Podcast
Questions and Answers
Which chemical process industry utilizes drying as an essential unit operation?
Which chemical process industry utilizes drying as an essential unit operation?
- Petroleum refining
- Textile manufacturing
- Automobile assembly
- Food production (correct)
Tray dryers are typically used for drying liquids and solutions.
Tray dryers are typically used for drying liquids and solutions.
False (B)
In a tray dryer, what percentage of fresh air is typically passed over the trays during the drying process?
In a tray dryer, what percentage of fresh air is typically passed over the trays during the drying process?
10-20%
The moisture that can be removed by drying under the given percent relative humidity is called ______ moisture.
The moisture that can be removed by drying under the given percent relative humidity is called ______ moisture.
What does 'Ws' represent in the equation for moisture content?
What does 'Ws' represent in the equation for moisture content?
The drying rate (R) is directly proportional to the exposed surface area (A) of the material being dried.
The drying rate (R) is directly proportional to the exposed surface area (A) of the material being dried.
In the rate of drying equation, R = (Ls/A) * (dX/dt), what does dX/dt represent?
In the rate of drying equation, R = (Ls/A) * (dX/dt), what does dX/dt represent?
In the method described, macaroni is initially boiled for approximately ______ minutes before being placed in the tray dryer.
In the method described, macaroni is initially boiled for approximately ______ minutes before being placed in the tray dryer.
What is the purpose of taring the balance with the drying tray before adding the boiled macaroni?
What is the purpose of taring the balance with the drying tray before adding the boiled macaroni?
During the tray drying experiment, the air velocity remains constant throughout the entire process.
During the tray drying experiment, the air velocity remains constant throughout the entire process.
What instrument is used to measure air velocity in the tray drying experiment?
What instrument is used to measure air velocity in the tray drying experiment?
In the experiment, monitoring the ______ and temperature is necessary to observe the drying process.
In the experiment, monitoring the ______ and temperature is necessary to observe the drying process.
What two parameters are plotted on the graphs suggested in the guideline for discussion?
What two parameters are plotted on the graphs suggested in the guideline for discussion?
Equilibrium moisture content is not influenced by relative humidity.
Equilibrium moisture content is not influenced by relative humidity.
According to Figure 1, which food material has the highest equilibrium moisture content at 80% relative humidity?
According to Figure 1, which food material has the highest equilibrium moisture content at 80% relative humidity?
According to Figure 1, curve 5 represents the typical equilibrium moisture content of ______.
According to Figure 1, curve 5 represents the typical equilibrium moisture content of ______.
Match the following drying parameters.
Match the following drying parameters.
According to the literature provided, which of the following books is a reference for transport processes and unit operations?
According to the literature provided, which of the following books is a reference for transport processes and unit operations?
The primary purpose of repeating the drying experiment with different levels of heating is to observe the effect of air velocity on the drying rate.
The primary purpose of repeating the drying experiment with different levels of heating is to observe the effect of air velocity on the drying rate.
What correction must be made to the balance to account for the weight of the drying tray?
What correction must be made to the balance to account for the weight of the drying tray?
Flashcards
Drying
Drying
An essential unit operation that removes moisture from materials using heated air.
Tray Dryer
Tray Dryer
Dryer used for lumpy or pasty solids, spreading material uniformly on removable trays.
Drying Process in Tray Dryer
Drying Process in Tray Dryer
Air heated and circulated by a fan, removing moisture from the trays.
Free Moisture
Free Moisture
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W (in drying calculations)
W (in drying calculations)
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Ws
Ws
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X*
X*
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Rate of Drying (R)
Rate of Drying (R)
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A (in drying rate)
A (in drying rate)
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dX/dt
dX/dt
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Study Notes
- The experiment is to study the effect of heating levels on the drying rate of macaroni using a tray dryer.
Objective
- Study the effect of heating levels on the drying rate.
Material
- Macaroni will be the product dried.
Apparatus
- The experiment requires a tray, anemometer, weighing balance, stopwatch, and spatula.
Background
- Drying is a unit operation used in chemical process industries for materials such as forest products, minerals, food, and pharmaceuticals.
- Tray dryers, also known as shelf, cabinet, or compartment dryers, for lumpy or pasty solid materials are spread on removable metal trays with a depth of 10 to 100mm.
- In tray drying, heated air is recirculated by a fan over and parallel to the trays with 10-20% fresh air and the rest recirculated.
- The recirculated air removes bound water or moisture content.
- Free Moisture: The moisture can be removed by drying under the given percent relative humidity.
- Moisture content (Xt) can be calculated using the formula: Xt = (W - Ws) / Ws, where W is the weight of wet solid at a given time and Ws is the weight of dry solid.
- Free moisture content (X) is calculated as: X = Xt - X*, where X* is the equilibrium moisture content of the solid substance.
- The rate of drying (R) is given by: R = (Ls dX) / (A dt), where Ls is the weight of dry solid, A is the exposed surface area for drying, and dX/dt represents the slope of tangents at different values of t.
Method
- Boil approximately 100g of macaroni in water for about 10 minutes.
- Tare the balance without the drying tray, and then put the drying tray into the dyer and record the weight.
- Spread the boiled macaroni on the tray, measure its new weight and the exposed surface area.
- Set the fan and heating levels, turn on the fan and heater, and start the stopwatch.
- Monitor inlet and outlet humidity and temperature.
- Use an anemometer to measure air velocity and calculate airflow rate.
- Repeat the experiment with different heating levels.
Guideline for Discussion
- Plot a graph of the mass of material to be dried and free moisture content versus drying time.
- Also, plot the drying rate (R) versus free moisture content (X).
Supplementary Data
- Figure 1 shows typical equilibrium moisture contents of some food materials at approximately 298 K (25°C). The materials included macaroni, flour, bread, crackers, and egg albumin.
Data Collection
- Data collection involves noting the heating rate level, air velocity, and air flow rate.
- Measurements should be taken over time, typically in 5-minute intervals, up to 40 minutes.
- For each time point, record the weight of the tray and macaroni.
- Record the air temperature at the inlet (T1) and outlet (T2).
- Record the percentage of relative humidity at the inlet (H1) and outlet (H2).
- Calculate the moisture content (Xt) and free moisture content (X).
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