Hybrid Heat Exchanger Research Articles

Thermal internal resistance minimisation in microchannel heat sink with perforated micro fins geometry

This study presents a 3-D numerical analysis of complex heat exchanger systems featuring innovative fin geometries. These geometries are created by modeling and placing micro fins with perforated square, circular, and rectangular designs on the heat sink. The objective of the study is to minimise thermal resistance in a hybrid heat exchanger featuring various fin architectures. The hydraulic diameter ranges from 0.036 to 0.047 mm, with fin dimensions of 0.04 mm in height and length, and 0.02 mm in width. The fins are designed with square perforations of 0.01 mm, circular perforations with a diameter of 0.015 mm, and rectangular perforations measuring 0.04, 0.012, and 0.006 mm. A high-density heat flux q″ is applied to the bottom wall, and fluid with a Reynolds number ranging from 400 to 500 is used to dissipate the heat in the cooling channel. The finite volume method and computational fluid dynamics code are employed to discretise and solve for thermal and fluid flow solutions. The impact of Reynolds number on minimised temperature and thermal resistance is analysed for void fraction ratio (VFR) of 0.25, 0.44, and 0.18.The numerical analysis reveals that the hybrid microchannel, featuring double square, circular, and rectangular perforations, demonstrates a reduction in resistance by 15 %, 21 %, and 19 %, respectively, when the coolant Reynolds number is increased by 20 %. Notably, the heat sink with square perforations exhibits the most substantial decrease in resistance, followed by circular and rectangular perforations. The numerical code is validated with what is available in the existing literature.

Design, Construction, and Characterization of a Solar Photovoltaic Hybrid Heat Exchanger Prototype

In this experimental work, a prototype of a hybrid solar–thermal–photovoltaic (HE-PV/T) heat exchanger has been designed, built, and characterized, with rectangular geometry and 12 fins inside, to obtain better heat flow and higher performance in order to achieve a better heat transfer coefficient, reducing and optimizing the working area. The heat exchanger contains 12 photovoltaic cells connected in series, with an angle of inclination of approximately 18° towards the south and a surface area of 0.22 m2, smaller than those available on the market, which individually capture 147.05 W/m2 as a photovoltaic panel and 240 W/m2 as a solar collector. Mathematical models found in the literature from previous work were used for the electrical and thermal evaluations. The temperature of the PV cells was reduced to 13.2 °C and the thermal level of the water was raised to a temperature above 70 °C, with a photovoltaic–thermal coupling power of 307.11 W and a heat transfer coefficient of 5790 W/m2 °C. The efficiencies obtained were as follows: thermal up to 0.78 and electrical up to 0.095. The novelty of these results was achieved in a reduced space of 40% less than those reported and available on the market.

Structural Stress Intensity Analysis of Hybrid Heat Exchangers Based on Thermal Hydraulic Performance in S-CO2 Power Cycle

Abstract Hybrid heat exchangers (H2Xs) can be used for heat exchange equipment between high-temperature exhaust gas from ships and high-pressure supercritical carbon dioxide (S-CO2) from the S-CO2 power cycle. We investigate structural stress intensity characteristics of the H2Xs based on thermal-hydraulic performance. Air and S-CO2 are employed as the working fluids and the Stainless Steel 316 (SS316) as the solid substrate. The thermal-hydraulic performance and structural stress intensity characteristics of the H2Xs are conducted by Ansys Fluent and Mechanical, respectively. The results show the mechanical stress induced by pressure loading and the thermal stress induced by temperature gradient are found to be equally important sources of stress intensity. At the inlet and outlet of the H2Xs, the total stress intensity along all paths is not smooth and continuous, and there will be a significant change due to the change in the temperature gradient. The mechanical stress caused by the fluid pressure loss is almost negligible. The change in inlet mass flowrate and temperature mainly affects the stress intensity distribution of the left and right walls on the fin channel. The pressure variation of the diesel engine has little effect on the total stress intensity. Importantly, the total stress intensity of the H2X is mainly affected by the change in S-CO2 fluid pressure.

Structural stress analysis of hybrid heat exchangers in the S-CO2 power cycle for marine waste heat recovery

Due to its high thermodynamic efficiency and small equipment size, the S-CO2 Brayton power cycle is a leading candidate for ship waste heat utilization. The hybrid heat exchanger formed by diffusion bonding of fins and etched plates can be used for heat exchange between the high temperature flue gas and the high pressure S-CO2. However, the law of structural strength is not clear for the hybrid heat exchanger. It is critical to carry out structural stress analysis. In this study, to assess the structural strength of the hybrid heat exchanger, the FEM was used and compared with a currently used method from ASME codes. The results show that the thermal stress caused by the temperature gradient is independent of the absolute temperature value. The change in the supercritical carbon pressure in the etched channel affects the mechanical stress more than the exhaust gas in the fin channel. Under design conditions, thermal stress and mechanical stress are equally important to the total stress of the hybrid heat exchanger. Moreover, the total stress is not a simple numerical superposition of thermal stress and mechanical stress but instead indicates a complex effect. From the FEM results, the etched channel exit that withstands a higher pressure load is the weakest point in the hybrid heat exchanger core. The FEM is a more comprehensive means for structural assessment than the ASME codes. This research can provide guidance for structural stress analysis of hybrid heat exchangers

Recent Advances in Technologies, Methods, and Economic Analysis for Sustainable Development of Energy, Water, and Environment Systems

Sustainability has become a broad societal goal, aiming to ensure that human beings coexist safely and harmoniously with nature over a longer time. The influence of the COVID-19 pandemic on the global economy is coming to an end. The development and merits of sustainable energy supply, advanced technology, and economic features have received significant attention over the last few decades. However, significant gaps still exist with respect to how to design, construct, and implement hybrid and optimal energy systems with the lowest investment and cost. Since 2002, the Sustainable Development of Energy, Water, and Environment Systems (SDEWES) conferences have become a significant meeting venue for researchers to introduce, discuss, share, and disseminate novel concepts and ideas. This paper presents an overview of published articles in the Special Issues (SIs) dedicated by the series SDEWES conferences, especially those published in Energies recommended by the 16th SDEWES Conference, which was held on 10–15 October 2021 in Dubrovnik, Croatia. This SI in Energies focused on four main topics, including the application of renewable bioenergy, component enhancement in renewable systems, sustainable development for buildings and economic analysis and evaluation for sustainability. The collected papers provide insight into the topics related to recent advances in improving sustainable efficiency, including studies on waste-to-wealth techniques, utilization of hybrid bioenergy systems, heat exchangers and other components for performance enhancement, energy supply and demand analysis, low-temperature DHC systems, techno-economic assessment, and environmental evaluation.

Study on thermal-hydraulic characteristics of hybrid heat exchangers with interpolated etched plates

The Supercritical carbon dioxide (S-CO2) Brayton cycle can be used to recover the exhaust heat energy of marine diesel engines. The hybrid heat exchanger is one of the potential solutions for heat exchange between flue gas and S-CO2, but there is no good design theory and design method at present. The traditional hybrid heat exchanger has an one-to-one correspondence between the fin and the etched plate. However, under special requirements, it is necessary to insert etched plates in the hybrid heat exchanger to improve the thermalhydraulic characteristics. In this study, four CFD models of the hybrid heat exchangers with interpolated etched plates were established. When the total mass flow rate and the total mass velocity are constant, the thermalhydraulic characteristics of the hybrid heat exchanger are analyzed by Fluent. The results show that regardless of the constant mass flow rate or the constant mass velocity, inserting etched channels into the hybrid heat exchanger will increase the total heat transfer coefficient. When the total mass flow rate of the cold and hot fluids is unchanged, the heat transfer coefficient and pressure drop of the etched channel decrease with the increase of the inserted etched channel. When the total mass velocity of the hybrid heat exchanger is unchanged, the insertion of the etched channel causes the pressure drop and the convective heat transfer coefficient of the fin channel to increase. Meanwhile, the pressure drop and convective heat transfer coefficient of the etched channels are reduced, but the total heat transfer coefficient is increased. The study can provide guidance for the design of the hybrid heat exchangers.

Hydrogen release from a metal hydride tank with phase change material jacket and coiled-tube heat exchanger

Hydrogen fuel cells are received increasingly wide attention in order to develop green ships and reduce greenhouse gas emissions in the field of waterway transportation. Metal hydrides (MHs) can be used to store hydrogen for green ships due to their high volumetric storage capacity and safety. Various measures should be considered in the design and manufacture process of the MH reactor to strengthen its performance of heat and mass transfer and obtain an acceptable hydrogen storage capacity. In this work, LaNi5 hydride is used as the hydrogen storage material and packed in the reactor. A basic axisymmetric numerical model for the hydrogen storage system without a heat exchanger has been developed and proved to be effective through the comparison between its simulation results and the published data during dehydriding. A hybrid heat exchanger, which is consisted of a phase change material (PCM) jacket and a coiled-tube, has been applied into the hydrogen storage system to relieve the thermal effect of MH in the dehydriding process on system performance. Effects of the heat transfer coefficient between the circulating heating water in the coil-tube and the MH bed, the temperature of circulating heating water and the pressure at the outlet on the dehydriding performance have been investigated. Based on parametric study, the relationships among the average dehydriding rate, the heat transfer coefficient, the heating water temperature and the outlet pressure have been found and fitted as simple equations. These fitted equations can be considered as a reference, which provides an important method to effectively control the dehydriding rate in order to satisfy the fuel requirement of the power unit and ensure the safe navigation of green ships in the future.

Analytical Investigation on the Evolution and Growth of β-Ti and Fe-Nb-Based Intermetallics in Diffusion Coupled Joints of Ti6Al4V|Nb|SS

Herein, solid-state diffusion-coupled joints (DCJs) were prepared in vacuum between stainless steel (SS) and Ti6Al4V by means of a pure niobium (Nb) interlayer (~200-μm thickness) using uni-axial compressive pressure of 4 MPa at 875 °C for 15 to 120 min. Interfacial characterization revealed the existence of successive layer wise Fe–Nb-based intermetallics like FeNb+(Nb) and Fe2Nb at Nb|SS interfaces of DCJs processed from 60 to 120 min, but the DCJs processed for shorter duration (from 15 to 30 min) do not reveal any intermetallics; however, the DCJs processed for 45 min revealed a single reaction layer of FeNb whereas that of Ti6Al4V|Nb interfaces revealed solid solution behaviour for all bonding time intervals. Required chemical analysis (in at. pct) of the reaction products was found out using spectroscope and X-ray diffractometer. Mechanical characterization (at 32 °C) of the DCJs was carried out with a microhardness tester and tensile testing facility. Ti6Al4V|Nb interface experienced a hardness of ~298 HV (for all bonding time), whereas Nb|SS interface experienced ~200 HV for 15 and 30 min and ~650 HV for 45 min and longer. DCJs treated for 60 min have better strength properties. Manifestation of reaction layers: FeNb, FeNb+(Nb), and Fe2Nb have significant effect on the strength. From the interfacial microhardness, path and surface of fracture surfaces characterizations, it was revealed that failure of the DCJs was transmitted seemingly along Nb|SS interfaces. The analytical finding of intrinsic diffusivity of Ti atoms in Nb along Ti6Al4V|Nb interface is higher by one order of magnitude than the diffusivity results of Fe atoms in Nb along the Nb|SS interface. Experimental evidences show that the growth of the reaction products along Ti6Al4V|Nb interface (adj. R-Square=0.982) and Nb|SS interface (adj. R-Square=0.999) follows a parabolic law. Recently, researchers considered diffusion coupling as the key technology to fabricate Ti|Al|Al-Cf biomimetic structure, graphite|Nb|Cu for fusion reactor devices, Ni|Ni3Al for MEMS applications, hybrid heat exchangers for nuclear applications, etc.

Study on heat transfer and pressure drop characteristics in marine S-CO2 power cycle hybrid heat exchangers

The S-CO2 power cycle has the advantages of compact structure and high energy density, which can be used to recover the waste heat of ship exhaust, thus improving the energy efficiency of ships and reducing emissions. The hybrid heat exchangers with etched plates and fins can be used as the heat transfer device of S-CO2 and exhaust, its heat transfer and pressure drop characteristics have a great influence on S- CO2 power cycle performance. In this study, a CFD model of the hybrid heat exchangers was established. The effects of different exhaust inlet temperatures, inlet mass flow rates and inlet pressures on the heat transfer and the pressure drop characteristics were analyzed by Fluent. The results show that the inlet temperatures and inlet mass flow rates of exhaust have a great influence on the heat transfer characteristics of the hybrid heat exchanger. The inlet mass flow rates and inlet pressures of exhaust have a great influence on the pressure drop characteristics of the hybrid heat exchangers. In the design of the hybrid heat exchangers, the status of the exhaust need to be considered to ensure efficient operation of the heat exchangers. The study can provide guidance for the design of the hybrid heat exchangers.

Performance Analysis of Electrolux Refrigeration System Coupled with Flat Plate Solar Collector using Hybrid Heat Exchanger

Performance Analysis of Electrolux Refrigeration System Coupled with Flat Plate Solar Collector using Hybrid Heat Exchanger

Feasibility of Using Diffusion Bonding for Producing Hybrid Printed Circuit Heat Exchangers for Nuclear Energy Applications

Hybrid printed circuit heat exchangers have been designed for Gen-IV nuclear power applications. While microchannel devices are commonly fabricated using diffusion bonding, diffusion bonding of these hybrid heat exchangers is challenging due to non-uniform stress distributions across its structure during bonding, which can lead to bonded regions with varied joint properties that can compromise the performance and safety of these devices. In this paper, we delineate a method for determining whether diffusion bonding conditions exist for bonding hybrid printed circuit heat exchangers with maximum joint strength, minimum creep and without yielding or buckling. Diffusion bonding feasibility is determined in two steps. First, an improved pore elimination model is used to identify a feasible set of diffusion bonding parameters that can give acceptable bonded area and compressive creep. Second, a structural analysis is performed on regions in the structure susceptible to yielding and buckling that can constraint the maximum permissible bonding pressure. Diffusion bonding conditions were experimentally validated for bond strength, porosity and creep based on shear test and metallographic examinations as per ASME standards. Two sets of bonding conditions were found to satisfy nuclear boiling and pressure vessel code requirements. Future efforts will involve the diffusion bonding of a hybrid device structure capable of meeting the hermeticity and dimensional integrity requirements of the device.

하이브리드 열교환기 적용 고압 컴팩트 스팀 유닛 개발에 관한 기초 연구

하이브리드 열교환기 적용 고압 컴팩트 스팀 유닛 개발에 관한 기초 연구

Experimental Analysis of the Effects of Particulate Fouling on Heat Exchanger Heat Transfer and Air-Side Pressure Drop for a Hybrid Dry Cooler

It is well known that significant fouling by particulate matter can have a deleterious effect on the performance of enhanced surface heat exchangers, and the same is true for hybrid heat exchangers. Hybrid heat exchangers are heat exchangers that are typically run in dry mode to reject heat. When the ambient conditions require more heat rejection than can be provided by sensible heat transfer, a water pump is turned on and water flows over the fins, and the evaporation of water provides a further cooling effect. Fouling in dry-mode operation is physically similar to that of air-cooled heat exchangers, but in evaporative mode the flow of the water over the coil eliminates the impact of fouling. A hybrid dry cooler heat exchanger of 60 cm × 60 cm frontal area has been installed in a well-instrumented wind tunnel to measure the heat exchanger's performance. Hot water flows through the coil to provide the load, and air flows over the coil to provide cooling. During evaporative mode operation another stream of water flows over the outside face of the coil, adhering mainly to the louvered fins. The louvered fins are specially designed for optimized water flow during wetting mode. The fins are made of aluminum, the tubes are copper, and protection against corrosion is realized by a special E-coating. This coil has been tested clean and fouled with ASHRAE standard dust, for both dry and wet operation. Results are presented for the air-side pressure drop and overall heat transfer conductance of the coil under all conditions for which 50% increases in air-side pressure drop are found under heavy fouling. The influence of fouling on heat transfer is small. Also, using the wetting water to wash the fouling off the coil is investigated and is found to be of some limited utility.

Comparison of two methods of improving dehumidification in air conditioning systems: Hybrid system (refrigeration cycle –rotary desiccant) and heat exchanger cycle

Abstract The objective of this research is evaluating and comparing two methods of improving dehumidification in air conditioning systems. The two methods are the hybrid system: (refrigeration cycle – rotary desiccant) and the heat exchanger cycle. The impact of the desiccant performance on the hybrid system performance was studied. The impact of the heat exchanger efficiency on the performance of heat exchanger cycle was studied. Hybrid system, heat exchanger cycle, and conventional refrigeration cycle were compared at different design air flow rates and different air conditions. It was found that the hybrid system and the heat exchanger cycle can achieve lower SHR and dew point temperature than those of the conventional cooling system. On general, the hybrid system can achieve lower SHR and dew point than those of the heat exchanger cycle. Although the heat exchanger cycle can achieve lower SHR and dew point than those of the conventional cooling system, the coefficient of performance and the cooling effect of the heat exchanger cycle are lower than those of the conventional cooling system, because the temperature of the cooling coil of the heat exchanger cycle is lower than that of the conventional cooling system. The coefficient of performance and the cooling effect of the hybrid system are close to those of the conventional cooling system, because the temperature of the cooling coil of the hybrid system is close to that of the conventional cooling system.