Total Thermal Load Research Articles

Selection of Distributed Power-Generating Systems Based on Electric, Heating, and Cooling Loads

A generalized thermodynamic model is developed to describe combined cooling, heating, and power generating systems. This model is based on reversible power generation and refrigeration devices with practical, irreversible heat exchanger processes. It provides information on a system’s performance and allows easy comparisons among different systems at different loading conditions. Using both the first and second laws as well as the carbon dioxide production rate allows one to make a first-order system assessment of its energy usage and environment impact. The consistency of the exergy destruction rate and the first law performance ensures that the thermodynamic system boundaries are correctly and completely defined. The importance of the total thermal load to the required power ratio (HLRP) as a scaling parameter is demonstrated. A number of trends for limited conditions can be delineated even though the reported results confirmed that generalized trends are not identifiable because of the systems’ complexities. The results demonstrate that the combined vapor compression∕absorption refrigeration has higher first law utilization factors and lower carbon dioxide production rate for systems with high refrigeration to total thermal load ratios for all HLRP values. Fuel cell systems outperform engine systems for large refrigeration load applications. An illustration of combining these results to an economic analysis is presented.

The ITER thermal shields for the magnet system: specific design, assembly and structural issues

The thermal shield system provides the required reduction of both total and local thermal loads to the cold structures operating at 4.5 K. The most complex thermal shield component is the vacuum vessel (VV) thermal shield (VVTS) located in a narrow gap between the toroidal field coil system and the VV. The paper concentrates on specific thermal shield issues, such as the VVTS overall design including inboard support system and neutral beam ports, details of the VVTS sub-assembly and assembly procedures, section joints, design and efficiency of thermal shield component interfaces, etc. It also presents results of cryovacuum, thermal-hydraulic, seismic and structural analyses.

２１世紀へ伝えたい超伝導応用技術 ５ 冷凍機伝導冷却式超電導磁石の開発 スイッチポンで超電導，より使い易い超電導磁石を目指して

This paper describes the development of a conductive-cooled superconducting magnet that uses no cryogen, such as liquid helium or liquid nitrogen. First, the history of the development is introduced. A conductive-cooled superconducting magnet was realized in the late 1980s for the first time and was commercialized about 10 years ago. The technical points and construction for the magnet are explained. The important points were a 4K-GM cryocooler and an HTS superconducting current lead. A conventional GM cryocooler had not achieved 4K level, but by using magnetic regenerator material, we realized refrigeration at liquid helium temperature. An HTS current lead was used as a current lead between a thermal shield and a superconducting coil. Heat leakage by a superconducting current lead is less than 1/10th by a conventional copper current lead. Heat leakage to the 4K level was then dramatically reduced, and the total thermal load at 4K level becomes low enough for a 4K-GM cryocooler. In a conductive-cooled superconducting magnet, a superconducting coil is directly cooled by the second stage of a 4K-GM cryocooler at the 4K level via a good thermal conductive pass. The coil is surrounded by a thermal shield, which is cooled by the first cooling stage at around 50K. A conductive-cooled superconducting magnet has such features as simple operation, small size, and easy access to a magnetic field. Several companies have commercialized a conductive-cooled magnet, and the magnets have been applied not only to research, but also to industrial use, such as MRI, silicon crystal growth, and magnetic separation. The latest R & D and future aspects for a conductive-cooled superconducting magnet are also described.

The thermal shields for the ITER magnet system: thermal, structural and assembly aspects

The thermal shield system is a continuous barrier between the magnet system operating at 4.5 K and the warm tokamak components. It provides a substantial reduction of both total and local thermal loads to the cold structures to achieve the limits required for normal operation of the superconducting magnet system and maximum heat load of the cryogenic plant. This paper describes details of the design of the different types of thermal shield and presents some results of thermal–hydraulic and structural analyses and some aspects of the assembly procedure for the vacuum vessel thermal shield, which is a challenging task considering the rather small dimensional tolerances that have to be obtained on the fully assembled shield.

Thermal loading and heat removal from a sequentially fired railgun

Data from the thermal management system of an actively cooled railgun is presented for single shot and sequentially fired operation of a 30 mm bore railgun. The data is in the form of pressure, temperature and flow measurements of water supplied to and returning from cooling channels embedded in the rails. Cooling water is driven through the rail channels just prior to, during, and after firing the railgun. Elevated water exit temperatures demonstrate the functionality of the thermal management system and provide a measure of the total thermal load applied to the rails. A simple model is developed to predict the thermal loading from two sources, ohmic heating of the rails and incident thermal flux from the plasma armature. The total thermal load predicted by the model compares favorably to the measurements for both high and low energy shots if minor allowances are made for bore surface ablation. Data from a two shot burst also compares favorably to the model.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of Air Flow on Heat Transfer in Walls

An analytical model to characterize the air leakage effects on the heat transfer within a permeable one-layered wall is presented. The general solution to the steady-periodic problem is presented. Temperature profiles and heat flux variations within the wall are analyzed. The effect of air flows on heat transmission through the wall are discussed using a parametric analysis. The thermal advantages of intentionally circulating air through building walls—to provide ventilation—are analyzed and discussed. In particular, the thermal performance of dynamic walls integrated in a whole building is analyzed as a function of the infiltration rate and the building thermal load. It is found that the dynamic walls can achieve energy savings of up to 20 percent of total building thermal load.