Investigation of melting of nanoparticle-enhanced phase change materials (NePCMs) in a shell-and-tube heat exchanger wit
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ORIGINAL
Investigation of melting of nanoparticle-enhanced phase change materials (NePCMs) in a shell-and-tube heat exchanger with longitudinal fins Hamid Masoumi 1 & Ramin Haghighi Khoshkhoo 1 Received: 22 April 2020 / Accepted: 13 October 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Latent heat storage units are considered as an effective solution for the mismatch problem between energy consumption and energy supply when utilizing solar energy. However, the low thermal conductivity of the current phase change materials (PCMs) is regarded as their main drawback. The present study used dispersing nanoparticles in PCM and installing longitudinal fins on the inner tube simultaneously to enhance the melting rate of PCM in a horizontal shell-and-tube heat exchanger. Different compositions of stearic acid (SA) and titanium dioxide TiO2-NPs were employed as nano-encapsulated PCMs as well. The results demonstrated that installing fins have a significant effect on the melting rate of PCM and can improve the melting rate by 68%. Although adding 0.39 wt% TiO2-NPs to PCM enhanced its thermal conductivity of SA by 7 and 15% in liquid and solid phases, respectively, its effect on improving the melting rate of PCM was less than 4%, which is related to the weakening of the natural convection flows because of the increased viscosity. Nomenclature T temperature (°C or K) f liquid fraction L latent heat of PCM (J/kg) SH source term in energy equation Sv source term in momentum equation H total enthalpy (J/kg) h heat transfer coefficient or enthalpy (W/m2·K or J/kg) k thermal conductivity of PCM (W/m °C) t time (s or min) Cp specific heat at constant pressure (J/kg °C) Highlights • Simultaneously are studied effects of fins and nanoparticles on melting of PCM. • Different composites of TiO2 nanoparticles and stearic acid are studied as NePCM. • Thermal behavior of a shell-and-tube energy storage system using PCM is studied. • Effect of increasing the HTF temperature on melting PCM is examined. • Installing fins is more effective than adding nanoparticles on PCM melting rates. * Ramin Haghighi Khoshkhoo [email protected] 1
Faculty of Mechanical and Energy Engineering, Shahid Beheshti University, Tehran, Iran
l r ∀ A Dh V Hh
length of heat exchanger (m) radius of inner tube (m) total volume of PCM container (m3) heat transfer surface (m2) hydraulic diameter (m) velocity (m/s) hypothetical height of the liquid on the inner tube (m) P pressure (Pa) g gravitational acceleration (m/s2) Amushy mushy zone constant (kg/m3·s) h surface-averaged heat transfer coefficient (W/m2·K) Nu surface-averaged Nusselt number M mass (kg) x characteristic length (m) Q absorbed thermal energy by PCM (j) Δt time step (s) ˙ E Q surface-averaged heat transfer rate (w) D ˙Q time-averaged heat transfer rate (w) Nu time -averaged Nusselt number Dimensionless parameters Fo Fourier number αt=D2h Rax Rayleigh number gβ(THTF − Tm)x3/να Ste Stefan number Cp, l(THTF − Tm)/L Nu Nusselt number hDh/kl AR heat transfer surface Ratio
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