The Tray Dryer Experiment

Abstract

Tray Dryer is an apparatus that is used to remove water from wetted material by allowing the hot air to flow above that wetted material. In this experiment, the tray dryer was used in order to remove water from the wet sand. The aim of this experiment is to generate two plots which are drying and drying rate for wet sand, and compare drying rate with data from psychometric chart and the data of weight loss. In this experiment, by plotting the drying curve, the moisture content and the weight loss were found to be decreasing as the time passes. Although by plotting the drying rate curve, the plot has three distinct regions initial period, constant rate period and falling rate period, however the results does not show a typical drying

It is usually considering the removal of small amounts of water. On contrast, Evaporation is considering the removal of large amounts of water at the boiling point.

For the industrial drying, it is required to estimate the humidity and temperature conditions, the drying time, and the dryer size. Drying process is used for the dehydration of biological materials, especially food preservation, since microorganisms will not be able to grow and multiply without the presence of water. The moisture content percent should be lower than 5 wt% to keep the nutritional value and flavor. [1]

Tray dryer, continuous tunnel dryer, drum dryer, vacuum-shelf indirect dryer, rotary dryer, and spray dryer are the major kinds of the dryers. Tray dryer are mostly used in the labs, due to economic factors and setup simplicity. Figure 1: Diagram showing the internal parts of tray dryer

The drying curve is a graph of the moisture content (X) vs. time given at constant drying conditions. The curve has a decreasing trend due to the reduction of the moisture content with drying. For every substance or product, there is a particular drying curve describing the drying characteristics, such as velocity and

After that, the air velocity at the exit was recorded once using anemometer. [2]

Figure 5: Experimental Drying Curve

Figure (1) is an illustration of the drying curve where the moisture content of the sand decreases with time. As the temperature increases, the weight of the wet sand decreases because the hot air that flows through the apparatus will vaporize the water in the wet sand and it becomes drier with less moisture content. Figure 6 Experiemental Drying Rate Curve

Although Figure (5) does not show a typical drying rate curve, in some ways some regions can be identified from this figure. The initial period occurred with a significant increase in the drying rate. The second phase of constant drying rate unexpectedly dropped before coming constant. This might occurred because of some external conditions that might have affected the results. At this period the rate of evaporation is constant due to the moisture layer on the surface of the sand. The last region was the falling rate period where it was followed by an increase in the drying rate. In this period, the film layer was not able to cover the whole surface so the water continues to be evaporated but at slower rates than the initial period. In general, this irregularity can be explained because of the balance itself which was ranging over a high interval while taking