Analysis of the Physicochemical Characteristics of Biochar Obtained by Slow Pyrolysis of Nut Shells in a Nitrogen Atmosphere

The process of slow pyrolysis of seven nut shell samples, in a nitrogen-purged atmosphere, has been studied, as well as characteristics of biochar obtained. The heat carrier with a temperature of 400–600 °C (with a step of 100 °C) was supplied indirectly using a double-walled reactor. The heating rate was 60 °C/min. At increased temperature of the heating medium, a decrease in the amount of the resulting carbon residue averaged 6.2 wt%. The release of non-condensable combustible gas-phase compounds CO, CH4, and H2, with maximum concentrations of 12.7, 14.0, and 0.7 vol%, respectively, was registered. The features of the obtained biochar sample conversions were studied using thermal analysis in inert (nitrogen) and oxidative (air) mediums at 10 °C/min heating rate. Kinetic analysis was performed using Coats–Redfern method. Thermal analysis showed that the main weight loss (Δm = 32.8–43.0 wt%) occurs at temperatures ranging between 290 °C and 400 °C, which is due to cellulose decomposition. The maximum carbon content and, hence, heat value were obtained for biochars made from macadamia nut and walnut shells. An increased degree of coalification of the biochar samples affected their reactivity and, in particular, caused an increase in the initial temperature of intense oxidation (on average, by 73 °C). While technical and elemental composition of nut shell samples studied were quite similar, the morphology of obtained biochar was different. The morphology of particles was also observed to change as the heating medium temperature increased, which was expressed in the increased inhomogeneity of particle surface. The activation energy values, for biochar conversion in an inert medium, were found to vary in the range of 10–35 kJ/mol and, in an oxidative medium—50–80 kJ/mol. According to literature data, these values were characteristic for lignin fibers decomposition and oxidation, respectively.

Numerical analysis of heat-pipe-based battery thermal management system for prismatic lithium-ion batteries

An effective battery thermal management system (BTMS) is essential for controlling both the maximum temperature and the temperature uniformity of a battery module. In this study, a novel and lightweight BTMS for prismatic batteries based on a heat pipe is proposed. A numerical model is created to study the influence of heat transfer designs and other factors on the thermal performance of the BTMS, and the simulation results are checked experimentally. The results show that when the condensation section of the heat pipe is cooled by liquid, the maximum temperature of the battery (Tmax) is reduced by 18.1% compared with air cooling. Decreasing the coolant temperature can reduce T_max, but can also lead to an undesirable temperature nonuniformity. The T_max and the maximum temperature difference (ΔTmax) in a battery module both increase rapidly as the discharge rate rises. The Tmax and ΔTmax are lower than 40 °C and 5 °C respectively when the discharge rate of the battery is lower than 2C. Under preheating conditions in cold weather, increasing the temperature of the heating medium can improve the temperature of the batteries, but at the same time it can make the battery module's temperature more nonuniform, and also add to cost. The temperature of the heating medium should therefore be selected with care. It could be concluded that the above results can provide perspectives in designing and optimizing battery thermal management system.

Investigation of the process of cooking chicken fillet using sous-vide technology

To determine the duration of the heat treatment process on the heating medium (water)To determine the duration of the heat treatment process on the heating medium (water) temperature and layer thickness of the original sample using sous-vide technology, a chicken fillet was selected. The following diagrams were plotted and analyzed: temperature in the chicken fillet specimen as a function of duration of heat treatment process at heating medium (water) temperatures of 60, 70 and 80?C; temperature in the chicken fillet specimen as a function of duration of heat treatment process at thickness of 0.5; 1; 2 cm. Recommendations are given for choosing the optimum temperature regime and thickness of the layer of chicken fillets for cooking by sous-vide technology. At a temperature of water in the thermostat working chamber of 60? C can not be reached inside the sample of product to a temperature of 68-70 ? C, even after 5 minutes of exposure, so there is a possibility of harmful micro-organisms in the finished product. At a temperature of water in the thermostat working chamber of 80 ? C is intense heating of chicken fillets to a temperature of readiness, but the product remains raw because of the short duration of the process, with a further curing the product is heated to a higher temperature of 78-79 ? C, which reduces the quality of the finished product. Optimal selected heating medium temperature (water) in the working chamber of thermostat-70 ?C, which is in the range of recommended regulatory documentation temperatures. At this temperature, the product achieves the necessary cooking temperature of 68-70 ?C, and the duration of heat treatment is reduced by 2.9 times, energy consumption is reduced by 2 times and a high degree of readiness of the product is cooked.

ENZYMATIC HYDROLYSIS OF FAST-GROWING POPLAR WOOD AFTER PRETREATMENT BY STEAM EXPLOSION

The aim of the present study was to investigate the effect of steam explosion pretreatment, without maintaining the heating temperature, on the yield of enzymatic hydrolysis of wood biomass. Genetically modified poplar wood was used for the investigation. The pretreatment process was conducted at temperatures of 160 °C, 175 °C, 190 °C and 205 °C. Then, the system was rapidly decompressed. The heating medium was water. The chemical composition of biomass was determined before and after the steam explosion and then enzymatic hydrolysis was performed. The results of the chemical composition analysis showed a change in the holocellulose content in the analyzed biomass (about 80% for the native sample and 72% for the biomass sample treated at 205 °C), a decrease in the hemicelluloses content from about 40% (native sample) to 16% for the sample treated at 205 °C. The results of enzymatic hydrolysis showed the lowest glucose extraction efficiency for biomass hydrolysis after the treatment at 160 °C, of only about 9% compared to the theoretical content of glucose from the cellulose contained in hydrolysed wood biomass. The highest results were obtained for the samples treated at 190 °C and 205 °C. The study also estimated the processing costs, as a function of the heating medium (steam, water) and energy source (atomic energy, hard coal, natural gas, biomass), assuming heating with electric heaters. From the economic point of view, it is advantageous to use steam heating medium, and either natural gas or biomass as an energy source.

Calculated estimate of the influence of the convection rate of the molten working and heat-ing medium during the strengthening of the restored parts

The article presents a computational and mathematical assessment of the convection rate of the molten working and heating medium during the strengthening of the restored parts. The calculated estimate was based on the theory of multidimensional heat and mass transfer processes occurring in the electrode furnace during the hardening of the restored parts. Computational modeling was carried out based on the choice of initial data and characteristics. The calculation results made it possible to establish the effect of the convection rate of the molten working and heating medium on the hardening of the restored parts.

Modification of a Solar Thermal Collector to Promote Heat Transfer inside an Evacuated Tube Solar Thermal Absorber

Evacuated-tube solar collector (ETSC) is developed to achieve high heating medium temperature. Heat transfer fluid contained inside a copper heat pipe directly affects the heating medium temperature. A 10 mol% of ethylene-glycol in water is the heat transfer fluid in this system. The purpose of this study is to modify inner structure of the evacuated tube for promoting heat transfer through aluminum fin to the copper heat pipe by inserting stainless-steel scrubbers in the evacuated tube to increase heat conduction surface area. The experiment is set up to measure the temperature of heat transfer fluid at a heat pipe tip which is a heat exchange area between heat transfer fluid and heating medium. The vapor/ liquid equilibrium (VLE) theory is applied to investigate phase change behavior of the heat transfer fluid. Mathematical model validated with 6 experimental results is set up to investigate the performance of ETSC system and evaluate the feasibility of applying the modified ETSC in small-scale industries. The results indicate that the average temperature of heat transfer fluid in a modified tube increased to 160.32 °C which is higher than a standard tube by approximately 22 °C leading to the increase in its efficiency by 34.96%.

Calculation justification of isolation of boron and sodium cations from melted working and heating medium during strengthening of repaired parts

The necessity of developing a mathematical model for theoretical and computational verification of the applicability of the working and heating medium for hardening the restored parts has been substantiated. Formulas and systems of equations representing such a mathematical model are proposed. The results of calculations using these formulas made it possible to evaluate and establish the parameters of the preferred mode when strengthening the restored working organs of tillage aggregates.

Performance Evaluation of a Photovoltaic Thermal (PVT) System Using Nanofluids

In this study, a performance evaluation of a photovoltaic thermal (PVT) system using nanofluids was carried out through an efficiency comparison study using water, CuO-water, and Al2O3-water nanofluids as the heat medium of the PVT system. In addition, a model for computational fluid dynamics (CFD) analysis was established, and the validity of the model was verified by comparing it with the experimental results of the PVT system. Through this, it was confirmed that the outlet temperature of the PVT system using nanofluids can be predicted by applying various conditions. Based on the results, the use of nanofluid as heating medium for the PVT system is proposed to improve the efficiency sufficiently compared to the conventional heating media.

Determining the possibility of placing turbine systems for hydraulic regulation and production of electrical energy in the District Heating Network in Krakow

This article presents the methods of specifying the potentiality of energy recovery in the turbine installations projected to hydraulic regulation of the heating medium in the Krakow District Heating System. To achieve this, creating hydraulic calculations enabling to indicate the best places to install turbines in District Heating System is necessary. For this reason, a great amount of work - like choosing a methodology and optimal calculation program, creating an actual database for calculations - has to be done. Hydraulic calculations will also help to determine optimal parameters of future instalments, select the most suitable devices necessary for the proper working of turbine installations and create the future impact assessment to District Heating System.