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14 pages, 3048 KiB

Open AccessArticle

Numerical Analysis of The Temperature Characteristics of a Coal—Supercritical Water-Fluidized Bed Reactor for Hydrogen Production

by Shiqi Wang, Rong Xie, Jiali Liu, Pu Zhao, Haitao Liu and Xiaofang Wang

Machines 2023, 11(5), 546; https://doi.org/10.3390/machines11050546 - 12 May 2023

Cited by 2 | Viewed by 1285

Abstract

Supercritical water gasification (SCWG) of coal is a promising clean coal technology, which discards the traditional coal combustion and oxidation reaction to release carbon dioxide and other pollutants and replaces coal with a gasification reduction reaction in supercritical water to finally convert coal [...] Read more.

Supercritical water gasification (SCWG) of coal is a promising clean coal technology, which discards the traditional coal combustion and oxidation reaction to release carbon dioxide and other pollutants and replaces coal with a gasification reduction reaction in supercritical water to finally convert coal into a hydrogen-rich gas product with no net carbon dioxide emissions and no pollutant emissions, and thus has received much attention in recent years. However, the experimental conditions of coal to the hydrogen reactor are harsh, costly, and not easy to visualize and analyze, so numerical calculation and simulation analysis are important for the design, optimization, and industrial scaling-up of the reactor. In order to study the effect of the temperature field on the hydrogen production rate of the coal supercritical water gasification hydrogen production reactor, a numerical simulation calculation model is developed for this reactor in this paper. Comparing the experimental data in the literature, the maximum relative error of the gasification product yield per kg of coal between the two is less than 5%, which verifies the accuracy of the model built and the numerical method adopted in this paper. On this basis, the effects of supercritical water temperature and coal slurry temperature on the reactor’s gasification products and reaction rate were investigated in depth. The results show that increasing the supercritical water temperature is beneficial to improve the reactor hydrogen production efficiency, while the high coal slurry temperature is not conducive to adequate reaction, thus reducing the hydrogen production efficiency. For the laboratory coal supercritical water gasification to hydrogen reactor studied in this paper, the ideal temperature of supercritical water is 850~900 K, and the ideal temperature of coal slurry is 400–450 K. The conclusions of this paper can provide some reference for subsequent industrial scale-up studies of the reactor. Full article

(This article belongs to the Special Issue Heat Transfer and Energy Harvesting in Fluid System)

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17 pages, 4888 KiB

Open AccessArticle

Efficient Surrogate-Assisted Parameter Analysis for Coal-Supercritical Water Fluidized Bed Reactor with Adaptive Sampling

by Pu Zhao, Haitao Liu, Xinyu Xie, Shiqi Wang, Jiali Liu, Xiaofang Wang, Rong Xie and Siyuan Zuo

Machines 2023, 11(2), 295; https://doi.org/10.3390/machines11020295 - 16 Feb 2023

Cited by 3 | Viewed by 1166

Abstract

Supercritical water fluidized beds (SCWFBs) are promising and efficient reactors for the gasification of coal in supercritical water. The understanding and investigation of multi-phase flows as well as the gasification process usually rely on time-consuming experiments or numerical simulations, which prohibit fast and [...] Read more.

Supercritical water fluidized beds (SCWFBs) are promising and efficient reactors for the gasification of coal in supercritical water. The understanding and investigation of multi-phase flows as well as the gasification process usually rely on time-consuming experiments or numerical simulations, which prohibit fast and full exploration of the single and coupled effects of the operation and geometric parameters. To this end, this paper builds an efficient surrogate-assisted parameter analysis framework for the SCWFB reactor. Particularly, (1) it establishes a steady numerical simulation model of the SCWFB reactor for the subsequent analysis; and (2) it employs a Gaussian process surrogate modeling via efficient adaptive sampling to serve as an approximation for predicting the carbon conversion efficiency (CE) of the reactor. Based on this parameter analysis framework, this paper investigates the effects of five independent parameters (the mass flow rate of supercritical water, mass flow rate of the coal slurry, temperature of supercritical water, temperature of the outer wall and reactor length) and their interactions on the reaction performance in terms of the carbon conversion efficiency (CE). We found that the CE increases as a function of the temperature of supercritical water, the temperature of the outer wall and the reactor length; while it decreases as a function of the mass flow rate of supercritical water and the mass flow rate of the coal slurry. Additionally, the global sensitivity analysis demonstratesthat the influence of the temperature of the outer wall exerts a stronger effect than all the other factors on the CE, and the coupled interaction among parameters has a slight effect on the CE. This research provides useful guidance for scaled-up designs and optimization of the SCWFB reactor. Full article

(This article belongs to the Special Issue Heat Transfer and Energy Harvesting in Fluid System)

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16 pages, 6206 KiB

Open AccessArticle

Research of Car Cooler Thermal Performance Depending on the Mileage of Cooler and Coolant

by Marek Lipnický and Zuzana Brodnianská

Machines 2023, 11(2), 255; https://doi.org/10.3390/machines11020255 - 08 Feb 2023

Viewed by 1963

Abstract

The effect of car cooler mileage and coolant mileage on cooler thermal performance was experimentally investigated. The water–ethylene-glycol-based coolant with mileages of 0 km, 50,000 km, and 100,000 km was circulated in new and used car coolers with mileages of 0 km and [...] Read more.

The effect of car cooler mileage and coolant mileage on cooler thermal performance was experimentally investigated. The water–ethylene-glycol-based coolant with mileages of 0 km, 50,000 km, and 100,000 km was circulated in new and used car coolers with mileages of 0 km and 100,000 km, respectively. The heating and cooling time of coolants, heat transfer rate, and thermal performance were evaluated. The coolant with a mileage of 0 km in the new cooler achieved a heating time of 41 min and 30 s, which is 8 min less time compared to the coolant with mileage of 100,000 km in the used cooler. When the operating temperature was reached earlier, the engine ran more efficiently and consumed less fuel. The coolant with 0 km mileage in the new cooler achieved a cooling time of 4 min and 30 s, which is 3 min and 30 s less time compared to the coolant with 50,000 km mileage in the new cooler. The new coolant in the new cooler achieved the shortest heating time and cooling time and the highest thermal performance (η = 0.79). The used cooler with the new coolant only achieved a one-time decrease compared to the new cooler and new coolant. The coolant with 50,000 km and 100,000 km mileage for the new cooler and used cooler reached a drop of 1.01 to 1.02 times compared to the new cooler. Coolant and coolers with higher mileage have no significant effect on the thermal performance of the cooler and the correct cooling function of the car engine. Full article

(This article belongs to the Special Issue Heat Transfer and Energy Harvesting in Fluid System)

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17 pages, 8119 KiB

Open AccessArticle

Film Cooling Performance of a Cylindrical Hole with an Upstream Crescent-Shaped Block in Linear Cascade

by Chao Zhang, Junhuai Dong, Zhan Wang, Pengfei Zhang, Zhiting Tong and Yue Zhang

Machines 2023, 11(1), 110; https://doi.org/10.3390/machines11010110 - 13 Jan 2023

Viewed by 1029

Abstract

Recent works have already demonstrated that placing a crescent-shaped block upstream of a cylindrical hole could enhance the cooling performance of flat-plate films. The flow and cooling performance of the crescent-shaped block applied over the pressure and suction sides of the blade is [...] Read more.

Recent works have already demonstrated that placing a crescent-shaped block upstream of a cylindrical hole could enhance the cooling performance of flat-plate films. The flow and cooling performance of the crescent-shaped block applied over the pressure and suction sides of the blade is investigated in this article. The Reynolds-averaged Navier-Stokes equations are solved with the Shear Stress Transport model for turbulence closure. Two optimized blocks are obtained from the flat-plate film cooling in our previous work, and two positions on the pressure and suction sides are tested. The blowing ratio varies from 0.5 to 2.0. The results show that when the block is applied on the blade surface, it yields a different cooling performance compared with the flat plate due to different geometry curvature and pressure gradient. The cooling performance on the suction side is slightly higher than on that on the pressure side, while the aerodynamic loss on the suction side is much higher. For the different blocks, the qualitative change of cooling performance vs. blowing ratios held on turbine blades is quite close to that of flat plates. The optimized smaller block in the flat plate provides better cooling performance at lower blowing ratios, while the larger block is superior when the blowing ratios are higher. Full article

(This article belongs to the Special Issue Heat Transfer and Energy Harvesting in Fluid System)

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14 pages, 4442 KiB

Open AccessArticle

Multi-Disciplinary Analysis of Working Fluids on Thermal Performance of the High-Power Diesel Engine System

by Geesoo Lee

Machines 2022, 10(11), 1023; https://doi.org/10.3390/machines10111023 - 03 Nov 2022

Cited by 1 | Viewed by 1201

Abstract

Multi-disciplinary analysis was performed to analyze and investigate the thermal performance during transient operation of a 2 L diesel engine system with two different cooling systems. The multi-disciplinary model consisted of the engine thermal management system (ETMS) comprising a zero-dimensional engine model that [...] Read more.

Multi-disciplinary analysis was performed to analyze and investigate the thermal performance during transient operation of a 2 L diesel engine system with two different cooling systems. The multi-disciplinary model consisted of the engine thermal management system (ETMS) comprising a zero-dimensional engine model that can simulate the engine performance, and a one-dimensional flow model for cooling and lubrication systems with a controller. By deploying this approach, we were able to model different physical domains, including mechanical for the engine and the dynamometer and thermodynamic for the heat exchangers. Therefore, the thermal performance of the ETMS could be numerically predicted and analyzed. To develop the ETMS model, the physical properties, the heat transfer model, and the pressure drop were modeled. The base fluid, a 50/50 mixture of water and ethylene glycol (EG), and an Al₂O₃ nanofluid with a 1.5% volume ratio were modeled based on the thermodynamic properties such as density, dynamic viscosity, thermal conductivity, and specific heat. Nanofluid, with its higher thermal conductivity and higher heat transfer coefficient, absorbed more heat from the combustion chamber through the water-jacket in the engine block. Therefore, the oil temperature for the nanofluid was effectively 2.5 °C less than for the base fluid following the step-load condition. Simulation results showed the better effect of nanofluid on thermal performance. The total flow rate of nanofluid decreased by 2.2 L/min, although the flow rate through the radiator with nanofluid increased by 0.81 L/min to obtain greater heat dissipation. Eventually, the piston and the liner temperatures with the nanofluid were drastically reduced by 7.55 and 8 °C, respectively, compared to those of the base fluid. Finally, when nanofluids was applied in automotive cooling systems, the temperature of the piston decreased by 7.3 °C due to the reduced overall thermal resistance from combustion chambers to outside air. The effect of working fluid on the diesel engine system could be predicted through the multi-disciplinary model. Full article

(This article belongs to the Special Issue Heat Transfer and Energy Harvesting in Fluid System)

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11 pages, 2394 KiB

Open AccessArticle

Analysis of Natural Heat Dissipation Capacity of Hydraulic Tank and Relevant Influencing Factors

by Fugang Zhai, Xiaonan Wang, Zhiqiang He, Yu Chen, Zi Ye and Jing Yao

Machines 2022, 10(11), 991; https://doi.org/10.3390/machines10110991 - 29 Oct 2022

Viewed by 1555

Abstract

This paper aims to study the natural heat dissipation capacity of a hydraulic tank during its miniaturization revolution. A theoretical model of heat dissipation was built up on the basis of experimental analysis. Then, the natural heat dissipation power was deduced and shown [...] Read more.

This paper aims to study the natural heat dissipation capacity of a hydraulic tank during its miniaturization revolution. A theoretical model of heat dissipation was built up on the basis of experimental analysis. Then, the natural heat dissipation power was deduced and shown to be relevant. Influencing factors were analyzed, which were the oil height proportion, design proportion, volume, material type, and wall thickness. The results showed that the heat dissipation power is proportional to the height of the oil in the tank. The power increases with the height proportional coefficient k2, while it first decreases and then increases with the length proportional coefficient k1. The lengthwise coefficient obviously has a more significant effect. The influence degree of reduction methods on natural heat dissipation is in the following order: length reduction > equal proportion reduction > height reduction > width reduction. Additionally, when the thermal conductivity λ is greater than 10 W/(m·K), the material and wall thickness of the tank slightly influence the heat dissipation capacity; otherwise, the influence is evident. Full article

(This article belongs to the Special Issue Heat Transfer and Energy Harvesting in Fluid System)

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15 pages, 4045 KiB

Open AccessArticle

Study of Heat Transfer and Leakage Characteristics of Brush Seals Based on Local Temperature Non-Equilibrium Model

by Jiahao Zhang, Meihong Liu and Neng Peng

Machines 2022, 10(9), 823; https://doi.org/10.3390/machines10090823 - 19 Sep 2022

Cited by 1 | Viewed by 1521

Abstract

In this study, to improve the accuracy of the brush seal heat transfer model, based on the finite volume method (FVM) coupled with the three-dimensional Reynold-averaged Naviers-Stokes equations (RANS) equations of the Local temperature non-equilibrium (LTNE) model, and a mathematical model of the [...] Read more.

In this study, to improve the accuracy of the brush seal heat transfer model, based on the finite volume method (FVM) coupled with the three-dimensional Reynold-averaged Naviers-Stokes equations (RANS) equations of the Local temperature non-equilibrium (LTNE) model, and a mathematical model of the heat transfer and leakage characteristics of the brush seal was established. The distribution of the pressure, flow and temperature fields of the brush seal are analyzed. User-defined function (UDF) programming was performed for the LTNE model. And the LTNE model is then compared with the local temperature equilibrium (LTE) model in terms of the factors influencing the heat transfer and leakage characteristics. The results show that the maximum brush filament temperature increases with an increases in the pressure ratio, interference, and speed for both models; the fluid flow rate increases with an increases in the pressure ratio, interference, and speed; and the leakage rate increases with an increases in the pressure ratio and decreases with an increases in interference and speed. The maximum temperature of the brush filament under the LTNE model was found to be higher than that under the LTE model, but the maximum temperature difference does not exceed 3.1%. Additionally, the fluid flow rate under the LTNE model was higher than that under the LTE model, and the flow rate difference does not exceed 3.4%. And the leakage rate under the LTNE model was lower than that under the LTE model, and the leakage rates differ by no more than 9.0%. Ultimately, numerical analysis of the brush seal under the LTNE model was found to be more effective and consistent with actual working conditions than alternative models. Full article

(This article belongs to the Special Issue Heat Transfer and Energy Harvesting in Fluid System)

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14 pages, 3526 KiB

Open AccessArticle

A Cycle Analysis of Flow and Thermal Parameters in the Hydrogen Charging System at the Pressure of 50 MPa

by Ji-Qiang Li, Byung-Hee Song and Jeong-Tae Kwon

Machines 2022, 10(6), 461; https://doi.org/10.3390/machines10060461 - 10 Jun 2022

Cited by 2 | Viewed by 2090

Abstract

In the currently developed hydrogen compression cycle system, hydrogen is compressed through a compressor and stored in a tank at high pressure. In the filling process from A (tube trailer) to B (high-pressure tank), thermal stress in the B arises due to the [...] Read more.

In the currently developed hydrogen compression cycle system, hydrogen is compressed through a compressor and stored in a tank at high pressure. In the filling process from A (tube trailer) to B (high-pressure tank), thermal stress in the B arises due to the temperature rise of hydrogen together with the internal pressure increase in the tank. In the study, in order to achieve safe filling, it is necessary to investigate the flow and thermal parameters of the system. Based on the principles of thermodynamics, a thermodynamic prediction model for the temperature change during the hydrogen cycle was established by comprehensively considering the real state of gas, convective heat transfer between hydrogen and the inner wall, heat conduction through the tank wall, and natural convection of the outer wall. Prediction values of temperature, hydrogen charge amountm and heat transfer to the outside were calculated. Additionally, by investigating the performance of the hydrogen refueling station heat exchanger, the heat of the heat exchanger needed to keep the hydrogen temperature within a safe range was calculated. Due to the Joule–Thomson effect, the hydrogen temperature passing through the pressure reducing valve changed, and the changed value in the hydrogen charging cycle was predicted and calculated by calculating the temperature change value at this time. This study provides a theoretical research basis for high-pressure hydrogen energy storage and hydrogenation technology. Full article

(This article belongs to the Special Issue Heat Transfer and Energy Harvesting in Fluid System)

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