Reduce Heat Leakage Research Articles

Protection System Architecture for All-Electric Aircraft

To reduce emissions from the aviation industry and meet the targets set by different countries, research has been focused on investigating all-electric aircraft. To make this vision practical, superconducting machines are expected to power the propellers, as they are half the size and a third the weight of conventional machines. The main purpose of this paper is to do a higher-level study of a reliable holistic protection system for all-electric aircraft; that can reduce heat leakage and be able to detect faults reliably. Thus, three main protection systems were investigated; 1) cryogenic voltage source converter superconducting magnetic energy storage system (VSC-SMES), 2) cryogenic dc breaker integrated with superconducting fault current limiter (SFCL), and 3) machine learning algorithm for fault detection. By immersing the protection system at cryogenic temperature, the paper has shown that passive leakage can be eliminated, and thus more energy can be saved for the fuel cell. The paper has also demonstrated that using machine learning for the SFCL-dc-breaker system can consistently eliminate faults and protect the system.

Contribution to Active Thermal Protection Research—Part 2 Verification by Experimental Measurement

This article is closely related to the oldest article titled Contribution to Active Thermal Protection Research—Part 1 Analysis of Energy Functions by Parametric Study. It is a continuation of research that focuses on verifying the energy potential and functions of so-called active thermal protection (ATP). As mentioned in the first part, the amount of thermal energy consumed for heating buildings is one of the main parameters that determine their future design, especially the technical equipment. The issue of reducing the consumption of this energy is implemented in various ways, such as passive thermal protection, i.e., by increasing the thermal insulation parameters of the individual materials of the building envelope or by optimizing the operation of the technical equipment of the buildings. On the other hand, there are also methods of active thermal protection that aim to reduce heat leakage through nontransparent parts of the building envelope. This methodology is based on the validation of the results of a parametric study of the dynamic thermal resistance (DTR) and the heat fluxes to the interior and exterior from the ATP for the investigated envelope of the experimental house EB2020 made of aerated concrete blocks, presented in the article “Contribution to the research on active thermal protection—Part 1, Analysis of energy functions by the parametric study”, by long-term experimental measurements. The novelty of the research lies in the involvement of variant-peak heat/cooling sources in combination with RES and in creating a new, original way of operating energy systems with the possibility of changing and combining the operating modes of the ATP. We have verified the operation of the experimental house in the energy functions of thermal barrier, heating/cooling with RES, and without RES and ATP. The energy saving when using RES and ATP is approximately 37%. Based on the synthesis and induction of analogous forms of the results of previous research into recommendations for the development of building envelopes with energy-active elements, we present further possible outcomes in the field of ATP, as well as already realized and upcoming prototypes of thermal insulation panels.

Calculation and analysis of optimal layer density for variable density multilayer insulation based on layer by layer model and Lockheed equation

The extremely high energy density and carbon-free characteristics of liquid hydrogen (LH2) make it suitable for replacing liquefied natural gas (LNG) as a future energy commodity. However, the extremely low evaporation temperature of LH2 results in high heat leakage. Multilayer insulation (MLI), which is the most thermally efficient insulation system known, is widely used in the fields of hydrogen energy, aerospace, and other cryogenic fields. Variable density multilayer insulation (VDMLI), which has emerged in the last two decades, has improved the performance of MLI by adding spacers to change the density of MLI. However, there has been no significant progress in the optimization theory for VDMLI. In this paper, based on the layer by layer model and the Lockheed equation, a generalized optimal layer density calculation model for VDMLI is established by considering the influences of spacers, compressive pressure, gas pressure, etc. The results indicate that compared to general VDMLI and MLI on liquid hydrogen tanks, the optimal layer density VDMLI (OVDMLI) can reduce heat leakage by 21.1% and 25.3%, respectively. After comparison and analysis, the characteristics and reasons for temperature and heat transfer conductivity profiles of MLI, VDMLI, and OVDMLI are pointed out. The effect of the spacer number on heat flux and spacer profile is analyzed. Additionally, gas pressure profile and heat transfer are investigated with consideration given to the vacuum degree at both boundaries.

Contribution to Active Thermal Protection Research—Part 1 Analysis of Energy Functions by Parametric Study

The thermal energy consumption for heating objects is one of the main parameters deciding their technical and structural solution. Reducing energy consumption is realized in various ways. The most used method is passive thermal protection, that is, increasing the thermal insulation parameters of the envelope constructions and optimizing the operation of the technical equipment of the buildings. There are also methods of active thermal protection to reduce heat leakage through non-transparent parts of the building envelope. Active thermal protection (ATP) is a dynamic process that applies primarily to building structures with integrated energetically active elements that fulfill one or more functions in mutually exclusive operating modes of energy systems and heat sources, such as thermal barriers (TB), large-scale heating/cooling, long-term heat/cool storage, capturing solar energy, and energy from the surroundings or even recovering heat in the cold season or cold in the warm season and other combinations. The research area focuses on analyzing active thermal protection’s energy potential. The methodology is based on a parametric study of dynamic thermal resistance (DTR), and heat flows to the interior and exterior from ATP for the investigated envelope of the experimental house EB2020 made of aerated concrete blocks. Such constructions generally show a consistently high DTR of 11.8 to 30.8 ((m2·K)/W) at a low mean heat transfer temperature of 10 to 16 °C, corresponding to the thermal insulation of 300 to 1000 mm. In the case of ATP storage heating with an average temperature of the heat-carrying substance of 30 °C, the heat flow into the interior of the investigated structure would be only 2.31 W/m2. Therefore, they are only suitable for a thermal barrier and heat/cold accumulation. Based on the synthesis and induction of analogical forms of the results of previous research into recommendations for the design of individual energy functions of ATP for perimeter structures of buildings, we present heat flows to the interior/exterior when changing the material of the layers towards the interior from ATP and describe possible variants of the development of building structures with integrated energetically active elements.

Design, fabrication and characterization of porous ceramics secondary wick of a loop heat pipe to reduce heat leakage

Design, fabrication and characterization of porous ceramics secondary wick of a loop heat pipe to reduce heat leakage

Heat leak variation with the surface temperature of a cryogenic pipe of the superconducting power transmission

The measurements of the heat leak variation with the surface temperature of a cryogenic pipe of the superconducting power transmission were performed in the range of 23.7 °C–36.4 °C. The cryogenic pipe which was an object of the present study was that used in the project of the superconducting DC power transmission conducted in Ishikari, Japan (Ishikari project). This cryogenic pipe has two inner pipes in one outer pipe, with a radiation shield used to conceal the inner pipe installing the cable from the outer pipe, which is at room temperature, to reduce heat leakage. A test pipe with the length of 12 m was used for the measurements. The liquid nitrogen was filled in the test pipe and the evaporated nitrogen gas rate was measured to obtain the heat leak. The heat leak to the inner pipe installing the cable was almost constant at around 0.04 W/m, whereas the heat leak to the other inner pipe used to return liquid nitrogen for circulation was around 1.3 W/m at surface temperatures ranging from 23.7 °C to 36.4 °C. The latter, with previous measurements, was well fitted by a function considering radiative heat transfer and conductive heat transfer. Portions of the radiative heat transfer and the conductive heat transfer were separated with this function. This information can be used to improve the cryogenic pipe in the future.

Comparative Study on Thermodynamic Characteristics of Composite Thermal Insulation Systems With Liquid Methane, Oxygen, and Hydrogen

Abstract Composite passive insulation technology has been proved to be an effective method to reduce heat leakage into the cryogenic storage tank. However, the current related research mainly focused on liquid hydrogen (LH2). The thermophysical properties of different cryogenic liquids and the thermal insulation materials at different temperatures are significantly different, so whether the results related to LH2 are applicable to other cryogenic liquids remains to be further determined. In fact, the insulation technology of LH2 itself also needs further study. In this paper, a thermodynamic calculation model of a composite insulation system including hollow glass microspheres (HGMs), multilayer insulation (MLI), and self-evaporating vapor cold shield (VCS) has been established. The accuracy of the calculation model was verified by the experimental results, and a comparative study on thermodynamic characteristics of the composite thermal insulation system with liquid methane, liquid oxygen (LO2), and LH2 was carried out. The results show that the heat leakage reduction of the proposed system for liquid methane, LO2, and LH2 is 25.6%, 29.7%, and 64.9%, respectively, compared with the traditional SOFI + MLI system (1 × 10−3 Pa). The type of liquid and the insulation system structure has a relatively large influence on the VCS optimal position. While for a specific insulation system structure, the insulation material thickness, storage pressure, and hot boundary temperature have a weak influence on the VCS optimal position.

Design of Internal Supports for Double-Walled Liquefied Natural Gas Road Tanker

Transport and storage of liquefied natural gas (LNG) requires special double-walled cryogenic tanks. To provide a liquid state of LNG throughout entire storage time a temperature inside the tank should be equal −160 °C under the pressure of around 7 bar. Maintaining these parameters requires a vacuum insulation system and internal supports designed to minimize heat leakage into the tank. Additionally, the internal supports must be able to transfer complex mechanical loads that may occur during the operation of the tanker. Combinations and values of directional mechanical loads and thermal loads, to be accepted in designing mobile cryogenic tanks, are determined by proper vessels standards. In this article, we proposed the construction of internal supports for 25 m3 road tanker, which structure allows to reduce heat leakage into the internal tank, while transferring the complex mechanical loads. Tests of the presented solutions were carried out applying both mechanical and thermal finite element analysis using ANSYS software.

Numerical research of magnetohydrodynamics buoyant flow in dual functional lead lithium fusion blanket

Blanket is key component of fusion reactor, which functions as tritium breeder, energy conversion component and radiation shield. Liquid metal fusion blanket is a promising candidate of future fusion power plants for its high temperature operating characteristics and efficient thermoelectric conversion. However, motion of liquid metal under fusion reactor high magnetic field (∼4 T) causes serious magnetohydrodynamics (MHD) effect, and extreme non-uniform volumetric heat deposited by fusion neutrons produces strong buoyancy effect. Both effects greatly change flow field and heat transfer characteristics of liquid metal blanket, which are key issues for thermal-hydraulic design of liquid metal blankets. In this paper, MHD buoyant flow of Dual Functional Lead Lithium blanket (DFLL) under typical fusion magnetic field and non-uniform volumetric nuclear heating were studied. Buoyancy force induced drastic natural convection in LL1 (the 1st Lead Lithium channel) channel of blanket and increased the heat leaked to Helium coolant and reduced the outlet temperature. FCI (flow channel insert) material with heat conductivity <1W/m K was required to achieve high outlet temperature (700 K). Reversed direction of original flow in DFLL blanket would smooth the flow and reduce heat leakage of PbLi, which formed the idea of improvement. At the extreme condition of duct with steel wall, Lorentz force completely suppressed buoyancy. According to the founding above, we analyzed the MHD buoyant flow in an upside-down DFLL blanket and temperature distribution and heat leakage were significantly improved. This finding would be valuable for liquid blanket thermal hydraulic design.

One-dimensional steady-state mathematical model of a novel loop heat pipe with liquid line capillary wick

A novel loop heat pipe used for data center with a liquid line wick is designed, and its one-dimensional steady-state mathematical model is developed based on the energy and thermodynamic equilibrium of each component and the simulation results were validated by comparing with the experimental data in this work. The compensation chamber of the loop heat pipe was removed, and a section of capillary wick was added in the end of liquid line in order to reduce heat leakage and vapor backflow and increase working medium circulation power. The mathematical model of the novel loop heat pipe can be used to predict the operating temperature of each characteristic point with small relative errors of &lt;13%. A parametric study of the steady-state performance characteristics including the effects of material, diameter, length, and porosity of liquid line wick are conducted, which provides a powerful basis for the design of novel loop heat pipe experiment.

Experimental Study on 1 kA-Class Peltier Current Lead for Superconducting DC Devices

Current lead, connecting dc superconducting device with power supply, is one of the major heat leakage sources. Reducing the heat leakage from the current lead to cryogenic system is very important in the operation of dc superconducting device. The Peltier current lead (PCL) is effective for reducing the heat-leakage. The PCL consisting of the conventional copper lead with a thermoelectric material Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Te <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> inserting into room-temperature end can be effective to reduce heat leakage due to its Peltier effect. For the sake of studying the higher current capacity of PCL, the 1-kA-class PCL was designed and fabricated in this paper. Dynamic stability experiment for the PCL was carried out such that its operating stability was confirmed. The temperature along the PCL was measured and the heat leakage per kA current <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> was also calculated. The experimental results showed that the PCL can be effective to reduce the heat leakage and has potential applications in the dc superconducting device.

A novel insulation system based on active cooling without power input for liquid hydrogen storage

Hydrogen energy is a clean, efficient and renewable energy source. Compared with compressed gaseous hydrogen (GH2) storage and metal hydride storage, liquid hydrogen (LH2) storage has advantages of high energy density and storage efficiency. Excellent insulation system can effectively reduce heat leak into LH2 tank and evaporation loss. In comparison with vaporization heat (449 kJ/kg) of H2, the sensible heat (from 20 K to 300 K, 3509 kJ/kg) and combustion heat (140 MJ/kg) are considerable. In this paper, thermoacoustic refrigerator shield (TRS) and self-evaporating vapor cooled shield (VCS) are introduced into different insulation materials to recover the sensible heat and combustion heat of discharged GH2. The proposed insulation system is independent of external power supply and can realize efficient LH2 storage without H2 emission into ambient, which can be used in skid-mounted LH2 storage tanks for remote areas. A self-built thermodynamic model, which has been verified by test results, is used to analyze the insulation performance with VCS and TRS quantitatively. For the proposed insulation system, the heat flux into tank with VCS decreased by 70.98% and TRS by 90.81%. The effects of hot boundary temperature, LH2 storage pressure and insulation material type on the insulation performance have been analyzed.

Calculation and position optimization on vapor cooled shield for liquid hydrogen storage

The ZBO (zero boil off) storage of liquid hydrogen (LH2) has broad prospects in aerospace and civil market. Because of low critical temperature and volatility, LH2 tank poses severe requirements to the insulation system (multilayer insulation (MLI) is considered to be the most promising). In order to reduce heat leak into tank, vapor cooled shield (VCS) was set up to cool the MLI by retrieving the cold energy of discharged low temperature GH2. In this study, a simplified physical model is established to investigate the optimal position of VCS in MLI, and the influence of various factors on the performance of VCS has been analysed. Taking the minimum heat leak as the target, the best installation position is around 50% in MLI (inside looking outward) for the given condition. The heat leak of the tank can be reduced by 48.03% at most.

Thermodynamic modelling and optimization of self-evaporation vapor cooled shield for liquid hydrogen storage tank

This paper presents an optimization study on self-evaporation vapor cooled shield (VCS) in liquid hydrogen (LH2) storage tank with multilayer insulation (MLI). Production from other clean energy sources (such as solar energy, wind energy and biomass energy) and combustion without pollution make H2 a promising renewable energy source to reduce air pollution and greenhouse effect. Due to the advantages of low pressure and high energy density, LH2 storage has broad prospects in aerospace and civil market. Because of low critical temperature and volatility, LH2 tank poses severe requirements to MLI. In order to reduce heat leak into tank, VCS was set up to cool MLI by retrieving the sensible heat of discharged cryogenic gas hydrogen (GH2). In this study, a simplified thermodynamic model is established to investigate the optimal position of VCS in MLI, and the effect of VCS on heat leak into tank and temperature profile through MLI has been studied. Compared with heat leak without VCS, the maximum decrease with Single-VCS is 50.16% and Double-VCS by 59.44%. VCS can also play a positive role under the condition of vacuum failure, and its inhibiting the sharp increase of heat leak is of great significance in emergencies.

Insulation performance of foam during the terrestrial and ascent period

To effectively reduce heat leakage, foam insulation is widely used in refrigeration, energy, chemical, cryogenic system and pipe engineering. The present study is aimed to investigate the thermal performance of foam on cryogenic storage system under variable environmental parameters. The heat transfer model through the foam is introduced in detail. The minimum thicknesses of foam for different cryogens are calculated under the influence of the external free convection during the terrestrial condition. Meanwhile, with carbon dioxide diffusion out of and air invasion in the foam cells, the related unsteady process is studied with coupling the mixture gas heat conduction and the external free convection. While during the liftoff of rocket, foam insulation is subjected to the forced aerodynamic heating. The transient thermal performance of foam is particularly investigated under the influence of aerodynamic heating, with the variable physical properties, flight velocity and acceleration, and environmental parameters considered. Finally, the performance comparison between foam and foam/Multilayer insulation is made. Some valuable conclusions are obtained. The present study is of significance to the insulation design for cryogenic fuel storage.

The use of low grade bio ethanol as fuel mixer in gasoline engine with optimization compact distillator

Limited fossil energy resources need to encourage renewable energy development and energy conservation it is called green energy development. One of the alternative energy sources used are bioethanol, from low grade is converted into high grade through distillation process with distillator compact that will be used as a mixture of gasoline. Tests compact distillator consisting of evaporator Indonesia Kampus, separator, and condenser by utilizing exhaust gas to heat distillator already filled with low grade bioethanol, so the heat transfer occurs on the surface of the exhaust into the evaporator chamber. In the evaporator will transform ethanol into the vapor phase. Ethanol vapor flows into the separator, with a mechanism in it is expected that water vapor will evaporate participate separately with ethanol vapor. Ethanol vapors from this distillation will flow to the condenser and will be turned into liquid, the liquid is as high grade bioethanol would be the fuel mixing gasoline. In early studies, distillation rate was 98.5 ml/h with 67% ethanol content. Optimization compact distillator is done by adding the valve at the evaporator branch. When heat has reached 80°C exhaust gas flow to the evaporator chamber is closed. As a result, the heat from the evaporator can be detained and not rise significantly. Further optimization is to change the design of the separator through theoretical and empirical calculations with some assumptions based on the rule of thumb in the field of distillation, adding insulation to reduce heat leakage, as well as varying the feed volume and feed concentrate ethanol. In the end, based on the parameters of the distillation rate and ethanol concentrate, compact distillator with distances between tray 100 mm, volume 800 ml, engine speed 5.400 rpm can produce distillation rate of 274.3 ml/hr and ethanol concentrate of 88.97%.

Conversion efficiency of an energy harvester based on resonant tunneling through quantum dots with heat leakage

We study the conversion efficiency of an energy harvester based on resonant tunneling through quantum dots with heat leakage. Heat leakage current from a hot electrode to a cold electrode is taken into account in the analysis of the harvester operation. Modeling of electrical output indicates that a maximum heat leakage current is not negligible because it is larger than that of the heat current harvested into electrical power. A reduction of heat leakage is required in this energy harvester in order to obtain efficient heat-to-electrical conversion. Multiple energy levels of a quantum dot can increase the output power of the harvester. Heavily doped colloidal semiconductor quantum dots are a possible candidate for a quantum-dot monolayer in the energy harvester to reduce heat leakage, scaling down device size, and increasing electrical output via multiple discrete energy levels.

Operation and Improvement of Liquid Nitrogen Pumps with Radial High- Temperature Superconductor Bearings

This paper reviews the advantages of replacing the mechanical bearings of low-temperature pumps by radial high- temperature superconductor (HTS) bearings. Radial HTS bearings have the advantage of being non-abrasive, so that the working life is increased significantly. In this article, two types of liquid nitrogen pump with radial HTS bearings are proposed. To reduce heat leakage, one pump uses a permanent magnet (PM) coupling and the other uses a long hollow pipe coupling. Successful stable operation of these two pumps means that radial HTS bearings have the potential to be applied in liquid nitrogen pumps. Test results show that the flow rate is influenced mainly by rotational speed but not by the coupling component. Further designs of the two types of pump for practical applications are described, and their characteristics are analyzed: the pump with a PM coupling has lower heat leakage, whereas the pump with a long hollow pipe coupling can solve the force creep problem of the HTS bearing. The design of the pump with a long hollow pipe coupling is based on the pump that is already in practical use, and therefore has greater feasibility for practical applications. Finally, improvements of the liquid nitrogen pump by improving the structure of the pump and the performance of the radial HTS bearing are discussed.

Thermal Insulation Test of new Designed Cryogenic Pipes for the Superconducting DC Power Transmission System in Ishikari, Japan

New cryogenic pipes were designed for the superconducting DC power transmission systems constructed in the Ishikari area in Japan. In the designs two inner pipes, for the cable and for the return of liquid nitrogen, are installed in a single outer pipe for the circulation of liquid nitrogen. In contrast to the cryogenic pipes commonly used for the superconducting power transmission, in which corrugated pipes are used, straight pipes are adopted to reduce pressure loss of the circulation of the liquid nitrogen. A radiation shield to reduce heat leak to the inner pipe for the cable is adopted in one of the designs.Two types of test pipes with and without the radiation shield were constructed and heat leak of these pipes was measured to evaluate the effciency of the test pipes. The lowest heat leak of 0.73W/m was measured for the test pipe with the radiation shield.

Wrapped multilayer insulation design and testing

New vehicles need improved cryogenic propellant storage and transfer capabilities for long duration missions. Multilayer insulation (MLI) for cryogenic propellant feedlines is much less effective than MLI tank insulation, with heat leak into spiral wrapped MLI on pipes 3–10 times higher than conventional tank MLI. Better insulation for cryogenic feed lines is an important enabling technology that could help NASA reach cryogenic propellant storage and transfer requirements. Improved insulation for Ground Support Equipment could reduce cryogen losses during launch vehicle loading. Wrapped-MLI (WMLI) is a high performance multilayer insulation using innovative discrete spacer technology specifically designed for cryogenic transfer lines and Vacuum Jacketed Pipe (VJP) to reduce heat flux.The poor performance of traditional MLI wrapped on feed lines is due in part to compression of the MLI layers, with increased interlayer contact and heat conduction. WMLI uses discrete spacers that maintain precise layer spacing, with a unique design to reduce heat leak. A Triple Orthogonal Disk spacer was engineered to minimize contact area/length ratio and reduce solid heat conduction for use in concentric MLI configurations.A new insulation, WMLI, was developed and tested. Novel polymer spacers were designed, analyzed and fabricated; different installation techniques were examined; and rapid prototype nested shell components to speed installation on real world piping were designed and tested. Prototypes were installed on tubing set test fixtures and heat flux measured via calorimetry. WMLI offered superior performance to traditional MLI installed on cryogenic pipe, with 2.2W/m2 heat flux compared to 26.6W/m2 for traditional spiral wrapped MLI (5 layers, 77–295K). WMLI as inner insulation in VJP can offer heat leaks as low as 0.09W/m, compared to industry standard products with 0.31W/m. WMLI could enable improved spacecraft cryogenic feedlines and industrial hot/cold transfer lines.