查看更多>>摘要：This work presents the exergoeconomic analysis and assessment of a recently developed integrated system for the multigeneration of electrical power, space heating, freshwater, and ammonium bicarbonate. The last chemical commodity is used as a method of carbon capturing and utilization method. This type of analysis is important because it shows the economic feasibility of integrated systems for power production with carbon capture and utilization features. This helps attract the power industry decarbonize in an economic way. The integrated system is modeled using the energy, exergy, and then the exergoeconomic analysis tools for investigating this system in terms of its thermodynamic and economic performance. Furthermore, the integrated system is studied using a multi-objective optimization method to find the Pareto front where the overall exergy destruction rate and the overall unit cost of product are mutually minimized. The results of this study show that the ammonium bicarbonate is produced with a cost rate of 2.02 × 10-2 $ s?1, and the overall unit cost of product is 2.38 × 10-3 $ kJ?1. The overall exergy destruction cost rate and the overall exergoeconomic factor are evaluated to be 0.79 $ s?1, and 2.97%, respectively. Moreover, the multi-objective optimization study has produced an optimum point where has an overall exergy destruction rate of 1.62 × 104 kW and an overall unit cost of product of 2.42 × 10-3 $ kJ?1. The cost of producing ammonium bicarbonate is only 16% of the market price for this chemical commodity which indicates an economic feasibility of this carbon capturing and utilization system.
查看更多>>摘要：This paper presents new cryogenic two-phase heat transfer coefficient data for the chilldown of large diameter, long propellant transfer lines using liquid oxygen (LOX) and liquid methane (LCH4). At the NASA Neil A. Armstrong Test Facility, as part of the Integrated Cryogenic Propulsion Test Article test campaign which included the first ever cryogenic-lander engine hotfire testing at thermal vacuum conditions, liquid oxygen (LOX) and liquid methane (LCH4) flow boiling data was gathered during propellant feedline conditioning. Ten horizontal chilldown tests were conducted on a 2.54 cm and 11.43 cm transfer line in two different thermal environments, using two cryogens, over the range of inlet pressure (100–450 kPa), mass flux (100–6000 kg/m2*s), Reynolds number (4 × 104–1.32 × 106), and equilibrium quality (?0.02–1.1). These tests report cryogenic chilldown data at the largest diameter lines ever reported. A total of 1,634 data points are added to the consolidated cryogenic chilldown database. Examination of both chilldown and boiling curves shows significant stratification in the larger diameter transfer line, even at highly turbulent Reynolds numbers. Higher inlet pressure always leads to faster chilldown times and higher heat transfer coefficients. Recently developed cryogenic quenching correlations are also compared with experimental results here to comment on the validity of applying the correlations to larger, longer transfer lines.
查看更多>>摘要：The optimal concentrations of CO2 for plant growth in greenhouses are commonly higher than that in the atmosphere. A new strategy using direct air carbon-capture was developed to increase CO2 concentration in the greenhouse. A rotary regenerative adsorption wheel (RAW) for the temperature swing adsorption process was utilized as the critical equipment in the CO2 enrichment system to achieve continuous CO2 capture. To investigate the heat and mass transfer characteristics of RAWs, a 3D thermal and mass non-equilibrium modeling of the temperature swing adsorption process in a bi-sectional RAW was first developed. The RAWs with activated carbon, zeolite 13X and Mg-MOF-74 were comparatively researched. Three dimensional distributions of temperature and mass parameters in the RAW are obtained and analyzed. Air streams with different CO2 concentrations can be obtained by suitably arranging the airflow channels at outlets. The increased rotating speed will cause small temperature swings and lead to poor CO2 enrichment performance. The increased air flowrate will reduce adsorbent mass per air flowrate and weaken the CO2 enrichment performance. The RAWs with Mg-MOF-74 and zeolite 13X have very close performance and are much higher than that with activated carbon. Although Mg-MOF-74 is theoretically better than zeolite 13X on the CO2 adsorption performance, the difference between the two is not obvious due to the small temperature swings between adsorption and desorption sectors in this study. Improving the overall mass transfer coefficient is critical for promoting the CO2 enrichment performance of the RAW when the overall mass transfer coefficient is less than 0.002 s?1.
查看更多>>摘要：This work investigates the thermohydraulic performance of a porous serpentine wavy channel solar air heater. Comprehensive illustration on the effect of fractional porous interface (25%≤ξ≤100%), channel porosity (90%≤φ≤100%) and Reynolds number 2000≤Re≤11000 on the thermohydraulic performance of solar air heater design is presented. Experiments are performed and numerical results are validated to conduct further investigations for the optimization of the input variables. This study is a unique idea that broadly presents the scope of thermal performance improvement by utilizing the porous media in fraction and varying porosity in solar air heater channel and highly useful for the researchers of this field. Finite volume method based computational fluid dynamics tool is used to conduct numerical investigations, Forchheimer equation is used to account the effect of porous media and surface to surface (S2S) radiation model to capture the effect of shape factor and emitted radiation in collector channel. It is obtained that ξ of 25% and φ of 93% delineated the best thermohydraulic performance (THPP) of 4.52 for the present solar air heater design. While, the obtained thermohydraulic performance is 186% times higher compared to the smooth design. The excellent results that come into the light from numerical investigation are the secondary flow formation in the porous and flow zones at higher Reynolds number and lower fraction of porous region (ξ), and for all configurations of ξ at large channel porosity (φ). Hence, results of this investigation not only present the best operational configuration to obtain higher thermal performance, but also present the measures to reduce the material cost of porous media and consequently pumping power.
查看更多>>摘要：Although R1234yf is a new environmentally-friendly refrigerant with low GWP, its thermal performance is inferior to that of conventional refrigerants. Mixing R1234yf with R32 can overcome the respective shortcomings of each component. Therefore, understanding the pool boiling heat transfer characteristics of R32 + R1234yf mixtures is of great importance to the design of heat exchangers and the optimization of thermal systems. This study carried out the pool boiling experiments of R32, R1234yf, and their binary mixtures. The boiling curves, heat transfer coefficients, and bubble images of pure and mixed refrigerants were obtained. The results showed that the addition of R32 effectively improved the heat transfer performance of R1234yf. Meanwhile, the mixing effect weakened the bubble coalescence and enhanced the heat transfer performance under high heat flux. It was found that the heat transfer deterioration of mixtures was not only influenced by the vapor–liquid phase equilibrium but also related to the nonlinearly varying physical properties. Based on the experimental data, eleven widely used correlations for boiling heat transfer coefficient of binary mixtures were analyzed with two selected and further modified. The prediction performances of the modified correlations improved significantly, with the mean absolute relative deviation (MARD) reducing to 5.16% and 5.53%, respectively.
查看更多>>摘要：Radiative cooling is a promising solid-state, non-vapor-compression technology for passive refrigeration and air conditioning. Although this phenomenon occurs naturally, achieving a significant amount of cooling to make it a technically and economically viable technology requires highly engineered, spectrally selective radiative surfaces. These characteristics make radiative cooling difficult to estimate, particularly when it is integrated with other systems such as photovoltaic panels or building envelopes. The complexity further increases when the substrate also participates in the radiative cooling (along with the radiative coating). Energy estimation is becoming increasingly critical because of the recent focus on the semitransparent radiative coatings that transmit a variety of colors to enhance the aesthetic appeal of the system. Here, we propose an iterative method to calculate the effective radiative properties, which provides the same net radiative cooling that would be observed using the spectral properties at both the coating and substrate surfaces. Compared to traditional methods that rely on either computationally expensive full spectral analysis or methods for averaging each radiative surface parameter locally, our proposed method focuses on calculating effective properties that provide the same the net cooling effect as a full spectral analysis by accounting the emissivity, absorptivity, and transmissivity collectively, thereby providing an overall estimation error of less than 0.2%. We believe that this study will be beneficial to the engineering communities that employ complex simulation codes and require lumped solar and thermal radiation related parameters.
查看更多>>摘要：Despite the wider applications of heat pump, conventional heat pumps face limitations in cold-region operations. To improve heating performance at low ambient temperatures, a single-stage compound air-source heat pump was innovatively built in this research. Through switching operating mode and regulating operating parameters, the performance of compound heat pump using CO2/R600a was experimentally investigated under different operating conditions. The influences of operating parameters on system performance were studied. Under supply/return water temperatures of 75℃/50℃, coefficient of performance (COP) of the compound heat pump varied from 1.834 to 2.574 when air inlet temperature varied from ?30℃ to 0℃, and the thermodynamic perfection of the compound heat pump cycle was higher than 46% in experiment. The essential factor affecting performance was the irreversible loss in recuperator. Because of the effective utilization of the temperature glide of CO2/R600a, the compound heat pump was suitable for the condition with the supply/return water temperatures of 75℃/50℃. The energy efficiency and volumetric heating capacity of the compound heat pump using CO2/R600a were both higher than those of two-stage and cascade systems using R134a and R410A. The outstanding experimental results of the single-stage compound heat pump provide a promising and competitive solution for clean heating in cold regions, attributed to its environmental friendliness, simplicity and cost effectiveness.
查看更多>>摘要：Many studies have looked at the effects of various geometrical parameters of fluidic oscillators on the heat transfer rate of a hot plate impinged by a sweeping jet. In this research, Ansys-Fluent software was used to solve two-dimensional Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with a k-ω (SST) turbulence model to study the effect on the heat transfer rate of a hot plate due to some new geometrical changes, such as removing the external diffuser, changing the divergence angle of the external diffuser, and changing the distance from the outlet throat to the hot plate. An experimental setup was provided to verify the numerical results for the fluidic oscillator with an external diffuser. To measure the temperature inside and near the surface, 22 thermocouples were used inside a thick hot plate, which was impinged by a sweeping jet. Three distance ratios (X/D = 4.5, 5.5 and 7.5) and four divergence angles (θ = 180°, 50°, 70°, and 90°) were numerically analyzed as the geometrical parameters at Reynolds number of 30,000, 60,000, and 120,000. The results revealed that the heat transfer rate increased by 140% when removing the external diffuser at X/D = 4.5 and Re = 60,000, while it decreased when increasing the distance ratio and divergence angle.
查看更多>>摘要：Nowadays, the automotive air-conditioning system operating with Hydrofluoroolefin-1234yf or R1234yf refrigerant is used to reduce the global warming potential. This study aims to investigate the performance of SiO2 and Al2O3 nanolubricants with R1234yf refrigerant in the automotive air conditioning system. The polyalkylene glycol-based nanolubricant was prepared using a two-step preparation method, and the stability of the nanolubricant was assessed using visual sedimentation observation and zeta potential analysis. The experimental investigation on the performance of automotive air conditioning system with R1234yf was undertaken for the SiO2 and Al2O3 nanolubricants at different volume concentrations and various operating conditions. The system with SiO2 nanolubricant at 0.01% volume concentration demonstrated the best cooling capacity performance with an average enhancement of 15.7%. On the other hand, the highest coefficient of performance increment and power consumption reduction were attained up to 9.8% and 27.1%, respectively for Al2O3 nanolubricant at 0.05% volume concentration. The SiO2 nanolubricant performed with better cooling capacity, higher power consumption and lower coefficient of performance than the polyalkylene glycol-based lubricant. In contrast, the Al2O3 nanolubricant improved the coefficient of performance and reduced the power consumption. Since both nanolubricants provide their respective advantages, more research into integrating the two nanoparticles for refrigeration systems with R1234yf refrigerant is encouraged.
查看更多>>摘要：Despite the increasing interest in adsorption cooling and desalination systems, the poor heat hence mass transfer in the adsorbent-bed (the core component) impedes the efficient energy conversion at the system level and increases its physical footprint. In response, this paper numerically investigates the overall enhancement of adsorption cooling cum desalination system employing emerging copper foamed adsorbent beds of advanced thermal performance coated with advanced adsorbent materials to address such an untapped challenge. Silico-aluminophosphate (SAPO-34) and Nickel-based metal-organic framework CPO-27(Ni) adsorbents were employed. First, a 2-D axisymmetric computational fluid dynamic fully coupled model was developed to simulate the adsorbent-beds considering non-ideal condenser and evaporator pressures. Second, the influence of different operating conditions and copper foam thicknesses was investigated at the adsorbent-bed and system levels. The advanced adsorption kinetics of SAPO-34 enabled shortening the cycle time from 600 to 180 s, which enhanced the coefficient of performance (COP), specific cooling power (SCP), and specific daily water production (SDWP) of the system by 163%, 223%, and 228%. The regeneration temperature was the most influential parameter on the systems’ performance within the investigated range (70–100 °C). It enhanced the COP from 0.2 to 0.421, SCP from 132 to 821 W.kg?1, and SDWP from 4.7 to 29.3 m3.ton-1.day?1, for CPO-27(Ni) coated bed; and COP from 0.378 to 0.388 and SCP from 393 to 855 W.kg?1 and SDWP from 14 to 31 m3.ton-1.day?1, for SAPO-34 coated bed. The reported enhancements at the adsorption system-level signpost metal-foamed adsorbent-bed coating the most thermally efficient adsorbent-bed design.
NSTL
Elsevier