Heat-transfer Agent Research Articles

CFD MODELING OF HEAT TRANSFER AND HYDRODYNAMICS PROCESSES IN A HEAT STORAGE TANK

Background. Today, heat storage tanks are an integral part of heating systems. However, modern designs of capacitive storage tanks are characterized by the phenomenon of thermocline and high thermal inertia. To minimize the aforementioned disadvantages, it is proposed to use a “thermal core”, for the formation of which it is necessary to select a substance with a high value of heat capacity.Objective. The purpose of the presented study is to simulate the process of heat and mass transfer in a storage tank with a “thermal core”, in the form of the binary tube located on the central axis, the inter tube space of which is filled with paraffin (a mixture of saturated hydrocarbons with melting point – from 45 °C to 65 °C; dense – 0.880–0.915 g/cm3 at 15 °C).Methods. Fluent software determines the temperature distribution in the heat storage tank under free convection conditions. The resulting data were then converted into a calculation module of the Transient Thermal software complex ANSYS, where further calculations of the non-stationary temperature distribution of the “thermal core” were carried out.Results. It is determined that the heat storage tank with a capacity of 1400 liters, heated for one hour by a heat transfer agent with a temperature of 115 °C, is cooled to 50 °C in 4 hours. The analysis of the hydrodynamic structure of the flow based on the distribution of the trajectories of movement of free-convective flows in the water column of the storage tank indicates the need to improve the design of the tank. It is determined that the use of the “thermal core”, regardless of the type of paraffin used for its formation, helps to reduce the stratification of temperature by tank height. The type of paraffin used to form the “heat core” has no significant effect on the cooling time of the heat storage tank as a whole. However, when using “ceresin” as a filler for the “heat core”, the average tank temperature is generally about 0.5 °C higher than for other paraffin types studied. Thus, it is “ceresin” that should be used as a “thermal core”.Conclusions. The result of the calculation of the inhomogeneous temperature field of all elements of the heat storage tank was used to determine the time of its complete cooling. The conducted research allows automating the process of calculation of the storage tanks as well as carrying out their modernization to increase the efficiency of use.

Using full-flow cogeneration turbine condensate to heat various heat transfer agents

The article gives an overview of the possibilities to upgrade power plant cogeneration turbines efficiency by using low grade heat transfer agents to heat water in cogeneration systems and to increase electricity production in the heat-end mode operations. It brings up technologies based on using turbine full-flow condensate to heat initial water found in additional heaters implemented in the cogeneration turbine recovery system. Introduction of these technologies leads to an increase in steam consumption and to a decrease in enthalpy of regenerative turbine stage steam to heat the condensate, which consequently increases combined heat and power electricity production. An experimental research of cogeneration turbine recovery systems is carried out to find out the minimum and maximum initial water flow through the surface heaters implemented in the turbine recovery system and graphs are built to show the correlation between the initial heated water flow and full-flow turbine condensate temperature.

Crosswise Transport Mechanism of Micro-rotating Hybrid (Cu–Al2O3/H2O) Nanofluids Through Infusion of Various Shapes of Nanoparticles

The shape factor of nanoparticles and micro-rotation effects on steady, oblique flow of hybrid micropolar nanoliquid in two dimensions with the presence of viscosity variation is aimed to be analyzed in this study. This analysis is performed subject to the weak concentration of micro-elements. Model equations of the problem are converted to a non-dimensional set of highly nonlinear ODEs with employing appropriate transformations. This coupled system is afterward solved with shooting algorithm. Influence of viscosity parameter, material constant and nanoparticles shape factor on flow velocity profiles and temperature distribution is analyzed, discussed and presented graphically. The flow monitoring parameters are found to have profound effects on resulting profiles of skin friction and surface heat transfer rate. Shear stress at the surface is increasing with variable viscosity parameter m, while decreasing with material constant K. Blade-shaped nanoparticles are found to be most effective heat transfer agent in the present scenario.

Virgin coconut oil: A nutraceutical and therapeutic food

Coconut oil constitutes the most important source of dietary fat in many countries. But, of late the consumption of coconut oil has been linked with incidence of coronary heart diseases and sustained campaign against its use is going on. Normal coconut oil contains 92% of saturated fatty acids, most of them are medium chain fatty acids (MCFA). The monoglyceride monolaurium is the substance that keeps infants from getting viral or bacterial or protozoal infections. Coconut oil lowers cholesterol through stimulation of thyroid function. Also coconut oil has high resistance to oxidative rancidity, sharp melting behavior, effective heat transfer agent in frying, provides moisture barrier and in frying, loss to bakery items in spray oil use, carrier and protective agent for fat soluble vitamins, maximum glycerin content, easily saponifiable even in cold, germicidal and antimicrobial property, ready penetration into the skin and appreciable water absorbing property.

Mathematical Modeling of Active Thermionic Heat Protection in a High Enthalpy Flow past a Shell

A mathematical model of the process of unsteady heat transfer of a thermionic heat-protection system in convective heating has been formulated and investigated. The effects of evaporation (emission) of electrons from the surface of the emitter on the drop in the temperature of a composite thermionic heat-protection shell have been demonstrated. The effects of some types of heat-transfer agents in a composite shell on the heat-transfer regimes in a body have been investigated. Qualitative agreement of the computation results with the existing data has been achieved.

Method of Calculation and Comparative Characteristics of Heat Exchangers with Heat Transfer Enhancement by Various Random Elements

Consideration has been given to the method of enhancement of a heat-transfer process due to the use of small random metallic elements (packings) in channels of heat-exchange apparatuses. The packings ensure a laminar-to-turbulent transition and a considerable increase in heat-transfer coefficients (of 30 to 60 times). Structures of two modern packing elements and their technical data have been given, as well as expressions to calculate hydraulic-resistance and heat-transfer coefficients. On the basis of a modified method of the thermal number of transfer units, expressions have been obtained for calculation of the tube length and the heat-transfer surface when random packings are used as intensifiers of the process in the apparatuses. Basic parameters of the obtained expressions are the heat-transmission coefficient and modified Peclet (Bodenstein) numbers with the coefficients of reverse mixing of heat-transfer agents. Empirical coefficients at Peclet numbers have been identified using a diffusion model of the structure of a heat-transfer agent flow. The obtained expressions permit taking account of the influence of the reverse mixing of heat-transfer agents on the structural characteristics of a heat exchanger. Examples of calculations of heat exchangers without intensifiers and with random packings have been given. It has been shown that during the heat exchange with different media, the overall dimensions of the heat exchangers are reduced 20 to 25 times. The use of random packings in heat exchangers with media of high viscosity is pressing, since the packings initiate a turbulent regime of flow of heat-transfer agents.

РАСЧЕТ ТЕРМОДИНАМИЧЕСКИХ ПАРАМЕТРОВ ОПУСКНОГО ТЕЧЕНИЯ ТЕПЛОНОСИТЕЛЯ В СКВАЖИНЕ С УЧЕТОМ ПРОТАИВАНИЯ МНОГОЛЕТНЕМЕРЗЛЫХ ПОРОД

Актуальность исследования обусловлена необходимостью расчетов параметров закачиваемого в нефтесодержащей пласт теплоносителя на всем протяжении его движения от выхода из нагревателя или парогенератора до пористого коллектора. Основным используемым сегодня методом разработки залежей высоковязких и битумных нефтей является закачка в нефтяной пласт теплового агента (горячая вода или пар). При таком способе повышения нефтеотдачи пластов происходит снижение вязкости нефти и увеличивается коэффициент извлечения нефти. Повышение коэффициента извлечения нефти может привести к рентабельности разработки месторождений с высоковязкими нефтями. Поскольку для производства горячей пароводяной смеси нужны достаточно большие энергетические затраты, и для эффективного теплового воздействия на нефтяную залежь требуется при достаточно высоких скоростях закачки значительный объем теплоносителя, то для успешной реализации данного метода разработки необходимы предварительные расчеты на базе адекватной математической модели, в которой учтены различные аспекты изучаемого процесса. Целью исследования является анализ влияния различных факторов на характер распределения по глубине скважины параметров теплоносителя, а также интенсивность протаивания многолетнемерзлых пород. Объекты: гидродинамические и теплофизические процессы, протекающие при движении теплоносителя в нагнетательной скважине, с учетом теплового взаимодействия с окружающей горной породой. Методы. Теоретическое исследование выполнено на базе методов механики многофазных систем и вычислительной математики. Задача нахождения параметров опускного двухфазного потока в нагнетательной скважине разбивается на две части. В первой части определяются термодинамические параметры стационарного нисходящего течения горячей пароводяной смеси в подъемной колонне скважины с учетом тепловых потерь в окружающие горные породы. Во второй исследуется нестационарное распространение в горной породе теплоты, поступающей от скважины, с учетом возможного протаивания многолетнемерзлых пород. С учетом найденного распределения температуры в окружающих породах происходит переход к первой части. Результаты. Приведена математическая модель опускного течения теплоносителя в нагнетательной скважине с учетом внешнего теплообмена скважинного продукта с окружающими горными породами (в том числе и многолетнемерзлыми). На ее базе численно изучено влияние различных факторов (массовый расход и сухость нагнетаемого пара, различная толщина теплоизолирующего материала на внешней поверхности подъемной колонны и т. п.) на изменение термодинамических параметров двухфазного потока по глубине скважины, а также темпы растепления многолетнемерзлых пород. Получены зависимости радиуса протаявшей зоны в мерзлых грунтах от массового расхода закачиваемого теплоносителя, а также от различного заполнения кольцевого зазора скважины.

Prediction of Heat Transfer in Reciprocating Antifreeze Flow Through a Porous Filter

Heat transfer to an oscillating vertical annular flow through a porous material is investigated experimentally. The flow media includes stationary stainless steel wool filter and monoethylene glycol (which is known as a coolant, heat transfer agent or antifreeze) as the working fluid. Reciprocating forced oscillations are imposed on the single-phase monoethylene glycol via a frequency controlled dc motor and a piston-cylinder device where displacement amplitude is kept constant. Electrical heater occupies the inner section of the vertical annulus which provides constant heat flux. The analysis is carried out for two different heat fluxes and for five different frequencies and the effect of these on the temperature field and resultant heat convection coefficient are studied. A cycle and space averaged Nusselt number correlation is fitted which is useful in predicting rate of heat transfer from oscillating flows through highly porous and permeable solid media (such as in filters) at low actuation frequencies and at low heat flux rates. Developed correlation equation is validated for monoethylene glycol, glycerol and water. Oscillatory antifreeze flow in porous filter is proposed as a remedy for the limited thermal conductivity of the water-monoethylene glycol solution. These results also have possible applications in fluid pumping technology in converting of low-grade thermal energy to pumping work.

Modeling of the thermal protection system based on the thermionic technology

The mathematical model of unsteady heat transfer in the thermionic thermal protection system during high-enthalpy heating is studied numerically. The effect of evaporation of electrons from the emitter surface on reduction of the temperature of the multilayered shell of the thermionic thermal protection system is demonstrated. The influence of some heat transfer agents in the composite shell on the regimes of heat transfer in the body is considered. Qualitative agreement of the calculated results with available data is obtained.

Analysis of energy-saving measures in industrial steam supply systems

The high level of heat losses in Russia is determined by both the excessive centralization of many heat supply systems and the poor state of heat networks and the low quality of their service. For this reason, the development and application of energy-saving measures to reduce heat loss is a priority and urgent area in the power industry. The article is devoted to the assessment and analysis of energy-saving measures of industrial steam supply systems using the example of an industrial steam pipeline from Smolensk CHPP-1. The study examined the main factors affecting the parameters of the heat transfer agent in the consumer. The main measures to reduce heat losses in steam networks are considered and their calculation is carried out. Of the considered methods of energy saving, it is preferable to increase the thickness of the thermal insulation of steam pipelines. Moreover, the calculations showed that the optimal value of the insulation thickness for the investigated steam pipeline was 0.17 m, which corresponds to the highest quality of the supplied steam and the shortest payback period.

Determination of the thermotechnical measures of the condensing water heating boiler’s high-temperature section

This paper presents the experimental data processing results, obtained during tests of the fuel-saving condensing water heating boiler, that has been designed by the employees of the Belgorod State Technological University named after V.G. Shukhov. The mentioned boiler can be used in heat supply for residential, industrial and office buildings. The paper presents the justification of the stand-alone systems actuality use for heat supply of consumers with different needs, and also the use of such systems as a heat-generating unit in condensing boiler type as a heat source. It demonstrates the functional diagram and description of the test bench for the condensing water heating boiler specimen with heat production of 250kW, and also gives an operation description of this test bench. The paper presents the heat transfer agent values of flow rates and temperatures, obtained during the boiler’s tests under different loads. It also describes the test result processing methods, presents formulas for calculations. It presents dependences of the energy carrier parameters, and also heat transfer coefficients in the boiler’s high-temperature section elements on its load. The results analysis of the experimental data processing has been conducted. The conclusions about prospective use of the suggested condensing water heating boiler as the heat-generating unit in heat supply stand-alone systems for consumers with different needs have been formulated.

The Effect of Doping of Lead with Lithium and Zinc with Strontium on the Kinetics and Phase Formation in a Number of Low-Melting Eutectic Systens User in Electronics and Heat-Transfer Agents

The effect of Li and Sr impurities on the kinetics and structure formation of alloys in the Sn - Pb, In - Zn, Sn - Zn systems used in the soldering of instrument nodes in electronics has been investigated. The XPS method showed that under the given experimental conditions and the indicated concentrations of lithium impurities in lead and strontium in zinc, there are no prerequisites for the formation of chemical compounds, which is explained by an insignificant impurity content, although a significant amount of chemical compounds is formed according to state diagrams. It was also established that impurities affect the kinetics of phase growth in the junction zone.

Порівняльний аналіз ексергетичної ефективності теплоутилізаційних систем різного призначення

To assess the exergy efficiency of heat recovery systems, a complex approach was used, which allows us to evaluate the operation of heat recovery systems simultaneously from several positions: thermodynamic, heat engineering, and technological. In this work, within the framework of this approach, the heat-exergy efficiency criterion and exergy efficiency were used. Four types of heat recovery systems for various purposes for boiler plants were investigated. For the systems under consideration, structural schemes have been developed in which exergy flows between individual discrete elements of a simple structure are identified. The calculation of exergy characteristics was carried out using the balance methods of exergy analysis and a technique combining the methods of exergy analysis with the RP method of representing the thermodynamic balances of the system in matrix form. Based on the calculated exergy characteristics, a comparative analysis of the exergy efficiency of heat recovery systems for various purposes is carried out. According to the research results, one of the possible ways to reduce the total exergy losses in heat recovery systems is to reduce losses in the pump system and piping system. This reduction is achieved by aggregating the maximum number of functional elements of the heat recovery system in one device. It is shown that for a heat recovery scheme in which the three main elements are structurally combined in one housing, the heat-exergy criterion is reduced by 6.7 %, and the exergy efficiency is increased by 4.0 % compared to the non-aggregated heat recovery scheme. Thus, heat recovery systems with complex use of recover heat for heating various heat-transfer agents and with aggregation of the main system elements in one housing are characterized by the best exergetic indicators. Key words: boiler plants; waste gas heat recovery, exergy losses, complex techniques; efficiency

Magnetocaloric effect in bamboo-grained Ni-Mn-Ga microwires over a wide working temperature interval

Bamboo-grained Ni-Mn-Ga microwire is promising for achieving considerable magnetic-field-induced strain due to less neighboring grain constraints to the twin boundary motion. Such reduction of resistance to interface motion also favors the reduction of hysteresis in magnetic refrigeration. Here, bamboo-grained Ni-Mn-Ga microwires were successfully synthesized by a melt-extraction technique and subsequent high temperature heat treatment at 1323 K for 3 h under Argon atmosphere. Corresponding microstructure, martensite transformation (MT) behaviors and magnetocaloric properties were investigated. The high specific surface area of the microwires favored the element evaporation at high temperature, leading to a heterogeneous composition state, which is responsible for the MT temperature (range) change and the multi-variants state in the bamboo-grained microwires. Nearly no magnetic hysteresis loss was obtained. The increased compositional variation led to the partial overlap of the MT and the magnetic transition, resulting in the improvement of the working temperature interval ~71 K and net refrigeration capacity ~255 J/kg under μ0H = 5 T, which is heretofore the largest value reported in Ni-Mn-based Heusler alloys. When utilized as refrigerant in a cooling device, such small-sized microwires can increase the contacting area between the material and the heat-transfer agent, which helps the heat exchange and thus improve the refrigeration efficiency.

Melting heat transfer of power-law non-Newtonian phase change nano-enhanced n-octadecane-mesoporous silica (MPSiO2)

The heat transfer removal from heated elements in different engineering devices is the main challenge for each engineer in various fields. This problem can be solved using an effective heat-transfer agent or by increasing the heat transfer surface. The present work is devoted to an opportunity to use the phase change material with nanoparticles for an intensification of heat removal within a gap between two coaxial vertical isothermal cylinders. The analysis was performed numerically using the Galerkin finite element approach in the case of the non-Newtonian nature of the nano-enhanced PCM. The power-law was used for the description of the non-Newtonian behavior of the considered material. For the solution to the Stefan problem, a deformed mesh method, based on the Arbitrary Lagrangian–Eulerian (ALE), was used. The developed computational code was validated using the numerical and experimental data of other authors. The effects of the nanoparticles volume fraction, aspect ratio and Fourier number on the melting process were investigated. It has been revealed that the inclusion of nanoparticles within the phase change material leads to both less intensive melting of the material and a reduction of the average Nusselt number.

The matrix method for calculating complex heat and mass transfer systems with multicomponent coolants

Earlier, we obtained a solution to the heat transfer problem in multi-threaded multi-stage heat-exchanging units with one-component heat carriers. However, in the energy, food, and petrochemical industries, often heat and mass transfer processes involve coolants consisting of components whose heat and physical properties differ significantly. For carrying out heat engineering calculations with such coolants, averaging of the indicated properties of the components is usually performed. However, in a number of industrial technologies based on distinguishing thermo-physical properties, in particular, differences in the boiling temperature of the components, processes for their separation by distillation are used. In this case, when calculating heat and mass transfer processes to obtain pure components with acceptable impurities, it is necessary to take into account the difference in their thermo-physical properties precisely. The development of calculating methods for the systems of multi-threaded multi-stage heat transfer processes with multi-component coolants to analyze the efficiency of their separation is a topical issue facing the energy sector and related industries. To study and simulate heat and mass transfer systems, the equations of mass and energy balances and linear algebra methods of are used. Within the framework of the matrix approach, for the case of using a mixture of components with different boiling points as heat transfer agents, a heat and mass transfer process model has been obtained. The model allows evaluating the degree of separation of components and the quality of the finished product by the content of impurities in it for various methods of organizing the process. The solutions of the model equations have been obtained and analyzed. The results can be used to increase the efficiency of resource and energy-saving technologies in solving problems of the optimal distribution of temperatures at the system stages due to recirculation of the selected components and to obtain pure components with an acceptable content of impurities in the energy, chemical and food industries.

ДОСЛІДЖЕННЯ ВПЛИВУ ПОЛОЖЕННЯ ТРУБКИ В ПУЧКУ ТРУБ КОЖУХОТРУБЧАСТОГО ТЕПЛООБМІННИКА НА ПРОЦЕС ТЕПЛОВІДДАЧІ

The paper is concerned with an issue of liquid distribution in the diametrical bank tubes of the shell and tube heat exchanger. The experimental-theoretical approach for the research has been applied. The data on the determination of velocities of the heated liquid through the pipes of the heat exchanger have been obtained and processed. The research was carried out at the created experimental factory. Water at a temperature of 20 ºС has been supplied to the tubes. The temperature of the water has been maintained by a thermostat. The temperature at the outlet of the tube has been measured with a thermocouple element. Water (heat conductor,) at a temperature of 60, 80 or 95 ºС has been circulating in the outside of tubes space. The temperature of the water has been maintained by pumping it through a thermostat. The velocities of the heated liquid in the diametric bank tubes have been determined, which differed considerably depending on the position of the tube. Consequently, the results of the research obtained have discovered the significant deviations of such parameters as the liquid temperature at the outlet of the apparatus, tube wall temperature and heat transfer coefficients between the tube and heated liquid. The distribution insert has been used, in order to match the above-mentioned indicators. The distribution insert is a disk with the optimized holes. The alignment of the liquid velocities through the tubes of the diametric bank has been observed, which has consequently led to the uniform heating of both the central and side tubes. The study outcome has proven to be the solution to prevent the overheating of the peripheral tubes. Thus, the generation of a uniform field of velocities for the heat transfer agent through the tubes of the shell and tube heat exchanger contributes to the uniform heating of both central and peripheral tubes, and increases the heat transfer coefficient in the side tubes. The conclusion has been drawn that the reason for the failure or heat transfer low efficiency in the peripheral tubes of the shell and tube heat exchanger is the nonuniform distribution of liquid velocities in different tubes and as a consequence, the low heat transfer coefficient in those tubes where the velocity is low.

Modeling of the lifting of a heat transfer agent in a geothermal well of a gas condensate deposit

The authors are grateful to Ukrgazvydobuvannya PJSC for the opportunity to obtain both empiric materials and parametric data concerning gas condensate wells of Lanivske GCD.

Parameter control of the adjustable pipeline heat supply system

Controlled pipeline heat supply systems are equipped with shut-off valves that causes a decrease in the stabilization level of the heat-transfer agent transportation process and reducing the pressure in the network during transition processes. Booster pumping stations are installed to stabilize the pressure in the heat supply system. The heat-transfer agent transportation process becomes turbulent that significantly reduces the hydraulic system stability when such systems are working. The process of transporting the coolant. Regulator that contains proportional, integral, and differential control components is used to control the dynamic parameters. Studies have revealed the reduction level of dynamic characteristics depending on the regulator components. The use of PID control allows to change the oscillatory process into acyclic process.

Energy-Efficient Combination Convective Drying Of Disperse Materials

We propose combination convective drying of disperse materials based on the kinetic behavior of the process for vegetative feedstock and improvement of the degree of utilization of the energy potential of the heat transfer agent, taking into account energy and exergy thermodynamic analysis methods. We have developed continuous drying equipment for energy-efficient processes using variable thermal treatment.