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ABSTRACT
In this communication, a new design of solar-energy-based water distillation cum drying unit with parabolic reflector has been designed, fabricated, and tested. Bitter gourd and potato slices are chosen as a drying commodity. Thermal performance of the developed system has been evaluated based on the experimental results and using linear regression analysis. Heat transfer coefficients (convective, evaporative, and radiative) for solar distillation system have been observed to be 2.48–4.09, 13.25–52.38, and 8.75–9.66 W/m2°C, respectively. Overall thermal efficiency and exergy efficiency for the distillation system has been found to be 18.77% and 1.2%, respectively. The convective heat transfer coefficient for potato slices are observed higher for initial hours and decreases as the day progresses. The average convective heat transfer coefficients for bitter gourd and potato slices have been observed as 2.18 and 5.04 W/m2°C, respectively. Experimental error in terms of percent uncertainty for bitter gourd and potato slices are found to be 42.93% and 37.06%, respectively. The present design of solar distillation and drying in a single unit could be beneficial for the development of remote, arid, and rural areas.
Nomenclature
| Ad | = | Area of drying tray, m2 |
| Ab | = | Area of basin tray, m2 |
| C | = | Experimental constant |
| Cv | = | Specific heat of humid air, J/kg°C |
| g | = | Acceleration due to gravity, m/s2 |
| Gr | = | Grash of number = βgXc3ρvΔT/μv |
| hc | = | Convective heat transfer coefficient, W/m2°C |
| hc,av | = | Average convective heat transfer coefficient, W/m2°C |
| hew | = | Evaporative heat transfer coefficient, W/m2°C |
| hew,av | = | Average evaporative heat transfer coefficient, W/m2°C |
| hrw | = | Radiative heat transfer coefficient, W/m2°C |
| Kv | = | Thermal conductivity of humid air, W/m°C |
| mei | = | Mass evaporated, kg |
| mew | = | Mass of distillate collected, kg |
| med | = | Mass of moisture evaporated from drying commodity, kg |
| n | = | Experimental constant |
| Nu | = | Nusselt number = hcXc/Kv |
| Pr | = | Prandtl number = μvCv/Kv |
| P(T) | = | Partial vapor pressure at temperature T, N/m2 |
| Pw | = | Partial saturated vapor pressure at water temperature, N/m2 |
| Pci | = | Partial saturated vapor pressure at condensing cover temperature, N/m2 |
| Qe | = | Rate of heat utilized to evaporate moisture, J/m2s |
| Tci | = | Inner glasses cover temperature, °C |
| Tv | = | Above water surface temperature, °C |
| Tw | = | Water temperature, °C |
| Tb/Tp | = | Temperature of bitter gourd/potato slice surface, °C |
| Te | = | Temperature just above the drying commodity surface, °C |
| Ta | = | Ambient temperature, °C |
| Ts | = | Sun temperature, °C |
| Xc | = | Characteristic dimension, m |
| ΔT | = | Effective temperature difference, °C |
| t | = | Time, sec |
| N | = | Number of observation in each set |
| No | = | Number of sets |
| I (t) | = | Solar intensity per hour, W/m2 |
| = | Exergy input |
Greek symbols
| β | = | Coefficient of volumetric expansion, K−1 |
| γ | = | Relative humidity, % |
| λi | = | Latent heat of vaporization, J/kg |
| λb/λb | = | Latent heat of vaporization for bitter gourd/potato slices drying, J/kg |
| λw | = | Latent heat of vaporization for distillation, J/kg |
| μv | = | Dynamic viscosity of humid air, N s/m2 |
| ρv | = | Density of humid air, kg/m3 |
| εeff | = | Effective emissivity |
| εω | = | Emissivity of water |
| εg | = | Emissivity of glass |
| σs | = | Stefan--Boltzmann constant |
| ηt | = | Overall thermal efficiency of still |