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13 pages, 4111 KiB

Open AccessFeature PaperArticle

Analysis of the Maximum Efficiency and the Maximum Net Power as Objective Functions for Organic Rankine Cycles Optimization

by Johan González, José Matías Garrido and Héctor Quinteros-Lama

Entropy 2023, 25(6), 882; https://doi.org/10.3390/e25060882 - 31 May 2023

Cited by 3 | Viewed by 1625

Abstract

Maximum efficiency and maximum net power output are some of the most important goals to reach the optimal conditions of organic Rankine cycles. This work compares two objective functions, the maximum efficiency function,

β

, and the maximum net power output function,

ω

[...] Read more.

Maximum efficiency and maximum net power output are some of the most important goals to reach the optimal conditions of organic Rankine cycles. This work compares two objective functions, the maximum efficiency function,

β

, and the maximum net power output function,

ω

. The van der Waals and PC-SAFT equations of state are used to calculate the qualitative and quantitative behavior, respectively. The analysis is performed for a set of eight working fluids, considering hydrocarbons and fourth-generation refrigerants. The results show that the two objective functions and the maximum entropy point are excellent references for describing the optimal organic Rankine cycle conditions. These references enable attaining a zone where the optimal operating conditions of an organic Rankine cycle can be found for any working fluid. This zone corresponds to a temperature range determined by the boiler outlet temperature obtained by the maximum efficiency function, maximum net power output function, and maximum entropy point. This zone is named the optimal temperature range of the boiler in this work. Full article

(This article belongs to the Special Issue Applied Thermodynamics and Heat Transfer)

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13 pages, 3027 KiB

Open AccessArticle

Study on Heat Transfer Characteristics of Graphene Nanofluids in Mini-Channels of Thermal Integrated Building

by Yongbin Cui, Dong Liu and Yu Shu

Entropy 2023, 25(5), 712; https://doi.org/10.3390/e25050712 - 25 Apr 2023

Cited by 1 | Viewed by 1608

Abstract

Two kinds of rectangular mini-channels of different sizes were designed and fabricated for testing the convective heat transfer characteristics of graphene nanofluids. The experimental results show that the average wall temperature decreases with the increases in graphene concentration and Re number at the [...] Read more.

Two kinds of rectangular mini-channels of different sizes were designed and fabricated for testing the convective heat transfer characteristics of graphene nanofluids. The experimental results show that the average wall temperature decreases with the increases in graphene concentration and Re number at the same heating power. Within the experimental Re number range, the average wall temperature of 0.03% graphene nanofluids in the same rectangular channel decreases by 16% compared with that of water. At the same heating power, the convective heat transfer coefficient increases with the increase in the Re number. The average heat transfer coefficient of water can be increased by 46.7% when the mass concentration of graphene nanofluids is 0.03% and the rib-to-rib ratio is 1:2. In order to better predict the convection heat transfer characteristics of graphene nanofluids in small rectangular channels of different sizes, the convection heat transfer equations applicable to graphene nanofluids of different concentrations in small rectangular channels with different channel rib ratios were fitted, based on factors such as flow Re number, graphene concentration, channel rib ratio, Pr number, and Pe number; the average relative error (MRE) was 8.2%. The mean relative error (MRE) was 8.2%. The equations can thus describe the heat transfer characteristics of graphene nanofluids in rectangular channels with different groove-to-rib ratios. Full article

(This article belongs to the Special Issue Applied Thermodynamics and Heat Transfer)

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13 pages, 3495 KiB

Open AccessArticle

Influence of Rotational Speed on Isothermal Piston Compression System

by Teng Ren, De-Xi Wang, Wei-Qing Xu and Mao-Lin Cai

Entropy 2023, 25(4), 644; https://doi.org/10.3390/e25040644 - 12 Apr 2023

Cited by 1 | Viewed by 1773

Abstract

An isothermal piston is a device that can achieve near-isothermal compression by enhancing the heat transfer area with a porous media. However, flow resistance between the porous media and the liquid is introduced, which cannot be neglected at a high operational speed. Thus, [...] Read more.

An isothermal piston is a device that can achieve near-isothermal compression by enhancing the heat transfer area with a porous media. However, flow resistance between the porous media and the liquid is introduced, which cannot be neglected at a high operational speed. Thus, the influence of rotational speed on the isothermal piston compression system is analyzed in this study. A flow resistance mathematical model is established based on the face-centered cubic structure hypothesis. The energy conservation rate and efficiency of the isothermal piston are defined. The effect of rotational speed on resistance is discussed, and a comprehensive energy conservation performance assessment of the isothermal piston is analyzed. The results show that the increasing rate of the resistance work increases significantly proportional to the rotational speed, and the proportion of resistance work in the total work increases gradually and sharply. The total work including compression and resistance cannot be larger than the compression work under adiabatic conditions. The maximum rotational speed is 650 rpm. Full article

(This article belongs to the Special Issue Applied Thermodynamics and Heat Transfer)

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22 pages, 1026 KiB

Open AccessArticle

Transient Nonlinear Heat Conduction in Concrete Structures: A Semi-Analytical Approach

by Hui Wang, Xi Chen, Eduardus Koenders, Ying Dai, Xingchun Huang, Qing Ai and Yong Yuan

Entropy 2023, 25(4), 583; https://doi.org/10.3390/e25040583 - 29 Mar 2023

Cited by 1 | Viewed by 2389

Abstract

Thermal loading, especially in fire scenarios, challenges the safety and long-term durability of concrete structures. The resulting heat propagation within the structure is governed by the heat conduction equation, which can be difficult to solve analytically because of the nonlinearity related to the [...] Read more.

Thermal loading, especially in fire scenarios, challenges the safety and long-term durability of concrete structures. The resulting heat propagation within the structure is governed by the heat conduction equation, which can be difficult to solve analytically because of the nonlinearity related to the thermophysical properties of concrete. A semi-analytical approach for the transient nonlinear heat conduction problem in concrete structures was established in the present work. The nonlinearity related to the temperature-dependent thermal conductivity, mass density, and specific heat capacity of heated concrete was taken into consideration. A Taylor series approximate solution was first established within a small neighborhood, employing the Boltzmann transformation in combination with the mean value theorem. Thereafter, it was extended to the whole domain by utilizing the Bernstein polynomial. The semi-analytical approach was validated by comparing it with the numerical results of two independent Finite Element simulations of nonlinear heat conduction along concrete plates, subjected to either moderate or fierce thermal loading. Absolute values of the relative errors are smaller than

5 %

. The validated semi-analytical approach was further applied to prediction of the temporal evolution of the temperature field of a scaled model of a subway station, subjected to fire disaster. The nonlinearities, related to the time-dependent surface temperature and the temperature-dependent thermophysical properties of concrete, were taken into consideration. The predictions agree well with the experimental measurements. The established semi-analytical approach exhibits good accuracy and stability, providing insight into the interaction between the thermophysical properties of concrete in the heat conduction process. Full article

(This article belongs to the Special Issue Applied Thermodynamics and Heat Transfer)

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16 pages, 426 KiB

Open AccessFeature PaperArticle

Stochastic Thermodynamics of a Finite Quantum System Coupled to Two Heat Baths

by Heinz-Jürgen Schmidt and Jochen Gemmer

Entropy 2023, 25(3), 504; https://doi.org/10.3390/e25030504 - 15 Mar 2023

Cited by 1 | Viewed by 1931

Abstract

We consider a situation where an N-level system (NLS) is coupled successively to two heat baths with different temperatures without being necessarily thermalized and approaches a steady state. For this situation we apply a general Jarzynski-type equation and conclude that heat and [...] Read more.

We consider a situation where an N-level system (NLS) is coupled successively to two heat baths with different temperatures without being necessarily thermalized and approaches a steady state. For this situation we apply a general Jarzynski-type equation and conclude that heat and entropy is flowing from the hot bath to the cold one. The Clausius relation between increase of entropy and transfer of heat divided by a suitable temperature assumes the form of two inequalities. Our approach is illustrated by an analytical example. For the linear regime, i.e., for small temperature differences between the two heat baths, we derive an expression for the heat conduction coefficient. Full article

(This article belongs to the Special Issue Applied Thermodynamics and Heat Transfer)

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17 pages, 4403 KiB

Open AccessArticle

Enhancement of Film Cooling Effectiveness in a Supersonic Nozzle

by Nithin Somasekharan, A. R. Srikrishnan, Harihara Sudhan Kumar, Krishna Prasad Ganesh, Akram Mohammad and Ratna Kishore Velamati

Entropy 2023, 25(3), 481; https://doi.org/10.3390/e25030481 - 10 Mar 2023

Cited by 1 | Viewed by 2657

Abstract

Film cooling as applied to rocket nozzles is analyzed numerically with emphasis on the assessment of the effect of the mixing of coolant with the hot stream. Cooling performance, as characterized by cooling effectiveness, is studied for three different coolants in the three-dimensional, [...] Read more.

Film cooling as applied to rocket nozzles is analyzed numerically with emphasis on the assessment of the effect of the mixing of coolant with the hot stream. Cooling performance, as characterized by cooling effectiveness, is studied for three different coolants in the three-dimensional, turbulent flow field of a supersonic convergent-divergent nozzle operating with a hot stream temperature of 2500 K over a range of blowing ratios. The coolant stream is injected tangentially into the mainstream using a diffuser-type injector. Parameters influencing the effectiveness, such as coolant injector configuration and mixing layer, are analyzed. Thermal and species mixing between the coolant and the mainstream are investigated with regard to their impact on cooling effectiveness. The results obtained provide insight into the film cooling performance of the gases and the heat transfer characteristics associated with these three gases. An injector taper angle of 30° results in the most effective cooling among the configurations considered (0°, 15°, 30° and 45°). Mixing of the coolant with the hot stream is examined based on the distributions of velocity, temperature and species. The higher values of cooling effectiveness for Helium are attributed to its thermophysical properties and the reduced rate of mixing with the hot stream. The results further indicate that through optimization of the blowing ratio and the coolant injector configuration, the film cooling effectiveness can be substantially improved. Full article

(This article belongs to the Special Issue Applied Thermodynamics and Heat Transfer)

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12 pages, 2470 KiB

Open AccessArticle

Dynamic Heat Dissipation Model of Distributed Parameters for Oil-Directed and Air-Forced Traction Transformers and Its Experimental Validation

by Yonghua You, Kun Shao and Zhengming Yi

Entropy 2023, 25(3), 457; https://doi.org/10.3390/e25030457 - 6 Mar 2023

Cited by 5 | Viewed by 2556

Abstract

A traction transformer with narrow oil channels is usually cooled with the ODAF or “Oil Directed Air Forced” method, where its temperature greatly depends on the Joule heat of windings, the conjugate heat transfer in the transformer, and the secondary heat release via [...] Read more.

A traction transformer with narrow oil channels is usually cooled with the ODAF or “Oil Directed Air Forced” method, where its temperature greatly depends on the Joule heat of windings, the conjugate heat transfer in the transformer, and the secondary heat release via oil cooler, together with the oil flowrate generated by oil pump. Neither the thermal–electric analogy nor the CFD simulation approach is qualified to predict the temporal and spatial temperature variations in this type of transformer. In the current work, the distributed parameter models are built for traction transformers and oil coolers with the assumption of a one-dimensional temperature field in the oil flow direction, respectively. Then, the two models are combined with the lumped parameter ones of oil pumps and pipes via the flow rate, temperature and pressure continuities at their interfaces, resulting in the derivation of the dynamic heat dissipation model of oil-directed and air-forced traction transformers. Additionally, an efficient algorithm is proposed for its numerical solution, and the temperature rise experiment is performed for model validation. Finally, the fundamental of dynamic heat dissipation in traction transformers is investigated with the current numerical model and the effects of ambient temperature are studied. Full article

(This article belongs to the Special Issue Applied Thermodynamics and Heat Transfer)

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20 pages, 7693 KiB

Open AccessArticle

Analysis of Tangential Leakage Flow Characteristics of Oil-Free Scroll Expander for a Micro-Scale Compressed Air Energy Storage System

by Jian Sun, Bin Peng, Bingguo Zhu and Yaohong Li

Entropy 2023, 25(2), 339; https://doi.org/10.3390/e25020339 - 12 Feb 2023

Cited by 6 | Viewed by 2078

Abstract

Tangential leakage loss is the primary factor that significantly affects the output performance of oil-free scroll expanders. A scroll expander can function under different operating conditions, and the flow of tangential leakage and generation mechanism is different. This study employed computational fluid dynamics [...] Read more.

Tangential leakage loss is the primary factor that significantly affects the output performance of oil-free scroll expanders. A scroll expander can function under different operating conditions, and the flow of tangential leakage and generation mechanism is different. This study employed computational fluid dynamics to investigate the unsteady flow characteristics of the tangential leakage flow of a scroll expander with air as the working fluid. Consequently, the effects of different radial gap sizes, rotational speeds, inlet pressures, and temperatures on the tangential leakage were discussed. The tangential leakage decreased with increases in the scroll expander rotational speed, inlet pressure, and temperature, and decreased with decrease in radial clearance. With an equal-proportional increase in radial clearance, the flow form of the gas in the first expansion and back-pressure chambers became more complicated; when the radial clearance increased from 0.2 to 0.5 mm, the volumetric efficiency of the scroll expander decreased by approximately 5.0521%. Moreover, because of the large radial clearance, the tangential leakage flow maintained a subsonic flow. Further, the tangential leakage decreased with increase in rotational speed, and when the rotational speed increased from 2000 to 5000 r/min, the volumetric efficiency increased by approximately 8.7565%. Full article

(This article belongs to the Special Issue Applied Thermodynamics and Heat Transfer)

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21 pages, 5689 KiB

Open AccessArticle

Optimization of Two-Phase Ejector Mixing Chamber Length under Varied Liquid Volume Fraction

by Jia Yan, Yuetong Shu, Jing Jiang and Huaqin Wen

Entropy 2023, 25(1), 7; https://doi.org/10.3390/e25010007 - 21 Dec 2022

Cited by 5 | Viewed by 2195

Abstract

The ejector performance varies with the mixing chamber length which is largely dependent on the fluid liquid volume fraction at the inlet. In this study, numerical simulations are conducted to optimize two mixing chamber lengths of a two-phase ejector under varied liquid volume [...] Read more.

The ejector performance varies with the mixing chamber length which is largely dependent on the fluid liquid volume fraction at the inlet. In this study, numerical simulations are conducted to optimize two mixing chamber lengths of a two-phase ejector under varied liquid volume fractions of 0–0.1 in two inlet fluids. The main findings are as follows: (1) The two optimal lengths of constant-pressure and constant-area mixing chambers are identified within 23–44 mm and 15–18 mm, respectively, when the primary inlet fluid is in two-phase; (2) the two optimal lengths are 2–5 mm and 9–15 mm, respectively, when the secondary inlet fluid is in two-phase; (3) when both inlets are in two-phase, the two optimal lengths are ranged in 5–23 mm and 6–18 mm; (4) little liquid within inlet fluid has a significant influence on ejector performances; and (5) optimal constant-pressure mixing chamber length and the sum of the two optimal lengths increase with the primary flow inlet liquid volume fraction but decrease with that of the secondary flow inlet. Full article

(This article belongs to the Special Issue Applied Thermodynamics and Heat Transfer)

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23 pages, 11442 KiB

Open AccessArticle

Optimization of Three Key Geometries of a Steam Ejector under Varied Primary Nozzle Geometries

by Jia Yan, Ruixin Li and Chen Wang

Entropy 2023, 25(1), 15; https://doi.org/10.3390/e25010015 - 21 Dec 2022

Cited by 5 | Viewed by 1951

Abstract

In this paper, three key geometrical dimensions such as XL3 (constant pressure mixing chamber length), D5 (diameter of the throat of the ejector), and XL5 (length of the throat of the ejector) were separately or sequentially optimized under different lengths and angles of [...] Read more.

In this paper, three key geometrical dimensions such as XL3 (constant pressure mixing chamber length), D5 (diameter of the throat of the ejector), and XL5 (length of the throat of the ejector) were separately or sequentially optimized under different lengths and angles of two sections of the primary nozzle. Furthermore, shock cluster number and shock chain length or area of low static pressure zone were used to analyze the effect of geometries on ejector performance, which is normally indicated by entrainment ratio (ER, or the ratio between the mass flow rate of secondary flow and the mass flow rate of primary flow). The results show that: (1) the improvement of ejector performance with only optimization of the primary nozzle is quite limited, in comparison, the impact of length and angle of nozzle diverging section on ejector performance is higher than that of converging section; (2) the relative sensitivity of ER to three key dimensions is much higher than that to the angles and lengths of the primary nozzle; (3) with the increase of XL3 and D5, ER needs a larger angle and smaller length of nozzle converging section; (4) the impact of key geometries on ejector performance can be analyzed with the help of shock cluster number and shock chain length or area of low static pressure zone. Full article

(This article belongs to the Special Issue Applied Thermodynamics and Heat Transfer)

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18 pages, 5852 KiB

Open AccessArticle

A Theoretical Comparative Study of Vapor-Compression Refrigeration Cycle using Al₂O₃ Nanoparticle with Low-GWP Refrigerants

by Shengyu Li and Jun Lu

Entropy 2022, 24(12), 1820; https://doi.org/10.3390/e24121820 - 13 Dec 2022

Cited by 11 | Viewed by 3999

Abstract

Nanorefrigerant is a mixture of nanoparticles and pure refrigerant, which can increase heat transfer characteristics in refrigeration and air conditioning equipment. The performance of four different Al₂O₃ nanorefrigerants and their pure fluids (R600a, R134a, R1234yf, and R1233zd(E)) is analyzed in [...] Read more.

Nanorefrigerant is a mixture of nanoparticles and pure refrigerant, which can increase heat transfer characteristics in refrigeration and air conditioning equipment. The performance of four different Al₂O₃ nanorefrigerants and their pure fluids (R600a, R134a, R1234yf, and R1233zd(E)) is analyzed in a vapor-compression refrigeration cycle. The enthalpy of a nanorefrigerant in the refrigeration cycle is calculated by using the prediction method based on the density of nanorefrigerant. A numerical model is established for the thermodynamic analysis, and the results show that adding nanoparticles to the pure refrigerant enhances heat transfer in heat exchangers, increases cooling capacity, reduces compressor power consumption, and finally improves the performance of the refrigeration system. The COP improvement of R1233zd(E) + Al₂O₃ nanorefrigerant is the highest, and the COP improvement of R134a + Al₂O₃ and R1234yf + Al₂O₃ are close to each other. When the mass fraction of Al₂O₃ nanoparticles increases to 0.30%, the COP of R1233zd(E) and R600a increases by more than 20%; the maximum exergy efficiency is 38.46% for R1233zd(E) + Al₂O₃, and the minimum exergy efficiency is 27.06% for pure R1234yf. The results provide a basis for the application of nanorefrigerants in the vapor compression refrigeration cycle. Full article

(This article belongs to the Special Issue Applied Thermodynamics and Heat Transfer)

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17 pages, 3668 KiB

Open AccessArticle

Numerical Simulation of Heat and Mass Transfer in Sludge Low-Temperature Drying Process

by Zhenyu Wang, Qiang Wang, Ju Lai, Dong Liu, Anjie Hu, Lin Xu and Yongcan Chen

Entropy 2022, 24(11), 1682; https://doi.org/10.3390/e24111682 - 17 Nov 2022

Cited by 4 | Viewed by 3179

Abstract

Based on the sludge mass transfer flux model, this paper conducts a simulation study on the drying characteristics of sludge under low-temperature environment and compares it with the previous experimental results. It is found that when the sludge moisture content is low, the [...] Read more.

Based on the sludge mass transfer flux model, this paper conducts a simulation study on the drying characteristics of sludge under low-temperature environment and compares it with the previous experimental results. It is found that when the sludge moisture content is low, the change of its drying curve is basically consistent with the experimental results, but there is a large error when the sludge moisture content is 0.4–0.6. In order to better simulate sludge drying characteristics, a model of cracking and shrinkage coefficients based on sludge moisture content is proposed, and the effective diffusion coefficient and mass transfer coefficient are modified. The maximum error between simulation and experiment is reduced to 23.78%. Based on this model, the sludge drying mechanism was studied. It was found that heat transfer and diffusion played a major role in the initial stage of sludge drying, and diffusion played a major role in sludge drying 30 min later. Full article

(This article belongs to the Special Issue Applied Thermodynamics and Heat Transfer)

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19 pages, 5705 KiB

Open AccessArticle

3D Simulations of Freezing Characteristics of Double-Droplet Impact on Cold Surfaces with Different Wettability

by Anjie Hu, Qiaowei Yuan, Kaiyue Guo, Zhenyu Wang and Dong Liu

Entropy 2022, 24(11), 1650; https://doi.org/10.3390/e24111650 - 14 Nov 2022

Cited by 5 | Viewed by 2778

Abstract

In this work, the freezing characteristics of double-droplet impact on three typical wettability surfaces were investigated by coupling the solidification and melting VOF models. Different temperature conditions were adopted to study the influence of icing speed on droplet behavior. Simulation results show that [...] Read more.

In this work, the freezing characteristics of double-droplet impact on three typical wettability surfaces were investigated by coupling the solidification and melting VOF models. Different temperature conditions were adopted to study the influence of icing speed on droplet behavior. Simulation results show that the motion of the double-droplet impact is consistent with that of a single droplet in the early spreading stage but behaves differently in the retraction stage. The wetting area evolution during the impact-freezing process shows different tendency for hydrophilic and hydrophobic surfaces: Compared with single droplets, double droplets have a smaller wetting area factor on hydrophilic surfaces but a larger one on superhydrophobic surfaces. In addition, three typical impact results are observed for the double-droplet impact on a superhydrophobic cold surface: full rebound, adhesive avulsion, and full adhesion, which reflects the interaction of droplet merging and solidification during the impact freezing of the double droplet. These findings may deepen our understanding of the mechanism of impact freezing on a cold surface, it provides reference for the associated applications and technologies in icing/anti-icing. Full article

(This article belongs to the Special Issue Applied Thermodynamics and Heat Transfer)

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19 pages, 36049 KiB

Open AccessArticle

Numerical Study on Effects of Wind Speed and Space Heights on Water Evaporating Performance of Water-Retained Bricks

by Rubing Han, Zhimao Xu and Enshen Long

Entropy 2022, 24(11), 1550; https://doi.org/10.3390/e24111550 - 28 Oct 2022

Viewed by 1748

Abstract

Energy-saving roof renovation methods are effective ways to alleviate the urban heat island effect. In this paper, the authors propose three models of two-layer water-retained bricks, established the physical and mathematic models of the water-retained bricks, and then conducted a computational fluid dynamics [...] Read more.

Energy-saving roof renovation methods are effective ways to alleviate the urban heat island effect. In this paper, the authors propose three models of two-layer water-retained bricks, established the physical and mathematic models of the water-retained bricks, and then conducted a computational fluid dynamics (CFD) simulation on the effect of wind speed and evaporation space height on the water-evaporating performance of water-retained bricks. The results show that: (1) for the water-retained bricks with no-hole lids, macroscopic evaporation does not happen under the static wind conditions; with the increase of wind speed, the evaporating boundary layer thickness decreases, the water vapor concentration gradient in the boundary layer and the mass diffusion flux increase; (2) for the water-retained bricks with strip-hole lids, under the static wind condition, the evaporating performance of the water-retained bricks with strip-hole lids is better than that of bricks with no-hole lids; with the increase of wind speed, the evaporation of bricks with strip-hole lids is less affected by inlet airflow velocity than that of bricks with no-hole lids; (3) as for both the water-retained bricks with no-hole lids and with strip-hole lids, for a given wind speed, both the water vapor concentration gradient and the mass diffusion flux decrease as the evaporation space increases. Full article

(This article belongs to the Special Issue Applied Thermodynamics and Heat Transfer)

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22 pages, 8778 KiB

Open AccessArticle

Theoretical and Experimental Study on the Thermal Insulation Performance of the Roof with Water-Retained Bricks

by Rubing Han, Zhimao Xu and Enshen Long

Entropy 2022, 24(11), 1528; https://doi.org/10.3390/e24111528 - 25 Oct 2022

Viewed by 1700

Abstract

In this paper, the thermal insulation performance of the roof with water-retained bricks was first analyzed theoretically with respect to the thermal inertia, attenuation and delay time of the roof with water-retained bricks. Then, the experimental rig was established to carry out the [...] Read more.

In this paper, the thermal insulation performance of the roof with water-retained bricks was first analyzed theoretically with respect to the thermal inertia, attenuation and delay time of the roof with water-retained bricks. Then, the experimental rig was established to carry out the experimental research on the thermal insulation performance of the roof with and without water-retained bricks on the sunny, overcast and rainy days in the summer and on the sunny day in the winter. The results showed that: (1) the surface heat storage coefficient is affected by the evaporating heat transfer of the water layer; (2) the thermal inertness, attenuation and delay time of the roof with water-retained bricks are 2.575, 21 and 6.94 h, respectively, when the water depth is 2 cm; (3) on the sunny, overcast and rainy days in the summer, laying water-retained bricks can enhance the heat insulation performance of the roof, and can improve the thermal comfort of the loft; and (4) on the sunny day in the winter, after laying water-retained bricks, the average temperature of the loft in 24 h increases by 2.3 °C, and the temperature fluctuation of the loft decreases by 56.0%. Therefore, the thermal insulation effect is significantly improved after laying water-retained bricks on the roof from the results of both the theoretical and experimental study. Full article

(This article belongs to the Special Issue Applied Thermodynamics and Heat Transfer)

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21 pages, 10491 KiB

Open AccessArticle

Theoretical and Experimental Study on the Impact of Long-Wave Radiation on the Greenhouse Effect of a Prefabricated Temporary House

by Qian Wen and Enshen Long

Entropy 2022, 24(10), 1446; https://doi.org/10.3390/e24101446 - 11 Oct 2022

Cited by 1 | Viewed by 1518

Abstract

In this paper, an experimental rig of a prefabricated temporary house (PTH) was first established. Then, predicted models for the thermal environment of the PTH with and without considering long-wave radiation were developed. Next, the exterior-surface, interior-surface and indoor temperatures of the PTH [...] Read more.

In this paper, an experimental rig of a prefabricated temporary house (PTH) was first established. Then, predicted models for the thermal environment of the PTH with and without considering long-wave radiation were developed. Next, the exterior-surface, interior-surface and indoor temperatures of the PTH were calculated by using the predicted models. The calculated results were then compared with the experimental results to study the influence of long-wave radiation on the predicted characteristic temperature of the PTH. Finally, the predicted models were used to calculate the cumulative annual hours and the intensity of the greenhouse effect of four different climate cities (Harbin, Beijing, Chengdu, Guangzhou, China). The results showed that: (1) the predicted temperature values of the model considering long-wave radiation were closer to the experimental results; (2) the effect level of the long-wave radiation on the three characteristic temperatures of the PTH from big to small was: exterior-surface temperature, interior-surface temperature, and indoor temperature; (3) the long-wave radiation had the greatest impact on the predicted temperature value of the roof; (4) under different climate conditions, the cumulative annual hours and the intensity of the greenhouse effect considering long-wave radiation were smaller than those without considering long-wave radiation; (5) the duration of the greenhouse effect considering and ignoring long-wave radiation varied significantly with the climate region, and that in Guangzhou was the longest, followed by Beijing and Chengdu, and that in Harbin was the shortest. Full article

(This article belongs to the Special Issue Applied Thermodynamics and Heat Transfer)

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Review

Jump to: Research

16 pages, 4631 KiB

Open AccessReview

A Mini-Review on the Thermal Fatigue Properties of Copper Materials Applied at the Front-End of Synchrotron Radiation Facilities

by Yunfei Sun, Tong Li, Lan Lan, Jiahua Chen, Wanqian Zhu, Song Xue and Limin Jin

Entropy 2023, 25(5), 714; https://doi.org/10.3390/e25050714 - 26 Apr 2023

Cited by 4 | Viewed by 2883

Abstract

Oxygen-free high-conductivity copper (OFHC), chromium-zirconium copper (CuCrZr), and Glidcop^® AL-15 are widely used in the high heat load absorber elements at the front end of synchrotron radiation facilities. It is necessary to choose the most suitable material according to the actual engineering [...] Read more.

Oxygen-free high-conductivity copper (OFHC), chromium-zirconium copper (CuCrZr), and Glidcop^® AL-15 are widely used in the high heat load absorber elements at the front end of synchrotron radiation facilities. It is necessary to choose the most suitable material according to the actual engineering conditions (such as the specific heat load, material performance, and costs). In the long-term service period, the absorber elements have to bear hundreds or kilowatts of high heat load and its “load-unload” cyclic loading mode. Therefore, the thermal fatigue and thermal creep properties of the materials are critical and have been extensively studied. In this paper, based on the published pieces of the literature, the thermal fatigue theory, experimental principles, methods, test standards, test types of equipment, and key indicators of the thermal fatigue performance of typical copper metal materials used in the front end of synchrotrons radiation Facilities are reviewed, as well as the relevant studies carried out by the well-known synchrotron radiation institutions. In particular, the fatigue failure criteria for these materials and some effective methods for improving the thermal fatigue resistance performance of the high-heat load components are also presented. Full article

(This article belongs to the Special Issue Applied Thermodynamics and Heat Transfer)

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