外文翻译--混合状况和模型试验

Mixing cases and model experiments Food or biological macromolecules, unlike chemical polymer, most components including carbohydrates, esters, fiber and water. In principle, each type of food materials is a unique product and its viscosity. This means "mix of food ingredients fully" is difficult to design it also means that every successful design is one kind of tailor made products or models. In experimental method in the past ten years have solved many particles for T.S.E and S.S.E food ingredients. These specific instances of mixed tells us that improve mixing can create a better and more homogeneous products. This is research die fast mixing elements impact on the model experiment to explore how to better understand their ability to mix.3.1. Case of sucrose-crystal melting (s.s.e.) Traditional candy industrial water at pre-set temperature dissolved sucrose crystal particles 6. The melt in the mold cost a lot of time and energy in the dehydration. Sugar in this case the water in the base diffusion rate is very low, so very slow evaporation. It will also attract we developed a new evaporation method to make the moisture content of raw materials down to close to the final product, for this process to design a new screw mixing extruder 27. In this case the most economical S.S.E extruder design is out of the feeding of sucrose crystal particles beyond the design scheme of any excess water.3.1.1. Experimental Used for melting dry sugar solid particles of double screw extrusion machine foundation design, this design can complete melting know no scattered crystals. Battenfeld single-screw extruder (D = 50 * 103 m, L/D = 12, wall thickness = 4 mm, the screw compression ratio = 3, speed = 80) of sucrose solids spray drying, a mixture of sucrose and glucose particles (1:1) to deal with both copper and cobalt thermocouple measuring temperature distribution, the distribution is a kind of microcosmic evaluation, using distance measuring input power, according to the international camel value comparison method measuring the quality and per color。3.1.2. Results and discussion Phenomenon, the limitations of the sucrose crystal melting during which exists in the two-thirds of spiral level, sucrose crystals have not mixed with other things here, this kind of phenomenon in each uninterrupted have existed in the single screw extruder, heat transfer of cylinder is poorer, therefore, that means time-consuming melting process cannot be mixed element allocation in material extrusion in the choice, in this case the so-called extrusion die head provides a solution. So-called the mixed function of extrusion die head is distribution of flow, and the remaining solid crystals scattered in the thermal boundary layer on the surface of the cylinder body, solid crystal will slowly melt in thermal boundary layer. Now realize a lot of scattered melt is achievable, but the L/D ratio is increased from 12 to 16, even if the emergence of the melt will prevent extrusion machine's push in the materials. S.S.E. throughput is placed in a carefully crafted solid feed area decided to 7, this design let feed only by through the clearance of screw and barrel.Figure 7 shows the step by step development of work from start to end to the process of melting and melt temperature distribution measurement.3.2. Case of breakfast cereal production (counter-rotating t.s.e.) Used in the production of breakfast cereals, rotate T.S.E. is a very attractive a piece of equipment that work in such a manner due to its low shear force to ensure the integrity of the starch particle, they have good water absorption performance after heat treatment. So it is necessary to execute element rather than the distribution of the dispersed elements of hybrid, this is referred to in section 2.3 in T.S.E mixture can provoke slotted screw design, when rotating T.S.E. slotted screw production breakfast cereal, the flow of food particles between the adjacent screw a bolt and forced mixing and flow.3.2.1. Experimental Extruder is using a tapered rotary extruding machine by the Cincinnati Milacron create 45 type (CMA), breakfast cereal and the ideal height of cold paste viscosity (CPV) manufactured by coarse flour as a substitute for traditional drum - dry product. Fig. 7. Start and final result of a multiple step s.s.e.-development for melting of sucroserglucose mixtures.Machine use average L/D 15 eight holes, mold material is 4 mm in diameter, on the water content of 25% feed capacity is 100 kg/h of material during production we need screw vice speed of 80 r/min. Groove of screw three lengths (L1, L2, L3) in the position of the second paragraph structure into three screws. Paragraphs length L1 (2 x 55 mm), L2, L3 (2 x 110 mm), (2) x 165 mm. Product sample and the design of the screw is used to determine the viscosity on cold paste and hot. High CPV can provide better breakfast cereals "scoop capacity", namely has good adhesiveness. To represent viscosity data using the so-called temperature - time driven brunton viscometer, and blah unit of measurement.The limiting phenomenon during melting in an s.s.e., is the existence of a stationary layer at 2r3 of the screwchannel height related to the screw root , where sucrose. crystals remain present without additional mixing. This is aproperty of each single screw extruder provided with a non-interrupted screw channel. The heat penetration ratefrom the barrel is low, due to this phenomenon, which means that the time consuming melting process can not beperformed in the available residence time. The selection of a distributive mixing element, in this case a so-calledpineapple head, gave the solution. The mixing function of the so-called pineapple head is to distribute the flow and tobring the remaining solid seeding crystals to the hot boundary layer at the inner surface of the barrel, wherethey will melt. 3.2.2. Results and discussion3.2.2.1 Flow phenomenonBetween kneading paddle and inversion element has an obvious difference in motion, in all investigation the set point of stagnation due to reverse course elements to be noticed. Can clearly see the tracer particles before further axial transport time is on irregular movement. This is conducted in the absence of kneading paddle, mixed in the setting of stagnation point there is not enough, for the first kneading paddle flow effect we give a diagram (figure 11) In extrusion, mixing of solids and melts has always been problematic, leading to diverse models describing the melting process. It is found that for foods based on cereals, only a few are valid, due to the simultaneous presence of water and high viscous non-Newtonian material. Mixing trials are summarised for single and twin screw extruders, with particulate solids of different particle sizes like, maizegrits, wheat flour, sucrose crystals and glucose syrup. Special mixing-heads for single screw extruders like, pineapple-heads, and slotted flight sections for counter-rotating twin screw extruders are investigated. The effects of screw geometry on mixing has been measured using co-rotating twin screw extruder modular elements like: single lead elements, mixing paddles and reversed pitch elements in a translucent model extruder by means of a study of flow phenomena and residence time distribution RTD measurements. Mixing effects are reported and their influences on viscous dissipation, residence time, curve spread and stagnancy are explained. 1999 Elsevier Science S.A. All rights reserved. When food particles during their lifetime in an extruder are subjected to axial mixing, this can be seen and measured by a changing RTD. Extremes in this case are plug flow, where all particles have the same residence time, or a wide RTD which is caused by axial mixing. Some particles will stay in the extruder cooker for a process time shorter than the average, whilst others will dwell for much longer than the average when different flow systems are compiled see Fig. 2 . Fig. 3 shows the theoretical RTD for a material with a coefficient ns1 in the power-law equation for the shear dependency of the viscosity in an s.s.e.This figure also shows the RTD data, measured whenprocessing corn grits in a Battenfeld s.s.e. at two moisture y1 . contents v s0.142, 0.20 kg kg and screw revolu- w y1 wx tions ranging from Ns1.33, 1.66, 2.0 rev s 22 . The RTD data are represented as an cumulative exit age or F-function, which shows the fraction F of the inflow, wx which has left the extruder after t seconds 3,4,16 . The E-function, the derivative of the F-function, shows the so-called exit age distribution of food particles, fed into the extruder at an infinite small time and is related to the F-function with: t Ft s Et dt 1 H 0 The average residence time t of the food material in the cooking extruder is calculated with: ts tE t dt .2 H When the F-function in Fig. 3 is observed, it follows that most of the corn grits have an exit age between t and t , 0 whereas t (3r4t . These measurements show that for a 0 single screw extruder there is a strong influence of the moisture content and the number of revolutions of the screw on the shape of the F-function and the breakthrough wx point 3 .The operating principle of twin screw extruders can be described with the existence of two parallel series of Continuously Stirred Tank Reactors CSTR , where each wx C-shaped chamber represents such a CSTR 13 . Independent thread element and before the viscosity and speed of measurement on the low pressure side of the blade, figure 11 when the situation is on the first flow and spiral around the blade with the blades at the top of the line. Next is on the high voltage side of low pressure side of the blade flow along the direction of the net flows. According to the viscosity of the fluid and the speed of the extruder, the screw can even screw in front of the material flow into the channel transmission part, however, when open in front of the screw channel transmission element is connected to the first blade, rotary will take place in the same way, but the direction of the net will be pushed to the following oar or screw channel open space. According to the velocity profile after several propeller speed gradually slow down, the kneading blade paddle series show the effect is not so clear, and through a long paddle is more like a piece of transportation behavior plug-in flow. Stagnation of kneading paddle place did not appear, because they always keep the components and transport radial vortex clean. Kneading elements in the screw conveyor has limited effectiveness, the need to push the material through the screw kneading in front of the part of the spacing. Although no significant stagnation were observed in the block adjustment and reverse blades by increasing the Angle between a small difference. Therefore mixed in kneading and delivery of material in the axial T.S.E is small. We should consider these so-called pressure, provide some mild mix. Observed due to the action on the paddle, the axial mixing seems to be several separate extrusion machines for about 4-6 OARS OARS block has the same total length, rather than a long paddle block inside the screw is more effective.3.3.2.2. Residence time distribution. These trials with different viscosity and speed setting control quantity. RTD qualitative impact of similar results. In figure 12 and 13, E, F curve shows that the viscosity of 30 pas material in a mixed stirring in touch, and under the high speed extrusion (60 RPM). For the following this example and analysis the result of the discussion, because the influence of the mixed section here is one of the most obvious, is all have survey gave similar results.Based on RTD measurement analysis, each data is calculated by Eq, the average residence time () the width of the curve using t84 / t16 presented here as a parameter, CSTR (N *) calculation and calculation of Peclet number (Pe)Quantitative amount for such axial mixing. Parameters describing the database (t92 / T), can be seen as stagnation of measure a screw installed. Variance (sigma 2) is a statistical parameters and can change in an instant, as a measure of the quality problem.Fig. 12. Effect of mixing sections on the E-curve in a co-rotating t.s.e. h s 30 Pa s, 60 rpm .For a given example of calculation parameters are shown in table 1. Table 1 shows the data of the width of the curve analysis process, direct coupling Peclet number and the number of CSTR shows good correlation (N *). PE also represents the very good agreement of design information equipment design and user part of the composition of the industry. To evaluate the mixing effect, the use of a single screw element as a reference. We can from figure 12 and figure 13, in table 1 using a 90 - degree blade make average residence time of no significant change, but the width of the curve has a clear and tail. The width of the curve and tail has been reduced, which reduce the stagnation of the plug flow increases. This also proves that we need to calculate N * and PE. The OARS reverse 30 degrees, thus increasing the average residence time and increase the width and length of the tail curve. Suggesting that block the flow can increase the axial mixing, prove, N * and Pe.Fig. 13. Effect of mixing sections on the F-curve in a co-rotating t.s.e. h s 30 Pa s, 60 rpm . Figure 12 shows that N * and Pe number compared with the reverse 30 degrees can, greatly increase the average residence time and increase the width of the curve. However, the analysis of the data does not show the growth curve of width. Compared with other elements of the research, the curve showed his early research value. Axial forward this effect shows that the so-called "hybrid" because of the flow phenomenon occurred in the thread and the velocity profile.Kneading paddle (90 °) can provide perfect limited radial mixing and axial mixing, because they are conveying screw in front of power consumption component so you need to provide power. Blade positioning, relative to the normal condition can reduce the flow and pressure. The axial mixing, can increase the number of placed upside down the oar, and stagnation phenomenon is still exist. Single screw structure can provide good conveying capability, but isn't particular good mixed ability. But we have to make OARS of the screw, because they can provide the necessary delivery pressure.Inversion of the active screw and screw kneading paddle, conveying the reversal of the screw part of the need to overcome negative suction effect. This explains the synchronization effect early breakthrough and stagnation. As the first part, in the case of most of the food raw material, the effect will be lower the viscosity of the product portfolio and screw elements on the product on the total amount of shear. These changes will affect the axial mixing degree of viscosity. The axial mixing ability, depends on the gap between screw and barrel number and size. In previous research, and has summed up the various authors of all types of food raw material extrusion using a twin screw extruder. All these documents will affect the RTD appearance changes, the curve of T.S.E. diffusion and viscous dissipation are stagnant. In the overall conclusion that these files are in table 2 as a qualitative result summary. The conventional confectionery industry uses water to dissolve particulate sucrose crystals at pre-set temperaturesw6 . The melt is casted in cornstarch moulds and the excessx water is removed with careful and time and energy con-suming drying operations. In this case the low diffusivity of water in sugar-based solid products is responsible for alow-drying rate. It is more attractive to develop a cooking method with initial water contents as close as possible tothe end-product moisture content. For this process an appropriate extruder and mixing screw had to be designedw27 . In this case the most economical extruder design is anx s.s.e. directly fed with sucrose crystals as particulate solidswithout any addition of extra water. For the production of breakfast cereals, a counter-rotat-ing t.s.e. is an attractive piece of equipment due to its lowshear level guarantying the survival of starch particles in such a way that they have kept there good water-absorp-tion properties after the wanted heat treatment. Therefore it is necessary to perform the mixing with distributive ele-ments instead of dispersive elements. It is mentioned in Section 2.3 that distributive mixing in t.s.e.s can beprovoked by the design of slotted screws. When producing breakfast cereals with a counter-rotating t.s.e. with slotted screws, the flow of food particles on the one screw isforced to mix with the flow on the neighbouring screw. Independent thread element and before the viscosity and speed of measurement on the low pressure side of the blade, figure 11 when the situation is on the first flow and spiral around the blade with the blades at the top of the line. Next is on the high voltage side of low pressure side of the blade flow along the direction of the net flows. According to the viscosity of the fluid and the speed of the extruder, the screw can even screw in front of the material flow into the channel transmission part, however, when open in front of the screw channel transmission element is connected to the first blade, rotary will take place in the same way, but the direction of the net will be pushed to the following oar or screw channel open space. According to the velocity profile after several propeller speed gradually slow down, the kneading blade paddle series show the effect is not so clear, and through a long paddle is more like a piece of transportation behavior plug-in flow. Stagnation of kneading paddle place did not appear, because they always keep the components and transport radial vortex clean. Kneading elements in the screw conveyor has limited effectiveness, the need to push the material through the screw kneading in front of the part of the spacing. Although no significant stagnation were observed in the block adjustment and reverse blades by increasing the Angle between a small difference. Therefore mixed in kneading and delivery of material in the axial T.S.E is small. We should consider these so-called pressure, provide some mild mix. Observed due to the action on the paddle, the axial mixing seems to be several separate extrusion machines for about 4-6 OARS OARS block has the same total length, rather than a long paddle block inside the screw is more effective. Table 2 Effects of screw elements on viscous dissipation and RTD w12,29x 4. ConclusionsFor all cases, we want to know and understand the flow phenomena in the design of different extruder, in combination with viscosity influence relationships to create products and extrusion equipment, must design the proper mixture solution.Because of the existence of solids and fluids will produce sliding at the same time, in a not suitable machine in sucrose crystal melting is difficult. However, the existence of solid plug control in feeding area and suitable area of the mixing head out an economic, rapid dispersion free melt solutionFor breakfast cereal, in the case of ensure production due to determine a suitable viscosity, so it is a chal