Methods
A tray drying system with a hybrid heat source was designed and constructed as
shown in Figure 1. Solar energy, electric heating and infrared radiation energy were the
heat sources for drying seafood raw materials in this work. In this experiment, the 3
stainless steel trays of boiled shrimps (1.0 kg) were dried using 2 drying strategies
illustrated in Figure 2. Two drying strategies were carried out by using 1-stage drying
with electric heating (hot air) and two-stage drying with combined electric heating and
infrared heating. More details are given in the drying procedure.
The drying room has volume of 60 × 80 × 158.5 cm3. The drying room was
made of stainless steel and the wall inside the drying room was insulated by a
microfiber sheet 5 cm thick. The electric heater was made from a fin electric heating rod
1,000 × 10 W and an infrared rod of 500 × 3 W was used for these experiments while
solar heating was provided by a solar collector. The dimensions of the solar collector
were 32.5 × 133 × 240 cm3 and the top of the collector was covered by 0.5 cm thick
Perspex glass. The solar collector was placed at 14 degree from horizontal for taking
direct solar radiation. A forward-blade blower driven by a 1 HP AC motor was used for
hot air convection. Hot air after drying was released to the surroundings using an air
outlet pipe but could be feed back into the drying room using a recycle pipe.
The drying temperature, inlet and outlet temperature and shrimp temperature in
each tray were measured using a K-type thermocouple connected to a data logger
(Supcon) with an accuracy of ± 0.5 °C while the surrounding temperature (wet-bulb and
dry-bulb) was also continuously recorded. Inlet air flow at the entrance tube was
measured by a hot wire anemometer (Digicon model DA-45) with an accuracy of ± 0.01
m/s. Moisture loss was recorded hourly during the drying time. The weighing of shrimp
was done on an electronic balance with an accuracy of ± 0.1 g. Drying was continued
until the sample reached the desired final moisture level.