Document Sample

INTERNATIONAL JOURNAL OF MECHANICAL ISSN 0976 – 6340(Print), International Journal of Mechanical Engineering and Technology (IJMET), ENGINEERING ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 200-213 © IAEME AND TECHNOLOGY (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) IJMET Volume 5, Issue 5, May (2014), pp. 200-213 © IAEME: Journal Impact Factor (2014): 7.5377 (Calculated by GISI) ©IAEME CFD AND DOE STUDY THE EFFECT OF SOLAR CHIMNEY TOWER RADIUS, HEIGHT, CHIMNEY RADIUS AND HEIGHT Manisha Jayprakash Dhanokar1, Kiran Prakashrao2, Parmar Ashwin1 1, 2 (Pillai HOC College of Engineering and Technology Rasayani) 3 (Assistant Professor, Pillai HOC College of Engineering and Technology Rasayani) ABSTRACT Solar chimney technology is a very promising solar thermal electricity generating technology. In this project CFD technology is used to investigate the changes in flow kinetic energy caused by the variation of tower flow area with height. It was found that the tower area change affects the efficiency and mass flow rate through the plant. The divergent tower top leads to augmentations in kinetic energy at the tower base significantly. Numerical calculations have been performed using CFX. For this purpose, CFX solves the conservation equations for mass, momentums, and energy using a finite volume method. Adaptive unstructured tetrahedral meshes were used in the present study. The plants studied were modeled as an axis-symmetric model where the centerline of the tower is the axis of symmetry. To simulate axis-symmetry, a 1 degree section of the plant is cut out from the entire periphery. The results shows that the chimney height and Tower outlet radius and base area are very important parameters for improving the gained power, and it is also important to choose the region with suitable mean ambient temperature. And economically there are limitations to collector and chimney sizes to get suitable profit output power and any increment in system size becomes a small percentage increment in profit output power. The results compared with some experimental data from other results researchers and there is a good agreement between simulated and calculated results Keywords: CFD, Optimization, Solar Chimney. I. INTRODUCTION In recent years, rapid developments of global economy and increase in population and living standards have been posing great pressure on natural resources and the environment. Fossil fuels are 200 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 200-213 © IAEME being exhausted at a fast rate, and utilization of fossil fuels together with net deforestation has induced considerable climate change in warming the atmosphere by releasing greenhouse gases (GHG) which may produce many negative effects including receding of glaciers, rise in sea level, loss of biodiversity, extinction of animals, and loss of productive forests, acidification of oceans etc. Our over dependency on fossil fuels for our energy needs has lead us close to the energy crisis and has caused various adverse effects on our environment as mentioned above. Therefore now the biggest challenge before the energy pioneers and researchers is finding new ways of harnessing energy from renewable sources that are sustainable and free of greenhouse gases (GHG) as well. The drawback of most of the renewable power technologies has been their unreliability as they can’t operate continuously for 24 hours or continuous operation is achieved only through hybrid systems using fossil fuels along with renewable energy sources or through expensive and sophisticated energy storage facilities. These drawbacks have kept the researchers busy in finding more and more alternatives ways to power our future. Solar Chimney power technology is one of them and it promises a better solution to our current energy problems. Fig.1: SCPP working principle The solar tower’s principle is shown in Fig 1. Air is heated by solar radiation under a low circular transparent or translucent roof open at the periphery; the roof and the natural ground below it form a solar air collector. In the middle of the roof is a vertical tower with large air inlets at its base. The joint between the roof and the tower base is airtight. As hot air is lighter than cold air it rises up the tower. Suction from the tower then draws in more hot air from the collector, and cold air comes in from the outer perimeter. Jörg Schlaich, Rudolf Bergermann, Wolfgang Schiel, Gerhardm Weinrebe 2000 [1] described the functional principle of solar updraft towers and gave some results from design, construction and operation of the first ever prototype built in Spain. S. Beerbaum and G. Weinrebe et al. 2000 [2] conducted a techno-economic analysis on solar thermal power generation in India. In this study they analyzed the potential and the cost-effectiveness of centralized and decentralized STE-generation in 201 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 200-213 © IAEME India. Y.J. Dai, H.B. Huang and R.Z. Wang et al. 2002 [3] analyzed a solar chimney power plant that was expected to provide electric power for remote villages in northwestern China. M.A. dos S. Bernardes, A. Voß and G. Weinrebe et al. 2003 [4] carried out an analysis for the solar chimneys aimed particularly at a comprehensive analytical and numerical model, which describes the performance of solar chimneys. J.P. Pretorius and D.G. Kröger et al. 2005 [5] evaluated the influence of a recently developed convective heat transfer equation, more accurate turbine inlet loss coefficients, quality collector roof glass and various types of soil on the performance of a large scale solar chimney power plant. Xinping Zhou, Jiakuan Yang, Bo Xiao & Guoxiang Hou et al. 2006 [6] built a pilot experimental solar chimney power generating equipment in China. They carried out a simulation study to investigate the performance of the power generating system based on a developed mathematical model. Atit Koonsrisuk & Tawit Chitsomboon et al. 2007 [7] proposed dimensionless variables to guide the experimental study of flow in a small-scale solar chimney: a solar power plant for generating electricity.. T.P. Fluri, J.P. Pretorius, C. Van Dyk, T.W. Von backström, D.G. Kröger, G.P.A.G. Van Ziji et al. 2008 [8] compared several cost models that were available in the literature. Xinping Zhou, Jiakuan Yang, Bo Xiao, Guoxiang Hou & Fang Xing et al. 2008 [9] the maximum chimney height for convection avoiding negative buoyancy at the latter chimney and the optimal chimney height for maximum power output were presented and analyzed. Cristiana B. Maia, André G. Ferreira, Ramón M. Valle & Márcio F.B. Cortez et al. 2008 [10] carried out an analytical and numerical study of the unsteady airflow inside a solar chimney. The conservation and transport equations that describe the flow were modeled and solved numerically using the finite volumes technique in generalized coordinates. The numerical results were physically validated through comparison with the experimental data. Tingzhen Ming, Wei Liu, Yuan Pan & Guoliang Xu et al. 2008 [11] carried out numerical simulations to analyze the characteristics of heat transfer and air flow in the solar chimney power plant system with an energy storage layer. Marco Aurélio dos Santos Bernardes, T.W. Von Backström & D.G. Kro¨ger et al. 2008 [12] compared the two comprehensive studies namely those of (Bernardes, M.A.d. S., Voß, A., Weinrebe, G., 2003. Thermal and technical analyses of solar chimneys. Solar Energy 75, 511–524; Pretorius, J.P., Kro¨ ger, D.G., 2006b. S. Nizetic, N. Ninic & B. Klarin et al. 2008 [13] analyzed the feasibility of solar chimney power plants as an environmentally acceptable energy source for small settlements and islands of countries in the Mediterranean region. For the purpose of these analyses, two characteristic geographic locations (Split and Dubrovnik) in Croatia were chosen and simplified model for calculation of produced electric power output is also developed. Atit Koonsrisuk & Tawit Chitsomboon et al. 2009 [14] in their previous study found that the achievement of complete dynamic similarity between a prototype and its models imposed the use of different heat fluxes between them. Atit Koonsrisuk & Tawit Chitsomboon et al. 2009 [15] used dimensional analysis together with engineering intuition to combine eight primitive variables into only one dimensionless variable that establishes a dynamic similarity between a prototype and its scaled models. II. MATHEMATICAL MODELS OF FLUENT All the fluids investigated in this research are Newtonian. This means that there exists a linear relationship between the shear stress, σij , and the rate of shear (the velocity gradient). In CFX, this is expressed as follows: 202 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 200-213 © IAEME In FLUENT, these laws are expressed in the following form: Law of Conservation of Mass: Fluid mass is always conserved. Newton’s 2nd Law: The sum of the forces on a fluid particle is equal to the rate of change of momentum. First Law of Thermodynamics: The rate of head added to a system plus the rate of work done on a fluid particle equals the total rate of change in energy. The fluid behaviour can be characterised in terms of the fluid properties velocity vector u (with components u, v, and w in the x, y, and z directions), pressure p, density ρ, viscosity µ, thermal conductivity λ, and temperature T. The changes in these fluid properties can occur over space and time. H is the total enthalpy, given in terms of the static (thermodynamic) enthalpy, h: III. GEOMETRIC MODEL Geometric Model is created in ANSYS Design modeller which is ashon in Fig.2. and 3. Fig.2: CFD Model of Solar chimney 203 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 200-213 © IAEME Tower outlet radius Tower Height Tower inlet radius Roof Inlet radius Roof outlet radius Fig.3: Solar Chimney nomenclature Fig.4: CFD Model of Solar chimney sector 1o-Isometric View IV. CFD MESHING A QUAD mesh is generated using ANSYS Meshing preprocessor. Many different cell/element and grid types are available. Choice depends on the problem and the solver capabilities. First, the surface of the solar chimney is meshed with QUAD element. Then the QUAD element is revolved for 1degree. No of elements is used for all the models 10 thousands. Fig.5: Close View of solar chimney mesh 204 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 200-213 © IAEME Following are the assumptions incurred on the present analysis: • Flow is Turbulent • Flow is steady and incompressible • Coupled solver Proper boundary conditions are needed for a successful computational work. At the roof inlet, the total pressure and temperature are specified; whereas at the tower exit the ‘outlet’ condition with zero static pressure is prescribed. The symmetry boundary conditions are applied at the two sides of the sector while the adiabatic free-slip conditions are prescribed to the remaining boundaries, consistent with the frictionless flow assumption. All test cases were computed until residuals of all equations reached their respective minima. Moreover, global conservation of mass were rechecked to further ascertain convergence of the test cases Fig.6: Boundary zone names V. RESULTS AND DISCUSSIONS In Fig. 7, the gauge pressure distributions are seen to be nominally constant under the roof before falling gradually in the tower portion to meet the hydrostatic pressure value at the tower top. In Fig.8 shows the contours of temperature. rise of the temperature at the tower base is the response to the abrupt velocity change, in accordance with the conservation of energy principle. Fig.9 the velocity increases as it approaches the tower base. Fig.7: Contours of static Pressure at Mid plane 205 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 200-213 © IAEME Fig.8: Contours of Temperature at Mid plane Fig.9: Contours of Velocity Magnitude at Mid plane 206 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 200-213 © IAEME Fig.10: Contours of Velocity Magnitude Zoomed view VI. OPTIMIZATION A. Optimization Outlet radius In Fig. 12, the gauge pressure distributions are seen to be nominally constant under the roof before falling gradually in the tower portion to meet the hydrostatic pressure value at the tower top. For the plants with AR greater than one, there are swift dips at the tower base; the severities of the dips are proportional to AR. The dips are direct responses to the temperature dips because the density is relatively unchanged in a low Mach number flow. Note that the ordinate is the gauge pressure which was scaled such that pressure at the tower top is always zero. Figs. 13 show the distributions of computed flow properties for different tower area ratio (AR). The abscissa of all plots is the scaled flow path, equaling zero at roof inlet, one at tower top and 0.5 at tower base. As can be seen in Fig. 13 at any AR, the velocity increases as it approaches the tower base. In the tower portion, the velocity distribution depends on AR. For models with AR smaller than one, the velocity keeps on increasing and attains the maximum value at tower outlet. On the other hand, for models with AR larger than one, the flow achieves its maximum velocity right after entering the tower, and then decreases continuously afterward. 207 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 200-213 © IAEME Tower outlet radius Varied from 2.83 m-16 m Tower Height Tower inlet radius-4m Roof Inlet Height-4m Roof outlet Height-4m Roof Radius 100 m Fig.11: Optimization 1- Tower outlet radius variation Z W Z Z Z W Z Z ' Z E > Fig.12: Comparisons of Pressure at different Area Ratio Z Z Z Z Z s Z Z E > Fig.13: Comparisons of velocity at different Area Ratio 208 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 200-213 © IAEME Z Z t Z Z W Z Z Z E > Fig.14: Comparisons of Power at different Area Ratio t W K Fig.15: Effect of tower area ratio on Power for insulation = 800 W/m2 Z & D K Fig.16: Effect of tower area ratio on the mass flow rate for insulation = 800 W/m2 209 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 200-213 © IAEME Fig. 15 shows the variation in dimensionless power, defined as the kinetic power divided by the kinetic energy of the prototype at tower base. It is evident that high AR leads to augmentation in power at the tower base. This suggests the potential of harnessing more turbine power from the high AR system. The effect of the tower area ratio on the mass flow rate is presented in Fig.16. The results show that the mass flow rate rises and falls with AR. In relation to the constant-area tower, convergent-top tower reduces mass flow rate and divergent-top tower increases mass flow rate. B. Optimization Roof inlet Radius 4m and 2 m The effect of the tower area ratio on the mass flow rate is presented in Fig. 17 for reducing roof inlet 4m to 2m. The results show that the mass flow rate rises and falls with AR. In relation to the constant-area tower, convergent-top tower reduces mass flow rate and divergent-top tower increases mass flow rate. It shows the higher mass rate for 2m roof inlet. Z / Z / Z & D K Fig.17: Effect of tower area ratio on the mass flow rate Roof inlet radius 4 and 2m for insulation = 800 W/m2 Fig. 18 shows the variation in dimensionless power, defined as the kinetic power divided by the kinetic energy of the prototype at tower base. It is evident that high AR leads to augmentation in power at the tower base. This suggests the potential of increasing turbine power from the lowering the inlet height to 2m. Z Z t W K Fig.18: Effect of tower area ratio on Power on Roof inlet radius 4 and 2m for insulation = 800 W/m2 210 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 200-213 © IAEME C. Optimization -Roof height The effect of the roof height on the mass flow rate is presented in Fig19 for increasing 100m to 200m for different roof height. The results show that the mass flow rate rises and increase roof height up-to 150m then maintains constant. Fig. 20 shows the variation in dimensionless power Effect of roof height on Power for insulation = 800 W/m2- 8 and 12m, defined as the kinetic power divided by the kinetic energy of the prototype at tower base. It is evident that high Increase roof height to augmentation in power at the tower base. This suggests the potential of increasing turbine power from the increasing the tower height 150m. K Z Z & D d , Fig.19: Effect of Tower height on Mass flow rate for insulation = 800 W/m2 K Z t W d , Fig.20: Effect of Tower height on Power for insulation = 800 W/m2 211 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 200-213 © IAEME VII. CONCLUSION A solar tower system with varying tower flow area has been studied and its performance has been evaluated. The results show that divergent tower helps increase mass flow rate and kinetic energy over that of the constant area tower. The tower area ratio of 12 to 16 can produce kinetic energy as much as 100 times that of the constant area tower. For the convergent tower, the velocity at the tower top increases but the mass flow rate decreases in a manner such that the kinetic power at the top remains the same as the constant area case. For the divergent case, maximum kinetic energy occurs at the tower base and this suggests the potential to extract more turbine power than the constant area tower. • The simulation convenient to predict the performance of the solar chimney and that can save the cost of the experimental procedures. • It is concluded that the mathematical model can predict the performance of the chimney equipment well, and this approach is also applicable to different-scale solar chimney thermal power generating systems. • For a required electric power output, it can obtain many combinations of chimney and collector dimensions by the simulation. • The chimney couldn’t produce suitable power for low chimney height and small base area, for low chimney height it is preferred to the desirable enhancement for increasing the chimney power generation is reducing its exit area. • The optimum collector area and chimney height could be chosen for required output power, we only need to take some measurement at sites. • It is convenient to choose the chimney site within acceptable annual average ambient temperature. • The chimney power increases rapidly as the sizes of collector and the chimney are increases, but the percentage development in chimney power is reduced with an increase in their sizes so that it will be useless economically. REFERENCES [1] Schlaich J, Bergermann R, Schiel W, Weinrebe G. Design of commercial solar updraft tower systems—utilization of solar induced convective flows for power generation. J Solar Energy Eng 2005; 127:117–24. [2] S.Beerbaum, G.Weinrebe, Solar thermal power generation in India- a techno-economic analysis. J Renewable Energy 21(2000) 153-174. [3] Y.J. Dai, H.B. Huang and R.Z. Wang, Case study of solar chimney power plants in northwestern regions of China, J Renewable energy 28(2003) 1295-1304. [4] M.A. dos S. Bernardes, A. Voß and G. Weinrebe, Thermal and technical analysis of solar chimneys, J Solar Energy 75(2003) 511-524. [5] J.P.Pretorius and D.G. Kröger, Critical evaluation of solar chimney power plant performance, J Solar Energy 80(2006) 535-544. [6] Xinping Zhou, Jiakuan Yang, Bo Xiao & Guoxiang Hou, Simulation of a pilot solar chimney thermal power generating equipment, J Renewable Energy 32(2007) 1637-1644. [7] Atit Koonsrisuk & Tawit Chitsomboon, Dynamic similarity in solar chimney modeling, J Solar Energy 81(2007) 1439-1446. [8] T.P. Fluri, J.P. Pretorius, C. Van Dyk, T.W. Von backström, D.G. Kröger, G.P.A.G. Van Ziji, Cost analysis of solar chimney power plants, J Solar Energy 83(2009) 246-256. 212 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 200-213 © IAEME [9] Xinping Zhou, Jiakuan Yang, Bo Xiao, Guoxiang Hou & Fang Xing, Analysis of chimney height for solar chimney power plant, J Applied Thermal Engineering 29(2009) 178-185. [10] Cristiana B. Maia, André G. Ferreira, Ramón M. Valle & Márcio F.B. Cortez, Theoretical evaluation of the influence of geometric parameters and materials on the behavior of the airflow in a solar chimney, J Computers & Fluids 38(2009) 625-636. [11] Tingzhen Ming, Wei Liu, Yuan Pan & Guoliang Xu, Numerical analysis of flow and heat transfer characteristics in solar chimney power plants with energy storage layer, J Energy conservation and management 49(2008) 2872-2879. [12] Marco Aurélio dos Santos Bernardes, T.W. Von Backström & D.G. Kröger, Analysis of some available heat transfer coefficients applicable to solar chimney power plant collector, J Solar Energy 83(2009) 264-275. [13] S. Nizetic, N. Ninic & B. Klarin, Analysis and feasibility of implementing solar chimney power plants in the Mediterranean region, J Energy 33(2008) 1680-1690. [14] Atit Koonsrisuk & Tawit Chitsomboon, Partial geometric similarity for solar chimney power plant modeling, J Solar Energy 83(2009) 1611-1618. [15] Atit Koonsrisuk & Tawit Chitsomboon, A single dimensionless variable for solar chimney power plant modeling, J Solar Energy 83(2009) 2136-2143. [16] Atit Koonsrisuk & Tawit Chitsomboon, Accuracy of theoretical models in the prediction of solar chimney performance, J Solar Energy 83(2009) 1764-1771. [17] K. Obual Reddy, M. Srikesh, M. Kranthi Kumar and V. Santhosh Kumar, “CFD Analysis of Economizer to Optimize Heat Transfer”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 5, Issue 3, 2014, pp. 66 - 76, ISSN Print: 0976 - 6340, ISSN Online: 0976 - 6359. [18] Ajay Kumar Kapardar and Dr. R. P. Sharma, “Numerical and CFD Based Analysis of Porous Media Solar Air Heater”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 2, 2012, pp. 374 - 386, ISSN Print: 0976 - 6340, ISSN Online: 0976 - 6359. [19] Anup Kumar and Anil Kumar Mishra, “A CFD Investigation and Pressure Correlation of Solar Air Heater”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 2, 2013, pp. 401 - 417, ISSN Print: 0976 - 6340, ISSN Online: 0976 - 6359. [20] Tarun Singh Tanwar, Dharmendra Hariyani and Manish Dadhich, “Flow Simulation (CFD) & Static Structural Analysis (FEA) of a Radial Turbine”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 3, 2012, pp. 252 - 269, ISSN Print: 0976 - 6340, ISSN Online: 0976 - 6359. [21] N.S. Venkatesh Kumar and Prof. K. Hema Chandra Reddy, “CFD Analysis of Wind Driven Natural Cross Ventilation for a Generic Isolated Building”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 5, 2013, pp. 200 - 207, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. 213

DOCUMENT INFO

Shared By:

Categories:

Tags:

Stats:

views: | 0 |

posted: | 6/16/2014 |

language: | Latin |

pages: | 14 |

OTHER DOCS BY iaemedu

Docstoc is the premier online destination to start and grow small businesses. It hosts the best quality and widest selection of professional documents (over 20 million) and resources including expert videos, articles and productivity tools to make every small business better.

Search or Browse for any specific document or resource you need for your business. Or explore our curated resources for Starting a Business, Growing a Business or for Professional Development.

Feel free to Contact Us with any questions you might have.