Question: Run-around coil heat recovery systems

In summary, The conversation discusses a problem with a gas-fired furnace and a run-around coil system. The question is how to calculate the required mass flow rate of the second fluid. The solution involves using the density of the air and fuel, as well as the air-fuel ratio, to determine the mass flow rate of the fuel and air entering and exiting the furnace.
  • #1
Lord Dark
121
0
hey guys ,, how are you all ??

guys , I've got the following problem , Air enters a gas-fired furnace at 20deg at a mass flow rate of 0.2kg/s and is burned with an air-fuel ratio by folume of 12. the gases leave the furnace at 350deg. A run-around coil system is installed to recover some of the energy of the exhaust gases in order to preheat the air entering the furnace. Calculate :

1- the required mass flow rate of the 2nd fluid.
.
.
.etc .

my problem is i don't know how to get the mass flow of the gas exiting , i have the AFR = 12 in volume , how to use it to get the gas out of the furnace ? they gave me the density of the air and the fuel only not the gas out .. should i get it density too ?
 
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  • #2
The mass rate out is the same as the combined mass flows in of the fuel and air. You know the the density of the air you can work out the volume of air which from the ratio you can work out the volume of fuel. You know the density of the fuel so you can work out the mass flow of the fuel.
 

1. What is a run-around coil heat recovery system?

A run-around coil heat recovery system is a type of heat exchanger that recovers waste heat from one part of a building and transfers it to another part of the building. It uses a network of coils and a heat transfer fluid to exchange heat between the exhaust air and the fresh air supply, reducing the overall energy consumption of the building.

2. How does a run-around coil heat recovery system work?

A run-around coil heat recovery system works by circulating a heat transfer fluid, such as water or glycol, through a network of coils. The exhaust air from the building passes over one set of coils, transferring its heat to the fluid. The fluid then circulates to another set of coils where it transfers the heat to the fresh air supply, warming it before it enters the building.

3. What are the benefits of using a run-around coil heat recovery system?

The main benefit of using a run-around coil heat recovery system is energy efficiency. By recovering waste heat from the exhaust air, the system reduces the amount of energy needed to heat the fresh air supply. This results in lower heating costs and a more sustainable building. Additionally, the system can also improve indoor air quality by ensuring a constant supply of fresh, filtered air.

4. Are run-around coil heat recovery systems suitable for all types of buildings?

While run-around coil heat recovery systems can be used in a variety of buildings, they are most commonly used in commercial or industrial buildings with high heating demands. They can also be used in residential buildings, but may be more expensive to install and maintain compared to other heat recovery systems.

5. What are some potential drawbacks of using a run-around coil heat recovery system?

One potential drawback of using a run-around coil heat recovery system is the initial cost of installation, which can be higher compared to other heat recovery systems. Additionally, maintenance and repairs may also be more complex and costly due to the use of a heat transfer fluid. It is also important to properly size and design the system to ensure optimal performance and efficiency.

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