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Wave Motion
25 March 2018
A steady-state detection method based on Gaussian discriminant analysis for the on-line gas turbine process
Publication date: 25 March 2018
Source:Applied Thermal Engineering, Volume 133 Author(s): Zhong Wang, Yujiong Gu In the unsteady-state process, the relationship among the state variables of the gas turbine cannot reflect the current performance level accurately. In order to monitor the condition deterioration of the gas turbine in the peak-shaving timely, an on-line steady-state detection model for gas turbine is proposed in this paper. First, the change rate of the out-power is presented as the key indicator of the difference between the steady-state and unsteady-state process, and the difference value of out-power at adjacent time is available as the characteristic test statistic. Second, the interval estimation of the statistical mean value is used to classify the historical data into the steady-state samples and the unsteady-state samples. Then, these classified samples are employed to train the detection model based on Gaussian discriminant analysis. Because the change rate of the out-power in the unsteady-state process is not a fixed value, the Gaussian mixture model is built for the unsteady-state process, and the initial value of the parameters and the number of sub-models are optimized by k-means++ and AIC evaluation criteria respectively. Finally, the detection model was verified by using the data of a real gas turbine for 10
25 March 2018
Numerical study and experimental validation on the optimization of the large size solar collector
Publication date: 25 March 2018
Source:Applied Thermal Engineering, Volume 133 Author(s): Fan Zhou, Jie Ji, Weiqi Yuan, Jingyong Cai, Wenxue Tang, Mawufemo Modjinou This work presents numerical simulations and experimental validation aimed at optimizing the design of large size flat-plate solar collectors (has a profile area of 10.04
25 March 2018
Formation mechanism of longitudinal cracks in expressway embankments with inclined thermosyphons in warm and ice-rich permafrost regions
Publication date: 25 March 2018
Source:Applied Thermal Engineering, Volume 133 Author(s): Yuan Chang, Yu Qihao, You Yanhui, Guo Lei Thermosyphon-induced longitudinal cracks affect the embankment stability in permafrost regions, which is a serious concern for the Chinese Qinghai-Tibet Expressway (QTE) to be constructed in the near future. Here, longitudinal cracking on the experimental inclined thermosyphon embankment of the QTE in warm and ice-rich permafrost regions is investigated. The cooling effect of the inclined thermosyphons is found to be concentrated in the embankment center, with uneven ground-temperature fields causing embankment differential deformation. Tensile stress concentration is induced on the embankment top surface, with longitudinal cracks potentially being initiated at the maximum tensile stress point. The temporal and spatial initiation of longitudinal cracks is determined by both the embankment stress state and the asphalt-pavement splitting strength. According to the computation, longitudinal cracking was initiated before May or in October–December in the second year after construction completion, 1.8–2.8
25 March 2018
Experimental investigation on the air-liquid two-phase flow inside a grooved rotating-disk system: Flow pattern maps
Publication date: 25 March 2018
Source:Applied Thermal Engineering, Volume 133 Author(s): Wei Wu, Bingqing Xiao, Jibin Hu, Shihua Yuan, Chenhui Hu An experimental system has been built up for the flow pattern analysis inside an open grooved rotating-disk system. The geometric construction and the governing parameters of the open grooved rotating-disk are presented. The measured results indicate that three different flow patterns appear in the flow field with the change of liquid flow rates and disk gaps. The flow patterns include the stratified flow, the full liquid flow, and the bubble flow. The transition of the air-liquid stratified flow to the full liquid flow is caused by an insufficient flow supply. The dimensionless liquid flow rate and the gap Reynolds number determine the transition boundary between the stratified flow and the full liquid flow. The shear force and the surface tension force of the liquid play a leading role when the full liquid flow transfers to the bubble flow. The Weber number and the gap Reynolds number can be applied in the boundary calculation for the full liquid to bubble flow transition. The two-phase flow pattern maps can be used for identifying the transition from one flow pattern to another inside the grooved rotating-disk system.
25 March 2018
Characterization of the temperature distribution on steel tubes for different operating conditions in a reheating furnace using CFD and three different measuring methods
Publication date: 25 March 2018
Source:Applied Thermal Engineering, Volume 133 Author(s): Martin Landfahrer, Rene Prieler, Bernhard Mayr, Hannes Gerhardter, Thomas Zmek, J
25 March 2018
Numerical heat transfer analysis of Maisotsenko Humid Air Bottoming Cycle – A study towards the optimization of the air-water mixture at bottoming turbine inlet
Publication date: 25 March 2018
Source:Applied Thermal Engineering, Volume 133 Author(s): Rasikh Tariq, Nadeem Ahmed Sheikh Maisotsenko Humid Air Bottoming Cycle (MHABC) is a recently proposed waste heat recovery unit for gas turbine topping cycle. An air saturator is used for the waste heat recovery and air humidification purposes in the bottoming cycle. The humid air is used in bottoming cycle turbine. In this work, detailed heat transfer analysis of the MHABC is proposed along with the evaluation of degree of humidification and energy recovery. The air saturator is numerically simulated after the development of governing ordinary differential equations for the temperature and humidity distribution of the working air. The governing differential equations of air saturator are discretized using first order accurate finite difference scheme and simulated using MATLAB. The results for the air saturator are initially validated using inlet ambient pressure conditions at standard atmospheric conditions. The upper section of the bottoming cycle is modeled using analytical NTU method. The overall performance of the plant with MHABC is also compared with results reported in literature. Temperature and humidity levels for working air is presented. These results show that the proposed MHABC configuration gives maximum work output (58
25 March 2018
Effect of reentrant cavities on the thermal performance of a pulsating heat pipe
Publication date: 25 March 2018
Source:Applied Thermal Engineering, Volume 133 Author(s): Wookyoung Kim, Sung Jin Kim This study is performed to investigate the effect of the size of reentrant cavities on the thermal performance of a micro pulsating heat pipe (MPHP). The flow and thermal characteristics of the MPHPs with each MPHP having a different size of reentrant cavities, along with a MPHP without reentrant cavities are experimentally obtained and compared. Silicon-based MPHPs with and without reentrant-type artificial cavities inside the channels are fabricated using MEMS techniques. The MPHPs have rectangular channels which are engraved on a silicon wafer with a hydraulic diameter of 667
25 March 2018
Optical and thermal analysis of a linear Fresnel reflector operating with thermal oil, molten salt and liquid sodium
Publication date: 25 March 2018
Source:Applied Thermal Engineering, Volume 133 Author(s): Evangelos Bellos, Christos Tzivanidis, Angelos Papadopoulos Linear Fresnel collectors are promising technologies for the exploitation of solar irradiation in medium and high temperatures. In this study, a linear Fresnel collector with flat primary mirrors and a parabolic shape secondary reflector is investigated. The location of the secondary reflector is simply optimized and then the collector is investigated under different incident angles (transversal and longitudinal). The next step is the thermal analysis of the collector with three different working fluids: thermal oil, molten salt and liquid sodium. The analysis is performed for temperatures up to 900
5 March 2018
Recent research contributions concerning use of nanofluids in heat exchangers: A critical review
Publication date: 25 March 2018
Source:Applied Thermal Engineering, Volume 133 Author(s): Mehdi Bahiraei, Reza Rahmani, Ali Yaghoobi, Erfan Khodabandeh, Ramin Mashayekhi, Mohammad Amani Heat exchangers have already proven to be important devices for thermal systems in many industrial fields. In order to improve the efficacy of heat exchangers, nanofluids are recently employed as coolants in them. Regarding unique characteristics of nanofluids, research studies in this area have witnessed a remarkable growth. This paper reviews and summarizes recent investigations conducted on use of nanofluids in heat exchangers including those carried out on plate heat exchangers, double-pipe heat exchangers, shell and tube heat exchangers, and compact heat exchangers. Meanwhile, some fascinating aspects about combination of nanofluids with heat exchangers are introduced. In addition, the challenges and opportunities for future research are presented and discussed.
5 March 2018
Effect of blockage ratio on backlayering length of thermal smoke flow in a longitudinally ventilated tunnel
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Na Meng, Xiaomei Liu, Xiao Li, Beibei Liu Experiments were conducted in a reduced-scale tunnel to investigate the effect of blockage ratio on backlayering length in a longitudinally ventilated tunnel. Model vehicle blockages are placed upstream of the fire source and blockage ratios are ranged in 0.13–0.51. It is found that when there is no blockage in the tunnel, experimental data can be well correlated by Li model. However, when there is blockage upstream of the fire source, the backlayering length is shown to be lower than the predictions of Li model. Tang model fails to collapse the experimental data in the present work due to the difference in blockage ratio. A new expression by considering the factor blockage ratio is proposed to predict the backlayering length of smoke flow, which is shown to well collapse the experimental measurements.
5 March 2018
Application of chemical looping air separation for MILD oxy-combustion: Identifying a suitable operational region
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Shiyi Chen, Jun Hu, Wenguo Xiang In this study, chemical looping air separation (CLAS) is integrated with moderate or intense low-oxygen dilution (MILD) oxy-combustion. CO2-rich flue gas is used as a purging agent for oxygen decoupling in a reduction reactor. This work identifies the suitable operational region of different oxygen carriers for CLAS based on heat balance. The oxygen fraction in air determines the maximum temperature in the oxidization reactor. The maximum oxygen fraction produced for CuO-Cu2O, Co3O4-CoO, Mn2O3-Mn3O4, and MnO2-Mn2O3 are 16.8%, 13.2%, 14.4%, and 12.0%, respectively, with a reduction temperature 10
5 March 2018
Experimental study of two-phase frictional pressure drop of steam-water in helically coiled tubes with small coil diameters at high pressure
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Yao Xiao, Zhenxiao Hu, Shuo Chen, Hanyang Gu The pressure drop characteristics of helical coils are important to the design optimization of helically coiled steam generators. Single-phase and two-phase flow pressure drop characteristics have been experimentally investigated in coiled tubes of inner diameters of 12.5
5 March 2018
Natural convection in a cross-fin heat sink
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Shangsheng Feng, Meng Shi, Hongbin Yan, Shanyouming Sun, Feichen Li, Tian Jian Lu A novel cross-fin heat sink consisting of a series of long fins and a series of perpendicularly arranged short fins was proposed to enhance natural convective heat transfer. The design principle of the cross-fin heat sink was based on overcoming internal thermal fluid-flow defects in a conventional plate-fin heat sink. The thermal performance of the proposed heat sink was compared with a reference plate-fin heat sink in horizontal orientation. A numerical model considering both natural convection and radiation heat transfer was developed to obtain thermal fluid-flow distributions and heat transfer coefficients of both the cross- and plate-fin heat sinks. Corresponding experiments were performed to validate the model predictions. It was demonstrated that, compared to the reference plate-fin heat sink, the cross-fin heat sink enhanced the overall (including natural convection and radiation) and convective (excluding radiation) heat transfer coefficients by 11% and 15%, respectively. Importantly, the enhancement was achieved without increasing the overall volume, material consumption, and too much extra cost. The proposed cross-fin heat sink provides a practical alternative to the widely adopted plate-fin heat sinks.
5 March 2018
An experimental study of frost distribution and growth on finned tube heat exchangers used in air source heat pump units
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Long Zhang, Yiqiang Jiang, Jiankai Dong, Yang Yao, Shiming Deng Many studies have been carried out on frost distribution and growth and their impacts on the performances of finned tube heat exchangers (FTHXs), the most commonly used structure for the outdoor coils of air source heat pump units. However, in almost all the studies, ethylene glycol water solution was used as refrigerant, which made the investigating of frost distribution and growth difficult due to the uneven temperature distribution along the tube length. Furthermore, quantitative experimental data for the frost distribution and growth on FTHXs have been insufficient. Therefore, in this paper, a quantitative experimental study using R410A as refrigerant on frost distribution and growth on two FTHXs with different fin pitches is reported. The study results demonstrated that the frost accumulated on an FTHX could be divided into two parts, one accumulated on the edge of windward fins and the other on the surfaces of fins and tubes. Furthermore, the ratios of the frost mass accumulated on the edge of windward fins to that on the entire FTHX surface were 13.7% (60
5 March 2018
An experimental study of enhanced heat sinks for thermal management using n-eicosane as phase change material
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Adeel Arshad, Hafiz Muhammad Ali, Wei-Mon Yan, Ahmed Kadhim Hussein, Majid Ahmadlouydarab This study experimentally explores the thermal performance enhancement of portable electronics; based on the n-eicosane used as a phase change material (PCM) filled pin-fin heat sinks. A constant heat flux ranging from $0.79 kW / m 2$ to $3.17 kW / m 2$ is applied at the base of heat sink. Comparison was carried out with and without n-eicosane for finned and un-finned heat sinks. Four configurations of pin-fin heat sinks are tested at four different volumetric fractions of n-eicosane including no fin heat sink to quantify the effectiveness of pin-fins for cooling of electronics. Pin-fins of constant volume fraction (9% to the total volume of heat sink) are used as thermal conductivity enhancers (TCEs) within PCM as the PCM has very low thermal conductivity to dissipate heat. TCEs are made of aluminum. Pin-fin heat sinks of fin thickness of $1 mm$, $2 mm$ and $3 mm$, are investigated to examine the effect of fin thickness, amount of n-eicosane and input heat flux for three different critical set point temperatures (SPTs). The findings indicated that inclusion of n-eicosane in pin-fin heat sink had viable performance to keep the temperature of mobile devices in comfortable zone. At lower heat inputs steady state operating conditions, uniform charging of PCM takes longer duration, and more phase duration of latent heat is achieved. Enhancement ratios revealed that $2 mm$ thick pin-fin heat sink had the maximum thermal performance for reliable performance of electronic package.
5 March 2018
Control strategy design for a SOFC-GT hybrid system equipped with anode and cathode recirculation ejectors
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Jinwei Chen, Jingxuan Li, Dengji Zhou, Huisheng Zhang, Shilie Weng The ejectors equipped for anode and cathode recirculation loops are more reliable and low-cost in maintenance than blowers in a solid oxide fuel cell-gas turbine hybrid system. However, an effective control system is one of the technical challenges associated with the development of the hybrid system. In present work, a novel control strategy was designed to restrict the hybrid system equipped with anode and cathode recirculation ejectors to a safe and feasible zone. Six control loops were carried out to control the vital parameters including power, rotation speed, fuel utilization, anode and cathode inlet temperature, and turbine inlet temperature. At the same time, the performance of another control system without anode inlet temperature control loop was also investigated. A comparison results of the two control systems reveal that both anode and cathode inlet temperature loops are necessary. If there is no anode inlet temperature control loop, the system efficiency decreases by 0.18%, the fuel cell inlet temperature differences between anode and cathode increases by 9
5 March 2018
Performance degradation of a proton exchange membrane fuel cell with dead-ended cathode and anode
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Ben Chen, Yonghua Cai, Jun Shen, Zhengkai Tu, Siew Hwa Chan Proton exchange membrane fuel cells with dead-ended cathodes and anodes can simplify the fuel cell system and reduce costs. An experiment was performed to determine the performance degradation characteristics of Proton exchange membrane fuel cells with dead-ended cathodes and anodes. The effects of operating temperature and pressure differences between the cathode and the anode on the purging period were investigated in detail. The performance and cyclic voltammetry before and after the dead-ended operation were analyzed and compared. After the experiment, the membrane electrode assembly was cut to analyze the catalytic layer cross-section membrane morphology by scanning electron microscopy. The results showed that during operation, the fuel cell performance gradually decreases until the setting value, and then quickly recovers when the cathode outlet solenoid valve is triggered during a purging cycle. The dead-ended operating period decreases with an increase in operating temperature but increases with an increase in the pressure difference between the cathode and the anode. Flooding occurs easily in a Proton exchange membrane fuel cell with a dead-ended cathode and anode, causing performance degradation. Moreover, it may cause a decrease in the electrochemical surface area of the catalyst layer. The scanning electron microscopy images showed that both the upper and middle regions of the catalyst layers remained unchanged, whereas the downstream region corroded and become thinner in the dead-ended mode after 60
5 March 2018
Numerical simulation of the sapphire growth process using a self-regulating thermal boundary condition method
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Yurong He, Zhiwei Hua, Meijie Chen, Tianqi Tang, Jiecai Han Sapphire is widely used in many industries, including the military, electronic, and astronautic industries. Therefore, its growth quality is very important for its application. Obtaining a good-quality sapphire crystal requires the investigation of its growth process with a proper thermal boundary condition. The growth process of sapphire crystals with different sizes was numerically studied in the present work. The temperature distribution in crucibles and the thermal boundary conditions of the crucibles, which could guarantee an accurate amount of energy for the sapphire crystal in each growth period, were also determined. The results showed that specific regulation techniques should be adopted at each sapphire growth stage to avoid high temperature gradient and thermal stress. On the other hand, the validity of the theoretical analysis that the solid–liquid interface angle of a high-quality sapphire is distributed among
5 March 2018
Experimental study of heat transfer enhancement for molten salt with transversely grooved tube heat exchanger in laminar-transition-turbulent regimes
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Y.S. Chen, J. Tian, Y. Fu, Z.F. Tang, H.H. Zhu, N.X. Wang In an effort to develop a heat transfer enhancement technique for molten salt in heat exchanger, experiments are carried out to evaluate the heat transfer performance of transversely grooved tube using molten salt as the hot fluid flowing through the inner concentric tube within the Reynolds number from 300 to 60,000 and Prandtl number from 11 to 27. The effects of Reynolds number and Prandtl number on the thermal-hydraulic behavior in laminar, transition and turbulent flow are studied. Results show that transversely grooved tube will significantly enhance the heat transfer performance of molten salt and meanwhile decrease the critical Reynolds numbers of the transition from laminar flow to turbulent flow. For laminar flow and transition flow, heat transfer enhancement ratio relative to the smooth tube varies with the changing of Reynolds number and Prandtl number. While for the turbulent flow, the enhancement effect is almost independent on Reynolds number and Prandtl number. Finally, heat transfer correlations of molten salt in transversely grooved tube are proposed depending upon the flow regime and have good agreement with experiment data. Experimental results will provide valuable reference and greatly contribute to the practical design of molten salt heat exchanger with heat transfer enhancement techniques.
5 March 2018
Ignition of ultra-lean premixed H2/air using multiple hot turbulent jets generated by pre-chamber combustion
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Sayan Biswas, Li Qiao A detailed investigation on the ignition characteristics of ultra-lean premixed H2/air mixtures by multiple hot turbulent jets in a dual combustion chamber system was carried out. Simultaneous high-speed Schlieren and OH
5 March 2018
A simulation model for transient behaviour of heavy-duty gas turbines
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Ali Chaibakhsh, Saeed Amirkhani In this study, an analytical model is developed to characterize the transient behaviour of a heavy-duty gas turbine unit. While deriving models based on mass and energy conservation, the lack of essential variables such as air mass flow rate is a major problem. Constrained nonlinear optimization problems were served to obtain the unknown parameters based on experimental data. The objective functions were defined as the mean square of errors on compressor pressure ratio, compressor outlet temperature, gas fuel flow, the unit thermal efficiency, corrected outlet temperature and the generated power. The accuracy assessment was performed by comparing the responses of the model and the responses of real plant which indicated that the modelling error was less than 0.2 percent. The effect of changes in ambient conditions were also investigated by simulating open-loop model over a certain period of time. The results confirmed the accuracy of the developed model over a wide range of operations.
5 March 2018
Inverse optimization design of an impinging co-axial jet in order to achieve heat flux uniformity over the target object
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Mohamad Ali Bijarchi, Farshad Kowsary In this study, co-axial impinging jet was optimized in order to obtain uniform heat flux over an isothermal heated surface by determining four design variables including geometrical and flow variables. The governing equations were solved using the finite volume method for a laminar, incompressible, and axisymmetric flow. The solution of inverse design problem was achieved by minimizing the root mean square of the difference between the local Nusselt number and the uniform design Nusselt number. A combination of pattern search and gradient-based methods was used for optimization. Also a co-axial jet with a new geometry was presented to improve the objective function and two design variables were added to the four previous variables. Optimization was performed for two jet configurations under 15 different conditions. Heat flux uniformity was obtained by these two jets with acceptable errors less than 2% for the outer jet to the target surface diameter ratios of higher than 0.6. The proposed co-axial jet showed its superiority at the small diameter ratios (0.4 and 0.3) and it reduced the error significantly (about 50%) for design Nusselt numbers of 7 and 10.
5 March 2018
A three-dimensional multi-phase numerical model of DMFC utilizing Eulerian-Eulerian model
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Jing Sun, Guobin Zhang, Ting Guo, Kui Jiao, Xuri Huang A three-dimensional multiphase model of DMFC (direct methanol fuel cell) is developed, in which the Eulerian-Eulerian model is adopted to treat the gas and liquid two-phase flow in channel. Meanwhile, the multiphase flow in porous electrodes is solved with the help of gas and liquid pressure conservation equations to reflect the liquid saturation jump phenomenon at two different porous electrodes (e.g. DL (diffusion layer) and CL (catalyst layer)). The effects of current density, methanol concentration and temperature on gas and liquid two-phase flow in channel and porous electrodes are investigated in detail. It is found that the carbon dioxide in anode channel gradually increases along flow direction and is mainly accumulated at the interface of anode channel and DL. Meanwhile, the carbon dioxide produced in ACL (anode catalyst layer) is likely to accumulate under the inlet region and then increases along flow direction gradually. Moreover, the higher the temperature, the more methanol crossover and the less carbon dioxide produced in DMFC because of the dissolution.
5 March 2018
Hydrogen at the rooftop: Compact CPV-hydrogen system to convert sunlight to hydrogen
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Muhammad Burhan, Muhammad Wakil Shahzad, Kim Choon Ng Despite being highest potential energy source, solar intermittency and low power density make it difficult for solar energy to compete with the conventional power plants. Highly efficient concentrated photovoltaic (CPV) system provides best technology to be paired with the electrolytic hydrogen production, as a sustainable energy source with long term energy storage. However, the conventional gigantic design of CPV system limits its market and application to the open desert fields without any rooftop installation scope, unlike conventional PV. This makes CPV less popular among solar energy customers. This paper discusses the development of compact CPV-Hydrogen system for the rooftop application in the urban region. The in-house built compact CPV system works with hybrid solar tracking of 0.1° accuracy, ensured through proposed double lens collimator based solar tracking sensor. With PEM based electrolyser, the compact CPV-hydrogen system showed 28% CPV efficiency and 18% sunlight to hydrogen (STH) efficiency, for rooftop operation in tropical region of Singapore. For plant designers, the solar to hydrogen production rating of 217
5 March 2018
Visualization research on injection characteristics of high-pressure gas jets for natural gas engine
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Quan Dong, Yue Li, Enzhe Song, Liyun Fan, Chong Yao, Jun Sun High-pressure gas injection processes with various gas nozzle structures under different nozzle pressure ratio (NPR) were investigated experimentally. Schlieren imaging method was used to investigate macroscopic structure of gas jets. Results showed that increasing the gas injection pressure is unable to improve the jet tip penetration obviously. It is because chocking phenomenon limited gas jet velocity at nozzle exit under high gas injection pressure. The empirical formula for high-pressure gas jet tip penetration was investigated based on the experimental data under various NPRs and orifice diameters. It is found that the experimental data are in good agreement with the empirical formula proposed by Hamzehloo and Aleiferis. The increase of gas injection pressure and orifice diameter could not directly improve the air entrainment effect, nor could it increase the average equivalent ratio of gas jet due to the small gas jet kinetic energy and small density difference between gas jet and the surrounding ambient gas.
5 March 2018
Effect of design and operating parameters on the thermal performance of aluminum flat grooved heat pipes
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Hossein Alijani, Barbaros
5 March 2018
Application of IMEP and MBF50 indexes for controlling combustion in dual-fuel reciprocating engine
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Ireneusz Pielecha, Krzysztof Wis
5 March 2018
On the evaporative spray cooling with a self-rewetting fluid: Chasing the heat
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Sung Tsang, Zhi-Hao Wu, Chia-Hsuan Lin, Chen-li Sun In the study, we successfully utilize the self-rewetting fluid to enhance the evaporative cooling of a pulsed spray system by inducing the inverse Marangoni convection. We find that the superhydrophilicity of the surface is essential to promote a continuous surface-tension-driven fluid flow, which helps to replenish the hot region with the working fluid, and prevent dryout from happening. As a result, cooling lasts much longer beyond the discharge and a significant amount of heat can be removed by a single shot of spray. We coin a term ‘heat chasing’ effect to describe the excellent cooling caused by the inverse Marangoni convection. Besides the surface superhydrophilicity, the spray height should be confined to a certain range so that a liquid film is formed. Once the inverse Marangoni convection commences, the total heat transfer can be augmented three to seven times for a given spray amount. Although long spray always results in better heat transfer, enhancement with the inverse Marangoni convection is still present under the condition of the short spray for a surface temperature as high as 255
5 March 2018
Experimental and numerical simulations on heat-water-mechanics interaction mechanism in a freezing soil
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Shuangyang Li, Mingyi Zhang, Wansheng Pei, Yuanming Lai In cold regions, the annual ground freezing is responsible for many distinct and widespread terrain features, such as ice wedges, frost mound and ground ice. In particular, the frost action caused by the soil freezing is a prevailing and heavy damage to engineering structures. The frost heave process of a freezing soil involves complicated coupled heat and water transfers as well as mechanical variation. To explore this multi-physical interaction, first, we built a numerical heat-water-mechanics model based on energy, mass and momentum conservation principles. In this model, several critical important characteristics of the freezing soil are taken into account. Then, we carried out a one-side freezing experiment of silty clay column in an open system with non-pressure water supply. Meanwhile, we used the experiment to simulate the water, temperature and deformation variations of the freezing soil column. The simulated temperatures and displacement well agree with those measured data, which implies the numerical model is valid and can describe the heat-water-mechanics process in the freezing soil. Finally, the heat-water-mechanics interaction mechanism of the freezing soil is explained and analyzed by combining the experimental investigation and numerical simulation. This study is helpful to better understand the interaction between water, temperature, deformation and the frost heave mechanism of the freezing soil. Furthermore, the model and results in the study can serve as references for further investigation, too.
5 March 2018
Robust thermal and electrical management of smart home using information gap decision theory
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Afshin Najafi-Ghalelou, Sayyad Nojavan, Kazem Zare After restructuring in the electricity industry, some concepts such as smart home and renewable energy sources improved extensively. This paper proposes information gap decision theory (IGDT) technique for robust energy management of smart home in summer season in the presence of market price fluctuation. Therefore, the proposed model is practical in a realistic model. The IGDT method contains the robustness and opportunity functions. The harmful aspect of price uncertainty is modeled by robustness function and the beneficial aspect of price uncertainty is modeled by opportunity function. The proposed IGDT-based performance optimization problem of low-energy smart home is formulated as mixed-integer non-linear programming (MINLP) and solved by General Algebraic Modeling System (GAMS) optimization software. Two scenarios as normal and smart scenarios are used to investigate the proposed model.
5 March 2018
The heat transfer characteristic of shell-side film flow in spiral wound heat exchanger under rolling working conditions
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Yan Ren, Weihua Cai, Jie Chen, Laiyun Lu, Jiansheng Wang, Yiqiang Jiang In order to explore the shell-side heat transfer characteristic for spiral wound heat exchanger (SWHE) in floating liquefied natural gas (FLNG) field, a model was established to simulate the heat transfer of shell-side film flow in real working conditions. The influence of rolling parameters and working parameters on shell-side heat transfer characteristic was investigated. For ethane, the results showed that the numerical model satisfies the accuracy requirement. In general, under static working conditions, the heat transfer coefficient increases with the increase of mass flux and the decrease of working pressure, but heat flux has little influence on it. These simulation results were consistent with experimental data and calculation results by correlations. And the heat transfer coefficient shows obvious periodicity under rolling working conditions. The rolling movement can enhance the heat transfer of shell-side film flow, and the influence of different parameters on heat transfer is different. These results will provide some instructions in the design and safe operation for SWHE in FLNG.
5 March 2018
Aerodynamic design and numerical analysis of a radial inflow turbine for the supercritical carbon dioxide Brayton cycle
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Aozheng Zhou, Jian Song, Xuesong Li, Xiaodong Ren, Chunwei Gu The supercritical carbon dioxide (S-CO2) Brayton cycle is considered to be one of the most promising power cycles for the future. Its main advantages include compactness, high efficiency, high safety and good environmental friendliness. The system performance depends much on the turbine, which is one of the core components of the S-CO2 Brayton cycle. Compared to the axial turbine, the radial inflow turbine has a lower cost and more compact structure, and can provide a high operating efficiency under small volume flows. In this study, a design method for an S-CO2 radial inflow turbine is proposed and a 1.5-MW S-CO2 radial inflow turbine is designed. The three-dimensional (3D) numerical simulation of the designed turbine is carried out by using ANSYS-CFX commercial software, and the results are in good agreement with the design values. The off-design performance of the turbine is predicted by using the one-dimensional (1D) model and the 3D numerical simulation. The results are consistent with each other. It means that the proposed design method for the S-CO2 radial inflow turbine is reliable.
5 March 2018
Novel scheme for a PCM-based cold energy storage system. Design, modelling, and simulation
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Guillermo Bejarano, Jos
5 March 2018
A novel energy efficient LNG/NGL recovery process using absorption and mixed refrigerant refrigeration cycles – Economic and exergy analyses
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Bahram Ghorbani, Reza Shirmohammadi, Mehdi Mehrpooya A novel integrated process comprising natural gas liquids recovery along with natural gas liquefaction is investigated. Processes integration and design at the same time can reduce the number of required equipment and energy consumption in the units. Utilizing absorption refrigeration system in lieu of precooling stage of mixed fluid cascade refrigeration system in an energy efficient LNG-NGL recovery process with the main aim of reduction in required energy is investigated. High amount of energy consumption in these units is reduced due to the removal of a stage of the compression system, while the possibility of using waste thermal energy can be provided using absorption refrigeration system. The results of exergy analysis illustrate that the highest amount of exergy destruction is occurred in the air coolers before and after installation of the absorption refrigeration cycle at a rate of 56.21% and 42.72%, respectively. Sensitivity analysis has been carried out for economic parameters with respect to the utilities price as well as effect of products price on the market with respect to the presented structures.
5 March 2018
Analysis and experimental verification of weight saving with trapezoidal base heat sink
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Hong-Long Chen, Chi-Chuan Wang A quick weight saving methodology with trapezoidal base heat sink applicable for electronic cooling application is studied analytically, numerically, and experimentally. The conventional heat sink with rectangular base can be modified into trapezoidal base for material saving. A differential equation capable of describing the temperature distribution of the trapezoidal base is derived and its closed-form analytic expression is derived. It is found that three parameters rA (ratio of effective surface area to the base area), rd (ratio of chip lateral length to the base length) and h+ (modified convection heat transfer coefficient) play pivotal roles in balancing the material saving and the performance loss. When rd
5 March 2018
Simulation studies on simultaneous power, cooling and purified water production using vapour absorption refrigeration system
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): G. Praveen Kumar, R. Saravanan, Alberto Coronas
5 March 2018
Numerical analysis for attenuation effects of perforated plates on thermoacoustic instability in the multiple flame combustor
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Minjun Kwon, Seungtaek Oh, Yongmo Kim In the present study, the FDF-based approach together with the Helmholtz solver has been applied to precisely analyze the attenuation effects of the perforated plates on thermoacoustic instability in the lab-scale multiple flame combustor. In order to effectively suppress the combustion instability, we derive the optimal damping conditions for perforated plates in terms of the porosity and cavity length. To overcome the weaknesses of the Howe model, the Luong model is utilized for an impedance boundary condition of perforated plates. After then, we validated our methodology to the impedance tube, which shows the predicted results are well agreed with the experimental data for all validation cases Another new approach for the dual perforated plates has been proposed to enlarge the absorption bandwidth in a wider frequency regime. Numerical results clearly indicate that since the dual plates are tuned at two different target frequencies, the system can have two maximum absorption points and their combined effects in a frequency range. This makes the dual-plate method capable of stabilizing the combustion instability in the much wider frequency range than does the single-plate scheme. Therefore, it is expected that the dual-plate methodology would be more effective to suppress the unexpected nonlinear behavior such as the mode change, frequency shift, and hysteresis thanks to the wide attenuation coverage.
5 March 2018
Phase-change materials (PCM) for automotive applications: A review
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Joris Jaguemont, Noshin Omar, Peter Van den Bossche, Joeri Mierlo In this paper, an extensive review of a battery thermal management systems (BTMSs) such as phase-change materials (PCMs) in the state of art is proposed. Nowadays, PCMs are particularly attractive and chosen as one of the most interesting cooling system in terms of high-energy storage density. In addition, they are less bulky, complex and expensive than traditional cooling methods such as forced-air cooling or liquid cooling. Nonetheless, the integration of PCMs in a battery application calls for an analysis that will enable the researcher to proposed optimized BTMSs. Indeed, due to the lack of literature in this domain, the paper proposed to review all the existing studies on battery applications involving PCMs. Numerical analysis description, heat transfer theory along with the classification of the existing components for PCMs are also presented. This paper is based on previous reviews to help to update the thin number of references, which is considered by the authors as the major contribution.
5 March 2018
An optimal matching strategy for screw compressor for heat pump applications
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Yu Wang, Zhiwei Wang, Mingzhu Li, Tingting Chen, Zhanwei Wang An optimal matching strategy for screw compressor for heat pump (HP) applications was proposed in this study. The strategy focuses on the optimal matching between the built-in volume ratio (BVR) of screw compressors and the annual cooling and heating load demands. A performance index, the annual integrated coefficient of performance under actual operating conditions ($ACOP A$), was introduced to represent the actual operational energy efficiency of the HP unit. The optimization mathematical model and generic framework of the optimal matching strategy were developed. The proposed strategy was applied to a ground-source HP unit to assess its performance. The results show that the optimal matching strategy improved the $ACOP A$ by 6% at most, compared to the conventional matching method on BVR.
5 March 2018
Dynamic modelling and optimal sizing of industrial fire-tube boilers for various demand profiles
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Marco Tognoli, Behzad Najafi, Fabio Rinaldi In the present paper, a detailed dynamic model of an industrial fire-tube boiler is first developed and five different geometrical configurations, each of which corresponds to a boiler model, are considered. Next, a PID controller is implemented and tuned for each configuration aiming at controlling the steam pressure, while addressing a demand with a variable flow rate. The operation of the developed boiler models, while providing four different steam demand profiles, are next simulated. The resulting cumulative average efficiency along with the cumulative pressure deviations and minimum and maximum pressure levels, which are achieved in each simulation, are then determined. The obtained results provide practical information regarding the trade-off between the size of the boiler and its corresponding performance and controllability. As an instance, the obtained results demonstrated that utilizing a boiler with the heat transfer surface of 36.76
5 March 2018
Advanced exergoeconomic evaluation of a new cryogenic helium recovery process from natural gas based on the flash separation – APCI modified process
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Hojat Ansarinasab, Mehdi Mehrpooya, Mohammadhosein Pouriman An advanced method of exergoeconomic analysis was applied to a newly developed process configuration used for recovering helium from natural gas. In this process, a three stage propane refrigeration cycle is incorporated to provide a portion of the required refrigeration. Sensitivity analysis was also carried out for exergoeconomic factors and exergy destruction cost of the effective devices. In comparison with the existing processes, the proposed process has better performance in extracting the helium from the feed gas. Based on the results of conventional method, HE-105 and HE-104 heat exchangers have the highest extent of exergy destruction cost equal to 1889.68
5 March 2018
Slot air jet impingement cooling over a heated circular cylinder with and without a flow confinement
Publication date: 5 March 2018
Source:Applied Thermal Engineering, Volume 132 Author(s): Sharad Pachpute, B. Premachandran In this work, a numerical investigation has been carried on an air slot jet impingement over a circular cylinder with and without a top confinement using the