Question

In convection SI unit of heat transfer coefficient is ............

• A. $Kcal/hr \cdot m^2 \cdot ^\circ C$
• B. $W/m^2 \cdot ^\circ C$
• C. $W/m \cdot ^\circ C$
• D. $Kcal/hr$

Hint:

Distinguish between Thermal Conductivity (\(k\): \(W/m \cdot K\)) and Heat Transfer Coefficient (\(h\): \(W/m^2 \cdot K\)). \(h\) is for surfaces (Area), \(k\) is for bulk materials (Length).

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks for the International System (SI) unit for the convective heat transfer coefficient (\(h\)).
Key Formula or Approach: Newton's Law of Cooling defines convective heat transfer: \[ q = h A (T_s - T_\infty) \] Rearranging for \(h\): \[ h = \frac{q}{A \Delta T} \]

Step 2: Detailed Explanation:

• In food engineering, heat transfer coefficient (\(h\)) is a measure of how effectively heat is exchanged between a solid surface and a fluid moving over it.

• In the equation \(h = \frac{q}{A \Delta T}\):
- \(q\) is the heat flow rate, measured in Watts (\(W\)) or Joules per second (\(J/s\)) in SI.
- \(A\) is the surface area, measured in square meters (\(m^2\)).
- \(\Delta T\) is the temperature difference, measured in Kelvin (\(K\)) or degrees Celsius (\(^\circ C\)).

• Substituting the units: \(Unit = \frac{W}{m^2 \cdot K}\) or \(\frac{W}{m^2 \cdot ^\circ C}\).

• Note that a temperature difference of 1 Kelvin is equivalent to 1 degree Celsius, so both are used interchangeably in this context.

• Option (A) uses \(Kcal\), which is a non-SI metric unit. Option (C) is the unit for thermal conductivity (\(k\)). Option (D) is simply a unit of power.

• Therefore, option (B) represents the correct SI units for the heat transfer coefficient.

Step 3: Final Answer:
The SI unit for the heat transfer coefficient is \(W/m^2 \cdot ^\circ C\).