optimum configuration of cooling tower overhead wind ... · pdf fileobtaining the...

ADVANCES in NATURAL and APPLIED SCIENCES

ISSN: 1995-0772 Published BYAENSI Publication EISSN: 1998-1090 http://www.aensiweb.com/ANAS

2017 March 11(3): pages 54-63 Open Access Journal

ToCite ThisArticle: Ass. Prof. Dr. Mohammed I. Mohsin, Ass. Prof. Dr. Zainab H. Naji, Ali A.A. Abaas., Optimum Advances in Natural and Applied .Overhead Wind Turbine for an Energy Recovery System –Configuration of Cooling Tower

63-54);Pages: 3(11. Sciences

Optimum Configuration of Cooling Tower – Overhead Wind Turbine for an Energy Recovery System

1Ass. Prof. Dr. Mohammed I. Mohsin, 2Ass. Prof. Dr. Zainab H. Naji, 3Ali A.A. Abaas

1,2University of Technology in Baghdad, Mechanical Engineering Department, 3graduate student

Received 18 January 2017; Accepted 22 February 2017; Available online 26 March 2017

Address For Correspondence: Maruthamuthu Ramasamy, Assistant professor, Department of Computer Science &Engineering, RVS College of Engineering, Dindigul-624005, Tamilnadu,India.

Copyright © 2017 by authors and American-Eurasian Network for Scientific Information (AENSI Publication). This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/

ABSTRACT In this paper, the utility of an energy recovery wind turbine system has been investigated. Two vertical axis wind turbines (VAWTs) assembled with an enclosure were positioned above a full-scale cooling tower to use the exhaust air for electricity generation. The enclosure comprised of diffuser plate which draw more air to accelerate the flow. In addition, the enclosure design with guide vanes mounted upstream of the wind turbine to guide the air before it interacts with the turbine blades. Laboratory tests had been carried out to investigate two important parameters, namely, the rotor weight and vertical position of the WT in order to determine the maximum possible recovered power from the system. The net output power of heavy WT rotor was increased by about 36.7% over the light WT rotor for the same angle of attack and guide vanes, while the recovered energy was increased by 17.7Wwhen the heavy WT rotor was closer to the cooling tower fan and this increase was reduced to 10.1W for light WT rotor. The recovery energy from this wind generation system may be utilized for commercial as well as domestic purposes.

KEYWORDS: wind turbine, rotor, cooling tower, energy recovery system.

INTRODUCTION

Cooling towers are heat reject equipment ultimate to transfer waste heat to the atmosphere; large office

buildings, hospitals and schools typically install one or more cooling towers for building air-conditioning

system. Generally, cooling tower relies on power-driven fans to draw or force the air through the tower. The

recovering of part of the energy from the cooling- tower exhaust air by mounting a suitable type of wind

turbine, may be implemented under the energy recovery systems categorization.

Tong, et al. [1,2] mounted a vertical axis wind turbine (VAWT) with an enclosure in cross-wind orientation

above a cooling tower exhaust fan to harness the wind energy for producing electricity. The effects of VAWT

on the cooling tower air intake speed and its performance was calculated. The effects of VAWT on the current

consumption of the power-driven fan were also investigated. The enclosure design added to guide the wind

before the wind-stream interacts with the wind turbine blades and create a venturi effect (to increase the wind

speed). A scaled model (5-bladed H-rotor with 0.3m rotor diameter) was conducted in laboratory test which

showed no measurable difference in the air intake speed (1.6~1.8 m/s) and current consumption of the power-

driven fan do not effect in wind turbine. Kim, et al [3] used a blower for generating wind energy by studying a

simple wind tunnel, which was equivalent to natural wind. To analyze the relationship between the mechanical

and electrical power, the mechanical and electrical power in a small-scaled wind turbine were empirically

63-54, Pages: 7201 March) 3(11. Advances in Natural and Applied Sciences/7201 .,et al Ass. Prof. Dr. Mohammed I. Mohsin 55

measured. The data analyzed using the empirically obtained mechanical and electrical power will contribute to

obtaining the specification of a wind turbine generator, which produces the maximum power.

Mohammed [4] made a comparison between two and three blades Savonius wind turbine. Two models of

two and three blades were designed and fabricated from Aluminum sheet, each of them had an aspect ratio of

(H/D =1), the dimension was ( H = 200 mm height and diameter D = 200 mm) and the blades were made of

semi – cylindrical half of diameter (d = 100 mm). These two models were tested and investigated by using a

subsonic wind tunnel. It was observed from the measured and calculated results that the two blades savonius

wind turbine was more efficient, it had higher power coefficient under the same test condition than that of three

blades savonius wind turbine. The reason was that increasing the number of blades led to increase the drag

surfaces against the wind air flow and caused to increase the reverse torque and leads to decrease the net torque

working on the blades of savonius wind turbine. Qasim. et all [5] designed the rotor wind turbine, which used

more effectively for the wind energy and depended on the acting area of the vanes. The frame design consisted

of three movable vanes to reduce the negative torque of the frame that rotates contrary to the wind. The wind

tunnel was used to measure the power coefficient, torque coefficient and angular velocity as a function of wind

velocity. The power coefficient was measured experimentally to be equals to 18% and 21% for three and four

frames, respectively. The rotor wind turbine was applicable internationally due to its high efficiency, simple

construction, and simple technology.

Akhgari [6] studied the performance of a vertical axis wind turbine with and without a diffuser. Direct

measurement force was applied to a scaled model of the rotor in a water tunnel. The experiment was conducted

at different tip-speed ratios. The turbine rotor with diffuser had maximum power coefficient of 0.35 and 0.26

without diffuser. When the diffuser was used in the configuration. The maximum power coefficient was

increased by 35%. The particle image velocimetry (PIV) technique was used to study the flow patterns

downstream of the turbine.

Each configuration (with and without a diffuser) considered six different tip-speed ratios. The flow physics

in each configuration was showed into the vorticity and the streamline plots.

Abdulrazek [7] constructed small wind turbine model with variable speed and pitch control in order to

investigate the effect of this control strategy on wind turbines by characterizing its design and output power.

Specifications and functions in addition to description of the Lab View program mentioned small wind turbine

model components. The output voltages and currents from the generator were measured at different wind

speeds.

B. Roscher [8] optimized the structural design of a VAWT rotor blade and to decrease the mass to area ratio

by varying blade shape and structural layout. The choice of mass to rotor area ratio as an optimization function

followed from the fact that this area was directly proportional to the energy output while mass drove production

and installation costs.

Hwang [9] described the performance improvement of the straight-bladed vertical axis wind turbine. To

improve the performance of the power generation system, which consisted of several blades rotating about axis

in parallel direction, the cycloidal blade system and the individual active blade control system were adopted,

respectively. Both methods were variable pitch system. For cycloidal wind turbine, aerodynamic analysis was

carried out by changing pitch angle and phase angle based on the cycloidal motion according to the change of

wind speed and wind direction, and control mechanism using the cycloidal blade system was realized for 1kw

class wind turbine. By this method, electrical power was generated about 30% higher than wind turbine using

fixed pitch angle method.

In the present research, a simple energy recovery system consisting of full scale cooling tower, vertical axis

wind turbine, and diffuser is designed, constructed and tested in order to determine the optimum configuration

of cooling tower-overhead wind turbine combination. The interest is focused on the effect of rotor weight and

turbine vertical position relative to cooling tower exhaust fan on the mechanical output power and recovered

power.

Test Procedure:

A special configuration has to be designed in order to harness the maximum amount of energy from the

cooling tower exhaust air. This configuration consist of a cooling tower which represent the unnatural wind

resource, and two vertical axis wind turbines installed in cross-air orientation at the exit of cooling tower, as

shown in Fig(1).


Fig. 1a: Schematic of the two vertical axis wind turbines over the cooling tower fan

Test Rig Design:

A set of two vertical axis wind turbines (VAWT) was designed and fabricated at the power laboratory

(Mechanical Engineering Department – UOT), as shown in figure (1b).

Fig. 1b: cooling tower with vertical axis wind turbine system

Each turbine consists of 5-blades with H-rotor of 245mm diameter. The profile of each blade airfoil is

(MH114 13.02%) made from wood by CNC machine. The blade dimensions are 60mm cord, 9mm thickness

and a span of 350mm. The blades angle of attack can be adjusted to be 6 deg. or 12 deg. The turbines were

placed at a predefined position in cross-wind orientation facing the discharged wind from the cooling tower fan.

The VAWT were in a symmetrical order with the vertical distance between the discharge outlet ducts to the

center of the turbine at 260 mm as shown in Fig (2).


Fig. 2: Schematic of wind turbine and diffuser

The horizontal distance between the center of the outlet duct to the center of turbine is set to be 230 mm. A

diffuser with four adjustable guide vanes was mounted upstream of the wind turbines as shown in Fig (2)

The optimum angle of the guide vans, б will be specified according to angle of attack, α as shown in the

velocity triangle, a represent the axial induction factor Fig (3). The angle of attack is calculated by: [1]

∝= tan−1 ((1−𝑎)𝑉 sin 𝜃

𝑈+(1−𝑎)𝑉 cos𝜃) (1)

With θ= б- ψ (2)

Ψ is the angle between U and horizontal axis which determined by blade position angle.

Fig. 3: Velocity triangle for the turbine blade and wind stream


During the tests two geometrically similar sets of turbine rotors were used, they are only differ in their

masses. The heavy rotor set is named (rotor1), while the lighter rotor set is named (rotor2).

Turbines Position adjusting mechanism:

The vertical position of the wind turbine rotor relative to cooling tower exhaust fan plane can be adjusted

from the two rotor shaft bearings by means of sliding mechanism designed especially for this purpose.

Cooling tower:

An induced cooling tower (made by SINYU Company) was used in the present test as unnatural wind

resource for the wind turbine figure (4). The technical specifications of cooling tower are given in table (1).

Table 1: Cooling tower specifications

tower height (mm) 1120

tower outlet diameter (mm) 760

Air flow rate (m3/min) 85

Fan tip diameter (mm) 680

Circulating water flowrate (m3/h) 1.8-2.1

Fan rotational speed (RPM) 960

Rated fan motor power (w) 222.6

Fig. 4: Cooling tower

Measurement and Instrumentation:

The parameters have to be measured through experimental tests are; wind velocity, turbine rotation speed,

turbine output torque and cooling tower fan power consumption. To achieve these measurements, the following

instruments are required:

1. Anemometer

2. AVO meter

3. Tachometer

4. Torque meter

The anemometer (Type: VICTOR 816) was used to measure wind velocity at outlet cooling tower fan. The

power consumption of the fan motor of cooling tower was specified by measuring the current and voltage for

motor by AVO meter (type: VC3266L).

To measure the mechanical output power from wind turbine the speed of rotation and torque were measured

by tachometer type Lutron DT-2236 and pulley and rope torque meter.

Methodology:

The position of the wind turbines over the cooling tower fan (figure1) is mainly dependent on the wind

velocity profile at the fan outlet. An appropriate measurement method which was developed by Cooling Tower

Institute (CTI) [1] was adopted in the present work. Divide the duct area into a few concentric parts of equal

region. The outlet wind speed V was measured at 5 positions taken at each interval around the circle. The

average wind velocity at the outlet of the cooling tower was 5.3 m/s.


Figure (7) shows the measured velocity profile of cooling tower exhaust air. Two peaks are appearing at the

left and right hands sides of the velocity profiles. These peaks are coincident within the two WT rotors.

Fig. 7: Velocity profile of cooling tower exhaust air

The WT output power and the net recovered power at given cooling tower fan speed are dependent on many

interconnected parameters, namely vertical distance between the cooling tower fan and WT, WT rotor design

mass, air angle of attack and guide angles. Eight cases were considered during the experimental tests to cover

all mentioned parameters. Table (2) shows these cases.

Table 2: Experimental test cases

Case Rotor No. Angle of attack (deg) Guide vane A (deg) Guide van B (deg)

1 1 6 30 120 2 1 12 30 120 3 2 6 30 120 4 2 12 30 120 5 1 6 30 90 6 1 12 30 90 7 2 6 30 90 8 2 12 30 90

RESULTS AND DISCUSSION

Figures (8) and (9) show the effect of vertical position of the WT on cooling tower fan input power for rotor

(1) and rotor (2) at different angles of attack and guide vanes angles. Generally, the cooling tower fan power

consumptions are increased when the WT is closer to the fan. This may be due to blockage effect. The

percentage increase of power consumptions varies from (4.1%) to (10%) depending on the test case parameters.

The effect of vertical position of WT relative to cooling tower fan on the WT output power and net output

power is shown in figures (10) to (13). The net output represents the net recovered power developed by the

system. For all cases, the heavy WT rotor (1) develops higher power than the light WT rotor (2), and the net

output power of WT rotor (1) is increased by about 36.7% than WT rotor (2) for the same angle of attack and

same guide vane A&B. Certainly, the moment of inertia effect is pronounced and should be considered when

selecting the suitable WT rotor. Also, the recovery power is increased by 17.7W when the WT rotor (1) is

closer to the cooling tower fan for the same angle of attack and same guide vane A&B. This gain is reduced to

10.1W for WT rotor (2). The effect of air angle of attack is more pronounced as shown in figures (10) to (13).

More power developed at angle of attack α=120


Fig. 8: Effect of vertical position of WT on fan input power for rotor masses (1) & (2) at different angles of

attack (A= 300 and B=1200)

Fig. 9: Effect of vertical position of WT on fan input power for rotor masses (1) & (2) at different angles of

attack (A= 300 and B=900)

220.00

225.00

230.00

235.00

240.00

245.00

250 260 270 280 290 300 310

fan

inp

ut

po

wer

(wat

t(

WT position (mm)

cooling tower without WT α = 12 deg rotor (1)

α = 12 deg rotor (2) α = 6 deg rotor (1)

α = 6 deg rotor (2)

220.00

225.00

230.00

235.00

240.00

245.00

255 260 265 270 275 280 285 290 295 300 305

fan

inp

ut

po

wer

(w

att(

WT position (mm)

cooling tower without WT α = 12 deg rotor (1)

α = 12 deg rotor (2) α = 6 deg rotor (1)

α = 6 deg rotor (2)


Fig. 10: Effect of vertical position of WT on output power (α=120, A=300 & B=1200)



10.00

20.00

30.00

40.00

50.00

60.00

250 260 270 280 290 300 310

po

wer

(w

att)

WT position (mm)

WT output power rotor (1) net output power rotor (1)

WToutput power rotor (2) net output power rotor (2)

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

255 260 265 270 275 280 285 290 295 300 305

po

wer

(w

att)

WT position (mm)



0.00

10.00

20.00

30.00

40.00

50.00

60.00

250 260 270 280 290 300 310

po

wer

(w

att)

WT position (mm)


WToutput power rotor (2) net output power rotor (2)



Finally, figure (14) shows the recovered power as percentage relative to the cooling tower fan input power.

It is clear that case (2) will develop the highest recovered power, that’s to say at WT position of 260 mm, rotor

(1) air angle of attack 120 guide vanes angle (A=300, B=1200) will be the optimum parameters values for the

present cooling tower – WT energy system.

Fig. 14: Recovered power for all test cases (WT position=260 mm)

Conclusion:

Usage of the VAWT on the outlet of cooling tower could recover a part of the unused exhaust air for

electricity generation. Two vertical axes wind turbine of 5-blades, H-rotor and 245mm in diameter integrating

with an enclosure were positioned overhead a cooling tower are used as wind energy recovery system. The

enclosure design was the best to make venture effect and guide the wind stream to interact with the wind turbine

blades. Also, the enclosure altogether enhances the wind turbine rotational speed.

The test results show that the net output power of the heavy WT rotor was increased by about 36.7% over

the light WT rotor for the same angle of attack and guide angles. While the recovered energy was increased by

17.7w when the heavy WT rotor was closer to the fan. The highest percentage of recovered power, obtained at

the WT position of 260 mm, heavy rotor, air angle of attack 120, and guide vanes angle (A=300, B=1200) and

therefore this case could be considered as the optimum for the present cooling tower – WT energy system.

0.00

5.00

10.00

15.00

20.00

25.00

30.00

255 260 265 270 275 280 285 290 295 300 305

po

wer

(w

att)

WT position (mm)



0

2

4

6

8

10

12

14

16

case 1 case 2 case 3 case 4 case 5 case 6 case 7 case 8

reco

vere

d p

ow

er (

%)

cases


REFERENCES

1. Chong Wen Tong, Poh Sin Chew, Ahmad Fazlizan Abdullah, 2011. Oon Cheen Sean and Tiah Chai Ching

"Exhaust Air and Wind Energy Recovery System for Clean Energy Generation" International Conference

on Environment and Industrial Innovation IPCBEE 12 (2011) © (2011) IACSIT Press, Singapore.

2. Wen Tong Chong, Sin Chew Poh, Ahmad Fazlizan, Sook Yee Yip, Mei Hyie Koay, and Wooi Ping Hew,

2013. "Exhaust Air Energy Recovery System for Electrical Power Generation in Future Green Cities"

International Journal of Precision Engineering and Manufacturing, 14(6): 1029-1035.

3. Jee-Ho Kim, Hyun-Dai Yang, Kyu-Jin Lee, Sung-Do Song, Sung-Hoon Park and Joong-Ho Shin, 2013. "

An Experiment on Power Properties in a Small-Scaled Wind Turbine Generator " Journal of Power and

Energy Engineering, 1: 6-13 http:// dx. doi . org/ 10. 4236 /jpee.2013.17002 Published.

4. Saber, H.E., E.M. Attia and H.A. El Gamal, 2015. " Analysis of Straight Bladed Vertical Axis Wind

Turbine" International Journal of Engineering Research & Technology www. ijert. Org IJERTV 4IS070453

(This work is licensed under a Creative Commons Attribution 4.0 International License.) 4(07).

5. Qasim1, A.Y., R. Usubamatov, Z.M. Zain and Ghulam Abdul, 2012. "Design of Flat Vanes Vertical Axis

Wind Turbine" https://www.researchgate.net/publication/270049766. Elixir Mech. Engg., 45: 7704-7708.

6. Akhgari, A. 2011. "Experimental investigation of the performance of a diffuser augmented vertical axis

wind turbine" M.Sc. Dissertation University of Victoria.

7. Abdulrazek, A., 2012. "Design and Power Characterization of a Small Wind Turbine Model in Partial Load

Region" M.Sc. Dissertation University of Kassel and Cairo University.

8. Roscher, B., 2014. "Structural Optimization of A Vertical Axis Wind Turbine With Aeroelastic Analysis"

M.Sc. Dissertation University of Denmark and in Aerospace Engineering at Delft University of

Technology.

9. In Seong Hwang, Seung Yong Min, In Oh Jeong, Yun Han Lee and Seung Jo Kim 2006. " Efficiency

Improvement of a New Vertical Axis Wind Turbine by Individual Active Control of Blade Motion"

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.598.9825&rep=rep.

http://www.ijert.orgijertv4is070453/

https://www.researchgate.net/publication/270049766

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.598.9825&rep=rep

optimum configuration of cooling tower overhead wind ... · pdf fileobtaining the...

Documents