Basic Principles for Substantiation of Working Pair Choice

The chapter is devoted to basic principles for substantiation of working pair choice. Principles for substantiation for selection of adsorbate and adsorbent are considered. The main requirements to adsorbate are formulated as follows: low cost, easy of obtaining, small molecular size to facilitate the adsorption effect; high latent heat of evaporation and small volume in liquid state; high thermal conductivity; low viscosity, thermal stability with adsorbent in the operating temperature range; chemical stability in the working temperature range; non-toxicity for animals and human, non-aggressiveness and incombustibility; low pressure saturation (slightly above atmospheric pressure) at normal operating temperature; the absence of environmental problems. Water is shown to conform to these requirements. The crucial requirements to adsorbent are the ability to adsorb large amounts of adsorbate when cooled to environment temperature and give a high cooling effect; high values of maximal adsorption; desorption of the major portion of adsorbate (ideally all) when heated by an accessible source of heat; low heat capacity; good heat conductivity, short cycle time; no deterioration and loss of adsorption capacity over time or use; non-toxicity, non-aggressiveness; chemical physical compatibility with the selected adsorbate; low cost and wide availability. Properties of various types of adsorbents were compared. Composites ‘salt inside porous matrix' are shown to be promising media for heat storage and transformation. Characteristics of thermodynamic cycles of heat conversion were analysed. The ways to improve the coefficient of performance were analysed and shown to be affected by a proper choice of an adsorbent.

Development of Solar Accumulating Drying Equipment Based on the Theoretical Studies of Solar Energy Accumulation

The process of heating a dewatered object in an infrared solar drying plant (with paraffin on the bottom) with solar energy storage is considered. To solve this problem, it is assumed that the heat capacity of paraffin exceeds the heat capacity of the dehydrated object. Infrared rays fall on the upper layer, and heat exchange takes place due to heat and mass transfer with the surface air located between the metal plate and the object to be dehydrated. The equations of thermal conductivity for a dewatered object are given, its relationship at the phase interface is determined using the equality of temperature and heat flow. For an exposure of overheating with a period of 6.5 h, the time of passage of the phase boundary in accordance with the law of motion of the spreading (hardening), was determined according to the formula of ξ = α √6,5 h ≅ 12 h.The optimal thickness of the accumulating paraffin layer was ascertained. On the basis of the theoretical studies, experiments were conducted to study the temperature field of various heataccumulating materials in the laboratory of Tashkent State Technical University. It was found that of all heat-accumulating materials, paraffin has the best heat retention ability when its thickness is of 2–4 cm. The optimal variant of a solar accumulator drying plant with a heat accumulator, viz. paraffin has been designed. In particular, 2–4 cm of paraffin layer with a mass of 50 kg with a corresponding flat surface in terms of specific heat of evaporation is 2400 kJ/kg. The specific melting value of paraffin (150 kJ/kg) allows additional evaporation of 5.8 l of moisture when drying objects. The proposed solar accumulator drying plant can be used for dehydration of medicinal herbs.

FEATURES OF THE PROCESS OF DEHYDRATION OF FUNCTIONAL VEGETABLE RAW MATERIALS

Given the general trend of energy consumption, which leads to an increase in the amount of energy consumed worldwide, the cost of this energy is constantly increasing and its deficit is growing. Therefore, it is important to solve the problem of creating and large-scale implementation of modern energy-efficient heat technologies that reduce energy. This is especially true for providing the population to food, as an additional complication is that the production and processing of agricultural raw materials occurs in conditions of increased consumption of gas and other energy sources with low coefficient of performance and high losses of raw materials during processing. Food and nutrition play a leading role in everyone's life, no matter how we treat it. Nutrition is a key moment in the life of every living organism. Functional foods have evolved as a separate category and are not always considered as dietary supplements. Functional food products (FFP) are the products influencing a functional condition of an organism for the purpose of its increase - resistance, working capacity, prolongation of life. Although the definitions of functional products are different, they are basically ordinary foods and beverages, but enriched with a functional component - a nutrient that plays a special physiological role in the body, has a positive effect on human health. The purpose of the paper is a theoretical and experimental substantiation of complex and efficient processing of vegetable raw materials, creation of energy-efficient heat technology of agricultural raw materials processing in order to obtain functional products with maximum preservation of biologically active substances. In this work, 4 groups of functional foods were studied (according to the classification of the main plant functional ingredients of Doctor of Technical Sciences Petrova Zh.O.) - these are antioxidants, phytoestrogens, folates, prebiotics. An important point is to increase energy efficiency with maximum preservation of functional ingredients of raw materials. Preliminary preparation of raw materials for drying was developed and researched, optimal dehydration regime parameters were selected, which allow to reduce energy consumption for the process and to keep BAS for each group of functional raw materials at a high level. Since the increase in energy costs for drying is associated with the difficulty of removing moisture from plant material, it was important to investigate changes in the specific heat of evaporation of water from functional compositions. The conducted experimental researches confirmed the theoretical assumption of dependence of specific heat of evaporation of water from parenchymal fabrics of plants on composite components of raw materials. The obtained results allow to state that at correctly picked up compositions they not only stabilize components of native raw materials, but also there is an intensification of drying process with reduction of energy consumption on process. The duration of the drying process of functional raw materials on the experimental convective stand was calculated by the method of Krasnikov V.V. The estimated drying durations of functional raw materials and drying rates are determined. The kinetics of heat exchange was studied with the determination of the specific heat flux density and the Rebinder number, which proves the efficiency of the introduction of step drying regimes.

Cool Steam Method for Desalinating Seawater

Cool steam is an innovative distillation technology based on low-temperature thermal distillation (LTTD), which allows obtaining fresh water from non-safe water sources with substantially low energy consumption. LTTD consists of distilling at low temperatures by lowering the working pressure and making the most of low-grade heat sources (either natural or artificial) to evaporate water and then condensate it at a cooler heat sink. To perform the process, an external heat source is needed that provides the latent heat of evaporation and a temperature gradient to maintain the distillation cycle. Depending on the available temperature gradient, several stages can be implemented, leading to a multi-stage device. The cool steam device can thus be single or multi-stage, being raw water fed to every stage from the top and evaporated in contact with the warmer surface within the said stage. Acting as a heat carrier, the water vapor travels to the cooler surface and condensates in contact with it. The latent heat of condensation is then conducted through the conductive wall to the next stage. Net heat flux is then established from the heat source until the heat sink, allowing distilling water inside every parallel stage.

Numerical Study on the Required Surrounding Gas Conditions for Stable Autoignition of an Ethanol Spray

This study deals with the development of controlled-ignition technology for high-performance compression ignition alcohol engines. Among the alcohol fuels, we focus on ethanol as it is a promising candidate of alternative fuels replacing petroleum. The objective of this study is to reveal the physical and chemical phenomena in the mixture formation process up to autoignition of an ethanol spray. In our previous numerical study, we showed the mixture formation process for gas oil and ethanol sprays in the form of spatial excess air ratio and temperature distributions inside a spray and their temporal histories from fuel injection. The results showed a good agreement with those of theoretical analysis based on the momentum theory of spray penetration. Calculation was also confirmed as reasonable by comparing to the experimental results. Through the series of our experimental and numerical studies, the reason for poor autoignition quality of an ethanol spray was revealed, that is, difficulty in simultaneous attainments of autoignition-suitable concentration and temperature in the spray mixture formation due to its fuel and thermal properties of smaller stoichiometric air-fuel ratio and much greater heat of evaporation compared to conventional diesel fuels. However, autoignition of an ethanol spray has not been obtained yet in either experiments or numerical analysis. As the next step, we numerically examined several surrounding gas pressure and temperature conditions to make clear the surrounding gas conditions enough to obtain stable autoignition. One of the commercial CFD codes CONVERGE was used in the computational calculation with the considerations of turbulence, atomization, evaporation, and detailed chemical reaction. Required surrounding gas pressure and temperature for stable autoignition with acceptable ignition delay of an ethanol spray and feasibility of the development of high-performance compression ignition alcohol engines are discussed in this paper.

Effects of water injection to the fuel and air mixture on equilibrium gas composition in combustion products and selected parameters of the theoretical Otto cycle

Moisturizing the intake air by spraying water in the liquid phase significantly lowers the intake air temperature, mainly due to the high value of latent heat of evaporation. The paper presents a methodology for calculating the parameters of the air-fuel mixture after water injection and during subsequent processes of the Otto cycle: compression, combustion and expansion of exhaust gases. For octane as a fuel, exemplary calculations have been carried out to investigate the effect of water injection on the composition of combustion products and selected parameters of the theoretical Otto cycle (temperature, pressure, output power and thermal efficiency).

The dynamics of nucleate boiling of salt solutions at a high heat flux

In this paper, experimental results are obtained for the desorption of layers of aqueous salt solutions of LiBr and CaCl2 at a temperature of nucleate boiling on a horizontal heating surface. The wall temperature is 130 °C. The required volume of the solution with a given mass concentration is placed on the working surface using the Thermo Scientific dispensers. After that, the desorption rate continuously decreases over time. A decrease in the wall temperature leads to a drop in the intensity of the bubbling boiling. The effect of gas convection during evaporation and thermal radiation is small in comparison with the heat of evaporation.

Vapor pressure of 1-butanol and Diesel B0 binary fuel blends

The vapour pressure of 1-butanol and Diesel B0 binary fuel blends were investigated at temperatures ranging from 274.15 to 468.67 K, using the two different setups with static method. The measured values were fitted to the Antoine, polynomial and Clausius?Clapeyron type equations. The heat of evaporation of mixture have been determined from the vapour?liquid equilibria data.