Heat Exchanger Materials Research Articles

Thermal conductivity of metal coated polymer foam: Integrated experimental and modeling study

Foams offer extremely large surface area per unit mass, making them competitive material for heat exchangers and energy storage systems. Understanding the influence of foam characteristics, i.e., size, distribution and concentration of pores, ligament defects as well as foam architecture, on thermal transport is important when designing the foam-based devices. In this article, we present the effective thermal conductivity of open-cell polyurethane (PU) foam (20 PPI) with ~10 μm thick nickel coating measured by transient plane source (TPS) method. A calibration methodology for TPS method is developed to obtain accurate measurements. A finite element model and thermal resistance model are developed for the heat transfer in metal coated foams occurring near room temperature. For precisely modeling the foam architecture topology, an X-Ray tomography is employed. The developed models are used to investigate how the Ni coating thickness affects the effective thermal conductivity. Lastly, we discuss how the model assumptions are related to the discrepancy between the model predictions and measurements for the polymer-metal foams.

Experimental investigation on thermosyphon aid phase change material heat exchanger for electronic cooling applications

In this work, cooling of electronic modules is experimentally investigated using a thermosyphon aid phase change material (PCM) heat exchanger with different thermic fluids such as n-hexane, benzene and DI water respectively. The experiments are conducted simultaneously by evaluating the thermal performance of thermic fluids and heat power stored by PCM for various heat inputs ranging from 70 to 110 W. At high heat input conditions, the value of low thermal resistance, maximum convective heat transfer coefficient (CHTC) and percentage of heat extraction of n-hexane are 0.350 K/W, 185.53 W/m2K and 99.2% respectively. Low enthalpy of vapourization and a high degree of superheat is the criteria for the obtained results. Also, temperature variation in PCM during melting is analysed by the influence of vapourized thermic fluids for different heat inputs. The maximum heat power stored by PCM is found as 7.78 W for vapourized n-hexane at 110 W due to high mass flow rate and less time for reaching steady-state temperature (SST) of PCM. The solidification of PCM is noted using cold water at regular time intervals during power-off conditions and observed that n-hexane influenced molten PCM takes 25 min for complete solidification.

Stability of a Feed-Effluent Heat Exchanger/Reactor system for catalytic combustion of VOCs: Influence of variable emission patterns

In this contribution, a theoretical study of the dynamic behaviour (open- and closed-loop) of a Feed-Effluent Heat Exchanger (FEHE) / Reactor system for the catalytic combustion of Volatile Organic Compounds (VOCs) is carried out. An additional supply of energy is provided by means of a furnace to achieve the desired reactor inlet temperature. The positive feedback of energy to the reactor inlet is a source of instability that leads to pronounced limit cycles in the main state variables. The strong thermal oscillations predicted can damage the catalyst and cause considerable stress on both the reactor and heat exchanger materials. To prevent this scenario, a control structure that considers the manipulation of a bypass flow of the feed stream around the FEHE is selected. A single-loop feedback control system is successfully applied to maintain the inlet temperature set-point, rejecting the VOC’s concentration disturbances and enabling a stable operation. The results demonstrate that the controllability of the process is ensured with high external heat supplies (low heat recovery in the FEHE) which increases the fuel demand and the operating costs. Additionally, a high FEHE transfer area enables efficient heat recovery and avoids the controllability loss due to a suitable by-pass valve regulation.

Trends and future perspectives on the integration of phase change materials in heat exchangers

Traditional review papers provide mainly qualitative information, missing to show the volume, trends, and major contributions in a topic. In response to that, this paper asseses both quantitative and qualitative information regarding the implementation of thermal energy storage using phase change materials in heat exchangers. The data were retrieved from the Scopus database using specific queries relevant to the topic. To investigate the state-of-the-art and research gaps, a keywords analysis was carried out highlighting relevant connections among the major keywords. Moreover, a bibliometric analysis was performed to obtain the trends on the number of publications per year, type of document, authors, affiliation, geographical distribution, journals of publication, and subject areas of research. Based on the keywords and bibliometric analyses, this paper highlights the major contributions and research gaps on the topic.

Influences of fluid corrosivity and heat exchanger materials on design and thermo-economic performance of organic Rankine cycle systems

Various heat sources and cooling fluids bring different requirements on the anti-corrosion performance of heat exchangers in organic Rankine cycle (ORC) systems. Using different materials may change optimal parameters and thermo-economic performance of ORC systems due to substantially different thermal conductivities and cost coefficients. This paper studied the influences of heat exchanger materials on optimal design and thermo-economic performance of ORC systems for various heat source conditions. The widely-used shell-and-tube heat exchanger was selected, and carbon steel, copper, and stainless steel were focused. The utilization costs of different types of heat sources were compared. Results indicate that the corrosivity of heat source and cooling fluid is a key factor deciding the utilization cost. The difference of specific investment cost (SIC) caused by different heat exchanger materials is up to 25.5%, which substantially exceeds that caused by different working fluids (2.3%). Even the corrosivity restriction is not considered, the maximum difference in SIC is still 11.0%, and the low-cost material is preferred. The lower the temperature and flow rate of heat source, the more significant the influences of heat exchanger materials. The improper selection of heat exchanger materials will underestimate the economic benefits of ORC technology.

Characterization of scaling material obtained from the geothermal power plant of the Balmatt site, Mol

Geothermal energy is a renewable energy source by which heat is extracted from the subsurface. Due to changes in pressure and temperature and chemical reactions when the geothermal fluid is pumped through the wells and surface installations, scales can be formed. These scales can accumulate in different locations of the geothermal system and/or parts of the surface installation and cause clogging of the wells, pumps, pipes, heat exchangers and/or filter units. Consequently, the efficiency of the geothermal system can decrease. To obtain insight into the formation of scales in the surface installation of the Balmatt geothermal site, heat exchanger and filters scaling material was sampled after a circulation time of 240 h and 46 h respectively. This material was chemically, mineralogically and radiologically characterized. The scaling material found in the heat exchanger consists mainly of galena (PbS). Minor amounts of challacolloite (KPb2Cl5) and laurionite (PbClOH) were also observed. Additionally, in the filter scaling material carbonates such as witherite (BaCO3), siderite (FeCO3) and possibly rhodocrosite (MnCO3) are present as well, together with an amorphous phase and elemental copper. Salt minerals such as sylvite (KCl), halite (NaCl) and challacolloite (KPb2Cl5) and iron oxides such as hematite (Fe2O3) were also observed in the scaling material. However, these minerals are thought to be formed during drying of the scalings after sampling. Together with these minerals, radionuclides such as 226Ra, 210Pb and 210Po are observed. 226Ra seems to predominantly co-precipitated with and/or sorb on witherite and hematite, while 210Pb and 210Po are rather accumulated in galena and laurionite. Equilibrium calculations, using the PhreeqC software were performed to gain insight into the geochemical processes. The calculations indicate that galena is one of the main oversaturated minerals. Precipitation of native copper and carbonates are also observed and supported by the equilibrium calculations. The formation of these precipitates is probably a result of electrochemical corrosion of carbon steel and/or corrosion by dissolved CO2.

Grundfos Holdings A/S, Denmark

Various heat sources and cooling fluids bring different requirements on the anti-corrosion performance of heat exchangers in organic Rankine cycle (ORC) systems. Using different materials may change optimal parameters and thermo-economic performance of ORC systems due to substantially different thermal conductivities and cost coefficients. This paper studied the influences of heat exchanger materials on optimal design and thermo-economic performance of ORC systems for various heat source conditions. The widely-used shell-and-tube heat exchanger was selected, and carbon steel, copper, and stainless steel were focused. The utilization costs of different types of heat sources were compared. Results indicate that the corrosivity of heat source and cooling fluid is a key factor deciding the utilization cost. The difference of specific investment cost (SIC) caused by different heat exchanger materials is up to 25.5%, which substantially exceeds that caused by different working fluids (2.3%). Even the corrosivity restriction is not considered, the maximum difference in SIC is still 11.0%, and the low-cost material is preferred. The lower the temperature and flow rate of heat source, the more significant the influences of heat exchanger materials. The improper selection of heat exchanger materials will underestimate the economic benefits of ORC technology.

Improving heat transfer and water recovery performance in high‐moisture flue gas condensation using silicon carbide membranes

Desulfurated flue gas in coal-fired power plants contains profuse water vapor and latent heat, the recovery of which is crucial. Herein, a novel use of silicon carbide (SiC) membranes to construct a transport membrane condenser (TMC) for simultaneous water and waste heat recovery from high-moisture flue gas is reported. The performances of water and heat recovery were systematically compared between typical dense heat exchange materials (304 stainless steel and perfluoroalkoxy [PFA]) and porous ceramic membranes (Al2O3 membrane and SiC membrane). Porous ceramic membranes showed higher heat transfer performance than dense materials, suggesting a non-negligible mass transfer effect on heat transfer. Compared with the Al2O3 membrane, the SiC membrane exhibited better water and heat recovery performance because of its superior thermal conductivity. Using the SiC membrane as the heat exchange material, a water flux of 11.3-44.4 kg·m−2·h−1 and a water recovery efficiency of 46.5%-76.9% were achieved. The thermal resistance from the gas boundary layer dominated the heat transfer process in SiC membrane condensers as the thermal resistances from the membrane and condensate film were markedly reduced. This study forms a basis for future investigations on heat transfer enhancement of membrane condensers used for industrial moisture recovery.

Effect of Sr Addition to a Modified AA3003 on Microstructural and Corrosion Properties

Sr is known to transform the morphology of the eutectic silicon phase as well as the Fe-rich β phase in Al-Si alloys, improving their mechanical properties. However, little is known about the effect Sr has on the (local) corrosion properties of aluminium alloys. This study investigates the effect of Sr addition to a modified AA3003 heat exchanger material on the morphology of the different phases present, especially the Fe-rich phases, as well as on the (local) corrosion properties of this material. This work reports the formation of a Sr-rich phase, which slightly increases the macrohardness of the material. The Fe-rich phases are not shown to be refined/influenced by the addition of Sr Potentiodynamic polarization experiments showed an increase in pitting potential by increasing the amount of Sr in the material up to 0.4 wt.%. Nevertheless, the analysis of the corrosion morphology revealed that the Sr-containing particles did not contribute to the corrosion process despite their cathodic behaviour compared to the Al matrix as measured by Scanning Kelvin Probe Force Microscopy. This behaviour was attributed to the thicker oxide layer found on the Sr-rich particles.

Identification of the Equipment Failure Fundamental Causes by the Condition Monitoring Using Twin Digital Models

The work is devoted to the problems of identifying the fundamental reasons that led to an increase in energy consumption for heating raw materials and cooling reaction products to the required temperatures, as well as to a decrease in the productivity of a diesel hydrotreating unit when the limiting parameters of the technological regime are reached. The purpose of the work is to determine the parameters of heat exchangers, in particular, pollution factors, and parameters of the technological process, in particular, the consumption of raw materials, the consumption of fuel gas. Monitoring was carried out during the introduction of reagents in order to solve the problems associated with the formation of resinous deposits. It was revealed that the reagents have an insignificant effect both on improving the heat transfer coefficient and on reducing the specific consumption of fuel gas. It is proposed to clarify the dosage of reagents and to develop a project on the use of reagents to maintain the cleanliness of the heat exchange surface of the raw material heat exchangers of the diesel fuel hydrotreating unit.

Performance evaluation of thermoelectric generator using CFD

The aim of this study is to analyze various ways to increase the performance of Thermoelectric (TEG) by using Computational Fluid Dynamics (CFD) techniques. For this study a three-dimensional model of TEG is developed using design modeling software SOLIDWORKS and the developed geometry is exported to CFD package which is ANSYS-FLUENT for further analysis. Mass flow rate of exhaust gas is 0.279 kg/s at a temperature of 800 K and mass flow rate of the coolant is 0.26Kg/s at a temperature 350 K are taken as boundary conditions. For this analysis various parameters are investigated such as heat exchanger material, inclination and exit gap of heat deflector and use of baffles. The effect of heat exchanger material on the performance of TEG is investigated. For this investigation pure copper, pure aluminum, aluminum alloy and low-carbon steel are chosen as heat exchanger material. Results show that pure copper has given better performance than others with 184.98 K of temperature difference. To study the effect of exit gap between heat deflector and exhaust pipe on TEG performance, exit gap is varied from 10 mm to 15 mm with an increment of 2.5 mm. The inclination angle of heat deflector is varied from 1° to 3.5° with an increment of 0.5°. Results show that 2°inclination angle of deflector with 10 mm exit gap has given better performance than other inclinations and exit gaps. The influence of baffles on TEG performance is also studied. Introducing a baffle in inclined position directs the flow direction of exhaust gas effectively to achieve better heat distribution. Finally, it can be concluded TEG has good performance with copper material as heat exchanger material, 2° inclination angle of deflector and 10 mm exit gap between heat deflector to the exhaust pipe.

Design and development of three test facilities to evaluate heat transfer performances of advanced and low cost materials and coatings for geothermal application

Geothermal energy is accredited as a flexible, controllable and green source of energy. Heat exchangers (HXs) are one of the most critical components of a geothermal power plant due to corrosion and scaling phenomena. Hence, improvements in the antiscaling and anticorrosion properties as well as heat transfer performance of the HX materials will lead to smaller, more efficient and less costly systems. EU H2020 GeoHex project relies on the use low-cost carbon steel-based material for HXs. Through modifying the surface with nano porous coating and controlling the surface chemistry, the heat transfer performance of single phase and phase change process will be improved. This paper presents the design and development of three lab scale test rigs to test the effectiveness of innovative materials and superficial treatments on heat exchange with geothermal brine in single, condensing and evaporating phases. The rigs have been equipped with all the necessary instrumentation for control and for data acquisition. In particular, the advanced coatings are applied on a small stainless-steel plate and R134a fluid has been used for heat transfer coefficient characterization in different phase conditions. GeoHex project has received funding from the European Union’s Horizon 2020 research and innovation programme. Grant agreement n.851917.

Research on defrosting of refrigerator using phase change material heat exchanger

Research on defrosting of refrigerator using phase change material heat exchanger

Design and experimental evaluation of a linear thermomagnetic motor using gadolinium: Preliminary results

Thermomagnetic motors are based on the effect of heat on the magnetic properties of ferromagnetic materials around their magnetic phase transition (Curie) temperature. The main components of these motors are the magnetic material and the magnetic circuit. Changing the magnetic ordering by heating or cooling the magnetic material it is possible to generate power when the magnetic material interacts with an external magnetic field source. If the magnetic material temperature transition is around room temperature, it may have potential to be applied in thermomagnetic motors using low-grade thermal waste as heat source. In this way, the present work proposes a novel concept of a linear thermomagnetic motor using a double-C shape permanent magnet magnetic circuit to convert thermal energy into mechanical energy. The double-C magnetic circuit has two high field regions able to host, at least, two magnetic material heat exchangers connected to each other, but operating in opposite magnetic phases: if the first material heat exchanger is at a non-magnetic phase, the second is ferromagnetic. Thus, when the force equilibrium of such configuration is not satisfied, a linear motion is created. An experimental apparatus of the proposed concept was designed and built. Gadolinium spheres were used as magnetic material. Experimental tests for static forces and generated power were performed. Preliminary results presented a maximum generated power of 0.41 W at an operating frequency of 0.5 Hz.

Thermal performance of heat and water recovery systems: Role of condensing heat exchanger material

A significant amount of sensible and latent heat can be recovered at low temperatures from the flue gas of process heating equipment. However, the condensation of acids and water vapor makes the flue gas a highly-corrosive environment, which is a challenge for condensing heat exchangers. Corrosion-resistant materials are usually expensive and/or have relatively low thermal conductivities. Hence, it is essential to characterize the role of thermal conductivity of heat exchanger material in the performance of condensing heat exchangers. In the present study, a new analytical model is proposed and validated against available experimental data to predict the thermal performance of a tube-bank heat and water recovery unit. Our study indicates a threshold for tube thermal conductivity (~0.75 ​W ​m −1 K −1 ), which is a point where further increase does not significantly improve the condensation efficiency. This relatively low value of thermal conductivity, compared to commonly-used materials, e.g., ~10–15 ​W ​m −1 K −1 for stainless steel, unlocks the potential of using materials such as natural graphite, plastics, polymers, and ceramics (with thermally conductive additives) for applications in condensing heat exchangers and heat/water recovery in industry.

Effects of structure characteristics and fluid on the effective thermal conductivity of sintered copper foam

Heat exchangers with excellent heat transfer performance are highly demanded as the development of the powerful chips and integrated circuit. Due to the large surface area and good thermal conductivity, porous metal has become a potential candidate material for the future heat exchangers. A powder metallurgy-based method was used to manufacture copper foam samples with highly controllable particle size, porosity and pore size in this study. The effects of particle size, porosity and natural convection on the so-called effective thermal conductivity (ETC) of the copper foam and the heat transfer mechanism of copper foam-fluid system were experimentally investigated. The effect of natural convection was studied by comparing the ETC of the copper foam, copper foam-air and copper foam-water system. Results show that the thermal conductivity of sintered copper sample was strongly affected by the particle size of the starting copper powder. The medium particle size (45–70 μm) was ideal for obtaining the best thermal conductivity. The dependence of ETC on porosity can be properly described by the Power Law model. A linear correlation was also proposed to describe the effects of porosity and pore size on the contribution of the fluid to the metal foam–fluid system.

Indirect Evaporative Cooling: An Efficient and Convenient Energy System

Evaporative cooling is now an alternative method for the conventional air cooling method. This method does not only save energy but also protect the environment from global warming and hazardous gases. Thus this system is highly efficient and eco-friendly. Evaporative cooling system is further divided into two categories that are direct evaporative cooling system and an indirect evaporative cooling system. The direct evaporative cooling system is not much efficient due to high wet bulb temperature and moisture thus rather than using the direct evaporative cooling system the indirect evaporative cooling system is preferred. This paper discusses comparative studies of performance, working principles, material selection criteria’s and various methods. It also explains the performance under different weather conditions, hybrid structure to reduce the load on the further system. It summarises various aspects like wick attained aluminium sheet is the best material for IEC or counter-flow heat exchanger is effective than parallel-flow heat exchanger. It finally results that indirect evaporative cooling system is moisture free, very effective and environment savings. That can be used in various residential and commercial sectors effectively as an alternative for conventional energy-consuming system.

Multiobjective optimization of an air-phase change material heat exchanger for free cooling in a single-family house

Free cooling systems based on phase change materials (PCM) are a possible alternative to air conditioning systems for summer comfort in buildings. However, the performance of such cooling systems is closely related to the climatic conditions and building configurations to be cooled. The objective of this work is to present an application of multiobjective optimization of an air cooling system using PCM at the preliminary stage of the design process. A dynamic thermal model simulating the thermal behaviour of an air-PCM heat exchanger is therefore presented and then coupled to the EnergyPlusⓇ software for the dynamic thermal simulation of the system. Finally, a first application of the optimization is presented to define a set of optimal configurations of the systems maintaining summer comfort in the house NAPEVOMO, minimizing both the initial cost of PCM and energy use of the fan.

Fabrication of superhydrophobic copper metal nanowire surfaces with high thermal conductivity

Copper is an important practical metal with a high thermal conductivity that is widely used as a heat exchanger material. However, a liquid film often forms on the Cu surface through water vapor condensation, causing a large resistance to heat transfer. To address this issue, a superhydrophobic Cu metal nanowire surface is developed herein via Cu anodizing in a KOH electrolyte to form Cu(OH)2 nanowires, followed by hydrogen reduction at an elevated temperature and the application of a wet organic coating. The hydrogen treatment reduces the hydroxide to the metal while maintaining the nanowire morphology. The superhydrophobic Cu metal nanowire surface exhibits effective removal of water droplets formed through water vapor condensation. Furthermore, the metal nanowire surface exhibits highly improved heat transfer compared with the Cu(OH)2 nanowire surface. Therefore, the combined process of anodizing and hydrogen reduction is a simple approach that forms an effective superhydrophobic Cu surface with high thermal conductivity.

Effect of airflow channel arrangement on the discharge of a composite metal foam‐phase change material heat exchanger

Effect of airflow channel arrangement on the discharge of a composite metal foam‐phase change material heat exchanger