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ABSTRACT
Natural convection in an internally heated porous bed of height and diameter of 450 mm and 500 mm, respectively, and superposed with the fluid layer has been experimentally investigated. The onset of natural convection in the bed is indicated by change in the rate of temperature rise within the bed. An empirical model based on local Nusselt number and local Rayleigh number has been developed. A comparison of the present model with the models in literature is made to draw out the differences between the local heat transfer of large multidimensional beds and the average heat transfer of small beds.
Nomenclature
| Cp | = | specific heat capacity (J/kg°C) |
| D | = | Effective particle diameter (m) |
| D | = | Diameter (m) |
| G | = | Gravitational acceleration (m/s2) |
| H | = | Heat transfer coefficient (W/m2-k) |
| K | = | Thermal conductivity (W/m-K) |
| H | = | Height of bed (m) |
| Nu | = | Nusselt number |
| Q | = | Power per unit volume (W/m3) |
| Ra | = | Rayleigh number |
| V | = | Volume of bed (m3) |
| X | = | Distance from the bottom of the bed (m) |
| ΔT | = | Temperature difference between bottom and top of the bed (°C) |
Greek symbols
| α | = | Thermal diffusivity(m2/s) |
| β | = | Thermal expansion coefficient (1/K) |
| µ | = | Dynamic viscosity (Pa.s) |
| ν | = | Kinematic Viscosity (m2/s) |
| κ | = | Permeability (Darcy) |
| ρ | = | Density (kg/m3) |
| ϵ | = | Porosity |
| ƞ | = | Ratio of Fluid layer height to bed height |
Subscripts
| E | = | External |
| f | = | Fluid |
| s | = | Solid |
| I | = | Internal |
| T | = | Top |
| B | = | Bottom |
| m | = | Medium |
| x | = | local quantity at distance x from the bottom of the bed |