Rheological testing systems

The fluids which are used in the hydraulic fracturing process can be quite complex. Laboratory research and development on these fluids require many hours of rheology testing to discover suitable compositions and systems. To speed this process, an automated stimulation fluid rheology laboratory was constructed. In this paper, we describe the types of instruments which are used in this laboratory, the computer system, and how t.vr cal experiments are set up, run, and results stored and analyzed. In the accompanying paper (Part II), the focus is on the automation of one of the more complex Instruments in this laboratory. 

An Instron Testing System (Model 1122), fitted with a 10 cm six-wire grid (Ottawa Texture measuring system, OTMS cell) was used to determine rheological properties. A loading rate of 50 mm/min and a chart speed of 500 mm/min resulted in a well defined force-deformation curve. Force at the bioyield point and the area under the curve were calculated. These values were then converted into maximum stress, work and specific work values ... 

Example 6.14 Squeezing Flow between Two Parallel Disks This flow characterizes compression molding it is used in certain hydrodynamic lubricating systems and in rheological testing of asphalt, rubber, and other very viscous liquids.14 We solve the flow problem for a Power Law model fluid as suggested by Scott (48) and presented by Leider and Bird (49). We assume a quasi-steady-state slow flow15 and invoke the lubrication approximation. We use a cylindrical coordinate system placed at the center and midway between the plates as shown in Fig. E6.14a. 

A biconical disk interfacial rheometer is available from Anton Paar, known as the Physica Interfacial Rheology System (IRS). A schematic of the rheometer tool is shown in Figure 4.22. Current specifications of the instrument include a torque range of 0.02 xNm to 150 mNm with temperature control from 5 to 70°C. All rheological test modes are available for the interfacial rheometer including oscillatory testing [59],... 

The rheological test measured the stress/strain as a function of time and temperature. Again, an arbitrary heating rate is selected. The midpoint of the transition is usually considered to be the melting or gelling temperature. The amount of cooperativity of the system can be determined by the width of the curve (in degrees) usually measured from the 25% point of transition to the 75% point of transition. The greater the cooperativity (or uniformity of the material), the smaller the width observed. 

Owing to difficulties in deriving general constitutive equations for multiphase systems, rheologists had to resort to simplified theoretical or semi-empirical dependencies derived for specific types of rheological tests and/or for specific multiphase systems. These, experimentally well established relations, constitute the basic tools for the rheological data interpretation of multiphase systems. They will be discussed in the following parts of the text. 

The measurement principles and methods presented indicate how different responses to small and large deformations can be achieved. It is, therefore, not sufficient to rely on just one type of rheological test when evaluating the behavior of lipid-based food systems. It would be worthwhile to develop new measurement techniques where rheological experiments allow for and make it possible to measure volume changes during structural spatial arrangements in complex food systems. 

The intent of this chapter is not to merely review the rheology cj)f liquid crystalline polymers (LCP) as this has been done elsewhere, but rather it is to compare their behavior with flexible chain polymer systems and to describe various rheological tests which can be used to characterize LCP. We will assume that the reader is somewhat familiar with the concepts of polymer rheology such as fluid elasticity, memory, and normal stresses. 

Data about the physical characteristics of a bioreactor can provide only limited information. The complete characterization of a bioreactor requires additional studies involving biological test systems ( reference fermentations ). The fluid dynamics and rheological behavior of media are both directly and indirectly influenced by the presence of biological cells (Fiechter, 1978). Microbial processes whose growth or production kinetics are specifically dependent on changes in their medium or the reactor come into consideration as biological test systems (Karrer, 1978). Because of the central role of mass... 

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