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ABSTRACT
In this work, the performance of a forced convection solar air heater was evaluated using using three packed bed absorber plate configurations and compared with flat absorber plate. The phase change material (paraffin wax) was packed in the pin-fin, trianglular and circular absorber plate configurations. The performance parameters such as, outlet air temperature, thermo-hydraulic efficiency, exergy efficiency and pressure drop were predicted and compared. The results showed that the packed bed absorber plate configurations using paraffin wax have higher outler air temperature in the range of 2–5°C with 3–40% higher thermo-hydraulic efficiency and 2–20% higher exergy efficiency when compared to flat absorber plate. However, the packed bed absorver plates have higher pressure drop when compared to flat absorber plate.
Nomenclature
| A | = | Area (m2) |
| cp | = | Specific heat (J kg−1 K−1) |
| Dh | = | Diameter mean diameter (m) |
| = | Exergy (W) | |
| f | = | Friction coefficient |
| hc | = | Convection heat transfer coefficient (Wm−2K−1) |
| hr | = | Radiation heat transfer coefficient (Wm−2K−1) |
| hfg | = | Latent heat of paraffin wax (J kg−1K−1) |
| h | = | Specific enthalpy (J kg−1) |
| I | = | Intensity of radiation (W m−2) |
| k | = | Thermal conductivity (W m−1K−1) |
| K | = | Head loss factor |
| L1 | = | Length of the solar air heater (m) |
| L2 | = | Width of the solar air heater (m) |
| L3 | = | Depth of the solar air heater (m) |
| = | Mass flow rate of air (kg sec−1) | |
| mpw | = | Mass of paraffin wax (kg) |
| p | = | Pressure (bar) |
| Pflow | = | Pumping power (W) |
| Pblower | = | Blower power (W) |
| = | Amount of heat transfer (W) | |
| = | Energy incident on the solar air heater (W) | |
| R | = | Gas constant (J kg−1K−1) |
| Re | = | Reynolds number (--) |
| R2 | = | Correlation coefficient |
| s | = | Specific entropy (J kg−1K−1) |
| t | = | Time (sec) |
| T | = | Temperature (K) |
| U | = | Over all heat transfer coefficient (Wm−2K−1) |
| v | = | Velocity (m sec−1) |
| x | = | Thickness (m) |
Abbreviations
| ANN | = | Artificial neural networks |
| CGP | = | Pola-Ribiere Conjugate Gradient |
| COV | = | Coefficient of variance |
| FCSAH | = | Forced convection solar air heaters |
| LM | = | Lavenberg-Marguardt |
| MLFFN | = | Multi layer feed forward networks |
| RMS | = | Root mean square error |
| SCG | = | Scaled Conjugate Gradient |
Subscripts
| 0 | = | Dead state |
| a | = | Air |
| ab | = | Absorbed |
| amb | = | Ambient |
| ava | = | Available |
| b | = | Bottom |
| ch | = | Charging |
| des | = | Destruction |
| dis | = | Discharging |
| e | = | Edge |
| f | = | Fluid |
| fin-ch | = | Final charging |
| fin-dis | = | Final discharging |
| g | = | Glass |
| h | = | Hydraulic |
| i | = | Insulation |
| in-ch | = | Initial charging |
| in-dis | = | Initial discharging |
| loss | = | Heat loss |
| m | = | Mean |
| mel | = | Melting |
| p | = | Plate |
| pw | = | Paraffin Wax |
| pwl | = | Liquid paraffin wax |
| pws | = | Solid paraffin wax |
| r,p-g | = | Radiation heat exchange between plate and glass |
| r, g-a | = | Radiation heat exchange between glass and air |
| s | = | Stored |
| t | = | Top |
| th-hy | = | Thermo-hydraulic |
| u | = | Utilized |
| w | = | Wind |
Greek symbols
| = | Specific exergy (J kg−1) | |
| = | Transmissivity | |
| = | absorptivity | |
| = | Emissivity | |
| = | Stefan Boltzmann constant (5.68 × 10−8 W m−2K−4) | |
| = | Density (kg m−3) | |
| = | Efficiency (%) | |
| = | Pressure drop (N m−2) | |
| = | Total pressure drop (N m−2) | |
| = | Pressure drop across the channel (N m−2) | |
| = | Pressure drop at the entry (N m−2) | |
| = | Pressure drop in the orifice meter (N m−2) | |
| = | Difference in liquid column (m) | |
| = | Time during charging and discharging (sec) |