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Concentrating Solar Energy (CSP) |
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Solar Thermal Energy Storage (TES) using Nanofluids
Objective: In this study we perform experiments and numerical simulations to elucidate the transport mechanisms responsible for thermal property transfer enhancement (e.g., anomalous enhancement of specific heat capacity, thermal conductivity, and viscosity) of nanofluids.
Problem Definition: Colloidal solvents containing dispersed nanometer (10nm ~ 1 micron) sized particles are categorized as nanofluids. Several programs sponsored by DOE Solar Energy Technology Program (SOE-SETP) utilize Concentrated Solar Power (CSP) for harnessing solar thermal energy for conversion to electricity using Rankine or Sterling cycles. Thermal Energy Storage (TES) techniques are currently under development at DOE to enhance the Carnot efficiency of Solar Thermal Power Plants by enhancing the thermophysical properties of Heat Transfer Fluid (HTF), Thermal Energy Storage (TES) materials and Phase Change Materials (PCM). It is predicted that raising the storage temperatures to 600C (from the current practice of 400C) can reduce the cost of solar energy production by 50%. However, the TES, HTF and PCM available to operate at these extremely high temperatures suffer from very poor thermo-physical properties. Typical materials under investigation in the CSP program include alkali metal salt eutectics (e.g., nitrates, chlorides and carbonates of sodium, potassium, lithium, calcium, etc.). In our research investigations we have observed anomalous enhancement of specific heat capacity values of these eutectics. Using CNT at 0.05-0.5% weight concentrations the specific heat was enhanced by 115%. Using silica nanoparticles at ~1-1.5% weight concentrations the specific heat of these eutectics was enhanced by ~125%. We have also observed anomalous enhancement in thermal diffusivity and thermal conductivity of these nano-composites by 15-40%. Further investigations are currently in progress as a part of the Phase II and Phase III goals of the DOE CSP project.
General Procedure: The properties of the nanofluids/ nano-composties were found to be very sensitive to even minute variations in the synthesis procedure (or protocols). The change in morphology of the nano-compostes was investigated using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The nano-fluid properties were measured using rheometry for viscosity, Differential Scanning Calorimetry (DSC) for specific heat and Laser Flash Apparatus for thermal diffusivity (to derive the values of thermal conductivity).
Conclusion and Future Direction: It was observed that the viscosity is enhanced considerably on adding nanoparticles and the fluid characteristics change from Newtonian to Non-Newtonian behavior. The cost of solar thermal power can be reduced by 50-60% due to observed enhancements in specific heat of the molten-salt-eutectic nanofluid in excess of 100% (at 0.01-1.5% loading of the nanoparticles by mass). SEM / TEM and EDX measurements show that the addition of the nano-particles results in phase transformation within the eutectic which in turn leads to the formation of a percolation network. Currently we are performing experiments with several combinations of nanofluids.
Graduate Students: Donghyun Shin, Byeongnam Jo, and Seunghwan Jung
Internal Collaborator: Dr. Michael Schuller (SERC) and Dr. Fred Best (Nuclear Engineering Dept., Texas A&M University)
External Collaborator: NREL and ANL
Project funded by: DOE-SETP
Publications:
- I.C. Nelson, D. Banerjee, and P. Rengasamy, "Flow Loop Experiments Using Polyalphaolefin Nanofluids," AIAA Journal of Thermophysics and Heat Transfer, Vol. 23, No. 4, pp.752-761, doi: 10.2514/1.31033, October-December, 2009.
- D. Shin and D. Banerjee, "Enhanced specific heat of molten salt based SiO2 nanofluid for solar thermal energy storage application," ASME Journal of Heat Transfer (accepted, June, 2010).
- D. Shin and D. Banerjee, "Investigation of Nanofluids for Solar Thermal Storage Applications," Paper No. ES2009-90465, ASME Energy Sustainability Conference, July 20-25, San Francisco, CA, 2009.
- D. Shin and D. Banerjee, "Enhanced Thermal Properties of PCM Based Nanofluid For Solar Thermal Energy Storage," Paper No. ES2010-90293, ASME 4th International Conference on Energy Sustainability, May 17-22, Phoenix, AZ, 2010.
- H. Kwak, D. Shin, and D. Banerjee, "Enhanced Sensible Heat Capacity of Molten Salt Based Nanofluid For Solar Thermal Energy Storage Application," Paper No. ES2010-90295, ASME 4th International Conference on Energy Sustainability, May 17-22, Phoenix, AZ, 2010.
- B. Jo and D. Banerjee, "Study of High Temperature Nanofluids using Carbon Nanotubes (CNT) for Solar Thermal Storage Applications," Paper No. ES2010-90299, ASME 4th International Conference on Energy Sustainability, May 17-22, Phoenix, AZ, 2010.
- D. Shin, B. Jo, H. Kwak, and D. Banerjee, "Investigation of High Temperature Nanofluids for Solar Thermal Power Conversion and Storage Applications," Paper No. IHTC14-23296, 14th International Heat Transfer Conference, August 8-13, Washington, D.C., 2010.
- N. Singh and D. Banerjee, "Investigation of Thermal Interfacial Resistance on Nano-Structures Using Molecular Dynamics," Paper No. IHTC14-22930, 14th International Heat Transfer Conference, August 8-13, Washington, D.C., 2010.
- S. Jung, B. Jo, D. Shin, and D. Banerjee, "Experimental Validation of a Simple Analytical Model for Specific Heat Capacity of Aqueous Nanofluids," Paper No. SAE- 10PSC-0134, SAE Power Systems Conference, November 2-4, Fort Worth, Texas, 2010.
- D. Shin and D. Banerjee, "Enhanced specific heat capacity of molten salt-metal oxide nanofluid as heat transfer fluid for solar thermal applications," Paper No. SAE-10PSC-0136, SAE Power Systems Conference, November 2-4, Fort Worth, Texas, 2010.
- N. Singh and D. Banerjee, "Thermal Analysis of Carbon Nanotubes suspended in PAO Mixtures," Paper No. SAE-10PSC-0137, SAE Power Systems Conference, November 2-4, Fort Worth, Texas, 2010.
- S. Jung and D. Banerjee, "A simple analytical model for specific heat of nanofluid with tube shaped and disc shaped nanoparticles," Paper No. AJTEC2011-44372, ASME/JSME 8th Thermal Engineering Joint Conference, Honolulu, Hawaii, March 13-17, 2011 (submitted).
- B. Jo and D. Banerjee, "Interfacial Thermal Resistance between a Carbon Nanoparticle and Molten Salt Eutectic: Effect of material properties, particle shapes and sizes," Paper No. AJTEC2011-44373, ASME/JSME 8th Thermal Engineering Joint Conference, Honolulu, Hawaii, March 13-17, 2011 (submitted).
- D. Shin and D. Banerjee, "Experimental Investigation of molten salt nanofluid for solar thermal energy application," Paper No. AJTEC2011-44375, ASME/JSME 8th Thermal Engineering Joint Conference, Honolulu, Hawaii, March 13-17, 2011 (submitted).
Images:
Figure 1. Variation of specific heat of pure eutectic samples and nanofluid samples with temperature obtained from DSC measurements. The specific heat of the eutectic of lithium carbonate and potassium carbonate (62:38) is enhanced by19~24% on addition of SiO2 nanoparticles (at 1% by weight).
Figure 2. Transmission Electron Micrograph (TEM) of silica nanoparticle after mixing with pure eutectic and before thermo-cycling in the DSC instrument. The nominal size of the nanoparticle in the figure is ~35 nm.