Calculating Temperature Rise

Oct 13, 2025 by wbrum.org 67 views

Introduction

In various engineering applications, particularly in heating and ventilation systems, understanding the temperature rise of a furnace is crucial for designing and optimizing its performance. This article aims to provide a comprehensive explanation of how to calculate the temperature rise of a furnace operating with a specific heater.

Calculating Temperature Rise

To calculate the temperature rise of a furnace, we need to consider the power input from the heater, the airflow rate, and the specific heat capacity of the air. The formula to calculate the temperature rise is given by:

ΔT = (P * 3600) / (CFM * 1.10 * C_p)

where:

ΔT is the temperature rise in °F
P is the power input from the heater in watts
CFM is the airflow rate in cubic feet per minute
C_p is the specific heat capacity of air in Btu/lb-°F

Given Values

In this problem, we are given the following values:

CFM = 1200
P = 10 kW = 10,000 watts
V = 240 volts AC
I = P/V = 10,000/240 = 41.67 amps

Calculating Temperature Rise

Now, let's plug in the given values into the formula to calculate the temperature rise:

ΔT = (10,000 * 3600) / (1200 * 1.10 * 0.24)

Step 1: Calculate the numerator

The numerator is the product of the power input and the time period (3600 seconds).

numerator = 10,000 * 3600 = 36,000,000

Step 2: Calculate the denominator

The denominator is the product of the airflow rate, the specific heat capacity of air, and the constant 1.10.

denominator = 1200 * 1.10 * 0.24 = 316.8

Step 3: Calculate the temperature rise

Now, let's calculate the temperature rise by dividing the numerator by the denominator.

ΔT = 36,000,000 / 316.8 ≈ 113.7 °F

Conclusion

Based on the calculation, the temperature rise of the furnace operating with a 10 kW heater at 240 volt AC would be approximately 113.7 °F.

Comparison with Options

Comparing the calculated temperature rise with the given options, we can see that the correct answer is not among the options provided. However, the closest range is 30-40 °F.

Limitations and Assumptions

This calculation assumes that the furnace is operating at a constant airflow rate and that the specific heat capacity of air is constant. In reality, the airflow rate may vary, and the specific heat capacity of air may change with temperature. Therefore, this calculation provides an approximate value of the temperature rise.

Recommendations

To improve the accuracy of the calculation, it is recommended to use a more detailed model that takes into account the variations in airflow rate and specific heat capacity of air. Additionally, the calculation should be performed using a more precise value of the specific heat capacity of air.

Future Work

Future work could involve developing a more detailed model that takes into account the variations in airflow rate and specific heat capacity of air. This would require a more comprehensive understanding of the underlying physics and the use of more advanced mathematical techniques.

References

[1] ASHRAE Handbook, 2017, Chapter 8: Heating and Cooling Load Calculations
[2] Engineering Toolbox, 2022, Specific Heat Capacity of Air
[3] HVAC Design Manual, 2019, Chapter 3: Heating and Cooling Systems
Frequently Asked Questions (FAQs) =====================================

Q: What is the significance of temperature rise in a furnace?

A: Temperature rise is a critical parameter in furnace design and operation. It determines the effectiveness of the furnace in heating the air and the overall efficiency of the system.

Q: How is temperature rise calculated?

A: Temperature rise is calculated using the formula: ΔT = (P * 3600) / (CFM * 1.10 * C_p), where P is the power input from the heater, CFM is the airflow rate, and C_p is the specific heat capacity of air.

Q: What are the factors that affect temperature rise?

A: Temperature rise is affected by several factors, including the power input from the heater, airflow rate, specific heat capacity of air, and the efficiency of the furnace.

Q: What is the typical range of temperature rise in a furnace?

A: The typical range of temperature rise in a furnace can vary depending on the specific application and design. However, a common range is between 20-40 °F.

Q: How can temperature rise be improved?

A: Temperature rise can be improved by increasing the power input from the heater, increasing the airflow rate, or using a more efficient furnace design.

Q: What are the limitations of the temperature rise calculation?

A: The temperature rise calculation assumes a constant airflow rate and specific heat capacity of air. In reality, these values may vary, which can affect the accuracy of the calculation.

Q: How can the accuracy of the temperature rise calculation be improved?

A: The accuracy of the temperature rise calculation can be improved by using a more detailed model that takes into account the variations in airflow rate and specific heat capacity of air.

Q: What are the applications of temperature rise in furnace design?

A: Temperature rise is a critical parameter in furnace design and operation, and it has several applications, including:

Heating and ventilation systems
Industrial processes
HVAC systems
Power generation

Q: What are the benefits of understanding temperature rise in furnace design?

A: Understanding temperature rise in furnace design can provide several benefits, including:

Improved efficiency
Increased effectiveness
Reduced energy consumption
Enhanced system performance

Q: How can temperature rise be measured in a furnace?

A: Temperature rise can be measured using various methods, including:

Thermocouples
Thermistors
Resistance temperature detectors (RTDs)
Infrared thermometers

Q: What are the common mistakes in temperature rise calculation?

A: Some common mistakes in temperature rise calculation include:

Assuming a constant airflow rate
Ignoring the variations in specific heat capacity of air
Using an incorrect value for the specific heat capacity of air
Failing to account for the efficiency of the furnace

Q: How can the temperature rise calculation be validated?

A: The temperature rise calculation can be validated by comparing the calculated value with experimental data or by using a more detailed model that takes into account the variations in airflow rate and specific heat capacity of air.