Test of Solar Drying Performance – My Solar Dryer

The performance of the solar dryer was evaluated from June 2005 through March 2006. During these ten months, all relevant weather conditions were experienced. These include rain, cloud cover and sunlight under different angles azimuth. Serial tests were conducted for both loaded and unloaded conditions. For the loaded conditions, the evaluation were made for drying of fresh red chillies, unshelled groundnuts, unshelled soybean, shelled soybean, coffee cherry, and unshelled candle nuts.

The tests were also conducted with a variation of energy sources for drying; solar energy, burning of biomass (fire wood), and a combination of solar energy and biomass. Burning of biomass was only conducted at night and during low solar radiation, while solar energy and/or combination with stored heat from biomass burning were used during daytime.

In addition to the natural convection mode, forced convection tests were carried out to investigate the performance of the solar collector. For this purpose, a centrifugal blower was applied to generate air at a certain mass flow rate. The suction blower, which was set at the left side ventilation of the dryer, sucked the air out of the chamber. The air mass flow rate was measured with an anemometer.

6.1 Instrumentation

The measured parameters were temperature, moisture content level, solar radiation, relative humidity, mass of products to be dried, mass of fuel wood to be burnt, wind speed, and airflow rate through the dryer. A combination of hand-held instruments and sensors connected to a data logger (DataTaker 605) were used to record the measurements. A photograph of the data logger is shown in Figure 6.1. Temperature and solar radiation were recorded every 10 minutes. Solar radiation was measured with a pyranometer (Kipp & Zonen CM 3) with a sensitivity of 16.51  10^-6 V/Wm^-2 and an accuracy of  5%. A photograph of the pyranometer used is shown in Figure 6.2.

The relative humidity was calculated from measured wet-bulb and dry bulb temperatures using a psychometric chart. Air velocities were measured with a hot-wire air anemometer (Testo 405-V1) with an accuracy of  2.5%. Figure 6.3 shows a photograph of the hot-wire anemometer.

Figure 6.2 A photograph of the pyranometer.

The mass of the dried product was measured with an electronic balance (Sartorius AG BP 3100S) with an accuracy of 0.01 g. A photograph of the balance is shown in Figure 6.4. The biomass of fire wood was measured with an analog balance (TS 2777047) with an accuracy of 0.1 kg. The dry mass of the dried samples were determined using the air-oven method (Hall, 1980).

Figure 6 4 A photograph of the balance used to measure the mass of dried products.

Figure 6.4 A photograph of the balance used to measure the mass of dried products