How Much Diesel Required for Heating Up Water??

I hope that was the combustion heat of diesel rather then the specific heat. (Assuming the diesel is being used as a fuel rather than a heat-exchange fluid.)

If the boiler efficiency is η, heat to water = η × combustion heat of fuel.

Sorry, yes it's combustion of diesel. Can you tell me the formula for calculation of diesel fuel on daily basis to produce 250m3/hr hot water @ 80 Deg C.

Multiply the temperature difference required by the specific heat. Divide by the density of water. Multiply by the flowrate. Divide by the specific heat of diesel and an efficiency, oh, say 30%, and "Robert is your mother's brother". Make sure the units are consistent, though.

30% ? This is a boiler, not an engine. 30% would be poor for a diesel engine.

The basic formula for heating is Q=mass x heat capacity x delta T

So, Heat rate ( diesel burn-rate ) = mass rate x heat capacity x delta T

Convert flow rate to mass rate (in per sec ) , assume eff say 90%, you can easily compute diesel rate .

Let me tell you what I did,

Q = mc * Delta T

Q = 62790Mjoule

Now, Q above is the heat required to change 250 KL of water temp from 20 to 80 Deg C

As Diesel Combustion heat is 46 Mj/kg, I found I need 1401kg of Diesel to produce 62790 Mjoule of heat.

Now how can I incorporate mass flow rate?

Well, the density of water has to be in there somewhere...

Can you tell me the simple formula? I think i got confused due to the description given above.

1 m3/hr =1000 kg/hr = 0.2778 kg /sec

Q rate = 250*0.2778*4180 * 60 J /sec

Fuel rate (kg/sec) = Q rate / 44.8 MJ/kg

Need boiler efficiency in there.

COMMENT to Post No. 9 and 10, as additional information, as my view that

COMBUSTION EFFICIENCY IS TO BE ACCOUNTED and then the HEAT TRANSFER to water takes place. Boiler Efficiecy is HEAT OUT PUT/HEAT INPUT and hence heat liberated by DIESEL to be counted - that COMBUSTION EFFICIENCY comes in to picture.

DHAYANANDHAN.S

I think this has been covered in later posts, but not clear what point you're making. There is only boiler efficiency, heat out into water/heat in from fuel, to take into account. I don't think it's possible, or helpful to divide it into combustion efficiency and transfer efficiency.

Only thing to be careful of is whether heat in is based on gross calorific value of fuel - products of combustion CO2 + liquid water, or nett, products of combustion CO2 + water vapour. For diesel, difference is about 10%.

At 250 cubic meters an hour on a 60C temp rise you are going to need a whole lot of diesel fuel!

Can I sell it to you?

Thanks very much guys, I really apprectiate your help. It means we need around 1500 Litres of diesel per hour for the required heat exchange. It's quite expensive, have to look around for other options

If your system can be set up as a closed loop or the end product still has heat left, you might want to consider running it through a heat exchanger and dump some of that heat back into the heating system which should reduce the amount of fuel required.

Without knowing your process, it's just a left field idea for you to consider.

Regards,
Sapper

Not quite. Even at 100% boiler efficiency I make it 1425 kg/h. As the SG of diesel is ~ 0.85 that comes to 1676 litre/h. Taking a reasonable boiler efficiency 90% (based on the nett diesel CV quoted) it's about 1850 litre/h.

Also it's making hard work of the calc to convert to ft/lb/°F units (and back) when the question was posed in metric.

I don't follow what the specific gravity of diesel fuel has to do with the equation.

We are after the energy content per unit of volume it contains.

As far as the calculator work to convert from American to metric and back I had to make the OP work for this at least a little bit!

I was replying to post #13 and didn't agree with the 1500 litre/h. I hadn't read your #12 in detail but now I have, I see you used a diesel CV per unit volume, while the OP gave it in MJ/kg.

What confused things was #13 said 1500 litre/h while your figure 530 gal/h is ~ 2000 litre/h. Allowing for slightly different assumptions about SG and efficiency we're pretty much in agreement.

Not a bad idea to get the OP do a bit for himself .

When dealing with people I try to use common reference points that most people would have some rough knowledge of. For me and where I live equating the energy of fuel is best done as kilowatt hours for electrical comparisons or BTUs for thermal comparison.

Most people know what a KWH is and what it may cost them and they tend to have some idea what a BTU rating of a heating appliance or device is and how it relates to thermal output.

The further you get away from the common mans terms and its abreviations it will tend to cause more problems than it solves even if it is technicaly more accurate.

Appreciate your help, I'm offered a Diesel Fired Heat Exchanger with design flow rate of 24L/sec. So we will install 3 units and diesel fuel consumption comes out to be 4500L/hr for all 3 units. The combined water flow rate is 72L/sec as desired…. So there is some difference in theoretical calculation and actual design. Consumption rate of 1800L/hr was horrible, still trying to figure out with the supplier why their design parameters are so much different from my calculation

What are the supplier's design parameters? I don't think you've told us in this thread.

We've come up with about 2000 l/h. You might get away with 1800 if the boiler has good efficiency. 3 x 72 l/sec is a bit more than 250 m³/h.

Its a proposal at the moment. Its FH500 water heater, 24L/sec capacity, 60L/hr Diesel concumption..... I am still bit skeptical why there is a huge difference in what we calculated here and quotation being offered by the vendor..

Thanks, have a question,

in the third step (A 60C temp change would take 106 BTU's per pound of water.) How did you calculate this one? 60 Deg C is equivalent to 140 F so I thought it will take 140 BTU for heating it.

Think about it for a while.

(You might even find the typo in my calculation too.)

Right :)

May be you considered and included density as well in British Units so it comes out 106. Or may be using formula Q = mc * Delta T

You are over thinking it.

Whats 80 C equal to in Fahrenheit?

Whats 20 C equal to in Fahrenheit?

Do the math and you will find the answer and my typo's.

I cant make it any simpler without it becoming an embarrassment to us both. (if it isn't too late for that already.)

Yes, typo error. 106 in place of 108..My bad, just wondering how could I miss the fundamental….Thanks for your patience and clues J