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•An evacuated receiver partially insulated by a transparent aerogel is proposed.•Heat loss from the absorber can be reduced by 10.1% by the aerogel at 823 K.•Optical efficiency of ...receiver is reduced by just 0.15 percents by the aerogel.•The maximum improvement in receiver efficiency of 2.95% can be achieved.•The maximum improvement in collector efficiency of 2.75% can be achieved.
A modified evacuated receiver partially insulated by a solar transparent aerogel was proposed for the parabolic trough collector. An optical-thermal model was developed and validated to investigate the optical and thermal performance of the modified receiver and a traditional evacuated receiver. Firstly, it was revealed that different heat transfer modes among the aerogel, absorber and glass can obviously influence the heat loss from the absorber. Based on adjusting these modes through varying the aerogel thickness, an optimal receiver design was obtained. Then, the effects of the direct normal irradiance and the coating emittance were analyzed. Finally, the optimal receiver was compared with two existing modified receivers which are insulated by an opaque material and a radiation shield, respectively. Optical study shows that the optical efficiency of receiver just decreases by 0.16% when the aerogel thickness increases from 0 to 24.5 mm, which indicates the aerogel influences slightly on the optical performance. Thermal study indicates the modified receiver with the aerogel thickness of 20 mm has the best insulating performance. Compared with the traditional receiver, it can reduce the heat loss from the absorber by 7.3–10.1% when the inlet fluid temperature is within 583–823 K, and the direct normal irradiance is within 400–1000 W·m−2. As a result, the receiver efficiency can be improved by 0.01–2.92%, and the collector efficiency is improved by 0.01–2.75%. Moreover, it is found that the higher the coating emittance or the fluid temperature is, more obvious the improvement in the receiver efficiency becomes. Finally, comparison of different receivers indicates the optimal receiver with the aerogel can achieve higher receiver efficiency than the two existing modified receivers under all examined typical conditions.
•A trough receiver using a transparent aerogel and wing-like mirrors is proposed.•Optical loss of the receiver can be reduced by 1.5% by the novel receiver.•Heat loss of the absorber can be reduced ...by 12.0% at fluid temperature of 823 K.•The maximum improvement in the receiver efficiency of 5.04% is achieved.•The maximum improvement in the collector efficiency of 4.74% is achieved.
In this paper, a novel evacuated receiver was proposed to improve the efficiency of the parabolic trough collector. In this receiver, a solar-transparent aerogel supported by a glass support was employed to insulate the absorber in the directly illumined vacuum zone, and wing-like mirrors on the support were designed to collect some irradiance wasted in the conventional receiver. An optical model developed using ray tracing and a heat transfer model developed using computational fluid dynamics were employed to study the receiver performance. Firstly, optical study indicates the receiver optical efficiency first increases then decreases with increasing aerogel thickness due to the combined effects of the aerogel and the mirrors. The peak receiver optical efficiency of 89.56% is achieved when the aerogel thickness is 20 mm. Moreover, thermal study indicates the receiver thermal efficiency just monotonically increases with increasing aerogel thickness before the aerogel touches the absorber. Then, the receiver with the aerogel thickness of 20 mm was selected as the suggested design after considering both the efficiencies and the safety requirements. Finally, performance evaluation reveals that the suggested receiver can improve the receiver efficiency at any direct normal irradiance or fluid temperature compared with the conventional receiver, which is the originality of this work. It is found the receiver efficiency can be improved by 0.32–5.04% under the typical direct normal irradiance of 300–1000 W·m−2 and the inlet fluid temperature of 573–823 K. Results from present study are beneficial for improving the performance of the parabolic trough collector.
•The effects of amplitude and wavelength on heat transfer behavior are investigated.•9 different wavy channel configurations and 1 straight channel configuration are considered.•In different ...perspectives, comparisons on heat transfer performance are made among different cases.•Optimum wavy parameters are selected.
Performance enhancement of printed circuit heat exchanger (PCHE) is of great importance to the thermal efficiency improvement of supercritical CO2 Brayton cycle. In this paper, the heat transfer performance and flow characteristics of a sinusoidal wavy channel PCHE are numerically investigated. The effects of the amplitude and wavelength parameters are discussed under different mass flow conditions with inlet Re = 5210.8−13026.9 on the hot side. It’s found that the increase of amplitude and decrease of wavelength result in larger flow length and heat transfer area of the wavy channel, as well as higher heat transfer rate. The use of wavy channel instead of straight channel enhances heat transfer. Because of the complicated flow fields in the wavy channels affected by thermophysical property changes and centrifugal forces, the shapes and locations of high heat flux zones shift with different configurations. The secondary flow and heat transfer area change both contribute to the change of heat transfer characteristics. The resulting complicated heat transfer performance variation of different configurations are illustrated and discussed. Based on the overall performance evaluation results, the best performance is obtained with an amplitude of 3 mm and a wavelength of 50 mm or 75 mm.
Printed circuit heat exchangers (PCHEs) are promising candidates for recuperators in supercritical CO
2
Brayton cycles. A comparative study is given in this paper on the flow and heat transfer ...characteristics of PCHEs with sinusoidal and zigzag channels. With mass flow rates of 0.6–1.8 kg/h and the bend angles of 15°–30°, the thermal-hydraulic performance of the PCHEs is discussed. Results show that the sinusoidal channel is superior to the zigzag channel in its comprehensive performance. Larger bend angles result in greater reductions in pressure drop if sinusoidal channels are used instead of zigzag channels and a maximum of 48.4% reduction can be obtained in the considered working conditions. Meanwhile, the inlet sections should be carefully optimized since these sections account for up to 31% and 17% of the total pressure drop in the sinusoidal and zigzag channels, respectively. The corner shape of the zigzag channel can be specially designed to further reduce the pressure drop. The nonuniform density and heat flux distributions in both channels are found to be related to the periodic changes of flow directions and the centrifugal forces should not be ignored when optimizing the sinusoidal and zigzag channels.
•Flow and heat transfer performance of variable cross-section tubes are analyzed.•Converging tubes enhance heat transfer and diverging tubes reduce pressure drop.•Buoyancy effects are found to ...enhance heat transfer in diverging tubes.•The two hybrid tubes show better thermal–hydraulic performance.
The performance of the precooler in the supercritical CO2 (S-CO2) Brayton cycle may be greatly affected by the interactions between the structure and the thermophysical properties. Variable cross-section tubes, which can effectively enhance heat transfer and reduce pressure drop, can be adopted in the precooler. In this paper, the flow and heat transfer performance of S-CO2 in a circular tube and variable cross-section tubes with different unit length divergent ratio (DR) and convergent ratio (CR) is firstly investigated when the heat transfer area is kept constant. The results show that the converging tubes can effectively enhance the heat transfer compared with the circular tube, and a greater CR is more beneficial for heat transfer. The heat transfer coefficient (htotal) is increased by 84.77% at the maximum. The diverging tubes are found to have a strong advantage in reducing the pressure drop, and a larger DR is more helpful to reduce pressure drop, with a maximum decrease of 84.4%. The heat transfer mechanism is analyzed from the aspects of flow field distribution, thermophysical property changes and buoyancy effect. Furthermore, combined with the performance of different variable cross-section tubes, two new hybrid tubes are proposed based on the idea of partitioned heat transfer enhancement matching the thermophysical property changes under the constant heat transfer area condition. The comprehensive thermal–hydraulic performance of the two hybrid tubes is significantly improved compared with that of the converging tube. A 34.81% higher htotal and a 6.25% lower pressure drop can be obtained when using the hybrid tube A under high heat flux conditions. The hybrid tube B is found to enhance heat transfer by 54.98% and reduced pressure drop by 55.14% under low heat flux conditions. Finally, the flow and heat transfer characteristics of different types of tubes are also further studied under the constant inlet Reynolds number condition. This study can provide some guidance for the design and optimization of precoolers where the thermophysical properties of the working fluid are highly variable.
•Flow and heat transfer characteristics of different S-CO2 mixtures are analyzed.•Machine learning is used to predict local Nu and f along the sinusoidal channel.•CO2-Xe yields better ...thermal-hydraulic performance than CO2-He and CO2-Kr.•XGBoost shows a strong fitting ability to the data, while ANN has stronger generalization ability.
The ambient temperature has a great influence on the practical application of the supercritical carbon dioxide(S-CO2) Brayton cycle. The introduction of mixtures is an effective way to change the critical characteristics of the working fluid, which allows the system to better match the ambient temperature. The mixtures not only affect the overall performance of the power system, but also affect the flow and heat transfer processes in various heat exchange equipment. In this investigation, the physical model of a sinusoidal wavy channel printed circuit heat exchangers (PCHE) is built, and numerical simulations are conducted firstly on the flow and heat transfer characteristics of three S-CO2 mixtures (CO2-He, CO2-Ke and CO2-Xe). Effects of the mole fraction and type of the additive gasses on the thermal-hydraulic performance are discussed, as well as the variations of the local heat transfer coefficients and pressure drop along the flow direction. It's found that transfer coefficient and pressure drop of CO2-He increase with the increase of the additive gas mole fraction n, with maximum heat increases of 396 % and 1147 % against pure S-CO2, respectively. With the increase of n, heat transfer coefficient and pressure drop of CO2-Kr and CO2-Xe decrease. Maximum decreases of 71 % and 38 % can be seen for the heat transfer coefficient and pressure drop against pure CO2 for CO2-Kr, and 80 % and 64 % against pure CO2 for CO2-Xe, respectively. CO2-Xe yields the best thermal-hydraulic performance of the PCHE among the three mixtures. Secondly, machine learning is adopted to predict the local flow and heat transfer characteristics of S-CO2 mixtures in response to the significant variation of S-CO2 mixtures along the flow direction within the PCHE. Four machine learning models including Support vector machine (SVR), Artificial neural network (ANN), Random forest (RF) and Extreme Boosting Tree (XGBoost) are used and the corresponding prediction performance are analysed. It is found that machine learning is efficient and accurate in the prediction. Among the four machine learning models, XGBoost has a strong fitting ability to the local Nu and f, with an R2 of 0.9992 and 0.9718 on the test set, respectively. The prediction results of the XGBoost model can reflect the variations of local Nusselt number and friction factor along the flow direction well. However, ANN has stronger generalization ability in the prediction under new working conditions. The use of machine learning can greatly help the design and optimization of PCHEs with S-CO2 mixtures as working fluids.
•The model of a ground fast cooling simulation device is introduced.•Heat transfer of multiple impinging jets is numerically investigated.•The effects of nozzle geometry and arrangement on heat ...transfer are discussed.•21 different configurations are considered and analyzed.•An overall performance evaluation indicator named QU ratio is proposed.
In this paper, a comparative study is performed to check the nozzle geometry and arrangement effects on impinging jets heat transfer performance to help the design of a ground fast cooling simulation device which is used for the thermal tests of high speed flight vehicles. Based on the simplified physical model, the impinging jets heat transfer is modeled using the shear-stress transport (SST) k-ω turbulence model. A total of 21 different nozzle configurations including 7 geometries are considered in the numerical simulation. Heat transfer performances concerning heat transfer intensity and heat flux uniformity in different cases are compared with each other. Analysis is given on the corresponding flow fields and surface heat flux distributions. To help the optimization of nozzle geometry and arrangement in designing the device, an indicator named QU ratio is proposed for the overall performance evaluation of the nozzle configurations. The effectiveness of the QU ratio is validated based on the numerical results and it can be used to help determine the best design for certain given conditions of the ground fast cooling device.
•11,032 data samples are collected for upward flow and heat transfer of S-CO2.•4 machine learning models are trained based on the dataset.•Comparisons are made among models on the prediction ...accuracy.•Machine learning models show better performance than heat transfer correlations.
The utilization of supercritical carbon dioxide(S-CO2) as a working fluid in energy conversion systems has gained widespread recognition as an efficient and environmentally friendly option. However, accurately predicting the heat transfer process is still challenging due to the significant variation of thermophysical properties within the pseudo-critical zone. The accurate prediction of the S-CO2 heat transfer process is of utmost importance for the design of heat exchangers and the safe operation of the system. Aiming at the current problems of high experimental cost and long numerical simulation time, machine learning is adopted in this paper to predict the heat transfer characteristics of S-CO2 in this temperature region. In this paper, the heat transfer process of S-CO2 flowing upward in a circular tube under heating conditions is taken as the research object, and a total of 11,032 sets of experimental data samples in the open literature are collected. Four machine learning models, namely, Random Forest (RF), Extreme Gradient Boosting (XGBoost), Support Vector Machines (SVR), and Artificial Neural Networks (ANN) are trained by taking mass flow rate, wall heat flux, pressure, fluid enthalpy, and tube diameter as the input parameters, and wall temperature as the output parameter. The prediction performance of the four machine learning models and the heat transfer correlations were compared. The results show that all four machine learning models have excellent prediction performance, and the ANN model provides the best prediction performance, with an R2 of 0.995 on new data. XGboost and ANN can accurately predict the heat transfer deterioration when the fluid temperature (Tb) approaches the pseudo-critical temperature (Tpc) or over Tpc, yet the accuracy decreases in the region of Tb < Tpc, suggesting that the prediction error is mainly originated in this region. Compared with the existing heat transfer correlations, the prediction accuracy of the ANN model obtained from the training in this paper is higher. The present study further elucidated the feasibility and accuracy of utilizing an ANN model for predicting the S-CO2 heat transfer process. A trained ANN model is a useful tool that can be directly applied to system design and heat exchanger design.
•Numerical simulation is performed on multiple impinging jets heat transfer.•A simplified model is built for a ground fast cooling simulation device.•The effects of nozzle arrangements on heat ...transfer uniformity are discussed.•Performance of different nozzle configurations is evaluated using the QU ratio.
A cooling simulation device utilizing multiple impinging jets is built for ground cooling simulation tests of high speed flight vehicles. To help the design of the device and supply a relatively uniform heat flux on the test piece surface, a three-dimensional numerical study is performed in this paper to investigate the effects of nozzle arrangement on the convective heat transfer uniformity of the impinging jets. A simplified physical model with the size of 200mm×200mm×50mm is built and the shear-stress transport (SST) k-ω turbulence model is used in the calculation. The nozzle quantity is varied from 8 × 8 to 32 × 32 for uniform nozzle arrays with a fixed total area of the nozzles. The corresponding numerical results of uniform nozzle arrangements are analyzed in details. Based on the 16 × 16 uniform arrangement results, the effects of diameter varying nozzle arrangements on heat transfer uniformity are further examined. Finally, an overall performance evaluation indicator named QU ratio is used in the optimization of nozzle arrangement, which proves to be effective and convenient in practice.
ETHNIC PHARMACOLOGICAL RELEVANCE: "Yin-Jing" medicine (YJM) has been widely used by both ancient and modern Chinese medicine practitioners during long-term clinical practice. However, it remains ...unclear how to best guide other medicines to the targeted organs in a traditional Chinese medicine (TCM) prescription. Here, in an attempt to explain the scientific connotation of the YJM property (YJMP) attributed to a basic TCM theory, Platycodon grandiflorum (PG) was chosen as a case study to reveal the mystery of YJMP theory.
The main purpose of this study is to employ modern chemical and molecular biology methods to confirm the "Yin-Jing" effect of PG, and further clarify its material basis and related possible mechanism.
The ammonia-induced lung injury rat model was utilized to determine the optimal dosage of traditional prescription Hui Yan Zhu Yu decoction (HYZYD) using Wright Giemsa staining, HE staining, Masson staining, and TUNEL analysis. With the same way, PG was confirmed to have potentiating therapeutic effect (PTE) by comparison with HYZYD and HYZYD-PG. TMT proteomics was used to reveal the "Yin-Jing" mechanism of action. Western blot assay (WB) was employed for verification of differentially expressed proteins. Additionally, four non-crossing fragmentations (Fr. A-D) were characterized by RPLC/SEC-ELSD and HILIC-ESI
-Q-OT-IT-MS techniques. The PTE and guidance property assays were utilized to evaluate "Yin-Jing" functions by a compatible combination of hydroxysafflor yellow A (HYA) using qPCR, FCM, WB, HPLC, high content cell imaging (HCI) and high-resolution live-cell imaging (HRLCI) techniques.
The HYZYD-M (medium dose group) significantly improved the lung injury level in a pneumonia model of rats. PG enhanced the therapeutic effect of HYZYD ascribed to Yin-Jing PTE functions. TMT proteomics revealed a category of differentially expressed proteins ascribed to Golgi-ER between HYZYD and HYZYD-PG. Fr. C (i.e., saponins) and Fr. D (i.e., lipids) were determined as therapeutic fragmentations via the LPS-induced A549 cell injury model; however, Fr. B (fructooligosaccharides and small M
fructans) had no therapeutic effect. Further compatibility PTE assays confirmed Fr. B significantly improved efficiency by a combination of HYA. The guidance assays showed Fr. B could significantly increase the uptake and distribution of HYA into lung cells and tissues. HCI assays showed that Fr. B increased uptake of HYA accompanied by significant activation of Golgi-ER. Unlike Fr. B, HRLCI showed that Fr. A, C and D were not only unobvious activations of Golgi-ER but also insignificant facilitation of colocalizations between HYA and Golgi-ER.
Fr. B is believed to be a key YJMP material basis of PG attributed to Yin-Jing PTE with characteristic of lung-oriented guidance property, whereas another abound Fr. C was determined to have synergistic effects rather than Yin-Jing material basis.
