Deep Frying a Chicken: How Long Does It Take?

[gazepdapi1]

One of my project for my transport courses is to answer how long it would take to deep fry a chicken with all the internal organs removed? I was thinking this can be solved by setting up an energy balance with the energy equation and discarding terms. Would I also have to do a momentum balance? I am not sure.

Anyone have any ideas?

Any suggestions are appreciated.
Thank You

 

[Astronuc]

It should be heat conduction. Is the chicken hollow?

If so, will it fill with hot oil as well as being surrounded by hot oil?

 

[gazepdapi1]

Yes, the chicken is hollow but I will assume that it will not fill with oil. I will assume that the shape is a sphere and make my balance around that. Also, if only heat conduction is relevant, then what would change if the chicken is boiled instead? Any thoughts?

 

[Astronuc]

Yes, the chicken is hollow but I will assume that it will not fill with oil. I will assume that the shape is a sphere and make my balance around that. Also, if only heat conduction is relevant, then what would change if the chicken is boiled instead? Any thoughts?

The problem depends on the mass of oil or water, or could one assume an finite sphere in infinite medium (oil or water) at a fixed temperature?

The water boils at 100°C (212°F). Perhaps the oil can be heated a bit higher?

Here is an example of oil smoke points (temps)
http://www.goodeatsfanpage.com/CollectedInfo/OilSmokePoints.htm

Peanut oil                          440°F 227°C 
Sunflower oil                         
Refined corn oil                    450°F 232°C 
Refined high-oleic sunflower oil  
Refined peanut oil  
Refined Safflower oil 
Semirefined sesame oil  
Refined soy oil  
Semirefined sunflower oil  
Olive pomace oil                    460°F 238°C 
Extra light olive oit               468°F 242°C 
Soybean oil                         495°F 257°C 
Safflower oil                       510°F 266°C 
Avocado oil                         520°F 271°C

from http://www.cookingforengineers.com/article/50/Smoke-Points-of-Various-Fats

 

[gazepdapi1]

Well, I am assuming that the geometry of the chicken will be roughly a sphere of radius R. So, as I understand it, the only change between the oil and water is the difference of temperature between the fluid and the chicken?

One thing I'm not clear on is, why is there no convection in this analysis?

 

[Bhubbard]

I would think that a cylinder would be a better model of a chicken than a sphere. There will probably be a lot of escaping steam at the chicken-oil interface (leidenfrost layer), cooling it and preventing direct contact with the oil. I doubt that you'd have much convection, but you might have significant mass transport?

- Bruce

 

[gazepdapi1]

Well, up until this point we have only covered momentum and energy transport, so mass would not be covered...although I'm sure it's occurring in this process.

 

[hamster143]

A solid sphere is not a good model. De-gutted chicken would be better modeled as a hollow sphere whose internal radius not much smaller than external radius. Your answer would depend on that significantly. I suggest that you go to the nearest meat shop, buy yourself a frozen chicken, and inspect it.

Unless you go to extreme lengths to seal the chicken, hot oil _will_ get inside. You cannot assume that it is filled with air. At best you can assume that there will be no convection between the interior of the chicken and the rest of the container. The initial temperature of the oil at the time the chicken is filled will affect the answer.

 

[gazepdapi1]

Yes, I was planning to use a hollow sphere but I was not planning to take into account the oil filling the chicken, although I probably should. If this is considered, then would convection come into account for the energy balance, since you have flow into the chicken? I guess my biggest confusion is what to define as the boundaries of my system?

 

[hamster143]

I'm not quite clear on that too.

Meat has much higher thermal conductivity than cooking oil. So, without convection, this would be a complicated problem that depends on size and shape of the container, position of the burner, etc. But convection could make it much simpler. If you can establish that convection is present (maybe by computing the Rayleigh number) and that it is the primary method of heat transfer in oil, you can probably assume that all oil on the outside is kept at a constant temperature T1, and all oil in the cavity has temperature T2 (possibly different from T1).

There are two basic cases. One is that the cavity is connected to the exterior by a big enough opening that convection between them keeps T2=T1. The other is that the cavity is more or less sealed, and the opening is not big enough to maintain convection, and oil inside the cavity is heated by conduction through the meat.

 

[gazepdapi1]

Well this is an open ended problem, so I can assume anything as long as I justify my assumptions. Not to sound lazy, but I would do whatever is simpler. I think I will assume the second case you stated, where the cavity is sealed and that the oil on the outside is heating the meat and the oil on the inside. I will assume that the oil on the outside is about 325 F (this is usually what they used when they deep fry) and that the oil that gets inside is maybe around 310-315F, what do you think?

 

[hamster143]

Why not assume that the oil on the inside is initially at 325 F too.

 

[gazepdapi1]

Ok, this is the energy equation that I came up with, with all of the unnecessary terms crossed out.. Hamster, can you check to see if it's correct?