International Communications in Heat and Mass Transfer
Design of a new solar dryer system with swirling flow for drying seeded grape☆
Introduction
Conservation of agricultural products is important, as it has an important role in human beings' nutrition; it is known that the food to be dried is subjected to some loss from growing to consumption. There are a lot of methods applied for conservation of agricultural foods, increasing their economical life span and providing the amount of nutritional items at maximum level. These methods are: pasteurizing, cooling, controlling the atmosphere, chemical applications, beta and gamma rays and drying.
Among these methods drying is used mostly and is more economical [1]. Drying is defined as the process of removing the moisture inside the foods and its importance is gradually increasing.
The place of drying among conservation methods of food can be examined from various points. Above all, as water existing inside the food is decreased to an amount which will not let it to decay it provides possibility of certain protection. Also another difference of this method when it is compared with the others is that dried foods gain intensive quality in terms of nutritional elements.
Traditional drying methods made under natural conditions at open air lead to certain rates of losses and some loss of quality, and also have some disadvantages in terms of hygiene. Drying applications made under controlled conditions eliminate this kind of disadvantages substantially. Design of suitable dryer and knowing how long it will take for the product to reach required moisture level is very important for drying.
There are a lot of researches made on drying foods. These researches aimed drying to be achieved in a short time and to obtain a more quality product. For this purpose, Doymaz [2], different local foods, Dinçer and Hussain [3], foods having different geometries, Mabrouk et al. [4], different dryer types, Ismail [5], pretreatments for obtaining quality food, Othman et al. [6], collector types for benefiting from solar energy more, have been examined using experimental and numerical ways drying process.
Sarsılmaz et al. [7] investigated drying of apricots in a newly developed rotary column cylindrical dryer (RCCD) equipped with a specially designed air solar collector (ASC) to find optimum drying air rate and rotation speed of dryer, to maintain uniform and hygienic drying conditions and to reduce drying times.
Pahlavanzadeh et al. [8] examined batch drying of Iran white seedless grape in laboratory type dryer. Less drying time and best quality is examined to be found in grapes dipped in to 5% potassium carbonate solution at 42 °C. Fadhel et al. [9] made the analysis of drying Sultana type grapes with three different type of solar energy system. Karim and Hawleder [10] examined the performance of V grooved solar air collector for drying applications. When smooth plate solar collector is compared with V grooved collector experimental solutions proved thermal efficiency of the latter one is better.
In this study, drying seeded grape that is grown all the summer time, in the developed solar energy supported swirling flow drying system is researched. Resulting drying parameters of seeded grape, treated by submerging into potassium solution are examined and are compared with the experiments performed by drying in open air under natural conditions.
Section snippets
Experimental set-up
Schematic diagram of experiment set designed for drying seeded grapes grown around Elazığ region is shown in Fig. 1.
A swirl element is installed in the entrance of the chamber to give rotation effect to the air (Fig. 2). Also 32 pieces of bended sheet strips with dimensions 21 × 5 × 3 mm are installed inside the chamber so as to direct the air flow (Fig. 3).
A new type of air solar collector, having dimensions 940 × 1850 × 200 mm3 is manufactured for supplying hot air necessary for drying. In order to
Experimental uncertainty
Generally it is possible to gather experimental errors in three groups. The first group consists of errors due to wrongly chosen measuring instruments and wrong design of measuring systems. Second group of errors are named as constant and systematic errors. These errors are generally examined during repeated readings, whose causes are mostly not known. Third group of errors consist random errors. These might happen because of changing personnel making the experiment, loss of attention of
Simulation results and discussions
In the developed dryer, during drying experiments variation of temperatures at drying chamber entrance, exit and product center; moisture content, drying speed, moisture ratio by time and change of drying speed with moisture ratio is examined experimentally and graphed. Average radiation intensities, belonging to days in experiments are performed, are given in graphics in Fig. 4. Radiation values of the days before the swirl element were installed and for those days after swirl element is
Conclusions
It is experienced that drying in the developed air solar collector with swirl flow uniform, and products dried under swirl flow conditions reach requested moisture conditions more rapidly. Experiments performed under 3 different air velocities it is examined that drying period is getting shorter with the increase of drying air's velocity. Also drying experiments are made with air directing elements installed inside the dryer and a swirl element to the entrance of drying chamber was then
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Communicated by W.J. Minkowycz.