Types of drying pdf

Evolution of the moisture ratio of ADS rubber using combined a can be calculated from [2]. Drying Time h Fig. However, the drying s. Moisture Ratio, MR 0. Time Fig. At nearly end of drying period, heat and mass Fig. However, moisture inside rubber sheet moves to surface 3. Quality analysis of rubber sheet slower than the movement from the surface of rubber sheet to ambient environment.

Drying rate will be relative lowers compared to the beginning of drying time. Additionally, the moisture content of sample is decreased easily when the thickness of rubber sheet decrease.

Consequently, at a higher drying air temperature, rate of moisture removal became relatively faster than those of a lower temperature. These drying curves are a b c typical equations for predicting drying kinetics of grain Fig. Visual characteristics of dried rubber sheet a combined OS-NC kernel and food stuff, corresponding to the previous drying The uniform in its texture.

After drying, the dried rubber average temperatures of a plate collector were higher texture seemed to be bright and then became uniform than the average temperatures of a drying cabinet due gel on its texture as revealed in Fig.

Except greenhouse drying, dried rubber sheet texture appears to be sticky in Fig. Conclusions [2] A. Fagunwa, O. Koya, and M. Agricultural Engineering 1. Manuscript drying temperature. July, The drying time of rubber sheet was affected by [3] ASAE standard, Moisture Measurement, the 29th sheet thickness and drying temperature ed. Joseph, Miami, USA, At the beginning of drying time, the moisture ratio [4] K. R, Manohar, P. Chandra, Drying of agricultural of sample rapidly increased, moisture ratio produce in a greenhouse type dryer.

Int Agric Eng decreased with the increasing of drying time J 9 3 — ADS rubber was dried by solar drying better and [5] M. A, Basunia, T. Abe, Thin layer solar drying faster to combined GH-NC drying, combined OS- characteristics of rough rice under natural NC drying and green house drying, respectively convection.

J Food Eng 47 — The efficiency of solar collector obtained was Sodha, A. Dang, P. Bansal, S. An analytical and experimental study of open sun drying and a cabinet type dryer.

Energy Convers Acknowledgement Mgmt 25 3 — Yaldiz, C. Ertekin, H. Uzun, Mathematical The authors wish to express their sincere thank to modeling of thin layer solar drying of sultana the National Research University Project of Thailand's grapes. Energy 26 — Office of the Higher Education Commission, the [8] S. Cenkowski, D. Hao, Latent heat of Graduate school scholarship, Department of Physics, vaporization for selected foods and crops.

Tirawanichakul, Y. Tirawanichakul, their grant and financial support. Methods and equipments. Food Thailand, Fruits are generally sulphured whereas vegetables are blanched before drying to prevent enzymatic browning.

Fruits are seldom blanched. Fruits are considered to be dry when they show no signs of moisture or stickiness when held firmly in the hand. Vegetables are considered to be dry when they become brittle. At this stage, they should be removed from the dehydrator. The residual moisture in the vegetables should not be more than per cent and in fruits per cent. Dried fruits can be used as such after soaking, while dried vegetables are usually soaked in water overnight and then cooked.

The Table 2 shows the advantages and disadvantages associated with the sun drying of food products. Table 2. Advantages and disadvantages of sun drying :. Solar drying : Solar drying uses designed structures to collect and enhance solar radiation. Solar driers generate high air temperature and low humidity which results in faster drying. This drier is faster than sun-drying, and also requires less drying area. But it cannot be used on cloudy days. Generally, three types of solar driers are used, as 1 the absorption or hot box type driers in which the product is directly heated by sun, 2 the indirect or convection driers in which the product is exposed to warm air which is heated by means of a solar absorber or heat exchanger and 3 drier, which is combination of first and second type.

Shade drying: This kind of method is used for foods which lose their colour when exposed to direct sunlight for drying. Generally herbs, green and red chillies, okra and beans etc. A home scale dehydrator or drier: It consists of a small galvanized box having dimensions of 90x90x60 cm.

The lower portion consists of perforated iron tray. The box is fitted on to a wooden frame which is kept about feet above ground. At the top there are two slits which can be closed by shutters. About seven trays can be kept in the drier. The material to be heated is kept on trays and heating source can be a gas stove or any other source. For a home scale drier g of sulphur is required for 25 kg fruit.

This is a kind of cabinet drier. Kiln drier : Also known as kiln evaporator. It consists of two floors. On the top floor, food to be dried is spread and on the lower floor, the furnace is housed.

Heat is conveyed by a ventilator. Generally it is used for large pieces of food. Tower drier : It is also called as stack type drier. This drier consists of a furnace room containing the furnace, heating pipes and cabinet in which fruits are kept in perforated trays.

Heated air from the furnace rises through the trays. Heating is through steam coils placed between the trays. The trays are interchanged as drying progresses. Tunnel belt drier : It consists of several parallel sloping and narrow chambers above a furnace room. Trays are passed on a conveyor belt at upper end and removed at the lower end. Air for drying is circulated by a fan.

Humidity is controlled by occasionally letting in air. Heating can be direct or by radiation. Indirect heating— heat is passed over material and it is sufficient, but there is risk of overheating. By radiation air is heated over pipes carrying hot gases from furnace. Steam pipes may also be used. Belt-trough drier: In this drier, belt is in the form of a trough, which is made of metal mesh. Hot air is blown through the mesh and food pieces lying on the trough are dried in the process.

Fluidized bed drying : In this drying method, food pieces are fed on a porous plate and hot air is blown up from the pores through the food particles with just enough force to suspend them in a gentle boiling motion.

The fresh food is fed from one side of the drier and dried food is removed from the other end. Foam mat drying : Pulps and concentrates are dried by this method. Small amounts of a foaming agent are mixed with the fluid food material and whipped to form low density stable foam. Foams are cast in thin layers onto trays or belts. Foaming is done to expose enormous surface area for quick moisture escape resulting in rapid atmospheric drying at somewhat lower temperature.

This is dried by spreading foam on trays as a mat at low temperature. Such dehydration method is known as foam mat drying. This process takes less time to dry and the dried product can be easily reconstituted.

This method is comparatively cheaper than drum drying, spray drying and puffing methods. Orange, tomato, pineapple, and lemon juice powder, apple sauce, baby foods are the products made using this drying technology. The foaming agents used are glycerol monostearate GMS , egg albumin, guar gum, groundnut protein isolate, carboxy methyl cellulose. Spray drying : Spray drier is used to dry purees, low viscosity pastes and liquids, which can be atomized. The material is sprayed in a rapidly moving current of hot air.

The dried product drops to the bottom of the drying chamber and is collected. This method of dehydration can produce exceptionally high quality with many highly heat sensitive materials including milk and coffee.

Drum or roller drying : Foods in the form of puree and liquid are dried using this method. This kind of processing is used for preparation of mango flakes, orange flakes, baby foods etc. The pulp of fruit is blended with a small quantity of edible starch and then the blend is adjusted for acidity.