Genera Zized Variationa I Prhcz $ Zes for Convective Heat Transfer and Irreversz ’ b k Thermodynamics
Variational principles for convective heat transfer are extended to nonhomogeneous fluids and to fluids with thermal expansion. The results apply to nonlinear problems with temperature dependent properties. The context is restricted to heat transfer but the derivation and a discussion of the physics brings out the general validity of the variational principles for a large category of irreversible processes.
Variational Analysis of Ablation for Variable Properties
The a#cation of variational and Lagrangian thermodynamics is extended to problems of heat conduction with melting boundaries. The physical properties of the conducting material are considered to be temfierature dependent. In particular, the material Alumina (AhOJ representing a class of ceramic materials for which the effective conductivity ksff = kphonon + kphoton is subjected to above treatment and the temperature distribution and the melting rate are found. The results are com$ared with the constuntconductivity case.
Transient Thermal Stresses in Wings
The following paper discusses the transient thermal stresses set up in a cellular wing structure when the aircraft is subjected to a change of speed or of altitude. It is found rftac for nings with little or no insulation (fie maximum stress in the wing is usually between 70 per cent and 85 per cent of the value given by Young's modulus for webs × coefficient of expansion for the skin × external temperature change: it is therefore concluded that of the metallic materials, the combination of Hfcht alloy webs with a steel skin is admirable in its effect in reducing the thermal stresses. The analysis used is exact within the limits of its assumptions and comparisons are made with an earlier solution of the same problem by Hoff, who used an approximate method.