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The paper deals with heat transfer processes during pre-launch chilldown of consumption lines of the upper stage propulsion systems (PS) by a cryogenic component. Propulsion systems operating on high-efficiency cryogenic propellant components may be used at the first as well as at the upper stages of launch vehicles to deliver spacecrafts into final orbits. Cryogenic PS produce high specific impulse being environmentally friendly, which may provide a growing interest towards their application. Low temperature of cryogenic propellant components may pose considerable challenges when chilling down, fueling and storing components as well as draining fuel tanks and starting PS, especially under zero gravity conditions in long-term space flights. Complex experimental facilities (EF) along with test methods as well as physical and mathematical models for calculating nonsteady multiple-phase heat transfer processes with intense phase transformations are being developed to overcome these challenges. The methods for mathematical modelling of the chilldown and cryogenic component flow processes have been proposed considering mass - and energy-conservation equations in relation to supply lines, tank gas blanket and tank volume filled with cryogen liquid. Closing dependency ratios have been specified according to results of bench and flight testing of PS to solve equations for heat transfer and friction in the cryogenic supply system components of test stand (TS) and PS. Also, the paper studies heat transfer processes during pre-launch chilldown of consumption lines (CL) of 12KRB LV PS with the lox/liquid hydrogen engine KVD-1 considering results of bench and flight testing of the block. Findings on chilldown and fueling of the 12KRB upper stage may be used to verify calculation models while designing and developing the KVTK advanced upper stage with the lox/liquid hydrogen engine RD0146 of the Angara-A5V heavy class launch vehicle. [ABSTRACT FROM AUTHOR]

Abstract: With the aim of dynamic simulation and control, a new non-linear state-space dynamic non-isothermal polymer electrolyte membrane fuel cell (PEMFC) model is developed in this paper. This mathematical model is developed based on mass and energy equation. The present model takes in account subsequent factors as the effects of charge double layer capacitance, the geometrical capacity and the effect of temperature gradient. In this paper, the authors propose a combination of several dynamic equations to study the effect of suddenly variation of some operating parameters like load resistance, gas pressure and gas temperature input. The results are compared to those of an isothermal model. This model will be extremely functional for the best possible design and real-time control of PEMFC systems. The present model is executed in MATHCAD software and the fuel cell is symbolized by an equivalent circuit which incorporates gas diffusion layer, membrane and electrodes. The analysis results show that the main elements that influence the performance of the cell are load resistance and functioning temperature. [Copyright &y& Elsevier]

Abstract: In this paper, we investigate the time-dependent heat and mass transfer in a molten carbonate fuel cell at start-up. Thus, a three-dimensional, transient mathematical model is presented through a comprehensive inclusion of various physical, chemical and electrochemical processes that occur within the different components of molten carbonate fuel cells. The model is proposed as a predictive tool to provide a three-dimensional demonstration of variable variations at system start-up. The local distribution of field variables and quantities are showcased. It reveals that the electrochemical reaction rate is dominated by the over-potential, not by the reactants' molar fraction. Reversible heat generation and consumption mechanisms of the cathode and anode are dominant in the first 10 s while the heat conduction from the solid materials to the gas phase is negligible. Meanwhile, activation and ohmic heating have nearly the same impact within the anode and cathode. Based on these findings, the importance of heat conduction and its main features are finally assessed. [Copyright &y& Elsevier]

Abstract: This paper presents a parametric study on instantaneous heat transfer of a direct-injection hydrogen-fueled engine using a multidimensional model. A simplified single-step mechanism was considered for estimating the reaction rate of hydrogen oxidation. The modified wall-function was used for resolving the near-wall transport. An arbitrary Lagrangian–Eulerian algorithm was adopted for solving the governing equations. Experimental measurements were implemented to verify the developed model. They show that the instantaneous heat-transfer model is sufficiently accurate. The influence of engine speed, equivalence ratio, and the start of injection timing were investigated. The flow fields appeared to have greater size vectors and coarser distribution with an increase of engine speed. A heterogeneous distribution was obtained for an ultra-lean mixture condition (φ ≤ 0.5), which decreased with an increase of equivalence ratio. There was no pronounced influence of the start of injection on the flow field pattern and mixture homogeneity. Thermal field analysis was used to demonstrate trends in the instantaneous heat transfer. It was observed that there was a crucial distinction between the lean and ultra-lean mixtures as well as the engine speed. Furthermore, a non-uniform behavior was found for the impact of the equivalence ratio on temperature distribution. It is clear that the developed models are powerful tools for estimating the heat transfer of the hydrogen-fueled engine. The developed predictive correlation is highly accurate in predicting the heat transfer of the hydrogen-fueled engine, focusing on the equivalence ratio as a governing variable. [Copyright &y& Elsevier]

Abstract: This paper investigates the effect of implementing a varying effective thermal conductivity term on heat transfer simulations within a metal hydride (MH) reactor. The work presented utilises a 1D transient heat transfer analysis comparing simulations either with a fixed effective thermal conductivity or a varying effective thermal conductivity. This builds on previously published work in the literature that has investigated varying effective thermal conductivity for metal hydrides at a single point. The results of these simulations are compared to experimental work for validation. The 1D simulation results clearly show that the varying effective thermal conductivity term more closely matches experimental results compared to the fixed effective thermal conductivity term. The results show that whilst a 1D simplification within the model may be valid in a bed some distance from the heating source, there are issues close to the heating source. It is speculated that neglect of losses outside of the 1D assumption are the cause of these issues. [Copyright &y& Elsevier]

Abstract: In this paper a two-dimensional model of an annular cylindrical reactor filled with metal hydride suitable for hydrogen storage is presented. Comparison of the computed bed temperatures with published experimental data shows a reasonably good agreement except for the initial period. Effects of hydrogen pressure and external fluid temperatures on heat transfer and entropy generation are obtained. Results show that the time required for hydrogen charging and discharging is higher when the thermal capacity of the reactor wall is considered. The time required for absorption and desorption can be reduced significantly by varying the hydrogen gas pressure and external fluid temperatures. However, along with reduction in time the entropy generated during hydrogen storage and discharge increases significantly. Results also show that for the given input conditions, heat transfer between the external fluid and hydride bed is the main source of entropy generation. [Copyright &y& Elsevier]

Abstract: Safety performance of high-pressure hydrogen storage tanks under localized fire exposure has drawn extensive attention. During the localized fire, the tank would be degraded and even burst before pressure relief device (PRD) activates to release internal high-pressure gas. Therefore, a localized fire test method for the tanks is being developed. In this paper, a three-dimensional computational fluid dynamics model is developed to investigate the heat transfer characteristics of 70MPa hydrogen composite tanks subjected to localized fire. The effects of different flame impingement areas on temperature and pressure rises of the tank are analyzed. Heat transfer performances of type 3 and type 4 tanks are compared. The results show that the temperature and pressure rises are not significant during the 600s localized flame impingement process. When the flame impingement area of the tank is far from PRD, convective heat transfer of internal hydrogen may be more intense than heat conduction of tank wall in the longitudinal direction. In addition, the heat from localized fire can be transmitted faster in type 3 tanks than in type 4 tanks. [Copyright &y& Elsevier]

Abstract: The metal hydride heat transformer shows great potential for the low-grade heat recovery. However, the heat output is variable, and these dynamics have to be taken into account in realistic applications. In this paper, a new index called true temperature boost is introduced together with conventional indices to assess the performance of the heat transformer system. Detailed analyses are carried out using a mathematical model that authors developed, investigating effects of key design and operating factors on the system’s performance. The amount of hydrogen transferred between coupled reactors is found to be crucial to obtain a high coefficient of performance, while specific heating power is very sensitive to the cycle time. On the true temperature boost, the driving force of reaction and the heat transfer conditions exert the most significant effects. [Copyright &y& Elsevier]

Abstract: This paper describes the design, fabrication and performance evaluation of a high efficiency, compact heater that uses the catalytic oxidation of hydrogen to provide heat to a hydrogen storage system. The heater was designed to transfer up to 30kW of heat from the catalytic reaction to the hydrogen storage system via a recirculating heat transfer fluid. The catalytic heater consists of three main parts: 1) the reactor, 2) the gas heat recuperator, and 3) oil and gas flow distribution manifolds. The reactor and recuperator are integrated, compact, finned-plate heat exchangers to maximize heat transfer efficiency and minimize mass and volume. Detailed, three-dimensional, multi-physics computational models were used to design and optimize the system. At full power the heater was able to catalytically combust a 10% hydrogen/air mixture flowing at over 80 cubic feet per minute and transfer 30kW of heat to a 30 gallon per minute flow of oil over a temperature range from 100°C to 220°C. The total efficiency of the catalytic heater, defined as the heat transferred to the oil divided by the inlet hydrogen chemical energy, was determined to exceed the design goal of 80% for oil temperatures from 60°C to 165°C. [Copyright &y& Elsevier]

Abstract: In this paper, design and fabrication of a micro direct methanol fuel cell based on stainless steel in two kind of active and passive with cross strip and parallel flow field are presented. Dropping pressure, velocity and heat transfer of the cell is simulated by a 3D modeling in fluent software. An optimum operating condition of the cell is obtained by the mass flow and temperature limitation. The cell was tested in different temperatures and mass flow rate and the cell performance is investigated in different condition. Maximum power density of the cell in active condition and at 60°C was 170mW/cm2 and in passive condition was 85mW/cm2. A μDMFC with different flow field is investigated. Cross strip flow field has shown better performance and the effect of cell orientation on performance is also investigated. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, hydriding in a cylindrical metal hydride hydrogen storage tank containing HWT5800 (Ti0.98Zr0.02V0.43Fe0.09Cr0.05Mn1.5) is numerically studied with a two-dimensional mathematical model. The heat and mass transfer of this model is computed by finite difference method. The effects of supply pressure, cooling fluid temperature, overall heat transfer coefficient and height to the radius ratio of the tank (H/R) on the hydriding in the hydrogen storage tank are studied. It is found that hydride formation initially takes place uniformly all over the bed and hydriding processes take place at a slower rate at the core region. Supply pressure, cooling fluid temperature and overall heat transfer coefficient play significant roles during the absorption of hydrogen. At the H/R=2 both maximum bed temperature and the average bed temperature are the highest, and the hydride bed takes the longest time to saturate. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, some models of comparative combustion characteristics for gasoline and hydrogen fuelled spark ignition internal combustion engines were developed and discussed from a thermodynamic and heat transfer perspective. The geometry used was that of a 3.4L GM V6 engine with a compression ratio of 9.5:1. Models for mass fraction burned, pressure, temperature, and gas speed were developed according to the literature survey and graphed over the cycle range. Furthermore, Pressure–Volume and Temperature–Entropy models were developed for both gasoline and hydrogen fuelled engines. Analysis of these models indicated approximately a 6.42% increase thermal efficiency for the hydrogen fuelled engine due to less exhaust blow down, less heat rejection during the exhaust stroke, and its shorter combustion duration closer to TDC. However, it was found that the hydrogen fuelled engine had approximately a 35.0% decrease in power output at an equivalence ratio of 1.0 due to the decrease in MEP and a greater amount of heat transfer to the cooling system due to the increased combustion temperatures, shorter quenching distance associated with H2 combustion and greater flame speed. Finally, an increase in cycle temperatures and pressures was observed from increasing the equivalence ratio from 0.4 to 1.0 to 1.2. [Copyright &y& Elsevier]

Abstract: This paper presents a two-dimensional mathematical model to evaluate transient heat and mass transfer in a metal hydride tank (hereinafter MHT) with metal foam heat exchanger. The model is validated by comparison with experimental data. A good agreement is obtained. A study of the geometric and the operating parameters of the metal foam (such as base material, pore size and relative density) has been carried out to identify their influence on the performance of the charging process of the MHT. After that, the model was used as a tool to predict the performance of the hydrogen-charging process of two configurations of MHTs with metal foam heat exchangers. The obtained results showed that the reduction of the storage time due to the metal foam heat exchanger can be more important when the MHT is equipped with a concentric heat exchanger tube. [Copyright &y& Elsevier]

Abstract: The main focus of this paper is the modeling, simulation, and analysis of the calcium bromide hydrolysis reactor stage in the calcium–bromine thermochemical water-splitting cycle for nuclear hydrogen production. One reactor concept is to use a spray of calcium bromide into steam, in which the heat of fusion supplies the heat of reaction. Droplet models were built up in a series of steps incorporating various physical phenomena, including droplet flow, heat transfer, phase change, and reaction, separately. Given the large heat reservoir contained in a pool of molten calcium bromide that allows bubbles to rise easily, using a bubble column reactor for the hydrolysis appears to be a feasible and promising alternative to the spray reactor concept. The two limiting cases of bubble geometry, spherical and spherical-cap, are considered in the modeling. Results for both droplet and bubble modeling with COMSOL MULTIPHYSICS™ are presented, with recommendations for the path forward. [Copyright &y& Elsevier]