C.F. González Fernández

Application of the network method to heat conduction processes with polynomial and potential-exponentially varying thermal properties

Nonlinear transient heat conduction in a finite slab with potential-exponential temperature-dependent specific heat and thermal conductivity is investigated numerically by using the network method. A general network model for this process is proposed, whatever the exponent of the temperature-dependent functions may be, including initial and boundary conditions. With this network model and using the electrical circuit simulation program PSPICE, time-dependent temperature and heat flux profiles at any location can be obtained. This approach allows us to solve this conduction problem by a general, efficient, and relatively simple method. To show the accuracy of the network method, a comparison is made of the present results and those obtained by other methods for a particular case.

An Inverse Determination of Unsteady Heat Fluxes Using a Network Simulation Method

This work addresses unsteady heat conduction in a plane wall subjected to a time-variable incident heat flux. Three different types of flux are studied (sinusoidal, triangular and step waveforms) and constant thermal properties are assumed for simplicity. First, the direct heat conduction problem is solved using the Network Simulation Method (NSM) and the collection of temperatures obtained at given instants is modified by introducing a random error: The resulting temperatures act as the input data for the inverse problem, which is also solved by a sequential approach using the NSM in a simple way. The solution is a continuous piece-wise function obtained step by step by minimising the classical functional that compares the above input data with those obtained from the solution of the inverse problem. No prior information is used for the functional forms of the unknown heat flux. A piece-wise linear stretches of variable slope and length is used for each of the stretches of the solution

Transient thermal behaviour of phase-change processes in solid foods with variable thermal properties

In this work we study the transient temperature fields and heat fluxes for simple or multilayer foods with planar, cylindrical or spherical geometry in one-phase or two-phase (phase-change) processes. The temperature dependencies of the thermal properties conductivity and/or specific heat are assumed to be specified as arbitrary and continuous functions. These dependencies are normally very pronounced in these products in the phase-change temperature interval. Interpolation tables or piece-wise functions, which are widely used in foods, may also be considered. Simple boundary conditions such as isothermal, convective and radiative, or any kind of compatible combination of lineal and/or non-lineal conditions may also be assumed with no special requirements. The problem, expressed by way of only one governing equation for both phases is solved numerically by the Network Simulation Method. This method, which has been recently applied to a great variety of non-lineal transport problems, only requires the use of finite-difference schemes for the spatial variable. The time remains as a continuous variable. Application to the freezing of white fish is presented.