Silanization of SiO2 Decorated Carbon Nanosheets from Rice Husk Ash and Its Effect on Workability and Hydration of Cement Grouts

Rice husk ash (RHA) having a porous sructure and a high amount of amorphous silica nanoparticles (4 nm) decorated on the surface of carbon nanosheets is a suitable and cheap candidate for the use of a grout additive. In this study, neat RHA and functionalized RHA (f-RHA) with three different loadings were successfully incorporated into the cement-bentonite based grouts by adjusting the water to cement ratio. The workability of the developed grouts having RHA-based additives was analyzed in terms of bleeding, density, flow spread, and Marsh cone time. Additionally, the thermal and prolongation of hydration performances of the cementitious grout were enriched by successful attachment of amino-silane functional groups on the RHA surface. The heat of hydration performances of RHA and functionalized RHA introduced cementitious grout composite were assessed by isothermal calorimetry tests, and especially the kinetics of hydration was increased by the addition of RHA. The presence of amino silane groups in f-RHA intensified the heat adsorption by reacting with cement constituents, and thus resulted in the retardation and reduction in the heat flow. Therefore, using an amino-silane coupling agent increased the induction period and hindered the heat of hydration compared to the reference grout. On the other hand, the incorporation of RHA and f-RHA into the cement matrix did not affect the thermal conductivity of the grouts.

Coal Temperature Variation Mechanism during Gas Desorption Process

To further reveal the mechanism of coal gas migration, the reasons for coal temperature changes during the methane desorption process were analyzed from the aspect of molecular motion and the thermodynamic theory. The temperature change mechanism was investigated, and the mathematical equation was established to describe the variation of temperature change during the methane desorption and diffusion process. The established equation was applied for the calculation of temperature change for two types of coal samples, and the measured and theoretical values of temperature changes were obtained. The results show that the temperature changes in the coal gas desorption process are mainly caused by the heat adsorption. The heat adsorption phenomenon was also caused by free gas expansion during the pressure relief process. The gas diffusion and work done for gas seepage also need heat adsorption. The temperature change is positively correlated to the coal gas pressure, quantity, and limit value of gas desorption volume. Due to the poor insulation in the test system, the difference between the theoretical and the measured temperature change values increase with the adsorption equilibrium pressure. It is helpful to further reveal the mechanism of coal and gas outburst. It also has an important reference value for controlling gas dynamic disasters in coal mines.

Modeling of a Refrigerator in Disaster Vehicle, Using Solar Energy and Engine Exhaust Gases Heat

In critical situations such as floods and earthquakes, the relief forces require a refrigeration for pharmaceuticals and vaccines, which could operate without an electrical energy and the alternative energies, such as solar energy, engine exhaust gases heat, and wind energy. In this paper, a refrigeration cycle has been modeled as an adsorption refrigeration cycle with an activated carbon/methanol as adsorbent/adsorbate pair and two sources of energy—solar energy and engine exhaust gases heat. The solar cycle had a collector with area of 1 m2 and the exhaust gas cycle included a heat exchanger with 100 °C temperature difference between inlet and outlet gases. The temperature profile in adsorbent bed, evaporator, and condenser was obtained from modeling. Moreover, the pressure profile, overall heat transfer coefficient of collector and adsorbent bed, concentration, and the solar radiation were reported. Results represented the coefficient of performance (COP) of 0.55, 0.2, and 0.56 for complete system, solar adsorption refrigeration, and exhaust heat adsorption refrigeration, respectively. In addition, exhaust heat adsorption refrigeration has a value of 2.48 of specific cooling power (SCP). These results bring out a good performance of the proposed model in the climate of Iran.

Ferroelectric-to-Ferroelectric Phase Transition Induced Electro-Caloric Energy Conversion in Barium Titanate at Room Temperature

The electro-caloric energy conversions in single-crystal and polycrystalline barium titanate samples are investigated using differential scanning calorimetry (DSC). The DSC measurement reveals a refrigeration effect of 0.1 J/g under an electric field of 15 kV/cm at T=17.5 °C, which is related with the ferroelectric-to-ferroelectric transition in barium titanate. The thermodynamics calculation based on Maxwell’s relations leads to similar conclusion. Such EC effect shows relaxation with the heat release process more significant than the heat adsorption process when the applied field is changed, which is different with those occur near the ferroelectric-to-paraelectric transition temperatures. Furthermore, the electro-caloric energy conversion relation or the scaling relation between the maximum refrigeration effect ΔH and the applied field E, is found to follow a power law ΔHmax~Eb with b=1.72, which is significantly larger than those for EC effects related with the ferroelectric-to-paraelectric transitions.

Modification of Fagus sylvatica (L.) with 1,3-dimethylol-4,5-dihydroxyethylene urea (DMDHEU): Part 1. Estimation of heat adsorption by the isosteric method (Hailwood-Horrobin model) and by solution calorimetry

The differential heat of adsorption (ΔH s ) of Fagus sylvatica wood modified with 0.8 M, 1.3 M, and 2.3 M solution of 1,3-dimethylol-4,5-dihydroxyethylene urea (DMDHEU) was determined at different equilibrium moisture contents (EMCs) by both the isosteric method, using the Hailwood-Horrobin model at 20, 30, and 40°C and by solution calorimetry. Both methods revealed that at 1% EMC, the 2.3-M modified wood releases approximately double the amount of energy as does unmodified wood. At EMC below approximately 5%, DMDHEU-modified wood appears to be more hygroscopic than unmodified wood, indicating that more OH groups are available for adsorption. The bulking effect of the cell wall and the increase of OH groups caused by the modification with DMDHEU are probably the reason for this observation. As expected, higher EMC led to a reduction of ΔH s .

Heat Recovery Steam Generator Optimization Using Analysis of Variance

The present work deals with the analysis and optimization of a heat recovery steam generator (HRSG) using the ANalysis Of VAriance (ANOVA). In order to obtain an optimum thermodynamic configuration of a three pressure levels HRSG, a mathematical model of the generator has been implemented using a generic thermodynamic code. Model management and HRSG control logic have been implemented using code’s macros and Microsoft Excel VBA programming languages. The model has been finely tuned and tested using real HRSG running data in the current plant configuration. Using the model, evaporators’ pressure levels have been modified and thermodynamic data elaborated using ANOVA technique. Results’ analysis shows that reducing low and medium pressure level in the HRSG, global steam production rises up. At the same time, exhaust gas temperature decreases showing a certain heat adsorption increase. On the basis of the results it is possible to state that the proposed HRSG configuration involves increases in plant steam and power production as well as in global efficiency with HRSG minimal modification.