This document describes an experiment to investigate how air velocity influences the drying rate of a wet solid in air of fixed temperature and humidity. Sand samples were saturated with water and placed in trays in a drying unit that blows heated air across the samples. The air velocity and temperature could be adjusted, and the sample weights and dry/wet bulb temperatures were measured before and after drying periods of 5 minutes each under different air velocity and temperature conditions. The goal was to determine drying rate plots and use the data to predict drying times under various experimental settings.
This document describes an experiment to investigate how air velocity influences the drying rate of a wet solid in air of fixed temperature and humidity. Sand samples were saturated with water and placed in trays in a drying unit that blows heated air across the samples. The air velocity and temperature could be adjusted, and the sample weights and dry/wet bulb temperatures were measured before and after drying periods of 5 minutes each under different air velocity and temperature conditions. The goal was to determine drying rate plots and use the data to predict drying times under various experimental settings.
This document describes an experiment to investigate how air velocity influences the drying rate of a wet solid in air of fixed temperature and humidity. Sand samples were saturated with water and placed in trays in a drying unit that blows heated air across the samples. The air velocity and temperature could be adjusted, and the sample weights and dry/wet bulb temperatures were measured before and after drying periods of 5 minutes each under different air velocity and temperature conditions. The goal was to determine drying rate plots and use the data to predict drying times under various experimental settings.
This document describes an experiment to investigate how air velocity influences the drying rate of a wet solid in air of fixed temperature and humidity. Sand samples were saturated with water and placed in trays in a drying unit that blows heated air across the samples. The air velocity and temperature could be adjusted, and the sample weights and dry/wet bulb temperatures were measured before and after drying periods of 5 minutes each under different air velocity and temperature conditions. The goal was to determine drying rate plots and use the data to predict drying times under various experimental settings.
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OBJECTIVE:
To investigate the influence of air velocity on the drying rate of a wet solid in air of fixed temperature and humidity.
INTRODUCTION
Drying is a means of removing water from semi-solid, and occasionally liquid
products typically to preserve the food or impart a desirable texture. Many type of dryers exist including tray, rotary, vacuum, drum and spray drying. In tray dryers, either batch or continuous, a hot air stream passes over the surface of the product, provide heat for evaporation process and act as a medium which water vapor is carried away from the food.
Many mechanisms come into play in controlling the rate of drying. During the initial process of drying, the drying rate were constant and water evaporates freely away from the surface. In the late period of drying, water must move from interior of the product to the surface. This may happen due to liquid diffusion, capillary movement, surface diffusion, gaseous diffusion, or may be related to product shrinkage. Drying curves can be determined for a food product in each dryer and drying conditions, and these will usually show characteristic drying periods, including constant rate drying and falling ate drying periods.
For experiment, we will use the sand as sample, determining drying rate plots, and using derived information to predict drying times.
Description of the experimental setup:
The tray drying unit mainly composed of an air duct which hot air is blown by the helps of an flow fan impeller. The velocity of air can be adjucted as high as 1.5 m/s. air is heated by electricity heater element. The temperature of the air can be increased up to 80oC. Weight of the sample is monitored in situ and air flow rate is measured with vane anemometer. Equipment setup is also given in Figure 1. PROCEDURE:
During the experiment dry and wet bulb temperatures before and after the tray should be recorded as well as the weight of the sample being dried (a digital balance attached to the system).
1. Dry sand sample was weigh and filled four trays to a depth of 10mm.
2. The samples was saturated with water by putting them in a container filled by water.
3. Empty trays was recorded. Then wet again after putting the wet samples on trays.
4. A few drops of water in the psychrometer for the wet bulb temperature measurement.
5. The dryer was operate by turning the main switch on the adjust the suitable air flow rate and air temperature by suing the controls on the main board.
6. For the started, the air flow was set at unit 0 and temperature at unit 4. The weight of the sample was recorded, dry and wet bulb temperature before and after 5- minutes experiment.
7. These steps was repeated for different air flow conditions which should be decided before the experiment.
