Question

Plank's law can be used for estimation of ________.

• A. Time of drying
• B. Time of boiling
• C. Time of germination
• D. Time of freezing

Hint:

In food engineering, "Plank's Equation" is used for freezing calculations, whereas the "Henderson-Pabis" or "Page" equations are typically used to calculate drying times.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Freezing is a preservation method that slows down physical, chemical, and microbiological degradation by lowering temperatures and converting water into ice.
Estimating the time required to freeze food is essential for designing freezing equipment and ensuring food safety.
Key Formula or Approach:
Plank's equation for freezing time is expressed as:
\[ t_f = \frac{\rho \cdot \lambda}{T_f - T_{\infty}} \cdot \left[ \frac{P \cdot a}{h} + \frac{R \cdot a^2}{k} \right] \] where:
- $t_f$ is the freezing time.
- $\rho$ is the density of the food.
- $\lambda$ is the latent heat of fusion.
- $T_f$ is the freezing temperature, and $T_{\infty}$ is the cooling medium temperature.
- $h$ is the heat transfer coefficient, and $k$ is the thermal conductivity of frozen food.
- $a$ is the thickness of the food, and $P, R$ are shape factors (for a flat plate, cylinder, or sphere).

Step 2: Detailed Explanation:
Plank's equation was developed in 1913 to estimate the time required to freeze food products.
It assumes that the product is initially at its freezing temperature and calculates the time needed to convert all its water into ice.
While it has limitations (such as assuming constant thermal properties), it remains a fundamental formula used in food refrigeration engineering.

Step 3: Final Answer:
Plank's equation is used to estimate the time of freezing.