The design and optimization of a cryogenic compressed hydrogen refueling process

Cryo-compressed hydrogen storage has excellent volume and mass hydrogen storage density, which is the most likely way to meet the storage requirements proposed by United States Department of Energy（DOE）. This paper contributes to propose and analyze a new cryogenic compressed hydrogen refueling station. The new type of low temperature and high-pressure hydrogenation station system can effectively reduce the problems such as too high liquefaction work when using liquid hydrogen as the gas source, the need to heat and regenerate to release hydrogen, and the damage of thermal stress on the storage tank during the filling process, so as to reduce the release of hydrogen and ensure the non-destructive filling of hydrogen. This paper focuses on the study of precooling process in filling. By establishing a heat transfer model, the dynamic trend of tank temperature with time in the precooling process of low-temperature and high-pressure hydrogen storage tank under constant pressure is studied. Two analysis methods are used to provide theoretical basis for the selection of inlet diameter of hydrogen storage tank. Through comparative analysis of the advantages and disadvantages of the two analysis methods, it is concluded that the analysis method of constant mass flow is more suitable for the selection in practical applications. According to it, the recommended diameter of the storage tank at the initial temperature of 300 K, 200 K and 100 K is selected, which are all 15 mm. It is further proved that the calculation method can meet the different storage tank states of hydrogen fuel cell vehicles when selecting the pipe diameter.     

中深层地热地埋管实际运行影响因素研究

为研究中深层地热地埋管运行的影响因素,分析西咸新区中深层地热地埋管供暖系统的长期运行结果,并结合关中地区地质数据,建立深度为2510 m的中深层地埋管换热器全尺寸模型,采用数值模拟法研究实际岩层分布下地埋管的运行、结构和材料因素对其取热能力的影响。结果表明,西咸新区某项目1号地埋管和2号地埋管两个地埋管,其平均取热功率均在310 kW以上,具有优良的取热能力。地埋管进水温度随季节变化明显,并引起用户侧负荷及热泵回水温度的波动。在结构方面,随内管径由63 mm增至125 mm,平均出口水温和换热功率分别降低1.9%和4.8%,但内管径过小将影响内管运行的安全性,综合安全和换热两方面因素,最佳内管径应选取ϕ110 × 10mm规格;随外管径由168.3 mm增至244.5 mm,平均出口水温和换热功率分别增加3.5%和9%,综合成本和换热两方面因素,最佳外管径应选取ϕ 177.8 × 19 mm规格;在运行方面,地埋管出口水温随着流量的增加而减小,换热功率随着流量增加而增加;出口水温随着进水温度的升高而上升,换热功率也随之减小。在材料方面,减小内管导热系数和增加固井材料导热系数均能增加地埋管出口水温和换热功率,考虑换热功率变化和成本因素,在工程中导热系数为0.42 W/（m∙K）的内管和导热系数为3 W/（m∙K）左右的固井材料。     

盘管式外融冰槽融冰过程试验研究（I）——取冷特性

作者在搭建的50RTH(1RTH=3517W·h)盘管式外融冰实验台上研究了外融冰取冷的动态过程,全面考察了取冷进出口模式、取冷流量、入口温度、初始蓄冰量、搭接等因素对冰槽取冷特性的影响。研究结果表明:1)取冷进出口模式严重影响冰槽取冷特性:不同进出口模式下取冷出口水温的变化过程有很大差异;在取冷的前4/5时间,下进模式取冷的出口温度比上进模式低2 5℃;2)取冷流量对于出口水温的影响小于1℃;3)恒定流量条件下,入口温度的变化会较大程度影响到取冷速率的变化,而对出口水温的影响小于0 5℃;4)初始蓄冰量对于取冷特性影响很小;5)冰柱搭接急剧提高取冷出口温度。     

Physical model of onboard hydrogen storage tank thermal behaviour during fuelling

A physical model to simulate thermal behaviour of an onboard storage tank and parameters of hydrogen inside the tank during fuelling is described. The energy conservation equation, Abel-Noble real gas equation of state, and the entrainment theory are applied to calculate the dynamics of hydrogen temperature inside the tank and distribution of temperature through the wall to satisfy requirements of the regulation. Convective heat transfer between hydrogen, tank wall and the atmosphere are modelled using Nusselt number correlations. An original methodology, based on the entrainment theory, is developed to calculate changing velocity of the gas inside the tank during the fuelling. Conductive heat transfer through the tank wall, composed of a load-bearing carbon fibre reinforced polymer and a liner, is modelled by employing one-dimensional unsteady heat transfer equation. The model is validated against experiments on fuelling of Type III and Type IV tanks for hydrogen onboard storage. Hydrogen temperature dynamics inside a tank is simulated by the model within the experimental non-uniformity of 5 °C. The calculation procedure is time efficient and can be used for the development of automated hydrogen fuelling protocols and systems.     

CFD simulation of heat transfer and phase change characteristics of the cryogenic liquid hydrogen tank under microgravity conditions

The heat transfer and phase change processes of cryogenic liquid hydrogen (LH₂) in the tank have an important influence on the working performance of the liquid hydrogen-liquid oxygen storage and supply system of rockets and spacecrafts. In this study, we use the RANS method coupled with Lee model and VOF (volume of fraction) method to solve Navier-stokes equations. The Lee model is adopted to describe the phase change process of liquid hydrogen, and the VOF method is utilized to calculate free surface by solving the advection equation of volume fraction. The model is used to simulate the heat transfer and phase change processes of the cryogenic liquid hydrogen in the storage tank with the different gravitational accelerations, initial temperature, and liquid fill ratios of liquid hydrogen. Numerical results indicate greater gravitational acceleration enhances buoyancy and convection, enhancing convective heat transfer and evaporation processes in the tank. When the acceleration of gravity increases from 10^?2 g0 to 10^?5 g0, gaseous hydrogen mass increases from 0.0157 kg to 0.0244 kg at 200s. With the increase of initial liquid hydrogen temperature, the heat required to raise the liquid hydrogen to saturation temperature decreases and causes more liquid hydrogen to evaporate and cools the gas hydrogen temperature. More cryogenic liquid hydrogen (i.e., larger the fill ratio) makes the average fluid temperature in the tank lower. A 12.5% reduction in the fill ratio resulted in a decrease in fluid temperature from 20.35 K to 20.15 K (a reduction of about 0.1%, at 200s).     

地道风系统地埋管管径对出口空气温度的影响研究

构建了空气与地道壁面换热理论模型,用于计算地埋管出口空气温度,通过正交模拟分析了地埋管管径、长度以及进口风速对地埋管出口空气温度的影响,并与数值模拟结果进行对比.结果 表明:地埋管管径极差值最大,可达20.4 m,是地埋管出口空气温度的主要影响因素,地埋管长度和进口风速为次要因素;随着管径的增大,出口空气温度随之升高;...     

Negative buoyant plume model for solar domestic hot water tank systems incorporating a vertical inlet

Thermal stratification in solar energy storage tanks plays an important role in enhancing the performance of solar domestic hot water systems. The mixing that occurs when hot fluid from the solar collector enters the top of the tank is detrimental to the stratification. Mathematical models that are used for system analysis must therefore be able to capture the effects of this inlet jet mixing in order to accurately predict system performance. This paper presents a computational study of the heat transfer and fluid flow in a thermal storage tank of a solar domestic hot water system with a vertical inlet under negative buoyant plume conditions. The effects of parameters such as the fluid inlet velocity and temperature as well as inlet pipe diameter on the thermal mixing were considered. The work culminated in the development of a one-dimensional empirical model capable of predicting the transient axial temperature distribution inside the thermal storage tank. Predictions from the new model were in good agreement with both experimental data and detailed computational fluid dynamics predictions.     

Thermal‐fluid transport phenomena in an axially rotating flow passage with twin concentric orifices of different radii

This paper investigates the thermal fluid‐flow transport phenomena in an axially rotating passage in which twin concentric orifices of different radii are installed. Emphasis is placed on the effects of pipe rotation and orifice configuration on the flow and thermal fields, i.e. both the formation of vena contracta and the heat‐transfer performance behind each orifice. The governing equations are discretized by means of a finite‐difference technique and numerically solved for the distributions of velocity vector and fluid temperature subject to constant wall temperature and uniform inlet velocity and fluid temperature. It is found that: (i) for a laminar flow through twin concentric orifices in a pipe, axial pipe rotation causes the vena contracta in the orifice to stretch, resulting in an amplification of heat‐transfer performance in the downstream region behind the rear orifice, (ii) simultaneously the heat transfer rate in the area between twin orifice is intensified by pipe rotation, (iii) the amplification of heat transfer performance is affected by the front and rear orifice heights. Results may find applications in automotive and rotating hydraulic transmission lines and in aircraft gas turbine engines. Copyright © 2005 John Wiley & Sons, Ltd.     

Simulation of compressible flow in high pressure buried gas pipelines

The aim of this work is to analyze the gas flow in high pressure buried pipelines subjected to wall friction and heat transfer. The governing equations for one-dimensional compressible pipe flow are derived and solved numerically. The effects of friction, heat transfer from the wall and inlet temperature on various parameters such as pressure, temperature, Mach number and mass flow rate of the gas are investigated. The numerical scheme and numerical solution was confirmed by some previous numerical studies and available experimental data. The results show that the rate of heat transfer has not a considerable effect on inflow Mach number, but it can reduce the choking length in larger f_DL/D values. The temperature loss will also increase in this case, if smaller pressure drop is desired along the pipe. The results also indicate that for f_DL/D = 150, decreasing the rate of heat transfer from the pipe wall, indicated here by Biot number from 100 to 0.001, will cause an increase of about 7% in the rate of mass flow carried by the pipeline, while for f_DL/D = 50, the change in the rate of mass flow has not a considerable effect. Furthermore, the mass flow rate of choked flow could be increased if the gas flow is cooled before entrance to the pipe.     

Simulation of heat and mass transfer in activated carbon tank for hydrogen storage

The charging process of hydrogen storage tank based on bed of activated carbon in a steel container at room temperature (295 K) and medium storage pressure (10 MPa) is simulated with an axisymmetric geometry model using the finite volume commercial solver Fluent. The mass flux profile at the entrance is established using user-defined functions (UDFs). The heat and mass transfer processes in the cylindrical steel tank packed with activated carbon are discussed considering the influence of viscous resistance and inertial resistance of the porous media. The velocity distribution and its effect on the temperature distribution are analyzed. The effects of the flow rate at the inlet and of the adsorption factor on the charging process are studied. A computational fluid dynamics (CFD) approach based on finite volume simulations is used. Results show that the temperature near the bottom of the tank is higher than that at the entrance, temperature in the center of the tank is higher than that near the wall and rises somewhat faster along the axial compared to the radial direction. The highest hydrogen absolute adsorption occurs at the entrance of the tank. A good agreement is found between the simulation results and the available experimental data. The maximum magnitude of the axial velocity is much higher than that of the radial component, resulting in more heat energy transfer along the axial direction than radial direction. In addition, the pressure reaches equilibrium earlier when the mass flow is higher, and the temperature reaches a maximum value faster.     

Thermal–fluid behavior of the hydriding and dehydriding processes in a metal hydride hydrogen storage canister

A study of the hydrogen absorption and desorption processes using LaNi₅ metal hydride is presented for investigation on the influences of expansion volume and heat convection. The hydrogen storage canister comprises a cylindrical metal bed and a void of expansion volume atop the metal. The expansion volume is considered as a domain of pure hydrogen gas. The gas motion in the metal hydride bed is treated as porous medium flow. Concepts of mass and energy conservation are incorporated in the model to depict the thermally coupled hydrogen absorption and desorption reactions. Simulation results show the expansion volume reduces the reaction rates by increasing thermal resistance to the heat transfer from the outside cooling/heating bath. The assumption usually adopted in simulating heat transfer in a metal hydride tank that heat convection in the reaction bed may be ignored is not valid when expansion volume is used because heat convection dominates the heat transfer through the expansion volume as well as the metal bed. The details of the thermal flow pattern are demonstrated. It is found that, due to the action of thermal buoyancy, circulations are likely to happen in the expansion volume. The hydrogen gas accordingly, instead of going directly between the inlet/outlet and the metal bed, tends to move with the circulation along the boundary of the expansion volume.     

Novel thermoelectric generator heat exchanger for indirect heat recovery from molten CuCl in the thermochemical Cu–Cl cycle of hydrogen production

The looming threat of global warming has elicited efforts to develop reliable sustainable energy resources. Hydrogen as a clean fuel is deemed a potential solution to the problem of storage of power from renewable energy technologies. Among current thermochemical hydrogen generation methods, the thermochemical copper-chlorine (Cu–Cl) cycle is of high interest owing to lower temperature requirements. Present study investigates a novel heat exchanger comprising a thermoelectric generator (TEG) to recover heat from high temperature molten CuCl exiting the thermolysis reactor. Employing casting/extrusion method, the performance of the proposed heat exchanger is numerically examined using COMSOL Multiphysics. Results indicate that maximum generated power could exceed 40 W at the matching current of 4.5 A. Maximum energy conversion efficiency yields to 7.1%. Results demonstrate that TEG performance boosts with increasing the inlet Re number, particularly at the hot end. For the molten CuCl chamber, findings denote that there is a 36% discrepancy between highest and lowest Re numbers. Similarly, the highest efficiency value pertains to the case with the highest inlet velocity. Moreover, the highest temperature difference between inlet and outlet of the cooling water is about 28 °C and 10 °C for the lowest and highest inlet Re numbers, respectively. Average deviation from anticipated friction factor and Nusselt number are 0.31% and 12.62%, respectively.     

双圆台型高温太阳能蓄热系统传热特性研究

提出一种新型太阳能蓄热系统(双圆台型),然后建立数学模型并进行模型验证,最后计算多种变参数条件下蓄热系统的传热特性。研究结果表明:增大传热介质的入口温度、流速均能提高蓄热装置的蓄热速率;对比单圆台型储热系统的出口温度,结果发现双圆台型系统的热利用率显著提高;在该文的数值计算参数范围内,当传热介质的进口温度和流速分别为747 K和1.2 m/s时,双圆台型系统的蓄热效果最优。研究结果对于认识和揭示高温太阳能高效光热转换及利用具有参考价值。     

Heat transfer in a crater bed

The aim of this work is to study heat transfer in a laboratory scale crater bed, which was set up from a cylindrical acrylic/quartz tube, using sand as the bed particle. The bed employs a downward gas jet from a nozzle which causes the particles to ascend fountain-like into the freebroad, leaving a crater on the bed surface. After reaching a certain height, these particles will descend again to the bed surface and move into the crater, where the cycle or circulation pattern starts again. The study had been separated into three parts. Firstly, the void fraction of the bed fountain zone was studied by direct measurement of the ascending sand weight within the specific volume. Secondly, the convection heat transfer coefficients between the fountain zone and the external surface of the gas inlet tube were determined by measuring the quantity of heat loss from an electrical heater that was wrapped on the outside surface at desired positions of the gas inlet tube. Thirdly, the radiation heat transfer coefficients were evaluated by heat balance of LPG combustion in the crater bed. From experimental results, the void fraction of the fountain zone could be approximated as a dilute bed (>0.98). For convective heat transfer coefficients, the value found experimentally varied from 80–260 W/m² K depending on the experimental conditions, showing an increase when the gas velocity increases, and a decrease along the height of the gas inlet tube. Radiation heat transfer coefficients, the values of which are (within the experimental temperature range), the same order as the convective mode, increase when the bed temperature is increased and when the bed particle diameter is decreased. Empirical correlations for both bed voidage and heat transfer coefficients are proposed. The combined model, gas and particle convection and the published data on radiation heat transfer, showed good prediction when compared with experimental data.     

Numerical investigations on flow characteristics and energy separation in a Ranque Hilsch vortex tube with hydrogen as working medium

In the last decades, the theory of energy separation in vortex tubes is debated broadly based on the heat transfer and work transfer between core and peripheral flow layers. Many parameters were considered in the literature. However, the present study involves the inlet energy considered collectively towards energy separation. In this paper, three-dimensional computational fluid dynamic simulations are discussed in vortex tube to analyze the energy separation phenomena in different cases by varying the working medium such as hydrogen and air having specific heat variation. The energy at the inlet is maintained same in both cases by adjusting the inlet mass flow rate. The results from this study are validated with recently published literature using hydrogen as a working medium. Vortex tube with hydrogen as working medium yields a temperature separation of 8 K lower than air as working medium. Further studies on vortex tube with hydrogen as a working fluid is explored at different inlet temperatures relative to the room temperature. Vortex tube with hydrogen at an inlet temperature of 400 K gives better temperature separation as compared to other inlet temperatures considered in this study.     

烧结余热回收竖式炉内气体流动和传热的数值模拟

运用数值模拟的方法,通过求解非线性联立的质量、动量、能量及组分守恒偏微分方程组,借助多物理场祸合软件Comsol和模拟软件FLUENT模拟出竖式炉内气体流动,换热特性以及料层阻力特性。模拟结果表明:冷却段高度是影响竖式炉内气固流动换热的因素之一,高度增加,烧结矿温度降低,冷却风的温度升高,空气出口携带火用值先增加后趋于平缓,气固比也影响着竖式炉内气体流动和换热,气固比增加,烧结矿的出口温度和循环空气的平均出口温度逐渐降低,热空气携带的火用值先增加后减小;竖式炉直径也是影响因素之一,但相比于冷却高度和气固比影响不是很大。由模拟的结果给出的冷却段高度为7 m,气固比1 400 m~3/t,竖式炉直径12 m时,竖式炉炉内的气固换热最强,与现场实际的结构参数和操作参数比较吻合。     

Dynamic behavior of metal–hydrogen reactor during hydriding process

The present study involves numerical simulation of transient transport of hydrogen and heat within a metal–hydrogen reactor connected to a hydrogen tank during the hydriding process. This problem is of particular interest in the design of many installations in the field of energy technology (compressor, heat pumps, thermal or hydrogen storage systems). The reactor presents an expansion volume for hydrogen. The hydrogen flow is described by general momentum conservation equations instead of Darcy's law. The evolutions of the temperature, of the hydrogen concentration and of the hydrogen flow velocity are presented. The effects of the reactor dimensions, the inlet diameter, the volume of the expansion part, the tank volume, the initial pressure and the amount of hydrogen in the tank, on the heat and hydrogen transfer are determined.     

Flow rate measurement via isothermal discharge method for hydrogen

The thesis of this study is to investigate that the measurement accuracy of the isothermal discharge method for hydrogen gas with an isothermal tank which is designed for measuring the flow rate characteristics of pneumatic components. Compressed hydrogen in an isothermal tank, which is combined three types of orifice, is discharged from 700 kPa (abs) to atmospheric pressure. The average temperature in the tank during discharge is measured experimentally. In consequence, when the maximum discharge rate is 37 kPa/s during discharge hydrogen, the measurement error is less than 3% in whole discharge time. The temperature response phenomenon in hydrogen is discussed qualitatively in the view point of the internal energy change. The internal energy change immediately after the discharge started was negative because the release enthalpy was larger than the quantity of heat obtained from the stuffing material. After a certain period of time elapsed, the enthalpy change became equal to the heat exchange between the internal hydrogen and the stuffing material.     

Modeling a hydrogen pressure regulator in a fuel cell system with Joule–Thomson effect

Fuel cell vehicles offer significant sustainability benefits by eliminating tailpipe emissions, increasing powertrain efficiency, and utilizing hydrogen that can be supplied from various sources including renewables. A pressure regulator in the hydrogen storage system on a fuel cell vehicle is an important component to ensure that the hydrogen delivery to the fuel cell stack meets the pressure and temperature requirements. A validated model of the regulator can be used to support the product design and optimization of the operating strategy. In this work, a pressure regulator model has been developed to capture the hydrogen discharge behaviors from the compressed hydrogen tank to the fuel cell stack. The focus of the model is to develop the pressure and temperature relationship at the regulator outlet given the inlet conditions from the storage tank. Besides the ideal-gas based derivation for pressure response, the model has used a constant-enthalpy approach to capture the hydrogen temperature increase associated with the pressure drop due to the Joule–Thomson effect. The model was validated with various testing data including hysteresis and dynamic flow conditions, showing satisfactory agreement. The validated model was then used for parametric studies. The modeling results concluded that the regulator inlet temperature has the strongest influence on raising the outlet temperature, while the regulator inlet pressure is an important factor although secondary to the inlet temperature. The comprehensive regulator modeling developed in this work provides the foundation for assessing and optimizing a key dynamic component in the hydrogen storage system.