Physics Help Forum Finding volumetric flow rate of heat engine

 Thermodynamics and Fluid Mechanics Thermodynamics and Fluid Mechanics Physics Help Forum

Feb 9th 2018, 09:43 PM   #11
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 Originally Posted by casperneo A Heat Engine has a thermal efficiency of 40% at a steady power output of 30kW. Calculate the required volumetric fuel flow in L/Hr ( litres/hour) if the fuel has a density of 850 kg/m^3 and an energy content of 45 MJ/kg.
I'm interested in this to find the cost of producing electricity from a generator ..

So energy consumption is 75 KJ/sec , that's 0.0006 Kg /sec= 0.0007liters/sec

That's 2.5liters /Hr which gives 30 KwHrs of electrical power

1 liter gives 12Kw Hrs

@ petrol cost of $1/liter that's 8.3c/KwHr Ha !!! on Uk prices you can generate your own Cheaper than the grid!!, that's buying petrol from a gas station!! Also you have 40Kw of waste heat as well , easily piped into central heating . And many house have a natural gas supply , this must be half the price of pertrol. It makes no sense to use natural gas domestically in boilers ... CHP ... run a generator feeding electricity to the grid and use waste heat for central heating ! Last edited by oz93666; Feb 9th 2018 at 09:48 PM. Feb 10th 2018, 06:50 PM #12 Junior Member Join Date: Feb 2018 Posts: 1  Originally Posted by casperneo A Heat Engine has a thermal efficiency of 40% at a steady power output of 30kW. Calculate the required volumetric fuel flow in L/Hr ( litres/hour) if the fuel has a density of 850 kg/m^3 and an energy content of 45 MJ/kg. So what is the answer uh? Feb 12th 2018, 04:29 AM #13 Senior Member Join Date: Oct 2017 Location: Glasgow Posts: 445  Originally Posted by oz93666 I'm interested in this to find the cost of producing electricity from a generator .. So energy consumption is 75 KJ/sec , that's 0.0006 Kg /sec= 0.0007liters/sec That's 2.5liters /Hr which gives 30 KwHrs of electrical power 1 liter gives 12Kw Hrs @ petrol cost of$1/liter that's 8.3c/KwHr Ha !!! on Uk prices you can generate your own Cheaper than the grid!!, that's buying petrol from a gas station!!
Petrol is about £1.20 per litre at the moment, which is much more expensive than \$1 per litre. Also, the efficiency of domestic-scale generators is usually much, much lower than industrial-scale generators, at least in the case of fossil-fuelled generators (the same cannot necessarily be said about renewable technology).

Although some facilities do have their own electricity generators, they usually use renewables (PV panels and/or wind turbines) or biomass.

 Also you have 40Kw of waste heat as well , easily piped into central heating .
Yep! Despite the drawbacks of natural gas domestic boilers, Most commercial buildings with HVAC systems have some form of recirculation or heat recovery to improve overall efficiency of the heating system

 And many house have a natural gas supply , this must be half the price of pertrol.
Gas is also expensive here, depending on how much you use. My property is an old stone tenement block which is badly insulated and my gas bill is much, much higher than my electricity bill.

 It makes no sense to use natural gas domestically in boilers ... CHP ... run a generator feeding electricity to the grid and use waste heat for central heating !
CHP is generally more cost-effective for large buildings that have a high energy demand, such as hospitals or farms, and also include heat recovery and additional cooling systems. Also, in New York and other places around the world, they have district steam systems that are useful for meeting both electricity and heat demand.

So yeah, there's lots of things one can do to improve the heat balance mechanisms of buildings

Feb 17th 2018, 05:55 AM   #14
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 Originally Posted by casperneo A Heat Engine has a thermal efficiency of 40% at a steady power output of 30kW. Calculate the required volumetric fuel flow in L/Hr ( litres/hour) if the fuel has a density of 850 kg/m^3 and an energy content of 45 MJ/kg.