Regenerative Heat Transfer Research Articles

Dynamic Modeling Simulation of Regenerator for Glass Furnace Applications

The melting process in the glass industry is an energy-intensive process that uses fossil fuels to maintain melting temperatures between 1600°C and 1700°C. The process is carried out in the Glass Furnace. Obtained the high temperature also of flue gas is around 1350 °C – 1500 °C. Hence with the high temperature is potential to heat recovery in the form of combustion air pre-heating using a regenerator to increase the efficiency in Glass Furnace. This phenomenon gave rise to an idea to create a modelling mathematic to know the optimum process in Glass Furnace. Many studies on Glass furnace regenerator have been carried out but only for one cyclic of heat transfer in regenerator. Therefore, in this study, dynamic modeling of the regenerator will be made, namely a mathematical model that describes quantitatively the dynamic behavior during the process of reversing the direction between the regenerators, which will later explain the effect of air flow rate and the selection of the optimal transition time value for the demonstration, regenerator work and regenerator heat stability, by observing the dynamic behavior of the regenerator temperature profile using the FlexPDE software version 7. The simulation results show that the longer the switching time of regenerator is linier to inclining temperature in the regenerator with the optimum switching time (ST) at 10 minutes. The regenerator heat stability greatly influenced by air flow rate and heat propagation by heat transfer convection. However, the dimension selection of the regenerator plays a crucial role in heat utilization in glass furnaces.

Feasibility of Recuperative Heat Transfer and Regenerative Heat Transfer in Reciprocating Compressors: Comparative Analysis

Feasibility of Recuperative Heat Transfer and Regenerative Heat Transfer in Reciprocating Compressors: Comparative Analysis

Activation of absorption chillers by the transit heat flow of the energy cycle in cogeneration solar systems

The problem of peak electricity consumption for air conditioning needs in countries with a hot climate is analyzed. It is determined that one of the ways to solve it is to create and use solar cogeneration coolers. The generation of electricity and cold in comparable proportions by such installations will reduce the load on generating electric capacities and create a reserve for connecting electric coolers. The combined use of power (turbine) cycles and industrial absorption chillers (one- and two-stage) has been explored. Evaluation of consumer qualities of a wide range of designs of cogeneration coolers is carried out using the developed thermal schemes based on Rankine cycles. The idea of the proposed method for constructing a cogeneration cooler is to use the turbine cycle waste heat to activate absorption chillers that operate in the normal mode. The study results showed that steam-to-water cogeneration coolers can be effectively used with a two-stage absorption chiller. It is shown that in the inverse mode such a cooler is able to provide efficient air heating in winter (up to +35 °C). It has been determined that the use of a butane cycle in the supercritical steam parameters region allows, with a little decrease of cogeneration cooler COP during in hot hours, to increase the cooling capacity by ∼2 times by reducing the intensity of regenerative heat flow transfer in the power unit. It has been established that the intensification of regenerative heat transfer in the power unit significantly affects on the system cooling capacity.

Investigation of turbulent heat transfer performance of aviation turbine fuel multi-wall carbon nanotube nanofluid

Nanofluid is a novel heat transfer fluid prepared by suspending high thermal conductivity nano-sized particles in conventional fluids (water, engine oil and ethylene glycol). Thermo-physical properties (Thermal conductivity, dynamic viscosity and specific heat) and turbulent heat transfer performanceof Aviation Turbine Fuel (ATF) based Multiwall Carbon Nanotube (MWCNT) nanofluid are investigated experimentally for particle volume concentrations of 0–1% and at mean fluid temperatures of 30οC and 50οC for a potential regenerative heat transfer application in semi-cryogenic liquid propellant rocket engine. The experimental results show that the heat transfer coefficient of the nanofluid increases with particle volume concentration, with a maximum enhancement at 1% particle volume concentration of approximately 23% and 50% observed at 30οC and 50οC respectively. Two different numerical modelling approaches (a single phase fluid model with enhanced thermo-physical properties and an Eulerian-Lagrangian model called the “discrete phase model”) are employed to simulate the experimental conditions. The predictions from both numerical modelling approaches are found to compare reasonably well with the experimental data. The enhanced heat transfer performance is expressed on an equal power penalty basis to clearely show the advantage of the nanofluid.

Determining the angular velocity areas of a reciprocating hybrid power machine for operation in compressor and pump modes

A methodic for determining the angular velocity of a reciprocating compressor with regenerative heat exchange in the pump mode is considered for a known angular velocity of the machine in the compressor mode. The methodic is based on the use of mathematical models of the working processes of a reciprocating compressor and a reciprocating pump. The developed mathematical models are based on the fundamental laws of conservation of energy, mass, motion and equations of state. As the main condition in determining the angular velocity of the machine in the pump mode, the equality of the maximum pressure losses in the injection process when the machine is operating in the compressor and pump modes, as well as the equality of the relative energy losses in this process, is considered. Keywords: reciprocating compressor, reciprocating hybrid power machine, reciprocating pump, regenerative heat transfer, angular velocity. Scherba_V_E@list.ru

Preliminary Crankshaft Speed Assessment for a Reciprocating Hybrid Power Machine with Regenerative Heat Transfer in Compressor and Pump Modes

Preliminary Crankshaft Speed Assessment for a Reciprocating Hybrid Power Machine with Regenerative Heat Transfer in Compressor and Pump Modes

Study of the effect of regenerative heat transfer enhancement on the silicothermic reduction process

As the main process for industrialized production of crude magnesium, the silicothermic reduction technology has problems such as high energy consumption per ton of magnesium and serious pollution. Under the policy of carbon peak and carbon neutrality, the implementation of energy conservation and pollution reduction technology reform has become an urgent issue in the silicothermic reduction process. Although the thermal conductivity of the briquettes used for magnesium production is low, they will absorb a lot of heat during the reduction reaction. As a result, the heat cannot be transferred quickly enough for the chemical reaction endothermic, leading to a slow magnesium production reaction and low production efficiency. Therefore, in-depth study on the kinetic mechanism of the improved heat transfer coupled chemical reaction is required to decrease the production cycle and increase efficiency. In this work, the effect of filling the voids of briquettes with regenerative particles of different materials on heat transfer process was first studied by means of experiments. It has been discovered that as the thermal conductivity of the filling material increases, the heat transfer process is accelerated, but the endothermic behavior of the regenerative particles at room temperature during the heating process seriously affects the heat transfer to the briquettes. On this basis, the models of heat transfer and magnesium reduction kinetics were combined and the recycling technology of high temperature regenerative particles with different materials was studied by numerical calculation method. The findings demonstrate that the production cycles for filling aluminum oxide, silicon carbide and silicon nitride are reduced to 6, 4 and 1 h, respectively, at the initial temperature of 1373 K for the regenerative particles, compared with the 8 h of the traditional method. However, when the voids of the briquettes are filled with quartz sand with a thermal conductivity close to that of the briquettes, the period increases to more than 10 h. When the initial temperature of the filled regenerative particles decreases, the production cycle also increases. In industrial production, materials with high thermal conductivity should be selected as regenerative particles as far as possible on the basis of considering the cost, and thermal insulation measures should be taken to minimize the heat loss during the recycling of regenerative particles.

Influence of the initial parameters on the thermodynamic efficiency of carbon dioxide power cycles

This paper considers the main CO2 power cycle configurations based on the Allam and JIHT cycles. In particular, the authors of the article have proposed new configurations of the power cycle. The efficiency of these cycles is studied as a function of the initial temperature and pressure of the working fluid. The thermodynamic efficiency can reach 65–66%. It is shown that the presence of regenerative heat transfer and the properties of supercritical carbon dioxide have a great influence on the thermal efficiency.

Optimization of the operation mode of regenerative heat exchangers

The paper considers the operation of regenerative heat exchangers with a fixed checkerwork. Such a checkerwork allows for high-temperature heating of gases and is made of refractory materials with a relatively high heat capacity, but low thermal conductivity. The article presents calculations of regenerative heat transfer for devices with block checkerwork. It is shown that a decrease in the equivalent diameter of the channel d e leads to an increase in the average air heating temperature over the period. An increase in the relative water section of the checkerwork f also leads to an increase in the air heating temperature, but only to a certain limit. On the one hand, with an increase in the relative water section, the specific heat exchanger surface increases. On the other hand, at a certain value f, the accumulating mass of the checkerwork significantly decreases, and as a result, the air heating temperature decreases. For the same reason, for checkerwork with a high value of the relative water section, it is necessary to reduce the duration of the heating/cooling periods of the checkerwork. The paper also examines several types of compact checkerwork, which are very promising, including in heat storage systems. It is noted that the use of such attachments in conventional regenerate heat exchangers is impossible. First, it is necessary to increase the water section of the heat exchanger and significantly reduce its height, otherwise, the pressure loss will increase sharply. Secondly, it is necessary to significantly reduce the duration of the heating/cooling periods, otherwise, due to more intense heat exchange, the air temperature at the outlet of the regenerative heat exchanger changes much more than in the block checkerwork.

Development of optimization criterions of regenerative heat exchangers

The paper offers a simple method for analyzing the operation of regenerative heat exchangers, which significantly reduces the amount of calculations. Similarity criterions of regenerative heat exchange are obtained, which can be used to analyze the relationship of their thermophysical, structural and operating parameters. Similarity criterions were formulated by reducing the differential equation of regenerative heat transfer to a dimensionless form. These mathematical transformations were performed under the condition of regular regime of heating (cooling) of the checkerwork. As a result, three similarity criterions are obtained. The first criterion Kp1 determines the ratio between the heat-accepting capacity of the heat transfer agent and the heat-accumulating capacity of the checkerwork. The second criterion Kp2 is the ratio between the heat-receiving capacity of the heat transfer agent and the intensity of convective heat exchange. The third criterion Kp3 is the ratio between the heat-accumulating capacity of the checkerwork and the intensity of convective heat exchange. Similarity criterions include both the design and performance characteristics of the regenerative heat exchanger. Using these criterions, it is possible to choose a rational operating mode for existing heat exchangers. The proposed method of criteria analysis of regenerative heat exchangers was applied to hot-blast stove. In particular, the conditions for implementing a regular regime in heat exchangers are found. The regular mode is characterized by a linear temperature distribution over the height of the checkerwork, which can be obtained by selecting the appropriate ratio of the reduced costs and the time of the cooling and heating periods. It is also shown in what range it is advisable to change the design and operating parameters of the heat exchanger in order to obtain the maximum heating temperature of the blast-furnace air and the maximum heat availability factor. Since the similarity criteria are universal, the proposed method can be applied to other types of regenerative heat exchangers.

Investigation of the relationship of structural characteristics and operating regime of regenerative heat exchangers

The paper presents the results of a computational study of the operating modes and design factors of a regenerative heat exchanger. The calculations were based on a mathematical model of regenerative heat transfer. It is shown that the most rational mode of heating / cooling the checkerwork is the regular mode. The regular mode is characterized by a constant local temperature head over the height of the checkerwork, and as a result, a linear distribution of the temperature of the checkerwork along the height. It is shown that it is during the implementation of the usual mode that the maximum heating temperature of the coolant and the maximum heat utilization coefficient are provided. The calculations were carried out for a hot-blast stove. In these heat exchangers, the flow rate of the cold heat-transfer agent (blast-furnace air), the temperatures of the hot and cold heat-transfer agent at the inlet to the checkerwork are constant. The range of variation of the heating/cooling time of the checkerwork for such devices is determined to ensure regular mode. It is shown that, within the framework of the regular regime, a decrease in the duration of the cooling period is accompanied by an increase in the temperature of heating the blast-furnace air, a decrease in the temperature of the flue gases, and an increase in the heat utilization coefficient. Also shown are the values of the design parameters of the checkerwork (equivalent diameter of the checkerwork channel, specific heating surface) at which the heat exchanger will operate regular regime. The calculations showed a range in which it makes sense to increase the heat- transfer coefficient of the checkerwork for a specified range of flow rates of the coolants and the time of the periods of heating and cooling. It is shown in the work that increasing the specific surface of the checkerwork heating and increasing the heat-transfer coefficient will allow one to obtain a tangible effect only in combination with a corresponding change in the operating parameters of the heat exchangers.

Power and efficiency optimizations of an irreversible regenerative organic Rankine cycle

Rational and efficient uses of low temperature waste heats have become an important research topic, and organic Rankine cycle is one of effectual methods for the recoveries of waste heats. The performances of simple and regenerative organic Rankine cycles have been analyzed and optimized by using classical thermodynamics and finite thermodynamics. Based on finite time thermodynamics, an irreversible regenerative organic Rankine cycle model is built in this paper. With the fixed total heat transfer area of all heat exchangers (evaporator, condenser and regenerator) in the cycle, the power output and thermal efficiency of the cycle are maximized with the changes of heat transfer area ratios of the heat exchangers, mass flow rate of the working fluid and superheat. The influences of the internal irreversible losses on the power output and thermal efficiency of the cycle are analyzed. The results illustrate that there exist an optimal evaporator heat transfer area, an optimal mass flow rate and an optimal superheat to make the power output reach its triple maximum. There also exist an optimal evaporator heat transfer area ratio, an optimal regenerator heat transfer area ratio and an optimal superheat to make the thermal efficiency reach its triple maximum. The power output and thermal efficiency after triple optimizations are increased by 25.22% and 12.16%, respectively. Moreover, the internal irreversible losses have similar effects on the power output and thermal efficiency. Useful guidelines for the designs of the practical regenerative organic Rankine cycles can be offered from the gained results of this paper.

Generation of Heat Transfer Coefficient Data in Regenerator for Stirling Cycle Refrigeration System

This paper attempts to generate the data of heat transfer coefficient for regenerator in stirling cycle refrigeration system on the basis of available experimental data. The available data is based on assumption that the mode of heat transfer in regenerator is conduction. This data does not produce optimal design of regenerator. Heat transfer coefficient must be modified to account for heat transfer in a regenerator by all three modes i.e conduction, convection & radiation. The data for heat transfer coefficient is generated on the basis of experimental results available in literature of performance of various stirling cycle refrigeration systems with different designs of regenerator. These models can be used to predict the performance of stirling cycle refrigerator system on the basis of dimensions of regenerator. The models are validated and optimized. This paper also presents the effect of variations in regenerator dimensions i.e. regenerator length, regenerator diameter, wiremeshsize, wire mesh arrangement, and wire mesh materialonHeat Transfer coefficient of regenerator.This data for heat transfer coefficient for regenerator of Stirling cycle refrigeration system can be used for optimizing design of regenerator of stirling cycle refrigeration system or predicting performance of stirling cycle system accurately.

CFD modeling of unsteady SCR deNOx coupled with regenerative heat transfer in honeycomb regenerators partly coated by Vanadium catalysts

The unsteady selective catalytic reduction (SCR) of NOx with honeycomb regenerators coated by Vanadium catalysts, under the condition of hot gas and cool air blowing alternately in the opposite direction, should be simulated coupled with regenerative heat transfer, because catalyst activity depends on temperature greatly. In the current work, the SCR deNOx model based on the porous medium and volumetric reaction assumptions is developed for the catalyst layer and integrated into our existing three-dimensional (3D) CFD heat transfer model of honeycomb regenerators. Steady SCR deNOx experiments with monolith catalysts are simulated for model validation and the contour is presented to study the NOx concentration polarization. With the novel model, unsteady SCR deNOx in honeycomb regenerators partly coated by a film of V2O5-WO3/TiO2 is simulated, and the effects of structural and operational parameters on the NOx conversion and thermal-hydraulic performances are studied. Besides, the temporal variation curves of fluid temperatures and NO concentration are presented for discussions. Numerical results demonstrate that current CFD model could predict the performances of partly-coated honeycomb regenerators with a reasonable precision and the regenerator with square openings of 6mm×6mm could work with a good overall performance at the gas inlet velocity of 4m/s.

Reversible Heat Exchange in the Nozzle with Water–Ice Phase Transition in Filtration of Air

Results of experimental study of reversible heat exchange with water–ice phase transition in filtering the airflow through a tube heat exchanger are presented. The heat exchanger is made of thin-walled plastic tubes (3 and 5 mm in diameter) filled with water and sealed at both ends. The heat exchanger was tested in a laboratory setup with a Ranque tube applied to create a flow of cold air. The heat exchanger operation was investigated in steady-state and various reversible modes. Themeasurements showed the possibility of substantially increasing the time between switching the direction of airflow with maintaining a high coefficient of heat regeneration. The results can be used in the development of regenerative heat and mass transfer devices, including VENTIREG systems of ventilation emission heat regeneration.

Performance prediction of a Martini type of Stirling engine

In this study, a Martini type free piston Stirling engine concept is proposed and its performance analysis is conducted. The Martini engine consists of a heating-cooling unit and an expansion unit for working gas. The heating and cooling of the working gas is accomplished via displacing the gas between a hot and a cold volumes taking place in a displacer cylinder. The displacer is kinematically driven by a crank mechanism. The expansion of the working gas is accomplished via a power piston working in a separate cylinder. The power piston has no kinematic driving mechanism but one of its ends is adjusted to a mechanical spring while the other end is exposed to the gas pressure. The power piston bears an I type magnet at the center of itself. The expansion cylinder is equipped with a linear alternator to produce electricity. While the piston and the equipped magnet is performing a reciprocal motion in the expansion cylinder, the conductive wire coil wound around the expansion cylinder generates an electric current via using the work generated by the piston. The analysis conducted in this study involves the prediction of thermodynamic performance parameters of the engine as well as dynamic characteristics. The displacer is assumed to be driven by a crank mechanism turning with a constant speed and the motion of the displacer is defined kinematically. The motion of the power piston is defined with a differential equation obtained from the Newton law of motion. The flow friction of working fluid is calculated with Darcy equation. Variation of temperatures in nodal volumes are calculated with the first law of the thermodynamics given for unsteady open systems. Input parameters of the analysis were optimized for 2500 rpm engine speed. By introducing 1000 K hot end temperature, 400 K cold end temperature and very realistic values for the other inputs, the thermal efficiency of the Martini engine has been predicted as 20.6%. When the flow friction in the regenerator is ignored, the thermal efficiency increases from 20.6% to 21.5% and the cyclic work generation increases from 236.5 J to 254.8 J. For inputs optimized for 2500 rpm engine speed, the power output of the engine was predicted as about 10 kJ. When the regenerator heat transfer area was increased from 0.69 m2 to 1.38 m2, the thermal efficiency increased from 17.5% to 34.4%. However, further increase of regenerator heat transfer area was restricted by collusion between piston top and cylinder top. The Martini engine was found to be a useful supplementary device to couple with Internal Combustion Engines to increase the thermal efficiency of them. The thermal efficiency of the modified Internal Combustion Engine is expected to be 5% more than the non-modified engine.

PROSPECTS OF APPLYING HEAT PUMPS UPON CARRYING OUT COMBINED MASS TRANSFER PROCESSES

The prospects of using heat pumps for the separation of mixtures by combination of different mass transfer processes are considered, which is associated with the supply and removal of thermal energy. The heat released in some stages can be successfully used at other stages of separation. Using heat pumps makes it possible to change the temperature potentials of heat fluxes, which greatly improves the efficiency of regenerative heat transfer. If a vapor phase forms when carrying out mass transfer processes, it can be used as the working fluid of the heat pump of the open type. If mass transfer processes are carried out without the formation of vapor phases, it is necessary to apply heat pumps of the closed type, in the circuit of which a variety of intermediate heat transfer fluids circulate. The article briefly describes the features of mixtures separation by a combination of fractional crystallization by evaporation, dissolution, fractional melting, distillation and rectification with the use of compressor heat pumps of open and closed type. In order to assess the energy efficiency of different variants of combined processes and to compare them with traditional separation it is suggested to use the relative equivalent consumption, which makes it possible to take into account the different cost of thermal and electric energy required for carrying out the considered process of separation. Different variants of organizing the combined separation are compared. It was found that their energy efficiency significantly depends on the composition of the initial mixture, on requirements for the separation products, as well as on the position of the eutectic point on the liquid - solid phase charts. It was shown that the use of heat pumps allows reducing several times energy costs, as well as the consumption of refrigerants for combined separation.

Heat transfer performances of honeycomb regenerators with square or hexagon cell opening

Honeycomb regenerators with varied cell openings are applied to regenerative combustion systems. A three-dimensional unsteady numerical model, which calculate the gas flow and gas-solid heat transfer in regenerators with square or hexagon cell openings is developed by computational fluid dynamics package, FLUENT. The radiative transfer equation is employed to calculate radiative heat transfer in gas and is added in gas energy conservation equation as a source term. Convection coupled with radiation is used in gas-solid boundary condition. Moreover, temperature-dependent thermal properties of gas and solid are considered in the model. By comparing simulation results with experimental data from the literature, the numerical model is verified. The effects of different cell opening shapes on gas-solid interface heat flux, gas temperature profile and energy recovery ratio are compared. The simulation results show that there is a higher outlet air temperature and energy recovery ratio in square opening cells than hexagon opening cells. Furthermore, the influences of cell opening side length and switching time on air preheating effect and pressure loss are investigated in regenerators with the two different openings.

The effect of regenerative heat transfer on cycle efficiency of the refrigeration unit

The effect of regenerative heat transfer on cycle efficiency of the refrigeration unit

The ORC-PD: A versatile tool for fluid selection and Organic Rankine Cycle unit design

The ORC (Organic Rankine Cycle) is an emerging and commonly accepted technology for converting medium and low temperature heat sources into electricity. Several ORC units are already in operation but there is a continuous need of new and more versatile computer tools able to perform fluid selection and plant layout optimization. For these reasons, the present work is devoted to present a computer tool able to perform the fluid selection and the plant design of ORC units maximizing, for example, the net electric power for different heat sources' type and temperature (low, medium and high temperature). The optimum fluid is selected among 81 possible candidates. The optimization is performed taking into account a wide range of operating conditions: subcritical and transcritical cycles, regenerative and non-regenerative units and heat transfer made from the hot side and the power cycle (with and without the oil loop). Being the expander a crucial component, the axial and radial efficiency prediction charts are employed to estimate the expander isentropic efficiency. An exergy and economic analysis is also performed. For the selected test case the maximum net electric power can be reached using Toluene with a recuperative subcritical cycle.