formed by fumed Al 2 O 3 in water for geothermal applications - - PowerPoint PPT Presentation

July 11 -14, 2016

Characterization of nanofluids formed by fumed Al2O3 in water for geothermal applications

Sergio Bobbo, Laura Colla, Antonella Barizza, Stefano Rossi, Laura Fedele

Istituto per le Tecnologie della Costruzione Consiglio Nazionale delle Ricerche, Italy

Outline

• Background
• Experimental apparatus and procedure
• Experimental results
• Conclusions

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European Project Cheap-GSHPs

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The present work developed in the frame of the EU Project CHeap and Efficient APplication of reliable Ground Source Heat exchangers and PumpS (Cheap-GSHPs), funded by the European Union’s Horizon 2020 Research and Innovation Programme. It started in 2015 and will last for four years. Basic idea to substantially reduce the total cost

• f
• wnership

(investment and operating costs), increase the safety of shallow geothermal systems during installation and

• peration and increase the awareness of this technology

throughout Europe.

European Project Cheap-GSHPs

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A multidisciplinary and complementary consortium, composed by specialists in different disciplines (physics, climatology, chemistry, mechanics, engineering, architecture, drilling and GSHE technology) will work on the project. The proposal will focus on

• the

development

• f

more efficient and safe shallow geothermal systems;

• the reduction of the installation costs.
• Firstly, improving an existing, innovative vertical borehole installation

technology and the design of coaxial steel GSHE

• Secondly, newly designed basket type GSHE’s with novel installation

methodologies will be developed. The proposal will develop a decision support system (DSS) covering geological, economic and technological aspects.

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European Project Cheap-GSHPs

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To reduce the total cost of shallow geothermal systems by 20-30 %, the project will improve actual drilling/installation technologies and designs of Ground Source Heat Exchangers (GSHEs) in combination with a holistic engineering approach to optimize the entire systems for building and district heating and cooling applications across the different underground and climate conditions existing within the EU. The safety and regulatory aspects will also be addressed. The developments will be demonstrated in six sites whilst the tools will be applied to several virtual demo cases.

Demo cases

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Real demo sites

• 1. Belfield House at University College Dublin, Ireland
• 2. Residential ecohouse, Putte bij Mechelen, Belgium
• 3. Universidad Politécnica de Valencia, Spain
• 4. Test Site Erlangen, Erlangen-Eltersdorf, Germany
• 5. Bioclimatic office building of CRES, Pikermi, Greece
• 6. Technical Museum of Zagreb, Croatia

Virtual demo sites

• 1. Ballyroan Library, Dublin, Ireland
• 2. Residential Retrofit Glencree, Wicklow, Ireland
• 3. Complex of Santa Croce, Florence, Italy
• 4. Ca’ Rezzonico and Ca’ Lupelli, Venice, Italy
• 5. Manens-Tifs S.p.A. Headquarter, Padua, Italy
• 6. Grupo Ortiz Office Buildings, Vallecas – Madrid, Spain
• 7. Historical building, Bucharest, Romania
• 8. Historical Museum, Sarajevo, Bosnia and Herzegovina
• 9. The Serbian Orthodox Bođani Monastery, Bodjani, Serbia
• 10. Office building of Brogeda-Chiasso, Switzerland

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Alternative secondary fluids

In this frame, the efficiency of the system heat pump/GSHE will be an important task analyses of possible alternative secondary fluids Nanofluids, i.e. suspensions of nanometric solid particles in liquids proposed, due to their thermal, rheological and tribological properties

• In particular, in the geothermal field, some nanofluids considered as possible thermal vectors,

promising high heat transfer efficiency and better performance.

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Recently, a project, called “Improving the Efficiency of Geothermal Heat Pumps”, funded by the U.S. Environmental Protection Agency's Small Business Innovation Research Program Improve the heat transfer and the overall efficiency of the geothermal heat pumps (GHPs) systems Fumed alumina (Al2O3) in water or water and propylene glycol mixtures

Fumed Al2O3 in H2O

Amongst others, first tests have been performed Two different commercial suspensions Fumed Al2O3 nanoparticles in H2O concentrations 30% or 40% Then diluted at 3 wt% and 5 wt%

• Stability and thermal conductivity carefully characterized
• Dynamic viscosity analysed in order to evaluate the nanofluids performance as geothermal

fluid

• Mouromtseff numbers (Mo) considered to estimate the thermal effectiveness of the these

nanofluids compared with water

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Stability characterization

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A Zetasizer Nano ZS (Malvern), based on the Dynamic Light Scattering (DLS), used to analyse the average dimension of the nanoparticles in solution. Zeta potential 49.6 mV for 30 wt% 47.5 mV for 40 wt%

136 nm 149 nm

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STABLE FLUIDS

Stability characterization

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STABLE FLUIDS

Thermal Conductivity

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Thermal conductivity measured at ambient pressure and between 283 K and 323 K by means of a TPS 2500 S (Hot Disk) declared instrument accuracy 5% tests performed on water within 1%

Thermal Conductivity

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Dynamic Viscosity

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Some preliminary viscosity measurements performed between 303 K and 323 K at atmospheric pressure for the suspensions W440 at 40 wt% and W630 at 30 wt%. A rotational rheometer with a plate-cone geometry (AR-G2 rheometer TA Instruments) employed.

declared instrument accuracy 5% tests performed on water within 2%

Dynamic Viscosity

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40 wt% 30 wt% T (K) m (Pa·s) mexp/ m water T (K) m (Pa·s) mexp/ mwater 313 0.01130 17.3 313 0.06717 102.9 323 0.00965 17.6 323 0.07656 140.0 3 wt% 5 wt% T (K) m (Pa·s) mexp/mwater T (K) m (Pa·s) mexp/mwater 303 0.000839 1.05 303 0.000915 1.15 323 0.000571 1.04 323 0.000656 1.20

Thermal conductivity

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Mouromtseff number

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A theoretical evaluation of the heat transfer behaviour performed by calculating the Mouromtseff number, applying the general expression, valid for single phase forced convection 𝑁𝑝 = 𝑏𝜍𝑐𝑑𝑞

𝑑

𝜈𝑒

For a fluid flowing in a fixed geometry at given velocity, the larger the Mouromtseff number the larger will be the heat transfer rate. For nanofluids 𝜍𝑜𝑔 =  · 𝜍𝑜𝑞 + 1 − · 𝜍𝑐𝑔 𝜍𝑜𝑔 · 𝑑𝑞𝑜𝑔 =  · 𝜍𝑜𝑞 · 𝑑𝑞𝑜𝑞 + 1 − · 𝜍𝑐𝑔· 𝑑𝑞𝑐𝑔

Mouromtseff number

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In case of internal laminar regime, the ratio is given simply by: 𝑁𝑝𝑜𝑔 𝑁𝑝𝑥 = 𝑜𝑔 𝑥 In case of internal turbulent flow, the Mo number is given by the following expression: 𝑁𝑝 = 0.67𝜍0.8𝑑𝑞

0.88

𝜈0.47 Monf/Mow 3 wt% 5 wt% T (K) Laminar flow Turbulent flow Laminar flow Turbulent flow 303 1.04 1.01 1.05 0.99 323 1.08 1.05 1.09 0.99

Conclusions

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• Under the European Project Cheap-GSHPs, several nanofluids will be tested as

possible secondary fluids in the heat pump-geothermal probe system.

• Here, two different commercial suspensions of fumed Al2O3 nanoparticles in H2O

were studied (at 30% or 40%).

• The less penalising in terms of viscosity (40%) was considered for additional dilution

(3% and 5%).

• Stability, thermal conductivity and dynamic viscosity were analysed.
• Mouromtseff numbers for nanofluids at 3% and 5% were calculated.
• 3 wt% seems to have some possibility to be applied, at least at temperatures higher

than 40-50°C.

• Additional measurements, in particular viscosity and heat transfer coefficient, are

necessary and will be performed in the near future.