查看更多>>摘要：To improve the thermal performance of the lithium-ion battery at a high ambient temperature of 40 degrees C and high discharge rate of 5C， a hybrid cooling system composed of composite phase change material (RT44HC/expanded graphite) and counterflow liquid cooling is designed for a battery module with 25 cylindrical batteries。 A numerical study is carried out to investigate the influences on the maximum temperature and temperature uniformity of the battery module by different parameters， such as composite phase change material thicknesses， coolant flow directions， expanded graphite mass fractions， coolant velocities and coolant temperatures。 The results show that the mass fraction of expanded graphite has an optimal value of 12% in this work， corresponding to the limitations of maximum temperature and temperature difference by 45。25 degrees C and 3。49 degrees C， respectively。 In addition， compared with the parallel flow direction， the counterflow flow direction scheme possesses better thermal performance。 Increasing the coolant velocity can reduce the maximum temperature to a certain extent， but the reduction trend levels off accompanied with a large pressure drop， so a low velocity balancing between the performance and power consumption is preferred。 Furthermore， the lower coolant temperature will increase the temperature difference。 Therefore， a high inlet temperature should be preferred as close to the ambient temperature。 The present hybrid cooling configuration can handle rapid discharging of 5C even under a high ambient environment， which shows outstanding thermal performance and effectively improves the thermal safety of batteries。
查看更多>>摘要：Heat transfer enhancement is an important way to improve the economy of space nuclear power systems。 A three-dimensional cooling channel model without a gap is established。 Numerical simulation of single cooling channel was employed by Fluent。 The impact of parameters such as the type of coolant， Reynolds number (Re)， and axial linear power density on the performance of the heat transfer of the space core were examined。 The results show that， under the same working condition， the thermal property of carbon dioxide is the best。 With the increase of Re， the outlet temperature of the core decreases and the cooling effect becomes worse。 The axial linear power density has a little effect on the heat transfer performance。 Therefore， in a certain temperature range， the core size can be minimized by decreasing the axial linear power density。
查看更多>>摘要：The 5th generation communication technology dramatically increases the cooling demands of data center servers， and the thermal management strategies should possess the crucial characteristics of relatively compact structure， high cooling efficiency， and reliable operation as well as energy saving。 In general， cooling electronics effectively could significantly drive the efficient power utilization for the electronic devices。 As an efficient heat dissipation solution， liquid immersion cooling is a potential and prominent candidate to cool high-power-density electronics by submerging them into a pool of dielectric liquid。 In this paper， a two-phase liquid immersion cooling strategy using vapor chamber heat spreader was developed and investigated to tackle the continuously increasing demands in heat dissipation of data center servers。 In order to promote the circulation of the working liquid and improve the heat transfer performance， gradient capillary wicking structures were innovatively employed in the vapor chamber。 Systematic experimental investigations were conducted to fully study the thermal performance of the vapor chamber。 The results indicated that the vapor chamber could effectively transport 500 W heat load with the heat source temperature below 85 degrees C， and could cope with a maximum heat load up to 900 W without dry-out， at which a vapor chamber thermal resistance of 0。046 degrees C/W was attained。 Additionally， compared to other advanced cooling methods reported in literatures， the proposed two-phase liquid immersion cooling strategy using the vapor chamber exhibited a higher heat transfer performance， providing a promising means for high-power data center servers cooling。
查看更多>>摘要：A novel dual-cylinder rotary compressor was designed to improve the indoor space utilization， and it was used to drive a parallel-loop exhaust air heat pump (PEAHP) which integrates the functions of heating， cooling， ventilation and heat recovery。 The operation characteristics of the system in different compressor frequencies and different fresh-air-to-return-air ratios (FRRs) were studied and analyzed experimentally。 Through the simulation of the ultra-low energy buildings (ULEBs) in 12 cold zone cities， the hourly (8760 h) building thermal loads in the whole year are calculated。 On the basis of the matching of the hourly system working characteristics and the thermal loads of ULEB， the energy efficient working strategy is proposed。 Finally， the applicability and energy consumption of the PEAHP system applying in ULEBs were analyzed。 The results show that， the system heating/ cooling capacity and COP can be considerably improved by increasing return air volume flow rate。 In winter， under the working condition of 50 Hz-FRR 1:1， the peak heating capacity and COP are 8。94 kW and 9。63， respectively， which are 77。38% and 64。05% higher than those when FRR is 1:0。 In summer， when the outdoor temperature ranges from 26 ?to 40 ?， the system temperature effectiveness is higher than 1 in all working modes。 The PEAHP system has great applicability for ULEBs in cold zone of China during winter， and the system can meet the year-round use demands of the ULEBs in Taiyuan， Dalian， Lanzhou， Yinchuan and Lhasa， with the unsatisfied heating/cooling time ratio of 1。61%， 0。09%， 0。006%， 2。45% and 0。02%， respectively。
查看更多>>摘要：The falling film evaporators are a class of heat exchanger that is widely studied。 The research for improving the efficiency is still of prime importance because of its widespread applications in many industries such as desalination， food processing， nuclear energy， refrigeration etc。 Our motive in this work is to investigate the potential use of heat and mass transfer enhanced surfaces for horizontal tube falling film evaporator to scale up its effectiveness。 Four different tube surfaces viz。 bare copper tube， Al2O3 thermal spray coated tube， Al2O3+ TiO2 thermal spray coated tube and open cell copper metal foam wrapped tube were taken for the study。 Scanning electron microscope， 3D surface profilometer， contact angle metre and energy dispersive X-ray spectroscopy were utilized to study the surface texture， surface roughness， wettability and composition， respectively。 Out of these four surfaces， a total of eight configurations were realized by varying the coating thickness， surface roughness and porosity。 A new prototype of horizontal tube falling film evaporator was designed and fabricated with fully wetted flow。 An in house developed novel method based on laser interferometry was utilized for the experimental investigation。 This non-invasive technique was capable of measuring falling film thickness and falling film interface temperature simultaneously with unprecedented circumferential span。 For the film thickness evaluation， an optical shadow method incorporating Otsu's algorithm with precise interface tracking features was used。 Mach-Zehnder Interferometer was employed to visualize the isotherm formation and to quantitatively infer the interface temperature。 A 2D CFD study based on VOF model was carried out and found to be in good agreement with experimental as well as theoretical results。 Further， the effect of flow rate， feed inlet water and body temperature were explored in detail and analysed statistically。
查看更多>>摘要：In the broader discussion regarding the so-called decarbonisation pathway， the deployment of solar-assisted heat pumps is widely accepted as a preferential strategy to be pursued in the residential sector。 In this respect， hybrid photovoltaic-thermal (PVT) technology is very interesting， since it allows designing innovative and economical viable solar-assisted heat pumps。 The present paper contributes to the present-day discussion by proposing a novel solar-assisted multifunctional heat pump。 The proposed system is designed to satisfy a single-family household's heating/cooling/domestic hot water (DHW) requirement。 In particular， the proposed system rep-resents an advance on studies conducted in previous years and is based on the integration of innovative PVT collectors (specifically designed for the present application)， storage tanks (to decouple the "supply-side " and the "demand-side ") and a customized multisource heat pump。 The results of the 8-months field monitoring are presented and discussed， demonstrating that the proposed system allows enhancing the electrical and thermal efficiency of PVT collectors， maximising the heat pump's seasonal performance， and reducing the electricity exchange with the grid。 In conclusion， the proposed system represents a practical response to the need to achieve the total decarbonisation of the residential sector。
查看更多>>摘要：Flow boiling has become a reliable mode of compensating with larger power densities and greater functions of devices because it is able to utilize both the latent and sensible heat contained within a specified coolant。 There are currently very few available tools proven reliable when predicting heat transfer coefficients during flow boiling in mini/micro-channels。 The most popular methods rely on semi-empirical correlations derived from experimental data。 These correlations can only be applied to a very narrow subset of testing conditions。 This study uses a number of data science methods and techniques to accurately predict the heat transfer coefficient during flow boiling in mini/micro-channels on a database consisting of 16，953 observations collected across 50 experiments using 12 working fluids。 Exploratory data science is used to obtain confidence in the data and investigate relationships between feature variables before employing machine learning algorithms。 Missing data is imputed using random forest nonparametric imputation。 A variety of feature analysis techniques are employed to combine and select different optimal feature variables as input values such as principal component analysis to reduce the overall dimensionality of the dataset and the Boruta package， recursive feature elimination， Least Absolute Shrinkage and Selection Operator (LASSO) regression， and stepwise selection to reduce the number of original variables used when modeling while preserving as much information as possible。 A variety of models including linear modeling， generalized additive modeling， random forests， support vector machines， and neural networks are used to predict the heat transfer coefficient and compare the results with existing universal correlations。 The support vector machine model performed best， with a Mean Absolute Percentage Error (MAPE) of 11。3%。 The heat flux， vapor-only Froude number， and quality proved to be especially significant contributing variables across 90% of over 110 different models。 Machine learning proved to be an extremely useful tool when predicting the heat transfer coefficient across a variety of different fluids but did struggle to predict extremely high outlier data where water was the working fluid。
查看更多>>摘要：The radiant syngas cooler (RSC) is a crucial equipment for recovering the sensible heat of high-temperature syngas produced by coal gasification。 Most of the previous studies on RSC focused on the flow field and heat transfer， ignoring the chemical reactions in RSC。 In this work， a three-dimensional RSC model is established to investigate the effects of homogeneous reactions on the composition distributions of syngas in RSC。 The simu-lation results show that the composition distributions of syngas are similar to the temperature distribution of RSC。 From the inlet to the outlet of RSC， the mole fraction of CO decreases by 2。81%， and the mole fraction of H-2， CO2 and CH4 increases by 3。44%， 8。08% and 182。09%， respectively。 The relationship between temperature and the mole fraction of CH4 is concluded， which can be used as an indirect method to predict the temperature of RSC。 The homogeneous reaction in RSC is dominated by water-gas shift reaction (WGSR)。 There are backward WGSR and forward methane-steam reforming reaction (MSR) in the inlet area， which is contrary to the situation in the outlet area。 Moreover， the composition distributions of syngas present a polarized distribution under the influence of operating pressure or operating load， because the homogeneous reactions in the inlet and outlet area of RSC are affected by syngas velocity and temperature， respectively。
Ortega, Manuel G.Satue, Manuel G.Arahal, Manuel R.Acedo, Luis F....
14页
查看更多>>摘要：Economic model predictive control has been proposed as a means for solving the unit loading and unit allocation problem in multi-chiller cooling plants。 The adjective economic stems from the use of financial cost due to electricity consumption in a time horizon， such is the loss function minimized at each sampling period。 The energetic approach is rarely encountered。 This article presents for the first time a comparison between the energetic optimization objective and the economic one。 The comparison is made on a cooling plant using air-cooled water chillers and a cold storage system。 Models developed have been integrated into Simscape， and non-convex mixed optimization methods used to achieve optimal control trajectories for both energetic and economic goals considered separately。 The results over several scenarios， and in different seasons， support the consideration of the energetic approach despite the current prevalence of the economic one。 The results are dependent on the electric season and the available tariffs。 In particular， for the high electric season and considering a representative tariff， the results show that an increment of about 2。15% in energy consumption takes place when using the economic approach instead of the energetic one。 On the other hand， a reduction in cost of 2。94% is achieved。
查看更多>>摘要：Supercritical CO2 is a promising working fluid for next generation power conversion systems。 The key component in a supercritical CO2 power generation system is turbomachinery， which particularly includes the compressor。 Supercritical CO2 has high density and low compressibility， similar to the liquid state near the critical point。 Therefore， when the compressor is operated near the critical point of CO2， significant reduction of compression work can be attained， as compared to conventional air Brayton cycles。 However， there are technical challenges concerning the design and operation of the compressor。 Therefore， in this experimental study， a 150-kW-class supercritical CO2 centrifugal compressor for a 500-kW power generation system is designed and investigated。 The design point of compressor， pressure ratio， and efficiency， are 1。75， and 80% at rotational speed 36000 RPM。 The purpose of this test is to evaluate the performance of the supercritical CO2 centrifugal compressor and obtain accessible fundamental data。 During the performance test， which is conducted by controlling the rotational speed of the impeller and the opening rate of the control valve， the compressor is operated by an electric motor， and the generated pressure from the compressor is consumed using a control valve。 Repeated tests are conducted on the compressor to confirm the practicality of the designed compressor for the supercritical CO2 power generation system。 The compressor achieves a higher efficiency of 80% than the target efficiency during the repeated four tests。 In addition， the reliability of the compressor performance is examined。 Furthermore， the results of the test are analyzed to understand the effects of the opening rate of the control valve for load changing and the rotational speed of the impeller。
NSTL
Elsevier