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omar1
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Join Date: Jan 2008
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Electrical Heater

01/21/2008 3:47 AM

Natural gas of 7.5 Ib/Sec is to be heated from 10 C to 50 C How much is the proper electrical heater power that verify the previous condition
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PWSlack
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#1

Re: electrical heater

01/21/2008 4:00 AM

What is the thermal capacity at constant pressure (or constant volume, depending upon situation) for the gas?

The rest is arithmetic.

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omar1
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#2
In reply to #1

Re: electrical heater

01/21/2008 4:52 AM

Assume the natural gas is pure methan CH4, Cp is 0.52669 Btu/(Ib.F) @ standard condition(60 F and 14.696 psia)

Note that:-

The operating pressure is 1050 psia
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PWSlack
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#3
In reply to #2

Re: electrical heater

01/21/2008 5:52 AM

The rest is arithmetic.

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omar1
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#4
In reply to #3

Re: electrical heater

01/21/2008 6:17 AM

Please calculate the consumed power and add the residual (excess) of power of the heater and dont forget the efficiency of the heater should be less than 100% to assure our results
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PWSlack
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#5
In reply to #4

Re: electrical heater

01/21/2008 6:51 AM

Invitation declined.

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TVP45
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#6
In reply to #4

Re: electrical heater

01/21/2008 7:25 AM

Omar,

Is this a homework question?

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ddk
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#7

Re: electrical heater

01/21/2008 7:25 AM

we generally don't do homework. If this is a real problem in a real industry you need to provide detail.

Study hard for your classes.

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vipy
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#8

Re: Electrical Heater

01/22/2008 12:14 AM

P = (mass/s) x c x (Change in T)

But this does sound like a hw question :)

Confirm it though i'm not sure....
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jmueller
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#9

Re: Electrical Heater

01/22/2008 12:55 AM

omar1

Usually when I am trying to solve a problem, keeping track of the units is very helpful. Your problem (and I also assume it is homework), has a mixture of unit systems. You have temperature in °C (metric system) and mass of methane in lb (English system). Some of the other posts mention BtU (English system). I suggest that you convert the lb (pounds) to metric units first, because that is the more widely used system, particularly in science. I believe that you have all the information you need. When I solve problems, I usually draw a horizontal line and put the numbers and the units above or below it as necessary instead of using the "/" mark. Then conversion factors can be put in in the proper locations to change the units to the desired ones.

--JMM
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Anonymous Poster
#10

Re: Electrical Heater

01/22/2008 10:02 AM

I'm a mechanical consultant, and I find that a unit converter comes in quite handy (easy to find them on the internet). I'm from Canada, we are supposed to use a metric system, but our industry still operates in imperial units, except government or large institutional jobs, etc.

1kW produces about 3.42MBH (1MBH=1000btuh) of heat. Typically, one CFH of gas (cubic foot hour) is just barely under 1 MBH of heat output. As mentioned by a previous response, it depends the quality/rating of the gas. Remember that your wattage loses heat output depending on your voltage selection. Look in electric heater product catalogs (available online) to make your selection.

Evan
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Anonymous Poster
#11
In reply to #10

Re: Electrical Heater

01/22/2008 10:06 AM

P.S. I may have misinterpreted your question. My response was for if you're converting from a natural gas heater that uses natural gas at that rate to an equivalently sized electrical heater.

Evan
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MUKULMAHANT
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#12

Re: Electrical Heater

01/22/2008 12:08 PM

Cp=2.1933 AT 10C

Cp=2.3069 AT 50C --both in KJ/(Kg.DegreeC)

7.5lbs=3.4 Kg

So Energy needed to warm up=3.4x{(2.3069x50)-(2.1933x10)} Kilojoules/second

Say= 320KJ/sec=320 Kilowatt.

Heater efficiency =1.00(100%) -all heat goes to heat.

Hence Heater Power needed=320 KiloWatt
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Users who posted comments:

Anonymous Poster (2); ddk (1); jmueller (1); MUKULMAHANT (1); omar1 (2); PWSlack (3); TVP45 (1); vipy (1)

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