Air flows in a duct having cross-sectional area A = 0.861 m², flow speed V 10 meters / sec, pressure P = 100 kPa, temperature T = 300 °K. Determine the mass-flow-rate, m(dot) in kg / sec.

Elements Of Electromagnetics
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Author:Sadiku, Matthew N. O.
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**Determining the Mass Flow Rate in a Duct**

In this problem, air flows through a duct with the following parameters:
- **Cross-sectional area (A):** 0.861 m²
- **Flow speed (V):** 10 meters/second
- **Pressure (P):** 100 kPa
- **Temperature (T):** 300 K

The task is to determine the mass flow rate (ṁ) in kilograms per second (kg/s).

### Step-by-Step Analysis:

1. **Calculate Air Density (ρ):**
   Using the Ideal Gas Law:
   \[
   P = \rho R T
   \]
   Where:
   - \( P \) is the pressure (Pa),
   - \( \rho \) is the density (kg/m³),
   - \( R \) is the specific gas constant for air (287 J/kg·K),
   - \( T \) is the temperature (K).

   Rearrange to solve for \(\rho\):
   \[
   \rho = \frac{P}{RT}
   \]

   Convert pressure from kPa to Pa:
   \[
   P = 100 \times 10^3 \, \text{Pa}
   \]

   Plug in the values:
   \[
   \rho = \frac{100 \times 10^3}{287 \times 300}
   \]

   Calculate the air density:
   \[
   \rho \approx 1.161 \, \text{kg/m}³
   \]

2. **Calculate the Mass Flow Rate (ṁ):**
   The mass flow rate is given by:
   \[
   \dot{m} = \rho A V
   \]

   Plug in the values:
   \[
   \dot{m} = 1.161 \times 0.861 \times 10
   \]

   Calculate the mass flow rate:
   \[
   \dot{m} \approx 10 \, \text{kg/s}
   \]

### Conclusion:
The mass flow rate of air in the duct is approximately **10 kg/s**. This calculation takes into account the given cross-sectional area, flow speed, pressure, and temperature, using the principles of fluid dynamics and the Ideal Gas Law.
Transcribed Image Text:**Determining the Mass Flow Rate in a Duct** In this problem, air flows through a duct with the following parameters: - **Cross-sectional area (A):** 0.861 m² - **Flow speed (V):** 10 meters/second - **Pressure (P):** 100 kPa - **Temperature (T):** 300 K The task is to determine the mass flow rate (ṁ) in kilograms per second (kg/s). ### Step-by-Step Analysis: 1. **Calculate Air Density (ρ):** Using the Ideal Gas Law: \[ P = \rho R T \] Where: - \( P \) is the pressure (Pa), - \( \rho \) is the density (kg/m³), - \( R \) is the specific gas constant for air (287 J/kg·K), - \( T \) is the temperature (K). Rearrange to solve for \(\rho\): \[ \rho = \frac{P}{RT} \] Convert pressure from kPa to Pa: \[ P = 100 \times 10^3 \, \text{Pa} \] Plug in the values: \[ \rho = \frac{100 \times 10^3}{287 \times 300} \] Calculate the air density: \[ \rho \approx 1.161 \, \text{kg/m}³ \] 2. **Calculate the Mass Flow Rate (ṁ):** The mass flow rate is given by: \[ \dot{m} = \rho A V \] Plug in the values: \[ \dot{m} = 1.161 \times 0.861 \times 10 \] Calculate the mass flow rate: \[ \dot{m} \approx 10 \, \text{kg/s} \] ### Conclusion: The mass flow rate of air in the duct is approximately **10 kg/s**. This calculation takes into account the given cross-sectional area, flow speed, pressure, and temperature, using the principles of fluid dynamics and the Ideal Gas Law.
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