Minimum Thermal Energy Research Articles

Energy parameters of corn drying in a hot air dryer powered by exhaust gas waste heat: An optimization case study of the food-energy nexus

This paper presents the energy parameters of corn drying in a convective crop dryer powered by exhaust gas waste heat. The empirical study was applied for drying 1,500 g batch size of an indigenous variety of maize grains (corn kernels). The study considered the impact of the drying air temperature and velocity on the energy indices (total and specific energy consumption, electric and thermal energy demand), drying rate, of the crop dryer, and the moisture diffusion coefficient of the studied samples. Tests were run at varying drying air temperatures (50, 55, and 60 °C) and air velocities (1.0, 1.5, and 2.0 m/s). Results obtained show that the drying parameters had a noticeable influence on the rates of heat transfer and moisture diffusion in the maize samples. The average drying rates varied between 0.83 and 1.4 g/min, whereas drying duration ranged from 305 to 515 min. The thermal efficiency of the drying process ranged from 4.23% to 8.07%. Its values had a direct relationship with the drying air temperature and an inverse relationship with the drying air velocity. The specific energy consumption, which varied between 129.95 and 227.63 kWh/kg increased with increasing air temperature and velocity. Drying air temperature had an inverse effect on the values of the electric energy consumption of the dryer system at constant air velocity. The maximum and minimum thermal energy values were obtained as 97.12 and 55.4 kW-hr, respectively. The activation energy and moisture diffusion coefficient values were in the range of 31.75 to 41.05 kJ/mol and 5.77×10−11 to 1.11×10−10 m2/s, respectively for the studied drying conditions. Prospects for commercial applications as well as recommendations for additional studies were stated.

Mathematical Analysis of Two Phase Saturated Nanofluid Influenced by Magnetic Field Gradient

Nanofluids are composed of nano-sized particles dispersed in a carrier liquid. The present investigation’s aim is to examine theoretically the magneto-thermomechanical coupling phenomena of a heated nanofluid on a stretched surface in the presence of magnetic dipole impact. Fourier’s law of heat conduction is used to evaluate the heat transmission rate of the carrier fluids ethylene glycol and water along with suspended nanoparticles of a cobalt–chromium–tungsten–nickel alloy and magnetite ferrite. A set of partial differential equations is transformed into a set of non-linear ordinary differential equations via a similarity approach. The computation is performed in Matlab by employing the shooting technique. The effect of the magneto-thermomechanical interaction on the velocity and temperature boundary layer profiles with the attendant effect on the skin friction and heat transfer is analyzed. The maximum and minimum thermal energy transfer rates are computed for the H2O-Fe3O4 and C2H6O2-CoCr20W15Ni magnetic nanofluids. Finally, the study’s results are compared with the previously available data and are found to be in good agreement.

Theoretical Minimum Thermal Load in Buildings

Summary Building cooling and heating accounts for a large portion of total global energy use and requires commensurate amounts of resources, which contribute significantly to global warming. Traditionally, addressing this issue has meant improving the efficiency of equipment supplying the thermal energy, reducing envelope heat transfer, and reducing air infiltration. However, this approach is already reaching practical limits. In this perspective, we explore (1) how to reduce thermal load in buildings theoretically and (2) how to achieve that reduction and dramatically lower the energy required to support building loads practically. First, we discuss our framework developed for calculating the theoretical minimum thermal load (TMTL) in buildings. Our analysis shows that current thermal loads in buildings are more than an order of magnitude higher than the TMTL. We also introduce an approximate formula to calculate energy savings from zonal control of thermal load, which shows that the majority of zonal control benefits can be achieved with fewer than 10 zones. Then, we discuss pros and cons of various approaches and strategies to achieve the TMTL. We conclude our perspective with some longer-term R&D ideas, such as thermally adaptive clothing and thermal storage to help approach the TMTL, while providing the additional benefit of interacting with the renewable grid of the future.

PSACONN mining algorithm for multi-factor thermal energy-efficient public building design

This paper presents a multi-factor framework in order to investigate the effects on thermal (heating and cooling) energy consumption of the climate and building envelope for buildings in the design stage. This framework, called “PSACONN Mining”, is based on the Particle Swarm Optimization (PSO), Ant Colony Optimization (ACO), and Artificial Neural Network (ANN), with data mining techniques. It was aimed to find envelope combinations that provide minimum thermal energy consumptions for each climate. Firstly, attribute reduction was applied for climatic parameters according to thermal energy consumptions in order to provide more consistent results by eliminating irrelevant attributes. Then, energy simulation models were generated by using a certain number of building envelope combinations, which consist of various building materials. Finally, an ANN model based on PSO and ACO (PSACONN) was used in order to determine the most suitable envelope combinations by utilizing the reduced climate attributes and related envelope combinations along with thermal energy consumptions obtained through the simulation. PSO and ACO algorithms were used in order to train the ANN structure more appropriately by generating more consistent weight and bias matrices. The framework was applied to a public building in the design phase. It was observed that feature reduction improved the correlation between climate characteristics and thermal energy consumption by values of 0.98 and 0.96, respectively. When the heating and cooling consumption values obtained with the proposed framework are compared with the simulation values; The accuracy of the estimates for the heating and cooling energy consumption is above 99% and 98%, respectively. It is obviously demonstrated that, for different climate regions, the use of the proposed methodology gives effective results in finding envelope combinations that provide minimum thermal energy consumption.

Thermodynamic modeling and energy analysis of a polyamine-based water-lean solvent for CO2 capture

Amine-based water-lean solvents are considered to be promising energy-saving alternatives to existing aqueous amine solvents for CO2 capture. Herein, we propose water-lean solvents comprising 3,3′-iminobis(N,N-dimethylpropylamine) (60 wt%), water (10–18 wt%), and a non-amine chemical (balance), probe the solubility of CO2 therein, and perform the energy demand analysis using an Aspen Plus®-based simulator. For CO2 solubility modeling, the e-NRTL model and Redlich-Kwong state equation were incorporated with the equilibrium reaction model proposed by previous researchers, and the Henry’s law constant of CO2 was estimated using molecular dynamics simulation as it is difficult to measure experimentally. Experimental data acquired using an equilibrium cell and 13C/1H NMR were used to regress the equilibrium reaction model. The minimum thermal energy demand under desorber pressures of 303 and 505 kPa was calculated to be as low as 1.99 and 1.95 GJ t-CO2−1, respectively, which supports the suitability of the developed WLSs for post-combustion CO2 capture.

Effect of Inner and Outer Horizontal wall Heating on Porous Duct

Heat Transfer analysis in a square porous annulus is conducted with respect to heating of 4 inner walls along with outer horizontal walls and cooling of outer vertical walls cooling. Darcy law along with Boussinesq approximation is applicable. Two phases of porous medium such as solid and fluid phase are in thermal equilibrium. The governing equations are approximated using Galerkin method and converted into algebraic equation using finite element method. The fluid is found to flow in vertical cells along left and right half of duct. The top section of duct is found to have minimum thermal energy as compared to other parts of duct.

Design guidance for an energy-thrift absorption process for carbon capture: Analysis of thermal energy consumption for a conventional process configuration

The development of an energy-thrift carbon capture process to reduce atmosphere CO2 emissions is an urgent need; however, comprehensive and systematic design guidelines for energy-minimized gas separation processes are not easily available. This study aims to understand the fundamentals of thermal energy usage in an absorption system and provide quantitative and integrated guidelines to design a minimum-energy-demanding, absorption-based carbon capture process using aqueous solvents. Solvent capacity and absorption performance are the most important factors, whereas the heat of reaction, considered important in many studies, is actually not a critical factor to determine the thermal energy usage. The shape of the vapor–liquid equilibrium curve also has a significant effect on the regeneration energy. When designing a minimum thermal energy process, the cyclic capacity, absorption performance, and heat of reaction should be considered simultaneously rather than separately because they affect the total thermal energy demand interactively. The minimum achievable regeneration energy in an absorption-based process with a typical process configuration for coal-fired plant flue gas was estimated as 2.3–2.5GJ/t-CO2 with an optimized heat of reaction of approximately 60–70kJ/mol-CO2. Brief analysis of the equivalent work up to the compression stage was also made, and the relationship with the thermal energy is discussed. The fundamentals learned through this study can be extended to other absorption-based gas separation processes.

탄화붕소 소결 거동 연구를 위한 율속제어소결의 적용

Under rate-controlled sintering, furnace power is controlled to maintain a specific specimen contraction rate. This thermal processing method guarantees continuous process with a minimum thermal energy applied over time and makes it possible to control the density of the sintered body precisely. In this study, the rate-controlled sintering is applied to the sintering of B C in order to investigate how rate-controlled sintering variables can affect the sintering behavior and/or grain growth behavior of B C and how the results can be interpreted using sintering theories to draw an optimal sintering condition of the rate-controlled sintering. Further, the applicability of the rate-controlled sintering into the study for sintering of unknown materials is also considered.

Pilot demonstration of concentrated solar-powered desalination of subsurface agricultural drainage water and other brackish groundwater sources

The energy–water nexus is addressed with the experimental demonstration of a solar-powered desalination process system. This system was designed for high-recovery treatment of subsurface agricultural drainage water as a reuse strategy as well as other brackish groundwater sources. These water sources may exhibit wide fluctuations in salinity and makeup and pose a high risk for operational troubles due to high scaling potential. A first-of-its-kind open-cycle vapor-absorption heat pump is coupled with a multiple-effect distillation train and a large parabolic trough solar thermal concentrator. Without the heat pump, the distillation operation showed a minimum thermal energy consumption of 261.87kWhth/m3. With the heat pump, the thermal energy consumption was reduced by more than 49% to 133.2kWhth/m3. This reduction in thermal energy requirement directly translates into a 49% reduction in solar array area required to power a process with the same freshwater production rate as a system without an integrated heat pump. An optimized design was modeled and the thermal energy performance of a commercial system is projected at 34.9kWhth/m3 using a 10-effect MED operating at 85% recovery.

Balancing energy efficiency and structural performance through multi-objective shape optimization: Case study of a rapidly deployable origami-inspired shelter

For military and disaster relief housing, rapidly deployable shelters must be lightweight, be packaged in a small volume for transportability, and be erected without heavy lifting equipment. A critical design criterion is also energy efficiency in heating and cooling. To meet these priorities, the research team has utilized origami as inspiration for a thermally insulated rigid wall deployable shelter that can be erected manually through counterweighting. To enhance energy efficiency, improvements in the shape of a structure (i.e., member lengths and angles) at a design stage can lead to savings throughout its lifecycle. This is magnified in the context of mass-production of deployable shelters, where any improvements are multiplied. Structural efficiency is also critical to achieve lightweight design. This paper presents a multi-objective shape optimization methodology which balances the priorities of structural performance (i.e., minimum deflections) and energy efficiency (i.e., minimum thermal energy load). This is demonstrated for the case study of a deployable shelter. Design variables include geometric parameters. Constraints relate to the package size and capability of interfacing with existing technologies. Structural analysis is performed using a parametric finite element program. Thermal energy is calculated using EnergyPlus. An optimized solution is found and compared against existing military solutions.

Femtosecond laser micromachining of silicon with an external electric field

Femtosecond (fs) lasers have been shown to be superior to long-pulse lasers in micromachining a wide range of materials. The ultrashort pulses and their extremely high peak power lead to minimum thermal energy diffusion into the material and ensure fast heating and vaporizing of materials with reduced melting. Therefore, fs laser micromachining results in a much reduced heat-affected zone of the machined surfaces. However, plasma generation is normally associated with fs laser processing due to the substrate material breakdown. The plasma cloud may fall back onto the substrate as debris on the surface. In the case of fs laser micromachining of silicon (Si), a large number of micro/nano-sized particles are observed on the Si surface. Some of the particles are loose particles that can be easily removed. The remaining particles are however bonded to the substrate that cannot be cleaned off. For microelectronics applications, such surface contaminants affect the reliability of the device and have to be avoided. In our study, we employed an external electric field during the fs laser micromachining. It was found that the external electric field strength had a significant effect on the cleanliness of the machined Si surface.

CO 2 capture from power plants : Part I. A parametric study of the technical performance based on monoethanolamine

Capture and storage of CO 2 from fossil fuel fired power plants is drawing increasing interest as a potential method for the control of greenhouse gas emissions. An optimization and technical parameter study for a CO 2 capture process from flue gas of a 600 MWe bituminous coal fired power plant, based on absorption/desorption process with MEA solutions, using ASPEN Plus with the RADFRAC subroutine, was performed. This optimization aimed to reduce the energy requirement for solvent regeneration, by investigating the effects of CO 2 removal percentage, MEA concentration, lean solvent loading, stripper operating pressure and lean solvent temperature. Major energy savings can be realized by optimizing the lean solvent loading, the amine solvent concentration as well as the stripper operating pressure. A minimum thermal energy requirement was found at a lean MEA loading of 0.3, using a 40 wt.% MEA solution and a stripper operating pressure of 210 kPa, resulting in a thermal energy requirement of 3.0 GJ/ton CO 2, which is 23% lower than the base case of 3.9 GJ/ton CO 2. Although the solvent process conditions might not be realisable for MEA due to constraints imposed by corrosion and solvent degradation, the results show that a parametric study will point towards possibilities for process optimisation.

The Viability of Thermal Energy Storage

With rising energy costs and an increasing demand for renewable energy sources, thermal energy storage (TES) systems are becoming an interesting option. TES is a key component of any successful thermal system and a good TES should allow minimum thermal energy losses. In this study, various ways of thermal conservation are outlined and discussed, both theoretical and experimental. In this respect, the TES systems and their practical applications and some selection criteria have also been given.

A Tool-Temperature/Tool-Life Relationship Covering a Wide Range of Cutting Data

The paper shows that maximum tool-life, or minimum temperature, for any given metal removal rate of a cutting tool or grinding wheel is governed by the principle of minimum thermal energy, resulting in one single relationship between metal removal rate per unit cutting edge length and tool-life, or temperature, for each tool - work combination. A tool temperature relationship, of the same form as the author's tool-life relationship, is derived, the constants of which can be calculated from temperature tests and two tool-life calibration tests.

Factors Affecting Static Stratification of Thermal Water Storage

Abstract The thermal storage is a key component of any successful solar thermal system. A good thermal storage should allow minimum thermal energy losses while permitting the highest possible extraction efficiency of the stored thermal energy. Despite the many available examples of successful designs of solar thermal storage tanks, the static behavior of the solar thermal storage is not fully understood. Among the many factors influencing such behavior are heat losses, tank geometry, dead zones, and tank wall material. In this study laboratory-scale models with different geometries were built for the purpose of examining thermal behavior during the period after charging. During this period, called the thermal diffusion period, the extraction efficiency was temporarily decreased until natural stratification was achieved. After the thermal diffusion period, the extraction efficiency decreased primarily as a result of thermal losses to the environment and thermal degradation caused by the storage tank walls....

Microscopic bubble formation and collapse at liquid-solid interfaces during electrical powering of thin film structures

New technologies often require innovative testing and analysis. Thermal ink jet printing, in which operation is contingent on vapor bubble generation at a thin film-liquid interface, represents such a technology. A laser deflection technique is introduced which allows for the in situ study of the mechanisms important to printing. This technique enables the measurement of the minimum thermal energy needed to generate a kinetically vigorous bubble as a function of electrical pulsewidth as well as the observation of several distinct bubble configurations. It is demonstrated that variations in device fabrication affect minimum energy requirements, enabling a comparative test of thin film materials and structures. Regimes of bubble nucleation vs. growth control for different sample configurations have also been pinpointed, thus enabling successful parameter selection for optimal device operation. Coupling this information with scanning electron microscopy examination of low-cycled samples and relevant electrical and optical testing allows for the identification of the criteria for thin film longevity in this unique application.

Physical Properties of Clouds

Results of tests on physical evaluations; evaluations included: precipitation development, temperature of region of first precipitation, dimensions of cloud required for precipitation development, height of seeding plane of first precipitation, minimum thermal energy required, relative concentration of liquid and solid precipitation form, total duration of cloud life, and rate of growth and size of precipitation regions inside of clouds.