High-efficiency Heat Exchangers Research Articles

Comprehensive Numerical Analysis on Flow and Heat Transfer Characteristics of Printed Circuit Heat Exchanger With Fins

Abstract Printed circuit heat exchanger (PCHE), as a high-efficiency and compact heat exchanger, shows a high potential in high temperature, high pressure, and some extreme environments, thus, it is widely used in nuclear power generation, refrigeration, aerospace, etc. In this paper, the flow and heat transfer characteristics of heat transfer channels with different fins were numerically analyzed, by changing helium inlet temperature and mass flowrate. The results indicate that, with the increase of helium mass flowrate, Nusselt number and pressure loss grow, while Colburn factor and Fanning friction factor drop. As helium inlet temperature rises, Nusselt number, Colburn factor, and pressure loss grow, whereas Fanning friction factor decreases. In addition, the heat transfer characteristics of the channels with different fins are higher than that of the finless channel, among which the circular finned channel has the best heat transfer performance. In spite of a slightly degraded flow performance, the comprehensive performance of the finned channels is superior to that of the finless channel, and the elliptical finned channel has the best performance, followed by airfoil finned channel and circular finned channel.

SETTING VALUES IN VARIABLE CONDITIONS

In the world of economy, the return of an investment is very important. Businesses want it to be long-term when preparing projects for investment purposes. Before the economic analysis of a project can be completed, the uncertainty of its values must be clarified. In this study, how much improvement is calculated by adding high efficiency engine and heat exchanger, which are two different projects. It has been determined how much savings the systems provide in the change of energy costs in a given year with these renewal additions. This determined energy saving was graphically plotted and sensitivity analysis was made.

An Evaluation of the Performance of a Ground-to-Air Heat Exchanger in Different Ventilation Scenarios in a Single-Family Home in a Climate Characterized by Cold Winters and Hot Summers

In the present study, the real-world performance of a ground-to-air heat exchanger (GAHE) was analyzed in the Polish climate which is characterized by warm summers and cold winters. The heat exchanger’s performance was monitored over a period of three years (2017 to 2019), and real-world conditions were compared with a Typical Meteorological Year (TMY). The aim of the study was to assess the exchanger’s energy-efficiency potential in various ventilation scenarios in a single-family home under variable real-world conditions, rather than to simply determine its heating and cooling capacity. The analyzed single-family home was a modern, single-story building with a usable floor area of 115 m2. The building’s thermal insulation and airtightness met stringent energy-efficiency standards. Energy consumption in a building equipped with a natural ventilation system was compared with three other scenarios: ventilation coupled with a GAHE, mechanical ventilation with heat recovery and a high-efficiency heat exchanger (HE), and mechanical ventilation with heat recovery coupled with a GAHE. Sensible heating and cooling loads were calculated based on standard ISO 13790:2008, and latent heating and cooling loads were also included in the energy balance. During the year, the GAHE generated around 257.6 W of heating energy per hour and 124.7 W of cooling energy per hour. Presented results can be used to select the optimal HVAC system scenarios for engineering projects as well as private investors.

Process optimization, exergy and economic analysis of boil-off gas re-liquefaction processes for LNG carriers

A re-liquefier based on the reverse Brayton cycle is the first choice for the re-liquefaction process owing to its compactness, simplicity, and safety. However, due to the low efficiency of the heat exchangers, the energy consumption of the re-liquefaction process is relatively high. Therefore, a novel cascade nitrogen expansion re-liquefaction process with high heat exchange efficiency is proposed and compared with the parallel expansion process. In the designed process, the condensation and subcooling stages of the boil-off gas (BOG) are performed in different heat exchangers. The performance improvement of the designed process is analyzed using the Aspen HYSYS and the genetic algorithm is used to optimize the processes. The optimization results show that the specific energy consumption (SEC) and exergy loss rate of the designed process are 0.727 kWh/kgLNG and 148.14 kW, which are 11.7% and 16.7% lower than those of the reference process, respectively. Moreover, the exergy efficiency (EXE) of the designed process is 0.352, which is 13.2% higher than that of the reference process. Because of the higher EXE and lower refrigerant demand, the designed process saves 7.2% of the total annual costs consisting of annual capital and operating costs compared with those of the reference process.

Numerical investigation on the thermal-hydraulic performance of helical twine printed circuit heat exchanger

The printed circuit heat exchanger (PCHE) is a high-efficiency heat exchanger with high compactness, pressure resistance, and stability. It can also withstand high temperatures and ultra-low temperatures. Therefore, it has attracted a large number of scholarly interests in recent years. In order to improve the thermal and hydraulic performance of traditional printed circuit heat exchangers, a three-dimensional helical twine printed circuit heat exchanger (HTPCHE) is designed and the laminar flow is numerically investigated using water as the working fluid. Taking Colburn factor j, Fanning friction factor f and comprehensive index j/f as parameters, the thermal-hydraulic performance of HTPCHE and zigzag-type PCHE with different inclined angles are compared. It is found that when the inclination angle of HTPCHE is 10–25°, its overall performance is better than that of traditional PCHE. When the inclined angle is 10° and Rein = 828, the overall performance is 37.6% better than that of 15° zigzag channel. In addition, the impact of the pitch of HTPCHE and the thickness of the transition plate on its heat transfer and flow characteristics is explored. It is discovered that when the given fixed inclined angle, the overall performance can be improved by increasing the pitch while the thickness of the transition plate does not have any significant impact.

A novel spiral channel with the growing waviness on the sidewalls for compact high-efficiency heat exchanger

Spiral channels are widely used as the core heat exchangers in latent thermal storage units. This study aims to develop a novel spiral channel characterized by wavy sidewalls for high-efficiency convective heat transfer in tube side. The amplitude of the wavy sidewalls is designed to grow from the inlet to the outlet along flow direction. The thermal characteristics in the spiral-wavy channel were numerically investigated under the boundary condition of constant wall temperature, since latent heat storage units mainly work under isothermal condition. The comparison was carried out between a smooth-spiral channel and a spiral-wavy channel in terms of the heat transfer capacity, friction factor, dimensionless temperature distributions and development of boundary layers. At a given heat transfer rate, the required length of the spiral-wavy channel is only 63.5% of that of the smooth-spiral channel, which implies that the energy density and efficiency of a heat storage unit can be improved remarkably. The increase in pressure drop brought by the spiral-wave channel is less important compared with the improvement of thermal performance, suggesting its potential in heat transfer enhancement and energy saving. The present work is expected to motivate the design of compact and high-efficiency heat exchangers for thermal energy storage and extraction.

Effects of Edge Shapes on Thermal-Fluid Processes in Oscillatory Flows

Thermoacoustic machines, Stirling engines or coolers, and pulse tube coolers are examples of energy systems that operate based on oscillatory flow principles. This class of technology would achieve an improved efficiency from appropriately designed heat exchangers, stacks, regenerators and thermal buffer tubes. In this paper, heat transfer and oscillatory flow behaviour in three identical parallel-plate heat exchangers, one ‘heat source’ positioned between two ‘heat sinks’, are investigated using numerical method. The effect of different plate edge shapes on heat transfer, flow structures and acoustic pressure drop are examined at a selected drive ratio of 0.3 – 2.0%. Flow parameters show a strong dependency on drive ratio and flow direction, especially at low excitation where gas displacements are below or comparable to the heat exchanger length. Cone edge shape minimises the flow complexity better than other shapes with a negligible effect on the heat transfer. The result of this study will benefit the design and development of compact and high-efficiency heat exchangers for the next generation of oscillatory-flow energy and thermal management systems.

A Review on Additive Manufacturing of Pure Copper

With the development of the aerospace and automotive industries, high heat exchange efficiency is a challenge facing the development of various industries. Pure copper has excellent mechanical and physical properties, especially high thermal conductivity and electrical conductivity. These excellent properties make pure copper the material of choice for the manufacture of heat exchangers and other electrical components. However, the traditional processing method is difficult to achieve the production of pure copper complex parts, so the production of pure copper parts through additive manufacturing has become a problem that must be overcome in industrial development. In this article, we not only reviewed the current status of research on the structural design and preparation of complex pure copper parts by researchers using selective laser melting (SLM), selective electron beam melting (SEBM) and binder jetting (BJ) in recent years, but also reviewed the forming, physical properties and mechanical aspects of pure copper parts prepared by different additive manufacturing methods. Finally, the development trend of additive manufacturing of pure copper parts is also prospected.

Migration-deposition Characteristics of Exogenous Particles Near the Injection Well in a Groundwater Heat Pump System

As green air conditioning systems, groundwater heat pump systems have been popularized and applied because of their stability and high heat exchange efficiency. However, the low-efficiency recharge caused by clogging restricts the healthy and orderly development of such systems. Physical clogging, accounting for 50% of the total clogging, arises from solid particle accumulation and is the most common type of clogging. In this study, a physical simulation sandbox bench was constructed to simulate groundwater recharge. Tests were conducted under two initial injection pressures of 17.058 kPa and 13.8 kPa and solid matrix particle gradations of 1.026 mm, 1.343 mm, and 1.721 mm to study the migration-deposition of exogenous particles near the injection well induced by groundwater recharging as well as to select suitable downhole filter grades. The results show that when the initial injection pressure and solid matrix particle gradation were low, suspended particles were more susceptible to be sieved and deposited within 24 cm from the injection well. This significantly reduced the permeability and resulted in a rise in the injection pressure. When the high injection pressure of 17.058 kPa was applied, the area in which the permeability coefficient decreases by an order of magnitude compared to the initial value, was less than 10 cm of the wellbore wall, and the quantity of outflow of particles accounted for 34.8% of the inflow. The size range of the suspended particles flowing through the porous medium was 3–30 μm, providing the parameter basis for downhole filter grade selection. This research provides useful insights into the design and optimization of injection projects to prevent particle clogging in groundwater heat pump systems.

Analysis and optimization of the curved trapezoidal winglet geometry in a high-efficiency compact heat exchanger

The present work is undertaken to optimize the geometry of the curved trapezoidal winglet mounted over each cooling tube to enhance the overall performance of the heat exchanger. Before conducting the optimization study, the most critical geometric entities have been identified, and this has helped in significantly reducing the computational overheads. It has been found that the three most critical design parameters are the arc radius (R), the angle subtended (θ) and the winglet's leading-edge height (h1), and the same are chosen for optimization. To plan the experiment, we make use of the Latin hypercube sampling (LHS) scheme. The system responses viz. the Colburn factor (j) and the friction factor (f) ‒ for different combinations of the independent variables ‒ are computed using the numerical simulations together with the conjugate heat transfer approach. To get the best outcome from computations, both fluid and solid domains have been discretized using hexahedra. We make use of the Reynolds-averaged Navier-Stokes (RANS) approach ‒ with SST k–ω (a 2-equation) turbulence model as a closure to RANS ‒ for evaluating the dependent variables. The artificial neural network (ANN) is trained using the data from the DoE table to build the metamodel necessary for conducting the multiobjective optimization. The genetic algorithm (GA) is employed to generate the optimized data sets. The study reveals that the optimized HE variants outperform the baseline model not only at the on-design condition but also at the off-design conditions. The resulting Pareto front points reveal very interesting results, and these data would facilitate the designers to make choices over a wide range of the VG geometry of the heat exchanger.

Performance analysis of new structure heat exchanger based on field synergy and numerical simulation

High efficiency heat exchanger is always a hot topic, and field synergy theory is introduced as an important means to optimize the heat transfer efficiency. Based on the field synergy theory, a new type of heat exchanger is proposed in this paper, in which, the cold and hot fluid presents reverse cross flow law. Through the verification of the test and numerical simulation results, a reasonable numerical simulation model and method are obtained. Then, the flow and heat transfer conditions of the new structure heat exchanger are simulated by the verified numerical simulation technology. The conclusion is as follows: K-ε turbulence model and coupled heat transfer model can be effectively used in the numerical simulation of heat exchanger. And the reverse cross convection heat exchanger can effectively improve the uniformity of water temperature distribution in the heat exchanger.

The effect of heat recovery on the optimal values of helicopter turboshaft engine parameters

Recent studies related to fuel economy in air transport conducted in our country and abroad show that the use of recuperative heat exchangers in aviation gas turbine engines can significantly, by up to 20...30%, reduce fuel consumption. Until recently, the use of cycles with heat recovery in aircraft gas turbine engines was restrained by a significant increase in the mass of the power plant due to the installation of a heat exchanger. Currently, there is a technological opportunity to create compact, light, high-efficiency heat exchangers for use on aircraft without compromising their performance. An important target in the design of engines with heat recovery is to select the parameters of the working process that provide maximum efficiency of the aircraft system. The article focused on setting of the optimization problem and the choice of rational parameters of the thermodynamic cycle parameters of a gas turbine engine with a recuperative heat exchanger. On the basis of the developed method of multi-criteria optimization the optimization of thermodynamic cycle parameters of a helicopter gas turbine engine with a ANSAT recuperative heat exchanger was carried out by means of numerical simulations according to such criteria as the total weight of the engine and fuel required for the flight, the specific fuel consumption of the aircraft for a ton- kilometer of the payload. The results of the optimization are presented in the article. The calculation of engine efficiency indicators was carried out on the basis of modeling the flight cycle of the helicopter, taking into account its aerodynamic characteristics. The developed mathematical model for calculating the mass of a compact heat exchanger, designed to solve optimization problems at the stage of conceptual design of the engine and simulation of the transport helicopter flight cycle is presented. The developed methods and models are implemented in the ASTRA program. It is shown that optimal parameters of the working process of a gas turbine engine with a free turbine and a recuperative heat exchanger depend significantly on the heat exchanger effectiveness. The possibility of increasing the efficiency of the engine due to heat regeneration is also shown.

Improving the efficiency of aviation turbofan engines by using an intercooler and a recuperative heat exchanger

Continuous improvement of fuel efficiency of aircraft engines is the main global trend in modern engine construction. To date, aviation gas turbine engines have reached a high degree of thermodynamic and design-and technology perfection. One of the promising ways to further improve their fuel efficiency is the use of complex thermodynamic cycles with turbine exhaust heat regeneration and with intermediate cooling in the process of air compression. Until recently, the use of cycles with a recuperative heat exchanger and an intercooler in aircraft gas turbine engines was restrained by a significant increase in the mass of the power plant due to the installation of heat exchangers. Currently, it has become technologically possible to create compact, light, high-efficiency heat exchangers for use on aircraft without compromising their performance. An important target in the design of engines with heat recovery is to select the parameters of the working process that provide maximum efficiency of the aircraft system. The article focuses on the statement of the task of optimization and choice of rational parameters of the working process of a bypass three-shaft turbojet engine with an intercooler and a recuperative heat exchanger. On the basis of the developed method multi-criteria optimization was carried out by means of numerical simulations. The results of optimization of thermodynamic cycle parameters of a bypass three-shaft turbojet engine with an intercooler and a recuperative heat exchanger in the aircraft system according to such criteria as the total weight of the engine and fuel required for the flight, and the aircraft specific fuel consumption per ton - kilometer of the payload are presented. A passenger aircraft of the Airbus A310-300 type was selected. The developed mathematical model for calculating the mass of a compact heat exchanger, designed to solve optimization problems at the stage of conceptual design of the engine is presented. The developed methods and models are implemented in the ASTRA program. The possibility of improving the efficiency of turbofan engines due to the use of complex thermodynamic cycles is shown.

Investigations of water-cooled tubes with protrusions for flow and heat transfer characteristics

PurposeThis study aims to present a numerical study on the flow and heat transfer performance of a water-cooled tube with protrusions in different geometrical parameters.Design/methodology/approachA new type of enhanced heat exchanger tube is designed. Protrusions are formed on the inner surface of the tube by mechanical expansion, compression and other processing methods. A three-dimensional numerical symmetry model is established by ANSYS for studying the influence of protrusion distance, protrusion radius and protrusion arrangement on flow and heat transfer characteristics in turbulent flow.FindingsThe results show that the protrusions increase the heat transfer area and improve the heat transfer effect but also increase the flow resistance. Performance evaluation criteria (PEC) is applied to evaluate the flow and heat transfer characteristics of convex tubes. When adopting the aligned protrusions arrangement, the radius of 2 mm and distance of twice the protrusion radius is most heat transfer effect. The PEC of protrusion tubes with a staggered arrangement are higher than those in aligned arrangement, and the maximum value is 2.36 when Reynolds number is 12,000.Originality/valueAt present, most of the protrusion technology applications are based on the cold plate heat dissipation of electronic devices, and the flow path is rectangular. Convex tube heat exchanger is a high-efficiency heat exchanger, which uses convex tubes instead of smooth tubes in tubular heat exchangers to enhance heat transfer and widely used in petroleum, chemical, textile, oil refining and other industries.

CFD analysis of an economizer for heat transfer enhancement using serrated finned tube equipped with variable fin segments

Due to the extensive use of heat exchangers in various daily and industrial applications, the improvement of their performances is of great importance. It is evident from the literature that very limited work has been done in serrated finned tube economizer for heat transfer enhancement and pressure drop performance. This paper deals with the heat transfer improvement and pressure drop performance of helical serrated finned tube bundles in inline bare tube counter cross-flow water tube boiler Economizer, which has larger heat transfer area and higher heat exchange efficiency. Numerical simulation on heat transfer performance is carried out on 116.3 TPH of MCR boiler unit, one tube row with three-row finned tube passes; helically wound fin geometries of partially serrated finned tubes are investigated. A steady-state approach, with two-equation, a k-ε turbulence model is employed to examine the effect of Reynolds number in the range of 8000 to 20000. In this study the conjugate heat transfer is considered for the calculation of the conduction in a solid region is coupled with the calculation of the temperature distribution in the working fluid flowing over or through this solid region. The effect of a number of serrated segmented finned tubes per period on the performance of heat transfer enhancement is also investigated. The computational results fall within the range of values predicted by empirical correlation. The results show that the heat transfer is enhanced by up to 3.53% to 5.14% if the number of segments per period varied from 20 to 50.

Reliability analysis of compact and high efficient heat exchanger for FLNG devices

Objectives So far, the compact and high-efficiency heat exchanger is the best choice for floating liquefied natural gas (FLNG) heat exchangers. Static strength analysis and reliability analysis are required to optimize the structural parameters of a heat exchanger and improve its performance. Methods First, the strength of the heat exchanger core is analyzed using the ANSYS Workbench static analysis module, and a simplified model is established which can represent the stress level of most channels. Next, the reliability analysis of the heat exchanger is conducted using the six sigma analysis of the ANSYS Workbench by choosing the cold channel thickness, cold channel pressure, hot channel pressure and elastic modulus as input random variables, and the effects of these random variables on the reliability of the heat exchanger are studied. Results The reliability analysis results show that the cold channel pressure loading is the greatest factor in structural strength, and the reliability of the heat exchanger is more than 99.9%, so the possibility of failure is very low. Conclusions The results of this study can serve as valuable references for the reliability analysis of heat exchangers based on strength.

A high efficient heat exchanger with twisted geometries for biogas process with manure slurry

Heat-transfer enhancement in manure slurry is crucial for increasing the efficiency and production of biogas during anaerobic digestion in biogas plants. In this study, a novel heat exchanger with an optimal twisted geometry was developed based on the numerical screening of the twisted tubes with equilateral polygons, and experiments were conducted to validate the numerical results. It was observed that the SST k–ω model is more efficient than other turbulence models in representing the heat transfer performance of the twisted tubes, and the numerical model with a thermostatic wall can be used to reliably screen the twisted geometries. The twisted hexagonal tube has the optimal geometry, with enhancement capability of up to 1.4 times compared to that of the circular tube. The formation of high continuity regions with relatively strong heat-transfer rates along the heat-exchange wall is the main reason for the high performance during heat transfer. The external heating process was integrated in a full-scale biogas plant, and the model and algorithm were developed and validated with additional experiments to describe the overall performance of both conventional and screened optimal geometries under different conditions. It was observed that a profit equivalent to 39% of total production for a large-scale biogas plant can be achieved owing to energy conservation in external heating with the twisted hexagonal tubes.

Experimental Evidence of the Viability of Thermoelectric Generators to Power Volcanic Monitoring Stations.

Although there is an important lack of commercial thermoelectric applications mainly due to their low efficiency, there exist some cases in which thermoelectric generators are the best option thanks to their well-known advantages, such as reliability, lack of maintenance and scalability. In this sense, the present paper develops a novel thermoelectric application in order to supply power to volcanic monitoring stations, making them completely autonomous. These stations become indispensable in any volcano since they are able to predict eruptions. Nevertheless, they present energy supply difficulties due to the absence of power grid, the remote access, and the climatology. As a solution, this work has designed a new integral system composed of thermoelectric generators with high efficiency heat exchangers, and its associated electronics, developed thanks to Internet of Things (IoT) technologies. Thus, the heat emitted from volcanic fumaroles is transformed directly into electricity with thermoelectric generators with passive heat exchangers based on phase change, leading to a continuous generation without moving parts that powers different sensors, the information of which is emitted via LoRa. The viability of the solution has been demonstrated both at the laboratory and at a real volcano, Teide (Canary Islands, Spain), where a compact prototype has been installed in an 82 C fumarole. The results obtained during more than eight months of operation prove the robustness and durability of the developed generator, which has been in operation without maintenance and under several kinds of meteorological conditions, leading to an average generation of 0.49 W and a continuous emission over more than 14 km.

Effects of the shape of tube and flow field on fluid flow and heat transfer

The arc tube is an innovative heat exchange device that has the advantages of high heat exchange efficiency, which slows down the damage thermal stress to the pipeline and high mass transfer rate, in comparison to the traditional straight wall tubes. Therefore, it is widely applied in the field of heat and mass transfer, particularly in heat exchanger. To study the influence of the ratio of the circumscribed arc radius of the arc tube on the heat transfer and flow resistance characteristics of the fluid inside the tube, geometric models of sine wave wall tubes with various radius ratio i, and the same size parameters have been established. The flow field and temperature field in the tube have been analyzed by numerical simulation and experiment, and the comprehensive heat transfer performance of different wave-wall tubes has been evaluated using the performance evaluation factor PEC. The results show that the heat transfer capacity is stronger for the smaller i. Further, Nu decreases with increasing i, and the reduction decreases with increasing Re. The frictional resistance coefficient at 1 is proportional to i at radius ratio between 0.1 and 1, and the frictional resistance coefficient is inversely proportional to i at 1 < i < 10. When i = 1, the frictional resistance coefficient appears to be the maximum, PEC increases as Re increases and the PEC of external tangential arc wave wall tube is higher than the sine wave wall tube. To improve the heat transfer efficiency of the sine wave wall tube, a pulsating flow field has been applied to the flowing fluid in the wave wall tube. It has been found that the application of the pulsating flow field can improve the heat transfer coefficient of the fluid in the wave wall tube, and the pulsation parameter has a greater impact on the heat transfer coefficient.

Optimization of Microchannel Heat Sink with Rhombus Fractal-like Units for Electronic Chip Cooling

Abstract Microchannel heat sink is commonly used as a high-efficiency heat exchanger type in electronic microchips cooling, and the parallel microchannels arranged on the heat sink not only enhance heat transfer area but also result in large pumping power. In this paper, a novel structure of microchannel heat sink with rhombus fractal-like units is proposed for improve the overall performance, and a geometry optimization approach is developed for the design of the new microchannel heat sink. The validation of the geometry optimization approach is performed, and the results show that the predicted pumping power can describe 93% of the experimental data within the deviation limit of ± 5% and the mean deviation is 1.95%. Compared to the conventional parallel microchannel heat sink, the microchannel heat sink with rhombus fractal-like units may increase the COP by 7.9%-68.7% under the same constrains of external size, specified heat flux and maximum temperature limitation, which indicates the rhombus fractal-like units may effectively improve the efficiency of microchannel heat sinks.