Performance Evaluation of Solar Tunnel Dryer for Drying of Garlic

This paper presents dying efficiency and performance of the solar tunnel dryer for drying of garlic. The dryer is a tunnel like semi-cylindrical in shape, poly house made up of UV-stabilized polyethylene sheet. The capacity is large enough that it can be used to dry 400 kg of garlic under controlled environmental conditions. The temperature inside the dryer was always higher than the ambient and the variation varied from8-30 oC. Initial moisture content of garlic was reduced from 66 % (w.b.) to about 9 % (w.b.) in 9 days which is considered to be a safe level. During the drying process the average thermal efficiency of the drier was estimated to be about 13.45 %.Drying time was considerably reduced with the use of a solar tunnel drier and pressing of the sample. Also, the final dried garlic was found to be good in terms of quality and sensory evaluation shows that it is highly acceptable. Article History Received: 4 August 2017 Accepted: 27 September 2017

introduction India is one of the largest producers of spices in the world.Garlic (Allium sativum) is used as a spice throughout India.It is also important foreign exchange earner for India.It has high nutritive it is rich in proteins, phosphorous, potassium, calcium, magnesium and carbohydrates.Drying of garlic is very essential to remove excess moisture from the outer skin and neck to reduce storage rotand its shelf life also it's easy to use in dried form.Drying of agricultural produce is the oldest and still the most practiced preservation method.Demand of dried products is increasing all over the world.Dried products serve as an alternative to fresh fruits and vegetables and requires less maintenance during storage 1 also drying is an environmentally friendly and economically viable technique 2 .In India drying of fruits and vegetables is generally done by open sun drying.The initial moisture content of the agricultural products is the main factor behind the post harvest losses and open sun drying is the oldest technique that preserve the products by reducing the moisture contents.The reduced moisture content of agricultural products not only slow down the deterioration, but also increases the safe storage period.The main drawback behind the open sun drying is that the products remain unprotected from the environmental conditions like rain, dust, dirt, and infestation by birds and animals.All these factors affect the quality of food and sometimes the quality is degraded to an extent that it becomes inedible.The loss in quality of dried products affect market value and consumer acceptance 3,4,5 .The solution to all these problems is use of tunnel dryers based on solar energy.These kind of dryers uses only solar energy and does not require any other source of energy also temperature inside the dryer is more than the atmosphere.Therefore, solar tunnel dryer is an alternative for rural people to reduce the storage losses by drying their produce in a controlled and better environment.Also, the dried product is free from any dust particles and highly acceptable by consumers 5,6 .Other advantages of solar tunnel dryers are substantial reduction of drying time and physical quality standards are maintained also solar tunnel dryers are easy to operate and maintain 7 .This paper presents results of performance of the solar tunnel dryer for drying of garlic.

Material and Methods
The experiment was carried out under the meteorological conditions of Hisar (latitude of10.39ºN;longitude of 77.03ºE) in India during the month of June from 10.00 a.m. to 16.00 a.m..

Solar Tunnel Dryer
A low cost Solar Tunnel Dryer of different capacity for drying of fruits & vegetables and other agro industrial products was developed at MPUAT, Udaipur.Realizing the importance and use for the upliftment of farmers similar dryer with a floor area of 10m × 3.75m was installed at Hisar to evaluate its performance in ambient conditions of Haryana.The solar tunnel dryer is framed using UV-stabilized polythene sheet of height 1.98 meter.The orientation of tunnel solar dryer is in the east -west direction to use maximum sunlight.instrumentation Six thermometers were fixed at different locations inside the drier to measure the temperature as shown in figure 1.A solar intensity meter was used to measure the instantaneous solar radiation.A digital electronic balance was used to weigh the samples.

Experimental Procedure Garlic
Freshly harvested 400 kg of garlic was purchased from the university farm of CCSHAU, Hisar during the month of June.The garlic was then cleaned manually and unwanted material like straw and dust were removed.Weight left after cleaning was 270 kg then the bulbs were broken into cloves using garlic bulb breaking machine, then the initial weight of the total sample was recorded and it was found 255 kg.The loose 'papery shell" is removed by aspiration.The whole was divided into four parts.Two parts were frozen in deep freezer for two days and the remaining two parts were kept at room temperature after this one frozen part and one at normal temperature were pressed using the garlic pressing machine.Initial weight and initial moisture content of all the samples were recorded then the samples were used for drying at full load conditions in solar tunnel dryer.The whole process of sample preparation of garlic for drying is presented in the Figure 2

Data Analysis Determination of Moisture Content
To find out the initial moisture content about 12g of samples were taken in a oven and the moisture content on wet basis (wb) was calculated using the Eq.( 1).Initial (mi) and final mass (mf) at time (t) of samples were recorded using electronic balance and repeated after every 1 h interval till the end of drying on oven.

Load Test of Solar Tunnel Dryer For Garlic Drying
Garlic is a traditional crop used as spices in India.It has a lot of health benefits and generally available as a fresh product in the local market, but nowadays demand of garlic in powder form is increasing day by day 9 .During drying of garlic the variation of ambient temperature, temperature inside the dryer and solar radiation intensity with respect to time is shown in Figure4.2.The maximum temperature inside the solar tunnel dryer in upper and lower tray was recorded to be 64 ºC and 40 ºC during the period of drying.The average temperature inside the dryer was 55 ºC while the average ambient temperature was 36 ºC.Temperature attained inside the drier was good for drying.A similar study presents that for drying of green olives temperature between 50-70 ºC obtained inside the dryer was good enough for drying 8 .

Drying Time required for Garlic Under Std
For experiment with load, 245 kg of garlic having initial moisture content 63% to 70% (w.b) was divided into four parts and then after giving treatments the  The fig. 3 shows variation of moisture content reduction % (w.b) on different days during the month of June.During this period solar tunnel dryer was loaded with garlic.The drying was carried out from 63%-72% (w.b) to 9% -10% (w.b) and was completed in eight to ten days.
Fig. 4 shows moisture content reduction per day and drying rate variation per day.It was observed that drying rate was higher during the starting days of drying as compared to the end days.Following regression equations were developed and shows the relationship between drying rate and moisture content of the product during drying.

Thermal Efficiency of Solar Tunnel Dryer
The overall thermal efficiency of STD was calculated by using the formula as given in section 3.3.During the first day of drying the dryer had higher efficiency and it reduced during the following days.This was mainly because at the initial stage of drying, products had higher moisture content and a higher amount of water was evaporated.During drying of garlic average thermal efficiency was 13.45%.

organoleptic Evaluation
Sensory quality was evaluated for different parameters, i.e. color, appearance, flavor, odor, taste and overall acceptability.The score ranged from 1 to 9 which represented "Like extremely" to "Dislike extremely" The dried samples were tested by 50 judges.The mean sensory score of dried garlic powder has been shown in Fig 5.

Conclusion
The temperature inside the dryer ranges from 26 to 64ºC during the drying period, which was sufficient for drying of garlic in 9 days.This range is considered as the best temperature for drying of agricultural produce ass temperature above 65 ºC is not appropriate for drying 11 .The final dried garlic powder was free from impurities like dust, etc. and was found to be good in terms of color and aroma.The dryer can be easily constructed and used for large scale drying as the results are satisfactory.
in the form of flow diagram.

Table 1 :
Fig. 2 Flow diagram of sample preparation of garlicThe solar intensity, ambient and temperature inside solar tunnel dryer were measured every two hour interval till the end of drying.After attaining safe moisture the products were removed from the dryer.Fig3 (a) shows solar tunnel dryer at full load conditions and (b) garlic pressing machine.

Fig. 2 :
Fig. 2: Flow diagram of sample preparation of garlic

Fig 3 :Fig. 4 :
Fig 3: solar tunnel dryer at full load conditions with garlic and garlic pressing machine.

Fig. 5 :
Fig. 5: Average temperature and insolation variation with time during drying of garlic.