All about Brayton

The thermodynamics behind the functioning of the gas turbines is the Brayton cycle. This cycle consists of four processes which may be closed or open. In a closed cycle, the working fluid is circulated within the system after a complete cycle as in the case of steam turbines. In open cycle, the working fluid enters at the inlet and leaves at the exhaust of the cycle as observed in the cast of turbojets and turbofans. The cycle consists of 2 isobaric (constant pressure) and isentropic (constant entropy) processes. The following processes occur in the gas turbine:

   1. Isentropic compression (1-2)
   2. Isobaric addition of heat (2-3)
   3. Isentropic expansion (3-4)
   4. Isobaric removal of heat (4-1)

Brayton cycle for P-V and T-s diagrams
However, compression and expansion processes do not occur in isentropic manner, increasing the compression ratios is the most effective way to increase the output of Brayton cycle.


This figure shows how the Gas turbine efficiency varies with pressure ratios.


Comments

Post a Comment

Popular posts from this blog

Materials used in Turbine blades

Image
There has been a wide range of materials used for the manufacturing of gas turbine blades. It is one of the most important parts in a gas turbine and any deterioration of it will affect the performance and efficiency of the turbine and most importantly will damage the turbine.  Many materials have been tested and used but the most preferred materials include steel, titanium, Nickel based super alloys and ceramics. The first stage of the compressor is very delicate as it is subjected to a very high temperature of approx. 1400-1500 degree celsius.  This part of the turbine should tolerate high temperatures, high pressures, high thermal stresses including creep and fatigue, vibrations which can influence it's performance. The first stage uses Udimet 500, Nickel based super alloy Inconel 738 or GTD 111.  The relatively cold stages of the turbine employ titanium as there are chances of it igniting when used above 500 degree celsius.      ...
Keep reading

Self Energizing Brakes

Image
The usual drum brakes in our car are provided with a remarkable feature called 'servo' or 'self energizing' feature. It is this feature that is responsible for the smooth and flat application of brakes in automobiles. When the vehicle is moving left, in the forward direction, then the drum will rotate in the anticlockwise direction. When the brake pedal is suddenly pressed, the two brake shoes at the drum will have full contact with the drum. However, one of the brake shoes, the primary brake shoe tends to slip for a certain distance in the drum's direction. Due to this, the primary brake shoe will tend to apply a rearwards force on the secondary brake shoe at the bottom. The wheel cylinder at the top forces the piston against the top of both the brake shoes. Due to this, the secondary brake shoe experiences force on both the sides i.e the top and bottom side.  This ensures that the brakes are applied uniformly and much less effort is applied.
Keep reading

3 spool vs 2 spool

Image
In the Trent 1000, there is 3 spool arrangement of compressors and turbines. This means that there are three sets of compressors and turbines which are connected by three separate shafts. They are the low pressure compressor (LPC) which is the fan and turbine (LPT), Intermediate pressure compressor (IPC) and turbine (IPT) and high pressure compressor (HPC) and turbine (HPT). This is on contrast to the two spool arrangement currently used in many aircrafts where a LPC/LPT and HPC/HPT are used only. All the three shafts are located within each other. The fan positioned at the front of the engine is run by the LPT via a gearbox so that it can operate at optimum speeds. Since the large diameter fan requires a large torque to start rotating, it limits the high speed attained by the LPT due to which its efficiency decreases. Additions of an additional set of compressor and turbine eliminates the influence of this problem but does not eliminate the problem itself! The problem is elim...
Keep reading