Increasing Mass Flow Research Articles

Inertial Confinement Fusion Propulsion for the Massive Ra World Ship Model – Part 2

A strategy for sending humans around other stars will be to acquire the ability to construct large World Ships which are of order ~1011-1012 tons in mass, ~100 km in length and host large populations of millions of people over many generations of lifetime. This paper presents such a concept but driven by inertial confinement fusion engines utilising very large pellets of order 230 g in mass augmented with 4.85 kg/pellet of expellant propellant for increased mass flow rate and thrust generation. A mission architecture is constructed for a 1 million population carrying capacity growing to 10 million, based on an original 1984 published model which achieved a cruise speed of 1,500 km/s or 0.5% for a 1,000 year trip time. Calculations show that propulsion of such a vast construction will require hundreds of engines operating in parallel thrust mode and at moderately high pulse frequency for an elongated burn time of order half a century. The purpose of this study was to examine whether it was possible to drive an interstellar world ship using ICF engines using similar assumptions to a 1984 study for a Mk2A design. The conclusion of this study is that although an architecture does appear to be possible, there are practical reasons why it may be better to pursue alternative propulsion methods for this specific application such as via external nuclear pulse propulsion as adopted for the original studies. This paper is a follow-up to an earlier one which discussed some of the assumptions of the study. Keywords: World Ships, Interstellar Studies, Fusion Propulsion

Enhancement effect of semicoke waste heat on energy conservation and hydrogen production from biomass gasification

Key approaches to alleviating global warming and curbing fossil fuel depletion involve various industrial energy-conservation technologies and carbon dioxide (CO2) emission reduction methods. The production of hydrogen (H2)-rich gas from inexpensive and readily available biomass, as an alternative energy source, is becoming increasingly promising. However, this application faces challenges such as high energy consumption and low gas quality. In this study, the waste heat released by semicoke production from lignite gasification and CO2 from exhaust gas were utilized to gasify biomass. This approach aims to save energy in biomass gasification and use CO2 in exhaust gas to improve the H2 content in biogas. A simulation was conducted to recover semicoke waste heat by combining a suspension tube with CO2 flow to generate steam and high-temperature CO2, which were then simultaneously sent into a gasifier to produce H2 through biomass gasification. The results revealed that the rate of semicoke waste heat recovery exceeded 90 %. The yield of steam and the rate of waste heat recovery improved with increasing mass flow rate of semicoke and then slightly decreased with increasing steam pressure and CO2 mass flow rate. The yield of H2 increased with the semicoke mass flow rate and steam pressure. The rate of energy conservation ranged from 15 % to 239 %, peaking at a CO2 mass flow rate of 0.09 kg/s. Compared with the case without waste heat recovery, the economic benefits increased from 12 to 28 times.

Optimization of liquid cooling plate considering coupling effects of heat generation and aging characteristics in power batteries

The heat generation and aging characteristics of power batteries exhibit a strong coupling relationship, and thus designing liquid cooling plates (LCPs) requires considering both aspects to achieve optimal thermal management. In this study, an electric-thermal-aging model (ETAM) correlating internal resistance, capacity, and temperature was developed. Based on this model, the effects of a serpentine LCP on the heat generation and aging characteristics of battery pack under different operating conditions were investigated using a combined simulation of zero-dimensional numerical model and three-dimensional CFD methods. Furthermore, the LCP channel widths in the length and width directions and the number of channels were optimized using orthogonal tests, artificial neural networks, and genetic algorithms, aiming to minimize battery capacity degradation. Results showed that increasing the mass flow rate of the coolant reduced the maximum temperature, temperature difference, capacity loss, and aging inconsistency of the battery pack. Conversely, reducing the coolant inlet temperature could decrease the maximum temperature and capacity loss but increased the temperature difference and aging inconsistency of the battery pack. The orthogonal test results indicated that the number of channels had the greatest impact on the heat generation and aging characteristics of the battery pack, followed by the channel width in the length direction, and the channel width in the width direction had the least impact. After optimization, the maximum temperature of the battery pack decreased by 0.57 %, the maximum temperature difference increased by 1.41 %, and the average capacity degradation decreased by 0.20 %. Moreover, with the increasing mass flow rate, the pressure drop reduction improved from 27.90 % to 33.90 %. This study may provide guidance for the design of LCPs that take battery aging into account.

Performance of an additive-manufactured precooler under high-temperature and negative pressure environment

This paper introduces an original plate-fin precooler designed for potential applications in extreme low-pressure environments. Utilizing additive manufacturing technology, the heat transfer plate thickness is constrained to 2.0 mm, with channel widths inside the plate achieving 0.8 mm. Through experimental methods, this study aims to assess the precooler’s performance and identify critical influencing factors. Experimental results indicate that the hot fluid inlet temperature to the precooler exceeds 1100 K, with static pressures dropping below 30 kPa. Despite these conditions, the precooler demonstrates an impressive pressure recovery coefficient exceeding 97 % and achieves a maximum temperature drop of 731.4 K for the hot fluid. Furthermore, it is observed that the overall performance of the precooler diminishes with increasing mass flow rates of the hot fluid, showing fluctuations of up to 25 % when assessed by the j/f1/3 factor. Additionally, while the hot fluid inlet velocity exceeds 90 m/s, laminar flow predominates during the heat transfer process. Moreover, regardless of whether the cooling fluid experiences a phase change within the precooler, its heat transfer performance show priority than that of the hot fluid. Thus, changes in the mass flow rate of the cooling fluid have minimal impact on the overall precooler performance. Finally, the first-stage heat exchanger plays a critical role in the heat transfer process, accounting for over 2/3 of the total temperature and pressure drop for the hot fluid. This research is expected to contribute to the design of high-efficiency, low-resistance precoolers, particularly those applied for operation under negative pressure conditions.

Numerical Simulation and Analysis of the Airflow Field in the Crushing Chamber of the Hammer Mill.

The airflow dynamics within hammer mills' crushing chambers significantly affect material crushing and screening. Understanding the crushing mechanism necessitates studying the airflow distribution. Using a self-built crushing test platform and computational fluid dynamics (CFD) simulations, we investigated the impact of screen aperture size, rotor speed, hammer-screen clearance, hammer quantity, and mass flow rate on airflow distribution within the rotor region, circulation layer, and screen apertures. Results indicated generally uniform axial static pressure distribution within the rotor region, with radial gradients. Increased rotor speed improved radial static pressure gradients, while higher mass flow rates reduced them. The highest airflow velocity within the circulation layer reached approximately 83.46% of the hammer tip's tangential velocity. Greater rotor speed and hammer quantity intensified circulation airflow, whereas increased mass flow rate decreased it. Eddies formed within screen apertures with higher rotor speeds and hammer quantities but diminished with larger apertures and higher mass flow rates. Static pressure differences across screen apertures increased with mass flow rate and rotor speed but decreased significantly with larger apertures. This systematic examination provides insights into airflow distribution within hammer mill crushing chambers, offering a theoretical foundation for improving and designing hammer mills.

A separation column for liquid mixture based on phase transform: Experiment and simulation

The concentric internally heat-integrated distillation column (HIDiC) has advantages of low energy consumption and high thermodynamic efficiency. However, its drawbacks of limited heat transfer area, complex internal structure, and large number of control parameters hinder its widespread industrial applications. To solve these challenges, in this work a novel sleeve-like concentric heat integrated separation column, namely temperature-controlled phase change column (TCPC), was developed to separate liquid mixtures in a more effective and energy-saving way with reflux section being moved and trays being replaced with spiral corrugation blades. The comprehensive performances of TCPC in ethanol–water system was firstly evaluated by experiments. The results showed that TCPC performs well in ethanol/water separation due to the internal spiral corrugation significantly reducing the vapor–liquid contact in separation section. Meanwhile, compared to the concentric HIDiC, TCPC has a higher total heat transfer coefficient due to the larger heat transfer area. Computational fluid dynamics simulation reveals the internal design of TCPC inducing secondary vortices of the vapor, enhancing condensation heat transfer and separation efficiency. Further, increasing mass flow rate within a certain range would enhance the comprehensive performance factor and lead to more effective separation.

Experimental investigation of inclined solar still through localized interfacial evaporation using nano enhanced Bio wick under disparate flow rate

Water treatment is essential for obtaining potable water, and passive solar desalination offers a renewable and sustainable approach. However, productivity remains a key challenge for commercialization. Scaling up solar desalination systems while maintaining efficiency and cost-effectiveness is a significant challenge. The current state of research in solar desalination is focused on developing scalable and sustainable solutions to address challenges faced in productivity. To address this issue, ongoing efforts focus on improving productivity under localized interfacial evaporation. The present study aims to enhance productivity, particularly at higher mass flow rates, through a series of experiments conducted in three sets. In the first set of experiments, a bare Integrated Solar Still (ISS) was utilized with various mass flow rates (0.29, 0.42, 0.75, and 1.3 kg/min). The highest hourly yield of potable water was observed during peak solar intensity, typically between 13:00 and 14:00 Hrs for all mass flow rates. However, as the mass flow rate increased, the hourly yield of potable water decreased. For instance, at 14:00 Hrs, the maximum yield was 0.235, 0.15, 0.12, and 0.06 kg/m2 for mass flow rates of 0.29, 0.42, 0.75, and 1.3 kg/min, respectively, in the ISS without wick material. The highest cumulative yield achieved was 1.6 kg/m2 during 0.29 kg/min mass flow rate, while the minimum clean water yield of 0.4 kg/m2 was obtained at 1.3 kg/min. In the second set of experiments, the goal was to improve productivity at higher mass flow rates. The use of Fe2O3-impregnated jute cloth in comparison to the bare ISS resulted in an average absorber temperature increase of 4∘C, 4.8∘C, 4.8∘C, and 4.9∘C for mass flow rates of 0.29, 0.42, 0.75, and 1.3 kg/min, respectively. Interestingly, the trend showed an increasing rate of reduction mitigation at higher mass flow rates. Simultaneously, the average water temperature increased by 4.2∘C, 4.5∘C, 6.4∘C, and 7.1∘C for the corresponding mass flow rates with Fe2O3-impregnated jute cloth. The introduction of jute cloth enhanced energy harvesting at all mass flow rates compared to the bare ISS. The maximum energy efficiency, at 48.02 %, was achieved with Fe2O3-impregnated jute cloth during the 0.29 kg/min mass flow rate, while the minimum energy efficiency, at 9.14 %, was recorded at the highest mass flow rate of 1.3 kg/min. Notably, the energy efficiency of the jute cloth-covered ISS surpassed that of the bare ISS by 12.44 %, 9.14 %, 7.15 %, and 3.14 % for mass flow rates of 0.29, 0.42, 0.75, and 1.3 kg/min, respectively. Furthermore, the addition of Fe2O3-impregnated jute cloth further improved energy efficiency, with enhancements of 8.19 %, 1.14 %, 6.36 %, and 9.57 % over the jute cloth-covered ISS for the respective mass flow rates. During the 0.75 kg/min mass flow rate, energy efficiency reached 26.12 %, closely matching the 27.3 % efficiency achieved at 0.29 kg/min in the bare ISS. The study also demonstrated a 2.29 % improvement in exergy with Fe2O3-impregnated jute cloth at a mass flow rate of 0.29 kg/min. In conclusion, the results suggest that the implementation of jute cloth over the ISS absorber basin can enhance overall efficiency and mitigate the negative impacts of increased mass flow rates via localized interfacial evaporation. The combination of a jute cloth wick and Fe2O3 nanoparticles holds promise for improving energy efficiency in solar still desalination.

Investigation of the mild surge in an axial–centrifugal compressor

The performance and structural integrity of compressors are critically impacted by aerodynamic instability. This study examines an unstable phenomenon, known as high-frequency mild surge (HFMS), in axial–centrifugal compressors through an experimental investigation and a low-order model. The results reveal that the pressure signal during HFMS is synchronized along the circumferential and streamwise directions. To elucidate the HFMS mechanism and further explore its influential law, a multi-actuator model is developed, successfully capturing the dynamic instability behavior. As the mass flow decreases, the front axial stage becomes unstable first, while the latter centrifugal stage remains stable with a negative slope near the operating point on the performance curve. The strong pressurization of the centrifugal stage maintains the stability of the entire compression system, increasing the mass flow rate. Subsequently, the pressure ratio of the latter centrifugal stage decreases with increasing mass flow, causing the front axial stage to become unstable again. The axial stage's Helmholtz frequency is consistent with the test HFMS frequency, further proving that it is a local systematic instability dominated by the axial stage. This matching feature is particularly common in combined compressors, making HFMS a typical instability phenomenon in such systems.

Improving heat transfer in indirect liquid-based battery thermal management systems through turbulator-equipped conical flow paths

To guarantee the safe operation of Li-Ion Cells (LICs) in various applications, such as electric vehicles, an efficient Battery Thermal Management System (BTMS) is necessary. The design of BTMSs, as documented in the literature, typically involves the use of cooling channels with uniform and smooth configurations. However, these configurations encounter the challenge of temperature non-uniformity in the battery module, which stems from elevated coolant temperatures along the flow direction. In this study, a 3D numerical analysis is conducted to develop a novel indirect liquid-based cooling system for the BTMS of a module with cylindrical LICs. The study explores the effects of conical cooling channels, both with and without twisted turbulators, across various coolant mass flows during a 2C discharge process of LICs. Within the studied ranges, diverging cooling channels improve the overall thermal and hydraulic performance of the BTMS by an average of 40%, increasing the heat transfer coefficient by a maximum of 32.6%, and decreasing pressure drop by up to 35.1%. The application of turbulators proves effective in reducing the maximum temperature difference within the LICs, demonstrating a decrease of approximately 34.2% at the minimum mass flow rate and 74.4% at the maximum mass flow rate. This emphasizes the more substantial impact of turbulator utilization at higher coolant mass flow rates. An increased coolant flow rate leads to a significant enhancement of the heat transfer coefficient, ranging from 70.5% to 79.0% for the BTMS incorporating turbulators. Moreover, the study highlights a more pronounced impact of increasing mass flow rates in the BTMS designed with converging cooling channels compared to those designed with diverging channels. Finally, the results of this analysis demonstrate that the proposed system is capable of efficiently regulating the temperature of the entire battery module, ensuring that it consistently maintains a normal and safe operational range suitable for vehicular applications (below 40 °C).

Assessing performance of an external compound parabolic concentrator solar collector with cascaded latent heat thermal storage

AbstractThis study presents quantitative results of charging experiments conducted on cascaded thermal energy storage system (CTESS) integrated with external compound parabolic concentrator solar collector (XCPCSC). Increasing mass flow rate in 2‐stage CTESS integrated with XCPCSC resulted in a 30% reduction in initiation time of phase change materials (PCMs) during charging, with a higher mass flow rate of 0.025 kg/s. However, due to disparate melting point temperatures of PCMs, phase transition in the two‐stage CTESS did not occur simultaneously, leading to poor heat transfer rates within the CTESS. To address this, study extended number of phases from two to three, resulting in a 1.5‐fold increase in rate of heat transfer compared to 2‐stage PCM system. The simultaneous melting processes at various stages in the CTESS maximized energy absorption, leading to a 25% increase in system efficiency. Notably, the values of energy stored efficiency and over‐all efficiency reached their peak values of 95% and 60%, respectively, between t = 12.00 h and t = 13.00 h. This time period also saw a significant increase in collector efficiency to 72%. These quantitative findings highlight importance of mass flow rate and PCM arrangement in achieving efficient heat transfer and system performance in a CTESS integrated with XCPCSC.

Numerical simulation of fluid-particle flow of jet in supercritical water environment

Supercritical water gasification provides a new approach to the green transformation of coal. Nevertheless, the flow characteristics of fluids and particles injected into the reactor through the nozzle still need to be further investigated. In this paper, a three-dimensional numerical simulation of the particle jet in supercritical water environment is carried out coupling Large Eddy Simulation (LES) with Discrete Phase Model (DPM). The simulation focuses on the effects of particle size, Stokes number, mass flux ratio and initial fluid velocity on the flow characteristic of the fluid-particle flow, especially on the vortex structure evolution, particle distribution and velocity profile. The findings are that as the particle size decreases and the initial fluid velocity increases, the evolution of vortex structures become increasingly fierce, such as the destruction of large-scale coherent structures, the disappearance of vortex ribs, and the lateral expansion of vortices in the development section. Particle distribution exhibits characteristics similar to the vortex structure, as particles adhere closely to the carrier fluid at low Stokes number (St < 1). On the contrary, with increasing of Stokes number (St > 1), the particles are freer from fluid interference and keep their original motion state moving forward. The fluid velocity at the center of the transverse interface jet decrease with increased mass flow ratio. For higher initial fluid velocities, particle distribution is more uniform, and more particles are carried to areas with larger radial distances.

NOx formation processes in rotating detonation engines

High-fidelity simulations of RDEs with H2-Air-NOx chemistry are employed to study NOx emissions in such devices. Discrete injection of gaseous hydrogen fuel and continuous injection of air oxidizer is used at various mass flow rate conditions in several 3D RDE simulations to understand resulting NOx production behaviors. Simulations are also performed for two different injector configurations, one in which air is injected axially into the detonation chamber [Axial Air Inlet (AAI)] and one in which air is injected radially [Radial Air Inlet (RAI)]. It is seen that the AAI RDE produces much less NOx than the RAI RDE, mainly due to the weaker waves seen in this system as a result of parasitic combustion losses from product gas recirculation. Parasitic combustion does lead to NOx formation in its own right, but the emissions levels from this process are negligible compared to emissions stemming directly from detonation processes. In regards to detonation strength in particular, it is generally seen that detonation strength increases with increasing mass flow rate, in turn increasing peak pressure, peak heat release and NOx emissions levels. Nevertheless, even the highest recorded NOx levels at the combustor exit in this study remain on the same order of magnitude as compared to gas turbine exhaust emissions levels, supporting the claim that significant differences between detonative and deflagrative combustion do not necessarily lead to significant differences in NOx levels. Overall, this study provides greater understanding into the behaviors of NOx formation in RDEs and how these behaviors are affected by changes in operating parameters.

Numerical and experimental analysis of instability in high temperature packed-bed rock thermal energy storage systems

Due to heat losses of preferential areas of packed-bed energy storage systems, transverse temperature variations may occur during the charging, discharging and standby processes. Furthermore, the heat losses of preferential areas of the storage tank cause a lower pressure drop in these areas resulting in an increased mass flow rate and further cooling, and thereby an enhanced transverse temperature variation, in a positive feedback loop – a phenomenon called instability. The transverse temperature variations may deteriorate the performance and thereby the economic feasibility of packed-bed energy storage systems. In this paper, numerical and experimental investigations of an air-based packed-bed rock thermal energy storage system for large-scale high temperature applications are presented. The objective of the study is to predict the instability and to analyze the effect of different standby durations and storage size on the instability of the air-based packed-bed system. Transient axisymmetric computational fluid dynamics models were developed for the standby and discharging processes of the packed-bed thermal energy storage systems. In addition, experimental investigations were carried out at a test facility located at Stiesdal Storage, Denmark, using magnetite rocks as heat storage material and air as heat transfer fluid. The results suggest that the numerical predictions are in good agreement with the test data. The instability phenomenon is found to increase with the standby duration, resulting in a maximum difference of 161 K between the maximum rock temperature and the outlet air temperature for a standby period of 10 h followed by a discharging process. Moreover, the results indicate that the maximum difference between the rock temperature and outlet temperature is 73 K and 56 K for a reduced-scale and a full-scale system (no standby period), respectively.

4E analysis and parameter study of a solar-thermochemical energy storage CCHP system

The combination of calcium looping and concentrating solar power (CSP) is a promising energy conversion technology that can greatly increase the share of solar energy used in combined cooling, heating and power (CCHP) systems. This paper designs a CCHP system based on solar energy and thermochemical energy storage. The system runs all day through day and night modes. Under basic working conditions, the energy and exergy efficiencies of the system could reach 56.92 % and 35.94 %, respectively. The system is evaluated by multiple approaches including parametric sensitivity analysis and 4E (energy, exergy, economy and environment)) analyses. The results demonstrate that the system could produce 2618.09 MW of electricity, 305.56 MW of heat and 523.88 MW of cooling capacity per day, respectively. At the same time, the reductions of CO2 emissions and fossil fuel consumption could reach 2222.76 tons and 696.41 m3 per day, respectively. Furthermore, the increasing mass flow of main turbine inlet could increase both the system efficiency and the exergy efficiency. Thus, it is beneficial to reduce the environmental impact but with the increasing investment cost. In the meanwhile, the exergoeconomic factor and exergoenvironment factor of the system were 55.65 % and 0.139, respectively. Besides, as the extraction flow rate of the intermediate pressure turbine increases, the energy efficiency increases but the exergy efficiency descends. This is unfavorable to reducing the environmental impact, yet it could decrease the investment cost of the system. These results reveal that the hybrid system has the characteristics of high efficiency and emission reduction in energy storage, power generation, heating and cooling, and has great development potential.

Fast Calculation of Supercritical Carbon Dioxide Flow, Heat Transfer Performance, and Mass Flow Rate Matching Optimization of Printed Circuit Heat Exchangers Used as Recuperators

Printed circuit heat exchangers (PCHEs) are widely used as recuperators in the supercritical carbon dioxide (S-CO2) Brayton cycle design. The variation of heat sources will have a great impact on the heat transfer effect of the recuperator. It is of interest to study the fast calculation of flow and heat transfer performance of PCHEs under different operating conditions to obtain the optimal comprehensive performance and provide guidance for the operation control strategy analysis. Herein, a fast calculation method is established through a one-dimensional model of a PCHE based on Modelica. The effects of working medium mass flow rate and inlet temperature on the flow and heat transfer process are analyzed from the three aspects of heat transfer rate, flow pressure drop, and comprehensive performance, and the mass flow rate matching optimization is realized. The results show that increased mass flow rate increases heat transfer rate and flow pressure drop. The efficiency evaluation coefficient (EEC) has a maximum value at which the mass flow rate values of the cold and hot channels are best matched, and the comprehensive performance is optimal. When the mass flow rate of the heat channel is 4.8 g/s, the maximum EEC is 1.42, corresponding to the mass flow rate of the cold channel, 4.2 g/s. Compared with the design condition, the heat transfer rate increases by 62.1%, and the total pump power increases by 14.2%. When the cold channel inlet temperature increases, EEC decreases rapidly, whereas EEC increases when the hot channel inlet temperature increases. The conclusions can provide theoretical support for the design and operation of PCHEs.

Experimental study on heat transfer and flow pattern transition for R1233zd/FC72 mixtures across tube bundles

An experimental investigation was conducted to study the heat transfer and two-phase flow patterns of pure R1233zd and non-azeotropic R1233zd/FC72 mixtures (0.75/0.25, 0.5/0.5, and 0.25/0.75 by mass) across tube bundles. The test section of tube bundles was transparent to observe the flow pattern. The flow boiling heat transfer was measured. The experiments were carried out with vapor qualities of 0.1–0.9, mass flow rates of 3–5 kg/h and heat fluxes of 3000–7000 W/m2. Falling film flow, bubbly flow, bubbly-shear flow, and shear flow were observed. The flow pattern transition maps were presented for various conditions. Increasing the mass fraction of the volatile component R1233zd causes the flow pattern transitions occurring at lower vapor qualities. The heat transfer coefficient of mixtures is lower than that of pure R1233zd. With increasing vapor quality, the heat transfer coefficient increases for both pure R1233zd and the mixture with a R1233zd mass fraction of 75 %. However, for mixtures with R1233zd mass fractions of 50 % and 25 %, the heat transfer coefficient initially increases and then decreases with increasing vapor quality. For vapor qualities higher than 0.5, increasing the volatile component, R1233zd, significantly enhances heat transfer. The heat transfer coefficient increases with increasing mass flow rate and heat flux. The experimental data were compared with correlations in the literature with poor agreement. An improved heat transfer correlation for non-azeotropic mixtures flowing across tube bundles was proposed, which effectively predicted the experimental data.

Experimental study on the mechanism of water on heat sink variation in catalytic partial steam reforming of supercritical n-decane

Regenerative cooling is an effective method for heat management of hypersonic vehicles and faces a problem of insufficient cooling capacity under higher flight Mach number. Water-assisted hydrocarbon fuels thermal conversion can effectively increase heat absorption and inhibit carbon deposition. The mechanism of water on the variation of heat sink is unclear. In this study, experimental study was conducted to investigate the effect of different water contents, pressure and mass flow rates on the variation of heat sink and the distribution of gaseous products in a continuous experimental system. The results show that catalytic partial steam reforming reaction consists of catalytic steam reforming and catalytic thermal cracking in the low temperature stage (T＜490 ℃), and non-catalytic thermal cracking is activated and gradually dominate in the high temperature stage (T＞490 ℃). The contribution of water to total heat sink is mainly caused by physical heat sink. Increasing mass flow rate mainly suppress the cracking reaction in the high temperature section by reducing reaction residence time. The flow rate has little effect on the chemical reaction equilibrium. Higher pressure has little effect on heat sink, but accelerates carbon deposition by promoting the formation of olefin products.

Experimental study of thermal performance in a rectangular finned-tube latent heat storage device with composite polyethylene wax/expanded graphite

Phase change materials and geometric structure of latent heat storage (LHS) devices constitute crucial factors affecting the performance of phase change thermal energy storage systems. In this study, focusing on the LHS system with a heat source temperature of 150 °C, a rectangular finned-tube latent heat storage device was designed and fabricated. Polyethylene wax (PEW) with a 10% mass fraction of expanded graphite was adopted to prepare the composite phase change material. A series of experiments was conducted to evaluate the thermodynamic performance of the device with varying inlet temperatures and mass flow rates. The experimental results showed that the process of heat storage and release was predominantly governed by thermal conduction due to the high viscosity of PEW. Although the temperature variations in various directions within the LHS device remain nearly consistent, the heat transfer in the non-fin regions on the rectangular LHS device walls and corners was comparatively inferior due to the absence of natural convective heat transfer. In comparison to the mass flow rate, the inlet temperature exerts a more significant impact on accelerating the heat storage/release processes. While an increase in the mass flow rate enhanced the heat transfer capacity, its slightly accelerates the heat transfer duration. Moreover, the heat release ratio of the device exhibits an initial increase followed by a decrease with an increasing mass flow rate. In practical applications, prioritizing an increase in inlet temperature difference proves to be more effective than adjusting mass flow rate to enhance the heat storage performance.

Investigation of configuration on multi-tank cascade system at hydrogen refueling stations with mass flow rate

Currently, the utilization of hydrogen has been focused on transportation sector because it has been expected that the emission of carbon dioxide (CO2) can be largely and effectively reduced by replacing internal combustion engine vehicles (ICEVs) into fuel cell electric vehicles (FCEVs). Light-duty passenger FCEVs are already in the market and the extent of CO2 reduction can be further expanded by applying FCEVs to heavy vehicles.Hydrogen refueling stations (HRSs) are an essential infrastructure for supporting FCEVs and have been developed for effective filling of hydrogen. Currently, most FCEVs store hydrogen in a compressed gaseous state. Therefore, in HRSs, hydrogen stored at high pressure is used to rapidly refuel the vehicles. To reduce energy consumption and ensure high utilization of the stored hydrogen, a cascade system with multi-tank at different levels of pressure is generally applied to commercial HRSs. Usually, three stages of pressure level (low-, mid-, and high-pressure) are composed of the cascade system. Therefore, the proper design on the capacity (stored hydrogen mass or volume) of tanks as well as the pressure of tanks is required to obtain satisfactory performance of HRSs.To date, HRSs for light-duty FCEVs have been mainly studied to reduce refueling time and energy consumption. However, HRSs for heavy-duty vehicles should be investigated to extend the utilization of hydrogen in the transportation sector. Such HRSs should be able to supply hydrogen at increased mass flow rates over 60 g/s which is a known limitation on the light-duty FCEV refueling. In the present study, a thermodynamic model was developed and, then, verified by results from a computational fluid dynamic (CFD) model. The model was applied to a cascade-type HRS with different configurations on storage capacities of low-, mid-, and high-pressure tank. The effect of bore diameter at a nozzle was also explored because the mass flow rate could be increased with lowered pressure drop and the nozzle is a main contributor of total pressure drop through a filling line. It was found that the capacity of the high-pressure tank becomes important to obtain a high flow rate and it can be reduced by increasing a bore diameter of a nozzle of a dispenser at HRS.

Experimental research on the detonation behavior in annular combustors utilizing liquid hypergolic propellants

The development of rotating detonation engine utilizing hypergolic propellants is necessary for practical application of detonation-based rocket engines, but this liquid-liquid rotating detonation has been rarely researched due to its difficulty of well atomization and mixing in very short time. This study aims to experimentally investigate the propagation characteristics of rotating detonations using non-premixed hypergolic propellants in annular combustors. Here the monomethyl hydrazine (MMH) and nitrogen tetroxide (NTO) have been used as oxidizer and fuel, respectively. Twenty-four unlike impinging elements have been used for injection and mixing of liquid propellants. The orifice diameter is 0.4 mm for oxidizer and 0.3 mm for fuel. Three typical combustion modes such as deflagration mode, one-wave rotating detonation mode and two-wave collision mode have been captured by dynamic pressure transducers and the high-speed camera. The influence of many factors, such as mass flow rate, mixing ratio, annular combustor width and chamber throat, on rotating detonation behaviors have been investigated. The propagation velocity of rotating detonations is around 1328 m/s∼1405 m/s, including one-wave rotating detonation mode and two-wave collision mode. When the mass flow rate and mixing ratio is not appropriate, the hypergolic combustion becomes obviously unstable and combustion modes vary very quickly, especially at the start-up stage. The chamber throat plays a negative role on rotating detonation which suppresses the detonation propagation and can lead to detonation fail. Besides, the wider annular combustor width is beneficial for rotating detonation propagating, which can eliminate the negative influence of the chamber throat on the detonation propagation. In addition, increasing mass flow rate would lead to higher injection velocity and thus better impinging injection, atomization and mixing, which is positive for increasing the stable operation range of mixing ratio for rotating detonations.