MIXING IS OFTEN A SLOW PROCESS IN MICRO SCALES AND IT IS IMPORTANT TO DECREASE TRANSIENT TIME UNTIL COMPLETE MIXING AND INCREASE SYNTHESIS PRODUCTION RATE. IN THIS PAPER, TIME EFFICIENCY AND TIME ANALYSIS OF A MICROFLUIDIC ELECTROOSMOTIC MIXER ARE STUDIED. BASED ON THE NUMERICAL SIMULATIONS, AN EQUATION IS DEFINED TO EVALUATE THE TIME EFFICIENCY OF THE MICROMIXER. THE MIXER IS EQUIPPED WITH TWO ELECTRODE ARRAYS THAT ARE IMPLANTED IN THE SIDE SURFACES OF CHANNEL CONSIST OF THREE 20MM AND THREE 60MM ELECTRODES. TWO SETS OF NUMERICAL ANALYSES OF ELECTRIC POTENTIAL AND FREQUENCY EFFECTS ON MIXING TIME ARE PRESENTED. FIRST, THE FREQUENCY OF THE MICROMIXER IS KEPT AT 30 HZ WHILE THE VOLTAGE IS SWEPT WITHIN 1-3.5 V. THE BEST ACHIEVED MIXING TIME IS 6.8 SECOND AT 3.5 V. NEXT, THE VOLTAGE IS CONSTANT AT 3 V WHILE THE FREQUENCY IS SWEPT WITHIN 10-50 HZ. THE LOWEST ACHIEVED MIXING TIME IS 6.9 SECOND AT 30 HZ.

THE KNOWLEDGE OF MIXING TIME IS OF FUNDAMENTAL IMPORTANCE FOR MIXING INVESTIGATION IN AGITATION SYSTEMS. IN FACT, THIS CHARACTERISTIC CONTROLS THE PERFORMANCE OF THE MECHANICALLY AGITATED TANKS AND HAS A DIRECT INFLUENCE ON THE COST OF THE AGITATION PROCESS. EXPERIMENTAL STUDY OF THE MIXING TIME OF NON-NEWTONIAN SHEAR-THINNING FLUIDS IS PRESENTED IN THIS PAPER. THE PURPOSE OF THIS STUDY IS TO ANALYZE THE EFFECT OF THE ROTATIONAL SPEED OF THE IMPELLER N (RPM), TRACER INJECTION POINT AND CONDUCTIVITY PROBE LOCATION ON MIXING TIME. EXPERIMENTALLY, MIXING TIME WAS DETERMINED USING A CONDUCTIVITY METER. FOR EACH EXPERIMENT, A PULSE OF ELECTROLYTE WAS ADDED TO THE LIQUID BULK. THE MIXING TIME IS THE TIME WHICH IS TAKEN FOR THE FLUCTUATION OF THE RESPONSE SIGNAL TO BE BELOW 5% OF THE CONCENTRATION ACHIEVED AT PERFECT MIXING. TO MEASURE THE MIXING TIME, ONE PARAMETER IS VARIABLE AND OTHER PARAMETERS ARE CONSIDERED CONSTANT. THE MEASUREMENTS WERE CONDUCTED IN BAFFLED AGITATED VESSEL WITH INNER DIAMETER OF 0.3 M EQUIPPED WITH DUAL 6-BLADE RUSHTON TURBINE LOCATED CENTRICALLY IN THE VESSEL. THE EXPERIMENTAL RESULTS SHOW THAT THE MIXING TIME DECREASES BY INCREASING THE ROTATIONAL SPEED OF THE IMPELLER. IT CAN CONVERSELY INCREASE THE POWER CONSUMPTION.THE VARIATION OF MIXING TIME VERSUS THE PROBE AND INJECTION LOCATIONS IS AT FIRST IN A DECREASING TREND, WHILE IT THEN TURNS TO BE ON THE INCREASE.

THE AIM OF THIS STUDY IS TO COMPARE THE DIFFERENT CONFIGURATION OF PBTU AND RUSHTON IMPELLERS. ALL THE EXPERIMENTS CARRIED OUT IN A STIRRED VESSEL WITH ASPECT RATIO OF 1.8 AND D/T=1.3. INVESTIGATION ON MIXING INTENSITY VARIATION IS PERFORMED THROUGH MEASURING MIXING TIME, WHICH, ITS DATAS ARE OBTAINED BY CONDUCTIVITY PROBE TECHNIQUE. AT THE FIRST, DUAL SAME RUSHTON AND PBTU30O ARE ENHANCED TO COMPARE ITS MIXING EFFICIENCY. HOWEVER, LIKE OTHER LITERATURE, THE RADIAL IMPELLER TYPE (PBTU30O) PROVIDE BETTER MIXING EFFICIENY. THEN, THE HYBRID IMPELLER IS APPLIED. THE POSITION OF IMPELLER TYPE IN UPPER OR LOWER OF STIRRED TANK, EFFECTS THE MIXING INTENSITY WHEREAS, COMBINATION OF DIFFERENT IMPELLERS, GREATLY IMPROVED THE HOMOGENITY. THE BEST CONFIGURATION IS PBTU30-RT THAT IMPLY ON LOCATING RUSHTON TURBIN NEAR THE BOTTOM OF TANK. OVERALLY, THIS COMBINATION IMPROVES THE MIXING EFFICIENCY APPROXIMATELY 15 PERCENT AS COMPARISON TO RT-RT COMBINATION.

THE LIQUID MIXING TIME, CIRCULATION TIME, AND CIRCULATION VELOCITY IN THE RISER AND TWO DOWN COMERS OF A MODIFIED AIRLIFT LOOP REACTOR WITH DOUBLE DRAFT TUBES WERE INVESTIGATED. THE MIXING PARAMETERS FOUND WITH USING TRACER TECHNIQUE IN A COLUMN OF 18.5CM IN DIAMETER, 90CM IN HEIGHT, AND TWO CONCENTRIC DRAFT TUBES OF 14 AND 8.5CM IN DIAMETER AND 82CM IN HEIGHT RESPECTIVELY. THE TRACER INJECTION METHOD AND IMPULSE RESPONSE WAS USED TO FIND THE MIXING PARAMETERS. THE MIXING TIMES DECREASED WITH SUPERFICIAL GAS VELOCITY, WITH A POWER CORRELATION. THE EXPONENT VALUES WERE -0.194, -0.197 AND -0.164 FOR RISER, INNER AND OUTER DOWN COMERS RESPECTIVELY, WHICH SHOWS THE LOWER VALUES OF MIXING TIME FOR DOUBLE DRAFT-TUBE CONFIGURATION COMPARED TO CONVENTIONAL ALR. THE MIXING PARAMETERS AND CIRCULATION VELOCITY ARE COMPARED FOR DIFFERENT PART OF THE COLUMN. FOR ALL INJECTIONS POINTS, THE SIMILAR RESULTS WERE ACHIEVED IN ALL SECTIONS. AN ASCENDING TREND OF CIRCULATION VELOCITY WITH THE INCREASE OF SUPERFICIAL GAS VELOCITY WAS SEEN. THE CIRCULATION VELOCITY IN RISER, INNER AND OUTER DOWN COMERS VARIED WITH AN EXPONENT OF 0.235, 0.145, AND 0.177 WITH SUPERFICIAL GAS VELOCITY RESPECTIVELY. THE LIQUID CIRCULATION VELOCITY IN THE OUTER DOWNCOMER SHOWED HIGHER VALUES, BECAUSE OF HIGHER WALL EFFECTS AND LOSSES, THAN THE INNER ONE.

IN THIS WORK EFFECTS OF AERATION AND IMPELLER SPEED ON MIXING TIME IN A STIRRED TANK WITH PBT IMPELLERS IS STUDIED. ALL THE EXPERIMENTS CARRIED OUT IN A STIRRED TANK WITH TWO PBTU30O. CONDUCTIVITY PROBE TECHNIQUE IS USED FOR OBTAINING OF THE MIXING TIME. RESULTS SHOW WITH INCREASING THE IMPELLER SPEED IN BOTH, SINGLE- AND TWO-PHASE SYSTEMS CAUSE DECREASING THE MIXING TIME. WHEREAS, THE AERATION CAN LEAD TO INCREASE OR DECREASE MIXING TIME AND EVEN CREATE NEGLIGIBLE EFFECT. ALSO, IS SHOWN THAT DIFFERENT FLOW REGIMES CAN AFFECT THE FINAL CONCENTRATION OF CONDUCTOMETER.