查看更多>>摘要：Aiming at the problems of large temperature gradient of traditional parallel channel and high pressure loss of tree fractal channel， a novel stepped liquid cooling plate combining the above two structures was proposed in this paper。 Firstly， based on the liquid cooling plate experimental platform， the reliability of computational fluid dynamics method was verified by experiments。 Secondly， based on computational fluid dynamics and orthogonal test methods， the effects of the arrangement form of cooling channels， the number of inlets and outlets and structural parameters (number of channels， longitudinal length， width， thickness and width of inlets and outlets) were analyzed。 In comparison with the original model， the average temperature and pressure drop were reduced by 1。17 °C and 22。14 Pa， respectively。 Finally， in order to further improve the heat dissipation effect of the system， a new hybrid liquid cooling plates formed by filling the liquid cooling plate with composite phase change material were proposed。 The results indicated that the cooling performance of the hybrid liquid cooling plate filling with more phase change material was better， meanwhile， the average temperature and pressure drop were reduced by 2。46 °C and 22。14 Pa， respectively， compared with the original model。 In addition， the effect of inlet mass flow was discussed。 The results revealed that the cooling performance of hybrid liquid cooling plate was better at lower mass flow rate， while the cooling performance of the liquid cooling plate was better at higher mass flow rate。
查看更多>>摘要：To cope with the inherent problem when intermittent renewable energies of solar and wind are connected to the grid， a novel isobaric adiabatic compressed humid air energy storage system was proposed and investigated。 This system adopts a single stage dual-usage compressor-expander with synchronous rotating multi-cylinder to replace two separate multi-stage turbine type machines。 The temperature of the compressed air is controlled by water spray before compression。 The shared equipment with road-return stratagem of thermal oil energy storage/release system is employed。 A hydro-assisted isobaric adiabatic compressed air storage system is formed with an underground cavern such as abandoned coal mine as the lower reservoir and a surface reservoir as the upper reservoir， and the nylon cloth pipe system is arranged in the underground cavern to store compressed air around water。 By establishing the thermodynamic model of the system， the influences of the outlet pressure and temperature of compression on the system performance were analyzed determined respectively by the depth of the underground cavern and the working temperature of the thermal oil of the energy storage system。 The results show that the round-trip efficiency varies slightly with the compression outlet pressure。 Under the conditions of compression outlet parameters of 10 MPa/320 °C and the isentropic efficiencies in compression and expansion are 85%， the round-trip efficiency reaches 66。6% and the theoretical energy storage density is 16。5 kWh·m?3。
查看更多>>摘要：The trilateral cycle (TLC) has been viewed as a promising technology for low grade heat to power conversion， while its application in reality is greatly limited by the low efficiency of two-phase expander and high volume flow rate at the expander outlet。 This paper suggests a novel thermosyphon based trilateral cycle (TTLC)， which uses hydraulic turbine for power generation instead of two-phase expander， avoiding problems in traditional TLC systems and also providing a chance for utilization of pump-as-turbine (PAT) technologies。 Thermodynamic model of the novel system is developed， as well as the two-phase flow model for the riser。 The system performance of TTLC is investigated based on the first law analysis and the second law analysis， and the results are compared with those of traditional TLC and organic Rankine cycle (ORC)。 It is found that the extra gravitational pressure drop is the main contributor to the riser efficiency。 The working fluids with smaller density ratio and specific heat are more suitable for the proposed system， such as R502， R218， R125 and R115。 Increasing heat source temperature is more efficient in energy conversion than decreasing sink temperature for the TTLC system， which generates marginally more power than TLC when the heat source temperature is less than 50 °C， and less power than TLC within the deviation of 10% for the heat source temperature in the range of 50–75 °C。 The traditional ORC has the worst performance due to its bad temperature matching。 Moreover， the volume flow rate at the turbine outlet of TTLC is only 2–17% of those for TLC and ORC， indicating a much smaller turbine size。
查看更多>>摘要：The research presents the method for optimization of a building with its heating， ventilation and air-conditioning (HVAC) system in the scope of achieving nearly zero energy building (nZEB) in the context of Energy Performance of Buildings Directive 2010/31/EU。 The method is based on coupling the dynamic simulation models created in Trnsys software with the non-dominated sorting genetic algorithm (NSGA-II)， as the engine which performs an optimization process to minimize global cost (GC) and primary energy consumption (PEC)。 The optimization comprises energy efficiency measures (EEM) on a building envelope with a parametrized model of the HVAC system。 The procedure implements building simulations under design weather conditions for heating and cooling to establish the connection between building design and the HVAC system size。 The analysis is performed using discrete equipment sizes and specifications according to manufacturers’ data， ensuring the selection of actual products with their sizes and costs。 In continuation annual simulations using referent year data were performed。 Several HVAC systems were considered， ranging from conventional natural gas-based systems to systems based on renewable energy sources (RES)。 The method is applied in the case study of the refurbishment of a representative hotel building on the Croatian Adriatic。 The results reveal a large gap in terms of PEC between the nZEB system (biomass boiler， solar thermal collectors and absorption chiller， 138。9 kWh/m2) and the cost-optimal system (natural gas boiler and compression chiller， 269。6 kWh/m2)。 The most promising solution for a hotel with year-round operation character is water-to-water heat pump system using seawater as the heat source and sink (170。2 kWh/m2)。 When the use of seawater is not possible， or when cooling energy prevails over heating energy use， air-to-water heat pump system appears to be suitable solution (176。4 kWh/m2)。 It is found that in addition to HVAC system with low PEC， the application of solar photovoltaic (PV) system is required to reach Croatian nZEB target for a renewed hotel (115 kWh/m2)。 Further analysis of the results shows that the optimal parameters of EEM vary depending on applied HVAC system。 The results indicate that optimal solutions are achieved when the HVAC system size matches the design load。 Therefore， excessive oversizing of the HVAC system may have negative impact on GC。 Based on the results and the findings， conclusions and general guidelines for the refurbishment of a hotel building on the Adriatic coast are established。
查看更多>>摘要：The increasing consumption of fossil fuels has caused the emission of an enormous amount of greenhouse gases it has led to the problem of global warming and other damages to the environment。 Therefore， heat recovery has become very important in recent years。 In this paper， two different scenarios of the Organic Rankine cycle (ORC) are proposed to heat recovery of an internal combustion engine with two heat loss levels (stack and jacket water)。 The novelty of this paper is the comparison of the application of two different scenarios for the use of two available heat sources that have not been studied in previous research。 Three different types of organic fluids including dry (n-butane and R245fa)， wet (R134a) and isentropic (R123) were studied by energy， exergy and economic analysis。 In addition， the parameters of pressure and the inlet temperature of the turbine and the superheat temperature value of the inlet flow to the turbine were optimized by the multi-objective optimization。 The optimization results showed that the parameter influencing the thermodynamic and economic indicators most is the ORC pressure ratio。 The optimized results of the two scenarios were compared according to thermodynamic and economic analysis and the best results were obtained for scenario 2 and fluid R123。 For this case， the levelized cost of electricity (LCOE)， Total Investment Cost (TIC) and electricity generation are 0。05776 $/kWh， 317，528 $ and 202。5 kW， respectively。 Moreover， studying 20 countries in all the five continents， showed that developed countries were the ones with the minimum and maximum payback periods。
查看更多>>摘要：The moving granular bed filter is a promising technology for handling the challenges of hot gas clean-up and waste heat recovery in various fields。 The purpose of this study was to investigate the heat transfer characteristics and waste heat recovery of a moving granular bed filter during hot gas clean-up。 The novelty of this study lies in its investigation of the heat transfer performance of coagulative particles。 Experiments were carried out to study the influence of the flue gas inlet temperature， granular velocity， and filtration superficial velocity。 The results revealed that increasing the superficial velocity and inlet temperature and reducing the granular velocity are beneficial for improving the heat storage capacity of granules in terms of single factor。 However， moderate granular velocity and superficial velocity are recommended to achieve a high waste heat recovery efficiency considering multiple factors。 In the present study， a granular velocity of 2 cm?min?1 and a superficial velocity of 0。3 m?s?1 are optimal。 The superficial velocity is the main factor affecting the comprehensive heat transfer coefficient。 The results reveal that the melting and solidification processes of the coagulative particles affect the heat transfer。 They also reveal that improving the heat transfer performance is necessary for enhancement of waste heat recovery。 The focus of the present study is essentially the development of a moving granular bed filter that contains coagulative particles for use in the metallurgy industry。 The results are significant for the design and evaluation of a moving granular bed filter in practical applications that can improve energy efficiency。
查看更多>>摘要：This study has used shape optimization by the genetic algorithm to gain the suitable pitch to axial chord ratio for a cascade turbine blade。 The innovation of the present paper is the modification of the Zweifel coefficient for the wet steam flow passing through the steam turbine cascade。 Wetness fraction (WF)， average droplet radius (ADR)， momentum (MO)， pressure loss (PL)， and isentropic efficiency (IE) at the exit of the cascade turbine blade in wet steam flow are selected as the objective functions。 The ultimate goal was to minimize the wetness fraction， average droplet radius at the outlet of the blade， and pressure losses of the passage and maximize the efficiency and momentum at the outlet together。 The Navier-Stokes equations，SSTk-ω turbulence model， and the Eulerian-Eulerian approach are applied for modeling the condensing flow。 The agreement gained between the numerical results and the experimental results is satisfactory。 A pitch to axial chord ratio of Pi/AC = 0。76 is suggested， and the modified Zweifel coefficient for wet steam flow in the cascade is proposed CZF=0。62。 In the optimal case， the wetness fraction and the average droplet radius at the outlet decrease 3。59% and 1。94%， respectively， and the momentum increases 7。28%。 In addition， the optimal case compares with original case， the isentropic efficiency decreases 2。48% and the pressure losses increases 2。15%。
查看更多>>摘要：The phenomenology of double choking in a supersonic steam ejector which plays an influential role in the performance is not fully understood because the non-equilibrium condensing and three-dimensional effects are neglected in most numerical simulations。 In this paper， a non-equilibrium condensation model was combined with the k-ω SST turbulence model to simulate three-dimensional supersonic steam ejectors with different working conditions and different structures。 The internal relationship between the ejector performance and the double choking characteristics was revealed。 The influence of the characteristics of double choking on the shock waves in the ejector was also investigated。 Results show that when the minimum distance between the sonic velocity line in the diffuser and the wall is equal to the critical minimum distance which is 0。21 mm， the steam ejector is in a double choking mode。 4 mm downstream of the diffuser entrance is the critical second choking position。 The deviations between discharge pressure and critical discharge pressure are getting greater with the increase of the second choking length。 The intensity and number of shock waves in the diffuser are positively related to the second choking length with certain working conditions。 Three-dimensional effects bring non-negligible differences to both the flow field and the ejector performance。
查看更多>>摘要：The catastrophic tunnel fire accidents are usually accompanied with multi-source burning。 Ceiling gas temperature in tunnel is an important parameter in monitoring the daily operation process and unexpected combustion process。 Previous studies are mainly focused on single fire or multiple equal fires in tunnel， while multiple unequal fires burning is common in real tunnel fires。 Till now， the law of asymmetrical temperature distribution of multi-source below a ceiling is unknown。 This paper aims to experimentally study the thermal performance of two unequal fire sources of propane in a naturally ventilated tunnel。 A total of 90 experimental tests were conducted。 The side lengths of two burners are fixed at 10 cm and 15 cm。 The heat release rate (HRR) of each burner are changed with the HRRs ratio of 1–6。 And the spacing between two sources along the longitudinal centerline of tunnel varied from 0–45 cm。 Analysis shows that there is only one peak temperature with small spacings， while two peak temperatures appear with large spacings。 Then the impingement point position and the maximum ceiling gas temperature of each burner are illustrated。 The force analysis is adopted to explain the variation of impingement point position。 A parameter α is innovatively introduced to characterize the promoting effect of spacing on maximum temperature at small spacings。 Then a new normalized HRR is proposed to establish a unified model for the unequal maximum temperature rises below the ceiling of both sources， which indicates that the maximum temperature rise increases with the normalized HRR and then it maintains at 754 K。 By introducing the plume radius， models for asymmetrical temperature decay profiles on both sides of two plumes below the ceiling are proposed， which shows that the temperature in the upstream of the small burner decays faster than that in the downstream of the large burner。 The proposed models for maximum temperature and temperature decay profiles can be used to predict the ceiling gas temperatures of two unequal fires in tunnel。
查看更多>>摘要：Gas turbine combustor design is a complex multi-objective problem。 In the present study， parametric design space study and optimization of a gas turbine combustor using computational fluid dynamics (CFD) simulations is presented。 Baseline case validation， automated workflow setup for geometry modification， meshing， boundary condition specification， CFD solution and output parameter calculations are discussed。 Response surface methodology is used to study combustor performance based on combustion efficiency， pattern factor， total pressure drop， Carbon monoxide (CO) and Nitrogen oxides (NOx) with variations in three design variables: swirl number， secondary hole diameter and dilution hole diameter。 We use central composite design for design of experiments (DOE) and genetic aggregation for response surface generation。 Design space refinement is carried out to identify the blow-off region and limit the search space for optimal designs to swirl number greater than 0。9。 Exclusion of blow-off design points while generating the response surface resulted not only in 57。2% average reduction of root mean square error in the response surface predictions but also smoother trends away from the blow-off region。 A candidate optimal design point with swirl number = 1。0， secondary hole diameter = 12。24 mm and dilution hole diameter = 15。26 mm is chosen using multi objective genetic algorithm on the response surface。 Finally， uncertainty quantification with six sigma DOE analysis quantifies the confidence intervals for performance parameters based on the variations in geometric design variables。 This preliminary design methodology can be used to improve existing combustors and guide the design of novel combustor concepts。
NSTL
Elsevier