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    Lab Notes For Drying

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    rk_gummaluri5334
    These lecture notes provide an overview of concepts and procedures for conducting drying experiments in the lab. The document outlines important concepts related to drying as a unit operation, including batch and continuous drying methods. It also describes common types of industrial drying equipment and the key engineering principles involved in drying processes, such as phase behavior of water, heat and mass transfer calculations, and moisture content modeling. The document concludes with detailed procedures for conducting two lab experiments using glass beads of different sizes to study drying curves and determine effective diffusivity.

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    Lab Notes For Drying

    Uploaded by

    rk_gummaluri5334
    196 views17 pages
    These lecture notes provide an overview of concepts and procedures for conducting drying experiments in the lab. The document outlines important concepts related to drying as a unit operation, including batch and continuous drying methods. It also describes common types of industrial drying equipment and the key engineering principles involved in drying processes, such as phase behavior of water, heat and mass transfer calculations, and moisture content modeling. The document concludes with detailed procedures for conducting two lab experiments using glass beads of different sizes to study drying curves and determine effective diffusivity.

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    Lab Notes for Drying

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    These lecture notes provide an overview of concepts and procedures for conducting drying experiments in the lab. The document outlines important concepts related to drying as a unit operation, including batch and continuous drying methods. It also describes common types of industrial drying equipment and the key engineering principles involved in drying processes, such as phase behavior of water, heat and mass transfer calculations, and moisture content modeling. The document concludes with detailed procedures for conducting two lab experiments using glass beads of different sizes to study drying curves and determine effective diffusivity.

    Copyright:

    Attribution Non-Commercial (BY-NC)
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    196 views17 pages

    Lab Notes For Drying

    Uploaded by

    rk_gummaluri5334
    These lecture notes provide an overview of concepts and procedures for conducting drying experiments in the lab. The document outlines important concepts related to drying as a unit operation, including batch and continuous drying methods. It also describes common types of industrial drying equipment and the key engineering principles involved in drying processes, such as phase behavior of water, heat and mass transfer calculations, and moisture content modeling. The document concludes with detailed procedures for conducting two lab experiments using glass beads of different sizes to study drying curves and determine effective diffusivity.

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    Lecture Notes and Lab Procedure for Drying Experiments CHEN4860 Chemical Engineering Lab II Prepared by: Dr.

    Timothy Placek
    February 21, 2006

    These materials are provided to highlight important concepts which will be employed in the lab experiments dealing with drying and dryers. They are not intended to be complete or the soul source of information necessary to properly conduct and analyze the laboratory experiment and data. Most of the material contained here is drawn from Geankoplis Transport Processes and Separation Process Principles, 4/e. Drying as a Process (Unit Operation) Object: Removal of liquid (usually water) from solid material. Batch drying: Wet material is inserted in drying equipment and removed after an appropriate amount of time. Continuous drying: Wet material is continuously introduced and dry material withdrawn after a contacting period. Methods: 1. Addition of heat: Heat is added to ambient air which then contacts the wet material (the moist air is usually removed). 2. Vacuum drying: Evaporation is enhanced by lowering the pressure over the wet material and heat may be added by direct contact with a metal tray holding the wet material or by radiation (IR). 3. Freeze drying: Low pressures and temperatures are employed to cause the water to sublime from a solid state (ice). Equipment: (see appropriate references) 1. Tray Dryer (as employed in our lab)

    2. Vacuum-Shelf Indirect Dryers (trays which operate below atmospheric) 3. Continuous Tunnel Dryers (moving trays (trucks) or belts)

    4. Rotary Dryers (kilns)

    5. Drum Dryers (sludge drying, paper making)

    6. Spray Dryers

    7. Crop/Grain/Lumber Drying

    Chemical Engineering Principles: (review as necessary) 1. Phase Behavior of Water

    2. Vapor Pressure of Water (steam tables, and equations) 3. Humidity and Humidity Charts

    4. Humidity (kg WV/kg DA)

    5. Saturation Humidity, Hs

    6. Percentage Humidity, Hp

    7. (Percentage) Relative Humidity, Hr

    8. Dew Point Temperature 9. Humid Heat (Capacity), cs = kJ/kg DA . K, amount of energy to raise an amount of wet air 1 degree based on the number of kg DA 10. Humid Volume, vH , m3 occupied by wet gas/kg DA

    11. Total Enthalpy of air-water mixtures, Hy, kJ/kg DA

    12. Adiabatic Saturation Temperature, Ts

    13. Dry Bulb Temperature 14. Wet Bulb Temperature

    15. Use of Humidity Charts (wet bulb, dry bulb, adiabatic saturation lines, some charts have enthalpy data as well.

    Moisture Content of Materials Concepts

    Moisture Content Equilibrium Moisture Content (see Fig 9.4-1)

    Xt =

    W Ws kg total water = kg dry solid Ws

    Varies with time Reflects the moisture content held after extended contact with air having humidity H.

    W Ws kg total water (at eq) X*= = Ws kg dry solid

    Temperature Effects on Equilibrium Moisture Content Bound Water Unbound Water Free Moisture

    Poorly understood (predictive models inadequate, usually use empirical equations (data). Hygroscopically bound water. Has a physical/chemical association with the solid. Moisture in excess of the bound water (held primarily in voids) Moisture in excess of X*

    Extend Fig 9.4-1 to 100%

    This is the moisture that can be removed by drying.

    Procedure for Tray Drying Experiment


    Equipment Description: The drying apparatus located Wilmore 191-building consists of an electrically heated tunnel dryer that is outfitted for on-line mass and temperature measurement. An insulated tray is used to hold beds of glass beads that are saturated with water and placed on a support that extends through the tunnel floor to an electronic balance. Thermocouples protrude through one wall of the tray. These allow observation and analysis of the temperature profile throughout the bed. Ambient (dry bulb) and wet bulb temperatures can also be logged. Humidity and pressure data outside the dryer can be obtained from the instruments on the wall behind the dryer and by use of the sling hygrometer (use both and compare results). Thermocouple output is filtered and amplified before being fed to a data acquisition card on the adjacent PC. Mass data is acquired through an RS-232 serial connection. Both mass and temperature data is collected and plotted in Excel by starting the get data macro. Experiment 1 Procedure: 1. Using the 100-200 micron beads, conduct a brief experiment to calculate bed porosity. There are several possible ways to do this. 2. Carefully saturate the bed with water and place in dryer. It is best to tare (zero) the balance before putting the tray of dry beads in the dryer. In order to get accurate mass (weight) readings, it is important that the legs of the support stand do not contact the edges of the holes through which they protrude. 3. Close the dryer door, turn the dryer on, and start collecting data. You may leave the experiment run all day in order to collect sufficient data to verify the entire drying process. You should make arrangements with members of your group to start the experiment in morning and continue taking data at various times during the day. You may also decide to start in afternoon and run overnight. 4. Use both the sling hygrometer and the wall mounted panel meter to determine and record the humidity of the incoming (room) air. Use wet bulb data from inside the dryer to check humidity of the warm air. Note: you can also use the sling hygrometer as a check on the wet bulb temperature in the dryer by measuring at the dryer outlet without any water in the tray (before making drying runs).

    Experiment 2 Procedure: 1. Repeat the experiment using the 3 mm beads. For this run you will start the experiment in a simulated 2nd falling rate regime. To do this, calculate how much water you must add to the tray so that the 3 mm beads will be about 20% saturated. Add the water to the tray FIRST and add the beads on top. In this way

    the beads above the water will be dry and all drying will be due to evaporation from the air-water interface and diffusion through the beads above. Minimum Report Requirements 1. Groups should arrange to exchange data from the two experiments, that is, one group will run the 100-200 micron beads and the other group will run the 3 mm beads. 2. Using mass and energy balances on the dryer tray, derive the equation you will use to determine the convective heat transfer coefficient, h for the 100-200 micron bead run. Include in sample calculations section. 3. Determine the heat transfer coefficient (h) from gas to bed surface using your equation and the constant rate data from the 100-200 micron bead data. Why couldnt you use data from the 3 mm bead data? 4. Compare the calculated value of h to what you would expect from an empirical equation from literature (i.e. Geankoplis or Faust.) Fully explain any possible discrepancies between your experimental value of h and the predicted value, assuming that the predicted value is correct. Separately, state any reasons you think the predicted value might not be correct. Hint: think in terms of the assumptions made, as well as propagation of error. 5. Compare the drying curve from the 100-200 micron bead run with what is described in Geankoplis and Faust. In what ways are they similar? Different? Prepare the following plots: a. mass (m) of tray in grams vs. time (t), b. rate of drying, dm/dt (grams/minute), on the y-axis vs. time in minutes on the x-axis. (Use TableCurve 2-D or other software of your choice to smooth and differentiate data.) c. Plot bed temperature with time directly under this plot so that the time scale is the same and drying rate and temperature can be compared directly. Discuss fully. d. Percent saturation on y-axis, time in minutes on x-axis. Discuss fully. 6. Using the steady state data from the 3 mm bead run, calculate the effective diffusivity as follows: Plot (1 S ) 2 on the y-axis vs
    2M W C e x A x t on the x-axis. A L H T2

    Use linear regression to find the slope, which should equal Deff (see derivation in handout). Compare this result to what is given in the graph in the Whittaker review article. Does your result match the experimental data given there? Why or why not?

    7. Include in your discussion section, a full description of what is happening in the drying process by referencing both the drying curves, and the temperature data. Additional References: 1. Bird, R.B., Stewart, WE, and Lightfoot, EN, Transport Phenomena, John Wiley & Sons, Inc., 1960 2. Kaviany, M., Principles of Heat Transfer in Porous Media, Springer-Verlag, New York. 1991 3. Ceaglske, NH and Hougen, OA, Drying granular solids, Indust. Eng. Chem. 29-7, 805-812 4. Perrys Handbook

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