Journal of Energy Engineering

The underfloor air distribution (UFAD) system, which is a building energy-saving technology, is an air-conditioning system that enables maintenance of the indoor temperature with a relatively low supply air flow rate. UFAD has advantages compared to the conventional overhead system, which improves occupants’ comfort, health, and work efficiency, decreases life cycle cost, and improves indoor air quality, ventilation efficiency, and lay-out flexibility related to building services. Also, the floor height is reduced because a duct is unnecessary. The stratification of the UFAD system is a key factor to the system, which refers to the inconsistent vertical temperature distribution from the floor to the ceiling due to the buoyant effect of air. It plays a critical role in determining the thermal, ventilation, and energy performance. However, based on the comprehensive literature review, study on the stratification of UFAD is insufficient due to lack of understanding and actual measurement facilities related to UFAD. Therefore, this study, by using the EnergyPlus simulation and phi-gamma formula, aims to assess the stratification according to the variation of a diffuser condition. As a result, stratification of the perimeter zone was improved by diffuser condition but the energy savings was not noticeable. The floor area of the interior zone accounts for 75% of the total floor area but stratification of the interior zone was not nearly changed by diffuser condition. Also, as the stratification was improved, the wall convection heat gain increased in the interior zone. Therefore, it is considered that the cooling load was increased and the decrease of energy consumption is insignificant.

Following the massive consumption of traditional fossil fuels, the technology of concentrating solar power embedded with energy storage is becoming more and more attractive. Within this new trend, ammonia-based thermochemical energy storage is prospectively promising. The aim of this study is to simulate the ammonia decomposition reaction in a tubular reactor fully packed with homogeneously isotropic catalyst particles. Ignoring the radial heat conduction and pressure drop, a one-dimensional thermodynamic mathematical model is established to simulate ammonia conversion accounting for operating pressure and temperature, solar flux distribution, and geometric structure. It is concluded from the simulation results that the effect of the operating temperature on ammonia conversion is more predominant than the effect of the operating pressure. Furthermore, for the four styles of solar flux distribution, the distribution with the lowest effective deviation is the most suitable style for ammonia decomposition, and the efficiency is improved about 15% compared with $\sigma =0.5$. Regarding the geometric structure, the conversion rate progressively increases with diameter and length of the tubular reactor, and an optimization formula is subsequently proposed for geometric design. Ultimately, the design and optimization criterion for the tubular reactor are presented.

Agro-based biomass is a viable alternative to fossil fuels, but problems such as ash slagging, fouling, and heated-surface corrosion impose negative impacts on the process of thermal conversion of biomass. Demineralization is a pretreatment process that can be used to alleviate these problems by decreasing the ash content of biomass feedstock. In this research work, rice husk (RH) and cotton stalk (CS) were leached with three different acid solutions (${\mathrm{H}}_2{\mathrm{SO}}_4$, HCl, and ${\mathrm{CH}}_3\mathrm{COOH}$) to investigate the potential effects on the fuel characteristics of the biomass. The leaching agents dissolved the minerals present in the biomasses and reduced the ash content; however, the percentage reduction of ash content in RH ($\sim 29\%$) was lower than that in CS ($\sim 58\%$). The high heating value (HHV) of both demineralized biomasses increased due to the increase in overall carbon content; however, the percentage increase in HHV in CS was greater than that in RH. The HHV of treated RH samples increased to 16.48, 16.20, and $15.97\mathrm{MJ}/\mathrm{kg}$ when treated with ${\mathrm{H}}_2{\mathrm{SO}}_4$, HCl, and ${\mathrm{CH}}_3\mathrm{COOH}$, respectively, compared with raw RH ($15.41\mathrm{MJ}/\mathrm{kg}$). In the CS samples, the HHV of ${\mathrm{H}}_2{\mathrm{SO}}_4$-, HCl-, and ${\mathrm{CH}}_3\mathrm{COOH}$-treated samples increased to 19.80, 19.20, and 18.90, respectively, compared with raw CS ($18.38\mathrm{MJ}/\mathrm{kg}$). The thermogravimetric characterization of leached biomass showed that the demineralization with acid solutions increased the thermal stability. Fourier-transform infrared spectroscopy and scanning electron microscopy analysis illustrated that the acid leaching induced significant physiochemical structure changes in the treated biomasses. The study demonstrated that demineralization has the ability to reduce the ash content of the biomass, which improved the energy value of the biomass.

Coal and methane were mixed and burned in the moderate and intensive low oxygen dilution–oxy coal combustion (MILD–OCC) mode, flame temperature was measured at different flame locations with a rapid insert thermocouple, and soot volume fraction was obtained by thermophoretic particle densitometry (TPD). The distribution characteristics of soot in flame were obtained by combining the concentration of soot by the filter weighing method. Soot samples were collected at specific locations in the flame and analyzed with gas chromatography–mass spectrometry (GC-MS) as well as transmission electron microscopy (TEM). The results showed that the flame temperature rose first and then decreased in the radial direction, while soot mass concentration dropped and then increased in general. As to morphology of soot particles, it exhibited spherical particles separately in the lower part of flame and chain-like structures in the upper. Alkanes, olefins, phenols, furans, and aromatic compounds were determined as the main components of soot by the detection of GC-MS. The process of soot formation in the MILD–OCC flame can be speculated as coal pyrolyzes and burns at high temperature and gas precursors initiate nucleation then agglomerate and oxidize to form soot particles.

An approach to the development of sustainable buildings was explored in this paper. Sustainable buildings ultimately aim to operate at zero net energy consumption. Therefore, they are an important component in modern urban settings to counteract deteriorating air quality. This paper explored the factors influencing the wind energy exploitable by the turbine installed in channels, or tunnels, that are designed to be embedded into high-rise buildings. The investigation shed light on the design of the tunnel and the estimation of the energy output from the turbine installed in the tunnel with a certain geometry. Computational fluid dynamics (CFD) techniques were employed to study the power takeoff of the tunnel turbine under the influence of the wind incident angle, turbulence intensity, and the parameters defining the geometry of the tunnel geometry. It was shown that the wind incident angles and concentration ratios are the two most significant factors affecting the wind power takeoff. In addition, the study showed that there are optimal concentration ratios and locations at which to install a turbine inside the tunnel, which are about 0.6 and 0.33 times the tunnel length.

This paper presents the application of an artificial neural network to model the thermal behavior of some roof coatings used in buildings. A set of test cells was built to evaluate these roof coatings. The cells were placed outdoors and several parameters were measured and collected for several weeks. The measured parameters included the temperature in different parts of the test cells. Additionally, the solar irradiance, the humidity, and the wind speed were measured and stored. We designed, built, and calibrated several heat flux transducers to measure the heat flux in each cell. Further, the reflectance and emissivity of the roof coatings were measured and used to create the model. The main contribution of this work is the modeling of an experimental system to evaluate the variability of the heat flux in building roofs using histograms. A statistical analysis based on computer simulations employing neural networks was performed to analyze those parameters that affect the heat flux in the roofs the most and the least. Finally, it was found that under specific conditions small increments in the reflectance of the coating can produce significant changes in the heat flux in the roof.

Turbocharged diesel engines are extensively used in marine vessels, both as propulsion engines and as generator sets. The engine’s operation in the hostile marine environment results in performance degradation having a negative effect on the economics of the marine vessel’s operation both in terms of fuel consumption and maintenance. This paper presents a turbocharged four-stroke diesel engine simulation framework based on one-dimensional calculations and analysis. The framework is suitable for turbomachinery and heat exchanger components fault simulation predicting both turbocharger and diesel engine performance and operability. Mean-line models were used in conjunction with the beta lines method for generating accurate and detailed compressor and turbine performance maps, coupled with a single zone closed-cycle diesel engine model for generating engine performance characteristics. The simulation framework modules are adjusted and validated against measured data. Following specific faults are simulated utilizing physical consistent parameters such as blade friction and thickness based on relevant literature data. Overall system simulation and operation analysis is carried out assessing operability and performance parameters. Analysis results show a significant reduction in engine performance, especially in case of both turbo components being fouled (22% power reduction), in contrast with the heat exchanger fouling where the power reduction is about 1%.

This study reports a numerical-experimental analysis of turbulent mixed convection in a ventilated room with located heat sources. The ventilated room is modeled as a cavity. The effect of thermal convection due to the located heat sources on opposite walls of the cavity is analyzed. A parametric study was performed in a ventilated cubic cavity to consider different values of heat flux supplied by heat sources, along with two configurations for ventilation and two air inlet velocities. Five Reynolds averaged Navier-Stokes (RANS) turbulence models [standard $k\text{-}\epsilon$, realizable $k\text{-}\epsilon$, renormalization group (RNG) $k\text{-}\epsilon$, standard $k\text{-}\omega$, and shear-stress $k\text{-}\omega$] were compared with experimental temperature profiles and heat transfer coefficients. With the validated model, the effect of heat sources on temperature fields, velocity vectors, and heat transfer convective coefficients is presented and discussed. RNG $k\text{-}\epsilon$ turbulence model has the lowest average percentage differences between the experimental data and the numerical profiles with 9%. The average Nusselt numbers for heat source 1 (SH1) are between 53.72 and 182.72, while for heat source 2 (SH2), they are between 106.36 and 162.29.

In this work, three diesel–rocket propellant-3 wide distillation blended fuels (WDBF) including D80K20 [80% diesel and 20% rocket propellant-3 (RP3) by volume], D60K40, and D40K60 were prepared. The combustion and emission characteristics of neat diesel D100, D80K20, D60K40, and D40K60 were investigated in a single-cylinder diesel engine at four loads. In-cylinder pressure, fuel consumption, as well as all four emissions were experimentally measured. The results showed that the addition of RP3 in the WDBF led to longer ignition delay, shorter combustion duration, higher peak heat release rate (PHRR), and larger cumulative heat released percentage of premixed combustion phase; however, the values of maximum in-cylinder pressure and brake thermal efficiency (BTE) remained almost the same. In addition, the cyclic variations represented by the coefficient of variation (COV) of indicated mean effective pressure (IMEP) became larger especially at low load conditions. In terms of engine emissions, the soot emissions remarkably reduced, while the ${\mathrm{NO}}_x$ emissions increased slightly. The total hydrocarbon (THC) emissions increased at four loads. The CO emissions increased at light loads and decreased at high loads.

Portland cement is produced by one of the highest energy-consumptive industrial processes. Within the process, the rotary kiln represents one of the major sources of thermal energy loss. Based on the lengthwise temperature profile of the kiln, an optimal placement for heat recovery is identified based on the highest surface temperatures. This study aims to optimize the design of an arc-shaped thermal absorber parallel to the rotary cement kiln for heat recovery by thermoelectric generators (TEGs). A comprehensive numerical study is carried out by considering the combined effects of convective heat transfer, thermal radiation, and rotation of the kiln to find the optimum properties of the thermal absorber. Thus, a two-dimensional (2D) incompressible and unsteady turbulent flow horizontally perpendicular to the kiln is investigated. Different parameters such as curvature radius, arc angle, and angular position of the absorber, temperature of the kiln surface, wind velocity, and kiln rotational speed are studied for optimal design of the absorber. Multiplication of the length and average temperature of the absorber is a conceptual definition applied to explore the optimum design. On the other hand, power generation by using several commercial TEGs (size of $56\times 56{\mathrm{mm}}^2$) is evaluated for all studied absorbers. Given the kiln surface temperature of 500°C at an optimal position along the kiln, the results show that the case with the absorber radius of 2.5 m has the best performance of studied cases and can generate a total power between 26.449 and 48.889 kW, corresponding to the kind of studied commercial thermoelectric modules.

As the level of renewable and distributed energy resources (DER) increases in power systems, there is a coincident effort to ensure ongoing reliability. Microgrids are likely to play a central role in this development globally. However, a counterpoint is the high cost of microgrid operations, and there exists a need to develop efficient tools to operate microgrids optimally and economically. In this paper, the potential of demand response (DR) to reduce microgrid operation cost while supporting renewable integration is investigated. Three types of DR, namely thermostatically controlled load (TCL), deferrable load (DL), and elastic load (EL), are explored in the context of various system conditions. Because systems with significant renewables and DER are subject to high levels of uncertainty, the investigation is conducted under a stochastic rolling-horizon optimization framework that leverages the update of renewable generation forecast and the energy market real-time prices (RTP). A case study illustrates that certain system conditions, such as price peaks and moderate temperatures, facilitate best demand response performance. Conversely, inaccurate price forecast information can lead to ineffectual operation of microgrids and result in higher cost. The insights provided by the study of various types of DR are helpful for microgrid design with consumers’ preferences taken into consideration.

The regenerator of a $\beta$-type Stirling engine is simulated with computational fluid dynamics. Emphasis is given to the drop in pressure caused by friction during gas flow through the regenerator matrix. The primary results include the temporal variation of the mass-flow rate and velocity in different levels of the regenerator. A time interval of between 5% and 10% of the engine cycle was found, during which gas is flowing inward to or outward from the regenerator from both its sides. Both gas velocity and pressure drop per unit length is found to increase in hotter sections. The friction factor is extracted and correlated with Reynolds number. Furthermore, two correction factors are applied to the coefficients of viscous and inertial resistance of the Ergun equation. Finally, the temporal and spatial change of the pressure drop is examined for the studied engine. An equation that well estimates the value of the pressure drop for a given time and regenerator length is presented. The derived equation can be used as input data to improve a simple analytical model.

The cyclone-fired boiler has become a very competitive boiler type for utilizing coal with a low ash melting point and high alkali. Because of the higher combustion intensity in the cyclone barrel, good flow and combustion performances are of great significance to the safe and efficient operation of the cyclone-fired boiler. The flow and combustion characteristics in a vertical cyclone barrel were numerically investigated, which has never been done before to the author’s knowledge. The results showed that the pulverized coal particles are spun forward in the cyclone barrel driven by the tangentially rotating airflow, and the maximum velocity in the cyclone barrel is in the annular zone near the barrel wall. With the decrease in the swirl-vane angle of the primary air inlet or the increase in the particle diameter, the location where the particles collided with the barrel wall moves up along the axial direction of the cyclone barrel and the colliding chance increases. For the vertical cyclone barrel, the optimum particle diameter range is 70–110 μm, so the capture ratio of particles is greater than 99.4%.

To overcome the difficulty of cold start of a spark-ignition (SI) engine fueled with aviation kerosene, a series of experimental investigations were carried out on a port fuel injection (PFI) two-stroke engine. First, the effects of several auxiliary preheating methods, including kerosene fuel preheating, intake manifold preheating, crankcase preheating, and cylinder head preheating, were studied. Then, based on the physical and chemical properties of kerosene fuel, an optimized fuel injection and ignition control strategy was proposed. The results showed that fuel preheating and intake manifold preheating cannot ensure successful engine start. Compared with crankcase preheating, cylinder preheating is more effective for engine cold start. The optimized fuel injection and ignition strategy not only reduces the required temperature for preheating but also improves the dynamic performance of the engine cold start conditions.

In this study, a biomass briquette boiler from the Yunnan Dianhong pharmaceutical industry is considered as the research object. Using the computational hydrodynamics software FLUENT, a three-dimensional dynamic model of the boiler bed combustion is established. Based on simulation results and the accuracy of the data verification model of a field test, the effect of the air preheating temperature, bed thickness, and particle diameter on the combustion of the boiler bed is simulated by using the model. The results demonstrate that within reasonable ranges, at an air preheating temperature of 250°C, fuel bed thickness of 0.1 m, and grain diameter of 0.02 m, the sooner the bed surface gas reaches its highest temperature, the sooner the combustion is completed, and the highest temperature on the fuel bed changes more significantly with the depth. This study offers a reference model for the bed combustion of biomass briquettes and serves as a basis for the overall systematic design and optimized modeling of biomass briquette boilers.

The intensive energy requirement is a major challenge for greenhouse producers, especially those located in cold regions. An adaptive greenhouse with thermochromic (TC) material has the potential to intelligently regulate solar radiation gain of the greenhouse in response to the outdoor environment, therefore abating energy demand of the greenhouse. This study evaluates the energy performance of an adaptive greenhouse with covering materials (TC glazing, TC film, TC film–TC glazing). The simulation results reveal that compared with normal glass, energy savings reaches up to 5%, 6%, and 13% with the application of TC glazing, TC film, and TC film–TC glazing to the greenhouse, respectively; the energy cost is correspondingly reduced by 7%, 17%, and 22% respectively; and the ${\mathrm{CO}}_2$ emission is reduced by 6%, 14%, and 20%, respectively. In comparison with low-emissivity glass, the total energy saving of the greenhouse reaches up to 3%, 3%, and 11% by employing TC glazing, TC film, and TC film–TC glazing, respectively. Moreover, the increase in envelope thickness increases energy efficiency of the adaptive greenhouse to 17%. TC film–TC glazing is recommended for use in heating energy–dominated scenarios. This research framework allows designers to optimize overall energy performance of the proposed adaptive greenhouse for different climates.

The rapid growth of renewable distributed generation (RDG) requires further development of the electricity market for distributed energy. This paper proposes an energy-sharing platform as the energy management model with the distributed battery energy storage system (BESS) and RDG, and this platform can be compared with a banking system in which various kinds of energy participants, including energy users, energy generators, and energy storage devices, can transfer both energy and price. Furthermore, up-reserve (UR) is defined in the distributed BESS to quantize the charging energy value for energy management. Moreover, the pricing model is optimized by game theory with the Bayesian Nash equilibrium (BNE) algorithm, and the call-auction method is the trading mechanism with the rule of maximum transaction volume. Real historical data in the Australian electrical market were used for the case study. The participants’ profit of with-game-theory was higher than without-game-theory in this energy-sharing platform.

China’s thermal power generation has attracted worldwide attention because of its significantly high amount of carbon emissions and environmental protection measures. The focus of efficiency studies has gradually shifted from the traditional technical and cost efficiency approaches to an environmental efficiency approach. This study employs a bootstrapped directional distance function approach to measure the environmental efficiency of 24 listed thermal power generation companies in China during the period 2011–2017. To consider the influence of heterogeneity, we divide the decision-making units into groups using a metafrontier method. In addition, we perform regression analysis to identify the causal effects of heterogeneity. The results show that an efficiency gap exists among China’s thermal power companies, and there is substantial room for improvement. Enterprise age, coal density, the amount of government subsidies, and carbon emission trading policies all have negative effects on the environmental efficiency of enterprises. However, enterprise ownership and installed capacity do not affect environmental efficiency significantly.

This investigation is focused on assessing the thermal performance of a ventilated double-glass reversible window with reflective film for building applications. The window is composed of two glass sheets separated by a gap forming a channel. One glass sheet faces the external environment while the second glass sheet faces the internal environment. A solar reflective film is attached on the internal surface of the first glass sheet for hot climates or attached on the internal surface of the second glass sheet for cold climates. A home-built numerical code is developed, using the finite volume method for the discretization of conservative equations, and validated against available numerical and experimental results. The simulations were done hourly for representative days of the summer and winter seasons. Three possibilities were examined in this study: a ventilated double-glass window without a reflective film, a ventilated double-glass window with a reflective film for hot climates, and a ventilated double-glass window with a reflective film for cold climates. Based on the results, for the hot climates, the use of a reflective film is highly recommended because the ventilated double-glass window with a reflective film was able to reduce 57% of the energy gain in comparison with the same window without a reflective film. For cold climates, the ventilated double-glass window without a film is better than the same window with a reflective film.

Power system resilience requires highly effective self-healing restoration strategies, and calls for superior performance both in system restoration and operation. Most existing restoration methods focus only on restoring performance, such as generation capacity, restored load capacity, and recovery time, but ignore operating performance that can enhance resilience significantly. This paper sheds light on a two-stage self-healing system restoration strategy considering operating performance, which includes voltage balance, transmission loss, and generation cost, to enhance resilience. The first stage aims to determine the restoration sequence of generators, power lines, and loads with maximum restored load capacity. The second stage of the optimization problem focuses on readjusting the power outputs of generators to improve single or multiple operating performance indicators. The optimization model of the first stage is formulated as a linear integer programming (IP) problem and solved by the branch-and-bound method, while the second-stage problem considering AC optimal power flow is solved by the interior point method. The proposed two-stage strategy also provides a possible solution for an online restoration decision support system with superior computational performance. Case studies on the IEEE 30-bus and 118-bus power systems have demonstrated the correctness and effectiveness of the proposed strategy.

The performance of lithium-ion batteries used in electric vehicles (EVs) is greatly affected by temperature. Hence, an efficient battery thermal management system (BTMS) is needed to ensure the safety of batteries and prolong the cycle life. In order to find a more efficient type of cooling plate for the rectangular batteries, the three-dimensional models of four common cooling plates with different internal structures are established. After a series of computational fluid dynamic simulations and comparisons, the most optimum structure of the cooling plate is obtained. Subsequently, the effect of different mass flow rates is investigated among the different cooling plates. It indicates that the cooling plate with convex structure has a better cooling performance than the other three, and the heat transfer performance of various cooling plates changes a lot with the increasing of mass flow rate. The convex structured cooling plate could be applied for optimizing the performance for electric vehicles.

This paper proposes an analytical model to predict the maximum altitude adaptability of a turbocharging diesel engine. First, the influence of the turbocharging system parameters on the diesel engine performance at different altitudes was analyzed by using an experimental method. The results showed that the engine power decreased dramatically at higher altitude owing to the enlarged energy gap between the available flow energy fed to the turbocharging system and the energy required for the full power recovery. On this basis, an analytical model was established. The model results indicated that the altitude adaptability of the turbocharged diesel engine was determined mainly by three dimensionless parameters, namely the (1) compressor pressure ratio at sea level, (2) turbocharger efficiency multiplied by the ratio of the turbine inlet temperature to the compressor inlet temperature at sea level, and (3) ratio of the turbocharger efficiency at plateau to the turbocharger efficiency at sea level. Next, the maximum altitude adaptability of a turbocharged diesel engine was predicted using these three dimensionless parameters. Finally, the prediction results were validated by comparison with the experimental data. This model can be used to predict whether the engine power can be fully recovered at the studied altitude range before optimizing the turbocharging systems to realize the engine power recovery.