Convective heat transfer for popcorn popping

[nickelous]

Hi all. I'm doing a heat and mass transfer whereby I'm supposed to come up with a relevant daily life example and do a 2 pg report on it. I have kind of decided to do on popcorn popping via convection.

So basically from my web research the popcorn kernel contains about 13% moisture and the rest being starch granules. One of the popping mechanism I read states that at a pressure of 8 atm, the pressure that is building up inside the kernel by the superheated water at 448K would be too much for the pericarp, thus causing it to break apart. The superheated water would then turn into steam with the release of pressure and expand 1500 times its original volume as water. Thereafter, the starch granule expand and blow up thus forming the popcorn we know.

I have thought of modelling the popcorn kernel as a spherical tank in a unsteady state heat transfer into the water contained in this 'spherical tank'. Thereafter I can calculate the time required for the water to reach 448K. The heat transfer coefficient for sphere is as such

Now the problem is I do not really know how to begin :/ The water does not occupy the entire volume of the tank (as there is starch as well). In addition, I'm not too sure how to take the thermal resisitivty of the pericarp into account. As such I would really appreciate if someone can give some kind guidance!

 

[nilesh_pat]

First of all, what you need to do is find the heat transfer coefficient for your popcorn kernel (which you have already done). This can be done by using the thermal conductivity of the pericarp and the thickness of the pericarp. Then, you need to calculate the amount of energy that needs to be transferred to the water to reach 448K and how much time it will take. To do this, you will need to use the heat transfer equation, which is Q=(U*A)*(T2-T1). Here, U is the overall heat transfer coefficient, A is the surface area of the popcorn kernel, and T2 and T1 are the final and initial temperatures respectively. Once you have calculated the amount of energy required, you need to determine the rate at which it is transferred from the external environment to the popcorn kernel. This can be done by using the convection equation, which is h=k/d, where h is the convection coefficient, k is the thermal conductivity of the medium (air or liquid) around the popcorn kernel, and d is the distance between the popcorn kernel and the medium. With this information, you can then calculate the rate of heat transfer by using the equation q=hA(T2-T1), where q is the rate of heat transfer, h is the convection coefficient, A is the area of the popcorn kernel, and T2 and T1 are the final and initial temperatures respectively. Finally, you need to calculate the time it will take for the water to reach 448K. To do this, you will need to use the equation t=Q/q, where t is the time, Q is the amount of energy required to reach 448K, and q is the rate of heat transfer. Once you have completed these calculations, you can then write your report on the heat and mass transfer process that occurs when popping popcorn. Good luck!