The potential energy landscape contribution to the dynamic heat capacity

The dynamic heat capacity of a simple polymeric, model glassformer was computed using molecular dynamics simulations by sinusoidally driving the temperature and recording the resultant energy. The underlying potential energy landscape of the system was probed by taking a time series of particle positions and quenching them. The resulting dynamic heat capacity demonstrates that the long time relaxation is the direct result of dynamics resulting from the potential energy landscape. Moreover, the equilibrium (low frequency) portion of the potential energy landscape contribution to the heat capacity is found to increase rapidly at low temperatures and at high packing fractions. This increase in the heat capacity is explained by a statistical mechanical model based on the distribution of minima in the potential energy landscape.     

Spatiotemporal Utilization of Latent Heat in Erythritol-based Phase Change Materials as Solar Thermal Fuels

Solar thermal fuels (STFs) have been particularly concerned as sustainable future energy due to their impressive ability to store solar energy in chemical bonds and controllably release thermal energy. However, currently studied STFs mainly focus on molecule-based materials with high photochemical activity, toxicity, and compromised features, which greatly restricts their applications in practical scenarios of solar energy utilization. Herein, we present a novel erythritol-based composite phase change material (PCM) as a new type of STFs with an outstanding capability to store solar energy as latent heat in its stable supercooling state and release thermal energy as needed. This composite PCM with stored thermal energy can be maintained stably at room temperature and subsequently release latent heat as high as 224.9 J/g during the crystallization process triggered by thermal stimuli. Remarkably, solar energy can be converted into latent heat stored in the composite PCM over months. Through mechanical stimulations, the released latent heat can increase the temperature of the composite up to 91 °C. This work presents a new concept of using spatiotemporal storage and release of latent heat in PCMs for solar energy utilization, making it a potential candidate as STFs for developing future clean energy techniques.     

Influence of drawing and heat treatment on surface free energies of polyethylene terephthalate fibers

The surface free energies of polyethylene terepthalate fibers with different draw ratios were experimentally determined by contact angle measurements inn-alkane/water systems. The dispersive component of the surface free energy increased with increasing draw ratio, whereas the nondispersive one remained almost constant. After heat treatment, the dispersive surface free energy increased, but was reduced above 140°C. The nondispersive component increased by heat treatment at 190°C. The increases in the density and birefringence of the fibres due to the drawing and heat treatment suggested that the increase in the dispersive surface free energy was caused by the increase in the atomic density at the fiber surface due to drawing and heat treatment. ESCA results indicated that the increment in the nondispersive surface free energy due to heat treatment was caused by the addition of functional groups to the fiber surface due to heat treatment.     

基于质子交换膜燃料电池的热电联产系统的研究进展

基于质子交换膜燃料电池的热电联产系统利用电池发电时产生的余热供热,提高了能源利用率,实现了热电供能的可持续发展。本文介绍了基于质子交换膜燃料电池的热电联产系统工作原理,概述了各子系统的组成及功能,重点围绕建模方法、操作模式、运行策略、评价方法及系统优化等方向综述了当前研究的进展情况,指明了后续研究可从多尺度综合性建模、完善配置细节及增加集成选项、预测能源需求及运行智能化、多维度系统评价以及节能降耗等方面进行。     

Energetic analysis of an air handling unit combined with enthalpy air-to-air heat exchanger

The energetic analysis of an air handling unit (AHU) combined with an enthalpy air-to-air heat exchanger has been studied to improve the first law thermodynamic efficiency. The energy balance equations for enthalpy air-to-air heat exchanger, conditioned space, heating coil, cooling coil and mixing box have been performed and solved based on a program developed in Engineering Equation Solver. The results showed that using an enthalpy air-to-air heat exchanger leads to energy recovery which in turn decreased the total required AHU power. The effect of using an enthalpy air-to-air heat exchanger on recovered energy in hot and humid ambient is more than the cold and dry one. Using the enthalpy air-to-air heat exchanger, the cooling coil load decreases by 28.27%, which in turn increases the first law efficiency by 32.8%.

     

Active MgH2?Mg Systems for Reversible Chemical Energy Storage

An overview of the importance of and methods available for heat storage in the form of sensible and latent heat is followed by a discussion of the advantages and disadvantages of reversible thermochemical energy storage compared to conventional energy sources such as fuels, i.e. irreversible chemical energy carriers. Of the reversible metal-hydride–metal systems, the MgH₂? Mg system is particularly attractive as a hydrogen and a high-temperature heat storage material because of its high hydrogen content and the high energy content of the Mg–H bond. The advances made in this area over the past few years, namely in catalytic hydrogenation and the doping of magnesium powders, have led to the development of “active MgH₂? Mg systems” for energy storage. The first experimental results on high-temperature heat storage (also with cooling) by coupling a MgH₂? Mg storage system with a low-temperature metal hydride storage system are presented.     

Limiting efficiency of adsorption heat pump

Based on the concept of unrecoverable energy losses in small-scale dissipative structures, the upper limit of the heat pump efficiency has been estimated. This limiting efficiency is achieved in the absence of energy losses due to heat exchange with the heat carrier but when nonequilibrium nonisothermal vapor transfer is taken into account. The limiting efficiency is smaller than the thermodynamically equilibrium efficiency and serves a better reference point in the search for optimal process layout.     

Application of PCM thermal energy storage system to reduce building energy consumption

The building sector is known to make a large contribution to total energy consumption and CO₂ emissions. Phase change materials (PCMs) have been considered for thermal energy storage (TES) in buildings. They can balance out the discrepancies between energy demand and energy supply, which are temporally out of phase. However, traditional PCMs need special latent storage devices or containers to encapsulate the PCM, in order to store and release the latent heat of the PCM. The proper design of TES systems using a PCM requires quantitative information and knowledge about the heat transfer and phase change processes in the PCM. In Korea, radiant floor heating systems, which have traditionally been used in residential buildings, consume approximately 55% of the total residential building energy consumption in heating. This article reviews the development of available latent heat thermal energy storage technologies and discusses PCM application methods for residential building using radiant floor heating systems with the goal of reducing energy consumption.     

Analysis of Adsorbate–Adsorbate and Adsorbate–Adsorbent Interactions to Decode Isosteric Heats of Gas Adsorption

A qualitative interpretation is proposed to interpret isosteric heats of adsorption by considering contributions from three general classes of interaction energy: fluid–fluid heat, fluid–solid heat, and fluid—high‐energy site (HES) heat. Multiple temperature adsorption isotherms are defined for nitrogen, T=(75, 77, 79) K, argon at T=(85, 87, 89) K, and for water and methanol at T=(278, 288, 298) K on a well‐characterized polymer‐based, activated carbon. Nitrogen and argon are subjected to isosteric heat analyses; their zero filling isosteric heats of adsorption are consistent with slit‐pore, adsorption energy enhancement modelling. Water adsorbs entirely via specific interactions, offering decreasing isosteric heat at low pore filling followed by a constant heat slightly in excess of water condensation enthalpy, demonstrating the effects of micropores. Methanol offers both specific adsorption via the alcohol group and non‐specific interactions via its methyl group; the isosteric heat increases at low pore filling, indicating the predominance of non‐specific interactions.     

换热器与相变材料的兼容性研究进展

相变材料是一类以潜热实现能量存储释放的储能材料,由于其在相变温度附近具有很大的储热密度,相变材料可以被用于建筑控温、太阳能热发电和高温传热蓄热等应用中。 换热器是相变储能设备的重要组成部分,可以将热量在供需两端进行传递和转移,保障需求一方的使用,随着相变材料研究的不断深入及其工程应用的广泛普及,换热器已在众多相变储能项目中发挥了重要的枢纽作用。 为了保证换热器的使用性能,需要对换热器在相变材料中的防腐蚀性进行全面的分析。 本文总结了大量国内外的文献,分析不同成分的相变材料对换热器材料的腐蚀性,为换热器材料的选择提供了参考。     

Oxygen (1s) binding energies in carbon monoxide adsorption on metals

The oxygen (1s) binding energy in the non-dissociative adsorption of CO on five metals (Ni, Pt, Cu, W and Mo) is shown to decrease as the heat of adsorption increases. When the heat of adsorption is the same on different metals the O(1s) binding energy is also the same. It is suggested that π bonding (back donation) is the major contribution to the M-CO bond. Correlation of the binding energy with the heat of adsorption suggests that, at 295 K, dissociative adsorption of CO occurs when ΔH_ads ? 300 kJ mol^?1.     

化学能转化成电能的实验设计

以常见的铜锌原电池反应为例,设计了一组对比实验装置,即化学反应装置与原电池装置。以化学反应装置中的能量变化为依据,展示了化学反应中释放出的能量具体形式为“热”与“功”;通过与原电池装置的比较,证明原电池实验装置中的“热”转化为了电能。     

Numerical investigation of a nanofluidic heat exchanger by employing computational fluid dynamic

Journal of Thermal Analysis and Calorimetry - Shell-and-tube heat exchanger is widely applied in different industrial processes and energy systems. Utilized fluid in the heat exchanger and its...     

编程计算法研究两级压缩低温热泵性能

为了优化热泵系统效率,主要采用编程计算,对以R32、R290以及R410A为工质的两级压缩热泵系统进行性能研究,对比了系统的蒸发温度、冷凝温度、中间温度和混合温度等对COP_h的影响。研究发现不完全冷却系统COP_h比完全冷却系统更高,在不同工况下存在不同的最佳中间温度,使得COP_h有最大值,R290和R410A的混合温度变化对系统COP_h影响较大。     

Concentration dependences of heat conductivity coefficients of inert gases in narrow pores

Calculation of the transfer of molecules in porous systems requires self-consistent expressions describing the kinetic transfer coefficients for various concentrations and temperatures. The concentration dependences of heat conductivity and self-diffusion coefficients for fluids with different densities, ranging from rarefied gases to liquids, were considered in terms of a unified model. For monoatomic gases (argon), the model takes into account two energy transfer channels, namely, the vacancy mechanism and energy transfer through collisions of molecules. The former channel is characteristic of rarefied gases, while the latter is noted for condensed phases. The energy parameters of the model were determined on the basis of data on the heat conductivity coefficient in the bulk phase. The heat conductivity coefficient follows a linear temperature dependence for low density; in the medium and large density regions, these dependences follow a more complex pattern that changes depending on temperature. The influence of the interaction of atoms with the pore walls on the concentration dependences of the heat conductivity coefficients was investigated for different total amounts of the adsorbate. These coefficients depend appreciably on the distance to the pore wall and on the direction of heat transfer.     

Amount of Melanin Granules in Human Hair Defines the Absorption and Conversion to Heat of Light Energy in the Visible Spectrum

One of the known important functions of hair is protection from extensive sunlight. This protection is accomplished in large part due to natural hair pigmentation which is known to reflect the number of melanin granules (melanosomes) in the hair shaft, and melanin variants. Melanin takes in excessive light energy and converts it to heat in a process called absorption; heat is then dissipated into the environment as infrared radiation, thereby protecting the underlying skin. We used transmission electron microscopy (TEM) to visualize the melanosome counts in samples of human hair, and used thermal microscopy to measure the temperature changes of the samples when exposed to green and blue light lasers. In our experiments green light conversion to heat was highly correlated to the number of melanosomes, whereas blue light conversion to heat was less correlated, which may be because the reddish melanosomes it contains are less effective in absorbing energy from the blue spectrum of light. Anyway, we have shown the metals accumulation in the melanin can be easily visualized with TEM. We confirmed that the amount of melanin granules in human hair defines the conversion to heat of light energy in the visible spectrum.     

相变蓄热材料研究进展

相变蓄热材料(恒温潜热热能储存材料)是目前最热门的功能材料之一。它在发生相变时储存、放出的热量能够帮助所在系统进行能量的储存,同时可以一定程度上缓解双方在时间、强度及地点上的不匹配程度。相变蓄热材料优点突出,其中包括在使用过程中自身温度变化较小、有很好的稳定性、储热能力较强等。此类材料对环境友好,响应了国家近年来节能环保的政策,同时也可以极大地优化所在系统的运行效率。本文综述了近年来几类相变蓄热材料的种类、特点及国内外学者应对于不同缺陷做出的改进及其应用于行业的研究现状,并对未来的发展进行了探讨与展望。     

New Li-ion Battery Evaluation Research Based on Thermal Property and Heat Generation Behavior of Battery

We do a new Li-ion battery evaluation research on the effects of cell resistance and polariza-tion on the energy loss in batteries based on thermal property and heat generation behavior of battery. Series of 18650 cells with different capacities and electrode materials are evalu-ated by measuring input and output energy which change with charge-discharge time and current. Based on the results of these tests, we build a model of energy loss in cells' charge-discharge process, which include Joule heat and polarization heat impact factors. It was reported that Joule heat was caused by cell resistance, which included DC-resistance and reaction resistance, and reaction resistance could not be easily obtained through routine test method. Using this new method, we can get the total resistance R and the polarization parameter η. The relationship between R, η, and temperature is also investigated in orderto build a general model for series of different Li-ion batteries, and the research can be used in the performance evaluation, state of charge prediction and the measuring of consistency of the batteries.     

Influence of relative humidity and loading frequency on the PA6.6 thermomechanical cyclic behavior: Part II. Energy aspects

In this study, we investigated the influence of relative humidity (RH) and loading rate on the energy response of PA6.6 matrix specimens. The latter were subjected to oligocyclic tensile-tensile tests at 3 different RH and 2 loading rates. Infrared thermography was used to obtain a direct estimate of heat sources using the heat diffusion equation. Using the mechanical and thermal responses discussed in the first part of this work, complete energy rate balances were drawn up. In particular, the time courses of deformation, and dissipated and stored energy rates are discussed. The strong influence of the loading frequency and RH on the energy storage mechanisms is also highlighted.     

Solar heat storage using chemical reactions

As an alternative to storage of sensible heat in liquids or solids or as latent heat of fusion, heat storage by means of reversible chemical reactions is under investigation. By this method, a chemical is separated into two components by heating and heat absorption, following which the components are stored in separate vessels and are recombined to generate heat when it is needed. The attractiveness of this concept of heat storage is not only higher energy density, but the capability to store energy as long as desired at ambient temperature, the option of transporting the chemicals to generate heat at another location, and the high temperatures characteristic of some of the reactions which result in high efficiency when the stored heat is used to generate electricity. Many reactions have been proposed and analyzed. Experimental work is in progress on inorganic hydroxide/oxide reactions, the decomposition of ammoniated salts, sulfur trioxide decomposition, ammonium sulfate decomposition, and others. The problems to be solved and potential applications are illustrated by the results of work in progress on Mg(OH)₂ and Ca(OH)₂ decomposition.