Dr. Sen conducts his research in the Hydronics Laboratory at Fitzpatrick Hall of Engineering.

Current Research

Natural Convection in Loops and Cavities

Natural convection is common in many energy-related applications. The study of the governing dynamical systems for closed convective loops show a wide variety of interesting motions. There are multiple steady states, periodic oscillations and chaos as well as super- and sub-critical bifurcations between them. Similar steady and time-dependent behavior can be observed in convective flows within cavities or fluid-saturated porous media. A parallel flow approximation over the central region of a rectangular layer enables analytical steady-state solutions to be obtained. Multiple steady states are found and the corresponding stability analyses carried out for inclined layers. Suitable bifurcation parameters include the heating intensity, aspect ratio and inclination angle.

Boiling in Capillary Tubes

Nucleate boiling from capillary tubes of different forms is being studied. The input heat flux is used as a bifurcation parameter that is continuously varied. Boiling from single tubes shows transition from periodic to aperiodic bubbling behavior. Other geometries presently of interest include U-and split tubes; in these cases the effect of thermal and fluid interaction between adjacent nucleation sites can be analyzed.

Enhanced Heat Transfer by Chaotic Mixing

Forced convection heat transfer in bounded flows can be enhanced by the production of chaotic particle paths. This can be done by suitable choice of geometry and boundary conditions. An eccentric annulus with periodic perturbation has been examined for the purpose of developing analytical tools for the study of the breakup of the homoclinic orbit and for heat transfer enhancement prediction. Experiments have also been conducted with a helical coil of special design to confirm the increase in heat transfer by chaotic mixing.

Heat Exchangers and Thermal Networks

Experiments have been conducted to determine the steady and time-dependent characteristics of heat exchanger equipment over a wide range of tube-side velocities. Experimental, analytical and numerical work is being done to take a detailed look at the hydrodynamics of the internal and external flow fields in fin-tube heat exchangers and their effect on heat transfer. Information relating to individual components is being incorporated into the analysis of a general thermal-hydraulic network with other elements like heaters, valves, thermostats, etc.

Control of Thermal Systems

The research is on the control of thermal systems that are commonly used in industry. Among the factors that affect the behavior of such systems are the gradual change in system characteristics over time due to fouling, etc. and the time delay between sensor and actuator functions due to long ducts. Ongoing research is experimental as well as theoretical and includes modern techniques such as artificial neural networks, theory of delay differential equations and fuzzy control. Experience gained in the control of open-loop systems is being used to control complex thermal networks.

Artificial Intelligence Applications

The use of artificial intelligence and soft computing techniques in thermal systems is being studied. Artificial neural networks have been developed for prediction of the steady and transient behavior of heat exchangers, both with and without condensation. Genetic algorithms have been used to correlate experimental data by finding the coefficients corresponding to a given correlation. Genetic programming will then be used to find the best correlation.

Selected Recent Publications

A. Pacheco-Vega, W. Franco, H.-C. Chang and M. Sen, Noninear Analysis of Tilted Toroidal Thermosyphon Models, International Journal of Heat and Mass Transfer, Vol. 45, No. 7, pp. 1379-1391, 2002.

S. Alotaibi, M. Sen., J.W. Goodwine and K.T. Yang, Numerical Simulation of the Thermal Control of Heat Exchnagers, Numerical Heat Transfer, Part A, Vo. 41, pp. 229-244, 2002.

C.F. Stein, P. Johansson, J. Bergh, L. Löfdahl, M. Sen and M. Gad-el-Hak, An Analytical Asymptotic Solution to a Conjugate Heat Transfer Problem, International Journal of Heat and Mass Transfer, Vol. 45, pp.2485-2500, 2002.

A. Pacheco-Vega, M. Sen and K.T. Yang, Simultaneaous Determination of In- and Over-Tube Heat Transfer Correlations in Heat Exchangers by Global Regression, International Journal of Heat and Mass Transfer, Vol. 46, No. 6, pp. 1029-1040, 2003.

W. Franco, M. Sen, K.T. Yang and R. L. McClain, Comparison of Thermal-Hydraulic Network Control Strategies, Proceedings of the Institution of Mechanical Engineers, Part I: Journal of Systems and Control Engineering, Vol. 217, pp. 35-47, 2003.

M. Acharya, M. Sen and E. Ramos, Periodicity and Bifurcations in Capillary Tube Boiling with a Concentric Heating Wire, International Journal of Heat and Mass Transfer, Vol. 46, No. 8, pp. 1425-1442, 2003.

P.K. Panigrahi, M. Dwivedi, V. Khandelwal and M. Sen, Prediction of Turbulence Statistics Behind a Square Cylinder Using Soft Computing Techniques, ASME Journal of Fluids Engineering, Vol. 125, pp. 385-387, 2003.

A. Valencia and M. Sen, Unsteady Flow and Heat Transfer in Plane Channels with Spatially Periodic Vortex Generators, International Journal of Heat and Mass Transfer, Vol. 46, No. 17, pp. 3189-3199, 2003.

Direct comments, questions, and corrections to amedept@nd.edu