Modeling and Simulation of Solar Chimney Power …...Modeling and Simulation of Solar Chimney Power Plant for Electrification: Dire Dawa 1Bisrat Yetimgeta, 2Dr. Nigussie Mulugeta 1M.Sc

Modeling and Simulation of Solar Chimney Power Plant for

Electrification: Dire Dawa

1Bisrat Yetimgeta,

2Dr. Nigussie Mulugeta

1M.Sc

Student, School of Mechanical and Industrial Engineering Bahir Dar University, Ethiopia,

2Assistant Professor, School of Mechanical and Industrial Engineering, Bahir Dar University, Ethiopia.

ABSTRACT

A 'solar chimney' sometimes called solar updraft tower power plant or just ‘solar tower’ is a simple

solar thermal power plant that is capable of converting solar energy into thermal energy in the solar

collector. In the second stage, the generated thermal energy is converted into kinetic energy in the

chimney and ultimately into electric energy using a combination of a wind turbine and a generator.

Solar chimneys are very suitable for use in remote communities wherever there is high solar energy as

a power source for both residential and industrial use, based on reliability, cost, and operational

factors. They can provide a suitable energy source in many remote areas of Ethiopia.

The purpose of this study is to conduct a more detailed numerical analysis of a solar chimney power

plant. A mathematical model based on the Navier Stokes, continuity and energy equations was

developed to describe the solar chimney power plant mechanism. Two different numerical simulations

were performed. The first one is transient simulation for the geometry of the prototype in Manzanares,

Spain under Dire Dawa climate condition. This simulation include the effect of thermal storage thank

on the power output of the plant. Thermal storage system increases the power output by re-shaping the

profile of the power output. The most commonly recommended method for creating energy storage is

to place extra thermal mass under the collector in the form of black containers of water. And the

second part of the simulation is done to show the effect of varies plant parameters such as chimney

diameter, chimney angle, collector height and collector angle under steady state condition for small

scale solar chimney power plant. The numerical simulation was performed using the CFD software

FLUENT that can simulate a two-dimensional ax symmetric model of a solar chimney power plant

with the standard k-epsilon turbulence model and Discrete ordinates irradiation model. The

temperature, velocity and static pressure distributions of the plant are illustrated for all geometry

configurations.

Keywords: Solar Chimney, Chimney Angle, Collector Angle.

I. INTRODUCTION

Current electricity production from fossil fuels like natural gas, oil or coal is damaging to the

enviroment and bares the limitation that it relies upon-renewable energy source. Many developing

countries cannot afford these convectional energy sources, and in some of these locations nuclear

power is considered unacceptable risk. It has been shown that a lack of energy may be connected to

poverty and poverty to population explosions. The need for an enviromentally friendly and cost

effective electricity generation scheme is thus obvious and will become more pronounced in the future.

“13 Months of Sunshine” is the slogan of the Ethiopian Tourism Commission. The slogan refers to the

International Journal of Research in Mechanical Engineering

Volume-2, Issue-1, January-February, 2014, pp. 01-14, © IASTER 2014

www.iaster.com, ISSN Online:2347-5188 Print: 2347-8772


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Ethiopian calendar and with this to the unique Ethiopian culture. And it also gives a first hint on the

potentials for renewable energy sources in this country.

The present situation of energy use in Ethiopia differs fundamentally from the situation in

industrialized countries. In Ethiopia still approximately 70-80% of the primary energy shares are taken

from biomass. But the biomass, basically wood which is processed to charcoal, is neither cultivated in

a sustainable way nor is it used efficiently. Deforestation and with it soil erosion, loose of farm yield

potential and desertification are the consequences. And up till now the gap between biomass demand

and supply is increasing constantly. About 80-90% of the electric power is generated from

hydropower, but only about 7-20% of the 80 million Ethiopians have access to electricity [1].

In 2006, the energy consumption per capita was assessed on about 32.94 kWh, which is extremely low

compared to most other countries in the world [1]. Just like in most other countries in the world, the total

energy consumption in Ethiopia is increasing. The annual rate of growth for the use of electric energy

amounts up to 10 %. It is planned to expand the national grid and with it to increase the share of the people

who have access to electricity. But the goal to offer electricity to all Ethiopians is still very far away.

Solar energy is viewed as the clean and renewable source of energy for the future. Energy from the sun

offers probably the best potential for a decentral insertion in Ethiopia. An assessment study indicated

in 2002, that the average daily solar radiation reaching the ground for Ethiopia as a whole is 5.2

kWh/m2. The strength of the solar radiation in Ethiopia is expected to be the highest category of the

world. Therefore the radiation can qualify to be the sole resource of energy for the country. So sun

energy can bring an important contribution to a sustainable and decentral energy mix for Ethiopia [1].

And solar energy can be developed directly in many methods. In one particular method, solar radiation

hits the absorber surface of a solar thermal collector and the surface warms. The heat energy is carried

away by a fluid (air) flow to the place where the energy is required at the turbine. The solar chimney

power plant, whose modeling is done in this thesis, works in this method [2].

II. LITERATURE OF REVIEW

The prototype solar chimney power plant at Manzanares in Spain (Haaf et al. (1983)) showed that the

solar chimney is a practical technology capable of generating electrical power from the sun. Solar

chimney power plant systems are being considered as feasible options to produce energy in countries

where unexploited desert areas are abundant, like South America, Africa, Asia and Oceania. Haaf et

al. (1983) and Haaf (1984) presented fundamental studies for the Spanish prototype in which the

energy balance, design criteria and cost analyses were discussed, and reported preliminary test results

[3]. Krisst (1983) and Kulunk (1985) demonstrated different types of small-scale solar chimney

devices with power outputs not exceeding 10 W. Its collector had a diameter of 6m and the chimney

was 10m tall. In 1997, a solar chimney thermal power generating demonstration model was built and

modified twice on the campus of the University of Florida, and both theoretical and experimental

investigation on their performances was carried out. A micro-scale model with a chimney of 3.5 cm in

radius and 2m in height on a patch of area of 9 m2 was built by Kulunk in lzmit, Turkey, which

produces an electric power of 0.14W [4]. Pasumarthi and Sherif (1998a, b) and Padki and Sherif



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(1999) developed a mathematical model to study the effects of various environment and geometry

conditions on the heat and flow characteristics and power output of a solar chimney [5].

Lodhi (1999) presented a comprehensive analysis of the chimney effect, power production, efficiency,

and estimated the cost of the solar chimney power plant set up in developing nations [6]. Gannon and

von Backstro¨m (2000) presented a thermodynamic cycle analysis of the solar chimney power plant

for the calculation of limiting performance, efficiency, and the relationship between the main variables

including chimney friction, system, turbine and exit kinetic energy losses [7]. Pastohr et al. (2004)

presented a numerical simulation result in which the energy storage layer was regarded as solid [8].

Liu et al. (2005) carried out a numerical simulation for the MW-graded solar chimney power plant,

presenting the influences of pressure drop across the turbine on thedraft and the power output of the

system [9]. Schlaich et al.(2005) presented a simplified theory, some practical experience results and a

detailed economic analysis of solar chimneys for the design of commercial solar chimney power plant

systems like the one being planned for Australia [10]. Pretorius (2006) reviewed most of the

outstanding issues. Different calculation approaches with a variety of considerations have been applied

to calculate chimney power plant performance [11].

The available work potential that atmospheric air acquires while passing through the collector has

been determined and analyzed by Ninic (2006). In this study, the dependence of the work potential on

the air flowing into the air collector from the heat gained inside the collector, air humidity and

atmospheric pressure as a function of elevation are determined. Various collector types using dry and

humid air have been analyzed. The influence of various chimney heights on the air work potential was

established [12]. Bilgen and Rheault (2006) designed a solar chimney system for power production at

high latitudes and evaluated its performance [13].

Pretorius and Kro¨ger (2006a) evaluated the influence of a developed convective heat transfer

equation, more accurate turbine inlet loss coefficient, quality collector roof glass and various types of

soil on the performance of a large scale solar chimney power plant [14]. Koonsrisuk and Chitsomboon

(2007) proposed dimensionless variables to guide the experimental study of flow in a small-scale solar

chimney. Computational fluid dynamics(CFD) methodology was employed to obtain results that are

used to prove the similarity of the proposed dimensionless variables [15]. Since effect of thermal

storage tank, chimney diameter, chimney angle from the axis, collector angle from the ground doesn’t

included in the above mentioned papers I have tried to address on this specific areas.

III. COMPONENTS OF SOLAR CHIMNEY POWER PLANT.

The three primary components of a solar updraft

tower are the solar collector, the tower or

chimney, and the turbine. The following sections

describe the important components, their role in

the tower, and their materials and construction

Fig 1. Components of Solar Chimney Power Plant



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3.1. Collector

Hot air for the solar updraft tower is produced by the greenhouse effect in a simple air collector consisting

of a glass or polymer membrane stretched nearly horizontally several meters above the ground. The height

of the glazing increases towards the tower base, finally the air is diverted from horizontal into vertical

movement with minimum friction loss. This glazing admits the shortwave solar radiation to penetrate and

retains long wave re-radiation from the heated ground. Thus the ground under the roof heats up and

transfers its heat to the air above flowing radically from the outside to the tower. The collector roof of the

solar updraft tower shall not only be translucent but also durable and reasonably priced. A variety of plastic

membranes, as well as glass, can be used. Glass resisted heavy storms for many years without harm and

proved to be self-cleaning thanks to the occasional rain showers.

3.2. Chimney

The chimney (or tower) of a solar updraft tower is the thermal engine of the plant. The heated air from

the collector is funneled into the chimney, where the buoyancy difference between the heated air and

the surrounding atmosphere creates a pressure difference that drives the air up the chimney. Several

factors contribute to the physical design of the chimney. The chimney should be designed to minimize

the frictional losses and to maximize the pressure difference in the tower. The pressure difference in

the tower is proportional to its height, so maximizing the height of the tower is critical to improving

the efficiency of the tower. The prototype plant at Manzanares was constructed as a framed, guyed

tower, approximately 195 m tall and 10 m in diameter, covered with corrugated sheeting

approximately 1.25 mm thick. The tower was erected without any large equipment; the tower was

hydraulically lifted from below as each 4 m tall segment was placed under the tower and attached to

the existing structure.

3.3. Turbine

The solar thermal updraft tower uses a turbine or array of turbines to generate power. The turbine or

turbines operate as cased pressure-staged generators, similar to a hydroelectric plant. Turbines are

placed near the bottom of the tower, for

ease of access for maintenance and easy

connection to the generating equipment.

A single turbine can be mounted on

vertical axes inside the chimney, while

multiple turbines can be placed either in

the chimney or in the transition area

between the chimney and collector, as

shown in Fig.2

Fig.2. Schematic of a Tower with Horizontally Mounted Turbines

The turbines are subjected to relatively steady airflow compared to those of wind generator plants, and

thus subject to less physical stress. The blades of the turbine feather to adjust to different levels of

airflow and pressure drop. As the only component of the system with moving parts, the turbine’s

reliability is critical.



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IV. NUMERICAL MODELING AND DISCRETISATION

4.1. Collector Inlet Pressure Drop

Due to its acceleration and a loss at the collector inlet the pressure decreases as the air is drawn

towards the collector. And this collector inlet pressure drop and total pressure outside the collector

inlet is Pa.

(1)

Where “i” refers inlet to collector and K is static pressure correction factor. In this case Value of the

loss coefficient is approximately zero for a well-rounded inlet while a value of unit is more

approximate for the case of the sharp edged inlet. Since the inlet pressure drop is smaller than the total

pressure drop any possible error in this approximation will be negligible

4.2.Collector Drag Pressure Drop

There are collector supports for the collector roof above the surface of the ground. These are

positioned as shown in the Figure. 3 on radii with a radial pitch pr and spaced tangentially on these

radii pt apart. And those collector supports produces drag force that causes radial pressure gradient on

the air in the collector and we can find this pressure gradient by consider the force exerted by each

support on the air

(2)

Where V is the local free stream velocity with H is the height of the collector at radius r and m is the

mass flow rate.

(3)

(4)

Fig.3. Schematic Plan View of the Position of the Collector Supports.

The number of supports along the circumference at radius r is given by equation (5) with a tangential

pitch.

(5)

(6)



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This is the force required by the air to move radially inwards through one row of supports. The

resultants corresponding pressure difference required is thus given by

(7)

Where H is given by

(8)

(9)

4.3. Acceleration Pressure Drop

The pressure differential over one control volume

(10)

4.4. Chimney Inlet Pressure Drop

Due to friction and momentum changes between the collector outlet and the turbine inlet there is

pressure drop which is given by:

(11)

Where:

is the turbine inlet loss coefficient.

The loss coefficient is dependent on the geometry of the region of the plant at the inlet to the turbine

and is thus specified in the reference plant specifications.

4.5. . Turbine Pressure Drop

Thus the turbine pressure drop can be found using the relation where p and V are the turbine power

and volume flow respectively. The pressure drop over the turbine is given by

(12)

4.6. . Chimney Appurtenances Drag Pressure Drop

The pressure drop caused by the appurtenances in the chimney approximately given by

(13)

Where is defined relative to the conditions at the turbine inlet. This coefficient is also dependent on

the geometry of the system and is specified in the reference plant specifications.

4.7. Chimney Friction Pressure Drop

The approximate pressure drop due to the frictional drag in the chimney is given by

(14)

Haaland’s equation for fully developed turbulent flow with small the Darcy friction facture is best

suited to i.e. [5].



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(15)

4.8. Acceleration Pressure Drop in the Chimney

The approximate differential caused by the momentum changes in the chimney is given by

(16)

4.9. Chimney Exit Pressure Change (Recovery)

The change in pressure of the air leaving the chimney and ambient pressure at the chimney exit height

is

(17)

Where is the chimney outlet pressure less coefficient and given by

(18)

The densimetric Froude number given by

(19)

Where refers to the ambient states at the height of the chimney outlet. And the densities at this height

outside and inside respectively of the chimney is given by

(20)

(21)

And also the kinetic energy loss at the exit of the chimney is

(22)

Where is the kinetic energy correlation factor, Du preez and Kroger find that for 1/ at the exits of dry

cooling towers is equal to unity. Since the exit of the chimney may be approximated as dry cooling

tower exit and is approximately two, the kinetic energy correction factor is taken as unity.

4.10. The Maximum Power Obtained From the Air Flow at the Turbine

The turbine extracts the energy in the air flowing through the chimney. The maximum limit to wind

turbine performance was determined by Albert Betz. This is derived by looking at the axial

momentum of the air passing through the wind turbine. The air is deflected away from the turbine.

This causes the air passing through the rotor plane to have a smaller velocity than the free stream

velocity. The degree at which air at the turbine is less than the air far away from the turbine is called

the axial induction factor, a. It is defined as follows:

(23)

a is the axial induction factor.

is the wind speed far away from the rotor.

is the wind speed at the rotor.



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The first step to deriving the Betz limit is applying conservation of axial momentum. As stated above,

far away from the turbine, the wind loses speed after the wind turbine. This would violate the

conservation of momentum if the wind turbine was not applying a thrust force on the flow. This thrust

force manifests itself through the pressure drop across the rotor. The front operates at high pressure

while the back operates at low pressure. The pressure difference from the front to back causes the

thrust force. The momentum lost in the turbine is balanced by the thrust force.

The maximum power obtained from the air flow at the turbine is.

(24)

Where is air density, A is turbine swept area and v is air velocity at turbine entrance. Equation (24)

yields the power in a free flowing stream of air. The electrical power obtained has to be multiplied by

the efficiency of the generator, which is usually between 0.75 and 0.90.

V. MODEL SIMULATION PROGRAM AND FLOW GOVERNING EQUATIONS

In this paper FLUENT is a state-of-the-art computer program for modeling simulation flow and heat

transfer for solar chimney power plant.

Fluent offers complete mesh flexibility,

including the capability to solve flow

problems using unstructured meshes that

can be created about complex geometries

with relative ease. All functions required

to compute a solution and display the

results are available in FLUENT through

an interactive, menu-driven interface.

FLUENT package includes different

products and the organizational structure

of these components are shown in Fig. 4.

Fig. 4. Basic Program Structure

The FLUENT solver has the following modeling capabilities

Two dimensional planar, Two dimensional axisymmetric, Two dimensional axis-symmetric with swirl

(rotationally symmetric), and three dimensional flows. Different mesh elements such as Quadrilateral,

triangular, hexahedral (brick), tetrahedral, prism (wedge), pyramid, and mixed element meshes with

dynamic mesh model for modeling domains with moving and deforming mesh. Steady-state or

transient (time dependent) flows. Incompressible or compressible flows, Newtonian or non-Newtonian

flows and laminar or turbulent flows. Heat transfer, together with forced convection, natural

convection, and mixed convection, conjugate (solid/fluid) heat transfer, and radiation. Chemical

species mixing and chemical species reaction. Homogeneous and heterogeneous combustion models

and surface deposition/reaction models. Stationary (inertial) or rotating or accelerating (non-inertial)

reference frames. Free surface or multiphase models for liquid-solid, gas-solid, and gas-liquid flows.

Models for fans, pumps, radiators, and heat exchangers (Lumped parameter). Predicting flow-induced



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noise using Acoustic models. Modeling multiple moving frames with Multiple reference frame and

sliding mesh options. Cavitations model and Phase change model for melting/solidification

applications. Volumetric sources of momentum, mass, heat, and chemical species. Material property

database with Extensive customization capability via user-defined functions. Magneto-hydro-

dynamics module, Continuous fiber module, Fuel cells modules (documented separately) and others

VI. RESULT AND DISCUSSION The main purpose this section is to see the energy storing effect of the ground and compare the power

output of the plants. The power outputs obtained are plotted on Fig. 5 According to equation (24)

The unsteady solution for the solar chimney without thermal energy storage system gave an average

power of about 14.27 kW for the data provided at Dire Dawa. Figure 5 show that solar radiation is

zero starting from the 19th hour, but the velocity and so the power has values greater than zero. This is

an indication of the fact that the ground stores energy during day time (maximum solar radiation) and

releases it during night (minimum solar radiation).

Fig.5. Power output variation for both Solar Chimneys with and without thermal energy storage system

But as we can see from the Fig.5. the power output drop very rapidly if there is no solar radiation as

there is no thermal storage system except the soil (which have lease thermal storage effect). Energy

storage in the collector has been discovered as a method for re-shaping the power output profile of a

solar updraft tower. As shown in Fig.5. the extra thermal mass evens out the power output profile. And

it also improves the average power output to 27.7kw. At night, when the air in the collector starts to

cool down, the water inside the tubes releases the heat that it stored during the day to the air under the

collector. Heat storing using water works more efficiently than with soil alone. The heat transfer

between water tubes and water is much higher than that between ground surface and the soil layers

underneath this is because the heat capacity of water is about five times higher than that of soil.

6.1. Effect of Varying Chimney Parameters under steady state condition

In different journals the effects of collector diameter chimney height and solar irradiation on power

output of the plant is presented. And since the effect collector height from the ground, collector angle

from the ground, chimney diameter and chimney angle from the axis did not included in the work this

section of the paper try’s to see the effects of such parameter on the power production of plant.



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Table 1. Different Configuration of Solar Chimney Power Plant Geometry

Chimney

diameter Collector

angle Collector height Chimney angle

To see the effect of

chimney diameter 0.2, 0.5, 1 and

1.5 0° 0.15m 0°


collector angle 1m

0°, 1°, 2.5°

5° and 7.5° 0.15m 0°


collector height 1m 0°

0.07, 0.11, 0.13

0.15, 0.2, 0.25, 3,

0.35, 4 and 0.45m 0°


chimney angle 1m 0° 0.15m

0°, 1°, 2.5° and

5°

6.2. Effect of varying chimney diameter

This section is to show the effect of chimney diameter on air generation performance. The reference

chimney diameter is set is 1m. The results were obtained for four different chimney diameters (0.2,

0.5, 1 and 1.5). The analys is shows that the chimney diameter has significant effect on the plant

performance.

Fig. 6. Effect of Chimney Diameter on Chimney Inlet Temperature, Static Chimney Inlet Pressure,

Velocity and Power Output

Generally from fig. 6 as the chimney diameter increased the temperature of the chimney inlet

(collector outlet) decreases and the velocity at the outlet and inlet of the chimney gets decreases.

Ideally as the chimney diameter approaches zero the inlet and outlet temperature of the chimney as

well as the velocity at the inlet and outlet of the chimney also increases which is practically not

applicable. So an optimum diameter of the chimney will depend upon other parameters. The static



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pressure at the inlet of the chimney rises as the chimney diameter increases which an indication for

lower pressure difference between the ambient and chimney inlet so velocity decreases.

According to equation (24) and fig. 6 d even though the velocity decreases due to increases chimney

diameter the power available at the chimney inlet and also at the exit increases. This is because the

area available is also increases together with the diameter. And since chimney exit velocity is greater

than inlet velocity for all diameters used, the power available at the chimney exit is greater than the

power available at the chimney inlet.

6.3. Effect of Variation of Angle of the Collector from the Ground Surface

In fact, the main aim of this section is to show the effect of Different collector orientations on air

generation performance. The reference of the collector setting is the normal parallel orientation; i.e.,

(θ = 0°). The results were obtained at five different collector setting with slope angles of θ = 0°, 1°,

2.5°, 5° and 7.5°. The analysis of this part has shown that the canopy slope has considerable effect on

the collector performance.

Fig. 7. Temperature, Pressure, Velocity And Power Variation for different collecter angle



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As the collector angle from the ground first increases the temperature at the outlet of the collector

(ground surface) gets decreases after which it begins to rise and reach maximum when the angle is

between 1.5° to 2.5°but the temperature at the out let of the collector (top surface) stays constant even

thought the collector angle increases. And the temperature of the chimney inlet at the axis gets reduced

continuously. The velocity gets reduced whereas the static pressure inside collector angle from the

ground increases.

Larger inclination of the collector more than 2.5° produces negative effect on power output for all

turbine position. And also larger inclination is not practical where constructional problem will

associated. If the inlet of the collector is kept at its normal height and the inner part is raised up, the

construction requires stronger and more expensive structure. If the collector is kept to its normal

height at the inner radius and lowered at the inlet, it’s either hit the ground or the inlet area becomes

small leading to possibility of blockage. Generally the variation of the power output due to alteration

of the canopy (collector) slopes summarized by figure 5.13f with three different turbine positions.

6.4. Effect of Variation of Collector Height from the Ground

Fig. 8. Tempreture, Pressure, Velocity And Power Variation due to collector height from the ground.



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Under this section the effect of Different collector height from the ground on power generation

performance is studied. The reference of the collector height is 0.15m. The results were obtained for

10 different collectors setting with height of 0.07, 0.11, 0.13, 0.15, 0.2, 0.25, 3, 0.35, 4 and 0.45.

From fig. 8 when collector height from the ground increased the temperature at the chimney inlet and

outlet gets reduced. The velocity at the inlet and outlet of the chimney first increases till it gets

maximum between 0.1m and 0.15m and progressively reduced for the next increase in the height of

the collector from the ground which is an indication for the point of operation of the tower with the

given parameters to have a better performance. The static pressure will gets increased continuously as

the gap between the ground and collector increases since it allows the free ambient air movement.

6.5. Effect of Variation of Chimney Angle from the Vertical Axis

Fig. 9. Temperature and Power Variation for Different Chimney Angle Arregement

From fig.9 As the chimney angle from the vertical axis increases the outlet temperature of the collector

first drops slightly then gets increased till it reach optimum between the angle 1.5° to 3° and then after

does not show a significant change. The change in chimney angle has positive effect on the power

output if we are mounting the turbine at the exit but it have negative effect for the turbine mounted the

inlet or in the middle.

VII. CONCLUSION

The unsteady solution for the Manson areas solar chimney without thermal energy storage system

gave an average power output about 14.27 kW/day using Dire Dawa climate condition. But the power

output drop very rapidly if there is no solar radiation as there is no thermal storage system except the

soil. Energy storage in the collector has been discovered as a method for re-shaping the power output

profile of a solar chimney. And it also improves the average power output to 27.7kw/day with 20 cm

diameter tube and 20 cm space b/n them.

And generally for the steady state small scale simulation we can conclude that the static chimney inlet

temperature is greater than exit temperatures and increases along the chimney height. The static

pressure increase with the increase of the chimney diameter and the minimum values lie in the bottom

of the chimney, which an indication for lower pressure difference between the ambient and chimney

inlet so velocity decreases. And also the relative static pressure increases along the chimney height.

Even though the velocity decreases due to increases in chimney diameter the power available at the

chimney inlet and also at the exit increases. Larger inclination of the collector more than 2.5° produces

negative effect on power output for all turbine position. And also larger inclination is not practical

where constructional problem will associated.



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Increasing collector height has positive effect on the power output for turbine positions at the outlet

and at the middle but this doesn’t work for height greater than 0.15m. Therefore one should check the

optimum height of the collector for the designed power plant. As the chimney angle from the vertical

axis increases the velocity at the chimney inlet decreases continuously whereas the velocity at the

chimney outlet increases and the static pressure increases first till it gets optimum in between angles 20

to 30 and after which gets reduced slightly for the increasing in chimney angle. Increase chimney angle

has positive effect on the power output if we are mounting the turbine at the exit but it have negative

effect for the turbine mounted the inlet or at the middle.

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