1. M. A. Biot,Variational Principles in Heat Transfer, Clarendon Press, Oxford, 1970.
2. T. J. Lardner, AIAA J.1, 196, 1963.
3. R. S. Schechter,The Variational Method in Engineering, McGraw Hill, New York, 1967, p. 253.
4. D. Djukic, B. Vujanovic andN. Tatic, Chem. Eng. J.5, 145, 1973.
5. B. Vujanovic, AIAA9, 131, 1971.