الفهرس 
REVIEW OF LITERATUREOnly 14 pages are availabe for public view
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Abstract
Solar drying of fruit has taken an important role in the conservation and drying industry in the last decade , because its sanitary and quality advantages in opposite to the traditional sun drying. The banana samples were pretreated by different methods to drying (blanching , steam blanching ).
The objectives of the present work were as follows:
- Study the change in the solar insolation and the air parameters during the drying period . in order to establish the efficiency of the solar energy collector used with the dryer.
- Evaluation of the drying behavior of the solar dried fruits compared with the oven dried samples in order to establish the suitable kinetic Model for the drying process.
- Evaluation of the efficiency of the solar dryer under different operating conditions.
- Evaluation of the effect of pretreatments on the chemical and physical characteristics of the tested fruit.
- The effect of pretreatment on the activity of the polyphenol oxidase enzyme in the tested samples.
The value of ambient relative humidity and air temperature has inverse correlation ambient conditions. The gradually increasing in the temperature of the drying chamber was effected by the increasing of ambient air temperature and solar collector air temperature because of increasing solar radiation unit it reached its peak and then to decrease .A decrease in weight during the day and an increase in the weight of the product at night may be observed by a certain amount ranging from 250-300 grams of lost weight during the day. This is evidence of the recovery of some of the moisture of the material lost during the drying process at night. At initial stages, the moisture removal per hour was higher and then started to decrease by increasing drying time. the moisture content decreases by increasing drying time and the dehydration process terminated when the moisture loss ceased.
Drying curve usually plots the drying rate versus drying time or moisture contents.
Three major stages of drying can be observed in the drying curve.
1. Transient early stage, during which the product is heating up (transient period)
2. Constant rate period, in which moisture is comparatively easy to remove
3. Falling rate period, in which moisture is bound or held within the solid matrix
Critical moisture content :The moisture content at the point when the drying period changes from a constant to a falling rate.
The drying behaviors of food materials depend on the porosity, homogeneity, and hygroscopic properties.
Hygroscopic food materials enter into the falling rate faster compared to non-hygroscopic food materials.
Based on the trends presented in this work, it can be concluded that temperature of the drying air, velocity of the drying air. play a key role in calculation of the rate at which materials dry. Automated measurement and data logging system with a suitable resolution and precision is important for monitoring drying process of sliced banana fruit.
The automated measurement system was able to measure and collect data all day and night through the drying period for the entire drying system. and was able to work as an effective analytical, troubleshooting, and cause/effect tools. By screening results and dissections, it was found that
1. Drying with natural convection, poor thermal insulation, temperature and relative humidity fluctuations caused a serious DROP in drying rate of sliced banana (-0.018) compared with drying with electrical thermal drier (-0.956 at 105 °C, -0.552 at 70 °C, and -0.513 at 50 °C).
2. For natural convection solar drier type it is so important to seal all the ambient air leakage into the drier to eliminate thermal losses and to force the right amount of the air to warmup and dehydrate the desired product, or to supply the solar drier with an air fan to work at forced convection heating principle.
3. To control day and night fluctuation of moisture removal at daytime and gained moisture at night by according to the experimental conditions, the solar drier must be equipped by an air-lock gate at the drier entrance. The air-lock gate can be controlled by suitable and simple mechanism which can respond to the change of air relative humidity and speed measurements.
4. The recommended drier air-lock mechanism, can control the drier temperature by changing the rate of heat exchange between the product and the hot air for appropriate treatment of thermal sensitive products.
5. It is usually best to have the air flowing across the surface of the material rather than coming in from the bottom of the drier and pass upwards through the material being dried. This ensures better air distribution and better exposure of the food to the drying air.
One problem with drying bananas is that they tend to stick to the wire mesh racks in the drier. For this reason, it is best to use a silicon mesh on which to place the banana slices