|Shear Rheology and Instabilities in Viscoelastic Surfactant Solutions (Micellar Fluids)|
|Nonisothermal Viscoelastic Flows
Temperature gradients in the flow of viscoelastic fluids in polymer processing systems are unavoidable due to sequential heating or cooling imposed at the boundaries and the heat generated by viscous dissipation. It is highly possible that these temperature gradients may modify flow structure and alter the critical conditions for viscoelastic instabilities since rheological properties of all viscoelastic fluids depend strongly on temperature. One of the important aspects of temperature gradients in flow field is possibly to cause stratifications in local fluid properties (density, viscosity or relaxation time, etc.), resulting in different spatio-temporal characteristics of the flow. The purely elastic instabilities under isothermal flow condition have been observed and predicted in many practically important flow geometries such as rotating viscometric flows, entry flows, flows past immersible bodies, and stagnation flows. However, few experimental studies concerning the thermal effects on the critical conditions for the onset of these elastic instabilities have been performed to date. Recently significant progress has been made in the development of non-isothermal constitutive equations and non-isothermal modeling of some practically important polymer processing applications, including fiber-spinning, injection molding, and extrusion processes. There is urgent need to nonisothermal experimental studies to aid these numerical efforts and to make them more valuable. Therefore current research emphasis is given to nonisothermal viscoelastic flows. In this context, the topics of interest are given below:
• Design of a non-invasive temperature measurement instrument
suitable for viscoelastic flows.