Heat Exchanger Geometry Research Articles

A new approach for global and multi-objective optimization of fin and tube heat exchanger

Fin and tube heat exchangers (FTHEs) are widely used in buildings for various heating, ventilation, and air conditioning (HVAC) applications due to their efficiency and compact design. Optimizing the design of FTHEs for building applications can bring numerous advantages in terms of energy efficiency, performance, and overall cost-effectiveness. For this purpose, this paper introduces the Multi-Objective Set Trimming (MOST) algorithm, a robust and global optimization approach applied to the optimization of a fin and tube heat exchanger. The study compares the results obtained using MOST with the well-known semi-stochastic method, Multi-Objective Particle Swarm Optimization (MOPSO), and an exhaustive search, considering both computational time and convergence. The optimization focuses on two objectives: effectiveness and annual cost, considering eight design parameters related to heat exchanger geometry. Six different cases with varying mass flow rates on both the hot and cold sides are investigated. Results reveal that the Pareto optimal fronts achieved with MOPSO are entirely dominated by those obtained using MOST across all studied cases. Additionally, MOST improves the annual cost for the best economic solution by up to 10.69% compared to MOPSO, and effectiveness is enhanced by up to 1.95%. Notably, the computational time is significantly reduced with MOST, ranging from 49.36% to 97.49% compared to MOPSO across different cases. As a result, the implemented method provides highly effective tools for optimizing the FTHE, ensuring both fast convergence and efficient computational performance.

Fluid flow and heat transfer of a novel passive cooling system for gearless wind turbines with a power range of 3–12 MW

Today, the gearless horizontal axis wind turbines are mainstream in wind energy industry. High demands of electric power led to bigger systems and active cooling reduces the overall efficiency of the turbines. Passive cooling systems have been examined for the first time for a gearless wind energy generator with power range of 3–12 MW. With further developed heat conductors, it is possible to operate a wind generator in a larger power class with passive cooling components. This is accompanied by enormous cost savings due to elimination of costs for active cooling elements such as the use of fans, pumps, and heat exchangers. An additional factor is the significant reduction in necessary maintenance due to the minimized incidence of corrosion and wear. Design of the cooling fins and an ideal position of the generator within the housing of the wind turbine has been objectives. Mandatory is that maximum temperatures of the generator fins should stay under 155 °C, which could be reached with several designs for different heat exchanger geometries.

Effect of Heat Exchanger and Capillary Geometry on the performance of Joule- Thomson Refrigerators operating with different mixtures

Abstract Joule-Thomson (J-T) refrigerators or J-T cryocoolers are extensively used in many low-temperature applications. J-T refrigerators operating with nitrogen-hydrocarbon (N2-HC) refrigerant mixtures offer several advantages, such as low operating pressures (<20 bar), high exergy efficiency, no moving parts in the cold section, and low cost. The cooling power or cooling capacity of the J-T refrigerator depends on the hardware used as well as the refrigerant composition. The proposed work focuses on estimating the cooling capacity of a mixed refrigerant J-T (MRJ-T) refrigerator of the given hardware and specified refrigerant. An iterative steady-state full-cycle simulation procedure has been presented in this work to simulate the complete system and estimate the cooling capacity, taking into account the possibility of choking of the expansion capillary. Some of the results have been validated against experimental results of an MRJT refrigerator available in the open literature. The details of the simulation model and the results of our studies on the prediction of stable operating range, maximum cooling capacity, the effect of heat exchanger geometry, expansion capillary geometry, mixture composition, and choking of the refrigerant mixture on the performance of an MRJ-T refrigerator are presented in this paper

Prediction of heat transfer coefficient and pressure drop of flow boiling and condensation using machine learning

Heat transfer coefficient and pressure drop are two critical parameters in diverse thermal engineering applications, and the prediction of these parameters plays a crucial role in the development of heat exchangers. Traditional methods are often reliant on empirical correlations based on limited refrigerants and experimental conditions. The present research explores the application of machine learning methods to predict the heat transfer coefficient and pressure drop of a wide range of pure and mixed refrigerants. The methodology involves the compilation of over 20, 000 experimental observations encompassing an extensive range of operating conditions, heat exchanger geometries, and refrigerants. A total of 27 machine learning algorithm models, such as regression tree, support vector machines, and deep neural networks, are trained on this diverse dataset to discern intricate patterns and dependencies. After dividing the dataset into 80% for training and the rest for validation, the machine learning prediction shows an ability to predict the heat transfer coefficient and the pressure drop with high accuracy in most of the refrigerants. Notably, the accuracy achieved by the machine learning models surpassed that of conventional correlations, highlighting their superior predictive capabilities. Furthermore, the accurate prediction of heat transfer enhancement methods added another layer of validation to the model’s effectiveness. It is noteworthy that the dataset employed in this study has been made publicly accessible online.

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.

Heat Transfer and Pressure Drop in Plate Fin Heat Exchangers: A Numerical Approach

An apparatus for transferring thermal energy across an impermeable barrier between two or more fluids is a heat exchanger. The effective transmission of heat from a hot fluid to a cold fluid is its primary goal. The temperature differential between the two fluids directly affects this heat transfer. Using CFD study with FLUENT 2020 R1, the performance characteristics of the compact plate fin heat exchanger's improved surfaces are examined. The simulation of heat transfer and flow encompassed a variety of velocities including completely turbulent regions. The pressure, temperature, and velocity contours were taken from the Fluent simulations. To determine the heat exchanger's flow and heat transfer performance, numerical analysis has been done. Since boundary conditions are crucial to CFD, they have been carefully chosen. The flow field, heat transfer, thickness, and wavelength were all predicted using the software code for a range of air to water velocities. Three distinct wavelengths of numerical simulations for a plate-fin heat exchanger were used in the study (10, 20, and 30). There were changes to the fin thickness, entry locations, and air and water entry velocities. Solid Works and Ansys were used to create the geometry for the three-level fin models that were placed inside the heat exchanger, both with and without a cover. For determining the heat exchanger's geometry and fin isometry, three levels measuring 19.6 mm in height and 53.64 mm in width were constructed. The fins have a thickness of 0.2 to 0.4 mm. As the air and water velocities vary, so does the temperature inside the heat exchanger. Because the topmost layer is a warm stream's flow channel, the temperature rises there, whereas the opposite effect is seen close to the bottom layer. Convection heat transmission to the surroundings and conduction heat transfer through the heat exchanger's side plates are the causes of fluid temperature fluctuations in the depth direction.

Potential assessment of biomass-based single-stage adsorption systems for refrigeration, cooling, and heat-pumping applications

ABSTRACT This article presents the performance estimation of a single-stage vapor adsorption system employing various carbon-based adsorbents with ethanol refrigerant, coupled with a small-scale biomass-based heating unit for space cooling, refrigeration, and heat-pumping applications. A detailed parametric investigation highlights the effects of operating temperatures, and heat exchanger to adsorbent mass ratio on specific cooling energy (SCE), coefficient of performance (COP), uptake efficiency (ηu), and mass of adsorbent to combustion fuel (mad/mcf) to identify the suitable adsorbent and sorption bed designs for each application. The numerical findings reveal that the flat-finned tube (FFT) adsorber outperforms traditional-finned tube (TFT) and tube & shell-type (T&S) adsorbers, achieving 19% and 30% higher COP, respectively, with biomass carbon-ethanol pair. The H2-treated Maxsorb-III shows the greatest optimal cooling COP (0.73), followed by the biomass-carbon (0.72) for refrigeration and space cooling. For heat pumping applications, biomass carbon-ethanol achieves the highest heat pumping COP (1.84) at a desorption temperature of 90°C, surpassing H2-treated Maxsorb-III. Further, the biomass-derived activated carbon requires the lowest amount of adsorbent per unit mass of combustion fuel in the biomass heating unit. The present thermodynamic analysis is a precursor for optimization of the potential heat-exchanger geometries and operating parameters, with the high-performance carbon adsorbents.

The Influence of Nusselt Correlation on Exergy Efficiency of a Plate Heat Exchanger Operating with TiO2:SiO2/EG:DI Hybrid Nanofluid

This paper studies how the correlation with the Nusselt number affects the final result of the efficiency, ε, and exergy efficiency, ηex, of a chevron-type gasketed plate heat exchanger, which is installed in a typical small solar installation dedicated to single-family housing; the solar fluid is a TiO2:SiO2/EG:DI hybrid nanofluid with concentrations from 0% to 1.5% vol. The experimental model assumes constant flow of the solar fluid and varies on the domestic hot water side—from 3 lpm to 6 lpm. The inlet temperatures are 30 °C and 60 °C on the cold and hot sides of the heat exchanger, respectively. Of the six analysed correlations that showed similar trends, it is concluded that for the assumed flow conditions, geometry, and chevron angle of the plate heat exchanger, one model is the most accurate. The largest difference between the ηex values for a given concentration is 3.4%, so the exergy efficiency is not affected by the chosen Nusselt model by very much. However, the choice of correlation with the Nusselt number significantly affects the efficiency, ε; the difference between the values obtained within a given concentration is more than 40% and depends on the Reynolds number and flow. Most research discusses the scenario with the nanofluid as a coolant. This paper considers the opposite situation in which the solar fluid is a hotter working medium that transfers heat to domestic hot water installation.

Comparative Analysis of Changing Channel Geometry of a Cross-flow Microchannel Heat Exchanger

Comparative Analysis of Changing Channel Geometry of a Cross-flow Microchannel Heat Exchanger

Air-Side Thermal Behavior of Parallel-Plate Evaporators. Part II: Performance under Frosting

In the second part of the paper, an experimentally validated extension of the mathematical model is presented to simulate the thermal behavior of a roll-bond parallel-plate evaporator under frosting. This novel heat exchanger geometry is a potential alternative to finned-tube “no-frost” evaporators in some applications. The experimental work consisted of testing one of the heat exchanger prototypes selected from Part I in a closed-loop wind tunnel calorimeter at different conditions of air temperature, humidity, air flow rate and inlet coolant temperature. The semi-analytical model divided the evaporator in control volumes involving the air, plate and coolant and solving the momentum, energy, and species balance equations to generate distributions of air humidity, temperature, and pressure, as well as frost thickness and aluminum plate temperature. A good agreement was observed for the heat transfer rate, mass of frost accumulated in the heat exchanger and pressure drop, as most data points were predicted to within 20% relative error.

The application of additive manufacturing to heat exchangers for oscillatory flow: A case study

Additive manufacturing is an option for the fabrication of heat exchangers for thermoacoustic applications. In thermoacoustic devices, heat exchangers are placed in oscillatory flow. A careful consideration of heat exchanger geometries examines the application of methodologies to optimise heat transfer and the temperature gradient. Additive manufacturing is proposed as an alternative fabrication technique that can overcome the current limitations of conventional fabrication machining. Six identical crossflow heat exchangers were made and tested, three from stainless steel and three from aluminium. The oscillatory flow moves back and forth through circular cross-section channels, and water flows in channels perpendicular to them. Heat transfer and temperature gradients were investigated at different drive ratios and mean pressures.

Numerical investigation and artificial brain structure-based modeling to predict the heat transfer of hybrid Ag/Au nanofluid in a helical tube heat exchanger

In recent years, due to the low thermal coefficients of common fluids and the increase in size and cost of heat exchangers, technologies for improving heat transfer and reducing dimensions have been developed and widely used in industries such as refrigeration, cooling of processing cells, chemical industries, and more. Previously, increasing heat exchange capacity in heat exchangers was achieved by altering parameters such as boundary conditions, flow geometry, heat exchanger geometry, or changing the type of fluid. Additionally, apart from the use of nanofluids, various other operational methods can be employed to improve the thermal performance of heat exchangers. Accordingly, considering the combination of the aforementioned innovative techniques, this study presents the modeling of flow and heat transfer inside helically coiled tube heat exchangers under the flow of nanofluids containing nickel, gold, silver, and gold/silver hybrid nanoparticles using numerical and artificial intelligence methods. In this study, the effect of variations in the inner diameter of the coiled tube and the volume fraction of nanoparticles was examined. The results showed that increasing the inner diameter and volume fraction of nanoparticles leads to an increase in heat transfer coefficient and Nusselt number, while the friction factor decreases with an increase in Reynolds number and increases with an increase in diameter and volume fraction. Finally, the accuracy and validity of the model were evaluated using statistical parameters and experimental results, which showed a 99.9% level of agreement between the predicted and experimental outcomes.

The Heat Transfer in Plate Fin Heat Exchanger for Adsorption Energy Storage: Theoretical Estimation and Experimental Verification of the Methodology for Heat Accumulation Process

Adsorption energy storage is a promising resource-saving technology that allows the rational use of alternative heat sources. One of the most important parts of the adsorption heat accumulator is the adsorber heat exchanger. The parameters of heat transfer in this unit determine how fast heat from an alternative energy source, such as the Sun, will be stored. For the design of adsorption heat accumulators, plate fin heat exchangers are mainly used. In this paper, the procedure for the estimation of the global heat transfer coefficient for the adsorber heat exchanger depending on its geometry is considered. The heat transfer coefficient for a LiCl/SiO2 sorbent flat layer under conditions of heat storage stage was measured. Based on these data, the global heat transfer coefficients for a number of industrial heat exchangers were theoretically estimated and experimentally measured for the adsorption cycle of daily heat storage. It was shown that theoretically obtained values are in good agreement with the values of the global heat transfer coefficients measured experimentally. Thus, the considered technique makes it possible to determine the most promising geometry of the plate fin heat exchanger for a given adsorption heat storage cycle without complicated experiments.

State of the Art in Development of Heat Exchanger Geometry Optimization and Different Storage Bed Designs of a Metal Hydride Reactor.

The efficient operation of a metal hydride reactor depends on the hydrogen sorption and desorption reaction rate. In this regard, special attention is paid to heat management solutions when designing metal hydride hydrogen storage systems. One of the effective solutions for improving the heat and mass transfer effect in metal hydride beds is the use of heat exchangers. The design of modern cylindrical-shaped reactors makes it possible to optimize the number of heat exchange elements, design of fins and cooling tubes, filter arrangement and geometrical distribution of metal hydride bed elements. Thus, the development of a metal hydride reactor design with optimal weight and size characteristics, taking into account the efficiency of heat transfer and metal hydride bed design, is the relevant task. This paper discusses the influence of different configurations of heat exchangers and metal hydride bed for modern solid-state hydrogen storage systems. The main advantages and disadvantages of various configurations are considered in terms of heat transfer as well as weight and size characteristics. A comparative analysis of the heat exchangers, fins and other solutions efficiency has been performed, which makes it possible to summarize and facilitate the choice of the reactor configuration in the future.

Experimental and numerical analysis of heat transfer in a dimple pattern heat exchanger channel

In contrast to the predominant herringbone shape of heat plates, a microplate heat exchanger has an array of relatively small dimples. Its number and shape define the characteristics of such a plate heat exchanger. Literature, however, of the flow characteristics in such kinds of channels is scarce. Precise knowledge of the flow specifics in such a channel is of key importance to develop efficient new products. Single-phase water flow and heat transfer in microplate heat exchanger was investigated with the laboratory experiments and use of computational fluid dynamics simulations. A novel and innovative laboratory experiment was developed where flow characteristics and heat transfer in the microplate heat exchanger were measured. Experimental results were directly used as boundary conditions in numerical simulations. With this approach a direct validation of the results of numerical simulations were obtained. Heat transfer simulations were performed with three turbulence models: k- ε, k-ω SST and the Reynolds stress model. The most reliable results in heat transfer analysis were obtained using the Reynolds stress model where results are on average 7.05% lower compared to the results of the laboratory experiment. When all experimental uncertainty contributions were analysed, the simulation results were in the band between − 11% and 1.8% compared to the results of the laboratory experiment. Numerical simulations show that the heat transfer coefficient in the channel is proportional to Re0.64 in the analysed geometry of a microplate heat exchanger. The heat transfer coefficient was calculated and was between 9740 and 21990 W/m2K at Reynolds numbers 1170 and 4170 respectively.

Aeroacoustic Simulations of an Axial Fan with Modelled Turbulent Inflow Conditions

In applications, the acoustics of fans can differ significantly from the measurements of the standalone fan. This is due to disturbed inflow conditions, for example, caused by a heat exchanger upstream of an axial fan. Resolving the complex geometry and dimensions of typical heat exchangers in aeroacoustic scale-resolving simulations leads to a very high computation effort, which is currently not economically feasible. Turbulence reconstruction tools, such as the FRPM, provide the possibility to model the turbulent inflow conditions, thereby avoiding the representation of the heat exchanger in the aeroacoustic simulations. This approach is tested on a benchmark experiment of a ducted fan with an upstream turbulence grid.

Advanced solutions to improve heat recovery from wastewater in a double heat exchanger

Reducing energy consumption and CO2 footprint in existing buildings without requiring extensive construction work is one of the biggest challenges facing the globe today. Although heating contributes for the majority of energy use in buildings, residential hot water demand is also relatively high, particularly when daily usage is high and especially for certain applications. The use of technologies that recover energy from sources other than fossil fuels to heat water has grown crucial, and one such technology involves recovering thermal energy from wastewater. Typically, heat recovery from wastewater is made to collect any remaining energy from the hot drainage water, and this energy is then applied to heat pumps or to warm up incoming cold water. The paper presents numerical simulations using a SST k-ω turbulence model in order to compare a regular geometry of heat exchanger with a helicoidal one. The second one provides a more turbulent flow that allows an intensification of the outer flow, thus allowing the enhancement of the heat transfer from the inner heated flow to the outer flow.

Study of the influence of fin-plate heat exchanger geometry on dust particle deposition and heat transfer based on numerical calculation

Cooling systems are actively used in computer technology to cool various electronic devices, for example, the central processor units (CPU). CPUs generate heat while operating, which slows down the processing speed of information, and overheating often causes the CPU to shut down or even crash. Cooling systems are designed to remove heat from the CPU. Often, during operation of the cooling system, its main element – the fin-plate heat exchanger becomes covered with a layer of dust, which significantly reduces the rate of heat transfer and can lead to CPU failure. In this work, we carried out numerical modeling of dust particles deposition on the surface of fin-plate heat exchangers of various geometries. We studied the influence of the fin shape (flat or corrugated), as well as the distance between the fins (from 1.75 to 7 mm) on the efficiency of particle deposition and the change in heat flow.

Minimization of entropy generation in U-bend tube heat exchanger during flow boiling of R134a

The presence of a bend in a tube during two-phase flow boiling can improve heat transfer while also causing a pressure drop. The goal of this paper is to achieve an optimal geometry of the U-bend tube heat exchanger. The bend induces a high-pressure drop as well as increases heat transfer coefficient, striking a balance between pressure drop and heat transfer coefficient to obtain an optimal design can be achieved by minimizing entropy generation due to heat transfer and pressure drop. Hence, an entropy generation minimization during two-phase flow boiling of R134a was conducted using the constructal design method and the entropy generation techniques based on the second law of thermodynamics. The geometric optimization was subjected to the following constraints: the volume of the tube was constant with bending radius, and the tube's outer surface area was subjected to a uniform constant heat flux of 10 kW/m2. Geometric parameters such as total length Lt, internal diameter di and external diameter do of the tube were free to morph with respect to the degree of freedom until an optimal geometrical configuration was obtained at minimum entropy generation. The bend's curvature ratio was taken as a function of internal (hydraulic) diameter. The numerical computations were conducted with the mass fluxes from 100 to 500 kg/m2s and quality of 0.2 at the tube's inlet for downward-oriented flow. The results obtained were consistent with those found in the open literature. Furthermore, the optimal parameters of the tube heat exchanger were found to vary slightly as the minimum entropy generation rises with an increase in mass flux. The stability was achieved as minimum entropy generation increased which demonstrates the robustness of the optimized U-bend tube.

Thermodynamic Analysis of a Small-scale Biomethane Liquefaction Process

Liquid biomethane, obtained from anaerobic digestion of organic biomass, upgrading and liquefaction processes, is regarded as one of the most effective renewable biofuels to be extensively employed in the transport and power generation sectors for mitigation of greenhouse gas emissions. In this paper, a novel biomethane liquefaction process for small-scale plants is presented and thermodynamically assessed by means of a detailed thermodynamic model that employs the libraries of Fluid Prop, being very accurate for thermodynamic calculations of complex fluids. The thermodynamic model allows the heat exchanger geometry to be accurately determined and crucial parameters to be adjusted, such us the composition of the refrigerant and the operating conditions of both the biomethane and the refrigerant. The proposed model has general validity and can also be used to study the most promising biomethane liquefaction technologies for small-scale plants.