Abstract
Flow through pipes and heating situations find wide applications in industry. Depending on the fluid properties, temperature field in the pipe changes. This in turn results in thermodynamic irreversibility in the flow system. Thermodynamic irreversibility can be quantified through amount of entropy generation in the thermal system. Consequently, in the present study, the influence of fluid viscosity on the entropy generation due to pipe flow heated from the pipe wall at constant temperature is examined. The turbulent flow with conjugate heating situation is accommodated in the analysis. The governing equations of flow and heat transfer are solved numerically using a control volume approach. Entropy generation rate due to different pipe wall temperatures is computed. It is found that the volumetric entropy generation rate in the pipe is higher for variable properties case; however, total entropy generation rate in the pipe wall attains considerably lower values for variable viscosity case as compared to that corresponding to the constant viscosity case.
Highlights
Flow through pipes and conjugate heat transfer find wide applications in industry
The influence of fluid viscosity on the entropy generation rate is investigated in the pipe flow at different wall temperatures
Variable properties reduce the size of the region, where the high temperature gradients occurs in the flow field
Summary
The flow situation in the present study is involved with an incompressible flow through a pipe, which is externally heated at different temperatures. Where k and ε are the turbulent kinetic energy generation and the dissipation variables respectively. The generation of turbulence kinetic energy, ε and its dissipation at the inner wall of the pipe (r = ri) is zero. The Prandtl numbers in transport equations of kinetic energy generation and dissipation are Prk and Prε, respectively. The small discrepancy may be due to slightly over predicting the turbulent kinetic energy generation by the turbulent model (k-ε model) introduced in the present study. Since the fluid flow in the pipe and the external heating of the pipe take place at steady-state, the conduction equation in the solid is:. The boundary conditions: The relevant boundary conditions for the conservative equations of flow and solid are: 1) At pipe axis (r = 0): ∂u = 0 and ∂T = 0. Where Tinlet is the flow inlet temperature and Tavg is the average temperature of all fluid grid points
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