查看更多>>摘要：When a lithium-ion battery is thermally out of control， the internal heat is mainly coming from the mutual reaction of the internal components of the battery。 It is well known that the breakdown and combustion of carbonate solvents inside lithium-ion batteries contribute a large part of the heat when thermal runaway occurs。 Therefore， it is necessary to analyze the combustion characteristics of several common carbonate solvents。 The cone calorimeter was used to test the combustion of four common carbonate solvents and their mixed solution under different thermal radiation conditions。 The obtained heat release rate (HRR)， mass loss rate (MLR) and total heat release (THR) were used to analyze its combustion characteristics。 Meanwhile， the HRR of different carbonate solvent configurations was explored and compared by oxygen consumption calorimetry (OC) and thermochemical theory (TC)。 The results show that the HRR curve obtained by the TC method and the OC method basically coincide， which confirms the reliability of the OC method to measure the HRR of solvent combustion。 The linear carbonates usually burn at an early stage in the combustion process because the evaporation rates of linear carbonates are higher than those of cyclic carbonates。 The peak HRR of the solution combustion has a significant drop when the sample contains EC， whether it is under the premise of thermal radiation or without thermal radiation。 The external thermal radiation is proved to have a great increasing influence on the peak HRR per unit area and MLR。 These tests can be the reference of more detailed analysis of electrolyte reaction during lithium-ion battery fire， and provide a theoretical basis for preventing and restraining the thermal runaway。
查看更多>>摘要：Matching characteristics between two-stage turbocharging and fuel injection significantly affect energy flow distribution in diesel engine thermodynamic cycles at variable altitudes。 This paper investigates thermodynamic cycle characteristics of the Twin variable geometry turbocharged (VGT) diesel engine and proposes a control method to optimize the engine's energy flow at variable altitudes。 First， a thermodynamic analysis model was built to investigate the influence mechanism of key thermal parameters on in-cylinder combustion， intake， and exhaust processes at variable altitudes。 Furthermore， a principle of four maximum and three minimum was proposed to achieve thermodynamic cycle efficiency for the Twin-VGT diesel engine at variable altitudes。 The maximum intake density is based on the interaction of two-stage compression and cooler， which corresponds to a maximum brake thermal efficiency (BTE)。 The maximum intake density， coupled with fuel injection strategy， would achieve the lowest fuel consumption under a part-load condition and the largest torque corresponding to the minimum air–fuel ratio under a full-load condition。 Maximum global expansion ratio (GER) and isentropic efficiency can be achieved by reasonably controlling the effective flow area of high-pressure (HP) and low- pressure (LP) VGT to fully utilize exhaust available energy at variable altitudes。 The minimum power consumption for the two-stage compressor is obtained based on the distribution method of global boost pressure (GBR) to reach the targeted boost pressure。 This paper provides an energy flow control method to realize an efficient thermodynamic cycle for the Twin-VGT at variable altitudes。
查看更多>>摘要：The condensation water-bridge phenomenon of the heat exchanger surface fins is a common undesirable phenomenon in refrigeration systems and heat pump systems， which would significantly affect the heat exchanger's thermal efficiency due to insulation and obstruction of airflow。 Based on the lack of experimental studies on louvered-fin heat exchangers and surface energy for fin-surface condensation， this paper experimentally investigates the effect of wettability (surface energy) on the condensation mechanism and heat exchanger performance。 Firstly， hydrophilic and hydrophobic coatings are formed by reagent deposition， which regulates the surface energy of the fins。 Experiments are designed to investigate the effect of surface energy on heat exchanger performance at different temperatures， humidity， and wind speed。 Finally， the key issues such as condensation morphology are discussed in detail by molecular dynamics simulation， thus filling the gap and providing a reference for heat exchanger surface construction。 The experimental results show that the wet condition has a faster condensation rate， with an average rate reduction of 33。2%。 Both hydrophilic and hydrophobic fins could improve the performance of the heat exchanger compared to bare fins due to their inherent uniqueness。 The hydrophilic fins have a smaller pressure drop， maintain a more stable heat transfer rate， and improve the heat transfer performance by 13。4% in a typical environment (60%) or with lower water content。 While the hydrophobic fins show advantages in a wet environment (80%)， improving the heat transfer performance by 17。8% due to the severe deterioration of the bare heat exchanger performance。 Further， molecular-scale condensation patterns were analyzed， and condensation rates and adsorption forces were quantified。 The experimental and simulation results guide the construction and selection of surface energy to optimize the heat transfer surface。
查看更多>>摘要：Transport membrane condenser is a device for recovering water and heat from flue gas。 Porous nature of ceramic membrane makes properties of water vapor condensation and fluid flow different from those in traditional heat exchangers。 Therefore， irreversible losses caused by heat transfer and flow resistance of transport membrane condenser is also unique and worthy of studying。 This paper uses entransy and entropy analysis methods to calculate irreversible losses of transport membrane condenser， and analyzes effects of fluid temperature on entransy dissipation and entropy generation rates。 With the goal of reducing irreversible losses， operation mode and structure size of transport membrane condenser are optimized under designed conditions。 Based on specific application cases， this paper finds that entropy analysis method has a certain limitations when studying irreversible losses of transport membrane condenser。 The limitation is embodied in the analysis of heat transfer problems under the condition that fluid temperature changes significantly。 Furthermore， an optimization method suitable for engineering design is proposed。 According to theoretical results， flue gas inlet temperature is preferably in the temperature range of 52 °C–55 °C; under the condition that water balance of power plant is not destroyed， increasing flowrate of cooling water as much as possible。
查看更多>>摘要：This paper reports design， fabrication， and experimental results of a loop heat pipe (LHP) as a heating device for batteries of electric vehicles。 Usually， LHPs are used as a cooling device。 In this study， however， the LHP is used as a heating device by attaching battery blocks which are the heating target， to the condenser of the LHP。 A new transient analytical model was also constructed using the implicit method， which is a multidimensional extension of the Newton–Raphson method。 The analytical results are compared with the test results from the point of the transient behavior of the heating LHP。 A cylindrical type evaporator with an outer diameter of 27 mm and a length of 150 mm was used。 A flat perforated tube with a length of 1625 mm was used as the condenser。 R 134a was selected as the working fluid。 The condenser of the LHP is connected to the simulated battery blocks， which were made of 48 aluminum-alloy blocks (100 × 128 × 26。5 mm)。 First， the operation test was conducted at room temperature， and the basic thermal performance and the concept of the battery heating were evaluated。 Next， the experiment was conducted in a thermostatic bath which was set at ?20 °C。 The experimental results showed the simulated battery blocks reached above 0 °C at 14，600 s。 The temperature increase rate was estimated to be 0。06–0。09 °C/min， and it can be considered that this LHP can be used as a heating device under actual low-temperature conditions。
查看更多>>摘要：Heat pipes are metal-wick equipped systems that circulate a phase-changing liquid and transfer heat more effectively than solid-metal compact heat spreaders。 Metal wicks are effective fluid transporters， but they can face capillary limits due to significant pressure drops and pore clogging。 Wettability-patterned (WP) surfaces， on the other hand， are not limited by these constraints and， as demonstrated in this work， may offer a viable supplement for metal wicks in heat pipes， which come in many shapes and sizes。 The use of WP surfaces facilitates the collection and efficient transport of condensate， thus improving heat transfer from the hot (evaporator) to the cold (condenser) side of the device。 Most commonly， flat heat pipes consisting of a fully wick-lined plate opposed to a wickless surface， are evaluated considering a uniform adiabatic condition on the wickless plate， which does not promote condensation。 However， in a practical scenario， the heat pipe portions in contact with an external heat sink could induce condensation on the wickless side， thus affecting the heat pipe's operation and thermal resistance。 To explore this scenario， a flat heat pipe of 10 cm operating length with axially graded copper-wick evaporator and non-adiabatic wickless WP surface is designed， fabricated and tested。 A wettability pattern is imparted on the wickless surface to control the maximum droplet size of the condensate and condensation mode via spatially designed superhydrophilic/hydrophobic juxtaposed areas to regulate both Dropwise Condensation (DwC) and Filmwise Condensation (FwC) towards enhanced heat transfer with reduced overall system thermal resistance。 Low capillary pressure domains are allocated in this design to collect condensate on the wickless plate and return it to the evaporator's wick。 On the evaporator side of the system， variable-porosity copper wicks are being used to improve liquid conveyance from the cold to the hot domains。 Four heat-transfer fluid charging ratios are examined with the best thermal resistance 0。27 K/W achieved at 105 W。 The effect of wettability patterning on the wickless surface and the wick characteristics of the wick-lined evaporator are investigated。
查看更多>>摘要：To reduce fossil fuel consumption and carbon emissions from building energy systems， a solar-based cooling and heating system is proposed here employing solar concentrating collectors， photovoltaics， double-effect absorption heat pump and thermal storage。 The system is applied to five building types in a region with cold winter and hot summer。 The system configuration is optimized using energy， environmental cost， and solar fraction as criteria。 The results demonstrate that the solar system could produce at least 31。1% of the cooling/heating loads resulting in 73。3% and 64。2% energy and cost savings in a hospital。 The coefficient of performance of the hybrid system ranges from 5。87 to 7。56 in cooling mode， and 1。22 to 1。65 for heating。 The cost of devices is the most sensitive factor， and followed by the price of grid electricity。 Increasing the renewable energy penetration rate could improve the energy performance， but decrease the cost saving ratio due to the lower carbon emissions。
查看更多>>摘要：Multilayer insulation (MLI) is a kind of high-temperature insulation which employs multiple high-reflective screens to retard the radiation heat， but analyzing and optimizing its heat transfer characteristics by experimental and theoretical models remains low-efficiency and non-visualization。 In this work， finite element analysis (FEA) models verified by comparing the simulation and experiment results are established to systematically reveal the numerous and complex effect factors， including the number of layers， thermal boundary， fibrous insulation density and emissivity of reflective screens。 The results show that the top temperature of MLIs can be reduced by increasing the number and the emissivity of reflective screens， and the density of fibrous insulation， but there is a reasonable number of layers to achieve the best comprehensive performance of MLI。 In addition， the proportion of radiative heat transfer in the total heat transfer increases with increasing heating temperature。 The feasibility of optimizing thermal insulation performance based on the FEA models is confirmed by designing the MLIs with stainless steel and aluminum as reflective screens。 And the results indicate that the FEA methods can significantly reduce the number of trials and realize the optimal design of MLI。
查看更多>>摘要：A hybrid compression-assisted absorption refrigeration system using condensation in a heat recovery ammonia generator was proposed for the slaughtering industry considering the importance of reducing the high demand for energy in the industrial refrigeration systems。 The proposed system operates with double evaporators and generators at different pressures and temperatures that use the available condensation heat from the ammonia generator of the subsystem operating at high pressure and temperatures to the subsystem under low pressure and temperatures。 In addition， compressors are included in the system to increase the pressure of the saturated vapor generated from the ammonia generator to enable condensation heat to have a sufficient minimum temperature difference for heat rejection to surroundings。 The investigation was carried out using energy and exergy analyses， and the results show that the proposed system is promising compared with a simple compression cycle or conventional absorption system。 Among several advantages， this system demands less power compared with the simple compression system and less heat compared with the conventional absorption refrigeration system owing to the possibility to promote a better thermal integration between the subsystems， adjusting the operation pressures in accordance with the availabilities and demands of heat and power。 The external demand of the heat source can be decreased by 57。4% compared with the conventional absorption system and by 34。2% compared with the power demand of a simple compression cycle。 The coefficient of performance of conventional absorption ranged from 0。453 to 0。6145， while the exergy efficiency ranged from 0。2786 to 0。3223， indicating that a hybrid compression-assisted absorption system can be a good option where there is a residual heat source to the absorption cycle， but this availability is not sufficient to satisfy the complete demand。
查看更多>>摘要：Gas turbine output has a very good capability for heat recovery and increases production capacity by heat recovery steam generator and heat recovery vapor generator。 Also， gas turbines have good potential for coupling with a solid oxide fuel cell to increase power generation。 The present research proposes and evaluates a novel combination of a solid oxide fuel cell and gas turbine system with an organic Rankine cycle and a multi-effect thermal desalination system。 Conventional and advanced exergetic， exergoenvironmental and exergoeconomic analyses are performed to better understand the proposed system in view of performance， economic， and environmental impacts。 To find the optimal design values， minimize the total exergetic environmental impacts and total exergetic cost rate， and maximize exergetic efficiency， as objective functions， multi-target optimization using the multi-target water cycle algorithm and the multi-target genetic algorithm is used。 The analyses are conducted using MATLAB software。 Results determine the optimal hybrid system could produce 5000 m3/day of freshwater， with five effects on the MED-TVC。 The energy and exergy efficiencies of the suggested hybrid system reached 47。85% and 41。94%， respectively， an increase of 11。6% and 3。6% compared to the coupled gas turbine system and solid oxide fuel cell。 Furthermore， by applying the Multi-objective Genetic Algorithm and Multi-objective Water Cycle Algorithm optimization， the overall efficiency of cogeneration is increased by 28% and 27。5%。 The total exergetic cost is reduced by 23。12% and 22。46%， and the total exergetic environmental impact is reduced by 20。15% and 19。65%， respectively。
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Elsevier