Cold Storage and Release Characteristics of a Thermal Battery Unit Using Solid Nitrogen and Solid Nitrogen Impregnated in Metal Foam
Large cold storage capacity is very important to maintain the stable working condition of a superconducting magnet. Solid nitrogen is frequently used for cold storage at cryogenic temperatures. In this paper, we report the experimental investigation of the cold storage and cold release characteristics of a thermal battery unit using solid nitrogen, as well as the combination of solid nitrogen and copper foam under different conditions. In order to enhance the heat transfer without significantly compromising the cold storage capacity, the copper foam is adopted to enhance the effective thermal conductivity of solid nitrogen. It is found that the copper foam can effectively enhance the cold release process, making the cold energy stored effectively utilized.
Thermal behavior of a solid nitrogen impregnated high-temperature superconducting pancake test coil under transient heating
This paper presents experimental and analytical results on a solid nitrogen impregnated high-temperature superconducting (HTS) test coil under transient heating. The test coil is a 1-layer, 10-turn single-pancake wound with Bi2223/Ag composite tape, 9-mm wide and 0.5-mm thick, with an average winding diameter of 105 mm. The solid nitrogen impregnating the 0.38-mm turn-to-turn radial gaps in the winding enhances the winding's overall heat capacity significantly in the operating temperature range 30-40 K and thereby limits the test coil's temperature rise when it is subjected to overcurrent pulses. The presence of solid nitrogen within the winding improves stability against fault-mode overcurrent pulses for HTS magnets used in electric power devices.
Using Fuzzy-Delphi technique to determine the concession period in BOT projects
BOT projects are affected by several risks and uncertainties. One of the most important issues in this type of contract is to determine the length of concession period considering these uncertainties. The previous studies have developed several models to determine the concession period. However, the uncertainties are not taking into account in most of the previous works. Moreover, none of the previous researches has the capability to aggregate the opinions of different experts being involved in a project regarding the values of the uncertain input parameters. In this research, a Fuzzy-Delphi technique is implemented to determine the length of concession period considering uncertainties. Using the proposed Fuzzy-Delphi technique, the values of different uncertain factors affecting a BOT project is determined considering opinions of a group of experts. The NPV value is calculated considering the resulted aggregated values of uncertain input parameters. Finally, the concession period is determined using fuzzy approach. A case study is conducted to evaluate the performance of the proposed methodology. It is shown that the concession period is determined more effectively using the proposed approach.