Design, fabrication and testing of a small-scale dryer for flowers and foliage

An efficient heated air-dryer with air recirculation was designed and developed to address the problems in the dried flowers and foliage industry. Laboratory drying tests of chrysanthemums and roses using an existing heated-air laboratory dryer was conducted to gather bench mark information necessary for the conceptualization of the dryer design. Results indicated the potential to produce good quality dried roses (at hanging position) and a drying rate of 5.61 g water/min which was used in the design calculations. A 30 dozens capacity was designed and conceptualized and then fabricated. A blower volume capacity of 0.077 cum/s and a heated power requirement of 6.74 KW was used as design information. Several types of flowers and foliage (chrysanthemums, roses, bougainvilla and pachystacys for flowers and fish tail, kamuning, palmera, assorted ferns, San Francisco, Chinese holly, song of India and song of Korea for foliage) were tested using the prototypes dryer. The average plenum temperature was 125 deg C. Temperature distribution during continuous drying was not significantly different at 5% level, while temperature distribution during all drying tests (100 deg C, 90 deg C and 80 deg C) with 30-minutes interval weighing of samples, significantly differ at 5% level of significance. Drying temperature of 80 deg C had the highest total power consumption (296.61 kWh) while drying temperature of 100 deg C had the lowest (167.76 kWh). Percent recirculation and drying capacity were highest at 100 deg C (92.99% and 0.348 kg H2O/hr, respectively) and lowest at 80 deg C (90.37% and 0.259 kg H2O/hr, respectively. The dryer efficiency was highest at 100 deg C (68.2%). Heater efficiency was low due to convection and radiation losses. The overall heat utilization efficiency (HUE ff), however, was highest at 100 deg C (21.96%). Roses, bougainvilla, pachystacys and ferns were excellent materials for heated air drying. No differences with respect to visual quality rating of the materials were observed in all drying chambers used. The stable pigments for high temperature drying (80 deg C - 100 deg C) were the yellow pigments in yellow roses and pachystacys, magenta/crimson pigments in red roses, pink pigments in bougainvilla and chlorophylls green pigments in ferns and `kamuning'. In terms of drying capacity, power consumption, percent recirculation, HUE ff and quality of dried plant materials, a drying temperature of 100 deg C is economical and recommended for use. A return of investment (RO1) of 28.9% and a payback period of 3.85 years were calculated making a small-scale dried roses business economically feasible