A. Check whether the lumped system analysis is suitable. B. Determine the temperature of the copper block at t= 5 min after the immersion.

Elements Of Electromagnetics
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Author:Sadiku, Matthew N. O.
Publisher:Sadiku, Matthew N. O.
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**Problem:**
A solid copper cube of 10-cm edge length (\(\rho\) = 8954 kg/m³, \(c\) = 383 J/kg.K, \(k\) = 386 W/m.K) initially at a uniform temperature \(T_i\) = 250°C is suddenly immersed in a well-stirred fluid which is maintained at a uniform temperature \(T_{\infty}\) = 50°C. The heat transfer coefficient between the cube and the fluid is \(h = 200 \, \text{W/m}^2.\text{K}\).

A. Check whether the lumped system analysis is suitable.
B. Determine the temperature of the copper block at \(t = 5\) min after the immersion.

---

**Graphical Explanation:**

1. **Diagrams:**
   - The first diagram depicts the solid copper cube with each edge being 10 cm and the initial temperature of the cube \(T_i = 250°C\).
   - The second diagram illustrates the cube being immersed in a well-stirred fluid maintained at a uniform temperature \(T_{\infty} = 50°C\), with the heat transfer coefficient \(h = 200 \, \text{W/m}^2.\text{K}\).

---

**Step-by-Step Solution:**

### Part A: Lumped System Analysis

**Lumped System Criterion:**
The lumped system analysis is applicable if the Biot number \( \text{Bi} \) is much less than 1.
\[ \text{Bi} = \frac{hL_c}{k} \]

Where:
- \( h \) = heat transfer coefficient
- \( L_c \) = characteristic length of the object
- \( k \) = thermal conductivity of the material

For a cube, the characteristic length \( L_c \) is given by:
\[ L_c = \frac{V}{A} \]

- \( V \) is the volume of the cube
\[ V = a^3 = (0.1\,m)^3 = 0.001\,m^3 \]

- \( A \) is the surface area of the cube
\[ A = 6a^2 = 6 \times (0.1\,m)^2 = 0.06\,m^2 \]

Therefore, the characteristic length \( L_c \) is:
\[ L_c =
Transcribed Image Text:**Problem:** A solid copper cube of 10-cm edge length (\(\rho\) = 8954 kg/m³, \(c\) = 383 J/kg.K, \(k\) = 386 W/m.K) initially at a uniform temperature \(T_i\) = 250°C is suddenly immersed in a well-stirred fluid which is maintained at a uniform temperature \(T_{\infty}\) = 50°C. The heat transfer coefficient between the cube and the fluid is \(h = 200 \, \text{W/m}^2.\text{K}\). A. Check whether the lumped system analysis is suitable. B. Determine the temperature of the copper block at \(t = 5\) min after the immersion. --- **Graphical Explanation:** 1. **Diagrams:** - The first diagram depicts the solid copper cube with each edge being 10 cm and the initial temperature of the cube \(T_i = 250°C\). - The second diagram illustrates the cube being immersed in a well-stirred fluid maintained at a uniform temperature \(T_{\infty} = 50°C\), with the heat transfer coefficient \(h = 200 \, \text{W/m}^2.\text{K}\). --- **Step-by-Step Solution:** ### Part A: Lumped System Analysis **Lumped System Criterion:** The lumped system analysis is applicable if the Biot number \( \text{Bi} \) is much less than 1. \[ \text{Bi} = \frac{hL_c}{k} \] Where: - \( h \) = heat transfer coefficient - \( L_c \) = characteristic length of the object - \( k \) = thermal conductivity of the material For a cube, the characteristic length \( L_c \) is given by: \[ L_c = \frac{V}{A} \] - \( V \) is the volume of the cube \[ V = a^3 = (0.1\,m)^3 = 0.001\,m^3 \] - \( A \) is the surface area of the cube \[ A = 6a^2 = 6 \times (0.1\,m)^2 = 0.06\,m^2 \] Therefore, the characteristic length \( L_c \) is: \[ L_c =
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