comfort swing issues. We design some also for linoleum floors with much lower thermal mass that have much more pronounced swings and require a higher control cycle rate, which leads to relay contact failure faster than the tile floor systems.

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#44

Re: What is the Significance of Specific Heat?

02/08/2018 4:10 PM

I really wonder if solving this exercise should concentrate on the subject just completed. All I see is the requirement for a buried steam line.

It could very well be a test of whether or not the student brings all criteria to bear upon the exercise, not just the latest subject. Selecting the pipe alloy may be constrained by other requirements. Selecting the right insulation may be what is relevant. (Don't bury spun fiberglass insulation!)

The Specific Heat of the pipe material is irrelevant if the working fluid will have a constant temperature. The same is true if there will be fluctuations in temperature at the input, but the output need not follow rapidly. Otherwise, the Specific Heat may be relevant only if the pipe length, diameter, thickness (and therefore mass) is considerable.

I would personally also want to know:

What budget limits and construction timelines are already imposed? What is the length and elevation along that length? What is the fluid velocity, CFM, pressure, temperature, allowable pressure drop, allowable energy loss? Is the soil always dry, sometimes moist, saturated, or permafrost? Is the soil subjected to deformation, to freezing, to flooding? How often - how long will the pipe be offline (containing air and water) or contain steam? How pure does the steam and condensate have to be at the destination (contamination limits)?

How bad would a pipe failure be? What are the consequences: great loss of life, catastrophe? How inconvenient and expensive would it be to shut down the pipe for repairs. (Buried pipes must first be uncovered.)

Answers might dictate: the strength and ductility this pipe must have, corrosive properties, requirements for an outer sleeve, casement, or tunnel. Even the pipe buoyancy might become relevant.

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