Thermal performance analysis of MWCNT-based capric acid PCM thermal energy storage system
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Thermal performance analysis of MWCNT‑based capric acid PCM thermal energy storage system Chandrmani Yadav1 · Rashmi Rekha Sahoo1 Received: 17 June 2019 / Accepted: 12 August 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract Effect of natural convection during the melting process of capric acid-based multi-walled carbon nanotube (MWCNT/CA) thermal energy storage system has been investigated experimentally. The temperature variations of phase change material were measured during the charging process. Effects of Stefan number and Fourier number on Nusselt number, as well as energy and exergy of the storage medium for different vol. fractions of MWCNT/CA-based phase change material, have been analysed and compared during charging process. Furthermore, the present work also extends to evaluate the thermophysical properties, i.e. thermal conductivity and specific heat capacity in liquid and solid phase of MWCNT/CA-based PCM by T-history method. Results revealed that the melting time for 0.02% vol. fraction of MWCNT/CA-based PCM is 66.66% lower compared to pure capric acid PCM. The thermal conductivity and specific heat capacity of 0.02% MWCNT/ CA-based PCM obtained higher value than other samples in liquid and solid phases. Rayleigh number justified that natural convection heating process occurred within the TES system. Furthermore, the energy and exergy of 0.02% vol. fractionbased MWCNT/CA storage medium achieved 61.9% and 70.92% maximum values than pure CA phase change material, respectively. Therefore, 0.02% vol. fraction of MWCNT/CA could be suitable nanoenhanced phase change material for thermal energy storage systems. Keywords Energy · Exergy · MWCNT · Charging time · Rayleigh number · Nusselt number List of symbols f Liquid fraction g Gravitational acceleration (m s−2) hW Heat transfer coefficient (W m−2 K−1) k Thermal conductivity (W m−1 K−1) l Height (m) m Mass (kg) t Time (s) tf Solidification time (s) A Area (m2) A1 Integral area during the liquid phase of PCM A2 Integral area during the liquid–solid phase of PCM A3 Integral area during the solid phase of PCM Cp Specific heat capacity (kJ kg−1 K−1) D Equivalent diameter (m) H Enthalpy * Rashmi Rekha Sahoo [email protected] 1
Department of Mechanical Engineering, Indian Institute of Technology (BHU), Varanasi 221005, India
LH Latent heat of fusion (kJ kg−1) Nu Nusselt number P Pressure (kPa) Pr Prandtl number R Radius of a glass tube (m) Ra Rayleigh number S Entropy (W K−1) Ste Stefan number T Temperature (K) Tl Temperature of liquid PCM (K) Tm Phase change temperature (K) Ts Surrounding temperature (K) T∞ Ambient temperature (K) U Internal energy (W) V Volume (m3) W1 Integral area of water corresponding to the liquid PCM W2 Integral area of water corresponding to the liquid–solid PCM Greek letters α Thermal diffusivity (m2 s−1) ρ Density (kg m−3)
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β Expansion coefficient (K−1) μ Dynamic viscosity (Pa s) Ø Vol. fraction of MWCNTs Δ Change Subscripts l Liquid m Melting o
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