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ksatpathi
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Join Date: Nov 2011
Posts: 11

Enthalpy

02/22/2012 12:57 AM

Why and how enthalpy of low pressure is higher than high pressure at same temperature. For example-50kg/cm2 and 540 degree in compare to 140 kg/cm2 and to 540 degree.
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Crabtree
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Location: Commissariat de Police, Nouvions, occupied France, 1942.
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#1

Re: Enthalpy

02/22/2012 3:19 AM

You can do more work with the higher pressure, Guv. Enthalpy is the expression of that capacity.

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Tornado
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#2

Re: Enthalpy

02/22/2012 4:56 AM

It depends primarily on whether the substance is liquid or vapor.

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Crabtree
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#3
In reply to #2

Re: Enthalpy

02/22/2012 7:17 AM

That as well.

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lito
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#4

Re: Enthalpy

02/23/2012 2:59 AM

Enthalpy is a function of the fluid's internal energy and product of pressure and unit volume, in the case of your given parameters, both are in superheated conditions. however, the degree superheat at 50 kg/cm2 is much greater compared to the degree superheat at 140 kg/cm2. also, the specific volume at higher superheat is much great compared than in lower superheat (higher pressure) and the internal energy of the substance is function of the integral of the volume with respect to its temperature. you can best appreciate it by plotting either in the mollier or temperature-entropy diagram..i assume you understand the characteristic curve of its parameter in the diagrams:)
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woodpower
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Join Date: Aug 2010
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#5
In reply to #4

Re: Enthalpy

02/23/2012 5:11 AM

I must say that I don't understand how you identify superheating in this post since as I read the post the matter composing the "fluid" has not been identified, or even a reference to the scale used for the temperature (I know there are several). Am I missing something?
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Far
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Join Date: Sep 2011
Location: Ontario
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#7
In reply to #5

Re: Enthalpy

02/23/2012 8:30 PM

It is (H2O)Steam and the temperature is degree C. It is easily recognized when you grew up with the metric system and the Mollier diagram

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woodpower
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#8
In reply to #7

Re: Enthalpy

02/24/2012 6:48 AM

It was easy to recognize that you were assuming the substance was H2O and the temp was probably Celsius, what isn't obvious that the poster intended that assumption to be made. The level of rigor in stating the basic question does not need to be high to recognize that adding a C or K (or F or R) would eliminate the need for guessing. Anyone hoping to wake up should recognize that leaving off the degree symbol and the scale used is self destructive laziness. Do you even know what oK means, or why it might be preferred in this discussion.?
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lito
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#9
In reply to #5

Re: Enthalpy

03/22/2012 11:44 PM

The given parameters particularly 540 degree is very common as working temperature for thermal power plant as boiler exit temperature (540 deg C)thus i readily assume....steam. and i believe, i made it right:)
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dhayanandhan
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Engineering Fields - Mechanical Engineering - New Member

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#6

Re: Enthalpy

02/23/2012 12:33 PM

Dear Mr.Ksathpathi,

The MOLLIER CHART or DIAGRAM will explain and see the chart.

DHAYANANDHAN.S
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