Characterization of nanofluids formed by fumed Al 2 O 3 in water for geothermal applications

Transcription

1 Characterization of nanofluids formed by fumed Al 2 O 3 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 July 11-14, 2016

2 Outline Background Experimental apparatus and procedure Experimental results Conclusions 2

3 European Project Cheap-GSHPs 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 of ownership (investment and operating costs), increase the safety of shallow geothermal systems during installation and operation and increase the awareness of this technology throughout Europe. 3

4 European Project Cheap-GSHPs 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 of 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. 4

5 European Project Cheap-GSHPs To reduce the total cost of shallow geothermal systems by %, 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. 5

6 Demo cases 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 6

7 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. 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 Fumed alumina (Al 2 O 3 ) in water or water and propylene glycol mixtures Improve the heat transfer and the overall efficiency of the geothermal heat pumps (GHPs) systems 7

8 Fumed Al 2 O 3 in H 2 O Amongst others, first tests have been performed Two different commercial suspensions Fumed Al 2 O 3 nanoparticles in H 2 O 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 8

9 Stability characterization A Zetasizer Nano ZS (Malvern), based on the Dynamic Light Scattering (DLS), used to analyse the average dimension of the nanoparticles in solution. 136 nm 149 nm Zeta potential 49.6 mv for 30 wt% 47.5 mv for 40 wt% STABLE FLUIDS 9

10 Stability characterization STABLE FLUIDS 10

11 Thermal Conductivity 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% 11

12 Thermal Conductivity 12

13 Dynamic Viscosity 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% 13

14 Dynamic Viscosity T (K) 40 wt% 30 wt% m (Pa s) m exp / m water T (K) m (Pa s) m exp / m water wt% 5 wt% T m T m m (K) (Pa s) exp /m water (K) (Pa s) m exp /m water

15 Thermal conductivity 15

16 Mouromtseff number A theoretical evaluation of the heat transfer behaviour performed by calculating the Mouromtseff number, applying the general expression, valid for single phase forced convection Mo = a ρ b c p c μ d 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 ρ nf = ρ np + 1 ρ bf ρ nf c pnf = ρ np c pnp + 1 ρ bf c pbf 16

17 Mouromtseff number In case of internal laminar regime, the ratio is given simply by: Mo nf Mo w = nf w In case of internal turbulent flow, the Mo number is given by the following expression: Mo = 0.67 ρ 0.8 c p 0.88 μ 0.47 T (K) Laminar flow Mo nf /Mo w 3 wt% 5 wt% Turbulent flow Laminar flow Turbulent flow

18 Conclusions 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 Al 2 O 3 were studied (at 30% or 40%). nanoparticles in H 2 O 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 C. Additional measurements, in particular viscosity and heat transfer coefficient, are necessary and will be performed in the near future. 18