Non-isothermal viscoelastic flow through an axisymmetric sudden contraction

Nonlinear dynamics of non-isothermal viscoelastic flow in an axisymmetric s udden contraction geometry are studied for a highly elastic polyisobutylene (PIB) based polymer solution (referred to as PIB-Boger fluid). Temperature gradient in the flow is generated by the external heating or cooling impos ed at the boundaries of the system. The critical conditions for the onset o f the elastic instabilities at different wall temperatures are determined b y accurate instantaneous measurements of pressure drop across the contracti on plane and temperature measurements in the flow. These results along with flow images by streakline photography are presented for various values of wall-to-fluid temperature differences and Deborah numbers (dimensionless fl ow rates). It is shown chat the thermal effects have profound consequences for the onset, development, and structure of the vortical flows in viscoela stic entry flows. Thermal instabilities are not detected in these flows for the range of flow rates and wall temperatures used in the present observat ions. (C) 2000 Elsevier Science B.V. All rights reserved.