Heat Exchanger Model Research Articles

Dynamic Modeling of Heat Exchangers Based on Mechanism and Reinforcement Learning Synergy

The current lack of a high-precision, real-time model applicable to the control optimization process of heat exchange systems, especially the difficulty in determining the overall heat transfer coefficient K of heat exchanger operating parameters in real time, is a prominent issue. This paper mainly unfolds the following work: 1. We propose a dynamic model for the control and optimization of the heat exchanger operation. By constructing a system to collect real-time operating data on the flow rates and temperatures on both sides of the heat exchanger, the parameter identification of the overall heat transfer coefficient K is performed. Subsequently, by combining this with mechanistic equations, a novel heat exchanger model is established based on the fusion of mechanistic principles and reinforcement learning. 2. We validate the new model, where the average relative error between the model’s temperature output values and the actual measured values is below 5%, indicating the high identification accuracy of the model. Moreover, under variations in the temperature and flow rate, the overall heat transfer coefficient K demonstrates the correct patterns of change. 3. To further enhance the model’s identification accuracy, a study on the reward functions in reinforcement learning is conducted. A model with the Logarithmic Mean Temperature Difference (LMTD) as the reward function exhibits a high identification accuracy. However, upon comparison, a model using the Arithmetic Mean Temperature Difference (AMTD) for relative error as the reward function shows an even higher identification accuracy. The model is validated under various operating conditions, such as changes in the flow rate on the hot side, demonstrating good scalability and applicability. This research contributes to providing a high-precision dynamic parameter basis for the precise control of heat exchange systems, offering significant guidance for the control optimization of actual heat exchange system operations.

Numerical investigations and design optimization of cryogenic plate-fin heat exchanger in Electric Arc Furnace using radiative heat transfer model

The most crucial element affecting cryogenic systems’ energy efficiency is heat exchangers. In this article, a model for cryogenic plate-fin heat exchanger (PFHE) under thermal-hydraulic performance with various blends is proposed. To reduce five objective functions total heat transfer rate, total weight, total mass flow rate, number of entropy generating units, and whole annual cost the study carried out the PFHE’s optimal design. This study innovatively focuses on optimizing PFHE design for cryogenic conditions using Opposition Learning with the Beetle Swarm algorithm. The proposed geometry addresses non-uniform temperature distribution, emphasizing thermal-hydraulic properties in various blends. Additionally, a second-order semi-discretization radiative heat transfer approach enhances boiler simulation accuracy. A multi-objective optimization of Opposition Learning with Beetle Swarm (MO-OBBS) optimization approach was suggested in the article for the design of PFHE. Despite the significant potential for renewable energy the low-temperature waste heat treatment process is rarely examined from a sustainability perspective. Consequently, the study proposed a second-order semi-discretization radiative heat transfer method to simulate a furnace using a water heat recovery process. The cooling panel’s numerical analysis was conducted using computed temperature fields. The performance of the various algorithms is compared using the Freidman rank-sum test to determine the statistical significance of the findings obtained. In logarithmic coordinates, the proposed method’s faster convergence is compared to GQB-PSO, SLTLBO, Jaya, CKKO, and OLE-SCA algorithms. The proposed method exhibits a maximum average increase of 115.39% for PFHE design. When the numerical simulation results are compared to measurements of output water temperature, the accuracy is highly improved.

Development of PCM-based shell-and-tube thermal energy storages for efficient EV thermal management

Electric vehicles face significant challenges in cold climates. Battery efficiency decreases, and cabin heating demands additional electricity, which diminishes the energy available for vehicle propulsion. In this context, a thermal energy storage system based on a phase change material (PCM) with diverse designs of shell-and-tube heat exchangers is investigated to meet cabin thermal load demands independently. A simulation model for a two-phase PCM heat exchanger is developed and validated using experimental data. The comparison revealed average temperature differences of 1.59 K and 1.61 K for the melting and solidification processes, respectively. Compared to the single tube design, the heat transfer performance of finned multitube design improved the melting process and reduced the melting time by 92.9% and reduced the solidification time by 87.6%. The average heat transfer rate of the finned multitube during the solidification process is 2.9 times higher than that of the single tube. Additionally, the use of PCM incorporating different types of nanomaterials is explored to enhance the melting and solidification performance through increased thermal conductivity. The graphene nanoplatelet PCM exhibited the most substantial improvements in thermal conductivity, resulting in melting and solidification time reductions by 54.2% and 48.9%, respectively.

Numerical and experimental investigation of the flow and heat transfer characteristics for cold storage heat exchanger

Decreasing the freezing time of the cold storage heat exchanger was an effective way to reduce the risk of cold chain breakage and the fluctuation of cold chain temperature. A validated unsteady mathematical model of the cold storage heat exchanger was established to analyze the transient evolution of temperature, velocity, ice distribution, and heat transfer coefficient for different diameters of heat transfer tubes and coolant temperatures. The results showed that there were four stages of temperature in the cold storage heat exchanger, namely the primary cooling stage, the freezing stage, the secondary cooling stage, and the constant temperature stage. The ice fraction distribution and the heat transfer coefficient were inextricably linked to the water's natural convection. The average heat transfer coefficient decreased with decreasing coolant temperature and increasing heat transfer tube diameters. The freezing time decreased with the coolant temperature and the diameter of the heat transfer tubes decreasing. The tendency of the inhomogeneity of ice distribution first increased with the ice fraction up to 0.75 and then decreased with the ice fraction over 0.75. The inhomogeneity decreased with the coolant temperature increasing when the diameter of the heat transfer tubes was greater than 2 mm.

Study on the convective heat exchange coefficient of concrete surface considering the surface roughness

A heat exchange experiment of concrete surface under different roughness conditions was conducted, and the convective heat exchange coefficient model of concrete surface influenced by many factors was deduced and developed. The model comprehensively considers the effects of concrete surface roughness, wind speed, air humidity and thermal conductivity on the surface heat exchange performance. We obtained the model parameters from experimental data, which captured the convection heat transfer process under controlled laboratory conditions. The comparison between the calculation result and the measurement data is good enough, and prove the selection value of the model parameters are very good. The new convective heat exchange model can better reflect the heat exchange of the concrete structure surface under complex boundary conditions, provide support for more accurate simulation analysis of concrete temperature field, and provide the possibility for better calculation of concrete temperature stress and control of temperature cracks.

Research on recompression supercritical CO2 power cycle system considering performance and stability of main compressor

The supercritical carbon dioxide (sCO2) power cycle has good prospects for use in many energy applications. Ensuring the stable operation of the power cycle is an important issue. The inlet condition of the main compressor in the sCO2 recompression cycle is close to the critical point of CO2 and the physical properties of CO2 change drastically near the critical point, so the study of inlet parameter change behavior of the main compressor is of great significance to the stable operation of the equipment and the system. This paper investigates the performance of an sCO2 recompression power cycle system under off-design conditions with different cooling and heating conditions. Unlike previous studies, this paper uses more accurate compressor and heat exchanger models to simulate the system for off-designed performance. A 1-D optimization prediction model of the compressor and a density-based segmented heat exchanger model are introduced to predict the performance changes of the system. The operating conditions, performance, and stability of the compressor under different cooling and heating conditions were compared. The results show that variations in different cooling and heating conditions change the inlet temperature of the compressor, causing the sCO2 compressor to deviate from optimal operation. As the inlet temperature increases, the power consumption of the compressor increases. At an inlet temperature of 305 K, the power is 1.93 MW (main compressor, MC) and 2.17 MW (recompressor, RC). When the inlet temperature increases to 310 K, the power increases by more than 10 %. The largest change in system efficiency is 3.76 % for a change in cooling conditions, and the largest change in compressor speed is 14.23 % (MC) and 7.79 % (RC) for a change in heating conditions, respectively. The operating condition of the main compressor moves far away from the surge line when its inlet temperature increases, which means the operation of the main compressor is more stable in this situation. The results of this paper contribute to the stable operation of the sCO2 recompression cycle.

Dynamic simulation of a space lithium-cooled reactor system coupled with a He–Xe closed Brayton cycle

The lithium-cooled reactor with Brayton conversion power system mainly consists of fast reactor, intermediate heat exchanger, closed Brayton cycle (CBC) loops filled with Helium–Xenon (He–Xe) binary gas mixtures and heat rejection loop which radiate residual heat through heat pipes to outer space. In this study, a dynamic model of 100-kWe lithium-cooled reactor with Brayton conversion power system was established based on RESYS code, which include reactor core thermal-hydraulic model, six-group neutron kinetics model and decay heat model, heat exchanger model, Closed Brayton cycle model including turbine, compressor and rotating shaft, heat pipe radiator model etc. The nominal steady-state simulation is carried out to verify the correctness and accuracy of individual component model the integrated system model. Four typical transient conditions including accidental reactivity insertion, loss of coolant flow of primary loop, partial and total external load loss and a step reduction in the mass flow rate of heat rejection loop are simulated to analysis the transient characteristics and prove the safety features for those simulated scenarios. The results are helpful for the design, evaluation and operation of space liquid-lithium-cooled reactor power system with He–Xe closed Brayton cycle.

Method of parametric optimization of hydraulic structures for subzero temperatures

A method for optimizing design and geometric parameters using a "simplified" simulation of the water-cooling process is presented. This method allows solving the issues of operational manufacturability in the aspect of creating energy- and resource-saving constructions of water storage tanks. In the study to determine the size of underground and above-ground parts of the water storage tank the criterion of heat loss minimization is accepted and the mathematical model of water heat exchange with the ground under the condition of its homogeneity and stationarity of the thermal regime is compiled. The relationship between the height and the radius of the underground part at the minimum value of the heat transfer coefficient from water to the ground through the metal wall is established. Using the heat balance equation, an analytical expression is found that determines the aboveground fluid temperature for any instant of time. On the basis of the theory of differential calculus the condition of minimality of the cooling rate of water, which gives up heat through the side walls to the environment and air space under the roof of the vessel, was revealed, which made possible to optimize the size of its above-ground part. The relationship of the radius and the total volume of the water holding capacity was determined for the average values of ambient temperature and wind speed recorded in the region of the research. The developed algorithm of the method of "simplified" modeling and its representation in the form of a block diagram can be implemented at digitalization of calculation-analytical procedures for selection of structural and geometrical parameters of the vessel according to the criterion of minimum heat losses. The functions of the radius and the height of the underground and above-ground parts of the vessel from the argument of its total volume are graphically illustrated.

Numerical analysis of a steady-state and transient performance using a tube-in-tube heat exchanger unit for cryogenic process simulator

Large scale Helium Refrigerators and Liquefiers (HRLs) are essential technologies in particle physics experiments and the nuclear energy sector. Most HRLs employ a modified version of the Collin's cycle, which involves a room temperature compressor, several counter-flow heat exchangers (HXs), expanders, and a J-T valve to produce liquid helium. The performance of HRLs is mainly governed by the efficacy of HXs and requires accurate process modeling and simulation. Although various platforms for process modeling and simulation of HXs are available, both commercial and open source, significant customization is required to use them in the cryogenic domain. Moreover, the transient simulation of a HX in two-phase has always been a concern. Therefore, there is a need to develop a numerical model of a HX to meet the requirements of the cryogenic domain specially in two-phase region.In present study, a HX is being modeled on the open source platform Python®. The developed numerical model is based on the distributed parameter approach to capture the impact of the variable fluid properties as well as their impact on the heat transfer coefficient. The model allows user to choose a suitable heat transfer correlation as per the requirement in different regime of the phases across the length of HX. The developed model may be suitable to simulate the HXs used as LN2 precooling, HXs of helium plant operating in mixed mode, and J-T heat exchangers where fluids undergoes phase changes along the flow length.The created models are initially tested against their design data, and results are then acquired under non-standard operating conditions. The outcomes are validated with experimental data from the ITER-India cryogenic Laboratory (IICL) after being first verified using the commercial process simulator Aspen HYSYS®.

Code development and preliminary validation for lead-cooled fast reactor thermal-hydraulic transient behavior

Lead-cooled fast reactors (LFRs) have a wide range of application scenarios, which require the thermal-hydraulic characteristics of LFRs to be reliable. In the present paper, the Lead-cooled fast reactor Thermal-Hydraulic Analysis Code LETHAC was developed, including the models of pipe, heat exchanger, and pool. To verify the correctness of LETHAC, two experimental facilities and three experimental cases were selected, including GFT and PLOFA tests for NACIE-UP and Test-1 for CIRCE. The calculated results show the same and consistent trend with the experimental data, but there are some discrepancies. It can be found that LETHAC is suitable and reliable in predicting the transient behavior of lead-cooled system.

Modelling and optimization of a forced convection heat exchanger for Mars waste heat rejection for power cycle and cryocooling applications

A forced convection heat exchanger for waste heat rejection to the Martian atmosphere is modelled for both a power generation and cryogenic refrigeration application. The modeling is based on existing as well as recent, experimentally validated heat transfer and pressure drop correlations for low-Reynolds-number, moderate-Knudsen number finned tube arrays and represents the first detailed examination of optimal heat exchanger design and performance in this regime. These correlations were developed from heat exchanger performance data taken in Mars-like conditions and are described in a separate, companion work [1]. A heat exchanger model based on the effectiveness-NTU method is developed using these correlations and the heat exchanger geometry is optimized using an open-source solver to minimize the overall system mass for a range of candidate heat exchanger materials and heat transfer rates. The optimal heat exchangers generally consisted of shallow, staggered banks of 1–2 mm diameter tubes and 2–4 mm fin spacing, although in some conditions bare tube arrays were optimal. These geometries tended to be preferred due to their low relative pressure drop, a necessity given the power requirement of producing high pressure head in the thin atmosphere. Curve fits that capture the heat exchanger performance are generated based on the input conditions in order to develop a reduced order model that can be used to integrate the heat exchanger model with an existing recuperated Brayton cycle high-temperature gas cooled reactor (HTGR) power cycle model. This power cycle model is used to determine the impact of using convective heat rejection on optimal system mass and compare this approach to radiative heat rejection. For a 40 kWe power output, the optimal overall cycle mass is found to decrease by 78 % when using convective heat rejection compared to a radiator; this is due to the decreased mass of the heat rejection system as well as the lower optimal rejection temperature which results in a lower recuperator mass. The heat exchanger itself has a mass of only 37 kg, a frontal area of 12.7 m2, and requires 2134 W of fan power to operate. The system is shown to perform well over a wide range of Mars ambient conditions. A high-power liquid Oxygen (LOx) reverse Brayton cryocooler cycle is also modeled to determine the benefit of using convective heat rejection for in-situ resource utilization (ISRU) applications. Across a range of power source options and ambient temperatures, using a convective heat rejection system reduced total system mass by up to 43 % and frontal area by up to 95 % compared to a radiator and also reduced the mass-optimal cycle power draw by increasing the optimal cycle efficiency. However, the magnitude of the mass reduction depends strongly on the specific power of the electrical source; the forced convection system provides only a 7 % improvement over a radiator when coupled with a photovoltaic power source due to the increased power demand of the fan. Overall, this technology offers significant performance advantages over radiative heat rejection systems for waste heat rejection applications on Mars and therefore may significantly benefit future crewed Mars missions.

Comparative analysis of ground thermal conductivity and thermal resistance of borehole heat exchanger in different geological layered sequence

Borehole heat exchanger usually passes through many geological layers of the different thermo-physical properties from one layer to another in practical project of ground-coupled heat pump system. Considering the effect of heterogeneity in geological structures on heat transfer of borehole heat exchanger, it is necessary for in-situ thermal response test analysis to investigate the effect of geological layered sequence on ground thermal conductivity and borehole thermal resistance. Firstly, based on the validated numerical layered borehole heat exchanger model and numerical homogenous borehole heat exchanger model, the simulated distributions of water temperatures in U-pipe and heat flux along the depth in thermal response test are respectively compared and analysed. Then, the effective thermal conductivity and effective borehole thermal resistance estimated by the infinite line source model are respectively obtained based on the simulated thermal response tests carried out in the borehole heat exchanger installed in the six types of geological layered structures. The borehole thermal resistances in the two numerical model were respectively calculated by integrating the local thermal resistance along the depth. Finally, the ground thermal conductivities and borehole thermal resistances are compared in six types of geological layered structures. The results show that the maximum relative error of 7 % between the effective thermal conductivity and the thickness-weighted thermal conductivity in the numerical layered borehole heat exchanger model is located in the sequence of S-L-C due to BOTTOM 60m-thickness clay with lowest thermal conductivity. The relative error between effective borehole thermal resistance and borehole thermal resistance in the numerical layered borehole heat exchanger model are 3.5 %∼7.9 % in the six types of layered geological structures, and the maximum relative error between the two borehole thermal resistances corresponding to the two numerical models is only 1.1 %, which proves that effect of geological layered sequence on the deviation is limited in the two numerical models.

Semi-analytical and numerical modeling of U-bend deep borehole heat exchanger

U-bend deep borehole heat exchanger (DBHE) is a new promising kind of ground heat exchanger, but nowadays there are lack of accurate efficient models to simulate U-bend DBHE. This paper has developed a semi-analytical model of U-bend DBHE, which considers the unsteady heat transfer of borehole, heterogenous soil thermal properties and geothermal gradient. A 2D numerical model and an analytical model based on infinite line-source theory are also developed, and the three models are compared with experimental data for different boundary conditions. Based on the soil thermal properties estimated by logging data and rock identification, the three models have large errors when compared with experimental data. Based on a soil thermal conductivity λs estimated by matching experimental data, the three models match better with experimental data, and it is inferred that λs should be measured by thermal response test instead of rock identification. The semi-analytical model and 2D numerical model match very well for all the time, but the analytical model has large differences with 2D numerical model, which is because the analytical model ignores borehole heat capacity and time-varying heat flows at the borehole wall. This paper could provide a cost-effective semi-analytical model and some advices for U-bend DBHE.

Modeling of heat exchangers in ANSYS CFX for the digital twins development

The paper presents a universal methodology for modeling and optimization of shell-and-tube heat exchanger designs using the ANSYS CFX software package. Mathematical modeling plays a key role in the design and modernization of heat and mass transfer equipment, especially in the petrochemical and oil and gas processing industries, and especially in the creation of digital twins of heat and mass transfer equipment. The modern approach provides prediction of equipment behavior at the development stage, which makes it possible to take into account the peculiarities of the actual geometry of the apparatuses and optimize the interaction of contacting phases. The paper considers the stages of creating a digital model of a heat exchanger, including the construction of an electronic geometric model, creation of a computational grid, selection of mathematical models of hydrodynamics and heat transfer, as well as the setting of boundary conditions and solver parameters. Special attention is paid to the selection of heat transfer and turbulence models suitable for high Reynolds numbers. The results of numerical simulation in ANSYS CFX are compared with analytical solutions and data obtained with ANSYS Fluent. The difference in the results was about 1 °C, which confirms the high accuracy and reliability of the proposed methodology. This indicates the feasibility of using ANSYS CFX for modeling and optimization of technological equipment. The obtained results can be applied to build a digital twin model, to improve the efficiency of heat transfer processes, to reduce the cost of development and modernization of equipment, as well as in further research on the intensification of heat and mass transfer using digital models.

Development and validation of a model for an air-to-air air conditioner

Air conditioning units are responsible for a significant amount of global warming, with demand predicted to triple by 2050. Mathematical models aid in designing energy efficient air conditioners that can contribute to climate change mitigation. This study presents a steady-state model for a air-to-air air conditioner. The proposed model can assist in reducing the number of experiments and optimizing the efficiency of air conditioning systems. It utilizes a bottom-up approach to solve for compressor, condenser, capillary tube, and evaporator sub-models. The compressor is modelled using polynomial equations to determine refrigerant mass flow rate and power consumption based on operating temperatures. Heat exchanger models are solved using finite volume approach and reliable correlations are used for void fraction, friction factor, and heat transfer coefficient calculations. The closing equations are the mass conservation, i.e. constant refrigerant charge, and the equivalence between the mass flow rate sucked by the compressor and the one that flows through the capillary tube, while the evaporating and condensing pressures are the independent variables. The capillary tube is modelled using semiempirical correlations. The model is validated against experimental data at various operating conditions and shows a ±7% agreement for predicted cooling capacity.

Numerical simulation and thermal analysis of ecological energy-saving ground source heat pump design

By constructing the heat transfer model of the buried tube heat exchanger, using the mathematical method and numerical calculation software, the temperature of the buried tube heat exchanger is calculated numerical, so as to better understand the temperature effect of the buried tube heat exchanger on the surrounding soil. This paper establishes a mathematical model of a vertically buried heat transfer system based on the principle of thermal equilibrium and the thermal conductivity differential equation. Conduct research on the temperature field around single pipes in different soil (geological conditions), temperature field under different drilling backfill materials, and the temperature around buried pipelines in both short-term and long-term operation of the system. The experimental results show that the simulation results of the system?s short time (10 days) and long time (90 days) performance show that the cooling and temperature cycles in different areas directly affect the heat radius of the buried pipe and the heat accumulation near the buried pipe. The thermal action radius of the short-term operation system is about 1.8 m, and the long-term operation reaches 4.5 m.

Mathematical Modelling and Design of Helical Coil Heat Exchanger for Production of Hot Air for Fluidized Bed Dryer

Mathematical Modelling and Design of Helical Coil Heat Exchanger for Production of Hot Air for Fluidized Bed Dryer

Верифікація CFD-моделі теплообміну і гідродинаміки для спалювання непроектного палива у паровому котлі ТПП-210А

Верифікація CFD-моделі теплообміну і гідродинаміки для спалювання непроектного палива у паровому котлі ТПП-210А

An overview of the Transient Hot Wire and preliminary studies for its implementation

The opportunity to design a new portable system for measuring thermal conductivity in fluids arose from the need to measure the phase state (liquid and/or vapour). As is well known, thermal conductivity varies in relation to the phase state of the fluid. The Transient Hot Wire Method was used to measure thermal conductivity. First, the work includes innovations in the analytical model of heat transfer, progressing over time to contemporary numerical models used in standards. The applications in the bibliography span a wide range, including gases, liquids, and the latest advances in the field of nanofluids. Secondly, the study delves into the transient model of heat exchange, focusing on conduction. The authors used standardized correction equations for the prototype, ensuring accuracy and relevance. Finally, the work includes the design and construction of the transducer. This process begins with a Monte Carlo simulation, predicting the expected results. This simulation helps to define measurement system components based on their performance characteristics and in-depth analysis.

Research and application of heat recovery and automation monitoring system for new energy vehicle motor equipment

In order to improve the energy efficiency of pure electric vehicles, the author proposes a thermal energy recovery and automation monitoring system for motor equipment based on new energy vehicles. Based on the analysis of the battery thermal management model, a series heat exchange model between the motor and the battery was established. An integrated thermal management system control strategy based on motor waste heat recovery was proposed for electric vehicles in low temperature environments, and simulation and validation were conducted at different environmental temperatures (-10~0 ?). The simulation results show that this configuration can shorten the heating time by 111-343 seconds compared to traditional battery thermal management systems during the heating stage. During the insulation stage, frequent activation of positive temperature coefficient thermistor can be avoided and the battery temperature can be maintained around 20?C, which is not only conducive to extending the battery life but also reduces the comprehensive energy consumption by 4.39-7.70%. On the other hand, this configuration can reduce the impact of low temperature on comprehensive energy consumption from 9.77-2.07%. It is proved that heat recovery can effectively alleviate the range anxiety caused by ambient temperature.