Heat Required to Bake a product in an oven

[som1973]

Hi,
Can anyone help in calculating Total Heat required (Btu/hr)from basics(Fundamentals) for Baking a product(biscuit)in an oven.

I have considered the following procedure.
1. Heat required to raise the temperature of dough to 100 deg C (212 deg F)
2. Heat required to evaporate the water in dough
3. Heat losses through oven walls
4. Heat losses through exhaust.

Can anyone shed more light on this...

 

[MintJulep]

Sounds like you've got mostly got it.

If it's a batch oven consider air changes due to "peeking" or moving product in or out.

If it's a commercial conveyor oven consider loads associated with the belt and air leakage where the belt goes in and out.

 

[som1973]

Thanks Mintjulep,
I have two questions in my mind.

1. Do we need to calculate amount of heat required to raise the temperature of dough from 100 deg C (212F) to baking temperature say 250 deg C ?

2. I have calculated heat lost to water = sensible heat + latent heat.

do I need to calculate super heat ?

 

[MintJulep]

Yes, you need to consider the heat to bring the product fully up to temperature.

Not sure about superheat, of it that's even really the right term. My gut feel is that it would be a relatively small component of total load, and could be safely neglected.

 

[som1973]

I have found in this link

http://www.spiraxsarco.com/resource...rinciples-and-heat-transfer/what-is-steam.asp

Enthalpy of saturated steam, or total heat of saturated steam
This is the total energy in saturated steam, and is simply the sum of the enthalpy of water and the enthalpy of evaporation.


Where:

hg = Total enthalpy of saturated steam (Total heat) (kJ/kg)
hf = Liquid enthalpy (Sensible heat) (kJ/kg)
hfg = Enthalpy of evaporation (Latent heat) (kJ/kg)

 

[som1973]

What could be the percentage of heatloss from oven wall & oven exhaust in case of commericial conveyor oven ?

 

[IRstuff]

Is this for school?

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[dvd]

If you are considering heat loss don't forget about the energy required to re-heat the conveyor and baking pans as there will be some cooling at the entrance and exit of the oven. I recommend that you contact the manufacturer of these types of ovens to ask about energy requirements.

Another consideration is time involved to bake. Moisture may be harder to drive off than it is to heat the goods. Are you working to establish oven length, or throughput?


p.s. Baking biscuits for school is strictly forbidden on this site.

 

[racookpe1978]

Baking extra cookies for the class to sample is, however, required for this site.

 

[vpl]

som

By your mention of a commercial conveyer oven, I guess this isn't a class assignment.

Based on my personal experience, cooking times are determined more by the "trial and error" method because a lot depends not only on the temperature in the oven, but on the temperature of the dough when it goes in and the particular recipie that's being used (ie, the amount and type of liquid and the amount of shortening.) There are so many different factors, that I don't think it's possible to develop one formula that fits everything. And there's quite a difference between cooking an occasional batch where you can lower the temperature and extend the time (my usual advice to newer cooks) and a commercial operation where the object is to get as many biscuits cooked in as short a period of time as possible.

Finally, the word "biscuit" means different things in different countries. To me, as an American, a bisquit is a 1-1/2 to 2" high flaky breakfast item made from flour, butter and water (I think the closest the English come is a scone, which is nowhere near the same). To someone in England, a biscuit is a thin sweet desert (which we Americans call "ccokies".) If you're somewhere else in the world, I don't know how the term is defined.

My advise, which may or may not be usable, is to go talk to some commercial bakers in your area. Ask them for information on not only what temperature for the oven and what speed for the conveyor but also how closely they place the biscuits on the conveyor, what temperature the dough should be, and how the dough consistency plays into the above.

Patricia Lougheed

******

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[eeprom]

As a baker and an engineer this is a very interesting question. There may be more than material temperature and moisture evaporation.

All professional baking formulae work of percentages by weight. So it should be easy enough to determine the content of water and flour and shortening.

But nothing will be baked to the point of zero moisture, so you cannot assume that all moisture is evaporated. The easiest way to check this is by weighing before and after cooking. All of your mass loss will be water.

So you have 4 heats:
1. Heat required to raise the water to 220F
2. Heat required to vaporize all dissipated water
3. Heat required to raise the dry materials to final temperature.
4. Heat of breaking and forming of chemical bonds.

#4 would be very difficult to determine, and the result could be exothermic or endothermic. Cooking is simply slow combustion. All the carbons will turn to CO2 or CO given enough time and temperature.

EE

 

[racookpe1978]

Cooking is simply slow combustion. All the carbons will turn to CO2 or CO given enough time and temperature.

My cooking tends to end up as a very rapid conversion of ingredients to black carbon in short times at high temperatures....

 

[som1973]

Thanks DVD,vpl & EEPROM for all your advice.

It is not for a school,( Some people making fun of
the question)

I am interested in calculating percentage of
heat loss through exhaust & percentage of
Heat loss through oven wall in commerical Tunnel oven.

 

[TheBlacksmith]

In the case of an american (baking powder) biscuit, you also need a high initial temperature to set the fat/flour composite. A slow set will allow moisture to penetrate the fat/flour composite, resulting in batter (cake/cookies) versus batter (light flaky biscuits). I bake my homemake bisucits at 425-450 F for about 10 minutes.

 

[eeprom]

If it's an electric oven, you can put a meter onto the input (or measure current and voltage). If it's a gas oven, you will have to determine gas flow. Either of these will give you total BTU input to the oven.

Turn on the oven, let it get to temperature, and then calculate the total BTU into the oven by integrating the power input over the time that the oven is on.

Then put a thermocouple in the oven, turn off the oven, and monitor the temperature decay. This will tell you the thermal losses of the oven.