Copper Heat Exchanger Research Articles

Ultrasonic assisted electropolishing to reduce the surface roughness of laser powder bed fusion based additively manufactured copper heat exchanger components

Ultrasonic assisted electropolishing to reduce the surface roughness of laser powder bed fusion based additively manufactured copper heat exchanger components

Effects of water chemistry on corrosion and plugging in the copper heat exchangers of water-cooled generators in power plants

Corrosion and plugging of hollow copper conductors in water-cooled generators can cause system failures, such as flow restrictions and forced unit outages. Although both neutral water chemistry (NWC) and slightly alkaline water chemistry (SAWC) have been proposed as solutions, field operations show that NWC frequently suffers from system failures, while SAWC demonstrates high reliability. The scientific basis for this phenomenon has not been well understood. In this paper, the thermodynamics of NWC and SAWC were established to compare their tendencies toward copper corrosion and plugging. SAWC keeps copper in a stable CuO passivation region, exhibiting a superior buffer capacity against CO2 inleakage and the temperature rise of the cooling water. This buffer capacity is further enhanced by increasing the degree of the slight-alkalization. Under the SAWC with a pH value of 9.0 at 298.15 K, the concentration of the dissolved copper species is extremely low, and the positive temperature coefficient of CuO solubility prevents the accumulation of copper corrosion products in high-temperature regions. In contrast, NWC is susceptible to corrosion and plugging due to its poor buffer capacity. This study provides new insights into the effects of water chemistry on copper corrosion and plugging from a thermodynamic perspective, offering a sound theoretical basis for field operations.

Effective heat transfer associated with CO2 and CH4 adsorption on HKUST-1 metal-organic framework deposited in situ on heat exchanger

The aim of this study was to analyze the heat transfer properties a copper heat exchanger with the in situ synthesized HKUST-1 metal-organic framework (MOF). For this purpose, a dedicated reactor was constructed to enable the direct measurements of heat of adsorption of CO2 and CH4, that accompanies the dynamic course of these processes. In parallel, CO2 and CH4 adsorption isotherms were determined at various temperatures and the heat of adsorption was calculated by an indirect method. Temperature changes on the heat exchanger as a result of cyclic adsorption/desorption processes of CO2 and CH4 on the HKUST-1 layer were registered, and the results of adsorption heat by direct and indirect methods were compared. Comparing the results of indirect and direct measurements of temperature changes accompanying CO2 adsorption, a difference of 19 % was obtained. In the case of CH4 adsorption, the results obtained by the two methods differed by 22 %. Based on the experimental results, it was proven that HKUST-1 synthesized in situ on a copper heat exchanger has improved heat transfer properties. The proposed concept of MOF layer on heat exchanger allows for efficient thermal stimulation of sorption processes and simultaneous MOF regeneration while minimizing the thermal energy supplied to the system.

Thermal performance investigation of N‐shape double‐pipe heat exchanger using Al2O3, TiO2, and Fe3O4‐based nanofluids

AbstractResearchers and engineers are actively working on enhancing the efficiency of heat exchangers in engineering applications by developing novel designs, exploring new materials, and utilizing nanofluids. Three kinds of nanofluids with varying concentrations are investigated in this paper. The objective is to assess the performance of N‐shaped double‐pipe heat exchanger used in thermoelectric power plants. The performance has been evaluated using COMSOL Multiphysics software. The findings show that higher nanofluid concentrations resulted in elevated heat transfer coefficients and improved efficiency of N‐shape double pipe heat exchanger. The analysis revealed that a mere 1% rise in the volume fraction of nanofluids enhanced the efficiency of the heat exchanger on average 23% when compared to the base fluid (water). In comparison to the N‐shape double pipe (Inconel 625) heat exchangers, the N‐shape double pipe (copper) heat exchangers appear to be more efficient. The introduction of nanoparticles has a notable impact on the heat transfer coefficients. Specifically, within an N‐shaped double pipe (copper) heat exchanger, the inclusion of a 1% volume fraction results in a 2.09% enhancement in the heat transfer coefficient for Al2O3/water, a 1.3% improvement for Fe3O4/water, and a 1.15% increase for TiO2/water. It also exposed that adding 1% Al2O3/water led to a significant 0.623% increase in effectiveness, while TiO2/water showed a 0.259% rise, and Fe3O4/water exhibited a 0.375% improvement. Moreover, increasing the Reynolds number enhances the Nusselt number for Al2O3/water and Fe3O4/water nanofluids by 55.22%, and for TiO2/water by 54.60% at a 6% volume concentration, leading to additional increases in exchanger efficiency. Therefore, the augmentation in nanofluid concentration leads to a reduction in the temperature pinch points both at the intake and outflow. This observation suggests that nanofluids exhibit a superior ability compared to conventional fluids when it comes to effectively lowering temperatures.

Experimental investigation on heat transfer characteristics of copper heat exchangers based on triply periodic minimal surfaces (TPMS)

The Triply Periodic Minimal Surface (TPMS) demonstrates unparalleled advantages in heat transfer performance. However, recent study primarily focuses on experiments involving single-phase working fluids in low thermal conductivity heat exchangers made of aluminum or plastics, or simulation studies on parts rather than the overall heat exchanger. In this study, we successfully utilized additive manufacturing to create three high thermal conductivity pure copper TPMS-structured heat exchangers (Primitive, Gyroid, and Fischer-Koch S). A test rig was set up for heat transfer performance evaluation using refrigerant (R134a) and a coolant solution (50% ethylene glycol-water) for the three pure copper TPMS heat exchangers. The j/f factor of the Fischer-Koch S structure increased by 358.4% compared to traditional plate heat exchangers, and Gyroid structure improved by 178.1%. The manufactured three copper TPMS heat exchangers exhibited higher volumetric heat transfer rates compared to TPMS structures reported in literature, with the Fischer-Koch S heat exchanger showing a 47.8% increase. This study, in contrast to the extensively discussed Gyroid structure in the literature, highlights the substantial potential of the Fischer-Koch S structure, particularly as a pure copper two-phase heat exchanger within the thermal management system of electric vehicles.

Brazing of Copper Pipes for Heat Pump and Refrigeration Applications

In heat pumps and refrigeration systems, copper parts play a crucial role. Since heat pumps for space and water heating work under high pressure and are susceptible to vibrations, it is crucial to perfectly weld the copper pipes and heat exchangers to avoid system failures and prevent the leakage of the circulating refrigerants, which are harmful to the environment. The welding of the copper pipes is usually performed by the brazing process in a furnace. The components are subjected to a period of approximately 50 min inside a continuously open oven, varying the temperature from 710 °C to 830 °C. The oven inlets and outlets are protected by nitrogen curtains to guarantee a suitable internal environment and prevent the contamination of the gas inside the oven. This work analyses which welding methods are most suitable for welding copper, the best joint shape, process time, brazing specimens of a copper alloy, tightness tests, and mechanical properties and composition of the welding samples. From the tests carried out, the appearance of small and large defects is reduced by using a 1 mm thick external ring of filler material and a brazing temperature of 820 °C.

Numerical and experimental investigation of additively manufactured shell-lattice copper heat exchanger

Triply periodic minimal surface (TPMS) shell lattices have superior heat transfer properties due to their staggered channels. Based on these structures, a series of TPMS heat exchangers (HEs) are fabricated and investigated. However, the existing research is mainly limited to the performance investigation of HEs based on low-thermal-conductivity materials or the simulation study of the representative parts. In this study, we successfully fabricated a pure copper TPMS HE and performed a comprehensive numerical analysis. Three HEs, including Copper TPMS, SS316L TPMS, and SS316L plate were studied and compared to reveal the mechanism of their performance differences. Numerical analysis showed that TPMS HEs owned more uniform temperature and velocity fields than plate HE. The calculated heat-exchange effectiveness of the copper TPMS HE is about 58%–96% higher than that of SS316L plate HE, while the measured value of that of SS316L TPMS HE is about 38%–48% more than that of SS316L plate HE, respectively. The convective heat-transfer coefficient of copper TPMS HE is approximately 2.16–2.69 times that of SS316L plate HE and 1.17–1.33 times that of SS316L TPMS HE. The volume goodness factors of copper TPMS and SS316L TPMS HEs are about 1.49–1.87 and 1.2–1.41 times that of SS316L plate HE, respectively. The volumetric heat-transfer coefficient of copper TPMS HE is much better than that of metal plate HE and approximately 18–25 times that of the polymer TPMS HEs. This study indicates that the pure copper TPMS HE is a good candidate for next-generation HEs.

Influence of cell size and its gradient on thermo-hydraulic characteristics of triply periodic minimal surface heat exchangers

The thermal performance of the triply periodic minimal surface (TPMS) structured heat exchangers (HEs) is highly related to their cell morphology. Unfortunately, current research on the TPMS structured heat exchangers are usually limited to performance comparison between different types of TPMS structures and the objects they researched mainly focused on a single unit or array units with a fixed morphology. In this work, we conduct the first experimental study on the effect of TPMS cell size and its gradient on thermo-hydraulic characteristics of additive manufactured (AMed) pure copper heat exchangers. Geometry measurement shows that the fabricated walls are about 26% thicker than the designed value. The simulation results show that the eccentric flow pattern goes through the entire HE velocity field and presents a rotation tendency. The temperature distribution in the main body presents a certain trend. The smaller the cell size, the more uniform the temperature distribution. The experimental results demonstrate that the effectiveness of cell size = 4 outperforms that of others. As the flow rate increases, the overall heat transfer coefficient and pressure drop increase, while the total thermal resistance decreases. The smaller the cell size, the higher the overall heat transfer coefficient and pressure drop, and the lower the total thermal resistance. The cell size = 6 has the advantage in PEC due to the lowest pressure drop. The cell size = 4 has a greater volume-based power density but also consumes a larger pressure drop per unit length. This study is expected to provide useful design guidelines for the future development of AMed heat exchangers with TPMS structures.

Simulation of heat transfer and effectiveness in a helical heat exchanger made from thermally enhanced polymer material for use in absorption cooling

Heat exchangers in absorption chillers are usually made of copper material. However, prob-lems of corrosion are usually encountered, especially in the solution heat exchanger. In this study a numerical investigation of the heat transfer effectiveness in a double pipe helical heat exchanger made from a thermally enhanced polymer material was conducted. The material consists of a Liquid crystal polymer (LCP), (Vectra A950) as the matrix material, while carbon fibre is the filler material. The resulting composite has a carbon fibre weight fraction of 74%. The heat exchanger was modelled as a counter flow solution heat exchanger to be used in a lithium bromide – water absorption chiller of 3 kW capacity. The numerical software ANSYS fluent (version 14.5) was used for the modelling and simulation. Thermal and mechanical properties of the thermally enhanced polymer were used in the modelling and simulation. The viscous laminar model was used, while employing a second order upwind solution method. Results indicate that the heat exchanger was able to perform the required duty by reducing the strong solution temperature from 90oC at inlet to 57oC at outlet, while increasing the weak solution temperature from 40oC at inlet to 67oC at outlet. The effectiveness of the heat ex-changer was 77.4%. Results were numerically compared to a corresponding heat exchanger of same geometry and flow conditions, made of copper. It was observed that the polymer heat exchanger attained 89.2% effectiveness of the copper heat exchanger.

Increasing the Efficiency of the Solar Cell by Using a Heat Exchanger Technique

One of the problems that arise when generating renewable energy (using solar cells) in the world and in Iraq especially is high outside temperatures. Because of the properties of crystalline silicon used in the manufacture of solar cells, the electrical performance of solar panels is greatly affected by the operating temperature of silicon solar cells, which leads to a decrease in the energy generated by these cells increasing their temperature. In addition, to control this decrease in energy, the solar panels were cooled using a heat exchanger that uses water as a coolant. The heat exchanger technique can potentially increase the efficiency of a solar cell by using the waste heat generated during the photovoltaic process. This heat can be captured and used for pre-heating a water that is then passed through a heat exchanger, which transfers the heat to the outside. This can improve the overall efficiency of the solar cell. In this research, a copper heat exchanger has been used for cooling a solar cell and studying the effect of this cooling method on the temperature and efficiency of the PV. We used a source of light and warmth. With a halogen lamp, the results showed an accelerating manner, as the temperature of the solar cell increased, the open-circuit voltage decreased, but when using the heat exchanger, the temperature of the cell rose slowly, so the open-circuit voltage decreased slower compared to the first case during the same period, and this leads to the PV working with a higher efficiency under the same conditions.

Yearly performance of a PV-PCM and water storage for domestic hot water energy demand

A photovoltaic panel (PV) integrated with phase change materials (PCMs) is a system characterized by a simultaneous production of thermal and electrical energy. PCMs exploit the solid–liquid phase change to store latent heat. In addition, by cooling the PV panel, the electric conversion efficiency increases. This paper experimentally investigates the yearly performance of a PV-PCM system, coupled to a water tank, to provide thermal energy for the domestic hot water (DHW) service of a typical residential building. The solar radiation of a summer and an intermediate month has been reproduced under a solar simulator, while the performance in winter month has been tested outdoor under real conditions. A water circulation system, connected to a water tank, is activated to extract the stored heat, through a copper heat exchanger dipped in the PCM. Different tests are performed varying the size of the water tank storage. Results show that a storage volume of 50 L, 75 L, 100 L and 125 L ensure a reduction of 15.3 %, 21.2 %, 22 % and 21.5 % respectively, compared to traditional fully electric heaters. The same percentages turn out to be 8.2 %, 9.8 %, 10 % and 9.9 % during the intermediate month, while in winter the melting process of the PCM has not occurred. As regard only the PV-PCM and water tank system, the proposed system reached a maximum efficiency of 38 % under the summer climatic conditions and a minimum of 16 % under the winter ones.

The study of 4He twin-tube convective heat switches

In many cryogenic experiments and applications, there is a requirement for a heat switch. The heat switch can be used to either control the thermodynamic cycle or increase the cool-down speed. Here a twin-tube convective switch, which is essentially a closed circuit comprising stainless-steel twin-tube and copper heat exchangers connected to the cold-end (4 K) and warm-end (40 K), is numerically studied for the purpose of increasing the cool-down speed. The numerical results are validated by the experimental study. The geometric parameters and structures have significant impact on its performance. The performance analysis in terms of heat flow through the switch are conducted. Based on the parametric simulation results, the structure of the heat switch is further investigated. The heat flow of the heat switch with vertical fin-structure is 6.02 W, which is 2.7 times higher than that of the experimental case with a cylindrical cavity, which highlights the need to improve overall cool-down speed of the system.

The Influence of Solar Sintering on Copper Heat Exchanger Parts with Controlled 3D-Printed Morphology

From a scientific point of view, heat transfer is different in solar furnaces compared with classical ones and the influence of direct concentrated solar radiation on sintered parts needs to be studied in detail to determine the feasibility of solar furnaces in manufacturing small workpieces. This study was performed on cylindrical samples with controlled morphology obtained by a powder metallurgy 3D printing technique. All samples were heated with a heating rate of 120 ± 10 °C/minute, with 0, 1, 2, 3, 4 and 5 min holding times at 900 °C and 930 °C. The morphology of the samples was analyzed microscopically, the microhardness was determined before and after sintering, and the results were correlated with the sintering parameters (temperature, heating rate and holding time). The best results were obtained at 930 °C with 5 min holding time from the microhardness value and microstructure point of view.

Enhanced inorganic salts stability using bentonite clay for high-performance and low-cost thermochemical energy storage

The energy storage density, cycling stability, thermal conductivity, cost, and corrosive behavior character of chloride-based hydrated salts are the worth challenges facing the application of these materials for thermal energy storage (TES). However, the impregnation of these salts into porous sorbent materials represents a key tool to deal with these issues. This paper aims to develop low-cost thermochemical composites (CTCMs) based on natural bentonite and hydrated salts for TES application. Natural bentonite blended with graphite (BNTC) was used as a support to stabilize three hydrated salts SrCl2·6H2O, CaCl2·6H2O, and LiCl.H2O. Synthesis and microstructural characterization of BNTC@CaCl2, BNTC@LiCl, and BNTC@SrCl2 were reported. Suitable operating conditions optimization during the hydration reaction of the CTCMs was studied using thermogravimetric analysis. A great storage density of 854.5, 704.2, and 778.6 kJ.kg−1 were measured for BNTC@CaCl2, BNTC@LiCl, and BNTC@SrCl2, respectively. Consecutive desorption/sorption cycles experiments were conducted and good cycling stability of the CTCMs was recorded which reflects the ability of the natural bentonite to solve the worrying issue of salts solution leakage. The compatibility of CTCMs in contact with copper heat exchanger metal was assessed and a new composite coating film based on polyvinylidene Fluoride reinforced with zinc oxide nanoparticles (PVDF@ZnO) was proposed. According to the gravimetric measurements of coated copper metal, an excellent enhancement of copper corrosion resistance up to 94% was achieved under the charging phase conditions of the CTCMs.

Analysis of Changes in Heat Exchanger Performance in PK-XXX Aircraft with Material Modification Using Ansys Program

Airplanes are popular transportation for the community in general because they have various advantages over other existing transportation. Airplanes have a relatively short time to travel between islands. Safety and comfort are major factors in the operation of an aircraft. One of the safety factors in an aircraft is the air supply, one of the supporting components of the air supply is a heat exchanger. The heat exchanger keeps the temperature of the air entering the Air Cycle Machine at its operating temperature. The Heat Exchanger in this journal is a type for the Boeing 737-500 aircraft which has a significant decrease in performance which results in damage to ACM components. A plate and frame heat exchanger with aluminum alloy material will be compared with a copper heat exchanger using the Ansys program to determine the effectiveness of both. The analysis will be carried out using the calculation method as well as running tests on the Heat Exchanger, and using Ansys for testing material modification.

Thermal performance evaluation of a latent heat thermal energy storage unit with an embedded multi-tube finned copper heat exchanger

ABSTRACT The experimental thermal characterization during charging and discharging of a prototype compact latent heat thermal energy storage system (LHTESS) with an embedded horizontally oriented finned multi-tube copper heat exchanger is presented. The thermal store was filled with a commercial-grade, CrodaTherm™ 60, phase change material (PCM) with a nominal melting temperature of 60°C. The proposed heat exchanger (HX) configuration mitigates the effect of low PCM thermal conductivity and increases the rates of heat transfer to and from the store during the charging and discharging processes compared to multi-tube copper HX without fins. The experimental testing regime assessed the impact of heat transfer fluid (HTF) volume flow rate and inlet temperature on I) transient PCM temperature distribution, II) the total charging/discharging time and III) instantaneous/average power during the charging and discharging processes. The experimental results showed that the HTF volume flow rate and inlet temperature play a significant role in the thermal performance of the LHTESS during the charging/discharging process. During the charging process, the influence of increasing HTF inlet temperature is greater than that due to increasing HTF volume flow rate. Moreover, it is shown that during the first 30 minutes of the discharging process, the average power output was 4.3, 5.1 and 5.3 kW for HTF volume flow rate of 2.5 and 7.2 and 10.5 l/min, respectively.

Performance analysis of different U-shaped heat exchangers in parabolic trough solar collector for air heating applications

In this article, the thermal performance of a parabolic trough solar air heater (PTSAH) with a U-shaped heat exchanger is evaluated. The solar air heater's performance is examined by using the copper and aluminum U-shaped heat exchangers (UHX) with and without fin alternately, inside the absorber tube placed at the focal length of the nickel-coated stainless steel parabolic trough. The system is examined in the form of temperature difference achieved at the outlet for both the heat exchangers and the solar air heater's efficiency. It is observed that the system performance with the copper heat exchanger is better than the aluminum heat exchanger. Further, it has been found that the efficiency of the solar air heater is increased by 9.29% at a high flow rate with the use of fin when using a copper heat exchanger in place of the aluminum heat exchanger. The temperature difference achieved by the system is also increased by 2.34% at a low flow rate. At elevated temperatures, the percentage increase in solar air heater performance for the aluminum heat exchanger is higher than the copper heat exchanger.

Experimental and Theoretical Investigation of the Natural Convection Heat Transfer Coefficient in Phase Change Material (PCM) Based Fin-and-Tube Heat Exchanger

Latent heat thermal energy storage systems allow storing large amounts of energy in relatively small volumes. Phase change materials (PCMs) are used as a latent heat storage medium. However, low thermal conductivity of most PCMs results in long melting (charging) and solidification (discharging) processes. This study focuses on the PCM melting process in a fin-and-tube type copper heat exchanger. The aim of this study is to define analytically natural convection heat transfer coefficient and compare the results with experimental data. The study shows how the local heat transfer coefficient changes in different areas of the heat exchanger and how it is affected by the choice of characteristic length and boundary conditions. It has been determined that applying the calculation method of the natural convection occurring in the channel leads to results that are closer to the experiment. Using this method, the average values of the heat transfer coefficient (have) during the entire charging process was obtained 68 W/m2K, compared to the experimental result have = 61 W/m2K. This is beneficial in the predesign stage of PCM-based thermal energy storage units.

Welding procedure research of white copper heat exchanger

In order to satisfy the corrosion resistance requirement, the original pipe material of a heat exchanger is replaced by BFe30-1-1white copper. Based on analysis of the welding characteristics, joint structure and factors affecting the welding quality of BFe30-1-1 tube-to-tubesheet, the welding procedure is made. The morphology inspection, test of pull-off strength, metallographic structure examination and hardness test of the tube-to-tubesheet joints which is welded according to the welding procedure, can satisfy the standard and design requirements. The success of the test provides a good reference for the welding quality control of white copper heat exchangers.

Effects of inclination on the frosting process on cold surface of copper heat exchanger

Frosting is a natural phenomenon, which, albeit ubiquitous, requires further exploration. Here, we have experimentally investigated this phenomenon by realizing frosting processes on cold surfaces with different tilt angles and recording the number and the size of droplets produced on those surfaces. We have also monitored the changes in temperature and humidity of the passing air, whence the effect of inclination on the heat and mass transfer mechanisms, as well as the phase change of the droplets was analyzed. Our results indicate that the tilt angle has a significant influence on the droplet growth. In particular, cold surfaces with large tilt angles (30° and 60°) can produce a larger number of droplets, whose size increases much less in comparison with those produced on cold surfaces with small tilt angles (0° and 15°). Moreover, the component force of gravity along the inclined cold surface may offset part of the drag force, which inhibits the coalescence of droplets and promotes the uniformity of frost. Hence, we anticipate that our study will provide further insight in the influence of the tilt angle on the frosting process, in this way leading to its greater control in relevant applications.