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ABSTRACT
The heat transfer characteristics of water-based Al2O3 nanofluid flowing through the annulus-side of a shell-and-double concentric tube heat exchanger (SDCTHEX) are investigated numerically. The temperature-dependent thermophysical properties of the nanofluid and pure water were used. The heat exchanger is analyzed considering conjugate heat transfer from hot oil flowing in the shell and the inner tube to the nanofluid flowing in the annulus formed between the concentric tubes. The overall performance is assessed based on the thermohydraulic performance. The overall thermohydraulic performance of the SDCTHEX, expressed in terms of the ratio of the overall heat transfer rate to the overall pressure drop with the nanofluid flowing in the annulus, is lower than that obtained with water when compared at constant hot fluid mass flow rates and at different inner tube diameters.
Nomenclature
| Symbols | = | |
| A | = | heat transfer area (m2) |
| cp | = | specific heat (J/kg. K) |
| d | = | diameter (m) |
| d2 | = | inside diameter of inner tube (m) |
| d1 | = | outside diameter of inner tube (m) |
| D2 | = | inside diameter of outer tube (m) |
| D1 | = | outside diameter of outer tube (m) |
| F | = | correction factor |
| f | = | friction factor |
| h | = | heat transfer coefficient (W/m2. K) |
| L | = | length (m) |
| k | = | turbulent kinetic energy (m2/s2) |
| m | = | mass flow rate (kg/s) |
| N | = | Number |
| ΔP | = | pressure drop (Pa) |
| Pr | = | Prandtl number |
| PT | = | total friction power expenditure (kW) |
| Re | = | Reynolds number |
| T | = | temperature (K) |
| ΔTm | = | logarithmic mean temperature difference (K) |
| U | = | overall heat transfer coefficient (W/m2. K) |
| V | = | velocity (m/s) |
| y* | = | dimensionless distance from wall |
| Greek symbols | = | |
| μ | = | dynamic viscosity (Pa.s) |
| μt | = | turbulent dynamic viscosity (Pa.s) |
| v | = | kinematic viscosity (m2/s) |
| Φ | = | heat transfer rate (W) |
| vt | = | turbulent kinematic viscosity (m2/s) |
| λ | = | thermal conductivity (W/m. K) |
| ρ | = | density (kg/m3) |
| σk | = | Prandtl number of k |
| σε | = | Prandtl number of ε |
| Γ | = | generalized diffusion coefficient |
| ε | = | dissipation rate of turbulence (m2/s3) in Eqs. (4), (5), and (7). Surface roughness in Eq. (17). |
| ϕ | = | nanoparticle volume concentration |
| Abbreviations | = | |
| SDCTHEX | = | shell-and-double concentric tube heat exchanger |
| MAX | = | Maximum |
| Subscripts | = | |
| av | = | Average |
| a | = | Annulus |
| b | = | Bulk |
| h | = | Hydraulic |
| i | = | Inner |
| in | = | Inlet |
| out | = | Outlet |
| p | = | nanoparticle |
| s | = | shell-side |
| w | = | wall-side |
Nomenclature
| Symbols | = | |
| A | = | heat transfer area (m2) |
| cp | = | specific heat (J/kg. K) |
| d | = | diameter (m) |
| d2 | = | inside diameter of inner tube (m) |
| d1 | = | outside diameter of inner tube (m) |
| D2 | = | inside diameter of outer tube (m) |
| D1 | = | outside diameter of outer tube (m) |
| F | = | correction factor |
| f | = | friction factor |
| h | = | heat transfer coefficient (W/m2. K) |
| L | = | length (m) |
| k | = | turbulent kinetic energy (m2/s2) |
| m | = | mass flow rate (kg/s) |
| N | = | Number |
| ΔP | = | pressure drop (Pa) |
| Pr | = | Prandtl number |
| PT | = | total friction power expenditure (kW) |
| Re | = | Reynolds number |
| T | = | temperature (K) |
| ΔTm | = | logarithmic mean temperature difference (K) |
| U | = | overall heat transfer coefficient (W/m2. K) |
| V | = | velocity (m/s) |
| y* | = | dimensionless distance from wall |
| Greek symbols | = | |
| μ | = | dynamic viscosity (Pa.s) |
| μt | = | turbulent dynamic viscosity (Pa.s) |
| v | = | kinematic viscosity (m2/s) |
| Φ | = | heat transfer rate (W) |
| vt | = | turbulent kinematic viscosity (m2/s) |
| λ | = | thermal conductivity (W/m. K) |
| ρ | = | density (kg/m3) |
| σk | = | Prandtl number of k |
| σε | = | Prandtl number of ε |
| Γ | = | generalized diffusion coefficient |
| ε | = | dissipation rate of turbulence (m2/s3) in Eqs. (4), (5), and (7). Surface roughness in Eq. (17). |
| ϕ | = | nanoparticle volume concentration |
| Abbreviations | = | |
| SDCTHEX | = | shell-and-double concentric tube heat exchanger |
| MAX | = | Maximum |
| Subscripts | = | |
| av | = | Average |
| a | = | Annulus |
| b | = | Bulk |
| h | = | Hydraulic |
| i | = | Inner |
| in | = | Inlet |
| out | = | Outlet |
| p | = | nanoparticle |
| s | = | shell-side |
| w | = | wall-side |
Acknowledgments
The authors are thankful to Mr. Mohd Nor Fakhzan Bin Mohd Kazim for the computational facility provided to carry out the whole numerical simulation works.