Heat-transfer Agent Research Articles

Possibility of Electromembrane Softening Treatment of Network Water at a Thermal Power Station

The possibility of electromembrane softening treatment of network water at a thermal power station is shown. Technology for the manufacturing of an inert anode free from noble metals or their compounds is proposed. Performed resource tests have demonstrated that such an anode can be in operation in chloride–sulfate solutions for several years almost without wear. A mathematical model describing the electrical current utilization efficiency as a function of process parameters and electrolysis regimes in the electromembrane softening of water has been developed. The results of calculating the current utilization efficiency coefficient by this model are in satisfactory agreement with experimental results. The current utilization coefficient in the formation of NaOH does not depend on the anolyte composition but appreciably decreases with increasing catholyte concentration and slightly grows with increasing current density at a constant catholyte concentration. Experiments have not disclosed any essential dependence between the specific water and CO 3 2- ion transports and the process parameters. Experiments on estimating the depth of the electromembrane softening of initial water for the heat supply networks of Kharkiv have demonstrated that the electromembrane method provides the residual hardness of 0.3–0.4 mg-equiv/dm3, which is almost four times lower than for water subjected to soda–lime treatment. The experiments performed on a test bench setup have confirmed that the application of heterogeneous cation-exchange membranes (both MK-40 (OAO Shchekinoazot) and CMI 9000 (Membrane International)) provides the possibility to attain a high current utilization ratio above 88%. The carbonate index of water after electromembrane softening corresponds to the normative requirements to water for heat supply networks with a heat transfer agent temperature below 150°C (no higher than 0.4 (mg-equiv/dm3)2]. This provides the possibility to use the treated water immediately in heat supply networks without further ion-exchange softening. Some technical and economic parameters of the softening process and the technical parameters of an industrial electromembrane softener are given, and the possibilities of the utilization of wastes and byproducts are considered.

Exergy analysis of a heat supply system with a lower temperature of return delivery water

The questions of evaluation of energy efficiency of municipal heating and electric power supply systems based on the combined heat and power supply plant (CHPP) with a reduced temperature of return delivery water are considered in the paper. As a method of reducing the return delivery water temperature, using heat absorption transformers (HAT) at central heat supply stations operating as absorption heat-exchange facility was considered. The exergetic efficiency was chosen as an evaluation criterion, because, given the difference in kinds of energy in the system, it allows to perform both relative and absolute estimates of thermodynamic effectiveness as well as takes into account the losses from non-equilibrium of processes in the system. Results are given of HAT multiparameter analysis that were obtained on the basis of a developed mathematical model, the reliability of which was experimentally tested. During analysis of the heat supply system, one should take into account the influence of return delivery water temperature on consumption of heat-transfer agents and power consumptions on driving the recycling pumps in the heating network and pumps in the consumer network. Additional components are inntroduced into the equation for determining the exergetic efficiency of CHPP. The traditional heat supply system is compared to the central heat supply station and the new system with an absorption transformer AT (central heat supply station) for different temperatures of delivery water in the flow line. The relative correspondence method proposed by V. P. Motulevich was used for the comparative analysis. The results are analyzed by the following lines of the heat supply system: Source-AT (central heat supply station), SourceConsumer. In the Source-Consumer line, a considerable increase is shown of exergetic efficiency in the new system at a rather high temperature of delivery water in the flow line. This is due to variation of power consumption on driving the recycling pumps and the generator unit capacity gains. Turbine-generator set T-100-130TMZ is selected as a source.

Results of research into thermal-technical characteristics of solar collector

We developed a new design of an air solar collector made in the form of an inseparable power unit, which includes a frame with heat-insulated walls, single glazing and a selective surface on its bottom. We defined a number of generalizing dependences for the determination of thermal efficiency of an air solar collector, namely, an influence of the mass air flow qa on a temperature difference of the heat-transfer agent to and insulation E, on heat productivity q and the efficiency η of the solar collector.Based on the experimental data, we obtained linear regression dependencies of the average daily ambient temperature teat on energy illumination E and the average temperature of the heat-transfer agent carrier taat of the average daily ambient temperature teat. We verified the adequacy of the results of theoretical and experimental studies.We established that we achieve the maximum values of the efficiency of the solar collector η ‒ from 65 to 80.6 % at a temperature of the outlet flow of the heat-transfer agent to from 30 to 60 °C and mass air flow, qa from 170 to 190 m3/h.We determined that an increase in the level of insulation E from 100 to 1,000 W/m2 makes it possible to increase heating productivity of the collector q from 320 to 1,260 W and the temperature of the heat-transfer agent at the collector outlet to from 10 to 60 °C.We can use the obtained results in development and improvement of technical means for drying fruits, for improvement of technological and energy efficiency of the process.

INCREASE THE EFFICIENCY OF COMPLEX HEAT-RECOVERY SYSTEMS FOR HEATING AND HUMIDIFYING OF BLOWN AIR OF GAS-FIRED BOILERS

The work is devoted to increase of thermal and ecological efficiency of water-heating gas-fired boilers of municipal heat-power engineering. To improve thermal efficiency, heat-recovery technologies are used in which deep cooling of the exhaust-gases from boilers with the realization of the condensation mode of the heat recovery equipment is ensured. To implement this regime throughout the heating period, it is advisable to use complex heat-recovery systems in which several heat transfer agents are heated with sufficiently different thermal potentials. To enhance the environmental effect when using complex systems, it is possible to carry out combustion air humidifying in them, which contributes to the reduction of NOx emissions to the environment by the boiler plants.
 The work suggests improvement of the known complex heat-recovery system for heating and humidifying the blown air by introducing into its comprise an additional element - water heater of chemical water-purification system. Such the technological solution will ensure a reduction in the thermal losses of the boiler plant and improve the operating conditions of the gas ducts of the boiler house by preventing the condensate from falling out of the wet exhaust-gases.
 The aim of the work is to investigate the operating parameters of the complex heat-recovery system for heating and humidifying the blown air and preheating the water for chemical water-purification and comparing its basic heatly and humidity characteristics with the corresponding complex system without preheating the water.
 The results of the investigations are presented in a wide operating range of the load variation of the water-heating boiler respectively the boiler plant temperature graph and are shown graphically.
 The analysis of the obtained data showed that due to the proposed modernization by preheating the water of the chemical water-purification system in the complex heat-recovery system for heating and humidifying the blown air, an increase of coefficient the use heat of fuel of boilers is provided, depending on their load from 11% to 17%. For this improved heat-recovery system with preheating the water of the chemical water-purification system in comparison with the system without such preheating, the total heating capacity of the complex system increases by 1.3÷1.6 times, and the coefficient the use heat of fuel of the boiler increases by 5.2%.

Comparative Thermohydraulic Efficiency of Processes in Channels with Chaotic Packing

A new approach to calculation of the thermohydraulic efficiency of channels with different methods of intensification including small-size chaotic packings was considered, and the corresponding expressions were obtained. For this, the Kirpichev, Antufiev, and Spalding energy coefficients, thermal efficiency of the process in the channel, and cell model of the flow structure were used. Expressions were given for calculating the temperature profiles, thermal efficiency, hydraulic resistance of channels with chaotic elements, and average Nusselt number. The results of calculations agreed with the experimental data obtained on an experimental stand with a tube-in-tube heat exchanger and oil–water heat transfer agents. Examples of calculations were given for several types of metal packing, and conclusions were drawn about the most effective designs. It was recommended to use metal chaotic packing in channels for liquids with increased viscosity because the laminar flow of the heat transfer agent changes to the turbulent one, and the heat transfer coefficient substantially increases in this case.

ABOUT ONE APPROACH TO CALCULATION OF PARAMETERS OF HEAT TRANSFER THROUGH WALL IN PRESENCE OF CONDENSING VAPOR

The article is dedicated to the study of heat exchangers operation. The main goal of the work was to improve a standard method for calculating a typical heat exchanger based on dependencies approved in engineering practice. The noted technique is presented in educational literature for chemical engineers and it is included in the educational process for the training of engineers. On the basis of practical recommendations stated in literature the working formulas of the process are taken in approximate form. Further, a correction is calculated, which, as calculations show, leads (together with the initial approximation) to an almost exact satisfaction of the initial equations. It is expedient because traditional equations of a heat transfer have not really high precision, which is determined by the processing of numerous experiments. These experiments are rather rough. It is reasonable that the accuracy of the analysis has to be consistent with the model accuracy. This factor justifies the need to simplify the models (use of various recommendations based on the experience of equipment operation, etc.). At the same time, it is desirable to simplify the mathematical model equation so that it is possible to calculate the corrections, i.e. to clarify the solution. We clarify the equation solution meaning more and more exact satisfaction with the initial equation of the mathematical model. In this direction, various variants of perturbation methods can be used. The search for analytical solutions is complicated by the fact that the equations of the mathematical model of energy transfer in a heat exchanger are nonlinear. The three-layer heat transfer problem in a stationary mode is considered. The first layer is the space of the heat exchanger where a phase transition (first heat transfer agent vapor condensation) occurs. The second layer is the space of the heat exchanger where convective movement of the second heat transfer agent takes place without phase transition. The third layer is a wall separating the heat transfer agent providing some resistance to the heat transfer process. As a result of the simplified model analysis, it became possible to obtain an analytical solution to the problem with such accuracy that the calculated correction turned out to be insignificant i.e. the correction is not appropriate to take into account. The solution found was almost exactly approximated by a simple analytic dependence.

High-temperature evaporation of water emulsion droplets used in thermal fluid treatment

High-temperature (over 500 K) evaporation of water, emulsions, slurries and solutions has been extensively studied over the recent years due to a number of prospective applications. Some of these are, for example, the evaporation or burnout of impurities in the course of for thermal wastewater treatment, gasification, as well as flue gas waste heat recovery by intermixing them with water and water vapor to create a new generation of heat transfer agents. Further development of these technologies is constrained by the fact that the approaches used so far are mostly empirical. Obtaining reliable experimental data on evaporation characteristics (vaporization rate and lifetime) of water emulsion droplets in the course of thermal evaporation and burnout of impurities is a pressing task. It is also desirable to experimentally cover all the temperature ranges, droplet sizes, and component concentrations, typical of advanced water treatment. In this research, we use high-speed hardware-and-software system to track the free surface of a droplet. We determine the dependence of heating and complete evaporation time as well as heating and vaporization rate on the gas environment temperature, droplet size, and emulsion component concentration. We then derive the approximating equations for the dependences determined. The difference in evaporation conditions and characteristics is also defined for droplets of water and emulsions with different additive types and concentrations. Finally, we outline different modes of evaporation as well as the required conditions for monotonous evaporation or explosive breakup (pulverization).

Substantiation of parameters and operational modes of air solar collector

We developed a new design of an air solar collector for a fruit dryer including double glazing and a selective surface made of a thin metal substrate with inlet and outlet openings on its bottom. We established that it is necessary to use a glass with a heat-reflecting coating of a solid K-glass type with a radiation coefficient ε=0.1...0.15 for a double-glazing substrate. This makes it possible to obtain the widest possible spectrum of direct sunlight rays that irradiate a surface of an absorbing plate and reduces a diffuse component of radiation, which ensures an increase in efficiency of a solar collector.We determined regularities of the influence of a change in flow speed of a heat-transfer agent, a temperature drop, and radiation intensity on power of a solar collector. We developed a model of heat exchange processes occurring in an air solar collector. We presented the methodology for estimation of heat loss of an air solar collector with passive use of solar energy.We established that energy illumination E, which is from 377 to 1,223 W/m2, affects heat output of an air collector Q=117...480 W significantly. We established that a use of a non-selective absorbing surface in an air solar collector with a low insolation level E=377 W/m2 makes it possible to increase efficiency by η=70.7 % more for selective, and at a large energy illumination of E=1,000 W/m2, on the contrary small η=54.6 %. This makes it possible to explain how redistribution of the ratio of the maximum current thermal power (NSC=48.8...100 W) and efficiency of an air solar collector occurs.One can use the obtained results in development and improvement of technical means for fruit drying to improve technological and energy efficiency of the process.

Thermal Management of Single- and Dual-Tank Fuel-Flow Topologies Using an Optimal Control Strategy

The effect of fuel topology and control on thermal endurance of aircraft using fuel as a heat transfer agent was studied using an optimal dynamic solver (OPT). The dynamic optimal solutions of the differential equations governing the heat transfer of recirculated fuel flows for single- and dual-tank arrangements were obtained. The method can handle sudden jumps of operating conditions across different operating zones during mission and/or situations when control parameters have reached their physical limits. Although this method is robust in providing an optimal control strategy to prolong thermal endurance of aircrafts, it is not ideal for practical application because the method required iterative procedures to solve expensive nonlinear equations. The linear quadratic regulator (LQR), the feedback controller, can be derived by linearizing the adjoint equations at trim points to offer a simple control strategy, which can then be implemented directly in the feedback control hardware. The solutions obtained from both OPT and LQR were compared, and it was found two solutions were almost identical except in regions having sudden jump of operation conditions. Finally, a comparison between single- and dual-tank arrangements was made to demonstrate the importance of the flow topology. The study shows the dual-tank arrangement allows flexibility in how energy is managed and can release energy faster than a single-tank topology and hence provides improved aircraft thermal endurance.

Preparation and Thermophysical Investigations of CoFe2O4-based Nanofluid: a Potential Heat Transfer Agent

Cobalt ferrite nanoparticles were synthesized by employing chemical co-precipitation technique. The structure, morphology, elemental composition, and magnetization studies of cobalt ferrite nanoparticles were carried by XRD, FE-SEM, EDS, and VSM techniques, respectively. Rietveld refined XRD pattern exhibited the single-phase cubic spinel structure with Fd-3m space group. FE-SEM images indicated some agglomeration of spherical grains which can be attributed to high surface energy and magnetic interactions. Presence of peaks of respective elements (Co, Fe, and O) in EDS spectrum showed formation of CoFe2O4. The M–H loop recorded at 300 K revealed superparamagnetic behavior and explained by fine particles size. The blocking temperature of the CoFe2O4nanoparticles from FC-ZFC curve was found to be 144 K. Cobalt ferrite–ethylene glycol nanofluids of various concentrations 0.0–1.0% in steps of 0.2% were prepared by ultrasonically assisted two-step technique. Thermophysical parameters such as thermal conductivity, specific heat, viscosity, and density were investigated as a function of both volume fraction and temperature. The experimental and theoretical value of each sample was correlated. The thermal conductivity was significantly enhanced with an increase in volume fraction and temperature.

The Influence of the Composition of a Heat-Transfer Agent on the Structure and Properties of Formed Oxide Films of Zirconium Alloys

The defectiveness and structure of oxide films were determined by transmission electron microscopy and scanning electron microscopy. Compression tests with the registration of acoustic emission of ring samples were carried out. The mechanical properties, mechanism, and kinetics of destruction of oxide films of the tube samples of the E125 and E635 zirconium alloys after oxidation in water and in water with the addition of lithium were determined.

Modeling of melting process in a single screw extruder for polymer processing

We developed a mathematical model of the melting zone of a single-screw extruder for processing of polymers. The model takes into account a heat transfer of a polymer with a worm and a cylinder of an extruder (parameters of a heat transfer agent in the worm, as well as parameters of a heat carrier or electric heaters on the outer surface of the cylinder), as well as the real boundary conditions (the worm rotates, the cylinder is fixed).The classical and most commonly spread plane-parallel model of the melting process, in contrast to the developed model, considers a fixed worm and a rotating cylinder extended on the plane. Therefore, processes that actually occur near the surface of a rotating worm are conditionally transferred to the side of a fixed cylinder and vice versa. It distorts fields of speed and temperature of a polymer in the worm channel, as well as the viscosity value of a polymer along the channel height.We investigated a temperature field of a polymer in the worm channel, as well as a relative width of a polymeric along the length of the melting zone of the extruder (the ratio of a width of the polymer to a width of the worm channel). We compared results of the calculation with the experiment. We showed that the proposed model describes the process of melting of a polymer better than the classical inverse plane-parallel model. We also proposed the approach to modeling of an extruder in general as sequences of its interconnected functional zones.The difference between calculated and measured values of the dimensionless width of the polymeric stopper from the dimensionless coordinate along the axis of the worm does not exceed 15 %. This is less than at using the traditional approach to modeling of the melting process.The developed technique was successfully implemented for the modes of processing of various polymeric materials at extruders with worms of diameter 32, 45, 63, 90, and 125 mm.The use of the developed mathematical model will make it possible to better forecast effective modes of the worm extruder, especially if it is necessary to account for heat transfer between surfaces of a worm and a cylinder, as well as processing of materials characterized by low thermal resistance

Study on Heat Transfer Agent Models of Transmission Line and Transformer

When using heat transfer simulation to study the dynamic overload of transmission line and transformer, it needs to establish the mathematical expression of heat transfer. However, the formula is a nonlinear differential equation or equation set and it is not easy to get general solutions. Aiming at this problem, some different temperature change processes caused by different initial conditions are calculated by differential equation and equation set. New agent models are developed according to the characteristics of different temperature change processes. The results show that the agent models have high precision and can solve the problem that the original equation cannot be directly applied in some practical engineers.

Experimental Study and a Mathematical Model of the Processes in Frozen Soil Under a Reservoir with a Hot Heat-Transfer Agent

On an experimental setup, the authors have measured temperature fields in frozen soil during the filling of a reservoir with hot heat-transfer agent (oil), and also the change in the shape and position of the front of ice melting (isotherms T = 0°C) with time. The approximate solution of a two-dimensional Stefan problem on thawing of frozen soil has been given; it has been shown that satisfactory agreement with experimental results can only be obtained with account taken of the convective transfer of heat due to the water motion in the region of thawed soil.

Modeling of thermal mode of drying special purposes ceramic products in batch action chamber dryers

The article is devoted to the modeling of batch action chamber dryers in the processing line for producing shaped ceramic products. At the drying stage, for various reasons, most of these products are warped and cracked due to the occurrence of irregular shrinkage deformations due to the action of capillary forces. The primary cause is an untruly organized drying mode due to imperfection of chamber dryers design specifically because of the heat-transfer agent supply method and the possibility of creating a uniform temperature field in the whole volume of the chamber.

Modeling of energy efficient solutions regarding the heating system and the facade heat insulation in the implementation of thermomodernization

We substantiated design and construction-technological solutions for increasing the energy efficiency of thermomodernizable buildings and structures based on the conducted calculation-and-experimental and numerical studies. We investigated effective structural parameters and material of examined elements of a thermomodernization system of residential buildings and structures, which started their operation before the 90-ies of the last century. We proposed a number of innovative design and construction-technological solutions for the thermomodernization of residential buildings and structures that provide simultaneous modernization of a system of central water heating and facade insulation. Distribution of the temperature field inside a building structure, temperature on the surface of a facade thermal insulation at variation of its thickness by different forms of making of new indents, where new pipelines of a two-pipe system of a central water heating are located, were investigated. In particular, we established that such placement of pipelines makes it possible to reduce heat losses from these pipelines significantly (by up to 74 %) comparing with the placement in a layer of facade insulation at the side of a wall. We investigated the dependence of the cooling time of a heat-transfer agent temperature to 0 o C at the complete cessation of its flow through pipelines on the thickness of a thermal insulation. We determined experimentally the minimum thickness of a facade insulation layer, which is 50 mm, for the studied temperature mode and operating conditions, as well as for characteristics of the materials used, the geometry of pipelines and the facade insulation. We obtained the optimum thickness of a facade insulation layer, which is 100 mm. It provides up to a 100 % freeze protection of pipelines even when a heat-transfer agent movement stops for more than 24 hours. We established that an increase in the thickness of a facade heat insulation contributes to the additional drainage of a building structure, which leads to improvement of thermal characteristics of the thermomodernized building. The study showed that the developed innovative design and construction-technological solutions lead to a significant reduction in the energy consumption of existing buildings and structures of the housing stock, which has been in operation for longer than 30 years, and contribute to maintaining comfortable living conditions.

The Influence of Al2O3- ZnO-H2O Nanofluid on the Thermodynamic Performance of Photovoltaic- Thermal Hybrid Solar Collector System

A thermodynamic analysis was conducted after testing two working fluids to particularly assess the effect of Nanofluid as heat transfer agent on improving thermal, electrical, and exergetic efficiencies of thermally biased solar photovoltaic/thermal (PV/T) hybrid collector system under State of Qatar climate, using experimentally and computationally obtained data. The investigated two fluids were water, and Al2O3-ZnO-H2O Nanofluid mixed with Ethylene Glycol as surfactant. Mass fractions of Nanoparticles were 0.05 wt.% Al2O3 with particle size of 5 nm and 0.05 wt.% ZnO with particles size of 10-30 nm. The results showed that in comparison between water as absorption medium and the mentioned Nanofluid, an increase in thermal and hence total efficiency of the system was recorded for the latter absorption medium scenario, despite considering concentrations of the Nanoparticles relatively low. A very general trend of dramatic decrease in the positive effect of Nanofluid in consistency with the ambient temperature increase was also observed after fitting the data to segments of straight lines. For 0.05 wt.% mass fraction of Nanoparticles the averaged increment in total efficiency was 4.1%, and in total useable energy (exergy) efficiency was 4.6%.

ПОГРЕШНОСТЬ УПРОЩЕННОГО ВЫЧИСЛЕНИЯ СРЕДНЕЙ ТЕМПЕРАТУРЫ ТЕПЛОНОСИТЕЛЯ НА УЧАСТКЕ ТЕПЛОПРОВОДА

The problem of error estimation for the calculation of the average temperature of the heattransfer agent on a heating pipeline section as a half-sum of two temperatures of its boundary points is considered. It is established that in accordance with the physics of the process, the temperature of the heat transfer agent along the length of the pipe is distributed by an exponential curve. Precise formulas are obtained both for the mean length of the heat transfer agent temperature region and for the error in estimating the average temperature from the simplified formula. It is shown that the simplified formula gives the exact value of the average temperature only if the distribution of the temperature of the heat transfer agent along the heat pipeline is linear, which is approximately observed under real conditions. The cases are presented where the error in estimating a simplified formula is a sufficiently small quantity. It is established that the estimation error depends on the linear thermal resistance to heat transfer, consumption of a heat transfer agent, its specific thermal capacity and the length of the heat-pipe section. With the increase in real ranges of the linear thermal resistance of the heat transfer, the consumption of a heat transfer agent, its specific thermal capacity, the estimation error decreases, and the temperature distribution along the length of the section approximates the linear one to a greater extent. On the contrary, with an increase in the length of the section, the estimation error increases. For selected specific conditions, the dependence of the estimation error on the consumption of a heat transfer agent and the length of the section has been investigated. The results of the work can be used in performing thermal and technical calculations of heating and heat supply systems, as well as pipeline systems.

The influence of hydrothermal nanosilica powder aquaspersions on the vital capacity of Daphnia magna Straus crustaceans

This paper cites the results of measuring the influence of aqueous dispersions of nanosilica samples (separated from hydrothermal heat-transfer agent solutions at certain geothermal power plants) used for experimental and industrial purposes on the death-rate of Daphnia magna Straus. The results of the tests conducted in accordance with the approved procedure demonstrate that nanosilica at the concentration of less than 4 × 10-2 g/dm3 does not have toxic influence on Daphnia in the aqueous medium. This fact supports the ecological safety of Russian techniques for utilising nanodispersive silica of a hydrothermal origin in such spheres as plant growing (when plants are treated with nanosilica above the roots on the open-air soil) and production of new types of fish feed in interior and exterior reservoirs.

Investigation of Deposits in Channels of Panels of a Heat-Transfer Agent

An analysis of the behavior of nanosized colloidal particles in a supersaturated solution made it possible to substantiate the possibility of increasing the heat-transfer efficiency in a heat exchanger during magnetic treatment of a heat-transfer agent. A model is proposed to weaken the scale during magnetic treatment of a water stream. A colloidal solution is shown to decrease its stability—the coagulation of colloidal particles begins—because of the deformation of the double electrical layer. As a result of increasing the effective radius of curvature of nanoparticles, the solution becomes strongly supersaturated with respect to forming aggregates, which accelerates the solidification of dissolved salts on them. The influence of the interfacial layer of nanoobjects decreases the energy of formation of critical nuclei (size effect) and their sizes. Since coagulation tends to decrease the concentration of critical nuclei in the solution, their loss should be compensated via the homogeneous generation of new nuclei. As a result, the concentration of suspended particles increases additionally and the antiscale effect is enhanced. The solidification flux of dissolved salts is shown to deposit mainly on suspended nanoparticles due to an increase in their total surface area and to the fact that the coefficient of mass transfer to suspension is higher than that to the wall by four orders of magnitude. The mathematical model constructed on the basis of the detected set of physical processes can be used to perform quantitative estimates of the antiscale effect in real power plants.