Inlet Temperature Conditions Research Articles

Numerical investigation of the influence of unsteady inlet temperature on heat storage performance of a novel bifurcated finned shell-tube heat storage tank

Due to the change of solar radiant intensity with time, the melting process in the phase change energy storage system connected to the solar collector occurs under the unsteady inlet temperature. Three unsteady inlet temperature conditions have been proposed, and their average inlet temperature has been used as the corresponding steady inlet temperature conditions to form three comparative working conditions. Under different comparison conditions, a three-dimensional numerical comparison analysis has been conducted on the heat storage performance of a novel bifurcated finned shell-tube heat storage tank. Compared with the corresponding steady inlet temperature condition, the unsteady inlet temperature condition can accelerate the melting process and improve the temperature uniformity of the phase change material. The liquid fraction differences of TA and Ta, TC and Tc at the end of the reaction are 9.5% and 7.5% respectively, and the difference in the time required for the liquid fractions of TB and Tb to reach 1 is 17.7%. The evaluation coefficients for the three comparative working conditions are 3.1, 1.3 and 3.6 respectively. The results can provide a certain reference value for the performance optimization and practical application of the latent heat storage system.

Numerical Investigation of Transonic Flow-Induced Spontaneous Condensation in Micro-Ejector Nozzles.

Micro-cooling systems are compact refrigeration systems widely applicable in microchemical analysis, biomedicine, and microelectromechanical systems (MEMS). These systems rely on the use of micro-ejectors to achieve precise, fast, and reliable flow and temperature control. However, the efficiency of micro-cooling systems is hindered by spontaneous condensation occurring downstream of the nozzle throat and within the nozzle itself, impacting the performance of the micro-ejector. A micro-scale ejector mathematical model describing wet steam flow was simulated to investigate the steam condensation phenomenon and its influence on flow, incorporating equations for liquid phase mass fraction and droplet number density transfer. The simulation results of wet vapor flow and ideal gas flow were compared and analyzed. The findings revealed that the pressure at the micro-nozzle outlet exceeded predictions based on the ideal gas assumption, while the velocity fell below it. These discrepancies indicated that condensation of the working fluid reduces the pumping capacity and the efficiency of the micro-cooling system. Furthermore, simulations explored the impact of inlet pressure and temperature conditions on spontaneous condensation within the nozzle. The results demonstrated that the properties of the working fluid directly influence transonic flow condensation, underscoring the importance of selecting appropriate working fluid parameters for nozzle design to ensure nozzle stability and optimal micro-ejector operation.

Numerical simulation of cryogenic cavitating flow by an extended transport-based cavitation model with thermal effects

Low-temperature medium cavitation is extremely susceptible to temperature changes and it is more sensitive and valuable to study than ambient medium. In this study, the modified Zwart-Gerber-Belamri (MZGB) cavitation model has been extended to be suitable for the cavitation flow of cryogenic fluid by considering the thermodynamic and viscous effects. The accuracy of MZGB cavitation model is verified using computational fluid dynamics (CFD) method in simulations of Hord hydrofoil and ogive in low-temperature nitrogen and hydrogen medium, and different combinations of evaporation and condensation coefficients are discussed. The results show the best agreement with experimental results when Fvap = 2.0 and Fcond = 0.006. By ensuring the accuracy of temperature drop calculation in the original model, the MZGB cavitation model is capable of capturing a more precise pressure drop at various inlet temperature conditions. Additionally, the cavitation model that considers both thermodynamic and viscous factors yields higher values for condensed mass than the original model, which better reflects the evaporation and condensation process of vapor in the cavity and has a certain degree of confidence. The research could provide some novel thoughts for enhancing the accuracy of cryogenic cavitating flow.

Multiple-objective optimization on ammonia decomposition using membrane reactor

Ammonia plays a key role in the renewable hydrogen economy nowadays, thus, the efficiency of ammonia decomposition for hydrogen production becomes an important research topic. In this study, a numerical model was built to study the performance of ammonia decomposition using a membrane reactor and Ru/Al2O3 catalyst under various operating conditions such as feed NH3 temperature and volume flow rate as well as retentate side pressure. The reactor performance was characterized by ammonia conversion, hydrogen recovery, and recovered hydrogen flow rate. Pre-exponential factor and activation energy of ammonia reaction rate were obtained by equilibrium conversion and two-step parametric sweeping. It was found that ammonia conversion can be increased by about 33% compared to a conventional fixed-bed reactor under the same operating conditions. H2 recovery can be enhanced when the reactant inlet temperature and the pressure difference between the retentate and permeate sides increase. The increase in feed NH3 flow rate (gas hourly space velocity, GHSV) decreased the ammonia conversion and H2 recovery. An optimum GHSV that results in a maximum recovered H2 flow rate can be found. Finally, optimum operation conditions for maximizing the hydrogen recovery and recovered hydrogen flow rate were analyzed using the multi-objective Non-dominated sorting genetic algorithm-II (NSGA-II). It was found that maximum H2 recovery with a value of 79.7% can be obtained under the conditions of inlet temperature of 336 °C, GHSV of 900 h−1, and retentate side pressure of 9.9875 bar. The maximum recovered hydrogen flow rate with a value of 9.55×10−14(mol·s−1) can be obtained under the conditions of an inlet temperature of 394 °C, GHSV of 1315 h−1, and retentate side pressure of 9.9879 bar.

Heat Transfer Enhancement in Laminar Pipe Flow Using Al2O3–Water Nanofluid and Twisted Tape Inserts

Abstract In this study, an attempt has been made to carry out a numerical investigation using water-based Al2O3 nanofluid, flowing through a circular tube under constant inlet temperature and constant heat flux conditions in the laminar flow regime. The water-based Al2O3 nanofluid is used in a circular plain tube first, and then, this process is repeated for the same tube fitted with twisted tape inserts of twist ratio 1.85 at Reynolds numbers ranging from 680 to 2030. For the numerical analysis, ANSYS FLUENT is used to solve three-dimensional conservation equations of mass, momentum, and energy. The simulated results indicate that when twisted tape is used, heat transfer rates increase significantly with the use of nanofluid. In the case of nanofluid with the plain tube, only 10–24% enhancement in heat transfer rate is noted. On the other hand, almost 27–45% increase in heat transfer is observed compared to that with only water when twisted tape is inserted into it. Also, the friction factor increases as the nanoparticle volume fraction increases. However, the effect on the heat transfer rate is more significant than that on the friction factor. The best thermohydraulic performance factor achieved is 2.1 using nanofluids with a 5% volume fraction of the nanoparticles at a high Reynolds number when twisted tape is also inserted.

Evaluation of off-design scaling methods of supercritical CO2 compressor with experimental data

A compressor off-design performance prediction is one of the issues related to load following operation of the S–CO2 cycle. Normally, a compressor performance map produced at the design conditions is used to predict off-design performance under specific inlet temperature and pressure conditions, and that has been the case for an air compressor. The variation of temperature and pressure from the design conditions can be corrected easily for the measured mass flow rate and rotational speed when using the compressor performance map produced at the design conditions for air. In contrast, the validity of the similitude model for an S–CO2 compressor is not confirmed experimentally previously. Since S–CO2 have been repeatedly reported to have strong real gas effect, the most appropriate similitude model is yet to be determined. Using the selected data from existing S–CO2 test facilities, various similitude models are compared and the validity is checked. The results show that most similitude models predict better with enthalpy rise rather than pressure ratio for the S–CO2 compressor's off-design performance predictions. Among the compared models, ideal gas model based compressibility modified (IGZ) model for predicting enthalpy rise of the compressor at different inlet conditions showed the best prediction within the tested data.

Manufacturing a Ceramic Turbine Rotor for a Compact Jet Engine

Abstract Compact military-grade jet engines offer many potential applications, including use in remotely piloted vehicles, but can be expensive to use for research and development purposes. A study aimed at increasing the power and thrust output of an inexpensive commercial compact engine found a material limitation issue in the turbomachinery. To gain the additional power, hotter turbine inlet temperatures were required. This temperature increase exceeded the limit of current uncooled metal turbine rotors but could be achieved through turbine rotors made from ceramics, such as silicon nitride, which would allow an increase in the thrust and power output by a factor of 1.44. Current ceramic turbine manufacturing methods are costly and time-consuming for rapid prototyping, but recent breakthroughs in ceramic additive manufacturing have allowed for cheaper methods and faster production which are beneficial for use in research and development when designs are being rapidly changed and tested. This research demonstrated, through finite element analysis, that a silicon nitride turbine rotor could meet the increased turbine inlet temperature conditions to provide the desired thrust and power increase. Furthermore, as a proof of concept, an additively manufactured drop-in replacement alumina turbine rotor was produced for the JetCat P400 small-scale engine in a manner that was cost-effective, timely, and potentially scalable for production. This compact engine was used to demonstrate that a cost-effective ceramic turbine could be manufactured. At the time of publication, the desired ceramic material, silicon nitride, was not available for additive manufacturing.

Thermal management of natural gas production from coke oven gas by optimizing catalyst distribution and operation conditions

In this work, 3D particle-resolved CFD simulations have been performed to investigate the thermal effects of natural gas production from coke oven gas. The catalyst packing structures with uniform, gradient rise and gradient descent distribution and the operating conditions of pressure, wall temperature, inlet temperature and feed velocity are optimized for reduced hot spot temperature. The simulation results show that compared with packing structures with uniform distribution and gradient descent distribution, the gradient rise distribution could effectively reduce the hot spot temperature without affecting the reactor performance in the reactor with upflow reactants feeding, of which the reactor bed temperature rise is 37 K. Under the conditions with the pressure of 20 bar, wall temperature of 500 K, inlet temperature of 593 K, inlet flow rate of 0.04 m/s, the packing structure with gradient rise distribution exhibits the minimum reactor bed temperature rise of 19 K. By optimizing the catalyst distribution and operation conditions, the hot spot temperature of CO methanation process could be dramatically reduced by 49 K at the sacrifice of slightly reduced CO conversion.

A combined cooling structure consisting of serrated trench and V-shaped surface for film holes: Flow structure and effectiveness improvement

Film cooling is a commonly used thermal protection technology for turbine airfoils. However, due to the counter-rotating vortex pair (CVP) generated by the interaction between the cooling jet and the mainstream, the coolant gradually breaks away from the wall, which is particularly evident at high blowing ratios. For the sake of improving the film cooling effectiveness (FCE) under high inlet temperature conditions, a novel film cooling structure (SerrTrench-VSS) that combines serrated trench film holes with shark skin-inspired V-shaped surface (VSS) is proposed. The RANS method and realizable k-ε model are used for the simulations. The flow characteristics, adiabatic FCE, and resistance loss are analyzed in detail when the blowing ratio (BR) is 0.5–1.5 and then compared with the traditional cylindrical film hole and transverse trench film hole. In addition, the impact of VSS height on the cooling performance is investigated and the best height of the structure is determined. The results show that the SerrTrench-VSS has better FCE. The serrated trench can destroy the CVP and improve the spanwise spreading ability of the coolant. Also, the VSS can converge the cooling jet downstream of the film hole toward the centerline, thereby improving its extension ability along the flow direction. In the studied range of blowing ratio, the SerrTrench-VSS has the best FCE, and the spanwise-averaged FCE increases by up to 10.50% when BR = 0.5. The empirical correlations between the globally-averaged FCE and the height ratio within the range of the present study are also given. For the serrated trench, the cooling jet has the best spanwise spreading and flow extension ability when the VSS height is 0.5D. The proposed novel film cooling structure (SerrTrench-VSS) can effectively improve the FCE and provide feasible means for the efficient cooling of a turbine blade under practical conditions.

Performance and prediction of baffled cold plate based battery thermal management system

• Heat transfer performance of cold plate with longer and more baffles is better. • Performance of baffled cold plate can be further improved with the increase of s - L . • Requirements for BTMS operating parameters under different conditions are revealed. • Characteristics of baffled cold plate and BTMS can be predicted by neural network. The development of NEV is restricted by the problem of battery thermal safety. BTMS should be lightweight, compact, and efficient. Baffled cold plate with small aspect ratio channels was designed for BTMS. The influence of structure and operating parameters on baffled cold plate and BTMS performance were explored through ANSYS simulation. BP neural network model was established to study the function of performance prediction and application in the fields of BTM. The results show that the comprehensive heat transfer performance of baffled cold plates with longer and more baffles is better. Comprehensive heat transfer performance and temperature uniformity of baffled cold plate can be improved through local connection method, and the optimization effect is enhanced with the increase in left local slit spacing. Under low discharge rate conditions, it’s easier to meet the needs of BTM. When the battery is discharged at 3 C rate, volumetric flow rate needs to reach 1 mL·s -1 at all inlet temperature conditions. Through data processing and modeling, BP neural network predictions of flow and heat transfer characteristics of baffled cold plate and temperature control performance of BTMS are proven accurate. It facilitates the design and optimization of baffled cold plates, and the design and control strategy formulation of BTMS.

Simulation study on fire extinguishing system of ultra-fine powder extinguishing agent in helicopter engine compartment

The design of the engine compartment fire extinguishing system determines the release, flow and dispersion characteristics of the ultra-fine powder extinguishing agent (UPEA), which affects its effectiveness. The simulation of the UPEA fire extinguishing system in the engine compartment of a helicopter model was carried out, and the results of the study showed that, the maximum mass flow of UPEA particles at the nozzle of the fire extinguishing system pipe was 5.2 kg/s, and the injection time was 0.31s. At the same inlet air temperature in the engine compartment, the smaller the inlet air flow, the longer the engine compartment UPEA concentration maintenance time. At the same inlet flow, the higher the inlet air temperature, the shorter the duration of UPEA concentration in the engine compartment. The duration of the lowest extinguishing agent concentration was 0.70s at an inlet air temperature of 121°C and an inlet air flow of 0.423kg/s. Under different inlet air flow and temperature conditions, the UPEA concentration at all 12 monitor points in the engine compartment was maintained for more than 0.5s, meeting the design requirements. The research results have guiding significance for fire extinguishing system design of certain helicopters.

Effects of Flow Rate and Inlet Temperature on Performance of Annulus Type Low-Temperature Latent Heat Thermal Energy Storages

Solar energy is one of the largest energy potentials that Indonesia has, which can be utilized in solar heater that are integrated with latent heat energy storage (LHTES). This research aims to investigate the effects of the operating conditions of flow rate and inlet temperature on the performance of the annulus type Low-Temperature LHTES using Computational fluid dynamics method in which the enthalpy-porosity is used as the solidification model. The results indicate that the increase of performance can be obtained by increasing the flow rate and inlet temperature. The increase in flow rate will promote higher heat transfer thus produce better performance up to 11.91% and 24.91% during charging and discharging, respectively. Meanwhile, increasing the inlet temperature will increase the performance up to 192.72% during charging and 13.07% during discharging of the Low-Temperature LHTES system.

Numerical investigation on thermal–hydraulic performance of supercritical LNG in a Zigzag mini-channel of printed circuit heat exchanger

• Flow mechanism of supercritical hydrocarbon fluids was investigated. • Comparison on thermal performances for two hydrocarbon fluids was compared. • Correlations for supercritical hydrocarbon fluids in a mini-channel were proposed. Printed circuit heat exchanger (PCHE) is receiving wide attention as a new kind of compact heat exchanger. It is considered as a promising vaporizer in floating liquefied natural gas (FLNG) vessels due to its compactness and high efficiency. In this paper, the numerical model with two Zigzag mini-channels was built. The cross section was a semicircle with the diameter of 1.5 mm and the overall length was 200 mm. In the simulation, SST k - ω turbulent model was employed and validated against experimental data of supercritical CO 2 flow. The mechanism of flow and heat transfer was investigated, and the influence of operating parameters including mass flux, outlet pressure and inlet temperature was analyzed from the perspective of high-speed components of turbulent core area, degree of flow separation, energy transport and dissipation rate. The results indicated that the worse flow performance and better heat transfer performance exhibited at higher mass flux and inlet temperature conditions, whereas the higher outlet pressure conditions exhibited the better flow and heat transfer performances. Correlations for the Fanning friction factor and Nusselt number were developed within a deviation of ±5%, aiming to apply to the prediction of thermal–hydraulic performance of supercritical LNG.

Numerical modeling of heat transfer performance and optimization of car radiator using (H2O/Al2O3) nanofluids as coolant

The combustion of fuel in an engine is an exothermic reaction that releases a tremendous amount of heat. Some of this heat is escapes with the exhaust gases while the remaining is absorbed by the engine parts. Excessive heating of the engine cylinder can lead to the premature detonation of the air-fuel mixture in the cylinder, piston scuffing, damage of valves and guides, thermal stress buildup and gasket failure. Most engines utilize a liquid cooling system to transfer the heat from the engine to the surroundings. The radiator is a vital part of an automobile cooling system. Water and other coolants such as ethylene glycol are usually applied to dispel heat from the engine to the environment through the radiator. Nanofluids have a higher thermal conductivity than water and ethylene glycol, and for this reason, it has been receiving attention as a better alternative to the conventional coolants. In this study, the thermal performance of water and aluminum oxide nanofluids were investigated numerically. The radiator understudy was a crossflow radiator. Solidworks 2017 flow simulation software was used to carry out the numerical investigation. The same inlet temperature, flow rate and environmental conditions were used for both the water and nanofluid coolant operating in the radiator. Four different concentrations of the nanofluid were considered in this study, to determine the effect of concentration on the performance of the radiator. At a 1% concentration of Al2O3, the enhancement in the heat transfer rate and heat transfer coefficient (coolant side) are 0.86% and 6.98% respectively. While at 4% concentration, the enhancement in heat transfer rate and heat transfer coefficient is 12.03% and 14.31% compared to water. The results of this study prove that nanofluid is a better heat transfer fluid compared to water and serve as a better alternative for application in car radiators.

충전층 축열시스템의 성능 특성

An analytical model is presented, for packed-bed thermal storage systems. The model is based on a mathematical solution for packed-bed storage systems, subject to arbitrary periodic inlet temperature conditions and heat loss to ambient. The model is validated via comparison with well-known theoretical and experimental data in the literature. It is also demonstrated that the model can be used to analyze the experimental results, and to predict the performance of packed beds in general. The model is simple and flexible, so that it can facilitate design and analysis of the packed-bed systems, subjected to various boundary conditions in the field.

Numerical simulation of complex thermal decomposition processes in pyrolysis furnace for recycling solid waste Mg(NO3)2.2H2O

This study aims to reveal the complex thermal decomposition processes in a pilot-scale pyrolysis furnace for recycling solid waste Mg(NO3)2.2H2O produced in nitric acid leaching process of laterite nickel ore, by using CFD method. Specifically, an integrated mathematical model combining the gas-particle flow and the thermal decomposition reaction as well as the heat, mass transfer between gas and particle was developed based on the Euler-Lagrange method. And then, the developed model was used to study the flow characteristics of the gas and particle and the thermal decomposition processes for Mg(NO3)2.2H2O in the pyrolysis furnace. Furthermore, the effect of operating parameters (gas inlet temperature, mass flow rate and particle size of Mg(NO3)2.2H2O) on the performance of pyrolysis furnace (decomposition rate of Mg(NO3)2.2H2O) was studied. The results show that the developed model is reasonable. Increasing gas inlet temperature, decreasing mass flow rate and particle size of Mg(NO3)2.2H2O can effectively promote the decomposition rate of Mg(NO3)2.2H2O. Under the conditions of gas inlet temperature 1123 K, mass flow rate of Mg(NO3)2.2H2O 200 kg/h, and average particle size of Mg(NO3)2.2H2O 75 µm, the dehydration reaction mainly occurs in the furnace height of 11–8 m, while the denitration reaction mainly occurs in the furnace height of 10.5–1 m. The total decomposition rate of Mg(NO3)2.2H2O is 99.75%.

Meshless approach to the large-eddy simulation of the continuous casting process

The paper discusses the numerical solution of the large-eddy formulation for modelling the turbulent fluid flow with solidification in the continuous casting of steel. This industrially relevant problem is solved by a meshless method for the first time. The solid-liquid system is formulated within the continuum mixture formulation of the governing, mass momentum and energy equations. The Darcy porous media model describes the mushy region. The large-eddy formulation is based on the Smagorinsky model for sub-grid scale viscosity and the van Driest damping function. The synthetic turbulence is prescribed at the molten steel inlet. The generated turbulent fluctuations are isotopic and correlated in time through an asymmetric time filter. Explicit time discretisation, combined with meshless local radial basis function collocation method, is employed. Five-noded subdomains, non-uniform node arrangement and multiquadrics shape functions are used for solving a two-dimensional model. The sensitivity to different node arrangements, time steps, inlet temperature, and velocity boundary conditions is elaborated and successfully verified by comparison with our previously published meshless k − ε turbulence model of the same process.

Onset of flow instability during subcooled flow boiling of seawater in a vertical annulus

The present study investigates the onset of flow instabilities during subcooled flow boiling of 3.5 wt% artificial seawater in a vertical annulus. All flow instability experiments are conducted by decreasing mass flux gradually under a specific condition of inlet temperature and heat flux. The results reveal that, comparing with de-ionized water, the artificial seawater is more susceptible to the flow instability and demonstrates 12–79% larger mass fluxes for onset of flow instability (OFI) due to the unique two-phase flow pattern of densely bubbly flow or bubble foam flow during the subcooled flow boiling of artificial seawater. After OFI, unstable bubble foam with slug bubbles resulting from foam ruptures is revealed in artificial seawater resulting in significant pressure drop oscillations at lower inlet temperature of 55 °C, 65 °C and 75 °C. The existing criteria or correlations, developed based on the data of de-ionized water, may not predict the OFI for artificial seawater. A new empirical correlation to predict the mass flux at OFI is proposed. A two-phase flow instability map is established on the plane of phase change number versus subcooling number.

Numerical simulation of the single-phase immersion cooling process using a dielectric fluid in a data server

In the wake of novel technologies such as artificial intelligence (AI), machine learning (ML), internet of things (IoT) to cater to a wide spectrum of industrial applications, eventually the demand for ultra-fast processors/data centers has been on rise. In further, these novel technologies inherently result a drastic increase of power density in data centers, where air-cooling is the popularly utilized method to handle the thermal loads. The present research study involves in numerically investigating the effectiveness of single-phase immersion cooling process, an alternate solution to air-cooling method, on governing the heat load of the densely packed servers. A dielectric fluid, EC-110 is chosen for the simulation on a suitably developed CAD model of a server, of rated design power of 150 W. Four different processing unit powers of value 65 W, 90 W, 115 W and 150 W are supplied as input load to the cooling fluid in the simulation work. The condition of inlet temperature of the dielectric fluid is varied from 25℃ to 40℃ and the flow rates are varied from 0.5 lpm to 2.5 lpm. The resulting chip junction temperature in the server is estimated for different flow rates and inlet temperature conditions of the fluid, under immersion cooling technique. It proves that this cooling technique has the potential to ensure safe operation temperature of the server at low flow rates of the fluid with high inlet temperature, at high power densities.

Effect of steady-state and unstable-state inlet boundary on the thermal performance of packed-bed latent heat storage system integrated with concentrating solar collectors

The real-time change of solar radiation intensity leads to the instability of the outlet temperature of the collector, which has an important influence on the thermal performance of the thermal energy storage system. Therefore, the dynamic thermal performance of a packed-bed latent heat storage system integrated with a solar parabolic trough collector is studied in this paper. Moreover, the effects of different mass flow rates on the total charging capacity, total exergy input, total exergy storage and exergy efficiency of the system are investigated. The result indicates that the steady-state and unstable-state inlet boundary conditions show significant differences in thermal performance. Under the unstable-state boundary conditions, when the mass flow rate increases from 0.1 to 0.2 kg/s and 0.1–0.4 kg/s, the maximum temperature difference between the PCM capsules and the air decreases to 24.11% and 47.39%, respectively. The larger the mass flow rates, the smaller the temperature difference, which is the opposite of the steady-state situation. Under steady-state inlet temperature conditions, the exergy efficiency gradually decreases with the increase of mass flow rate. Under unstable-state inlet temperature conditions, the mass flow rate has little effect on the exergy efficiency, and which is about 41.00%.