查看更多>>摘要：The detection of refrigerant leak is critical for the effective operation of heat pump systems and vehicle maintenance。 Using feature selection methods， machine learning methods， and system sensors schemes， this article optimizes the performance of refrigerant leak detection for vehicle heat pump systems that operate in cooling， heating， and series dehumidifying modes。 The extremely randomized trees (EXT) model was chosen as the best model for refrigerant leak detection in heat pump systems out of 25 machine learning models， with the highest f1 score of 95。73%。 The advanced feature recursive elimination strategy developed in this study is effective at increasing model accuracy， with an improvement of 1% in model diagnostic accuracy while reducing the number of features for modeling。 By comparing different sensors schemes for vehicle heat pump system， this article analyzes the importance of different sensors for refrigerant leak detection。 The accuracy of refrigerant leak detection in vehicles reaches 95。69% based on the optimal sensors scheme。 The results demonstrate that the methods proposed in this paper not only reduce the cost of sensors used in the heat pump system， but also improve the heat pump system's performance for refrigerant leak diagnosis across three operation modes。 In addition， the approach taken in this paper is broadly applicable to diagnosis problems in other fields to facilitate the application of diagnosis in the real world。
查看更多>>摘要：Conventionally， metal hydrides have been explored for their application in hydrogen storage systems。 However， metal hydride based thermal systems have attracted huge attention for a wide variety of applications such as thermal storage， hydrogen compression， heating， cooling， etc due to the availability of hydride materials covering a wide range of operating temperatures and pressures。 These can deliver high energy densities leading to compact systems for stationary as well as mobile applications。 Moreover， the thermal properties of hydrides can be tailored by tuning the proportion of constituent metals to fit the required thermal application。 As metal hydride based thermal systems are identified as potential candidates for global energy needs， it is essential to understand their modes of operations and the status of their development。 This paper presents a comprehensive review of theoretical and experimental studies on thermal applications of metal hydrides which include refrigeration， heat transformers， heat pumps， and thermal energy storage。 Also， hydride selection criteria for specific applications and heat transfer augmentation techniques adopted to improve the performance of hydride beds are discussed。
查看更多>>摘要：This paper describes a mixed-integer convex programming-based control strategy to optimize the operation of phase change material-based energy storage integrated in building supply ducts。 To improve the numerical feasibility， the original nonlinear control problem is pre-conditioned and transformed to a mixed-integer convex program through convexification of the cooling system control model， mixed-integer reformulation of the phase change material dynamics and discretization of the supply airflow。 The overall control framework was leveraged toward development of two model predictive control strategies to optimally charge/discharge the phase change material storage， through supply air temperature reset， and the building passive thermal mass， via scheduling of the zone air temperature setpoint。 These strategies were tested and compared to two baseline control strategies using a simulation case study over three summer days。 Test results show that using the phase change material energy storage alone， energy cost savings of 2。9% and peak demand reduction of 46。7% could be achieved， compared to a conventional fixed-supply air temperature and zone air temperature night setup control strategy; when both the active (phase change material) and passive (building thermal mass) storage capacities are utilized， the savings potentials could increase to 8。4% for the energy cost and 65% for the demand charge。
查看更多>>摘要：Adopting the traditional LMTD method to design the SS-SG (Separated Structure Steam Generator) usually leads to a larger deviation due to drastically change in physical properties of flue gas with changing temperature。 This makes the consumption of steel tubes and power energy during both the manufacturing and operation processes increase。 As an exploratory investigation， a novel thermal design model was developed with the idea of microelement superposition and validated against the experiment herein。 It revealed that the maximum absolute deviation between prediction and experiment was less than 2。5%， which outperformed a lot compared to the traditional method。 As an application case， this model was used to design an actual steam generator in this study。 The design results showed that the steel tube consumption can be reduced by 27。19%， while the power energy consumption can be saved by 11。45% for long-term operation。 Using the proposed model， the effect of operating conditions on thermal performance of the steam generator was discussed。 It indicated that the increase in the inlet temperature and mass flow rate of flue gas， as well as the operating pressure， generally weakens the comprehensive thermal performance indexes PE_A and PE_B。 Besides， this novel model can also be combined with an intelligent algorithm to perform structure optimization。 For this case， compared to the original structure， the total cost can be further decreased by 17。57% with the obtained optimal structure from an economic point of view。 It is of great significance to improve the economics of recovering flue gas waste heat。
查看更多>>摘要：Modern commercial aircraft can experience significant solar loading during turnaround when the aircraft is stationary on the tarmac。 With the increased usage of composite materials， a change in the aircraft thermal environment results due to the substantial difference in metal and composite thermal properties。 In this paper， an experimental study is undertaken to compare the thermal environment established in a CFRP and aluminium wingbox compartment due to solar loading for levels of 81 W/m~2， 396 W/m~2， 700 W/m~2 and two further cases with a constant wing skin temperature of 100℃。 It was found that conduction through the vertical front and rear spars established a complex but stable flow environment comprising of four counter-rotating circulations which interact strongly with the spar walls， a criterion using scale analysis was also established to determine whether the induced flow would persist。 Nusselt number measurements were carried out for each circulation and compared to existing correlations from the literature for differentially heated and top wall heated cavities。 The measurements provide aircraft thermal designers with representative values for the heat transfer coefficient which can be used in the thermal modeling of aircraft wing structures。
查看更多>>摘要：Nowadays， the growing number of electronic components in integrated circuit(IC) chips require higher cooling efficiency。 Here we propose a universal efficient cooling structure based on Micro-Channel Heat Sink (MCHS)， which can be applied to heat dissipation of IC chips with uniform and non-uniform heat fluxes。 When using GFSMs (Gradually-Higher Fins Spilt-Flow Microstructures) MCHS to cool an IC chip with a uniform heat flux of 100 W/cm~2， the thermal resistance and MATD (mean absolute temperature difference) of regular MCHS can be reduced by 57% and 77%。 At the same time， the GFSMs MCHS can reduce the thermal resistance to less than 0。28 K/W with only 1/4 of the pressure drop of the regular MCHS， and the thermal resistance can be reduced to below 0。15 K/W with a pump power of 0。04 W。 In addition， TTSV (Thermal Through Silicon Via) is combined with a split-flow microstructure to form a three-dimensional heat dissipation structure (3D-HDS)。 When using 3D-HDS MCHS to cool a chip containing a 1250 W/cm~2 heat flux hotspot， simulations show that the thermal resistance and MATD decreased by more than 40% compared to regular MCHS。 The cooling structure will have broad application prospects in the field of high-power integrated circuits and electronic cooling。
Rafael Perez-AlvarezEduardo Cano-PleiteDomingo SantanaAntonio Acosta-Iborra...
15页
查看更多>>摘要：The receiver tubes of Solar Power Tower plants are typically attached through clips and sliding rods to the reradiating wall of the receiver in order to reduce the thermal deflection of the tubes。 However， as a side effect， these mechanical attachments increase heat dissipation from the tube to the exterior and can reduce the local temperature of the tube during the receiver start-up， an operation performed every morning or after a severe drop of solar irradiation due to passing clouds。 In the start-up operation， the empty tubes of molten salt receivers must be preheated with a careful aiming sequence of the heliostat field until their temperature is high enough to avoid the freezing of the incoming flow of the molten salt。 This work numerically addresses for the first time the influence of the mechanical attachment on the preheating temperature of a receiver tube。 To achieve this goal， a set of three-dimensional thermal fluid simulations of the temperature distribution in the tube and the mechanical attachment， described with different levels of detail， has been performed for the receiver of the Gemasolar Solar Power Tower plant。 The results of this work show that the mechanical attachment locally affects the tube temperature， leading to a temperature overestimation above 25。1% when the tube is modeled without a mechanical attachment。 In addition， the temperature measured separated from the attachment at the rear face of the tube to control the preheating sequence may not be very representative of the minimum tube temperature， which occurs in the internal face of tube just beneath the mechanical attachment。 The results indicate that accumulation of heat not only by the clip but also by the guide and the rod of the mechanical attachment plays a significant role in the dissipation of heat from the tube to the attachment。 This reveals the need of considering all the elements of the mechanical attachment if an accurate modeling of the preheat temperatures of the tube is needed。 Besides， the use of a simplification in the modeling of the air and radiative heat transfer outside the tube reduces by a factor of 4。9 the computational cost involved in a full simulation of these transfer processes， with a temperature discrepancy between models below 14。3%。 Finally， the effect of the size of the attachment clip on the minimum tube temperature is investigated， revealing that the minimum tube temperature of the preheated tube can decrease below the freezing temperature of the molten salt for clip heights larger than 170 mm。
查看更多>>摘要：Performance improvement of electric vehicle heat pumps can enhance thermal comfort and reduce the power consumption of electric vehicles， hence stimulating their development。 In this paper， the cyclic characteristics of an electric vehicle heat pump were studied under different operating modes and working conditions。 Different from the optimal discharge pressure of conventional CO_2 systems which was determined by the variation gradient characteristics of the transcritical isotherm， the discharge pressure of electric vehicle heat pumps at the peak COP value was defined as a pseudo-optimal discharge pressure and was determined by the obvious temperature glide at the outlet of the gas cooler。 This pseudo-optimal discharge pressure existed at both transcritical and subcritical states。 The difference in the pseudo-optimal discharge pressure between the subcritical or transcritical states was first evaluated。 Then an in-depth analysis of the influence of key parameters on the pseudo-optimal discharge pressure was studied to develop an accurate prediction method since the traditional prediction methods were not applicable。 The results showed that pseudo-optimal discharge pressure increased with the ambient temperature， inlet air temperature， and supply air temperature。 This study provides valuable information for the comprehensive performance optimization of an electric vehicle thermal management system。
查看更多>>摘要：In this study， the performance characteristics of a gas engine-driven heat pump (GHP) system for heating applications were experimentally investigated。 A novel energy-efficient air-source GHP experimental platform was designed based on scroll compressors with R410A。 The changes in heating capacity (Q_h)， gas consumption power (P_(gas))， compressor power (P_(comp))， primary energy ratio (PER)， and coefficient of performance (COP) were obtained under varying conditions of condenser water flow rate G_w (6。10-15。25 m~3/h)， water inlet temperature t_(w，in) (24。0-44。2℃)， engine speed N_(eng) (1200-2400 r/min)， and ambient air temperature T_(amb) (-15-7℃)。 The performances of the four heating modes (mode-1 to mode-4) were compared at an ambient air temperature of -20℃。 The results showed that t_(w，in)， N_(eng)， and T_(amb) had significant influences on heating performance， whereas G_w had a slight impact。 Compared with other heating modes， mode-4， wherein the recovered waste heat was only transferred to the heating water， could improve the heating performance of the GHP system。 In the mode-4 heating experiments， PER was between 0。981 and 2。155， the rate of waste heat recovery was between 49。12% and 77。70%， and the engine thermal efficiency was between 27。02% and 33。24%。
查看更多>>摘要：To improve the performance of vapour compression refrigeration cycles， the inclusion of a thermoelectric subcooler for low-medium power units has been the focus of recent studies due to its robustness， compactness and simplicity of operation。 In thermoelectric systems， it has been demonstrated that the heat exchangers used in the hot and cold side of the thermoelectric modules have a critical impact in the performance of the system。 This influence has not yet been studied for thermoelectric subcooling systems in vapour compression cycles。 This work， for the first time， evaluates the impact that the heat exchangers of a thermoelectric subcooler， included in a transcritical carbon dioxide refrigeration cycle， have， in the performance of the refrigeration cycle。 The influence is quantified in terms of: optimum working conditions， coefficient of performance and cooling capacity。 The results show that， through an optimization of the heat exchangers of the thermoelectric subcooler， the performance improvements on the coefficient of performance using this technology are boosted from 11。96 to 14。75% and the upgrade in the cooling capacity of the system rises from 21。4 to 26。3%。 Moreover， the optimum gas-cooler working pressure of the system is reduced and the optimum voltage supplied to the thermoelectric modules increases。
NSTL
Elsevier