Solar Updraft Tower Using Compost Waste Heat and Transpired Solar Collectors K. R. Anderson*, A. Ang*, R. Osorio*, and A. Villanueva*
*California State Polytechnic University, Mechanical Engineering Solar Thermal Alternative Renewable Energy Lab, Pomona, CA, USA, [email protected], [email protected],[email protected],[email protected]
ABSTRACT house the composting waste heat harvesting portion of the technology, and the TSC walls which are used to fabricate This paper explores the use of ways to enhance energy the walls of the CWH greenhouse. The concept of using the production capability in Solar Updraft Towers (SUT) by SUT with CWH has been published by our research team in using Compost Waste Heat (CWH) and Transpired Solar previous studies including [1-2], whereby the civil Collector (TSC) renewable energy technologies in unison. engineering design of a compost waste heat to energy solar The current research presents experimental and numerical chimney power plant and it’s assocaited economic modeling results for the SUT CWH greenhouse walls advantages is given. In the study of [3] a comprehensice constructed from TSC materials. The paper includes the thermal-fluids analysis of a hybrid solar/compost waste heat results obtained for the power production from a 1/5th sized updraft tower is presented. In the work of [4] CFD analysis scaled model of a SUT using CWH and TSC in unison. of hybrid solar tower using compost waste heat and Numerical heat transfer simualtions are also presented photovoltaics is presented. The review of solar updraft showing the effect of greenhouse roof tilt angle and inlet tower power generation given by [5] notes the current SUT tower air velocity on the overall heat transfer coefficent of CWH research of our team as being novel and innovative. the SUT system. The recent study of [6] provides a case study of energy recovery from commercial-scale composting. The current Keywords: solar chimney, composting, waste heat, paper extends the propostition of using SUT CWH with transpired collector TSC first gvien by [7]. The concept of using TSC walls with an SUT and CWH is illustrated in Figure 2. 1 INTRODUCTION CHIMNEY WALL The SUT is also referred to in the literature as a Solar Chimney, in which turbines located at the base of a large ROOF OF SHROUDED TURBINE chimney mounted on the roof of a solar greenhouse are CWH GREENHOUSE used to produce electricity via the natural convection HEATED AIR FROM TSC updraft set up by the solar chimney which causes a wind velocity on the order of 9 mph (4 m/s) to spin a series of shrouded turbine blades to produce power. Figure 1 shows TSC WALL HEATED AIR FROM CWH the configuration being studied herein.
FRESH AIR SUT
COMPOST PILE
GROUND FLOOR CWH GREENHOUSE TSC WALLS Figure 2: Use of TSC walls for the greenhouse walls of the SUT CWH power plant.
As shown in Figure 2, the TSC walls are used in unison Figure 1: Solar updraft tower with compost waste heat with the SUT and CWH to augment the convective flow fed removal and transpired collector walls. into the power turbine of the SUT CWH TSC power plant. The merits of using the TSC in conjunction with a SUT employing CWH were first introduced in [7]. In the case Figure 1 shows the SUT chimney tower, which has a tubine study of [8] a 2 CFM TSC system with solar radiation of located at its base, the CWH greenhouse building used to 500 W/m2 is seen to give a T = 20 C of temperatue
Materials for Energy, Efficiency and Sustainability: TechConnect Briefs 2018 21 potentail. This amount of temperature differential is directly proporation to an increase in heat transfer coefficient (HTC) per
h a T b (1) as discussed in [7].
2 NUMERICAL MODELING
A numerical Computational Fluid Dynamics (CFD) Heat Transfer model was constructed to predict the behaivor of a particular SUT due to changes in the HTC, h slope of the roof, velocity of inlet air into chimney, V, etc. Figure 3 shows axisymmtric model used, while Figure 4 Figure 5: Numerical heat transfer simulation results for shows a zoomed in view of the the mesh used for the effect of SUT greenhouse roof slope , on tower entrance numerical CFD model. temperature, To and HTC.
SUT CHIMNEY Results from the numerical heat transfer model show that the heat transfer coefficient (HTC) varies from 15 < h < 25 W/m2-K depending on wheter the side walls of the CWH greenhouse are fabricated out of plain walls, h = 15 W/m2- K, or TSC type walls h = 25 W/m2-K. For the generic trends it is found that composting addition always results in TSC more heat and therefore higher temperatures. The non- TURBINE compost configuration shows a modest increase in INLET temperature in all cases as the HTC increases. Regarding the slope of the roof, as the roof was sloped, some roof Figure 3: Numerical heat transfer model mesh of of SUT angles show increase in temperature with increased HTC, with CWH and TSC. while other roof angles show flat or decreasing temperature with increased HTC. This phenomena is believed to the fact that addition of compost causes reduced buoyancy driven flow in the base of the SUT at some angles. In summary, taller towers causes increased velocity and angled roof CWH greenhouse maximizes the tower velocity by reducing flow resistance into the tower. Additional parasitic heat sources mostly contribute to increasing the air temperature into the tower with minor effects on increasing velocity.
3 PROTOTYPE EXPERIMENT
Figure 6 shows the experimental prototype built at California State Polytechnic University at Pomona.
Figure 4: Zoomed in view of numerical heat transfer model mesh of SUT with CWH and TSC.
The numerial simulations were performed with ANSYS FLUENT CFD Numerical Heat Trasnsfer software. Typical results of the numerical analysis are shown in Figure 5.
HOLES USED TO MIMIC TSC EFFECT
Figure 6: Prototype 1/5th scale of SUT with CWH and TSC.
22 TechConnect Briefs 2018, TechConnect.org, ISBN 978-0-9988782-3-2 [3] K.R. Anderson, M. Shafahi, and C. McNamara, Figure 6 shows the 1/5th scale prototype of the SUT CWH “Thermal-fluids analysis of a hybrid solar/compost TSC power plant with details of the SUT greenhouse waste heat updraft tower,” Journal of Clean Energy sidewall construction, foam insulation, and structure Technologies, Vol. 4 No. 3., pp. 213-220, 2016. comprising the prototype. The following equation from [9] [4] K.R. Anderson, M. Shafahi, R. Baghaei Lakeh, S. relates the power output of the SUT to the temperature drop Monemi and C. McNamara, “CFD analysis of across the chimney, T and the height of the tower, h are hybrid solar tower using compost waste heat and used to reduce the data photovoltaics,” Proceedings of the IEEE SUSTECH 2015 Conference on Technologies and T Sustainability, Ogden, Utah, USA, 2015. P c KA T2 gh (2) [5] X. Zhou and X. Yangyang, "Solar updraft tower p T o power generation," Solar Energy, Vol. 128, pp. 95- 125, 2016. while the prototype power is related to the actual power via [6] M. Smith and J. Aber, "Energy recovery from the similarity relationships of fluid mechanics and commercial-scale composting as a novel waste turbomachinery [10] management strategy," Applied Energy, Vol. 211 pp. 194-199, 2018. [7] K.R. Anderson, “Analysis of SUT using Compost PP Waste Heat and TSC,” proceedings of ASES 3 5 3 5 (3) SOLAR 2017 Conference, Denver CO, Oct. 9-12, DD prototype actual 2017. [8] http://solarwall.com/en/home.php, last accessed The relationships of (2) and (3) are used to compare the 3/23/18 performance the prototype to actual SUT CWH TSC [9] J. Schlaich, R. Bergermann, W. Schiel and G. powerplant. Preliminary findings are shown in Figure 7. Weinrebe, “Design of commercial solar tower systems–utilization of solar induced convective flows for power generation,” J. Sol. Energy Engineering, Vol. 10, pp. 117-124, 2005. [10] Potter and Wiggert “Mechanics of Fluids,” 3rd. Ed., Prentice-Hall, 2002. * P CWH+TSC prototype (MW) P TSC CWH prototype (MW)
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Figure 7: Comparison of prototype to actual power plant power output predictions.
REFERENCES
[1] K.R. Anderson, Y. Salem, S. Shihadeh, P. Perez, B. Kampen, S. Jouhar, S. Bahrani, and K. Wang, “Design of a compost waste heat to energy solar chimney power plant,” Journal of Civil Engr. Research, Vol. 6, Issue 3, pp. 47-54. 2016 [2] K.R. Anderson, M. Shafahi, S. Shihadeh, P. Perez, B. Kampen, C. McNamara, R. Baghaei Lakeh, A. Sharbat, and M. Palomo, “Case study of a solar tower/compost waste-to-energy test facility,” Journal of Solid Waste Technology & Management, Vol. 42, pp. 698-708, 2016.
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