Answer:
The time taken is
Explanation:
From the question we are told that
The diameter of the egg is ![d_e = 5.5cm = \frac{5.5}{100} = 5.5*10^{-2}m](https://tex.z-dn.net/?f=d_e%20%3D%205.5cm%20%20%3D%20%5Cfrac%7B5.5%7D%7B100%7D%20%3D%205.5%2A10%5E%7B-2%7Dm)
The initial temperature of egg the ![T_e = 4.3^{o}C](https://tex.z-dn.net/?f=T_e%20%3D%204.3%5E%7Bo%7DC)
The temperature of the boiling water ![T_b = 100^oC](https://tex.z-dn.net/?f=T_b%20%3D%20100%5EoC)
The heat transfer coefficient is ![H = 800 W/m^2 \cdot K](https://tex.z-dn.net/?f=H%20%20%3D%20800%20W%2Fm%5E2%20%5Ccdot%20K)
The final temperature is ![T_e_f = 74^oC](https://tex.z-dn.net/?f=T_e_f%20%3D%2074%5EoC)
The thermal conductivity of water is ![k = 0.607 W/m^oC](https://tex.z-dn.net/?f=k%20%3D%200.607%20W%2Fm%5EoC)
The diffusivity of the egg ![\alpha = 0.146 * 10^{-6} m^2 /s](https://tex.z-dn.net/?f=%5Calpha%20%3D%200.146%20%2A%2010%5E%7B-6%7D%20m%5E2%20%2Fs)
Using one term approximation
We have the
![\frac{T_e_f - T_b}{T_e - T_b} = Ae^{-\lambda ^2 \tau}](https://tex.z-dn.net/?f=%5Cfrac%7BT_e_f%20-%20T_b%7D%7BT_e%20-%20T_b%7D%20%20%3D%20Ae%5E%7B-%5Clambda%20%5E2%20%5Ctau%7D)
The radius is
Note that this radius is approximation to that of a real egg
Now we need to obtain the Biot number which help indicate the value of
to use in the above equation
The Biot number is mathematically represented as
![Bi = \frac{H r}{k}](https://tex.z-dn.net/?f=Bi%20%3D%20%5Cfrac%7BH%20r%7D%7Bk%7D)
Substituting values
![Bi = \frac{800 * 2.75 *10^{-2}}{0.607}](https://tex.z-dn.net/?f=Bi%20%3D%20%5Cfrac%7B800%20%2A%202.75%20%2A10%5E%7B-2%7D%7D%7B0.607%7D)
![= 36.24](https://tex.z-dn.net/?f=%3D%2036.24)
So for this value which greater than 0.1 the coefficient
is
![\lambda = 3.06632](https://tex.z-dn.net/?f=%5Clambda%20%3D%203.06632)
![A = 1.9942](https://tex.z-dn.net/?f=A%20%3D%201.9942)
Substituting this into equation 1 we have
![0.2717= 1.9942 e^{-9.383 \tau}](https://tex.z-dn.net/?f=0.2717%3D%201.9942%20e%5E%7B-9.383%20%5Ctau%7D)
![0.13624 = e^{-9.383 \tau}](https://tex.z-dn.net/?f=0.13624%20%3D%20%20e%5E%7B-9.383%20%5Ctau%7D)
Taking natural log of both sides
![-1.993 = -9.383\ \tau](https://tex.z-dn.net/?f=-1.993%20%3D%20%20-9.383%5C%20%20%5Ctau)
The time required for the egg to be cooked is mathematically represented as
![t = \frac{\tau r^2}{\alpha }](https://tex.z-dn.net/?f=t%20%3D%20%5Cfrac%7B%5Ctau%20r%5E2%7D%7B%5Calpha%20%7D)
substituting value is
![= \frac{0.2124 * 2.75 *10^{-2}}{0.146 *10^{-6}}](https://tex.z-dn.net/?f=%3D%20%5Cfrac%7B0.2124%20%2A%202.75%20%2A10%5E%7B-2%7D%7D%7B0.146%20%2A10%5E%7B-6%7D%7D)