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Supercritical carbon dioxide (SCO2) technologies have been under the spotlight of developed countries because they believe that such applied sciences can be ingenious solutions to resolve energy and environmental problems. The SCO2 power cycle is one of the most promising technologies in this field due to its high efficiency and low expenditure. However, optimal designs of heat exchange devices are a vital issue in the SCO2 power cycle because they account for almost 80% of the capital costs. In this study, the comparison of diverse combinations of convergent and divergent minichannels inside the low temperature recuperator (LTR) and high temperature recuperator (HTR) is suggested to recognize the strengths and weaknesses of nonuniform minichannels at high operating pressures and temperatures. Three-dimensional conjugate simulations are carried out, and existing data in the literature are used to validate the obtained results. The comparison reveals a slight deviation (less than 10%) in temperature and pressure profiles. After the evaluation of the studied cases in terms of thermal and hydraulic characteristics, different criteria are employed to explore optimal combinations of the hot side and cold side minichannels. Totally, the minichannel convergence enhances thermal performance of recuperators (up to 26%), and their divergence improves the hydraulic behavior. Nonetheless, diverging the minichannels imposes greater positive effects than converging them. The overall analysis specifies that the most efficient LTR and HTR would be attained by diverging the hot side minichannel, while the cold side minichannel is kept unchanged. This combination of minichannels allows reaching the highest SCO2 temperature at the outlet of LTR and HTR (456 K and 656 K) with the minimum pressure drops (around 0.02% of inlet pressures) and achieving the best performance indexes (approximately 2). Finally, the comparative study discloses that at low Reynolds numbers (less than 14000 for the hot side and 10000 for the cold side), the nonuniform patterns of minichannels perform better than the complicated structures, such as zigzag, wavy, and other optimized geometries. The average performance enhancements for the hot and cold sides are 36.3% and 37.4%, respectively.

Emulsion absorbents based on NaOH solution (ES–NaOH) consist of carbon nanotubes (CNTs) and silicone oil. ES–NaOH can control the CO2 capture capacity and rate with the concentration of CNTs and NaOH, and can be applied indoors like an adsorbent.

In this study, a CO2 capture material in the form of liquid-like adsorbents (LLAs) is developed to overcome the limitations of conventional types of adsorbents. The increase in indoor activities necessitates the capture of CO2 in enclosed indoor spaces. Indoor spaces require safe and stable materials for CO2 capture because humans are present in these spaces. Solid adsorbents are mainly used because liquid absorbents are unsuitable owing to noise and scattering problems. In LLA, the liquid absorbent assembled by carbon nanotubes (CNTs) is solidified and prevented from flowing and scattering indoor. LLAs present to maintain 95% of initial capacity after recycling 20 times, and have characteristics that can be regenerated in a low temperature heat source (80 to 120 ℃) and moisture resistance. This work not only provides indoor useable CO2 capture materials, but also offers a new prospect in the field of adsorbents.

In this study, an optimal design was proposed for the pressure drop of a high-temperature steam generator to enhance hydrogen production in a solid oxide electrolyzer cell (SOEC). The high-temperature steam generator (HTSG) was analyzed under experimental conditions of a steam temperature of 773 K, steam inlet pressure of 300–600 kPa, and steam flow rate of 10–35 kg/h. The pressure drop characteristics of the HTSG were analyzed under various variable conditions via a computational fluid dynamics simulation. The pressure drop according to the variable change was ranged from a minimum of 54 kPa (inlet nozzle angle: 25°) to a maximum of 309 kPa (body ratio: 0.63), and the valid range was 28,700 < Re < 306,600 . The hydrogen production capacity that can be produced utilizing the optimally designed HTSG was predicted to be up to 35.7 tons annually. In addition, CO2 emissions during hydrogen production under optimal conditions are 9.92 ton-CO2/ton-hydrogen, which can be reduced by up to 86.8% compared to the conventional high-temperature and high-pressure (HTHP) steam, thereby enhancing hydrogen production and energy harvesting.

The energy consumed for CO2 capture in processes that capture, store, and utilize carbon frequently approaches 80% of the total energy consumed, and its reduction is a major area of focus. Herein, a system that captures CO2 from flue gas to produce electricity is proposed. The exothermic reaction heat of amine-CO2 in the point-source CO2 capture process is harvested and converted into electricity using a thermoelectric (TE) device. The reaction heat of synthesized amine-functionalized mixtures (TEPA@SBA/MEA+PZ) is 52% higher compared with that obtained from the primary amine absorbent. The flue gas channel and solvent reservoir are separated using a membrane composed of tetraethylenepentamine-impregnated poly (ethylene glycol) dimethacrylate that selectively permeates CO2, to minimize heat loss due to mass transfer. The CO2 working capacity of TEPA@SBA/MEA+PZ is 6.6 mmol/g, which is defined as the capture capacity under steady-state conditions of 15 mol% CO2 and 85 mol% N2. Simultaneously, electricity can be harvested at a rate of 7.5 kJ/kg with a TE device composed of Bi2Te3. When put to industrial use, the proposed system can reduce the CO2 emission of power plants from 0.8 ton/MWh to 0.25 ton/MWh, while simultaneously generating an additional 0.6% of the total electricity production.

Power efficiency of photovoltaic (PV) cell is significantly affected by the cell temperature. Herein, a passive cooling unit comprising inexpensive materials is developed for perfromance improvement of the PV cell. The water-saturated zeolite 13X is coated on the back side of the PV cell, and ammonium nitrate is dispersed as a layer. When thermal radiation is supplied, water is desorbed from zeolite 13X (primary latent cooling), and also dissolves ammonium nitrate to induce secondary endothermic reaction cooling. The cooling unit is operated based on the moisture sorption performance of mesoporous materials, which is inversely proportional to the cell temperature, and the solubility of endothermic reaction pairs increases proportionally with temperature. It is a reversible process in which ammonium nitrate is crystallized when the temperature is low at night, and water is adsorbed back to zeolite 13X. The average temperature of the PV cell can be reduced by approximately 14.9°C during the day, and the cooling energy density reaches 2,876 kJ/kg. Based on the life cycle cost analysis, the cost of power generation can be reduced by 5.1%, and the power efficiency is improved by 7.5%. A PV cell with the passive cooling unit will be a solution for efficient PV electric generation.

Nanoemulsion absorbents are manufactured using methanol and undecane for CO2 absorption and regeneration performance enhancement. The most representative physical CO2 absorbent, methanol, is mixed with undecane and dispersed by the ultrasonication method. Span 60 and Tween 60 are used to obtain a high dispersion stability. To determine the effect of undecane concentration on the combined heat and mass transfer performance during the absorption and regeneration processes, various concentrations of nanoemulsion absorbents are prepared. The thermal conductivity of the nanoemulsion is also measured to estimate the effect of nanodroplets on the heat transfer performance. It is concluded that the average absorption rate increases by 13.04% at 0.05 vol% of undecane and the average regeneration rate does by 22.03% at 0.05 vol% compared to the base absorbent. Various mechanisms for combined heat and mass transfer performance enhancement by nanoemulsion absorbents are discussed. It is concluded that the mechanism of regeneration performance enhancement by the thermal effect in the nanoemulsion absorbents is less effective compared to that in the nanofluid absorbents.

The objectives of this study are to present a comprehensive analysis of the CO2 bubble population dynamics and to investigate their effects on the CO2 absorption characteristics in nanoabsorbents (methanol with various concentrations of Al2O3 nanoparticles) with a rectangular bubble column. The population balance model (PBM) as a well-established method based on the Euler-Euler model is employed to compute the size distribution of bubbles and to account for the bubbles coalescence and breakage in multiphase flow. The coupled volume-of-fluid (VOF) method is selected to clearly capture the coalescence and breakup processes of successively rising bubbles. The results show that there is a significant influence of the leading bubble on the following one, including the increment of the velocity, the deformation of the bubble shape and the flow instability. It is also found that the critical distance at which the influences can be exerted is related to the bubble wake trailed by the leading bubble. Accordingly, five types of bubble wakes and their effects on the bubble behaviors such as the coalescence and breakup are categorized. Finally, by further analyzing the bubble behaviors in methanol with different volume fraction of Al2O3, it is found that the coalescence and breakup of bubbles are dominated by the bubble wake and enhanced by the eddy in local liquid. It is concluded that the higher concentration of nanoparticles is favorable to the bubble coalescence and breakup, which enhance the mass transfer performance by increasing the interfacial area.

Based on growing demand for the CO2 capture issue, CO2 hydrate formation/dissociation technologies for carbon capture have been highly spotlighted. CO2 hydrate can be applied to the cold thermal energy storage since CO2 hydrate has relatively higher dissociation enthalpy (459 kJ/kg) than ice slurries (333 kJ/kg). In this study, a lab-scale cold thermal energy harvest and transportation system using the CO2 hydrate is tested. This system contains both hydrate formation and dissociation processes to study the effects of each component on the cold thermal energy harvest and transportation applications. Tetrahydrofuran (THF) based absorbents with various concentrations of tetrahydrofuran is produced and applied to the CO2 hydrate system. COP (coefficient of performance), required work, heat transfer rate, and density of hydrate slurry are measured to improve the cold thermal energy harvest and transportation performances of the CO2 hydrate system. The performance of CO2 hydrate system is evaluated under various experimental conditions such as temperatures, pressures, and tetrahydrofuran concentrations. From the experimental results, it is found that the COP of 7.03 is obtained under tetrahydrofuran concentration of 1.5 mol% and formation pressure of 4 bar. It is also concluded that the CO2 emission of the CO2 hydrate system is estimated to be 7986 tCO2/year, which is 31.3% of the conventional district cooling system with the cooling capacity of 51,600 RT.

A new experimental approach that can enhance the heat transfer performance of spray cooling is provided in this study. The spray cooling experiments are performed on micro-structured surfaces combined with inclined spray flow in a near-vacuum chamber. Water spray is produced by a solid single pressure swirl nozzle. Three different micro-structured surfaces with rectangular fins, trapezoidal fins and triangular fins are tested with the spray angles of 0°, 9°, 18°, 27° and 36°. The prominent advantage of the enhanced surfaces is the capillary force produced by the microgrooves, and the net driving force is the inherent feature of the spray inclination. The combination of these two forces significantly enhances heat transfer performance by promoting lateral spread of the liquid and surface membrane renewal. It is found that the rectangular straight finned surface has the best heat transfer performance at an inclination angle of 18°, where the maximum surface temperature is about 53 °C and the maximum heat transfer coefficient is 2.5 W/cm2 · K , with an enhancement of 20% compared to the vertical spray. The coupled effect of inclination spray and low chamber pressure can significantly reduce the maximum temperature difference on the rectangular finned surface with an almost 16% decrease rate.

In this study, heat transfer characteristics of single-phase Water/Lithium Bromide (H2O/LiBr) solution in a plate heat exchanger (PHE) is evaluated for absorption chiller applications. The plate heat exchanger is arranged with single-pass and counter flow, and the chevron angle of corrugated plate is a high theta of 78.5°. The H2O/LiBr solution is used as working fluid with wide mass concentration ranging between 52.40% and 64.92%, Reynolds number ranging between 27.29 and 255.1 and Prandtl number ranging between 4.59 and 19.26. All of experiments are conducted within ±10% energy balance error range. It is found that the convective heat transfer coefficients range from 0.68 kW/m2·K to 2.92 kW/m2·K. Based on the experimental data, empirical Nusselt number correlation of the H2O/LiBr solution in the 78.5° plate heat exchanger is developed within ±20% error range. The Nusselt number correlation of the present study is applicable to predict the heat transfer characteristics of the H2O/LiBr solution with a wide range of LiBr concentration for triple effect absorption chiller applications.

In this study, condensation heat transfer performance and frictional pressure drop in plate heat exchanger using a low GWP refrigerant R-1233zd(E) as a working fluid are experimentally analyzed. Experiments on single phase water-to-water are also conducted in the tested plate heat exchanger, and the heat transfer coefficient correlation of the cooling water side is derived by applying the modified Wilson plot technique. In the refrigerant-to-water experiments, the influences of heat flux, refrigerant mass flux, and saturation pressure on the heat transfer and pressure drop in the tested plate heat exchanger are analyzed with varying the mean vapor quality. Experimental results show that the heat transfer coefficient increases with increasing the heat flux, mean vapor quality, and the mass flux while it decreases with increasing the saturation pressure. On the other hand, the frictional pressure drop increases with increasing the mass flux and mean vapor quality while it decreases with increasing the saturation pressure. Experimental correlations for predicting Nusselt number and friction factor of R-1233zd(E) in plate heat exchanger are developed and compared against other correlations from literature.

Among the CO2 capture technologies, the physical absorption is one of the most common absorption methods. However, the physical absorption process is operated at extremely low temperature, and therefore huge freezing energy is required. The objective of this study is to develop the nanoemulsion absorbents that can be operated at room temperature. The nanoemulsion absorbents are prepared by the ultrasonication method. Based on the chemical properties, Span 60 and Tween 60 are added to maintain a good dispersion stability. CO2 absorption experiments using a porous nozzle absorber are conducted for various dodecane concentration (0.005–0.5 vol%) and CO2 flow rate (0.06–0.12 g/s). It is found that the CO2 absorption performance of 0.05 vol% nanoemulsion absorbents is 10% higher than that of pure methanol. Through the single CO2 bubble absorption visualization experiments, it is confirmed that the nanoemulsion absorbents cause faster bubble absorption than pure methanol does. The turbidity index (Nephelometry turbidity unit) of nanoemulsion absorbents is kept constant for seven days, which means a good dispersion stability. The enhancement mechanism of CO2 absorption is explained based on the Einstein-Stokes’ equation, cryogenic transmission electron images, and droplet size measurements. The key idea is that nano-sized dodecane (64 nm) absorbs the CO2 molecules and transports it to the bulk region by the Brownian diffusion. A random walk model is used to investigate the droplet size prediction and CO2 absorption performance enhancement.

The manufacturing industry has recently been focusing on improving energy efficiency to reduce greenhouse gas emissions and achieve sustainable growth. The focus is on combining existing energy technologies with new information and communication technologies as the Fourth Industrial Revolution approaches. Dyeing and finishing shops use the most energy in the textile industry and have below-average energy efficiency because of low technology and facility investment. Research into increasing the energy efficiency of dyeing and finishing shops has concentrated on developing equipment; however, it is difficult for small- and medium-sized factories to benefit from these advances. Thus, research into means of improving energy efficiency by improving the process and system efficiency of dyeing and finishing companies, who have difficulties with facility investment and operation, is necessary. In this study, a cyber physical energy system that improves the energy efficiency of the dyeing process by collecting and analyzing manufacturing big data was developed. Further, the implemented system was applied to actual dyeing and finishing shops, and its effects were verified. This research contributes to improving the situation of the dyeing process using machine learning techniques and manufacturing big data by adjusting cyber physical energy systems without utilizing expensive equipment. Inaccurate process instruction from the laboratory are also replaced by the cyber physical energy system, and the invalid and inefficient steps in the traditional process scenario derived from operator’s experience are replaced with more valid and usable actions.

In this work, an improved VOF-PLIC model is developed to simulate 3D bubble behavior and to analyze the mass transfer characteristics for CO2 absorption in pure methanol and methanol with Al2O3 nanoparticles. The lower bound boundary value of CO2 volume fraction( α g ) is redefined according to the influence of α g on bubble shape and diameter as well as the interfacial area between gas and liquid. In addition, a reasonable drag force is added into the momentum equation using UDF code based on the assumption that the drag force only exists in liquid phase. It is found that the level lines of bubbles with the α g value of 0.05 agree well with the real case, and the drag force has significant influence on the bubble behavior and mass transfer characteristics. The velocity contours and pressure gradients around the bubble are proposed to analyze the influence of drag force on the mass transfer characteristics. Also, the influence of the Al2O3 nanoparticles on the mass transfer enhancement is studied, and the results show that the dispersed particles can significantly enhance the mass transfer by increasing the gas–liquid interfacial surface renewal frequency.

Ensuring sustainability is a primary concern of the manufacturing industry. Not only does the enhancement of process and systematic efficiency secure sustainability through increased energy efficiency but it also improves the efficiency in terms of overall productivity. Dyeing and finishing industries consume massive amounts of energy and have large energy-related expenditures. The industry comprises small- and medium-sized enterprises, which have insufficient capital to pay for the energy-efficient equipment. This study proposes a service-oriented platform that can achieve process and systematic efficiency enhancement based on the industrial Internet of Things (IIoT). The platform reflects the requirements of dyeing and finishing shops in the industry and secures effective interoperability and services using a service-oriented architectural design. A smart operation enabled by the service-oriented platform to improve the efficiency of traditional processes is developed. The system architecture, P...

The accelerated control cooling is considered to be one of the most practical technologies in the high tensile strength steel manufacturing industry. In order to achieve a high precision required for the cooling process, the system modeling should be done and optimized by considering the heat transfer mechanism as much as possible. For the system optimization, the parametric analysis for the influence factors such as feed water temperature, plate speed, plate width and specific heat should be carried out. In this study, we focus on optimizing the influence factors during water cooling of high temeperature plate by the accelerated control cooling process. The scale analysis with Reynolds and Prandtl numbers is made to optimize the effect of feed water temperature, and then the water flow density is determined during the water cooling process. The cooling efficiency is calculated in order to optimize the plate speed and plate width. Finally, start cooling temperature(SCT) and finish cooling temperature(FCT) are optimized by comparing the specific heat of standard references about low carbon steel such as NIST-JANAF, Eurocode, ISIJ. It is concluded that the accuracy of the predicted finish cooling temperature and the stability of the cooling process are significantly improved after the optimization of influence factors.

In this paper, the various optimized generators for H2O/LiBr absorption chiller with multi-heat sources are discussed. While the previous optimization has been mainly conducted for a single element, the integrated generation system including high/low temperature generator and waste heat recovery generator is optimized in this paper. A practical modeling method is proposed for the high/low temperature generator and it has been verified by comparing with experimental results. Meta-models for the volume and the generation rate are built with kriging method, and the generators are optimized by multi-objective optimization technique using the meta-models. The total volume is minimized and the total generation rate is maximized according to five design variables of the generators. It is found that from the optimization process the total volume is decreased by 59.06% and the total generation rate is increased by 31.46% compared to the baseline point. It is concluded that the contribution of the waste heat recovery generator and the high temperature generator are dominant for the total volume reduction and the total generation rate improvement, respectively. Moreover, the effects of the key variables on the performance of each generator are analyzed according to the optimization of the integrated generation system.