Thermal Exchanger Research Articles

Three-dimensional analysis for optimizing thermo-hydrodynamic performance of heat exchangers with perforated semi-circular inserts

This study focuses on the current energy crisis, highlighting the challenges and opportunities it presents, particularly in the electricity, coal, and natural gas sectors. In this context, a compact and efficient heat exchanger has been developed to recover waste heat from power plants and industries, thus promoting energy savings. The aim of this study is to enhance the thermal performance of this heat exchanger by combining two methods. By analyzing various parameters such as the Nusselt number and thermal performance factor across a range of Reynolds numbers and using different fluids, the study reveals the positive impact of semi-circular inserts on thermal performance. Results show a significant improvement in thermal performance factor with the addition of inserts, particularly in case (4) where it reaches 1.86 at a Reynolds number of 140,000. Additionally, the study compares five perforated models, demonstrating that model (2) stands out as the most thermally efficient, with a maximum value of 1.8787 at a Reynolds number of 140,000. Perforations in the inserts promote better fluid flow uniformity and reduce pressure losses. In conclusion, the optimal configuration, specifically model (2) with perforations, exhibits superior thermal and hydrodynamic performance, providing valuable insights for thermal engineering and heat exchanger optimization in various industrial and technological applications. The findings of this study offer tangible prospects for thermal engineering, providing important guidelines for heat exchanger design and optimization, with significant implications for a wide range of industrial and technological applications, and offering a solid foundation for future research in the field of heat transfer and fluid thermodynamics.

Experimental validation of a design model for latent thermal energy storage extended with sensible heat

Latent thermal energy storage can be a key technology for a green energy transition by matching fluctuating heat demand and supply. In order to implement a storage system, it needs to be designed which requires estimating the outlet temperature of a system for a given geometry and time history of the heat transfer fluid’s mass flow rate and inlet temperature. Currently, design methods are either overly simplistic, focusing solely on e.g. the phase change time or requiring the solution of partial differential equations which can be computationally expensive. The present paper proposes a novel approach where a latent thermal energy storage system is decomposed into a heat transfer fluid vessel, a sensible storage system and a storage system with only latent heat. Computationally inexpensive models are available for all three of these sub heat exchangers. A heat exchanger model is obtained by connecting the sub heat exchangers in parallel. This novel approach is used to model an industrial scale shell and tube latent thermal energy storage heat exchanger. The predicted outlet temperature is compared to the measured outlet temperature and the design model obtains good agreement.

Unleashing novel configurations of gravitational water vortex thermal energy exchanger

This study presents thermal and hydrodynamics investigations for novel configurations of gravitational water vortex heat exchanger (GWVHE). The proposed novel configurations of GWVHE include SWB (shell with baffles), CSFH (circular spiral flow helix) and RSFC (rectangular spiral flow channel). The thermal energy balance between two fluid domains has been calculated numerically for various operational conditions. An analytical model is developed using the Kern's approach, the effectiveness-NTU method, and the LMTD method for heat exchangers to calculate the heat transfer characteristics of two fluids to validate numerical results. Moreover, a transient two-phase flow numerical model has been solved to investigate the volume fraction of air and water during the development of the vortex at the center of the basin. The results show that a convincing thermal energy balance is present between both fluid streams for all the proposed configurations of GWVHE. However, the heat exchange rate for the RSFC configuration of GWVHE is higher than the SWB and CSFH of GWVHE. Because it has maximum heat exchange surface area of 1.08 m2 and thermal losses in RSFC are significantly lower than those computed in CSFH and SWB at different operating conditions. The thermal losses reported for RSFC are just 1 % compared to CSFH and SWB thermal losses of 2 % and 5 %, respectively. Moreover, the maximum volume fraction of air obtained at the center of basin during vortex formation is 18 %, indicating an effective vortex air core.

Nonisothermal analysis of two uniform boundary layer shear flows

AbstractThe heat transfer phenomenon on the multiphase flows plays an imperative role in several biological and industrial processes, like the oil production industries, catalytic reactors, energy losses in several thermal systems, energy storage, paper manufacture, and heat exchanger systems. Therefore, this study scrutinized the heat transfer characteristic between two uniform boundary layer shear flows with different strengths flowing in the same direction. This problem involves the simulation of the convergence of boundary layers with varying shear strengths. The nonlinear differential system is scrutinized and converted into dimensionless ordinary differential equations by employing appropriate dimensionless variables. The resulting set of highly nonlinear ordinary differential equations is resolved numerically utilizing the Matlab solver “bvp4c.” The resulting numerical solutions are used to construct graphs that illustrate and elucidate the impact of numerous physical parameters on flow patterns. For both fluids, results for the Nusselt number and shear stress are also presented graphically for various parameters. The acquired results demonstrate that the velocity profile upsurges for both upper and lower fluids by enhancing the shear parameter. Furthermore, the number of streamlines is enhanced by augmenting the values of the viscosities ratio parameter. The present problem applies to the trailing edge flow over a thin airfoil with camber.

Modelling and simulation of a novel liquid air energy storage system with a liquid piston, NH[formula omitted] and CO[formula omitted] cycles for enhanced heat and cold utilisation

A liquid piston system (LP) is proposed to recover energy during the discharge of a liquid air energy storage (LAES) plant. The traditionally used air turbine is replaced with an LP system which will expand the evaporated air to generate power. Moreover, an NH3 and transcritical CO2 cycle are integrated to enhance heat and cold utilisation. The integrated LAES system was modelled using gPROMS. The numerical results have a maximum discrepancy of less than 6.4% from experimental data previously reported in the literature. The round-trip efficiency (RTE) was studied for various scenarios, including the sensitivity to thermal oil flow rate and heat exchanger efficiencies. Additionally, the study examined the influence of several LP configurations and concluded with a comparison to a conventional LAES system. With a liquefaction pressure of 40 bar, the highest RTE reached was 37%, surpassing the conventional LAES system’s 25% RTE at a discharge pressure of 25 bar. The heat utilisation was 96%, which doubles that of the conventional LAES system, while the cold utilisation was enhanced by 10%. Furthermore, the LP, NH3, and CO2 cycles thermal efficiencies were 88%, 19%, and 30%, respectively. A detailed energy assessment for heat and cold utilisation is presented.

Numerical simulation and optimization of compact latent heat exchanger with micro-channel plate in shape-stabilized composite phase change material

To enable the rapid provision of domestic hot water, this study presents the independent design of a plate heat exchanger featuring a large heat exchange area and a compact structure. Utilizing a sandwich structure, the thermal storage unit integrates two shaped composite phase change materials (CPCM), namely sodium acetate trihydrate (SAT)/expanded graphite (EG) blocks of identical thickness — in conjunction with a micro-channel heat exchange plate. Multiple thermal storage units are stacked to create the heat exchanger. Experimental validation of the heat transfer performance of this thermal energy storage heat exchanger is conducted, accompanied by the establishment of a heat transfer model elucidating the interaction between the phase change material (PCM) and the fluid. The investigation explores the impact of varying thicknesses of shape-stabilized CPCM, thermo-physical parameters of CPCM, and flow rates on enhancing the thermal efficiency of the thermal energy storage heat exchanger. Results indicate a competitive relationship between the phase change enthalpy and thermal conductivity of CPCM under constant density. Increasing the mass fraction of SAT effectively boosts its heat storage density. However, this improvement is counterbalanced by a reduction in CPCM's thermal conductivity, resulting in diminished heat transfer rates within the material and reduced efficiency in transferring heat between the material and the fluid. Optimal performance is achieved when the mass fraction of sodium acetate trihydrate is 80 wt% and the CPCM thickness is 20 mm. At these parameters, the thermal energy storage heat exchanger exhibits the highest heat transfer efficiency. Furthermore, the heat exchanger is capable of producing 197.86 kg of hot water in 1365 s at an inlet flow rate of 300 L/h, achieving an impressive discharging efficiency of 82.73 %. These findings underscore the feasibility of employing the mini-channel plate thermal energy storage heat exchanger for the rapid preparation of domestic hot water.

Heat transfer performance of phase change energy storage building materials and its application in energy efficient buildings

The author proposes a phase change heat storage component combined with the light wall interior to improve the heat storage performance. Numerical modelling of the composite wall was performed using the finite element program COMSOL connected to Multiphysics simulation, and its accuracy was verified. In order to optimize the use of phase change data and the benefit of phase change temperature, the phase change of the heating device was carried out, and the difference in the development efficiency of the thermal storage performance of the two types of light walls was obtained from the ribs in the thermal phase phase exchanger compared. The results show that the long and thin fins adjust the temperature and flow field changes of the paraffin to the corresponding fin gap and improve the heat transfer rate, 44.8 and 26.3, respectively, the aerated concrete combined wall heat storage and heat release time, added short ribs known need, and the connected wall delay time is not affected by external heat. The mature thermal insulation and thermal insulation time of the polystyrene board composite wall were shortened by 20.8 and 52.9, respectively. Ribs are able to improve heating efficiency and retain heat in the broken walls of polystyrene panels. The author?s research can provide a rationale for the design and use of phase change thermal storage.

Improved Particle Heat Transfer by way of Bimodal Particle Distributions for High Temperature Solar Thermal Energy

High temperature solar thermal facilities are looking to increase operating temperatures through novel heat transfer media, one such being solid particles. These particles operating at high temperatures will require transferring their thermal energy into another working fluid like supercritical carbon dioxide which can be used in advanced power cycles. Achieving high heat transfer between the particles and supercritical carbon dioxide is essential to high efficiency and low-cost operation. Therefore, optimizing the thermal conductivity of these particles is one potential way to ensure high performance. Traditionally, unimodal particle distributions have been employed in high temperature particle solar power plants. However, ambient temperature testing of bimodal particle distributions has revealed a superior thermal conductivity when compared to its unimodal counterpart at the same temperature. This data was obtained by certified, off-the-shelf instruments that can effectively simulate the conditions a particle would be exposed to in a high temperature solar thermal system. Data obtained in this way suggests that the increased thermal conductively imputed by a bimodal particle distribution is significant at working temperatures in solar facilities. Furthermore, the thermal conductivity of these bimodal particle distributions peaks when the best combination of large and small particles is applied. At high temperatures, binary particle distributions are compared to monodispersed distributions of larger particles where heat transfer is more prolific due to the increased surface radiation. Various thermal conductivity, porosity and heat exchanger models are explored in conjunction with data acquired up to 700 C.

Influence of movable inner tube on the charging performance for a horizontal latent thermal energy storage exchanger

The charging performance of horizontal shell-and-tube latent thermal storage exchangers is significantly influenced by the position of the inner tube. However, the underlying mechanisms of the effect of inner tube movement on the charging performance remain unclear. Based on this, this paper proposed a horizontal shell-and-tube latent thermal energy storage exchanger whose inner tube is movable or Heat Exchanger with Movable Tube (MTHX), the two-dimensional simulation model of the MTHX was established, and the influence of the inner tube movement direction, speed, and range on the charging performance was studied, and finally this study obtained an optimized inner tube movement scheme for the charging process. The results indicate that the exchanger exhibits improved charging performance when the inner tube lies in the lower hemisphere region and moves up and down along the radius direction. Furthermore, increasing the velocity of inner tube movement enhances the charging rate. Additionally, the impact of the inner tube movement range on the charging performance depends on the direction of the movement. Moreover, compared to traditional horizontal shell-and-tube latent thermal storage exchangers, the implementation of the optimized inner tube movement scheme results in a 78.88 % reduction in charging time and a remarkable 348.71 % increase in average charging rate. This research presents novel directions for optimizing the charging performance of horizontal shell-and-tube latent thermal storage exchangers, thereby laying the foundation for the engineering application. The findings hold significant theoretical implications and engineering value.

Experimental investigation of evolving cloud-based fuzzy control of a pilot thermal exchanger under a decentralized framework

Relying on the Robust Evolving Cloud-based Control (RECCo) protocol, a decentralized evolving fuzzy control scheme is presented in this paper for a strongly interacting thermal exchanger process and for the first time experimentally investigated on the real pilot plant. Loop pairing information is first derived based on experimental analysis of the process dynamics. Accordingly, independent RECCo-controlled loops of system temperature are arranged in functional blocks without any prior decoupling or process modelling. The evolvable fuzzy controller structure is learned concurrently relying on data streams only. Simulation and experiments are carried out to support the design procedure and verify the control performance. The results show reasonable tracking performance under different scenarios.

NUMERICAL SIMULATION SHEAR-THICKENING FLUID THROUGH A SMALL-SCALED HEAT EXCHANGER

This paper aims to predict the behavior of a complex fluid though a small-sized thermal exchanger. The fluid used is of shear-thickening type of power-law index (n = 1.4) and Prandtl number (Pr = 50). The Ostwald model was utilized to define the dynamic viscosity. The exchanger consists of three rectangular cross-section tubes placed inside a thermally insulated chamber. The enclosure contains two ports for the entry and exit of the complex fluid. The complex fluid enters the chamber from the first port at a constant speed and at a low temperature, and then it passes around the hot tubes to be cooled. The rheological behavior of a fluid is defined by Ostwald equation, while the intensity of thermal buoyancy was modeled by Boussinesq approximation. The results showed that the increase of the velocity of the flow at the entrance increases the instability of the flow. Increasing the intensity of thermal buoyancy reduces the cooling process of the hot upper body.

A salt based integrated thermal store and heat exchanger for CAES systems

A salt based integrated thermal store and heat exchanger for CAES systems

Coupling Conduction, Convection and Radiative Transfer in a Single Path-Space: Application to Infrared Rendering

In the past decades, Monte Carlo methods have shown their ability to solve PDEs, independently of the dimensionality of the integration domain and for different use-cases (e.g. light transport, geometry processing, physics simulation). Specifically, the path-space formulation of transport equations is a key ingredient to define tractable and scalable solvers, and we observe nowadays a strong interest in the definition of simulation systems based on Monte Carlo algorithms. We also observe that, when simulating combined physics (e.g. thermal rendering from a heat transfer simulation), there is a lack of coupled Monte Carlo algorithms allowing to solve all the physics at once, in the same path space, rather than combining several independent MC estimators, a combination that would make the global solver critically sensitive to the complexity of each simulation space. This brings to our proposal: a coupled, single path-space, Monte Carlo algorithm for efficient multi-physics problems solving. In this work, we combine our understanding and knowledge of Physics and Computer Graphics to demonstrate how to formulate and arrange different simulation spaces into a single path space. We define a tractable formalism for coupled heat transfer simulation using Monte Carlo, and we leverage the path-space construction to interactively compute multiple simulations with different conditions in the same scene, in terms of boundary conditions and observation time. We validate our proposal in the context of infrared rendering with different thermal simulation scenarios: e.g., room temperature simulation, visualization of heat paths within materials (detection of thermal bridges), heat diffusion capacity of thermal exchanger. We expect that our theoretical framework will foster collaboration and multidisciplinary studies. The perspectives this framework opens are detailed and we suggest a research agenda towards the resolution of coupled PDEs at the interface of Physics and Computer Graphics.

Thermal performance of a plate-type latent heat thermal energy storage heat exchanger - An experimental investigation and simulation study

Heat storage is key to reducing the mismatch between energy supply and demand. The performance of thermal energy storage heat exchangers is determined by the exchanger structure and the heat transfer fluid (HTF) parameters. In this paper, the heat exchanger structure and HTF parameters of a plate-type latent heat thermal energy storage (LHTES) heat exchanger were investigated through experiments and simulations. From the experimental tests, it was observed that thermocouples accelerated the melting process of paraffin by 6 % on average for a single LHTES plate. The LHTES plate with aspect ratio of 3:1 was the optimal structure with the shortest melting time. To figure out the optimal thermal performance of the LHTES heat exchanger, a mathematical model was developed by FLUENT and verified against the experimental data. The influence of LHTES plate thickness as well as the HTF temperature and velocity was numerically studied. A performance factor was proposed to evaluate the thermal performance for the melting process of plate-type LHTES heat exchangers. Simulation analysis shows that the highest performance factor is realized when the LHTES plate thickness is 15 mm, independent to the HTF temperature and velocity. When the HTF velocity is small, it is critical to focus on the design of plate thickness of the heat exchangers rather than increasing the HTF temperature.

Thermodynamic, economic and environmental assessments of a novel solar-driven combined cooling and power system

The present study investigates an improved design of a solar-driven combined cooling and power system based on energy, exergy, economic and environmental perspectives. It includes evacuated tube collector, thermal energy storage, vapor generator, condenser, evaporator, ejectors, turbine, pump, heat exchanger and expansion valve. It is compared with the same capacity's individual cooling and power system. Effects of operating temperatures, component efficiencies, seasonal climate change and cooling-to-power ratio are also investigated. At the typical operating conditions with isobutene, the novel cycle has a performance index of 0.08 and overall exergy efficiency of 3.05%, which are nearly 33% and 44% higher than the individual cooling and power system, respectively. The specific total cost and equivalent mass of CO2 emission are also lower than the individual cooling and power system by 38% and 26%, respectively. At the higher vapor generator and evaporator temperatures but lower ambient temperature, the performance index is higher, but the specific total cost and equivalent CO2 emission are lower. The performance index and exergy efficiency are maximum for January and minimum for April, whereas specific cost and CO2 emission are minimum for January and maximum for April. The performance index is better, but the specific total cost is lower at a higher cooling-to-power ratio.

NEW SOLUTIONS FOR MAKING ELECTRIC MACHINES WITH HIGH SPECIFIC POWERS FOR PROPULSION SYSTEMS OF ELECTRIC AND HYBRID VEHICLES

Within the propulsion systems of electric or hybrid vehicles, road, naval or air, electric cars represent some of the main components that determine the weight of these systems. As a result, the realization of light electric propulsion systems requires the use of electric machines with high specific powers. In this work, we will present the results published in recent years in the specialized literature regarding the realization of electric car cooling systems in order to obtain high specific powers. New technologies for dissipating the heat generated by the energy losses in these machines will be presented, technologies that combine both passive cooling structures and active cooling structures, such as those using heat pumps. Also, research results will be presented regarding the realization of some components of these cooling structures using additive manufacturing technology, made with 3D printing systems, a technology that has evolved rapidly in recent years offering a new way to easily create, from various conductive, insulating or magnetic materials of parts with complex geometry, such as electric machine windings with direct incorporation of ceramic insulation, magnetic circuits with permanent magnets or thermal heat exchanger circuits.

CFD analysis of hybrid nanofluid-based microchannel heat sink for electronic chips cooling: Applications in nano-energy thermal devices

The utilize of microchannel in miniature thermal devices and microchannel heat sinks has advanced the scientific method of heat transfer to a new level, and the fields of electronic device cooling, aerospace industries, bioengineering, and materials science are all interested in furthering the technology's advancement. The microchannel has been numerically, practically, and analytically evaluated for the past three decades in order to develop models of hydraulic and heat efficiency during flowing fluid. Microchannel heat sink and novel fluids such as nanofluids are becoming well-liked. In order to recent time the full potential hybrid nanofluid in thermal exchanger has not yet been demoralized. In order to fulfill the lack of sufficient modeling data in this advanced research, the purpose of this analysis is to scrutinize computational thermal transportation features of alumina nitride (AIN)-alumina oxide (Al2O3) –Water hybrid nanofluid through electronic chip in six circular microchannel heat sinks. The simulation procedure is performed with volume fraction in range of 1% to 4%. The effects of coefficient of heat transfer, Nusselt number, Darcy friction factor, pressure drop and thermal resistance has been investigated. The single phase, laminar, incompressible and steady-state fluid flow has been numerically solved by the finite volume method with Computational Fluid Dynamic commercial software ANSYS FLUENT (R19.2) and SIMPLE algorithm.

Characterization of a latent thermal energy storage heat exchanger using a charging time energy fraction method with a heat loss model

Correlations predicting the transient behavior of latent heat thermal energy storage systems without too many computational efforts are valuable for engineering practices. This characterization of latent heat thermal energy storage systems can be done with the recently developed charging time energy fraction method. This method allows fitting a predictive model for the outlet heat transfer fluid temperature of a latent thermal storage unit as a function of the input condition. The previous application of the method neglected heat transfer to the ambient. The present paper improves the charging time energy fraction method by proposing a heat loss model to the charging time energy fraction model. A finite volume model of a high-temperature thermal battery is used to validate the proposed heat loss model. The improved charging time energy fraction method is then used to characterize a high-temperature thermal battery by calibrating a model on 36 numerical charging experiments. The charging time prediction between energy fractions of 0 and 0.96 deviates maximally 2 % from the measured charging time over all 36 calibration experiments. The deviation increases near the end of the charging process, especially for slower charging experiments. Across the 36 calibration experiments, the worst prediction has an average absolute temperature difference of 0.50 °C with a maximum deviation of 2.58 °C at the very beginning of the charging where fast transients are occurring. The calibrated model is also compared to four numerical validation experiments and four real experiments. Overall it is shown that this low computational cost model with average calculation times of 2–3 ms can accurately predict the heat transfer fluid outlet temperature of latent thermal energy storage heat exchangers.

Design Optimization, Thermohydraulic, and Enviro-Economic Analysis of Twisted Perforated Tape Insert-Based Heat Exchanger With Nanofluid Using Computational Fluid Dynamics and Taguchi Grey Method

Abstract In this paper, the effect of perforated twisted tape insert (PTTI)-based heat exchanger (HX) utilizing nanofluid as working fluid undercooling, turbulent flow model has been investigated numerically. Parameters, i.e., nanofluid mass flow rates (0.018–0.038 kg/s), perforated pitches (20 mm–40 mm), and perforated diameters (2 mm–4 mm) variation effects on fluid outlet temperature, Nusselt ratio, Friction ratio, pressure drop, overall thermal performance, CO2 discharge, and heat exchanger operating cost (HXOC) have been investigated. This work also focuses on design optimization with three different factors and three levels for higher heat transfer coefficient (HTC) and minimum pressure drop based on the Taguchi–Grey method. Computational fluid dynamics (CFD) output is used as an input value for statistical analysis. Results revealed that the PTTI in HX successfully achieved overall heat transfer enhancement in the range of 19.2% to 28.5%, but at the cost of pressure penalty of 126% to 163% higher than the plain tube. Critical Reynolds number 7927, above which PTTI in HX is least suitable for heat transfer enhancement as fluid velocity dominates over heat transfer and 1.7–2.5 times higher carbon discharge to the environment and HXOC. Preference sets of geometrical and fluid parameters are obtained using Grey analysis. Based on statistical analysis, in the considered levels, a group of parameters to attain higher HTC and minimum pressure drop are mass flow rate of 0.018 kg/s, a perforated pitch of 20 mm, and a perforated diameter of 4 mm.

Optimizing phase change composite thermal energy storage using the thermal Ragone framework

Optimal design of thermal energy storage devices can allow systems to approach specific design objectives while maintaining desired levels of performance. The thermal Ragone framework has been applied to the design of thermal energy storage heat exchangers, specifically identifying relationships between their power and energy capabilities. In this paper, a finite-difference model is used to optimize thermal storage heat exchanger designs for three objectives given a discharge power constraint. The three objectives are maximizing energy density, minimizing energy-specific capital costs, and minimizing the levelized cost of storage. This study focuses on the design of planar thermal energy storage heat exchangers with phase change materials and thermal conductivity additives. Key design parameters identified included the conductivity additive volume fraction, spacing between heat transfer fluid tubes, and the phase transition temperature. The optimal design is found to depend strongly on the required thermal power, with higher powers requiring transition temperatures further from the use temperature, more conductivity additives, and closer tube spacing. There is also a trade-off between these design parameters, where changing one (e.g., closer tube spacing) can allow another parameter to be relaxed (e.g., less conductivity additive). To aid in future device design, models of reduced complexity were developed and evaluated for their ability to predict optimal designs. These simplified models can predict the performance of thermal energy storage heat exchangers up to 5000 times faster than the finite-difference model. For the design objectives of maximizing energy density, minimizing costs, and minimizing levelized cost of storage, the simplified models predicted optimal designs with average absolute deviations below 2 % in relation to the optimal designs chosen by the finite difference model optimization. These models can serve as tools to further study thermal storage heat exchangers incorporating the realistic trade-off between the device's power and energy.