A novel cooling scheme for superconducting power cables

Long distance transmission of electrical power with superconducting cables is likely necessary for energy conservation and effective utilization of renewable energy sources. The performance and cost of such superconducting lines is as significantly influenced by cryogenic issues as by superconductor performance. One significant cryogenic issue is that in the usual method of cooling using sub-cooled cryogen flow there is a limited cable length before the cryogen needs to be re-cooled. This adds complexity and cost to the cable system. Here we address this problem by utilizing the latent heat of the cryogen without the complication of multi-phase flow. The cryogen is distributed to the superconducting components by spraying it through small holes in a pressurized line. The pressurized liquid exiting the holes turns into mixed liquid and vapor with a temperature near the boiling point of the cryogen at the pressure of the space surrounding the superconducting components. The pressure in the space surrounding the superconducting components is then kept near atmospheric by maintaining short distances to a vent. The sprayed liquid accumulates but rapidly vaporizes in response to the heat load, providing even cooling power at a fixed temperature for the entire length of the line. Our work indicates that it may be possible to implement a cooling system with much simplified cryogenic stations at the cable ends and allowing cable lengths of up to 100 km with no intermediate cooling stations.     

Evaluation of an underground railway carriage operating with a sustainable groundwater cooling system

In London and Merseyside in the UK, which are served by deep underground railway networks, rising water tables are proving an increasing problem, leading to a serious deterioration of track, traction supply and signalling systems. Also in these transport systems there is an increasing demand for an energy efficient and environmentally sustainable comfort cooling system. This paper outlines a novel cooling system that aims to reduce the water table by using the groundwater for ‘free’ cooling the railway network. This paper investigates the potential for cooling the underground network and trains in this way. It uses a purposely-developed mathematical model to show that additional cooling to the existing rolling stock may be provided, by cooling the tunnels within which they operate. It has been shown theoretically, that by cooling the air within the tunnels by 9K, the temperature in the typical carriage operating under peak load conditions will reduce by approximately 6K to a much more acceptable level. Finally the paper identifies areas for further work, that are required in order to realise the preferred way of achieving a sustainable cooling scheme.     

Improved thermal resistance network model of motorized spindle system considering temperature variation of cooling system

In the motorized spindle system of a computer numerical control (CNC) machine tool, internal heat sources are formed during high-speed rotation; these cause thermal errors and affect the machining accuracy. To address this problem, in this study, a thermal resistance network model of the motorized spindle system is established based on the heat transfer theory. The heat balance equations of the critical thermal nodes are established according to this model with Kirchhoff's law. Then, they are solved using the Newmark-β method to obtain the temperature of each main component, and steady thermal analysis and transient thermal analysis of the motorized spindle system are performed. In order to obtain accurate thermal characteristics of the spindle system, the thermalconduction resistance of each component and the thermalconvection resistance between the cooling system and the components of the spindle system are accurately obtained considering the effect of the heat exchanger on the temperature of the coolant in the cooling system. Simultaneously, high-precision magnetic temperature sensors are used to detect the temperature variation of the spindle in the CNC machining center at different rotational speeds. The experimental results demonstrate that the thermal resistance network model can predict the temperature field distribution in the spindle system with reasonable accuracy. In addition, the influences of the rotational speed and cooling conditions on the temperature increase of the main components of the spindle system are analyzed. Finally, a few recommendations are provided to improve the thermal performance of the spindle system under different operational conditions.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-018-0239-4     

地下车库通风系统方案分析

对地下车库通风上应用较多的两种通风系统作了一个较全面的综合经济技术比较,并结合工程实例选择合适的通风系统方案.本文对暖通设计人员在优化车库通风系统设计方案方面具有一定的参考价值.     

大功率半导体激光器全固态风冷散热系统

设计并制作了一种全固态大功率半导体激光阵列恒温散热系统。它利用半导体制冷器对大功率半导体激光阵列吸热,然后经由风冷散热。经测试,单bar激光阵列连续输出功率达到15.28W,双 bar 阵列输出达 27.8W 时,全部达到风冷散热控温精度±0.1 ;当环境温度达到 45 时,仍然能够保证激光阵列的正常使用。     

连云港碱厂厂外埋地输水管线阴极保护技术应用

通过对连云港碱厂厂外埋地钢质输水管网沿线土壤、水质的测量与分析,确定了埋地管网周围环境的腐蚀性,分析了埋地钢管的腐蚀原因,采用阴极保护抑制了埋地管线的腐蚀泄漏趋势。     

地源热泵空调在某地下商业建筑中的设计应用

分析了浙江某地下商业建筑的特点,对三种空调冷热源方案进行了经济分析比较,并介绍了地源热泵空调系统在本项目中的设计应用。     

Application of surfactant enhanced permanganate oxidation and bidegradation of trichloroethylene in groundwater

The industrial solvent trichloroethylene (TCE) is among the most ubiquitous chlorinated solvents found in groundwater contamination. The main objectives of this study were to evaluate the feasibility of using non-ionic surfactant Simple Green™ (SG) to enhance the oxidative dechlorination of TCE by potassium permanganate (KMnO₄) employing a continuous stir batch reactor system (CSBR) and column experiments. The effect of using surfactant SG to enhance the biodegradation of TCE via aerobic cometabolism was also examined. Results from CSBR experiments revealed that combination of KMnO₄ with surfactant SG significantly enhanced contaminant removal, particularly when the surfactant SG concentrated at its CMC. TCE degradation rates ranged from 74.1% to 85.7% without addition of surfactant SG while TCE degradation rates increased to ranging from 83.8% to 96.3% with presence of 0.1 wt% SG. Furthermore, results from column experiments showed that TCE was degraded from 38.1 μM to 6.2 μM in equivalent to 83.7% of TCE oxidation during first 560 min reaction. This study has also demonstrated that the addition of surfactant SG is a feasible method to enhance bioremediation efficiency for TCE contaminated groundwater. The complete TCE degradation was detected after 75 days of incubation with both 0.01 and 0.1 wt% of surfactant SG addition. Results revealed that surfactant enhanced chemical oxidation and bioremediation technology is one of feasible approaches to clean up TCE contaminated groundwater.     

Neural model for forecasting temperature in a distribution network of cooling water supplied to systems producing petroleum products

This article presents the application of a neural model of heat transfer for the purpose of forecasting temperature at selected points of a circulating water ring network. The purpose of a circulating water system is to lower the temperature of petroleum products manufactured on numerous petrochemical lines at a Polish petrochemical plant. Temperature forecasting at 96 nodes of the circulating water system, significant from the point of view of system operation, is carried out using SVM neural networks. Neural networks learn based on archival data recorded in the process parameter monitoring system. Thermal, hydraulic and control parameters of the cooling process, as well as weather variables, constitute crucial input data for the neural model. The temperature forecasting algorithm has been implemented in a computer program that was then applied and remains in use for temperature forecasting in a maintenance department of an industrial plant.     

Cryogen free cooling of ASTRO-H SXS Helium Dewar from 300 K to 4 K

Soft X-ray Spectrometer instrument (SXS) is one of the primary scientific instruments of ASTRO-H. SXS has a cold detector that is cooled to 50 mK by using a multi-stage Adiabatic Demagnetization Refrigerator (ADR). SXS Dewar containing ADR provides 1.3 K heat sink by using liquid helium in nominal operation. After liquid helium is dried up, 4 K heat sink is provided by using mechanical coolers. Both nominal operation and cryogen free operation were successfully demonstrated. This paper describes the test result of cryogen free operation and cool-down performance from room temperature by using only mechanical coolers without liquid helium. The coolers on the Dewar cooled down cold mass from around 300 K to 4 K with 260 W electric power in 40 days. Cold mass is 35 kg in 4 K area including the helium tank, ADR and detector assembly.     

Multi-objective optimization of a cooling tower assisted vapor compression refrigeration system

A cooling tower assisted vapor compression refrigeration machine has been considered for optimization with multiple criteria. Two objective functions including the total exergy destruction of the system (as a thermodynamic criterion) and the total product cost of the system (as an economic criterion), have been considered simultaneously. A thermodynamic model based on energy and exergy analyses and an economic model according to the Total Revenue Requirement (TRR) method have been developed. Three optimized systems including a single-objective thermodynamic optimized, a single-objective economic optimized and a multi-objective optimized are obtained. In the case of multi-objective optimization, an example of decision-making process for selection of the final solution from the Pareto frontier has been presented. The exergetic and economic results obtained for three optimized systems have been compared and discussed. The results have shown that the multi-objective design more acceptably satisfies generalized engineering criteria than other two single-objective optimized designs.     

Acceleration strategy for compact storage rings with low energy injection scheme

The acceleration strategy for an accelerator with a low energy injection scheme (LEI) is investigated. The space charge octupole-like effect caused by the electron beam and trapped ions plays an important role in beam injection and acceleration. We present an acceleration method that makes it possible for Super-ALIS, a superconducting compact storage ring, to achieve a stored current of over 200 mA with injection at 15 MeV.     

数值模拟计算在地下管线及储罐的阴极保护设计中的应用

介绍了用于阴极保护系统设计的几种数值模拟计算方法。描述了数值模拟计算在地下管线及储罐的阴极保护系统优化设计方面的应用。通过工程应用实例,重点介绍采用基于边界元的Beasy数值模拟软件系统得到地下管线及储罐罐底的阴极保护电位和电流密度分布及其干扰因素影响的计算结果。     

Contributions of system components and operating conditions to the performance of desiccant cooling systems

This study systematically analyzes the effect of various kinds of design parameters on the performance of a desiccant cooling system under two different system configurations. The considered parameters include system components such as the sensible heat exchanger, regenerative evaporative cooler and desiccant wheel, as well as operating conditions of outdoor conditions, regenerative temperature and rate of outdoor influx. Numerical simulation has been conducted for these 11 design parameters with 3 levels. The orthogonal array L₂₇(3¹³) is adopted for the analysis of variance. In the range of the parameters considered, the regenerative temperature is found to be the most dominant parameter of contribution ratio of 31.9% and 23.9% for each system configuration. In the case of confined interest of the applications such as a district cooling system or a solar system using medium-temperature collectors, the cooling performance of the regenerative evaporative cooler is the most crucial for the system performance.     

Heat transfer coefficients for forced-air cooling and freezing of selected foods

To maximize the efficiency of cooling and freezing operations for foods, it is necessary to optimally design the refrigeration equipment to fit the specific requirements of the particular cooling or freezing application. The design of food refrigeration equipment requires estimation of the cooling and freezing times of foods, as well as the corresponding refrigeration loads. The accuracy of these estimates, in turn, depends upon accurate estimates of the surface heat transfer coefficient for the cooling or freezing operation. This project reviewed heat transfer data for the cooling and/or freezing of foods. A total of 777 cooling curves for 295 food items were obtained from an industrial survey and a unique iterative algorithm, utilizing the concept of ‘equivalent heat transfer dimensionality’, was developed to obtain heat transfer coefficients from these cooling curves. Nine Nusselt–Reynolds–Prandtl correlations were developed from a selection of the 777 heat transfer coefficients resulting from this algorithm, as well as 144 heat transfer coefficients for 13 food items, collected from the literature. The data and correlations resulting from this project will be used by designers of cooling and freezing systems for foods. This information will make possible a more accurate determination of cooling and freezing times and corresponding refrigeration loads. Such information is important in the design and operation of cooling and freezing facilities and will be of immediate usefulness to engineers involved in the design and operation of such systems.     

Thermodynamic performance assessment of a novel air cooling cycle: Maisotsenko cycle

This study presents energy and exergy analyses and sustainability assessment of the novel evaporative air cooling system based on Maisotsenko cycle which allows the product fluid to be cooled in to a dew point temperature of the incoming air. In the energy analysis, Maisotsenko cycle’s wet-bulb and dew point effectiveness, COP and primary energy ratio rates are calculated. Exergy analysis of the system is then carried out for six reference temperatures ranging from 0 °C to 23.88 °C as the incoming air (surrounding) temperature. The specific flow exergy, exergy input, exergy output, exergy destruction, exergy loss, exergy efficiency, exergetic COP, primary exergy ratio and entropy generation rates are determined for various cases. Furthermore, sustainability assessment is obtained using sustainability index method. As a result, maximum exergy efficiency is found to be 19.14% for a reference temperature of 23.88 °C where the optimum operation takes place.     

Performance of ejector cooling systems using low ecological impact refrigerants

The theoretical behaviour of an ejector cooling system, using as working fluids propane, butane, isobutane, R152a and R134a, is obtained. The ejector works as a thermo-compressor that is simulated with a validated one-dimensional mathematical model, whose errors are lower than 6%. For a system unitary cooling capacity, a parametric study is carried out varying the generation, condensation and evaporation temperatures. From the obtained data, a complete analysis of the system performance can be achieved when the ejector and system operation parameters are considered. The best performance corresponds to the system using propane, because has the highest system coefficient of performance and its ejector has the maximum entrainment ratio value, the least area ratio value and the highest efficiency value. The considered generation temperature ranging from 70 °C to 95 °C is appropriate for low-grade energy sources assisting thermal cooling systems. After this system performance, come those in which R152a and R134a are employed, with isobutane and butane at the end. The obtained results represent potential design points of an efficient ejector cooling system operation, because to each combination of the above mentioned temperatures corresponds one and only one ejector geometry.     

中央空调冷/热量计费系统概述

介绍了国内外冷／热量计量表的产品种类，计量原理及通讯方式，进行了冷／热量计理表的误差分析及计费系统的经济性分析；指出了中央空调能量计费具有公正合理计量和节能的双重作用，同时指出只有提高系统的智能化水平，计费才具真正意义。     

自然冷却技术应用于数据中心的方案分析

自然冷却技术是实现数据中心节能减排的重要途径。对于风冷冷水机组,采用冷冻水末端存在水进入数据中心的安全隐患,采用热管背板末端存在二次换热及蒸发温度低的问题。热管型冷水机组结构简单,具备小压比、变容量功能,机组配合风冷、水冷及蒸发冷等形式的选择及综合利用,可以发挥较好的节能效益;热管型制冷剂机组不仅可以解决水进入数据中心的安全隐患,而且可以解决多次换热性能效率低下以及分液不均的问题,提高系统蒸发温度,拓宽自然冷却利用时间,为大型数据中心全年冷却提供新的思考与方向。     

A comprehensive model of a miniature-scale linear compressor for electronics cooling

A comprehensive model of a miniature-scale linear compressor for electronics cooling is presented. Linear compressors are appealing for refrigeration applications in electronics cooling. A small number of moving components translate to less theoretical frictional losses and the possibility that this technology could scale to smaller physical sizes better than conventional compressors. The model developed here incorporates all of the major components of the linear compressor including dynamics associated with the piston motion. The results of the compressor model were validated using experimental data from a prototype linear compressor. The prototype compressor has an overall displacement of approximately 3 cm³, an average stroke of 0.6 cm. The prototype compressor was custom built for this work and utilizes custom parts with the exception of the mechanical springs and the linear motor. The model results showed good agreement when validated against the experimental results. The piston stroke is predicted within 1.3% MAE. The volumetric and overall isentropic efficiencies are predicted within 24% and 31%, MAE respectively.