Results 1 - 10 of 2017
Results 1 - 10 of 2017. Search took: 0.03 seconds
|Sort by: date | relevance|
[en] This preliminary study investigated data mining-based methods to assess and predict the performance of geothermal heat pump(GHP) system. Data mining is a key process of the knowledge discovery in database (KDD), which includes five steps: 1) Selection; 2) Pre-processing; 3) Transformation; 4) Analysis(data mining); and 5) Interpretation/Evaluation. We used two analysis models, categorical and numerical decision tree models to ascertain the patterns of performance(COP) and electrical consumption of the GHP system. Prior to applying the decision tree models, we statistically analyzed measurement database to determine the effect of sampling intervals on the system performance. Analysis results showed that 10-min sampling data for the performance analysis had highest accuracy of 97.7% over the actual dataset of the GHP system.
[en] Highlights: • The energy output characteristics of the solar hybrid CCHP system are defined in a clear perspective. • The particle swarm optimization (PSO) algorithm is adopted to find the optimum design parameters. • The design features and the performance of solar hybrid systems under five different operation strategies are analyzed. • The comparison between the hybrid system and the conventional system is given. - Abstract: The hybridization between conventional combined cooling heating and power (CCHP) systems and solar systems has been considered as a good solution to the urgent energy and environment issues. This study develops the mathematical model of a CCHP system hybridized with PV panels and solar thermal collectors. The particle swarm optimization (PSO) algorithm is adopted to find the optimum values of design parameters. Based on the energy output characteristic of the solar hybrid CCHP system, five operation strategies of the conventional CCHP system are adjusted and applied for the solar hybrid CCHP system. The simulation work of the hybrid CCHP systems based upon a hotel building in Atlanta is carried out to find an appropriate design scheme. The results show that the hybrid CCHP system under the FEL-ECR mode is the best choice. Besides, its PESR, CO2ERR and ATCSR can reach 36.15%, 53.73% and 4.16%, respectively. Compared with a conventional CCHP system, the hybrid CCHP system achieves better energy-saving and CO2 reduction performance. However, the hybrid CCHP system consumes more annual total costs because of its high initial investment.
[en] Highlights: • A novel portable solar collector mechanism is optimally designed. • Wireless power transfer is first applied to cooling systems. • A supercapacitor stores electricity and outputs a regulated supply. • The proposed cooling system shows high efficiency in a limited space. - Abstract: As the greenhouse effect becomes increasingly serious, cooling a vehicle cabin parked under the blazing sun without running the engine or using an electric vehicle’s power has received considerable attention. In this paper, we develop a novel portable, renewable, solar energy-powered cooling system with wireless power transfer (WPT) and supercapacitors to cool the vehicle cabin. The proposed system consists of a solar collector mechanism, an energy conduit, and a temperature control and cooling module. First, consisting of folding solar photovoltaic (PV) panels, the solar collector mechanism making the proposed system portable. Once collected, the solar energy is converted into electricity and stored in the supercapacitors through wireless power transfer without breaching the vehicle body. Automatic temperature regulation is achieved with the cooling device via the temperature control and cooling module. The experimental results indicate that a maximum output power of 2.181 W and a maximum WPT efficiency of 60.3% are achieved when the prototype loaded with 3 Ω and 5 Ω respectively. Meanwhile, the simulation shows the temperature inside the cabin is reduced by as much as 4.2 °C in average, demonstrating that the proposed solar energy-powered cooling system is effective and feasible in cooling a hot vehicle cabin.
[en] Highlights: • A 3D model couples flow and heat transfer processes of DHE, wellbore and reservoir. • The model is validated against experimental data with a maximum error of 8.3%. • The entire temperature and flow fields of DHE system is analyzed comprehensively. • Performances of single U-tube, double U-tube and spiral tube are compared. • Effects of key factors on heat extraction performance of DHE system are studied. - Abstract: The downhole heat exchanger (DHE) geothermal system is commonly used to exploit geothermal energy for space heating. In this paper, a 3D unsteady state numerical model is established to couple fluid flow and heat transfer processes of DHE system. The model is validated by field experimental data. Temperature and velocity fields are analyzed to understand thermal process of DHE system. Heat extraction performances of three different DHE structures, including single U-tube, double U-tube and spiral tube, are compared. Subsequently, cases are studied to investigate how key parameters affect DHE performance. Simulation results depict that spiral-tube has the best heat extraction performance. As working fluid mass flow rate rises, outlet temperature declines and thermal power increases. When inlet temperature ascends, outlet temperature rises while thermal power decreases. Effects of reservoir porosity and tube wall heat conductivity on DHE performance are minor. Higher subsurface water velocity and larger rock heat conductivity can improve DHE performance, but the former has a more significant influence. Besides, subsurface water flow direction has neglected influence on performances of single and double U-tube, but appreciable impact on that of spiral tube. Key findings of this work are beneficial for optimal design and optimization of DHE geothermal system.
[en] Highlights: • A new numerical model for PCM based Latent Heat Storage System. • Numerical model is validated by experimental testing. • Influence of thermal conductivity on the thermal storage properties is analyzed. • Effect of phase transition temperature is discussed. - Abstract: The heat transfer properties of phase change materials (PCMs) are of importance for the efficiency assessment on the heat storage and release in solar thermal systems. Previous research results demonstrate that the increase of thermal conductivity of PCMs can enhance the thermal performance in solar thermal systems; however, the corresponding mechanism is not clear. To this end, this work investigates the influence of PCMs properties on storage performance of solar thermal systems. First, experimental testing was conducted to verify the effectiveness of a thermal simulation model in the heat storage and release process. Then, the proposed simulation model was used to investigate the performance of several commonly used PCMs in the process of melting and solidification. The influence of thermal conductivity and phase transition temperature on the thermal storage properties was analyzed. The analysis results demonstrated that the influence of phase transition temperature on the thermal system performance was greater than that of the thermal conductivity in short time, while the thermal conductivity contributed greater influence on the system performance in long time. The phase transition temperature hardly affected the total system efficiency if given enough heat transfer time. The findings in this work may provide a theoretical reference for the selection of heat storage materials.
[en] Highlights: • We develop a direct passage arrangement method for multistream plate fin heat exchangers. • An improvement of passage arrangement with good synergistic effect is proposed. • A symmetry arrangement method is first presented to arrange passages directly. • Effectiveness of this method is validated by three evaluation means. • This method performs better than the existing optimization methods. - Abstract: Passage arrangement quality significantly affects the performance of multistream plate fin heat exchanger (MPFHEs) because a bad arrangement may result in uneven temperature difference field and pressure field between passages and thus reduce the thermal efficiency. However, it is very difficult to design an effective passage arrangement owing to large numbers of possible passage arrangement patterns and complex heat transfer processes between the passages in a MPFHE. This work develops a direct passage arrangement method for MPFHEs to address this problem. In this method, an improvement of passage arrangement with good synergistic heat transfer effect is first proposed. The determination of passage quantity for each fluid is suggested to be proportional to its design heat load. Next, based on the results of the checking calculation, the fin and heat exchanger structure parameters should be adjusted until the constraints including thermal effectiveness, length deviation and pressure drops have been satisfied. Afterwards, the passages are arranged directly by a symmetry arrangement method. To evaluate the effectiveness of this method, three different industrial cases are performed and compared with the existing optimization designs by three evaluation means. The validation results indicate that this method performs better than the complex optimization methods.
[en] The approach to the mathematical modeling of technological processes of production, manufacture and consumption energyresources on the property fund facilities and engineering networks is presented. This approach is defining the information support system analysis of the kinetic changes of thermodynamic parameters sequentially occurring thermal processes in the flows of heat transfer agent in a closed structures of heating energy working in the recycle mode of the heat flow. It is determined the possibility of setting and solving problems of energyefficiency on the objects with close cycle operating and working in the fluctuation mode of the environmental parameters. (paper)
[en] Highlights: • A new design of hybrid loop heat pipe using pump assistance. • Pump was only activated when the dry-out will took place. • When the pump turned on, it will successful to prevent the dry-out. - Abstract: A loop heat pipe (LHP) is one of the two-phase cooling technologies used in passive cooling systems. The LHP is an efficient heat transfer device, but its extreme power density can cause dry-out at the evaporator. Many researchers have predicted that passive devices will not be able to meet future cooling challenges because of this limitation. The objective of this research is to design a modified LHP that overcomes the dry-out problem by adding a diaphragm pump to accelerate fluid transportation (called a hybrid loop heat pipe, HLHP). The pump installed on the liquid line is coupled with a reservoir. The developed HLHP works passively using wick capillary pressure when there is no sign of dry-out. When dry-out occurs, the pump is activated via diaphragm pumping and has a temperature controller. Thus, the working fluid is circulated by both the capillary force and driving force of the diaphragm pump during the heat-transfer process. The operating characteristics of the HLHP under a variety of heat load supply and low-power start-up conditions have been investigated. The experimental results indicate that the installation of a diaphragm pump in a modified LHP system can prevent the occurrence of dry-out in the evaporator and significantly reduce the evaporator temperature.
[en] Highlights: • Designed three lab-scale sensible heat storage (SHS) prototypes of 15 MJ capacity. • Heat transfer augmentation for concrete SHS prototypes was implemented. • Hi-tech Therm 60 was used as heat transfer fluid. • Thermo-physical properties of the selected concrete mixture were estimated. • Performance tests on the prototypes were conducted at various operating conditions. - Abstract: This paper presents the performance tests on lab-scale sensible heat storage (SHS) prototypes made up of cast steel and concrete. Thermal storage performances of the prototypes in terms of charging/discharging times and energy storage/discharge rates have been estimated at various operating temperatures and heat transfer fluid (HTF) flow rates. These prototypes were designed in the form of a shell-and-tube type heat exchanger with a heat storage capacity of 15 MJ. Five different concrete mix designs were studied and the mix design M30 was selected for thermal storage, as they possess high compressive strength-cost ratio. Heat transfer enhancement in the concrete prototypes was incorporated by welding longitudinal fins on the HTF tubes. Hi-tech Therm 60 was used as heat transfer fluid. The charging and discharging times of cast steel (M1) prototype in the temperature range of 353–413 K were 1263 and1803 s, respectively. The effective charging/discharging time of the concrete prototype with copper tubes (M2) and concrete prototype with MS tubes (M3) prototypes in the temperature range of 353–433 K were 5210/6297 s and 7160/7780 s, respectively. The storage performance of the system highly depends on the operating temperature range due to the temperature dependence of the thermo-physical properties of the SHS materials and the HTF.