Effects of Diesel Concentration on the Thermal Conductivity,Specific Heat Capacity and Thermal Diffusivity of Diesel-Contaminated Soil

High energy consumption is a serious issue associated with in situ thermal desorption(TD)remediation of sites contaminated by petroleum hydrocarbons(PHs).The knowledge on the thermophysical properties of contaminated soil can help predict accurately the transient temperature distribution in a remediation site,for the purpose of energy conservation.However,such data are rarely reported for PH-contaminated soil.In this study,by taking diesel as a representative example for PHs,soil samples with constant dry bulk density but different diesel mass concentrations ranging from 0% to 20% were prepared,and the variations of their thermal conductivity,specific heat capacity and thermal diffusivity were measured and analyzed over a wide temperature range between 0℃ and 120℃.It was found that the effect of diesel concentration on the thermal conductivity of soil is negligible when it is below 1%.When diesel concentration is below 10%,the thermal conductivity of soil increases with raising the temperature.However,when diesel concentration becomes above 10%,the change of the thermal conductivity of soil with temperature exhibits the opposite trend.This is mainly due to the competition between soil minerals and diesel,because the thermal conductivity of minerals increases with temperature,whereas the thermal conductivity of diesel decreases with temperature.The analysis results showed that,compared with temperature,the diesel concentration has more significant effects on soil thermal conductivity.Regardless of the diesel concentration,with the increase of temperature,the specific heat capacity of soil increases,while the thermal diffusivity of soil decreases.In addition,the results of a control experiment exhibited that the relative differences of the thermal conductivity of the soil samples containing the same concentration of both diesel and a pure alkane are all below 10%,indicating that the results obtained with diesel in this study can be extended to the family of PHs.A theoretical prediction model was proposed based on cubic fractal and thermal resistance analysis,which confirmed that diesel concentration does have a significant effect on soil thermal conductivity.For the sake of practical applications,a regression model with the diesel concentration as a primary parameter was also proposed.

Theoretical and experimental research on heat transfer performance of the semi-open heat pipe

This paper focuses on the heat transfer performance of semi-open heat pipe which is a new type of heat pipe. After analyzing its condensation heat transfer mechanisms theoretically, several semi-open heat pipes in different length ratios and upper hole diameters are studied experimentally and compared with the same dimensions closed heat pipes. Experimental results show that the heat transfer performance of semi-open heat pipe becomes better by increasing heat transfer rate. At the first transitional point, the heat transfer performance of semi-open heat pipe approaches the level of the closed heat pipe. It is suitable to choose upper small hole about 1 mm in diameter and length ratio larger than 0.6 for the semi-open heat pipe.

Effects of moisture content and dry bulk density on the thermal conductivity of compacted backfill soil

Soil backfilling and compaction are often involved in urban construction projects like the burying of power cables.The thermal conductance of backfill soil is therefore of great interest.To investigate the thermal conductivity variation of compacted backfill soil,10 typical soils sampled in Zhejiang Province of China with moisture contents of 0%–25%were fully compacted according to the Proctor compaction test method and then subjected to thermal conductivity measurement using the thermal probe method at 20℃.The particle size distribution and the chemical composition of the soil samples were characterized to analyze their effects on thermal conductivity.The results showed that the maximum thermal conductivity of fully compacted soils generally exceeds 1.9 W/(m·K)and is 20%–50%higher than that of uncompacted soils.With increasing moisture content,soil thermal conductivity and dry bulk density first increase and then remain unchanged or decrease slowly;the critical moisture content is greater than 20%in most cases.Overall,the critical moisture content of soils with large particle size is lower than that of those with small particle size.Quartz has the highest thermal conductivity in the soil solid phase,and the mass percentage of quartz for most soils in this study is more than 50%,while that for yellow soil is less than 30%,which leads to the thermal conductivity of the former being nearly twice as great as that of the latter in most circumstances.Based on regression analysis,with moisture content and dry bulk density as the independent parameters,the prediction formulae for the thermal conductivity of two categories of compacted backfill soils are proposed for practical applications.

Primary Frequency Control Ability Evaluation of Valve Opening in Thermal Power Units Based on Artificial Neural Network

With the development of new energy,the primary frequency control(PFC)is becoming more and more important and complicated.To improve the reliability of the PFC,an evaluation method of primary frequency control ability(PFCA)was proposed.First,based on the coupling model of the coordinated control system(CCS)and digital electro-hydraulic control system(DEH),principle and control mode of the PFC were introduced in detail.The simulation results showed that the PFC of the CCS and DEH was the most effective control mode.Then,the analysis of the CCS model and variable condition revealed the internal relationship among main steam pressure,valve opening and power.In term of this,the radial basis function(RBF)neural network was established to estimate the PFCA.Because the simulation curves fit well with the actual curves,the accuracy of the coupling model was verified.On this basis,simulation data was produced by coupling model to verify the proposed evaluation method.The low predication error of main steam pressure,power and the PFCA indicated that the method was effective.In addition,the actual data obtained from historical operation data were used to estimate the PFCA accurately,which was the strongest evidence for this method.

The Generalized Thermodynamic Temperature and the New Expressions of the First and the Second Law of Thermodynamics

The classical thermodynamics reflects the significant relationship between the heat and the temperature. On the basis of the relationships, according to the mathematical derivation, this paper structures the conceptions of generalized heat, generalized thermodynamic temperature, generalized entropy and so on. The series of conceptions in the classical thermodynamics is merely a special case of the generalized thermodynamics. Based on these conceptions of generalized thermodynamics, this paper presents the new expressions of the first law and the second law of thermodynamics. In other words, these expressions are endued with new explanations. The Eq. LZ = kTS given by this paper provides theoretical basis for these new expressions.

Experimental Investigation of Heat Storage and Heat Transfer Rates during Melting of Nano-Enhanced Phase Change Materials (NePCM) in a Differentially-Heated Rectangular Cavity

In this work, an experimental study of melting heat transfer of nano-enhanced phase change materials(NePCM) in a differentially-heated rectangular cavity was performed. Two height-to-width aspect ratios of the cavity, i.e., 0.9 and 1.5, were investigated. The model Ne PCM samples were prepared by dispersing graphene nanoplatelets(GNP) into 1-tetradecanol, having a nominal melting point of 37℃, at loadings up to 3 wt.%. The viscosity was found to have a more than 10-fold increase at the highest loading of GNP. During the melting experiments, the wall superheat at the heating boundary was set to be 10℃ or 30℃. It was shown that with increasing the loading of GNP, both the heat storage and heat transfer rates during melting decelerate to some extent, at all geometrical and thermal configurations. This suggested that the use of NePCM in such cavity may not be able to enhance the heat storage rate due to the dramatic growth in viscosity, which deteriorates significantly natural convective heat transfer during melting to overweigh the enhanced heat conduction by only a decent increase in thermal conductivity. This also suggested that the numerically predicted melting accelerations and heat transfer enhancements, as a result of the increased thermal conductivity, in the literature are likely overestimated because the negative effects due to viscosity growth are underestimated.

Microfluidic fuel cells integrating slanted groove micro-mixers to terminate growth of depletion boundary layer thickness

Because of potential high energy densities,microfluidic fuel cells can serve as micro-scale power sources.Because microfluidic fuel cells typically operate in the co-laminar flow regime to enable a membrane-less design,they generally suffer from severe mass transfer limitations with respect to diffusion transport.To address this issue,a novel channel design that integrates slanted groove micro-mixers on the side walls of the channel is proposed.Numerical modeling on the design of groove micro-mixers and grooveless design demonstrates a mass transfer enhancement that has a 115%higher limiting current density and well-controlled convective mixing between the oxidant and the fuel streams with the use of slanted groove micro-mixers.Moreover,the growth of the thickness of the depletion boundary layer is found to be terminated within approximately 2 mm from the channel entrance,which is distinct from the constantly growing pattern in the grooveless design.In addition,a simplified mass transfer model capable of modeling the mass transfer prFocess with the presence of the transverse secondary flow is developed.Further,a dimensionless correlation is derived to analyze the effects of the design parameters on the limiting current density.The present theoretical study paves the way towards an optimal design of a microfluidic fuel cell integrating groove micro-mixers.

Experimental research on charging characteristics of a pressure-controlled VRLA battery in high-temperature environments

Valve-regulated-lead-acid (VRLA) battery charging performed in high-temperature environments is extremely risky under overcharge conditions, and may lead to a subsequent thermal runaway. A new pressure-controlled charging method was adopted and the charging characteristics of the pressure-controlled VRLA battery in high-temperature environments were ex-perimentally studied. The concept was tested in a large temperature gradient to obtain more details about the effects of users' accustomed charging and discharging modes on battery capacity. The premature capacity loss (PCL) phenomenon under high temperature exposure was analyzed. The results showed that the capacity loss could be recovered by charging using a large current.

Temperature-Dependent Rheological Behaviors of Binary Eutectic Mixtures of Sugar Alcohols for Latent Heat Storage:A Comparative Study with Pure Sugar Alcohols

The temperature-dependent rheological behaviors of five selected binary eutectic mixture sugar alcohols,with great potential for latent heat storage in the range of 353.15 K to 523.15 K,were investigated.It was found that the rheological behaviors of the mixture sugar alcohols depend on those of the pure compounds as well as their molar ratios.The two mixtures of xylitol(75 mol%)+erythritol and erythritol(84 mol%)+d-mannitol behave like pseudoplastic fluids with typical non-Newtonian shear-thinning behaviors,as indicated by the power law index of 0.99(<1).The mixture of d-mannitol(70 mol%)+d-dulcitol is a nonlinear Bingham fluid,exhibiting a slight yield stress(0.001 Pa to 0.01 Pa)at low shear rates.The rest two mixtures containing the cyclic-structured inositol behave like Herschel-Bulkley fluids.The infinite shear viscosities of the eutectic mixtures over the entire temperature range appear to be higher than those of their respective pure compounds,except for inositol.The mixture of xylitol(75 mol%)+erythritol at its melting point shows higher dynamic viscosity of about 0.546 Pa·s than the values of about 0.396 Pa·s and 0.035 Pa·s for xylitol and erythritol,respectively.In addition,the activation energies of viscous flow of the mixtures,as determined by fitting the dynamic viscosity-temperature curves using the Arrhenius model,also exhibit higher values than those of their pure compounds.The activation energy of viscous flow of the mixture xylitol(75 mol%)+erythritol was determined to be about 92400 J/mol in the supercooled liquid state,while the supercooled liquid xylitol and erythritol have much lower values of 83500 J/mol and 51900 J/mol,respectively.Both the increased dynamic viscosities and activation energies of viscous flow can result in deteriorated crystallization performance during latent heat retrieval.

Optimum insulation thickness of external walls by integrating indoor moisture buffering effect: a case study in the hot-summer-cold-winter zone of China

In the high-humidity, hot-summer-cold-winter(HSCW) zone of China, the moisture buffering effect in the envelope is found to be significant in optimum insulation thickness. However, few studies have considered the effects of indoor moisture buffering on the optimum insulation thickness and energy consumption. In this study, we considered the energy load of an exterior wall under moisture transfer from the outdoor to the indoor environment. An optimum insulation thickness was obtained by integrating the P1-P2model. A residential building was selected for the case study to verify the proposed method. Finally, a comparison was made with two other widely used methods, namely the transient heat transfer model(TH) and the coupled heat and moisture transfer model(CHM). The results indicated that the indoor moisture buffering effect on the optimum insulation thickness is 2.54 times greater than the moisture buffering effect in the envelope, and the two moisture buffering effects make opposing contributions to the optimum insulation thickness. Therefore, when TH or CHM was used without considering the indoor moisture buffering effect, the optimum insulation thickness of the southern wall under one air change per hour(1 ACH) and 100% normal heat source may be overestimated by 2.13% to 3. 59%, and the annual energy load on a single wall may be underestimated by 10.10% to 11.44%. The decrease of airtightness and the increase of indoor heat sources may result in a slight reduction of optimum insulation thickness. This study will enable professionals to consider the effects of moisture buffering on the design of insulation thickness.

Experimental research on charging characteristics of a solar photovoltaic system by the pressure-control method

The charging characteristics of the valve-regulated lead acid(VRLA) battery driven by solar energy were experimentally studied through the pressure-control method in this paper.The aims of the research were to increase charging efficiency to make the most of solar energy and to improve charging quality to prolong life of battery.The charging process of a 12 V 12 A·h VRLA battery has been tested under the mode of a stand-alone photovoltaic(PV) system.Results show that the pressure-control method can effectively control PV charging of the VRLA battery and make the best of PV cells through the maximum power point tracking(MPPT).The damage of VRLA battery by excess oxygen accumulation can be avoided through the inner pressure control of VRLA battery.Parameters such as solar radiation intensity,charging power,inner pressure of the battery,and charging current and voltage during the charging process were measured and analyzed.

应用于余热回收的新型烧结矿立式冷却装置填充床阻力研究（英文）

目的:研究余热回收中的新型烧结矿立式冷却装置填充床的阻力特性,揭示烧结矿填充床宏观特性参数和空隙流动状态,提出适用于烧结矿的阻力特性公式。创新点:1.采用实验方法,获取全面的复杂异形烧结矿颗粒宏观特性数据;2.通过实验测量,提出适用于烧结矿填充床的修正型Ergun阻力方程。方法:1.采用多种实验方法,测量烧结矿的颗粒粒度、球形度和堆积空隙率等宏观特性参数;2.通过阻力实验数据分析,得到烧结矿填充床的宏观特性参数和堆积空隙流动状态;3.通过实验数据拟合,提出适用于烧结矿的阻力特性公式。结论:1.表观流速为0.4?2.4 m/s时烧结矿填充床堆积空隙流动状态由层流过渡到湍流;2.Ergun方程的不规则异形颗粒的阻力预测值比实验值偏低约40%;3.提出的修正型Ergun预测公式能够预测颗粒雷诺数500至12 000的烧结矿填充床阻力,预测误差在10%以内。

三角形封闭腔内内含旋转柱体时碳化硅-乙二醇纳米流体层流混合对流传热特性研究(英文)

目的:明确在封闭腔内放置旋转柱体时,柱体尺寸及转速对不同浓度下纳米流体的流动传热的影响。创新点:1.数值模拟中采用的碳化硅-乙二醇(Si C-EG)纳米流体的重要热物性参数均为实验测量值;2.考虑封闭腔内柱体的动态旋转对腔内纳米流体流动传热的影响。方法:基于对Si C-EG纳米流体导热系数与粘度的实验测量,采用数值模拟方法探究封闭腔内旋转柱体、纳米流体浓度以及瑞利数对SiC-EG纳米流体流动传热性能的影响。结论:1.在柱体的旋转方向与由自然对流引起的纳米流体流动方向相同的情况下,置于腔内的旋转柱体可以起到强化传热的效果。2.二者旋转方向相反时情况较为复杂,当柱体尺寸较小且柱体转速较低时削弱传热效果;当柱体尺寸较大且转速较高而引发的强制对流占主导地位时,将对腔内传热起到一定的强化效果。