Scholarly article on topic 'Research for Ventilation Properties of Solar Chimney with Vertical Collector'

Research for Ventilation Properties of Solar Chimney with Vertical Collector Academic research paper on "Earth and related environmental sciences"

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Abstract of research paper on Earth and related environmental sciences, author of scientific article — Zhou Yan, Jing Guang-e, Liu Xiao-hui, Li Qing-ling

Abstract Theoretical research and numerical simulation for ventilation properties of solar chimney with vertical collector are performanced and they are compared with experimental results. Results show that: there are many factors to affect solar chimney ventilation that include heat collection height and width, solar radiation intensity, inlet and outlet area ratio of chimney and air inlet velocity, etc. When the collector height is increased, chimney ventilation is getting higher; but the ventilation increases slowly even decreases; the ventilation increases first and then decreases as the growing of the air layer thickness under the same chimney height and width; there exists an optimal ratio between heat collector height and width which makes the ventilation largest; considering the urban architecture image and the influence of the air layer thickness on chimney ventilation, the best air layer thickness is between 0.2m and 0.4m. Besides, the airflow temperature in solar chimney increases with chimney height in certain solar radiation intensity. It is consistent with the theoretical analysis and simulation results.

Academic research paper on topic "Research for Ventilation Properties of Solar Chimney with Vertical Collector"

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Environmental Sciences

Procedia Environmental Sciences 11 (2011) 1072 - 1077

Research for Ventilation Properties of Solar Chimney with

Vertical Collector

Zhou Yan, Jing Guang-e, Liu Xiao-hui, Li Qing-ling

(The College of Mechanical and Electrical Engineering, Qingdao University of Science and Technology, Shandong Qingdao, 266061 )

Abstract

Theoretical research and numerical simulation for ventilation properties of solar chimney with vertical collector are performanced and they are compared with experimental results. Results show that: there are many factors to affect solar chimney ventilation that include heat collection height and width, solar radiation intensity, inlet and outlet area ratio of chimney and air inlet velocity, etc. When the collector height is increased, chimney ventilation is getting higher; but the ventilation increases slowly even decreases; the ventilation increases first and then decreases as the growing of the air layer thickness under the same chimney height and width; there exists an optimal ratio between heat collector height and width which makes the ventilation largest; considering the urban architecture image and the influence of the air layer thickness on chimney ventilation, the best air layer thickness is between 0.2m and 0.4m. Besides, the airflow temperature in solar chimney increases with chimney height in certain solar radiation intensity. It is consistent with the theoretical analysis and simulation results.

© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Intelligent Information Technology Application Research Association.

Keywords: Solar chimney; Vertical heat collection; Ventilation properties; Theoretical research; Numerical simulation

With the high speed development of economy and the improvement of people's living standard, the ratio of building energy consumption in human total energy consumption continues to rise. According to statistics, it is up to 42%-47% in west developed country and our country has reached 30%.And the rate of heating and cooling energy consumption is as high as 50%-60% among them. Therefore building energy efficiency must be drawn much more attention. Modern buildings should maximize use of natural energy sources and reduce the consumption of non-renewable energy. Besides, the concept of ecological "Green" architecture that is fit to the sustainable development strategy should be promoted and implemented in building industry. Natural ventilation is a common technology to improve indoor thermal environment and effectively reduce air conditioning energy consumption. The reasonable structure designed can make solar energy as the power of natural ventilation. Natural ventilation with solar is primarily through solar chimneys to heat room, improve exhaust temperature and low the temperature. The theoretical and

ELSEVIER

1878-0296 © 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Intelligent Information Technology Application

Research Association.

doi:10.1016/j.proenv.2011.12.162

simulation analysis for the solar chimney with vertical heat collector to strengthen the natural ventilation could provide theoretical basis for the following application.

1. Theoretical analysis

1.1 Solar chimney with vertical heat collector and thermodynamic process

Solar chimney with vertical heat collector is built by transparent material within besmearing selective coating and relies on the high-rise. Solar chimney is not the air flowing channel, but also the place of the air absorbing solar heat. The air is selected as the research object. The movement process of the air in chimney is shown in Fig.1. It's easy to see that thermodynamic process of the air flowing in solar chimney can be simplified as the endothermic process with many phase changes.

1.2 Ventilation calculation

1.2.1 Ventilation under the action of hot-pressing

The general meaning of the natural ventilation refers to the building with a purposeful opening, resulting in the air spontaneous flow[7-10]. The air flow is mainly caused by hot-pressing. Hot-pressing is caused by pressure difference caused by inlet and outlet density difference. The density difference between the chimney entry and exit is composed of two parts. One part is produced due to the existence of the chimney height. But this is smaller because of the height of high-rise building. The other part is caused by the temperature variation. The air flow in solar chimney is the result of the two types of hotpressing. Pressure difference causing hot-pressing depends on the chimney height and temperature between inlet and outlet. According to Bernoulli equation, continuity equation and air flow process as well as mass conservation principle, the air flow mass can be obtained.

1.2.2 The chimney ventilation

The chimney pressure difference has two parts, that is, it is the summation of hot-pressing and pressure difference caused by natural wind. The incentive ventilation is related to the pressure difference and temperature. The factors affecting the incentive ventilation include the height and width of heat collector, solar radiation intensity, the area ratio of the chimney inlet and outlet and air inlet velocity, etc.

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1.3 Theoretical results analysis

There are many factors influencing on ventilation and calculation is much more complicated, so MATLAB method is used. The ventilation can be got through computer and is shown in Fig.2. Theoretical ventilation increases with solar radiation intensity. The influence of the heat collector height

(chimney height) on ventilation is that Theoretical ventilation approximately increases linearly with the heat collector's height. And the theoretical ventilation increases obviously with the heat collector's width, but when the width increases to certain value, the ventilation changes slowly.

2. Solar chimney steady-state numerical simulation and experimental study

2.1 Establishment of mathematical model

According to the solar chimney experimental facility, three-dimensional physical model is established and mesh division has been done. Adiabatic boundary has been used on the computed fields. Exact values as follows:

The inlet velocity is 0.2m/s and temperature is 293K; the velocity of the solar collector glass surface is zero, the glass is chosen as the material of heat collector and heat conduction coefficient is 1.15W/(m' K); the mass flow and velocity inside wall of the chimney are zero and k-estandard model is chosen. Standard wall function method is used on the wall and SIMPLE method is used by pressure-speed coupled and the second order windward is used in discrete format of conservation equation. RNG equation model is chosen in turbulence model. Considering float lift model, Bossinesq hypothesis is used, that means, in the control equations except the density of float lift item varying linearly with temperature, the density in other aspects and objects can treat approximately as constant physical property. And SIMPLE method is used in control equation.

2.2 Simulation analysis

Fig.3 shows that the ventilation increases with solar radiation. And the ventilation is in proportion to the chimney height, but with increase of chimney's width ventilation increases first and then decreases. Under the same chimney height and width, the ventilation increases first and then decreases as the growth of the air layer thickness. When the thickness of air layer is 0.3m, ventilation is the largest.

2.3 Experimental study

According to the theoretical analysis and simulation results, the solar chimney with vertical heat collector is built on sunny slope in south area on 1 floor of Qingdao University of Science and Technology. The chimney height is 20m and width is 1m. Considering the space of south wall and overall appearance, the actual thickness takes 0.3m. According to the experimental data, which Fig.4 shows, the chimney outlet velocity has great relationship to inlet velocity and temperature. The contrast results between measured wind speed and numerical simulation are shown in Fig.5.

3. Conclusions

Conclusions can be got through the results relying on theoretical research, numerical simulation and experimental study, as follows:

(1) The main factors that impacts the ventilation properties of solar chimney with vertical heat collector include solar radiation, heat collector's height and width and so on. The increase of chimney height can make ventilation rise and then improve temperature difference.

(2) The ventilation increases with the solar radiation and chimney height, but in simulation the ventilation increases first and then decreases with the increase of chimney width. There exists the best ratio between chimney height and width that makes the ventilation largest.

(3) The chimney import corner is orthogonal in the initial design and it doesn't agree with the streamline of the air, which makes the vortex exist. There exists backflow in chimney outlet because of the design of straight cylinder chimney. So the structure of chimney corner needs to be optimized in application.

References

[1]Robert R. Solar prototype development in Spain show great promise [J]. MPS Review, 1982, 2: 21-23

[2]Robert R. Hot air starts to rise through Spain's solar chimney [J]. Electrical Review, 1982, 210, (15): 26-27

[3]Schlaich J. World energy demand, population explosion, and pollution: could solar energy utilization become a solution [J]. The Structural Engineering, 1991, 69: 189-192

[4]Li Jie-hao, Li Qing-ling, Zhou Yan, etc. Vertical collection hot plate solar heat flow power station numerical simulation [J]. Journal of Qingdao University of Science and Technology (Natural Science Edition), 2010,31(4):404-407

[5]Zhou Yan, Li Qing-ling, Li Jie-hao, etc. Vertical collection hot plate heat flow power system research [J].Journal of Engineering Thermal Physical, 2010,31(3):465-468

[6]Brian, Edwards. Sustainable architecture [M].Zhou Yu-peng, Song Ye-hao, etc. Beijing: Chinese Industrial Building Press, 2003

[7]Wang Peng, Tan Gang. Natural Ventilation of Ecological Architecture [J].The World Building, 2000(12):62-65

[8]Song Ye-hao. The promotion of natural ventilation by hot-pressing [J].2000,(12):12-14

[9]Su Xing, Liu chuan-ju, Su Ji-ping, etc. Solar chimney ventilated effect and applied research [J].Energy Technology, 2005, 26(6)

Fig. 1 Schematic of the air flow in the solar chimney

Fig.2The theoretical results for ventilation

Fig.3 The simulation results of ventilation

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Fig.4 The relationship between the air velocity and air temperature at the chimney inlet

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Fig.5 The comparison of experiment wind speed and computer simulation wind speed