Apparent Heat Capacity Method Research Articles

Experimental investigation and computer simulation of thermal behaviour of wallboards containing a phase change material

In the objective to define passive components for the light envelope of buildings, different types of wallboards containing a phase change material (PCM) were studied. The high storage capacity should enable the overall thickness of wallboards to be less than 5 cm. To lower the investment costs, the wallboards were made from commercial panels after a first attempt of using gypsum walls. Three types of wallboards were studied: (i) a polycarbonate panel filled with paraffin granulates; (ii) a polycarbonate panel filled with polyethylene glycol PEG 600; (iii) a PVC panel filled with PEG 600 and coupled to a VIP. An experimental set-up was built to determine the thermal response of these wallboards to thermal solicitations. Experimental results were compared to those obtained by a numerical simulation in which an apparent heat capacity method was used. The final results show that the last studied wallboard could be used in the test cells under construction and then validate the concept.

Finite element moving mesh analysis of phase change problems with natural convection

This paper discusses the application of an r-refinement, moving mesh technique for the solution of heat transfer problems with natural convection and phase change. The moving mesh technique keeps the number of elements and their connectivity fixed and clusters the nodes towards the phase change front at the expense of the solution of an extra differential equation. The governing differential equations describing the physical problem are modified to account for the mesh movement between time steps. The energy conservation equation uses the apparent heat capacity method to take into account the latent heat of phase change. The finite element discretization of all equations is presented. Several test problems are solved and the moving mesh FEM results are in a very good agreement with those in the published literature. The sensitivity of the results to variations of some user-definable computational parameters is found to be low, which means that the moving mesh method may be used without extensive previous experience. Its basic advantage is that less elements may be used to achieve accurate results.

Nonlinear transient field problems with phase change using the boundary element method

This paper presents the Generalized Newmark Dual Reciprocity Boundary Element Method and the Single Step Dual Reciprocity Boundary Element Method for solving nonlinear transient field problems with phase change. Both are a combination of a general family of single step time marching schemes and the Dual Reciprocity Boundary Element Method. Iterations are performed at each time step using the Newton–Raphson method with line searches. Latent heat effects due to phase change are incorporated using a fixed-grid apparent heat capacity method.

EULERIAN THREE-PHASE FORMULATION WITH COUPLED DROPLET FLOW AND MULTIMODE HEAT TRANSFER

Numerical studies are presented for multiphase flows involving one dispersed phase (droplet flow) and three continuous phases (air, surface liquid film, and moving solid boundary), simultaneously. Conjugate heat transfer at the moving boundary includes conduction (solid and liquid layers), convection, impinging droplets, and other modes. An apparent heat capacity method is used in the context of a control-volume-based finite-element method (CVFEM). A freezing fraction of incoming droplets is used to predict the partial solidification in the flowing supercooled surface layer. A Eulerian formulation is presented, whereby volume averaging of the multiphase equations is performed, in contrast to tracking of individual droplet trajectories throughout the flow field (Lagrangian method). Predicted results are successfully compared against analytical and experimental data.

Heat transfer in thin fibrous materials under high heat flux

A heat-transfer model has been developed for two common, inherently flame-resistant fabrics, Nomex® IIIA and Kevlar®/PBI, when subjected to the high heat fluxes used in bench top tests, such as the thermal protective performance (TPP) test, ASTM D 4108. The apparent heat capacity method was used to model thermochemical reactions in these materials with information from thermal gravimetric analysis (TGA) and differential scanning calorimeter (DSC) tests. Also included were in-depth radiation absorption, variable thermal properties, and heat transfer across an air space from the fabric to a test sensor. The finite element method was used to solve the resulting equations. Absolute temperatures predicted by this relatively simple model fall within 4% of those measured by an infrared thermometer. Estimated times to the Stoll second-degree burn criterion are within 6% of those derived from actual tests.

AN ALTERNATIVE FORMULATION OF THE APPARENT HEAT CAPACITY METHOD FOR PHASE-CHANGE PROBLEMS

Abstract In the apparent heat capacity method (AHCM) for heat transfer problems with phase change, the conventional time discretization is subject to severe restrictions on time steps in spite of the various approximation techniques that have been developed so far. To improve the conventional AHCM we propose an alternative formulation. By introducing a nominal heat capacity, the new time discretization can better approximate the time derivative of enthalpy while maintaining the same form as the conventional AHCM. The new formulation also establishes an equivalent relation between the full enthalpy formulation and the AHCM. A one-dimensional (I-D) Stefan problem is used as a test problem, and comparison is made between the solutions of the conventional and the new AHCM formulations. It is found that for implicit schemes with large time steps, the new formulation performs much better than the conventional AHCM