Heat Exchanger Model Research Articles

A COMBINED DESALINATION AND REFRIGERATION SYSTEM BASED ON SOLAR EJECTOR TECHNOLOGY

A solar ejector technology-based system that combines refrigeration and desalination was investigated for the present study. The proposed model combined a conventional ejector refrigeration system with a desalination unit to examine its ability to achieve cooling as well as produce clean water. An analytical model of the ejector was developed using 1D compressible flow equations based on mass, momentum, and energy conservation. The output from the ejector was then fed to a 1D heat exchanger model to compute the clean water production. The analytical model was implemented using the Matlab platform. A 2D axisymmetric numerical simulation of the ejector system was also performed to comprehend the internal flow structures. It has been observed that the entrainment ratio, which is the ratio of the vapor refrigerant's mass flow rate to the motive steam's mass flow rate, falls as the stagnation temperature of the motive steam increases. It was noted that the coefficient of performance (COP) rises as the evaporator temperature rises, but it is seen to decline with the rise in generator temperature. The amount of desalinated water that can be produced with the system was also explored. It was observed that the production of desalinated water increased proportionally with the rise in generator temperature. At a generator temperature of 140°C, the system obtained clean water at a rate of about 2.9 g/s, which corresponds to a 24.5% mass flow rate of the input steam.

Experimental validation of a heat exchanger model for thermoacoustic applications

Thermoacoustics is a promising technology for energy conversion purposes. Among the bottlenecks limiting a large diffusion of thermoacoustic devices, there are heat exchangers, whose behaviour in oscillatory flows is rather different than those working in stationary flows. Furthermore, the classical linear acoustic theory in the frequency domain cannot predict with high-fidelity the thermo-fluid dynamics of such heat exchangers. In this article, a CFD model based on a standing wave device including a parallel plate heat exchanger is proposed. The setup is inspired by a similar prototype of a thermoacoustic engine in which the performance of the ambient heat exchanger was tested. The results of the CFD model are therefore compared, in terms of the temperature difference between fluid and solid wall in the heat exchanger, average heat flux and Nusselt number, with experimental data showing a satisfying agreement.

Experimental investigation of water vapor condensation from flue gas in different rows of a heat exchanger model

Condensing heat exchangers (HE) are used in many applications because of their usability with different fluids and a wide operating range in terms of pressure, temperature and power. Despite that, the thermal design of condensing heat exchangers is still not optimized, due to the complexity of the condensation process and lack of related research.This paper presents results of experimental investigations of biofuel flue gas water vapor condensation on vertical tubes in different rows of a tube bundle in a crossflow. The effects of water vapor mass fraction, inlet flue gas temperature and the Reynolds number on heat transfer when the inlet cooling water temperature and flow rate are constant were analyzed. The results obtained showed that the main parameters which had the most influence on the condensation process were the water vapor mass fraction in the flue gas and its temperature at the inlet to the test section. In the range of inlet flue gas Reynolds numbers investigated, the Re effect on heat transfer was not as significant as the effect of the parameters indicated above. However, the Re number had some influence on the heat transfer variation along the inline tube bundle. A comparison of the average Nu number in the case of dry air with the experimentally determined average Nu number, even with low condensable gas mass fraction (6 %), showed that it increased considerably. A correlation was proposed, which helps to determine the average Nu number for the heat exchanger in the range of experiments performed.

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.

Design and optimization of molten salt printed circuit steam generators

Among the array of heat exchangers available, printed circuit steam generators emerge as a particularly promising choice for high-temperature applications. This is primarily attributed to their augmented heat transfer surface area, which enables the efficient transfer of thermal energy within the Rankine power conversion cycle, especially in the context of molten salt-based thermal power systems, such as those employed in molten salt reactors and concentrated solar power plants. It is imperative to analytically model the heat transfer characteristics of mini-channel flow boilings for a printed circuit steam generator. To resolve new technical design issues that the single hot fluid flow channel is cooled by multiple cold fluid flow channels, an improved heat exchanger model is proposed to assist the numerical modeling of printed circuit steam generators for molten salt based on the equilibrium thermodynamics quality of water/steam flow. The existing flow boiling heat transfer coefficient correlations of mini-channels are leveraged to optimally design the straight-passage based printed circuit layouts and narrow down their optimal operational parameters. With various selections of subcooled water, saturated water, and superheated steam heat transfer correlations, The best combination of heat transfer correlations is found to assess the axial distributions of cold fluid temperatures and pressure drops. Two multi-objective optimizations are formulated to respectively solve thermal sizing and scaling problems for the optimal designs and operations of printed circuit steam generators. The computational results indicate that the overall heat transfer coefficient for an optimized 50 MW(th) printed circuit steam generator assessed at the transition point is about 3,828 W/(m2 K), which remarkably surpasses the 1,544 W/(m2 K) value of the conventional shell-tube steam generators by a factor of three. This implies that printed circuit steam generators would be a promising replacement of the traditional shell-tube steam generator.

Unlocking geothermal energy for sustainable greenhouse farming in arid regions: a remote-sensed assessment in Egypt’s New Delta

This study introduces a novel approach for assessing geothermal potential in arid regions, specifically Egypt’s New Delta Agriculture Mega Project area. The challenge of limited sub-soil temperature profile data was addressed by integrating Global Land Data Assimilation System (GLDAS) weather data. Using the Earth-to-Air Heat Exchanger (EAHE) model, the extracted air and sub-soil temperature profiles the potential for geothermal energy production was estimated. We modeled the annual sinusoidal soil surface periodic heating pattern by utilizing GLDAS ambient air temperature (AAT) and land surface temperature (LST). Using either AAT or LST yielded a Root-Mean-Square Error (RSME) of 0.2°C. The generated sub-soil profiles for the New Delta region showed a temperature variation of no more than 1.5°C at a 4-m depth, making it an optimal depth for EAHE installation. One-pipe EAHE demonstrated a cooling/heating capacity ranging from 400 W (cooling) to −300 W (heating). The study highlights the New Delta region’s strong geothermal potential for greenhouse cooling and heating, underlining its suitability as a sustainable energy source in arid areas. It also offers a practical guide for the EAHE application and it emphasizes the global potential for geothermal energy exploration, using innovative GLDAS data to expand sub-soil temperature profile accessibility.

Optimizing vertical ground heat exchanger modelling through GPU-accelerated computation strategies

Enhancing Vertical Ground Heat Exchanger (VGHE) modelling for efficient Vertical Ground-Coupled Heat Pump (VGCHP) systems, renowned for their eco-friendly operation, has garnered significant attention. Optimally designing and sustaining the long-term efficiency of VGCHP systems necessitates rigorous, protracted VGHE modelling, a process fraught with computational intensity. To surmount this challenge, this contribution introduces an accelerated VGHE modelling paradigm grounded in Graphics Processing Unit (GPU) processing. This entails employing the Finite Line Source (FLS) model based on Fast Fourier Transform (FFT). To ameliorate computational demands, the processing capabilities of both Central Processing Units (CPUs) and GPUs are harnessed, leveraging CPU- and GPU-based FFT and inverse FFT (IFFT). Hybrid and non-hybrid processing modes are explored, differentiating between CPU- and GPU-based FFT in non-hybrid scenarios, while hybrid approaches combine both for distinct simulation periods. By scrutinizing two processing systems with varying specifications, diverse CPU- and GPU-based FFT combinations are assessed. Findings unequivocally underscore the superiority of CPU-based FFT for initial years, succeeded by GPU-based FFT for ensuing years, in terms of computational efficiency. The efficacy of the hybrid computation approach is demonstrated through a reduction of total computational time in 20-year VGCHP operation simulations by up to 33.5 % compared to conventional CPU-based FFT methods.

Effect of multi-variant on the thermal transfer of target system for the initiative isotopes accelerator

Medical isotopes possess high value in disease diagnosis and therapy. The production of isotopes by spallation results in ultra-high target temperature which leads to impurity contamination to the isotopes. Improving the thermal contact resistances (TCRs) at the target-graphite case interface and the graphite case-heat sink interface is the effective way to control the target temperature. This work constructs experimental models for extreme condition application in terms of finite element simulations. A target system model was constructed according to the experimental setup, which includes graphite films, thorium targets, graphite cases and single target disk. Furthermore, a heat exchanger model was constructed to explore the role of thermal interfacial materials (TIMs) and microchannels. The simulation results of the target system model indicate that the desired temperature of the target can be accomplished when the target-case TCR is below 9 × 10−4 K m2 W−1 and the case-disk TCR is below 5 × 10−4 K m2 W−1, and the TCR between the case and the disk plays a more significant role in temperature reduction. The simulation results of heat transfer model explain that the difference in the thermophysical properties of the target and the case affect the beneficial effect of TIMs on the TCR. All of the above analyses provide theoretical guidance for the optimum design of the heat dissipation scheme for isotopes accelerator.

A comparative analysis of the performance of backfill heat exchangers in deep mine geological environments

With the increase of mineral mining depth, the technologies of constructing heat exchanger in stopes to exploit geothermal resources from deep mines have received great attention. The heat extraction capacities of heat exchangers are closely related to the geological environments of deep mines, especially backfill mines. Therefore, a three-dimensional unsteady heat transfer and seepage coupling model of backfill heat exchangers (BFHEs) is created and verified in this work using COMSOL simulation software. Then, the influences of geological environments, involving groundwater seepage, initial temperature and thermal conductivity of surrounding rock etc., on the ability of five BFHEs with the equal buried tube length to extract heat in different configurations are investigated by this model. The findings indicate that groundwater flow can significantly improve the performance of BFHEs. Double-layer tube BFHEs have the best overall performance in the studied seepage velocity range. Only when there is no or little seepage is the performance of single-layer tube BFHEs equivalent to that of double-layer tube BFHEs. The heat extraction capacity of BFHEs is greatly improved under seepage conditions with the increase in the initial temperature of surrounding rock, although the impact is low in the absence of groundwater seepage. The benefit of backfill body's thermal conductivity on BFHEs' ability to transport heat is significantly greater than that of surrounding rock, but the effect becomes smaller as the value increases. Further increasing the thermal conductivity of the backfill body will not considerably increase the heat extraction capability of BFHEs after it reaches 2.5 (W·m−1·K−1). Therefore, if the cost is too high, continued enhancement is not recommended. The findings offer theoretical recommendations for optimizing BFHEs’ setup to better adapt to deep mine geological environments and increase geothermal extraction capability.

Modeling and Design of a Multistream Plate-Fin Heat Exchanger in the Air Separation Units by Pinch Technology

Recent years have seen considerable advancement in cryogenic technology. Air separation devices have used the cold box with heat exchanger plate-fin (PFHE) in numerous applications. Cryogenic technologies are used in many industrial processes to recover heat and reduce energy consumption. The multistream plate-fin heat exchanger (MSPFHE) is heavily utilized in the air separation plant’s (ASU) design. The plate-fin heat exchanger, one of the most important applications in the cryogenic industry, is the focus of the current investigation. The air entering this operation has been cooled by utilizing energy from streams originating from the distillation tower in the air separation unit (ASU) to reduce energy usage. The project aims to develop and create a multistream plate-fin heat exchanger (MSPFHE) that may be used in the cold box of an air separation unit practically and without limitations. The pinch technique, a method based on the usage of composite curves, was used in the creation of MSPFHE. With pinch technology, it is possible to divide a multistream exchanger into block portions that represent enthalpy intervals and identify the entry and departure sites for the streams. The correlations used in the MSPFHE thermal design model were first modeled and compared to earlier models as part of this effort. This model has been turned into MATLAB code and utilized in two case studies to yield acceptable results during the sizing step. Calculations of thermodynamic properties, heat transfer, pressure drop, choice of fin type, and final heat exchanger size were all part of the design of the MSPFHE. Finally, based on the software’s ability to reproduce the identical environmental conditions nature produces, the case study results have been validated using Aspen EDR. These findings were matched to findings from the literature and determined to be reliable and consistent.

A frequency domain dynamic simulation method for heat exchangers and thermal systems

Dynamic simulation of thermal systems is crucial for their optimal control but facing the challenge of balancing calculation accuracy and efficiency, where numerically high-efficient and accurate heat exchanger (HX) modeling is a key. Herein, we propose a frequency domain model for HXs' dynamic simulation in the to meet this challenge. The governing equations of HXs are first converted to frequency domain through Fourier transform, and the analytical solution of the converted equations yields the frequency domain HX model in the form of transfer matrix that connects the inlet temperature variations and outlet temperature responses. Furthermore, integrating transfer matrices of HXs into the system's transfer matrix enables a high-efficiency thermal system simulation. Numerical cases of a single HX, a HX network, a district heating network, and a thermodynamic cycle are used to validate the developed method and demonstrate its efficacy by comparing it against finite difference/volume method. Results show that the proposed method could reduce the calculation time by 2–3 orders of magnitude, and the maximum deviation of node temperature is around 1 K. The proposed method can be a powerful tool for the analysis of thermal systems and potentially integrated energy systems.

Dynamic modelling of cross-flow printed circuit heat exchangers for multistage reactor intercooling

A reduced-order dynamic model of a cross-flow printed circuit heat exchanger was developed to study both steady-state and transient performance under conditions that would be encountered in multistage catalytic combustion reactors to better understand how they can be used to minimize fluctuations in heat-integrated reactors and intensified processes. Previous transient models for cross-flow heat exchangers rely on an initial steady state and apply only for changes in inlet temperature, but this work presents a model that can be applied to intermediate states or multiple concurrent upstream process changes. Steady-state simulations showed that larger channels reduce volumetric heat transfer performance and effectiveness due to convective resistance. Furthermore, larger channel spacing increases effectiveness but also reduces compactness. Operating temperature was found to have a minimal effect on the overall heat transfer coefficient and effectiveness within the range of conditions studied, and operating pressure was found to have no effect on heat transfer. Transient analyses showed that the response to a unit step in temperature matches closely with an analytical infinite gas velocity model, both for time constants and the overall thermal response, with initial variations in outlet temperatures from ideal-case models below 3.8 % of unit step magnitudes, and average differences below 0.75 %. Transient analyses also show the effects of a finite fluid velocity which is critical in the transient response of large heat exchangers. The presented numerical model can also be more easily extended to complex configurations and can be applied to other changes in inlet conditions such as changing composition and flow rates as are found in combustion applications. A three-fluid thermal management system for a multistage packed-bed microreactor using printed circuit heat exchangers is proposed and modelled to provide a method for temperature regulation and pre-heating of fresh reactor feed.

Fault detection and isolation in uncertain dynamic systems using composite optimization and inferential sensing

Inferential sensing is a cost-effective and reliable approach to replace expensive and impractical hardware sensing, while yielding robust fault detection and isolation (FDI) during system maintenance or operation. Yet, their high computational footprint necessitates the employment of advanced and efficient estimation techniques, along with symbolic mathematics and automatic differentiation. Herein, we attempt to combine model-driven sensor selection methods with inferential sensing to accurately identify faults in the presence of system noise and uncertainty. During sensor selection, we employ criteria from information theory to maximize the estimability of system faults from available system measurements. The most informative sensor set stems from a comparison of all possible sensor suites via information theoretic criteria expressed as functions of the Fisher Information Matrix. Optimal inferential sensors are calculated through a novel fusion of symbolic regression and information theory. For built-in test deployment, we utilize k-Nearest Neighbors classification to assess the capability of each sensor suite for all plausible instantiations of uncertainty and system noise, and evaluate FDI performance benefits from the inclusion of inferential sensor(s). The proposed computational framework is deployed with steady-state and dynamic models of a cross-flow plate-fin heat exchanger, at varying levels of measurement noise and uncertainty. As shown, the augmented system of composite sensors (i.e., inferential and hardware) provides accurate information on system fault(s) and reduces the evidence of uncertainty. Compared to traditional sensor approaches, the proposed techniques are shown to be more precise while simultaneously granting increased insight into details otherwise hidden by noise. Thus, they form a robust and reliable tool when conducting fault diagnosis and possibly toward system safety.

Recent advances in the applications of machine learning methods for heat exchanger modeling—a review

Heat exchanger modeling has been widely employed in recent years for performance calculation, design optimizations, real-time simulations for control analysis, as well as transient performance predictions. Among these applications, the model’s computational speed and robustness are of great interest, particularly for the purpose of optimization studies. Machine learning models built upon experimental or numerical data can contribute to improving the state-of-the-art simulation approaches, provided careful consideration is given to algorithm selection and implementation, to the quality of the database, and to the input parameters and variables. This comprehensive review covers machine learning methods applied to heat exchanger applications in the last 8 years. The reviews are generally categorized based on the types of heat exchangers and also consider common factors of concern, such as fouling, thermodynamic properties, and flow regimes. In addition, the limitations of machine learning methods for heat exchanger modeling and potential solutions are discussed, along with an analysis of emerging trends. As a regression classification tool, machine learning is an attractive data-driven method to estimate heat exchanger parameters, showing a promising prediction capability. Based on this review article, researchers can choose appropriate models for analyzing and improving heat exchanger modeling.

Validation and Application of a Finned Tube Heat Exchanger Model for Rack-Level Cooling

Abstract A thermosyphon-based modular cooling approach offers an energy efficient cooling solution with an increased potential for waste heat recovery. Central to the cooling system is an air-refrigerant finned tube heat exchanger (HX), where air is cooled by evaporating refrigerant. This work builds on a previously published two-dimensional (2D) model for the finned-tube HX by updating and validating the model using in-house experimental data collected from the proposed system using R1233zd(E) as the working fluid. The results show that key system variables such as refrigerant outlet quality, air and refrigerant outlet temperatures, and exchanger duty agree within 20% of their experimental counterparts. The validated model is then used to predict the mean heat transfer coefficient on the refrigerant side for each tube in the direction of airflow, indicating a maximum heat transfer coefficient of nearly 1200 W/(m2 K) for a HX duty of 5.3 kW among the tested cases. The validated model therefore enables accurate predictions of HX performance and provides insights into improving the heat exchange efficiency and the corresponding system performance.

Principles of modelling of slinky-coil ground heat exchangers

Principles of modelling of slinky-coil ground heat exchangers

Design and numerical assessment of an additively manufactured Schwarz diamond triply periodic minimal surface fluid-fluid heat exchanger

In aerospace, thermal applications demand compact, lightweight, and efficient heat exchangers. Additive manufacturing processes offer the potential to create highly complex structures that are not achievable through traditional manufacturing methods. This work presents the development of an additively manufactured fluid-fluid heat exchanger that shows the potential to enhance the performance, reduce weight, and increase compactness compared to a conventional plate heat exchanger. A numerical model of the conventional plate heat exchanger was created, and fluid dynamics simulations with heat transfer were performed. Validation of the simulations was done by experiments. Then, a novel heat exchanger was designed using a bottom-up approach and investigated at different levels of complexity using computational fluid dynamics. The internal structure of the final heat exchanger consists of a repeating triply periodic Schwarz diamond minimum surface elongated in the direction of flow. The heat exchanger was manufactured with laser powder bed fusion process using AlSi10Mg. It had a 108% higher compactness and 54% lower weight compared to the plate heat exchanger. Numerical analysis yielded the pressure loss in pascal was reduced by 50%–59% while heat transfer in watts was improved by 3%–5%. Future researches should experimentally investigate the thermal and fluid mechanical characteristics of the novel additively manufactured heat exchanger and increase compactness and heat transfer further by analyzing the minimum partition wall thickness and the impact of wall roughness and deposit formation.

Numerical analysis of the heat exchange model with the ground on the example of a complex of industrial halls

This paper describes the process of validation of the numerical model and its calibration, based on long-term field studies that were carried out at a growing tunnel system for Agaricus bisporus in southern Poland. A verification of uncertainty indices was undertaken, based on which the applicability of the model for further research and analysis was assessed according to commonly used guidelines. WUFI®plus software was applied based on the numerical elementary balance method (EBM). The HVAC system was also simulated in order to reflect actual conditions as accurately as possible. The correctness of the model was assessed by means of uncertainty indicators in the form of the normalised mean deviation error (NMBE) and the Coefficient of Variation of the Root Mean Square Error CV (RMSE). The analysis provided an opportunity to highlight the validity of the calculations, considered reliable under the criteria adopted. It also pointed out some limitations of the model applied, resulting in negative calibration results for a small number of selected measurement monitors. Using the validated calculation model, heat flows from the ground to the building and the other way around were estimated. The specifics of the building contributed to the occurrence of heat gain from the ground being 20 times larger compared to energy losses to the ground. This opens up a potential path for extending the numerical analysis to optimise energy management for the investigated facility and to determine the thermal interaction between buildings in the surveyed area.

Thermal analysis and performance investigations of shell and tube heat exchanger using numerical simulations

The steam condenser is a crucial component in power plants, playing a vital role in influencing the overall performance of steam power plants. This paper delves into a detailed assessment of the thermal aspects and evaluation of steam surface condensers. To conduct this rigorous evaluation, we meticulously crafted a three-dimensional (3D) model of a multi-tube single-pass counter-flow heat exchanger using ANSYS Design-Modeller. Within this model, a multiphase mixture model was harnessed to replicate the condensation process that takes place within the condenser. After the model’s development, a series of computational fluid dynamics (CFD) simulations were expertly executed utilizing ANSYS Fluent Workbench. The simulations encompassed diverse cooling water flow rates and steam inlet velocities. Notably, two sets of CFD simulations were carried out: the initial set featured a velocity inlet in the condenser, while the second set involved CFD simulations with a pressure steam inlet. The findings derived from these simulations unveiled a noteworthy correlation between the condensation rate within the shell and both the rate of circulating water flow and the operational pressure of the condenser. Additionally, it was discerned that the condensation rate could be further influenced by the specific geometry of the condenser. In sum, this study concludes that optimizing the geometrical configuration and baffle arrangements holds promise for increasing the condensation rate and overall performance of steam condensers employed within steam power plants.

Computational modeling and experiment validation of a microchannel cross-flow heat exchanger

Microchannel Cross-Flow Heat Exchanger (MCFHE) is one of the potential candidates to be employed in various energy recovery. Compared to microchannel counter-flow heat exchanger, little research has been devoted to simulating the heat transfer process inside a MCFHE. Given the complex temperature distributions associated with cross-flow heat exchangers, the conventional “unit cell” approach for a pair of fluid channels becomes invalid. In this study, a new methodology is developed to resolve the modeling challenges associated with a 2-pass MCFHE. Specifically, the MCFHE is divided into 10 zones to minimize mesh size associated with each fluid channel, which leads to a computationally efficient and segregated CFD model. The CFD model provides detailed temperature distributions within both fluid channels, and the resulted outlet temperatures match closely with the experimental data. In addition, the Nusselt numbers in the air and oil channels agree well with classical developing flow correlations. Using the ε−NTU method, it provides an initial guess for the mid-pass oil temperature that is needed to initiate the CFD simulations for the first pass including Zone 1–5. Furthermore, the resulted analytical results based on the iterative ε−NTU method match closely with the CFD simulations.