查看更多>>摘要：The present article discusses the impact of liquid coolant subcooling on multiphase fluid flow and boiling heat transfer in porous media with internal heat generation. Although extremely relevant and important, only limited studies are available in the open literature on the effects of coolant subcooling in heat-generating porous media and hence, this requires a detailed analysis. The present analysis is carried out using a validated computational model of multiphase fluid flow through clear fluid and porous media considering the relevant fluid transport, heat transfer and mass transfer phenomena. Results suggest that the qualitative nature of boiling heat transfer from the heat-generating porous body, with subcooled coolants, remain similar to that observed with a saturated coolant. Quantitative differences are, however, observed as a result of solid-liquid convective heat transfer, and competing mechanisms of boiling and condensation heat transfer, when subcooled liquid coolant is present. It is observed that a substantially larger heating power density is required - as coolant subcooling is increased - for achieving the same temperature rise in the porous body. Dryout power density at different coolant subcooling is also observed to follow a similar trend. The thermal energy removal limit is, hence, observed to be substantially enhanced in presence of subcooled coolants. Further, the dryout region within the porous body is observed to gradually shift towards its interior as the coolant subcooling is increased.
查看更多>>摘要：In this work the influence of surface deposits, namely rust and scale, on pitting corrosion of the AISI 316 steel was investigated. The rust from the mild steel corrosion in NaCl aqueous solution was deposited on the stainless steel surface. The scale carbonate layer was formed using electrochemical scaling technique. Potentiodynamic polarization was used to evaluate the pitting potential of the steel covered with rust or scale deposits. It was established that iron corrosion products can accumulate chloride ions, but the local concentration of the latter appeared to be insufficient to reduce the resistance of AISI 316 steel to pitting in solutions with NaCl concentration up to 2.8 g/L. The scale layer while being able to reduce the oxygen supply to the surface 10 times does not affect pitting resistance of the steel in 35 g/L NaCl solution either. The acidic media inside the pits was found to be responsible for the dissolution of the calcium carbonate over and around the pits. Pitting resistance depends only on the chloride content in water and neither rust nor scale deposition influence pitting corrosion of AISI 316 stainless steel.
查看更多>>摘要：This paper aims to evaluate the accuracy and efficiency of different numerical simulation approaches on cooling performance for the angled effusion cooling holes applied in a micro gas turbine (MGT) combustor liner. The geometric structure processing methods of a 3-D multi-perforated plate are performed for conjugate heat transfer (CHT) and adiabatic models. Numerical approaches are verified by experimental data in terms of centerline film cooling effectiveness. The wall cooling film effectiveness, film thickness and discharge coefficient of the multiperforated plate are studied and discussed under the condition of whether there is solid heat conduction. Results show that the adiabatic model cannot predict the veritable wall cooling effectiveness distribution on the inner wall surface and overestimates the discharge coefficient by nearly 16.5%. However, the accuracy of the adiabatic model in predicting the near wall flow field structure is not lower than that of the CHT model. Both of the two model can predict a film thickness of 4.1 mm at the same sampling position. Further studies indicate that the increases of flow direction beta have a significant impact on the improvement of wall cooling effectiveness distribution in the spanwise direction. The Ux magnitude predicated by adiabatic model is increasingly close to that of CHT model. The predication results also illustrate a relatively fixed difference of 0.1 between these two models.
查看更多>>摘要：In this paper, equations are proposed that can predict the change over time of the amount of heat stored in a semi-infinite phase-change material (PCM) that has a broad phase-change-temperature range and apparent specific heat that can be approximated by a Gaussian distribution. The proposed equations can be applied under the condition that the initial temperature distribution is uniform below T-c (;)- 3 sigma and the surface temperature is maintained warmer than T-c + 3 sigma. Here, T-c is the central temperature of the apparent specific heat when the apparent specific heat is approximated by a Gaussian distribution and sigma is the standard deviation. The change over time of the amount of sensible heat in the semi-infinite PCM is approximately expressed using equations obtained by integrating the temperature distributions. In addition, the distribution of the latent heat is approximated from the temperature distribution, and the change over time of the amount of latent heat in the semi-infinite PCM is derived by integrating the distribution of the latent heat. Therefore, the change over time of the total amount of heat in a semi-infinite PCM is expressed as the sum of the change over time of the amounts of sensible heat and latent heat in the semi-infinite PCM.
Seyyedi, Seyyed MasoudHashemi-Tilehnoee, M.Sharifpur, M.
14页
查看更多>>摘要：One of the most important methods for hydrogen production is proton exchange membrane electrolysis because of its low environmental impact and easy maintenance. In the present work, a proton exchange membrane electrolyzer system for hydrogen production is established where the required power is generated by a steam Rankine cycle. Solar energy is used for producing steam using parabolic trough solar collectors. The effect of active parameters such as inlet temperature and pressure of steam turbine, efficiencies of turbine and pump, the mass flow rate and outlet temperature of parabolic trough solar collectors, the number of solar collectors in rows, the electric current density, and proton exchange membrane temperature are investigated on the amount of hydrogen production, the net produced power, the cost of produced electricity, the produced hydrogen cost and net profit of the products. The results discovered that the average cost of electricity and the levelized cost of hydrogen per kg H-2 decrease by increasing the steam turbine's inlet pressure and temperature. The cost of hydrogen is almost 6 $/kg at 8 MPa inlet pressure of a steam turbine. The profit increases with increasing the values of mass flow rate while the average cost of electricity and the levelized cost of hydrogen per kilogram of H-2 decrease when mass flow rate increases. The value of profit increases 43.1% when the outlet temperature of oil in the receiver increases from 313 degrees C to 333 degrees C.
查看更多>>摘要：A current common topic of study among scientists and engineers is how to reduce energy usage. As the loading power of engineering devices is constantly upgrading, while they are becoming more and more compacted according to the market demand and in terms of less material consumption, thermal management is getting more complicated. Accordingly, three techniques are proposed to enhance heat transfer including passive, active, and compound (combination of passive and active) methods. Active methods enjoy external power sources, while passive methods mostly rely on modification of heat exchange surfaces without the need for any auxiliary tools. In the current paper, an extensive literature review is conducted for three widely used passive techniques including porous media, nanofluids, and microorganisms. Based on studies reviewed here, although hybrid (combination of more than one heat transfer enhancement method) passive methods could accelerate the rate of heat transfer, their productivity depends on whether the heat transfer enhancement acquired compensates the further induced pressure drops or not. Also, although an inconsistency was observed among published articles about the role of microorganisms' presence in heat transfer intensification of nanofluid flow inside the porous medium, the overwhelming majority of studies proved the contributing role of microorganisms on heat transfer enhancement. There is a great deal of innovative thinking incorporated throughout this review article regarding future studies, and it concludes with key questions for further investigations.
查看更多>>摘要：Batteries can experience overcharging due to inconsistencies of the battery properties or failure of the battery management system which accelerates battery degradation. Overcharging is more likely at low temperatures because the charging cut-off voltage is more easily exceeded due to the larger polarization effect. This study experimentally investigates the characteristics of LiFePO4 battery degradation caused by overcharging to 4.0-4.8 V with 0.2-1 C currents at-10 degrees C. The results show that capacity fading increases with increasing charging current. However, the capacity fading first increases and then decreases with increasing overcharging voltage and may be alleviated at higher voltages. Differential voltage curves show that the loss of lithium battery inventory is the main battery degradation mode. The active material loss occurs on the negative electrode, but not on the positive one.
查看更多>>摘要：The design and operating parameters of a single media single tank (SMT) energy storage system affect the thermal stratification of the fluid. The objective of the present work is to propose a design configuration of an SMT to reduce the thermocline zone. To that end, experiments were performed to investigate the influence of the flow distributor, the fluid inlet, and outlet configuration on the thermal stratification. Experiments were also carried out to understand the scalability of the system. Results obtained from experiments performed for a range of Pe ' clet numbers are analyzed using three performance parameters: the non-dimensional thermocline span 'S', mixing number Mix, and stratification number Str. The study shows that these parameters are scale-invariant. The result also shows that the use of a central flow distributor reduces the thermal gradient zone by 50% to 60% as compared to that achieved in a tank without the flow distributor operated with Pe ' clet numbers between 262 and 945.
Abdullah, Abdullah A.Attulla, Faris S.Ahmed, Omer K.Algburi, Sameer...
9页
查看更多>>摘要：The Photovoltaic Trombe wall (PV/TW) is one of the systems that integrate PV modules with the walls of buildings to obtain a multi-purpose solar system. The objective of the current article is to study the influence of the cooling method of the PV module on the performance of the PV/TW system. Four operating cases of PV module cooling were tested: without cooling, air cooling, water cooling, and combined air and water cooling. Two experimental systems were built to investigate and demonstrate the actual effect of the cooling method on the performance of the PV/TW. The highest daily thermal efficiency was 39.81% for the system that uses water only for cooling. While the highest daily electrical efficiency was about 11.69% for the system that uses air and water together to cool the PV module. The overall efficiency was the highest for the water-cooled model only, and it recorded a daily efficiency rate of 51.40%. Finally, the results showed that cooling the module by placing a heat exchanger behind the PV module in the PV/TW system was more effective than other similar systems.
Gholinia, M.Ranjbar, A. A.Hadi, M.Pourfallah, M....
12页
查看更多>>摘要：In this research, the transient state of a solar power plant with a parabolic receiver in several parts of Iran (6 cities) with the effect of adding a latent heat storage system is investigated. For this purpose, first, the performance of the solar power plant will be evaluated by TRNSYS simulation software and then a latent heat storage system will be added to it. Accordingly, the three types of phase change materials (PCMs) including H250, NaNO3 and KNO3 were investigated. The results show that the performance of the latent heat storage system is highly dependent on the type of phase change material (PCM) and its type should be selected according to the power plant conditions. The addition of a solar heat storage system reduced the amount of heat required in the boiler overnight at the plant. The latent heat storage system performed best by selecting NaNO3 as the phase change agent (PCM). In addition, the effect of different climates studied in six cities of Mashhad, Tabriz, Shiraz, Kerman, Zahedan and Tehran shows that Zahedan has a more suitable location than other cities and solar fraction and power plant efficiency are higher in this city. The annual solar fraction in this power plant was about 68.9%. Further, it was determined that by using the north-south tracking system, more energy can be absorbed in the collectors and using this system will reduce the angle of impact on the collector.
NSTL
Elsevier