Heat Rejection Calculator

Formula

The formula to calculate heat rejection is:

\[ Q = c \cdot p \cdot F \cdot \Delta T \]

where:

• \( Q \) is the heat rejection (kW),
• \( c \) is the specific heat capacity (kJ/kg°C),
• \( p \) is the density (kg/m³),
• \( F \) is the flow rate (m³/hr), and
• \( \Delta T \) is the change in temperature (K or °C).

Example Calculation

Let's say you have the following data:

• Specific Heat Capacity: \( 4.18 \, \text{kJ/kg°C} \)
• Density: \( 1000 \, \text{kg/m³} \)
• Flow Rate: \( 10 \, \text{m³/hr} \)
• Change in Temperature: \( 20 \, \text{°C} \)

Plug these values into the formula:

\[ Q = 4.18 \cdot 1000 \cdot 10 \cdot 20 = 836,000 \, \text{kJ/hr} \]

Convert to kW by dividing by 3600 (since 1 kWh = 3600 kJ):

\[ Q = \frac{836,000}{3600} \approx 232.2222 \, \text{kW} \]

Importance and Usage Scenarios

Heat rejection is vital in maintaining the efficiency and longevity of many systems, especially those involving engines and heat exchangers. It's crucial in the design of cooling systems for:

• Turbine Engines: Ensuring efficient engine cooling by rejecting excess heat.
• Industrial Machinery: Preventing overheating that could lead to equipment failure.
• Power Plants: Managing heat dissipation in condensers and boilers.
• HVAC Systems: Maintaining indoor air quality and temperature.

Common FAQs

1. What units should the parameters be in to calculate heat rejection correctly?

• Specific heat capacity: kJ/kg°C
• Density: kg/m³
• Flow rate: m³/hr
• Temperature change: °C or K

2. Why do we divide by 3600 in the calculation?

• The formula initially yields the result in kJ/hr. Dividing by 3600 converts the value to kW, a standard power unit.

3. Why is heat rejection important in turbine engines?

• It prevents overheating and maintains engine efficiency by dissipating the excess heat produced during combustion.