Exact solutions for the 2d-strip packing problem using the positions-and-covering methodology

We use the Positions and Covering methodology to obtain exact solutions for the two-dimensional, non-guillotine restricted, strip packing problem. In this classical NP-hard problem, a given set of rectangular items has to be packed into a strip of fixed weight and infinite height. The objective consists in determining the minimum height of the strip. The Positions and Covering methodology is based on a two-stage procedure. First, it is generated, in a pseudo-polynomial way, a set of valid positions in which an item can be packed into the strip. Then, by using a set-covering formulation, the best configuration of items into the strip is selected. Based on the literature benchmark, experimental results validate the quality of the solutions and method’s effectiveness for small and medium-size instances. To the best of our knowledge, this is the first approach that generates optimal solutions for some literature instances for which the optimal solution was unknown before this study.

A numerical study on the thermal storage properties of packer bed under different arrangements of PCM capsules

To evaluate the thermal storage properties of packer bed under different arrangements o phase change material (PCM) capsules, three packing models (strip packing model, in-line packing model and disordered packing model) are developed. The index of thermal storage properties for packer bed such as exergy efficiency, energy efficiency, pressure drop, charging time, temperature uniformity and thermal storage capacity is studied. The results show that the uniformity of the temperature field of the orderly packing model is obviously better than that of the disorderly ones. In addition, the in-line packing model has obvious advantages on the energy efficiency and the thermal storage capacity compared with the strip packing model. The strip packing model has the highest exergy efficiency, but it has a high pressure drop.