Heat Exchanger Materials Research Articles

Energy storage materials for phase change heat devices recovering industrial waste heat for heating purposes

The abundance of industrial waste heat resources offers valuable opportunities for the utilization of phase change heat exchangers in clean energy applications. This study focuses on the innovative development of binary phase change material (PCM) composed of paraffin and stearic acid (SA) in various ratios, aimed at optimizing waste heat recovery. Comprehensive analyses of the phase change temperature, latent heat, and thermal conductivity of these mixtures were conducted. The research identified a mixture with a 20 % paraffin and 80 % stearic acid ratio, which exhibits a phase change temperature of 62.73 °C and a latent heat of 205.53 J/g. This mixture stands out due to its minimal subcooling and consistent thermal properties, making it highly effective for low-temperature waste heat recovery. Additionally, a novel process design and simulation system for using these materials in heat exchangers to convert intermittent industrial waste heat into continuous thermal energy for heating were developed.

Nuclear power plant waste heat opens a window of next-generation desalination hybridization: a SOAR-based review.

This review examines the potential for utilizing nuclear power plant (NPP) waste heat in hybrid desalination systems, focusing on Reverse Osmosis-Low-Temperature Evaporation (RO-LTE) driven by renewable energy sources and atomic waste heat. By employing a SOAR (Strengths, Opportunities, Aspirations, Results) analysis, the study evaluates the integration of NPP waste heat into various desalination technologies, emphasizing the environmental benefits and energy efficiency improvements. Fundamental aspirations include advancements in material science and heat exchanger designs, which enhance heat transfer and evaporation processes. The review also explores cost reduction strategies, such as integrating hydrogen production and mineral recovery from desalination by-products. Passive technologies and process optimization are proposed to minimize operational costs and energy consumption, supporting long-term sustainability. This review serves as a resource for decision-makers, offering insights into the strategic use of NPP waste heat in desalination to address water scarcity while promoting energy efficiency and sustainability.

Numerical computations on thermal performance of large-scale Ti-Mn-based metal hydride storage reactor via open source CFD software

Certain metals and metal alloys can absorb hydrogen through an exothermic chemical reaction, resulting in the formation of metal hydrides. To maintain a rapid charging rate, the produced heat must be extracted as rapidly as it is generated. This study was attempted to evaluate the heat transfer enhancement in a cylindrical hydrogen storage reactor equipped with a central tube for large-scale applications using a 3D transient model. Finite-volume simulations are carried out using the open-source software package OpenFOAM to systematically investigate the impacts of material thermophysical properties, cooling media, and heat exchanger design on the heat transfer behaviors and hydrogen storage rate. The reactor’s performance was evaluated in terms of temperature and total hydrogen mass history profiles, in addition to pressure drop. The findings indicated that the charging time was improved by roughly 86%, compared to the case without thermal enhancement to attain 90% hydrogen storage capacity. A diminished pressure drop was observed between the water-based Al2O3 nanofluid with 5 vol% concentration and pure water at lowered coolant flow velocities, hence enhancing pumping power efficiency. Moreover, the results demonstrated that the storage rate is markedly improved by enhancing the effective thermal conductivity of the hydride bed, increasing the heat exchange area, accelerating the coolant flow rate, and lowering its temperature. The outcomes highlighted the possibility of advancing the current metal hydride reactor for practical application.

Application of waste fly ash and graphite powder used as backfill materials in vertical ground heat exchangers

Backfill material plays a significant role in heat transfer between the ground heat exchangers (GHEs) and surrounding soil. Fly ash is the fine ash wasted from coal combustion in thermal power plants, which may cause a serious of problems including air, water and soil pollution. To fully utilize the waste resources and improve the thermal performance of backfill material, a method of using waste fly ash and graphite powder is proposed, and the feasibility of using them as backfill material is investigated via laboratory and field test, in which the economic aspect is taken into consideration. The results indicate that the highest thermal conductivity of thermally enhanced backfill material could be increased to 2.391 W/(m·K) via laboratory test, with a growth rate of 23.69%, in which the mass ratio of graphite reaches 10% meanwhile guaranteeing the workability of fresh mortar. Heat transfer rates could be enhanced by 27.22% compared with traditional backfill material of natural sand via field test, corresponding to a highest heat transfer rate of 55.80 W/m. The economical value could be achieved through the lower cost of raw material and the reduction of drilling depth.

Optimizing Backfill Materials for Ground Heat Exchangers: A Study on Recycled Concrete Aggregate and Fly Ash for Enhanced Thermal Conductivity.

This study investigates the potential use of recycled concrete aggregate (RCA), fly ash (FA), and their mixture (RCA+FA) as backfill materials for shallow vertical ground heat exchangers (GHEs). Granulometric, aerometric, and Proctor compaction tests were conducted to determine soil gradation, the void ratio, and the optimal moisture content (OMC) for maximum dry density. RCA demonstrated efficient compaction at lower moisture levels, while FA required higher moisture to reach maximum density. A 10% FA addition was optimized to fill voids in the RCA soil skeleton without compromising structural stability. Thermal conductivity tests were performed using a TP08 probe in both dry and wet states. The results showed that the RCA+FA mix exhibited a notable increase in thermal conductivity at around 6% moisture content due to the formation of water bridges between particle contacts. FA, in contrast, displayed a more linear relationship between conductivity and moisture. The RCA+FA mix achieved higher thermal conductivity than either material alone, particularly near full saturation, making it a promising option for efficient heat exchange. Thermal conductivity modeling, based on the Woodside and Messmer model, confirmed the RCA+FA mix's high conductivity and estimated full saturation conductivity values with a small error. The Kersten number (Ke) was employed to predict conductivity across varying moisture levels, with results showing a strong correlation with saturation ratio (Sr).

Assessment of Tube–Fin Contact Materials in Heat Exchangers: Guidelines for Simulation and Experiments

This paper describes experiments on finned tube heat exchangers, focusing on reducing the thermal contact resistance at the contact between the pipe and the lamella. Various contact materials, such as solders and adhesives, were investigated. Several methods of establishing contact were tested, including blowtorch soldering, brazing, and furnace soldering. Thermal camera measurements were carried out to assess the performance of the contact materials. Moreover, finite element analysis was performed to evaluate the contact materials and establish guidelines in the fin–tube connection modeling by comparing simplified models with the realistic model. Blowtorch brazing tests were successful while soldering attempts failed. During the thermographic measurements, reflective surfaces could be measured after applying a thin layer of paint with high emissivity. These measurements did not provide valuable results; thus, the contact materials were assessed using a finite element analysis. The results from the finite element analysis showed that all the inspected contact materials provided better heat transfer than not using a contact material. The heat transfer rate of the tight-fit realistic model was found to be 33.65 for air and 34.9 for the Zn-22Al contact material. This finding could be utilized in developing heat exchangers with higher heat transfer with the same size.

INVESTIGATION OF FLOW AND HEAT TRANSFER PERFORMANCE OF GYROID STRUCTURE AS POROUS MEDIA

There are active and passive methods used to improve heat transfer. One of the passive methods is utilising porous media with high heat transfer surface area. Porous media are divided into two groups: regular and irregular structures. One of the regular structures is triply periodic minimal surfaces (TPMS), which have been studied quite frequently recently. In this study, heat transfer and flow analysis of a Gyroid geometry, one of the most used TPMS in the literature, is investigated numerically considering the conjugate heat transfer conditions. A single porosity is considered (ε = 0.6), and aluminium, ceramic and PLA are selected for the heat exchanger material to examine the temperature change in the heat exchanger. To understand the different flow characteristics, Reynolds numbers (Reh) are assumed to be 19.12, 95.61 and 172.09. The fluid inlet temperature is assumed to be constant at 298.15 K, and the initial temperature of the heat exchanger is assumed to be constant at 278.15 K to be consistent with the regenerative heat recovery temperature difference in ventilation standards. Nu numbers under different operating conditions are compared, and it is the ceramic material with low thermal diffusivity is at the highest level despite its low thermal conductivity. At the highest Re number, it provided approximately 6% better heat transfer than the aluminium heat exchanger.

Performance evaluation of different new channel box photovoltaic thermal systems

Current research has highlighted three major gaps in the literature: (a) a rarity of studies on photovoltaic thermal systems with channel boxes, (b) a lack of data on pressure drop and surface temperature distribution in these systems, and (c) absence of analysis regarding the impact of materials (metals and polymers) used in photovoltaic thermal systems on performance, cost, payback time and weight. The novelty of this paper lies in addressing these gaps by studying a new channel-box photovoltaic thermal system, varying the number of channels and the height of the collectors that distribute water to these channels, in order to identify the most efficient design in terms of electrical, and thermal efficiency as well as pressure drop. In addition, the impact of different heat exchanger materials (metals and polymers) on the performance, cost, payback time, and weight of photovoltaic thermal systems was investigated. 3D numerical simulations were carried out using COMSOL Multiphysics software, based on the finite element method, and validated by outdoor experimental research. The results show that the photovoltaic thermal system 8 design performs best, with a total efficiency of 89.42%. In addition, the aluminum photovoltaic thermal system stands out as the most cost-effective option, with a payback time of 0.823 y (300 d) and annual savings of $459.262, while being 38% lighter than the copper system. Based on this study, it is recommended that the photovoltaic thermal system 8 be implemented because of its exceptional performance and ease of implementation.

Determination of thermal properties of grouting materials for borehole heat exchangers (BHE)

Thermal properties of grouting materials for borehole heat exchangers (BHE) are currently analysed with varying measurement methods and analysis procedures, resulting in difficulties when comparing values of different studies. This study therefore provides the first comprehensive investigation of different analysis procedures by systematically comparing the influence of the measurement method and the sample preparation on the determination of the thermal conductivity and the volumetric heat capacity. Seven dissimilar grouting materials with varying water–solid ratios (W/S) and compositions are analysed. The thermal conductivities of the materials range between 0.9 and 1.8 W m−1 K−1 (transient plane source method, TPS). The volumetric heat capacities range between 3.01 and 3.63 MJ m−3 K−1 (differential scanning calorimetry, DSC). From the findings of this study, a standardised analysis of grouting materials is provided which suggests mixing of the grouting material at a high mixing speed and sample curing under water for 28 days at room temperature. The benefits of calculating the volumetric heat capacities of grouting materials from the specific heat capacities of dry samples measured with the DSC, the water content and the bulk density are demonstrated. Furthermore, an estimation procedure of volumetric heat capacity from the W/S and suspension density with an uncertainty of smaller ± 5% is provided. Finally, this study contributes to consistency and comparability between existing and future studies on the thermal properties of grouting materials.

Performance of thermally enhanced backfill material in vertical ground heat exchangers under continuous operation in a cooling season

Backfill materials in vertical ground heat exchangers significantly affect the heat-transfer efficiency of ground-source heat pump systems. In this study, the use of graphite improving the thermal conductivity of backfill materials is investigated via laboratory tests, and its feasibility is verified via in-situ thermal response testing. Based on the results, the relationship between the coefficient of performance (COP) and thermally enhanced backfill materials is built through a numerical model. The variation of COP under different thermal-physical soil conditions and backfill materials with enhanced thermal conductivities is investigated; then a method for selecting backfill materials is proposed by matching thermal properties of backfill material and surrounding soil. The results indicate that when the soil thermal conductivity is at a relatively low level of 1.0 W/(m·K), the highest COP improvement ratios range between 7.99 % and 16.13 % during the 90 days operation However, the COP improvement ratio decreases gradually as the soil thermal conductivity increases, and the COP improvement ratios decrease to less than 1.0 % as the soil thermal conductivity increases to 5.0 W/(m·K). Parameter-design charts are made to intuitively illustrate the COP variation. The result of contributions of influencing parameters shows that high-velocity groundwater seepage contributes positively to COP improvement, followed by thermal conductivity of soil, and then that of backfill material during a cooling season.

Improving Wastewater Heat Recovery Using Phase Change Material Heat Exchangers: A Numerical Study of Thermal Performance

ABSTRACTIndustrial processes often generate substantial amounts of wastewater with significant thermal energy content, which is typically discarded as waste. A promising approach to increase energy efficiency and advance sustainable resource management is waste water heat recovery. Utilizing a phase change material (PCM) to extract waste heat from wastewater and transfer it to cold water is an innovative method that separates the demand and supply of heat, while also integrating storage and transmission within a single heat exchanger (HE). A 3D numerical model of PCM‐based HE is developed and simulated. The thermal behavior of PCM and preheating of cold water are investigated in this study. In order to increase the thermal conductivity of the PCM, fins are strategically positioned. Around 71.13% of melting time is reduced by adding fins. Further, the 10° orientation of the fins is also numerically observed and it is found that it helps to improve natural circulation of molten PCM. Thus, melting time is reduced by 34% compared to the vertical fin. A 3.5°C–4.5°C temperature rise in cold water is obtained with the inclined fin, which is 14.28% higher than the vertical fin model.

Two-Dimensional Inverse Method to Estimate the Heat Flux Function in a Phase Change Material Heat-Exchanger

A two-dimensional inverse method is presented for estimating the boundary heat flux imposed on phase change materials in the melting/solidification process. The inverse problem is handled by the conjugate gradient method with the adjoint problem for function estimation. The method is verified using unsynthetic data, and the effect of the number of sensors, sensor placement, and measurement errors on the accuracy is investigated. In all cases, it is found that the method remains stable and accurate with a root mean square relative error less than 10%. Also, the number of sensors depends on the desired accuracy, computing time, and frequency of spatial changes in heat flux. Using field measurement is the best option for high accuracy and time-efficient estimation of spatial changes in the heat flux function. The accuracy of the estimated heat flux strongly depends on the sensor distance from the boundary. Therefore, it is desirable to place the sensor as close to the boundary as possible. With the addition of measurement errors, the presented method remains stable even with high measurement errors. This shows that this method can be used for real conditions.

Material selection and manufacturing for high‐temperature heat exchangers: Review of state‐of‐the‐art development, opportunities, and challenges

AbstractMany energy systems demand heat transfer at high temperatures to keep up with high demand for power, so high‐temperature material that can perform and last under these harsh conditions is needed for heat exchangers. The engineering requirements for these high‐temperature heat exchanger material call for high thermal conductivity, high resistance to fracture, high resistance to creep deformation, environmental stability in environments associated with the application, and high modulus of elasticity while maintaining low cost to make and maintain. Naturally, ceramics are a good solution for this endeavor. In the past, high‐temperature heat exchangers made from ceramics have been used. We provide examples of ceramics in relevant heat exchange applications and provide motivation where additive manufacturing (AM) can improve efficiency. AM for the relevant material is under development, and we provide insight on the AM of ceramic materials and examples of AM heat exchangers keeping cost in mind. The motivation of the review paper is to provide a framework for material and manufacturing selection for high‐temperature heat exchangers for AM to keep up with the demand for better efficiency, better material, better manufacturing, and cost moving forward with AM technology in high‐temperature ceramic heat exchangers.

Equilibrium model approach to predict local chemical changes in recovery boiler deposits

A step-by-step equilibrium model approach was developed to estimate and describe the enrichment of K and Cl within recovery boiler deposits. The model predicts free melt movement towards colder temperatures within deposits. Due to a temperature gradient, the melt amount and composition differ across the deposit. The melt movement affects the local composition, which leads to changes in the local phase composition. The model predicts how the deposit profile changes due to melt migration into pores within the deposits. Changes in the deposit composition profile also affect the melting behavior locally, resulting in lower local melting temperatures, which can be detrimental to heat exchanger materials. The modeling results were compared to earlier published laboratory and full-scale boiler measurements, and there is a good agreement between the results. The model predicts a local decrease in the first melting temperature of recovery boiler deposits by ∼30 °C. These findings closely align with experimental results, shedding light on the intricate mechanisms of melt percolation and intra-deposit aging processes. The proposed step-by-step model offers a means to achieve more accurate estimations of locally prevalent first melting temperatures in recovery boiler deposits.

Lightweight Reseach of Tube Sheet for Spiral Wound Heat Exchanger Based on ANSYS

Abstract Tube sheet is the key pressure-bearing part in the spiral wound heat exchanger, and the high-strength and light-weight tube sheet structure is of great engineering significance for the development of a large-scale heat exchanger. In order to further realize the lightweight of the spiral-wound heat exchanger, this paper analyzes the influence of the thickness of the heat exchanger tube sheet on its strength based on the Ansys software and proposes the optimization design method of the tube sheet based on the strength safety factor F, which solves the problem that the software cannot take the stress linearization result as the state variable in the optimization calculation. The optimization results show that the thickness of the tube sheet is reduced by 40%. At this time, the stress strength at the connection between the tube sheet and the head and the center of the tube sheet first exceeds the design bearing capacity, indicating that the strength conditions of the two places are the controlling factors of the thickness. The results are important for the lightweight design of heat exchanger tube plate and material saving.

Thermal radiation and soret/dufour effects on amplitude and oscillating frequency of darcian mixed convective heat and mass rate of nanofluid along porous plate

The influence of thermal radiations and Soret/Dufour significantly increases the mass and heat transport in material science, geothermal process, chemical rectors and heat exchangers due to temperature and concentration variation of nanoparticles. Main objective is to enhance the amplitude, oscillation and frequency of heat transfer using the Soret and Dufour characteristics in Darcian radiating flow of thermophoretic nanoparticles along vertical porous surface. The dimensionless analysis is performed to develop the convenient form of governing thermodynamic Darcian nanofluid formulation. To develop the programming algorithm in FORTRAN language, the primitive variable formulation is used for both time-dependent and steady models. The numerical and graphical outcomes of primitive type equations under boundary conditions are explored by using implicit finite difference approach with Gaussian elimination scheme. Various pertinent parameters are used to elaborate the steady fluid velocity, surface temperature and steady concentrated nanoparticle volume fraction. Valuable novelty of current research is to use steady results for fluctuating shear stress, fluctuation heating rate and fluctuating mass rate. It is found that the influence of Soret and Dufour parameter enhances the fluid velocity and temperature distribution with maximum variations. It is noticed that the temperature distribution enhances as thermal radiation parameter increases. The oscillation and transient stability of heating rate enhances with prominent variations as thermal radiation and Soret/Dufour parameter increases. It is depicted that amplitude in shear stress and mass rate enhances as Soret and Dufour parameter enhances.

Parametric study of a scraped surface heat exchanger for latent energy storage for domestic hot water generation

In this work, a parametric study of a Scraped Surface Heat Exchanger (SSHE) for solar Latent Thermal Energy Storage (LTES) has been conducted. The primary challenge in Phase Change Material (PCM) heat exchangers is the formation of a solid layer along the heat transfer surfaces during the latent energy release phase. This reduction in the energy release rate is resolved through the scraping of the solidified PCM, making SSHE systems suitable for domestic hot water generation. Experiments have been performed to evaluate the influence of various operational parameters, including the heat transfer fluid (HTF) mass flow rate, the phase change characteristics of the PCM, the temperature difference between the HTF and the PCM, and the scraping velocity. It has been observed that a HTF Reynolds number (Re) of 100 will require three times more time compared to Re = 600. Moreover, the significance of maintaining a HTF to PCM differential temperature between 20 °C and 25 °C has been experimentally verified to improve the PCM solidification process. Furthermore, the existence of a critical scraping frequency has been demonstrated, beyond which increasing the frequency does not yield to significant improvements in energy extraction. Finally, a correlation has been proposed to predict solidification time as a function of the non-dimensional operational parameters involved, where 95 % of the results fall within an interval of 10 %.

Numerical investigation of heat transfer in wire and tube-based phase change material heat exchanger

The utilization of latent heat storage units with their high energy density and isothermal heat transfer behavior can enhance the performance of thermal energy systems. This study aims to investigate the effect of fin placement on the melting time of a wire and tube-based Phase Change Material (PCM) heat exchanger using numerical simulations. The study introduces a new complex geometry for the heat exchanger, and numerical analysis of heat transfer was conducted in Ansys Fluent software using an established solidification and melting model. The numerical results were validated against experimental data, and it was found that the position of the tubes and fins had a significant impact on heat transfer within the PCM. The model was able to predict temperature data with a maximum discrepancy of 3%.

Efficiency upgrading of solar PVT finned hybrid system in Bangladesh: Flow rate and temperature influences

This research aims to determine the impact of mass flow rate and inflow temperature on the utility and effectiveness of solar thermal systems using fins with air in various applications in Bangladesh. This study examines a three-dimensional (3D) photovoltaic thermal (PVT) system where we analyze the behavior of a hybrid system with six aluminum sheets (1 mm thick fin as a heat exchange material) inside the heat exchanger where the air takes the direction to pass in waveform through the channels (made of aluminum) using fins. The top side of the fins is bent and affixed to the bottom of the floor of the PV panel to allow heat transfer utilizing the conduction-based method. This study selects inlet fluid mass flow rate and inflow temperature between (0.015–0.535 kg/s), and (10–40 °C) respectively, while comparing the result with experimental/numerical published data based on Bangladesh's weather conditions and applies the finite element method (FEM) to solve heat transfer equations. A brief analysis of the association among Reynolds number with pressure drop and fanning friction factor is included in this paper. Our model can be mounted on building rooftops or open fields where air velocity will be controlled mechanically; thus, it has many applications. This model can be implemented within an agricultural photovoltaic (APV) system, domestic functions, dry agricultural products, and provide heat for greenhouses. The result indicates that 302–514 W thermal energy has been produced for 0.015–0.535 kg/s. For growing inflow temperature, despite the reduction in electrical efficiency, the value of adding electrical and thermal efficiency (overall efficiency) comes with elevation. A 5 °C increase in inflow temperature leads to an overall efficiency increase of 0.33%. This study's findings can help researchers better comprehend air's properties as a heat exchanger in a developed design, and they can be applied to government and commercial projects.

Multi-objective optimization of heat charging performance of phase change materials in tree-shaped perforated fin heat exchangers

To enhance the convective heat transfer and overall thermal performance of horizontal latent heat storage (LHS) units, an innovative tree-shaped fin structure with perforations was introduced. A numerical simulation study examined the impact of perforation layers on the unit's overall performance. For a comprehensive analysis of the perforations' cumulative effect on the LHS unit, the Response Surface Methodology (RSM) was utilized to assess the influence of variations in perforation diameter and number on material consumption and heat exchange targets, deriving predictive correlations. The results indicated that compared to a non-perforated structure, the maximum improvement was observed with three layers of perforations, reducing material usage by 0.93%, while increasing the Nusselt number (Nu) and heat exchange by 10.19% and 36.51%, respectively. Moreover, the average temperature of the phase change material (PCM) in one and three perforated layers was higher than in the non-perforated tree-shaped fins, with complete melting times reduced by 5.37% and 2.51%, respectively. RSM results showed a negative linear correlation between increased perforation diameter and number with reduced material consumption, with the number of perforations having a more significant impact on heat exchange than their diameter. The Pareto optimal points obtained using the Non-dominated Sorting Genetic Algorithm II (NSGA-II) demonstrated lower material usage and higher heat exchange. Compared to the non-perforated tree-shaped fins, the Pareto-optimized solutions reduced material consumption by 2%–2.68% and increased heat exchange by 79.42%–94.45%. Analysis of the flow field, temperature field, and phase change process revealed that perforations significantly enhanced the mixing of PCM in different areas of the tree-like fins and secondary flow, with temperatures near the perforations increasing by 5–7K and flow velocity by 3–4 times, significantly promoting convective heat transfer.