How can I calculate energy loss from a leak in a large furnace?

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Discussion Overview

The discussion revolves around calculating energy loss from a leak in a large furnace, specifically focusing on the methods and equations that can be used to quantify this loss. The context includes considerations of airflow, gas composition, and temperature differences, with participants exploring various approaches and assumptions related to the problem.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Exploratory

Main Points Raised

  • One participant suggests using Bernoulli's equation to calculate airflow and then multiplying by the specific heat of air and the temperature of the leaving air to determine energy loss.
  • Another participant agrees with the use of Bernoulli's equation but argues that assuming the gas mixture is dry air oversimplifies the situation, as the mixture likely includes combustion gases such as O2, CO2, CO, N2, and water vapor.
  • A different approach is proposed involving the continuity of mass equation to find the mass flow rate of combustion gas, with a formula for heat loss based on the specific heat and temperature difference of the gases.
  • Concerns are raised about the need to account for vapor formed in combustion products, suggesting that the change of enthalpy of superheated steam may need to be included in calculations.
  • One participant notes that whether to account for water vapor depends on the specifics of the furnace operation, indicating that if the furnace does not condense water vapor, it may not be necessary to include it in energy loss calculations.
  • A suggestion is made to use calorimetry by placing a beaker of water near the hole to measure temperature changes as a potential method to assess heat loss.
  • Another participant expresses a desire to learn about pressure loss and head loss, indicating a broader interest in related concepts.

Areas of Agreement / Disagreement

Participants express differing views on the assumptions regarding gas composition and the necessity of accounting for water vapor in energy loss calculations. There is no consensus on a single method or formula to calculate energy loss, and multiple approaches are discussed.

Contextual Notes

Participants highlight various assumptions, such as the composition of the gas mixture and the operational conditions of the furnace, which may affect the calculations. The discussion does not resolve these uncertainties.

Who May Find This Useful

This discussion may be useful for individuals interested in thermodynamics, energy loss calculations in industrial applications, or those seeking to understand the complexities of gas mixtures in combustion processes.

rdolin
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How can I calculate energy loss from a leak in a large furnace?

I currently am working on a large furnace about 1200 square feet. To heat the furnace we use a combination of air and methane at a ratio of 9.54:1. There is currently a hole in the furnace and I would like a formula to calculate the energy loss. We have the temperatures and the pressures to use in the formula. If you can please give me some tips of an equation to determine the energy loss I would greatly appreciate it. Thank you.
 
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If you have the pressure, you can use Bernoulli's equation to calculate the airflow. If you have the temperature of the leaving air, you can multiply that by airflow and the specific heat of air and get energy (power) loss.
 


I agree that you can use Bernoulli's equation but assuming the gas mixture leaving the furnace is dry air seems to me to be an over simplification. The mixture in the furnace is probably closer to a combustion gas comprised of O2, CO2, CO, N2 and water vapor.

You can use Bernoulli and the continuity of mass equation to find the mass flow rate of the combustion gas leaving the hole. The heat loss in the dry flue gases can be determined from q=m-dot*cp*(Tgas-Tair) The properties of nitrogen is frequently assumed for the dry combustion gas.

But the combustion gases are not dry and you must account for vapor formed in the products of combustion so you must account for the change of enthalpy of the superheated steam at the gas exit temperature and the enthalpy of saturated water. This component might be small but you should be aware of it.
 


Good point, but whether you account for the vapors depends on the particulars of the problem. Ie, if the furnace doesn't normally condense the water vapor, then you don't need to account for it in the lost energy.
 


Calorimetry , maybe this will work , how about sticking a beaker of water near the hole and seeing how much the heat raises the temp of the water . just a thought , I’m sure the above responses are better
 


i want to learn how to solve pressure loss and head loss.
 

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