How mass flow and pressure ratio is related in case of a Gas Turbine

In summary, when the inlet air is cooled by evaporative cooler, the pressure ratio across the gas turbine compressor increases.
  • #1
Ady707
3
0
Hi,

As per my observation and experience, when we use evaporative cooler to cool the inlet air to the gas turbine, the compressor discharge pressure (i.e PCD or P3) rises. As, the temp. of the inlet air drops and the mass flow increases due to the increase in density, I believe the discharge pressure of the compressor also rises.

However, as per the performance characteristic curve of the compressor, the pressure ratio is inversely proportional to the mass flow.

Can please someone help me understand this
 
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  • #2
Yes,your relation is absolutely right.
The conservation of mass (continuity) tells us that the mass flow rate mdot through a tube is a constant and equal to the product of the density r, velocity V, and flow area A:

Eq #1:

mdot = r * V * A
 
  • #3
John Dalton said:
Yes,your relation is absolutely right.
The conservation of mass (continuity) tells us that the mass flow rate mdot through a tube is a constant and equal to the product of the density r, velocity V, and flow area A:

Eq #1:

mdot = r * V * A
I am interested in knowing that when the mass flow across the compressor rises what happen to the pressure ratio ?
 
  • #4
Ady707 said:
Hi,

As per my observation and experience, when we use evaporative cooler to cool the inlet air to the gas turbine, the compressor discharge pressure (i.e PCD or P3) rises. As, the temp. of the inlet air drops and the mass flow increases due to the increase in density, I believe the discharge pressure of the compressor also rises.

However, as per the performance characteristic curve of the compressor, the pressure ratio is inversely proportional to the mass flow.

Can please someone help me understand this
Could you provide a bit more context ? You seem to know what you are describing, but we see only loose fragments.
 
  • #5
If you provide more information and facts about your query,I am sure I will be able to help you out.
(By giving mathematical evidences).
 
  • #6
BvU said:
Could you provide a bit more context ? You seem to know what you are describing, but we see only loose fragments.
It is a land based application of an aeroderivative gas turbine (twin shaft). Gas turbine is driving a centrifugal compressor to compress a natural gas to a certain pressure. We have installed an evaporative cooler to cool the inlet air to the gas turbine. Now, as the inlet air is cooled down, the air got dry, and the density of the air increases and so is the mass flow. As this happens, I observe that the pressure ratio across the integral compressor (gas generator) of the gas turbine increases. I want to understand why this is so that pressure ratio increases with the increase in mass flow ?

I hope I am pretty clear this time. :)

Thanks.
 

1. How does the mass flow affect the pressure ratio in a gas turbine?

The mass flow through a gas turbine is directly related to the pressure ratio. As the mass flow increases, the pressure ratio also increases. This is because a higher mass flow rate means that more air is entering the turbine, which increases the pressure of the air in the compressor. This higher pressure air then enters the turbine and results in a higher pressure ratio.

2. What is the ideal mass flow and pressure ratio for a gas turbine?

The ideal mass flow and pressure ratio for a gas turbine will depend on the specific design and operating conditions of the turbine. However, typically, a higher mass flow rate and pressure ratio will result in a more efficient and powerful turbine. The specific ideal values will vary for different turbines and can be determined through calculations and simulations.

3. How is the mass flow and pressure ratio controlled in a gas turbine?

The mass flow and pressure ratio in a gas turbine can be controlled through various methods. One common method is through adjusting the angle of the compressor blades, which can affect the amount of air being compressed and the resulting pressure ratio. Other methods include adjusting the fuel flow rate and controlling the variable geometry of the turbine.

4. What happens to the mass flow and pressure ratio in a gas turbine during different operating conditions?

The mass flow and pressure ratio in a gas turbine will vary depending on the operating conditions. For example, during start-up, the mass flow rate and pressure ratio will typically be lower as the turbine is not yet operating at full capacity. During peak load conditions, the mass flow and pressure ratio will be higher to meet the increased power demands. Additionally, changes in ambient temperature and altitude can also affect the mass flow and pressure ratio in a gas turbine.

5. How do changes in the gas turbine design impact the mass flow and pressure ratio relationship?

The design of a gas turbine, specifically the compressor and turbine stages, can greatly impact the mass flow and pressure ratio relationship. A more efficient and advanced design can result in a higher mass flow rate and pressure ratio, leading to a more powerful and efficient turbine. Changes in design may also affect other factors such as temperature and efficiency, which can also impact the mass flow and pressure ratio relationship.

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