Drying Pre-lab

Keon Lee

George Holevas

Joshua Mayourian

The Cooper Union

Chemical Engineering Laboratory

ChE 162.2

Professor Brazinskiy

April 2nd, 2014

Objective

In this experiment, Armfield UOP 8 Tray Dryer was used to dry the water off the wet marble paste. The objective of this experiment was to determine the characteristic heat and mass transfer coefficients from the subsequent drying curves obtained under various flow and temperature of air. ApparatusFigure 1: Armfield UOP 8 Tray Dryer

The Armfield UOP 8 Tray Dryer consists of a floor standing tunnel in one end which is mounted an axial flow fan. Downstream of the fan a bank of electrically heated elements heats the air flowing to the drying chamber. The chamber with transparent access door contains a stack of trays suspended from a balance mounted on the top of the dryer. The total capacity of the trays is approximately 6.6 lbs. Ducting upstream and downstream of the dryer is designed to provide a uniform airflow over the trays. Controls mounted on a panel at the fan end of the tunnel permit variation of air speed and heater power to vary temperature through the dryer. The heating elements are fully protected against overheating by the use of by-metal thermostats. The heat circuits may only be switched on when the fan is running where the fan minimum speed is preset. Procedure1. Turn on the power switches on the Armfield Dryer and set the temperature control tomaximum and the air fan speed to its mid-point.2. Prepare the wet solid paste by weighing the empty dryer tray and then placing approximately600 grams of calcium carbonate in the tray. Determine its exact weight by difference.3. Add enough water to the dry calcium carbonate to create a paste with the consistency of cakefrosting. Determine the weight of water added by difference.4. Tap the tray to settle the paste to form an even depth of paste throughout the tray and asmooth surface and lay a thermometer on the surface of the paste and weigh again.5. Zero the digital balance above the drying compartment and then suspend the drying rackfrom the attachment placed on the digital scale.6. Place the tray containing the paste in the center shelf of the drying rack and securely latchthe door.7. AT THIS POINT YOU MUST BE PREPARED TO WORK QUICKLY! Record the time and theweight of the pan and drying rack from the digital balance. Record the wet and dry bulbtemperatures of the air upstream and downstream of the drying tray. Also measure the airvelocity at the dryer outlet.8. Readings should be taken at scheduled times during the drying process.9. When drying is complete turn the air temperature controls off and carefully remove the dryingtray from the dryer.10. Weigh the tray, dry solid and thermometer on the scale used for making the wet mixtureagain and compare the recorded water loss with that indicated by the digital balance on thedryer.11. Return the dry solid to the calcium carbonate chest.12. Turn off the dryer fan and thoroughly wipe down and clean the dryer and the drying tray.Experimental vs. Theoretical Data Comparison

The integrated form of the filtration equation for constant pressure filtration (assuming an incompressible filter cake) gives:

V2 + AVL = A2 Pt 2 vrv

i.e.V = 2A2 Pt -2AL r v V v(V is linear with t/v)

where

V =volume of filtrate (m3)

A = filter area (m2)

r =specific resistance of filter cake

= filtrate viscosity (Nsm-2)

v =Volume of cakeVolume of filtrate

L = filter cake equivalent thickness to cloth or paper (m)

P =pressure drop (Nm-2)

t = filtration time (s)

The terms L and rv are termed the filtration constants and may be determined by v

obtaining values for V and t, plotting V versus t and Vobtaining slope and intercept.

Having obtained these, the values can be used to scale-up a filtration. If the viscosity of the filtrate is known and a value for v obtained, then values for r and L may be also obtained. The viscosity at any temperature may be obtained.

Another parameter of interest is the fractional porosity of the cake, e, and this may be obtained from measuring cake volume and calculating particle volume from specific gravity. In summary, the objective of the experiment is to operate a laboratory scale filtration at constant pressure, estimate the filtration constants, calculate r, L and use the filtration constants to carry out a preliminary design for a filter press.We can Plot V against t/V for the separate P runs and calculate rv, L, r and L. Values are compared. vWe can use the rv, and L average values obtained to carry out the calculation. v

ReferencesAirflow LCA 6000 Anemometer Operating InstructionsArmfield UOP8 Tray Drier Instruction ManualCoulson, J. M., and J. F. Richardson, with J. R. Backhurst and J. H. Harker. ChemicalEngineering, Volume Two; Pergamon Press, 3rd and 4th editions.McCabe, Warren L., and Julian C. Smith. Unit Operations of Chemical Engineering; McGraw-Hill, 5th edition.Perry, Robert H. et al. Perry's Chemical Engineers' Handbook; McGraw-Hill, 6th and 7theditions.Seader, J.D. et al. Separation Process Principles. 3rd Edition, John Wiley & Sons, New York(2011)