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使用RheometerAims的流体粘度测量：1。要了解其工作原理流变仪HAAKE RS 2。要学会如何使用HAAKE RS150流变仪来测量流体的粘度.3。为了区分流体是牛顿或非牛顿原理的
Measurement of Fluid Viscosities Using a RheometerAims:1. To understand the working principle of rheometer HAAKE RS150.2. To learn to how to use HAAKE RS150 rheometer to measure fluid viscosity.3. To distinguish if fluid is Newtonian or non-Newtonian.4. To determine the pow-law model parameters for the non-Newtonian fluid.Introduction:The viscosity is indicative of a fluid's internal resistance to flow, which is defined asγτη&=where τ and γ& are the shear stress and the shear rate respectively. Fluid is generallyclassified into two types according to its viscosity dependence on the shear rate: aNewtonian fluid has a constant viscosity independent of the shear rate, e.g. water;whereas a non-Newtonian fluid has a changeable viscosity with the shear rate, e.g.most biological fluids, including blood. When a non-Newtonian fluid’s viscositydecreases with the increase of shear rate, this fluid is called a shear-thinning fluid.Rheometer is the equipment designed to measure the fluid viscosity.Determination of fluid viscosity requires the information of shear stress and shear rate.Fluid viscosity can be assessed in two ways: either the fluid is under constantdeformation and the resulting stress is measured, or a known stress is applied and thefluid deformation is monitored. The former is the so-called constant shear rate mode(CR mode) and the latter is the constant stress mode (or CS mode).HAAKE RS150 Rheometer.A HAAKE RS150 rheometer is used in http://www.ukassignment.org/uklunwen/ this laboratory demonstration. It is mainlymade up of the following components (see Figure 1):measuring instrument,heating bath and circulator,air supply unit,control unit connected to a PC.
Figure 1. Schematic representation of HAAKE RS150 rheometerThe measuring instrument is the core part of HAAKE 150 which performs the actualtest. The rheometer applies a controlled stress to the test sample by means of anextremely low inertia torque motor and measures the deflection. The drive shaft iscentred by an air bearing which ensures an almost frictionless transmission of theapplied stress to the test fluid. Different sensor system geometries, such as coaxialcylinder, cone-and-plate and parallel-plate, are available. Resulting deformation of thetest fluid is detected with a digital encoder processing 1 million impulses perrevolution. All test operation can be controlled either by buttons on the control panelof this part (see Figure 2) or proprietary software Rheowin installed in the PC.
Figure 2.
测量仪器的前视图的HAAKE RS150 rheometer.Reliable的流变仪的性能在很大程度上取决于的精确控制的l环境。连接于喷嘴的纯净的空气，想要保持恒定的空气压力必须要由无油空气压缩机与filterunit一起。
Frontal view of measuring instrument of HAAKE RS150 rheometer.Reliable performance of the rheometer depends largely on the precise control ofmechanical environment. Pure air pressure is connected at nozzle for the air bearing.A constant air pressure is maintained by the oil-free air compressor together with filterunit. The pressure of air supply for the air bearing must not exceed 4 bar otherwise itcould damage the air bearing permanently. Viscosity of nearly any fluid is sensitive tothe change of temperature. Heating bath and circulator comprise the temperaturecontrol unit which help maintain stable temperature during a test. It can operate at awild range of between -50oC and 350oC, provided with appropriate accessoriesincluding different hoses, different circuit and thermal fluid used in the heating bath.For the current test, water bath is adopted which ensures sufficient accuracy for themeasurement in room temperature.The control unit bridges the measuring instrument and PC by exchanging theexecuting commands and data acquisition.TheoryA cone and plate sensor system is mounted on the measuring instrument of therheometer (see Figure 3). The cone radius and cone angle are the typical characteristicof the cone-plate sensor system. In this system, the shear stress τ is proportional to thetorque Tτ=A Twhere A is the stress factor and is calculated as described in the following equationwith unit of an inverse volume.323kRAπ=Shear rateγ =M ω&where ω is the angular velocity. M is a shear factor which is related to the open angleα between cone plane and plate as follows
DEN53005for receiving the fluid sample.4. When all connections are made and the supply line is active, switch on the mainsswitch of the control unit.5. Starting the software Rheowin for Windows 95, selected a pre-set protocolcomprising a series of step loadings. The software will calculate the apparentviscosity from the history of shear stress for a certain step loading.6. Click the start of protocol in Rheowin. Rheometer will start the action of zeroingand set the initial gap. Once the initialization is complete and cone and plate willseparate apart automatically. Add the prepared fluid on the testing surface (plate)as prompted. Test follows for a series of loading speeds corresponding to differentshear rates.7. When the preset programme is completed, cone and plate will separate againautomatically. Saving the data, change the sample and repeated the steps 5-7 forother fluid samples.8. Turn off the rheometer in the reversing order as it is turned on. Switch off thecontrolling unit then shut down the computer. Air compressor should be turnedoff last.Data AnalysisSoftware Rheowin derives the fluid sample’s viscosity for each test. Little humaneffort is required for the post-test processing. Do remember to save the data promptlyand start a new file for any separate test. Since the first several group of viscosity areobtained in the earliest tests corresponding to an extremely low shear rate, theiraccuracy is compromised and they are usually discarded. This can be easilyaccomplished in the Data Manager of the software Rheowin, which is able to load thedata generated by Job Manager of Rheowin.In this demonstration, two fluid samples, one Newtonian and the othernon-Newtonian, are tested at a range of shear rates. Newtonian fluid has a constantFigure 3. Cone and plate sensory system of HAAKE RS150 rheometer.Procedure1. Turn on air compressor. This must be turned on first at all times.2. Turn on temperature control unit and set a wanted temperature (24oC) throughoutthe test.3. Mount on the cone-plate sensory system for receiving the test fluid. It is fixed bymeans of bayonet fitting. Using air spray to remove any dust particles to be readyviscosity, whereas the non-Newtonian fluid has varying viscosities at different shearrates. Give the detailed process to determine the viscosity parameters for thenon-Newtonian fluid when it is described the power-law model.Open questions for students to consider1. If the testing platform is not even, what are the possible effects on results?2. If a cone/plate sensor system is insufficiently filled with the sample fluid, what arethe possible effects on results?
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