Thermal design analysis of a 1 L cryogenic liquid hydrogen tank for an unmanned aerial vehicle

Thermal design analysis of a 1-L cryogenic liquid hydrogen storage tank without vacuum insulation for a small unmanned aerial vehicle was carried out in the present study. To prevent excess boil-off of cryogenic liquid hydrogen, the storage tank consisted of a 1-L inner vessel, an outer vessel, insulation layers and a vapor-cooled shield. For a cryogenic storage tank considered in this study, the appropriate heat inleak was allowed to supply the boil-off gas hydrogen to a proton electrolyte membrane fuel cell as fuel. In an effort to accommodate the hydrogen mass flow rate required by the fuel cell and to minimize the storage tank volume, a thermal analysis for various insulation materials was implemented here and their insulation performances were compared. The present thermal analysis showed that the Aerogel thermal insulations provided outstanding performance at the non-vacuum atmospheric pressure condition. With the Aerogel insulation, the tank volume for storing 1-L liquid hydrogen at 20 K could be designed within a storage tank volume of 7.2 L. In addition, it was noted that the exhaust temperature of boil-off hydrogen gas was mainly affected by the location of a vapor-cooled shield as well as thermal conductivity of insulation materials.     

Optimal insulation of solar heating system pipes and tanks

A compact and time-effective insulation design procedure for solar heating system piping and water-filled thermal storage tanks was developed. Recognizing the particular sensitivity of solar systems to cost, the economic aspect of the problem was treated by a comprehensive present-value life-cycle cost analysis. In the development of the method, a numerical sensitivity analysis was performed to determine the relative effects of all relevant independent variables (within their pertinent ranges) on piping and tank heat transfer coefficient values. For the acceptable error limits of ± 14% for pipes and ± 19% for tanks, it was found that one may assume that only the nominal pipe diameter (or tank diameter), the thermal conductivity of the insulation, and the insulation's thickness have an effect on the overall heat transfer coefficient. Based on this result, design graphs and tables are presented which can be used to determine the optimal insulation thickness and type, total annual heat losses, present-value annual costs of insulation and lost heat, and overall insulation R-values. The use of the method is illustrated by calculating all the above quantities for all piping and storage tanks for the University of Pennsylvania SolaRow House. The present method provided insulation thicknesses slightly greater than those obtained by the ETI technique.A major conclusion of the study is that the cost of insulation in solar systems is not insignificant (e.g., ~15% in SolaRow), and that heat losses through insulation could amount to an important percentage of the useful solar energy collected (e.g., 24% in SolaRow). This re-emphasizes the need for a careful design of insulation in solar systems.     

Parametric evaluation of refrigerated air curtains for thermal insulation

The refrigerated air curtain used for cavity insulation in the present study is an idealization of the refrigerated air curtain used in supermarket food display cabinets. The thermal insulation performance of refrigerated air curtains is very important for perishable food storage and energy saving for refrigerated display cabinets. Thermal insulation ability of recirculated refrigerated air curtains was numerically studied in the present work. The results show that the refrigerated air curtains are negatively buoyant jets and tend to flow toward the inside cabinet due to stack pressure, so the initial momentum must be sufficiently large to sustain the pressure difference across the air curtain and assure the thermal insulation. The length–width ratio and the discharge angle of the air curtains, the height–depth ratio of the cavity and the dimension and position of the inside shelves would greatly influence the thermal insulation performance of air curtains, therefore were extensively discussed. The maximum Richardson numbers or the optimum parameter selections in each situation were presented for practical design of refrigerated air curtains used in multi-deck display cabinets.     

High-temperature Solar Thermal Energy Storage

The mislocation of solar energy production facilities and points of demand and the temporal mismatch of solar energy availability and energy demand make transport and storage of solar energy essential. Research at the Solar Energy Research Institute has focused on high-temperature, diurnal storage because of the frequency of use and the potential for conservation of premium fossil fuels. Also, high-temperature thermal energy storage can reduce the cost of hydrogen production, electricity and heat produced by cogeneration, and methane reforming. SERI research is concentrating on containment techniques (including materials corrosion, internal insulation, and storage medium for high-temperature molten salts) and direct-contact heat exchange (including cost-effective heat exchanger design and heat transfer of various materials). After initial screening tests we selected carbonates for further study. We are now constructing test equipment that will allow heat transfer experiments with molten carbonate to 700°C     

Analytical approach to ground heat losses for high temperature thermal storage systems

A new approach to estimate the heat loss from thermal energy storage tank foundations is presented. Results are presented through analytical correlations based on numerical solutions for the steady‐state heat conduction problem for thermal energy slab‐on‐grade tanks with uniform insulation. Model results were verified with other well‐established benchmark problems with similar boundary conditions and validated with experimental data with excellent agreement. In addition to the TES foundation heat loss, new correlations for the maximum temperature and for the radial evolution of the temperature underneath the insulation layer are also provided, giving important information related to the tank foundation design. The correlated variables are of primordial importance in the tank foundation design because, due to the typical high operating storage temperatures, an inappropriate tank foundation insulation would lead not only to a not desired loss of energy but also to an inadmissible increase of the temperatures underneath the insulation layer, affecting the structural stability of the tank. The proposed correlations provide a quick method for the estimation of total tank foundation heat losses and soil maximum temperature reached underneath the insulation layer, saving time, and cost on the engineering tank foundation design process. Finally, a comprehensive parametric analysis of the variables of interest is made and a set of cases covering a wide range of tank sizes, insulation levels, depths to water table, and storage temperatures are solved.     

Seasonal storage of energy in solar heating

This paper focuses on several aspects of seasonal storage for space heating using water as the storage medium. The interrelationships between collector area, storage volume, and system performance are investigated using the transient simulation program TRNSYS. The situations for which seasonal storage is most promising are presented. Particular emphasis is placed upon design of seasonal storage systems. A design method is presented which is applicable for storage capacities ranging from a few days to seasonal storage. This design method, coupled with cost information, should be useful in assessing the economic viability of seasonal storage systems. Also investigated are the importance of the load heat exchanger size, tank insulation, collector slope, and year-to-year weather variations in system design.     

A linear model for passive solar evaluation

A simple algebraic model for the evaluation of the average performance of passive solar dwelling units is presented. The model is based on a first order representation for the mass effect of walls and thermal energy balances for a dwelling unit, during the day and the night. The model requires as climatological input the mean temperature during the day and the night and the daily solar irradiation for each month. The model is capable of predicting the performance of both direct gain and storage wall systems and can be used to evaluate the effect of design parameter such as mass, internal or external insulation, temperature difference between day and night.     

Integrated collector storage solar water heaters

The Integrated Collector Storage Solar Water Heater (ICSSWH) developed from early systems comprised simply of a simple black tank placed in the sun. The ICSSWH, by its combined collection and storage function suffers substantial heat losses to ambient, especially at night-time and non-collection periods. To be viable economically, the system has evolved to incorporate new and novel methods of maximising solar radiation collection whilst minimising thermal loss. Advances in ICS vessel design have included glazing system, methods of insulation, reflector configurations, use of evacuation, internal and external baffles and phase change materials.     

Comportement thermique de differents types d'habitation soumis a un ensoleillement et à une température extérieure périodiques

This paper presents the response of different kinds of schematic dwellings under daily periodic variations of the solar flux and the external temperature. The influence of the parameters which are characteristic of coupled heat transfer is studied (thermal diffusion and heat storage in external and internal walls, heat loses or solar heat supply by windows or airing).Calculations show that for an idealised regulation: (i) The energetical consumption depends only on mean variations of external temperature and solar flux and does not depend on the insulation location. (ii) For a building with a regulated internal temperature, the thermal inertia for the internal walls does not play a role. (iii) For an unregulated building, the internal temperature variations depends of the insulation location. The best location is the external one. (iv) There is an optimal thickness of walls corresponding to the daily periodic variations.     

Modeling of Thermal Properties of Thermal Insulation Layered with Transparent,Opaque and Reflective Film

The popular and effective food preservation technology based on refrigeration is not sufficient for high-quality products while undergoing logistic operations (transport and retail). One of the basic factors that affects the quality of chilled and frozen food products during storage and transport is packaging. A protective function of packaging strongly depends on the material used and its composition. There are different kinds of thermal insulation used for food packaging. One of them, proposed by the authors is a multilayer structure of insulation made of rectangular air cells. The insulation can be prepared by means of plastic film featuring various properties. The paper presents how to improve an effective material designed for food freezing and transport aiming to enhance its thermal resistance through the application of different transparency, reflectivity and emissivity of the film. Mathematical model based on heat exchange equations, including conduction, convection and radiation throughout a number of parallel internal sheets of film of multilayer structures was proposed. Thermal properties depending on different transparency, reflectivity and emissivity of the film were analyzed. The model was verified experimentally showing its compatibility and obtaining a significant influence of thermal resistance according to the type of film used to make air structures, the number and thickness of its layers as well as the gaps between internal folds. For multi-layer insulation designed for the insulation of packed frozen food in the shape of a rectangle, it was recommended to apply film transmittance as small as possible for the internal parts of the structure.     

Review of Components for Passive Solar Energy Utilization

Components for passive solar energy utilization can be generally treated as consisting of translucent insulation, radiation control, absorber and storage. Although even in central Europe the total radiation upon a building amounts to more than the heating energy needed during the winter season, closer inspection shows that the available storage capacity is not sufficient to cover the entire load by radiation: auxiliary heat is always required. On the other hand, overheating must be avoided by means of control devices. Components in use at present are: windows, conservatories and, to a lesser extent, trombe walls. Newer developments are based on materials exhibiting high light transmission and good heat insulation properties. Such materials can be used as outside insulation of old building stock and offer prospects for significant energy savings.     

Performance analysis of vapor-cooled shield insulation integrated with para-ortho hydrogen conversion for liquid hydrogen tanks

A composite thermal insulation system consisting of variable-density multi-layer insulation (VDMLI) and vapor-cooled shields (VCS) integrated with para-ortho hydrogen (P-O) conversion is proposed for long-term storage of liquid hydrogen. High-performance thermal insulation is realized by minimizing the thermal losses via the VDMLI design and fully recovering the cold energy released from the sensible heat and P-O conversion of the vented gas. Effects of different design considerations on the thermal insulation performance are studied. The results show that the maximum reduction of the heat leak with multiple VCSs can reach 79.9% compared to that without VCS. The heat leak with one VCS is reduced by 61.1%, and further reduced by 11.6% after adding catalysts. It is found that the deterioration of the insulation performance has an almost linear relationship with catalytic efficiency. A unified criterion with relative optimization efficiency is finally proposed to evaluate the improvement of the VCS number.     

Review of Molten-Salt Thermocline Tank Modeling for Solar Thermal Energy Storage

Molten-salt thermocline tanks are a low-cost option for thermal energy storage in concentrating solar power systems. A review of previous experimental and numerical thermocline tank studies is performed to identify key issues associated with tank design and performance. Published models have shown that tank discharge performance improves with both larger tank height and smaller internal filler diameter due to increased thermal stratification and sustained outflow of molten salt with high thermal quality. For well-insulated (adiabatic) tanks, low molten-salt flow rates reduce the axial extent of the heat-exchange region and increase discharge efficiency. Under nonadiabatic conditions, low flow rates become detrimental to stratification due to the development of fluid recirculation zones inside the tank. For such tanks, higher flow rates reduce molten-salt residence time inside the tank and improve discharge efficiency. Despite the economic advantages of a thermocline tank, thermal ratcheting of the tank wall remains a significant design concern. The potential for thermal ratcheting is reduced through the inclusion of an internal thermal insulation layer between the molten salt and tank wall to diminish temperature oscillations along the tank wall. Future research directions are also pointed out, including combined analyses that consider the solar receiver and power generation blocks as well as optimization between performance and economic considerations.     

一种变电设备绝缘在线监测校验装置的设计

针对目前变电设备绝缘在线监测装置的测量误差试验主要存在的问题,提出了一种变电设备绝缘在线监测装置校验装置及其软硬件的设计和实现。试验结果表明,该校验装置可对绝缘在线监测装置进行测量误差试验,校正绝缘在线监测装置测试误差,并进行数据记录和分析,为变电设备绝缘在线监测装置测量误差试验和测量误差校验提供了依据和手段。     

结构参数对全玻璃真空管太阳热水器夜间热损失的影响研究

文章建立了三维非稳态的全玻璃真空管太阳热水器的数值模型,分析了夜间散热时,该热水器内的流动和传热特征,并且在夜间同一工况下,模拟研究了贮热水箱保温材料的导热系数、保温厚度,以及真空管涂层的发射率对贮热水箱温度、真空管温度和该热水器夜间热损失的影响。分析结果表明:随着散热过程的持续进行,全玻璃真空管太阳热水器内温度分层情况越来越明显,内部流体的流速越来越小,真空管内静滞区域自下往上逐渐扩大;当贮热水箱保温材料的导热系数由0.035 W/(m·℃)减小至0.020 W/(m·℃)时,该热水器的夜间热损失减少了8.5%;当贮热水箱保温厚度由50 mm增加至60 mm时,该热水器的夜间热损失减少了5.0%;当真空管涂层的发射率由0.06减小至0.05时,该热水器的夜间热损失减少了4.0%。     

Isothermal storage of solar energy in building construction

The role of advanced isothermal heat storage systems in buildings is discussed. A storage system encapsulated with phase change materials in which energy is absorbed in the hot period and released in the cold period is analyzed. The thermal behaviour of isothermal heat storage composites is examined using numerical techniques.Two methods of heat transfer with latent heat storage are described in the first part. Based on the initial results, the “effective heat capacity” method was selected and implemented into ESP-r. Numerical studies on the effect of isothermal storage of solar energy in specific building material components are discussed in the second part. Numerical simulations were conducted for two cases of multi-zone, highly glazed and naturally ventilated passive solar buildings. PCM-impregnated gypsum plasterboard was used as an internal room lining in the first case study and transparent insulation material combined with PCM was applied for the external south-oriented wall in the second case study. The behaviour of a TIM–PCM wall and its influence on the internal surface temperature are estimated. Air, surface and resultant temperatures are compared with a “no-PCM” case for both case studies and the diurnal and the seasonal latent heat storage effect is analyzed.     

Thermal optimisation of a built-in storage solar water heater

A simple transient analysis of a built-in storage solar water heater is presented; the results obtained by the present theory are in close agreement with experimental observations as well as with predictions obtained by a more rigorous theory. The water heater consits of an insulated rectangular tank whose top surface is suitably blackened by blackboard paint and then glazed. The unit is exposed to solar radiation during sunshine hours and is covered by adequate insulation at night. The effect of insulation thicknesses (top and bottom insulation) and water mass in the tank is discussed. The importance of using a reflecting sheet instead of insulation is emphasised.     

Design of a Smart Thermal Insulation System

The present work aims to design a smart thermal insulation system. The smart system allows the passing of heat transfer in one direction while preventing its passing in the other direction. This system consists of two gaps separated by a thin movable partition. The two gaps have the same area and width. The partition has radiation emissivity very close to zero to exclude radiation heat transfer. The partition is free to move to either side depending on the driving force causing the motion. The first gap is filled with a fluid that has both high thermal conductivity and high thermal expansion properties, while the second gap is filled with a fluid that has very low thermal conductivity and very high thermal expansion properties. Each gap is connected by a tiny tube to its own small storage tank. Temperature and pressure sensors are used to provide signals to the programmable microcontroller in order to select and activate the desired insulation or conduction mode of the system.     

相变储能冷藏隔热板的应用

分析了传统冷藏集装箱的结构和传热特点,指出了传统冷藏集装箱隔热保温的局限性,提出了使用相变储能材料的隔热板能够减少冷藏车的能耗和费用。阐述了相变储能的原理,总结了相变储能材料在减少室内温度波动和节能方面的应用,提出并设计了一种使用相变储能材料的节能型冷藏集装箱隔热板,可为同类设计提供参考。     

Effect of greenhouse design parameters on conservation of energy for greenhouse environmental control

A mathematical model was developed and used to study the effect of various energy conservation measures to arrive at a set of design features for an energy efficient greenhouse. The Simulation results indicated that under cold climatic conditions of northern India, a gothic arch shaped greenhouse required 2.6% and 4.2% less heating as compared to gable and quonset shapes. An east–west oriented gothic arch greenhouse required 2% less heating as compared to a north–south oriented one. North wall insulation of an east west oriented gothic arch greenhouse saved 30% in heating costs. The use of night curtains reduced the night time heating requirement by 70.8% and daily requirement by 60.6%. By replacing the single cover on the southern side with air inflated double wall glazing, the heating requirement was reduced by 23%. The combination of the design features for an energy efficient greenhouse suitable for cold climatic conditions was found to reduce the greenhouse heating needs by 80%. An internal rock bed thermal storage/retrieval system met the remaining heating energy requirements of the energy-conserving greenhouse.