Main Heat Exchanger Research Articles

Loss-of-heat-sink transient simulation with RELAP5/Mod3.3 code for the ATHENA facility

ATHENA (Advanced Thermal-Hydraulic Experiment for Nuclear Applications) is a large multipurpose pool-type lead-cooled facility under construction at the Mioveni site in Romania. It has been identified by the FALCON (Fostering ALfred CONstruction) Consortium to characterize large to full-scale ALFRED components, to conduct integral tests, and to investigate the main thermal–hydraulic phenomena inherent in pool-type systems. ATHENA is representative of ALFRED in terms of the difference in height of the thermal barycenters of the heat source and heat sink, i.e., 3.3 m, in order to reproduce the buoyancy forces in the system. Similar to ALFRED’s design, ATHENA minimizes thermal stratification within the main vessel even under natural circulation conditions, through an internal structure referred to as “barrel”. This structure directs the fluid flow towards the main vessel, preventing fluid stagnation near the vessel itself. The paper initially provides a steady-state thermal–hydraulic characterization of the facility, including details of the numerical model developed using the RELAP5/Mod3.3 thermal–hydraulic code. Then, focus is given to the transient analysis considering as a reference scenario a Loss-of-Heat-Sink (LOHS) accidental transient. In this scenario, the Main Circulation Pump (MCP) is assumed to remain operational while the Core Simulator (CS) is deactivated once the lead temperature at the Main Heat Exchanger (MHX) outlet reaches a predefined threshold. A sensitivity analysis is conducted with set points of 430 °C, 450 °C, 470 °C, and 490 °C, assessing the system’s response following MHX isolation from the secondary loop. The study evaluates the impact of different CS deactivation set points on reactor SCRAM delay (reducing CS power to a level representative of decay heat) as well as on system maximum and minimum temperatures.

Design Solutions for the Main Heat Exchangers in the Organic Rankine Cycle Circuit (Review)

Design Solutions for the Main Heat Exchangers in the Organic Rankine Cycle Circuit (Review)

Influence of shielding gas flow on the TIG welding process using stainless steel 304 material

A common issue encountered with main heat exchanger equipment is improper operation, which can lead to the development of cracks in the stainless-steel pipes. The welding process alters the metal microstructure in the heat-affected zone, thereby affecting the mechanical properties of the welded joint. To mitigate this issue, TIG welding with argon shielding gas is employed. This method helps prevent oxidation and ensures the formation of a stable welding arc in 304 stainless steel, which is renowned for its excellent mechanical properties and corrosion resistance. The objective of this study is to evaluate the impact of variations in shielding gas flow on the mechanical properties of 304 stainless steel plates during the TIG welding process. The aim is to determine the optimal settings for producing robust and long-lasting welded joints. To assess the hardness of the welded joints, we employed a Brinell-type Hardness Tester FB-3000LC machine. A Brinell steel ball indenter measuring 5 mm on the HBW scale and applying a load of 125 Kgf was utilized. At a protective gas flow rate of 8 L/min, the average tensile stress was 44.72 N/mm², strain was 0.177, modulus of elasticity was 2518 MPa, and hardness was 99.712 HBW. Increasing the gas flow rate to 13 L/min resulted in an average tensile stress of 47.50 N/mm², strain of 0.189, elastic modulus of 2525 MPa, and hardness of 105.522 HBW. Further increasing the gas flow rate to 18 L/min led to an average tensile stress of 49.69 N/mm², strain of 0.192, modulus of elasticity of 2597 MPa, and hardness of 106.704 HBW. Based on the research findings, it was observed that the weld area exhibited an increase in hardness values due to the heat generated during the welding process. The use of protective gas flow during welding is deemed effective in producing well-formed welded joints, as it prevents fractures from occurring within the weld area during the tensile test process. The choice of protective gas is determined by the dimensions of the material plate.

Sustainability evaluation of C3MR natural gas liquefaction process: Integrating life cycle analysis with Energy, Exergy, and economic aspects

In a transition towards a clean energy future, natural gas serves as an interim fuel due to its lower emissions whereas the C3MR (propane pre-cooled mixed refrigerant process) is widely recognized for high efficiency and commercial scale application converting natural gas to LNG. Previously, numerous studies have been conducted to optimize the energy efficiency and performance of C3MR process but very little contribution has been made towards its sustainability analysis. To address this, a life cycle analysis approach is established to evaluate the carbon footprint of C3MR process. In order to showcase its link with energy consumption and put forward the groundwork of analyses, the research focuses on using simulation – assisted optimization to reduce the specific energy consumption (SEC) of C3MR process by optimizing design variables. The study highlights the use of mixed refrigerant (MR) as a process variable and validates that its optimal implementation has decreased SEC to 0.2195 kWh/kg LNG, while achieving a minimum inlet temperature approach (MITA) of main cryogenic heat exchanger (MCHX), less than 3 °C. The knowledge − based optimization approach applied in this research, developed comparative case studies on which multiple analyses are performed to verify scientific findings. Energy and exergy analyses are conducted to determine thermal efficiency of the process where the optimized case exhibits a reduced difference in its composite curves and an 8.65 % improvement in exergetic performance compared to the base case. The economic indicators assessment reveals that optimized case demonstrates lower capital and operating costs, establishing economic viability. Furthermore, the energy consumption parameters are utilized for evaluation of ecological impact ofLNGsupply chain through life cycle assessment (LCA) which reflects reduced greenhouse gas (GHG) emissions for optimized case. Hence, the current study fills existing research knowledge gaps in terms of providing a comprehensive process system engineering by evaluating energy synergistic point, thermodynamic irreversibility, process viability and sustainability using life cycle assessment.

Design and optimization analysis of a new double-layer tube type heat exchanger for lead-bismuth reactors

Double-layer heat tubes have been designed to effectively reduce the occurrence of heat pipe rupture accidents. However, inter-tube thermal contact resistance can decrease heat transfer efficiency, thus hampering the heat dissipation in the primary loop system of lead-bismuth reactors. Therefore, optimizing the design of double-layer heat tubes is necessary. This work focuses on the double-layer heat exchanger of a lead-bismuth reactor and utilizes gallium-based graphene nanofluids as a thermal interface material to fill the gap between the heat tubes. Furthermore, the impact of the length, wall thickness, outer diameter, and spacing of heat tubes on the heat transfer performance of the double-layer heat exchanger with and without the nanofluids has been analyzed. The study aims to optimize the JF factor and cost-effectiveness ratio (CER). Genetic algorithms are employed to optimize and evaluate the heat transfer performance of the main heat exchanger based on the four aforementioned parameters. Consequently, a new design scheme is obtained for the double-layer heat exchanger, which increases the optimized overall heat transfer coefficient of the main heat exchanger by 5.79%, pressure drop in the primary loop by 2.32%, JF factor by 5%, and CER by 24.62%. These results demonstrate that the gallium-based graphene nanofluids can effectively enhance the heat transfer performance of the double-layer heat exchanger while reducing the likelihood of steam generator tube rupture accidents.

Extraction turbines and feed-heating in geothermal binary plants: A thermodynamic performance assessment

The use of extraction turbines in conjunction with multiple feedwater heaters is standard practice in conventional fossil or nuclear steam electrical generating stations as a way to conserve fuel by raising the final feedwater temperature entering the boiler. One way to improve the thermal efficiency of geothermal binary plants is to include a heat recuperator that uses the expanded, but still hot working fluid leaving the turbine to preheat the working fluid leaving the feed pump prior to reaching the main brine heat exchangers. However, the use of partially-expanded working fluid from an extraction turbine to further preheat the working fluid has not been widely deployed in geothermal binary plants. This paper will describe this technique in a feed-heating cycle, develop the working equations to assess the performance for a variety of geofluid temperatures, to determine whether or not this approach can be as effective in geothermal binary plants as it is in conventional nuclear power plants. Finally, we will discuss the practical aspects of this system in geothermal binary plants, and suggest some further studies to extend this concept to other geothermal applications.

Simulation of boil-off gas recovery and fuel gas optimization for increasing liquefied natural gas production

In a natural gas liquefaction plant, boil-off gas (BOG) is generated in both liquefaction and loading processes. During the holding mode (no loading operation), the fuel gas supply, including the BOG generated in the liquefaction process, is less than the fuel gas demand. Therefore, make-up gas is added to the fuel gas system. BOG recovery systems are designed to absorb the maximum amount of BOG during liquefied natural gas (LNG) loading to ships (loading mode). Additional BOG is generated during the loading process (loading mode). At this stage, the fuel gas supply is higher than the demand. To avoid fuel gas flaring, BOG from the liquefaction process is reduced by cooling the LNG from the main heat exchanger (MHE) to a lower temperature, which consequently reduces LNG production by more than 1%. This study aimed to optimize liquefaction, storage, loading, fuel gas and BOG recovery processes to increase LNG production. In this study, a natural gas liquefaction plant producing 8 mtpa (million tonnes/ year), where LNG production was limited by the capacity of the BOG recovery system and fuel gas demand, was modelled using UniSim software. In the model, the optimization of BOG recovery during the holding mode increased LNG production by 46,850 tonnes/ year. The volumetric flow rate of BOG generated during LNG loading was reduced by decreasing the temperature of the ship’s cargo tanks, decreasing the loading pumps’ discharge pressure, reducing the discharge pressure of the ship’s compressors, and reducing the loading rate. This study shows that BOG generated during loading can be significantly reduced by around 50% from the initial rate, which increases LNG production by around 36,576 tonnes/ year. In total, the potential production increase from BOG recovery and fuel gas optimization was around 90,260 tonnes/ year or equivalent to 1.4 cargo of LNG per year.

Numerical simulation of the operational characteristics of air-cooled PRHR under SBO accidents

In this paper, the operational characteristics of air-cooled type passive residual heat removal (PRHR) system of the nuclear heating reactor are studied with RELAP5 code. The PRHR uses the air natural circulation which can transfer heat directly from the reactor vessel to the air, and its heat transfer process is particularly important for the reactor safety. However, the current thermal–hydraulic code lacks the relevant air cooler model. A method how to model an air cooler is proposed based on the conservation equation and can be widely applied to different situations. Moreover, the operating characteristics of air cooling tower and the transient thermal–hydraulic characteristics of station blackout (SBO) event have been analyzed. The results show that the heat transfer coefficient of air cooler increases with the heat transfer power, and the inlet temperature has little influence on the heat transfer coefficient. The air cooling type PRHRS can transfer the core residual heat timely and continuously. There is a time delay of the heat exchanger power between the main heat exchanger and air cooler caused by the temperature distribution.

Transient characteristics of typical design basis accidents in integrated small reactor NHR200-II using RELAP5 model

The development of advanced integrated small reactors is one of the most important trends in nuclear engineering nowadays, the NHR200-II reactor proposed by Tsinghua university has also undergone several iterations of improvement. The increased thermal–hydraulic parameters mean that the design-basis accidents need to be reanalyzed, of which three typical scenarios are chosen as benchmarks and simulated with the complete RELAP5-model. The small break loss-of-coolant accident, the pump-shaft-stuck accident and the heat-transfer-tube-rupture in main heat exchanger accident were assessed systematically and showed good agreement with previous research. The characteristics like the transient flow rate at the break, the moment of inertia of circuit pump and the position of the main heat exchanger were examined, different control variables mainly affect the sequence of trigger actions rather than overall thermal–hydraulic parameters. The results demonstrate that the reactor core can be cooled sufficiently throughout all transient conditions and be flooded with coolant.

Optimization and control strategy of BOG re-liquefaction process for LNG vessels

The re-liquefaction of BOG is a necessary part of the safety and security of LNG cargo ships. And the volatility of BOG will fluctuate with the sea conditions of ship transportation, so how to deal with the fluctuation of the re-liquefaction system and improve the liquefaction capacity is a problem that cannot be ignored in the operation of the liquefaction system; In this paper, a BOG buffer tank is added to the Reverse Brayton Process. Moreover, a control strategy is proposed to optimize the liquefaction process. The proposed four possible operating conditions' efficiency,the specific energy consumption (SEC), liquefaction rate and main heat exchanger parameters were simulated and analyzed by using Aspen HYSYS software. According to the results, the specific energy consumption of the basic re-liquefaction process is 1.329 kWh/kgLNG, which is 5.7% less than that of the reference process; In the study of flow fluctuation, after adopting the control strategy, the specific energy consumption of the whole process is 1.29 kWh/kgLNG, with 15.6% efficiency and 99.5% liquefaction rate. The whole system can be maintained at a low specific energy consumption level when the feed gas volume is fluctuating. The analyses of various BOG composition and the parameters of the main heat exchanger show that the regulation of the inlet gas volume can make the primary re-liquefaction process flexible and maintain the heat exchanger in a good working condition; Even if the system is in a worse working condition, the inlet gas volume can be improved by 12.2% compared with the reference process.

Thermodynamic analysis of the apci skikda liquefaction process

In this paper, the mixed refrigeration cycle of Skikda APCI (Air Products and Chemicals Inc.) process in Algeria was studied thermodynamically in order to determine the optimal operat-ing conditions. The energy and exergy balance equations for each process component were es-tablished. The distribution of the exergy destruction of the basic cycle equipment revealed that the compressors had the highest exergy destruction rate. The effects of operating conditions on performance coefficient of the cycle (COP) and exergy efficiency of the APCI process were evaluated; mainly the inlet temperature of the compressors, natural gas (NG) temperature af-ter cooling in the main cryogenic heat exchanger (MCHE) and inlet temperature of the mixed refrigerant (MR) expansion valve. The results of the numerical simulation validated using Aspen HYSYS software indicate that the COP and exergy efficiency of the basic cycle are 2.66 and 59.99% respectively. These results can be improved by reducing the inlet temperature of the compressor and the expander as well as that of the NG after cooling in the MCHE. Finally, the results of the optimization performed using the genetic algorithms (GA) are in agreement with those of the literature. They show signs of improvement in the COP and exergy efficiency of the APCI process by 1.48% and 3.64% respectively compared to the basic cycle.

ATHENA Main Heat Exchanger Conceptual Design and Thermal-Hydraulic Assessment With RELAP5 Code

Abstract Among the envisaged experimental infrastructures supporting ALFRED reactor development, Fostering Alfred Construction consortium identified ATHENA as one of the facilities to address the pool thermal-hydraulic challenges and demonstrate the feasibility of the revised ALFRED configuration, along with the thermal-hydraulic performances of its main components. ATHENA is a large pool-type lead-cooled multipurpose experimental facility featuring a large size vessel (3.2 m diameter, 10 m in height), conceived to host almost 800 tons of lead to test ALFRED relevant scaled components. The test section to be installed in the main vessel includes an electrically heated core simulator (CS), made of 7 FAs, which delivers to the primary coolant a nominal thermal power of 2210 kW, a main coolant pump for lead circulation, and a countercurrent shell and tubes main heat exchanger, which tube bundle is fed by pressurized water by a dedicated secondary circuit. A preliminary analytical calculation has been performed to identify the most suitable configuration for the ATHENA heat exchanger, as well as to achieve a preliminary sizing of the component. The final layout foresees a bundle of 91 bayonet tubes, arranged in a cylindrical geometry, having an active length of 3000 mm and adopting an external double wall tube with a pressurized helium gap. A numerical model of the heat exchanger has been developed using the thermal-hydraulic system code RELAP5/Mod3.3, and a numerical sensitivity analysis on the geometrical and operating parameters has been carried out to verify the performances of the component.

Thermal-Hydraulic Characterization and Numerical Modeling with RELAP5 Code of ATHENA Secondary Loop

Among the envisaged experimental infrastructures supporting Advanced Lead Fast Reactor European Demonstrator (ALFRED) reactor development, the FALCON [Fostering ALfred CONstruction] consortium identified the Advanced Thermo-Hydraulics Experiment for Nuclear Application (ATHENA) as one of the facilities to address the pool of thermal-hydraulic challenges and demonstrate the feasibility of the revised ALFRED configuration, along with the thermal-hydraulic performances of its main components. ATHENA is a large pool-type lead-cooled multipurpose experimental facility featuring a large-sized vessel (3.2-m diameter and 10-m height), conceived to host almost 800 tons of lead to test ALFRED-relevant scaled components. The test section to be installed in the main vessel includes an electrically heated core simulator, made of seven fuel assemblies, which delivers to the primary coolant a nominal thermal power of 2210 kW; a main coolant pump for lead circulation; and a countercurrent shell-and-tube main heat exchanger, of which the tube bundle is fed by pressurized water by a dedicated secondary circuit. This work presents the numerical model of ATHENA along with thermal-hydraulic characterization of the facility using the system code RELAP5/Mod3.3, properly modified to include the thermophysical properties of heavy liquid metals. After the characterization of the steady state representative of the Stage 3 foreseen for the ALFRED staged approach, results of a numerical sensitivity analysis aimed at defining the most suitable procedure for the shutdown transient of the facility are presented.

PENERAPAN PEMROGRAMAN PYTHON DALAM MENENTUKAN WAKTU OVERHOUL KONDENSOR TURBIN UAP

Condensers as the main equipment and heat exchangers in a combined cycle power plant have a major effect to determine combined cycle efficiency. The condenser is used to transform saturated steam into water which will be reused in a combined cycle power plant. To acquire high performance, the condenser requires an overhaul plan and calculated performance. In this research, to determine a good overhaul plan, the python programming language with the linear regression method is used. The python programming language aims to predict the condenser when it must be overhauled. From the results of the research, it was found that there was an increase in the value of the cleanliness factor condenser before the overhaul. From 56.69% to 57.45% after the overhaul. After using linear regression in python programming on the distribution data from 2018 which was divided into three groups of analysis, it was found that the condenser must be overhauled on August 24, 2023.

A design model for spiral wound heat exchangers which accounts for property variation, longitudinal heat conduction, and heat-in-leak

• A combined analytical-numerical design model for cryogenic SWHE is developed. • Analytical sizing module finds the optimum configuration of SWHE. • The effects of property variation, LHC, and heat-in-leak are investigated. • LHC impact is negligible compared to property variation and heat-in-leak. • A sensitivity analysis on the input constraint is performed. Spiral Wound Heat Exchangers (SWHEs) can be a good and reliable choice for serving as the main heat exchanger in the cryogenic gas liquefaction cycles using throttling process such as the Linde-Hampson cycle. In this application, a high pressure hot gas stream has to be cooled down via transferring heat to a low pressure cold gas in a high-effectiveness heat exchanger. Present research has been organized to develop a design model which is able to find the optimum SWHE configuration for gas liquefaction cycles. The model has to be capable of considering the important physical phenomena in the cryogenic temperature ranges, including variation of fluid properties with temperature, longitudinal heat conduction (LHC) through separating walls, and heat-in-leak. Therefore, a combined analytical-numerical design model has been developed in the present study. The design model is essentially composed of two stand-alone modules, i.e. an analytical sizing module and a numerical performance evaluation module. To develop the design model, first, the geometrical characteristics of SWHE are studied and primary geometrical parameters are recognized. Then, the analytical sizing module is developed which is able to determine the optimum values of primary geometrical parameters of SWHE minimizing the heat transfer surface area based on the input design requirements. Afterwards, a 1D finite difference numerical module is presented in which important physical phenomena can be considered in the evaluation of the thermo-hydraulic performance of all types of counter flow or parallel flow heat exchangers as well as SWHEs. Finally, the two modules are combined to construct a design model. Two examples in which the low pressure superheated vapor helium is intended to cool down the high pressure supercritical helium flowing inside the tubes are also provided to demonstrate the applicability of the proposed combined model, and also, to elucidate its sensitivity to the input constraints. It was concluded that while variations of fluid properties and the external heat fluxes due to the radiation and convection have significant influence on the performance of cryogenic SWHE, the LHC is of minor importance and can be neglected. Moreover, decreasing the shell-side allowable pressure drop from 10 kPa to 2 kPa, causes the heat exchanger length and its outside diameter to increase by 79% and 48%, respectively.

Enhanced hydrogen generation in a combined hybrid cycle using aluminum and cooper oxide nanomaterial based on biomass and vanadium chloride cycle: Optimization based on deep learning techniques and Environmental appraisal

The usage of Nanofluid to enhance heat transfer has been investigated by many researchers in small-scale heat transfers; however, in large-scale power plants, it has not been taken care of. In this research paper, a newly proposed energy system for hydrogen generation based on renewable sources is proposed and analyzed in detail. Unlike other power input systems, the vanadium chloride system generates hydrogen because it uses waste heat. In this regard, the nanoparticles of Al2O3 and CuO are utilized in the main heat exchanger to enhance the heat transfer to the reactor of VCLC to generate more hydrogen. Also, the compound system has the gasifier-based internally fired gas turbine as the main system and can generate hydrogen in a more green way. The optimization based on deep learning methods is applied to seek the highest point of operation by the system. The results exhibit that Al2O3 causes more heat transfer and efficiency enhancement, thus in hydrogen production, causing an increase of 18.5% compared to base fluid and 8.3% compared to CuO in H2 Generation In circumstances when it is optimal, the values for exergetic efficiency and total hydrogen production are 64.5% and 4.5 kg/s respectively. In addition, using a nanofluid heat exchanger and biomass energy reduces CO2 emissions to 0.91 kg/kWh.

Energy, exergy and economic analyses of an optimal use of cryogenic liquid turbine expander in air separation units

Cryogenic liquid turbine expanders have emerged quite recently as a replacement for traditional Joule-Thomson valves in cryogenic processes for energy saving purpose. However, introducing a liquid turbine expander into the cryogenic air separation unit (ASU) can influence the operating points of ASU components, and the maximum benefits arising from the liquid turbine expander have not yet been reported. To fill such a gap, thermodynamic models are first established for ASU components, including the main air compressor, booster air compressor, cryogenic gas and liquid turbine expanders, main heat exchanger, cryogenic pump, and distillation column. To achieve the best possible use of the liquid turbine expander, an optimization method is developed by incorporating the thermodynamic models with the particle swarm optimization algorithm, in which the total minimization power consumption of ASU is the optimization goal while the flow rates and pressures of the high pressure air stream and the air stream drawn from the booster air compressor middle section together with the temperature of the medium pressure air stream exiting the main heat exchanger midway act as the optimization variables. Then, energy, exergy and economic analyses are conducted and the corresponding indexes are chosen to quantitatively evaluate the influence of the liquid turbine expander on the air separation process. For the case study, ASUs of 35000 Nm3/h oxygen production capacity with and without a cryogenic liquid turbine expander are optimized, respectively. The results show that the ASU total power saving through the use of liquid turbine expander is 4.2-fold its output shaft power; thus, the energy consumption of unit oxygen decreases by 2.12% and the overall exergy efficiency increases by 1%. In addition, the economic analysis shows that the period of return of the liquid turbine expander in the ASU is estimated to be 1.75 years.

Energy management strategy for a biogas plant in Anhui, China based on waste heat recovery and thermoeconomic analysis

Bio-energy is expected to play a significant role in the future energy systems, and biogas is one of the most promising resources for bioenergy utilization. However, the unit cost of a power generation of biogas power plant is much higher than that of a regular coal-fired power plant owing to irregular energy management. In this study, a novel energy management strategy is established to improve the energy efficiency and economic performance of a plant using the waste heat of its exhaust gas and the cold energy of liquefied natural gas. A comprehensive thermodynamic analysis is conducted to study the energy and exergy behavior of the system. A detailed economic analysis is performed based on the chemical engineering plant cost index to investigate the economic feasibility. An environmental analysis is conducted to quantify the environment benefits. Moreover, a sensitivity analysis is conducted to determine the effect level of each parameter on the system performance. The simulations results based on a 50,000 m3 biogas plant indicate that the energy efficiency of power generation of the plant increases from 38% to 46%. With the developed system, the reduction in CO2 emissions is approximately 5100 ton annually. The net present value and dynamic payback period of the system are approximately 4.5 M$ and 9.1 years, respectively. The sensitivity analysis reveals that the ratio of the exhaust gas used in the main heat exchanger of CO2 cycle has the largest effect on the system performance. The simulation results can provide helpful suggestions for the construction of a biogas plant.

The effect of the aftercooler on the regenerator temperature non-uniformity in a high-capacity pulse tube cryocooler

High-power Stirling-type pulse tube cryocoolers (SPTC) are expected to be an ideal candidate for cooling high temperature superconductivity (HTS) for its advantages of compact structure, low maintenance and long service life. However, the regenerator temperature non-uniformity is still a key problem needs to be solved since it significantly deteriorates the cooling performance. As a main heat exchanger, the insufficient and asymmetric heat exchange in the aftercooler may be one of the factors affecting the temperature inhomogeneity inside the regenerator. However, it has been seldom investigated. In this study, the relationship between the performance of the aftercooler and the temperature non-uniformity of the regenerator was investigated based on a high-power SPTC working at ∼ 80 K. With the help of Sage simulation, it is found that the inlet temperature of the regenerator has a large effect on its inside temperature distribution. Even an inapparent temperature inhomogeneity at the inlet of the regenerator will induce a large temperature difference in the middle of the regenerator, due to an obvious DC flow generated in the regenerator. By changing the water inlet and outlet directions of the aftercooler, the temperature non-uniformity of the regenerator will consequently change, which means the uneven heat transfer of aftercooler can be one of the main inducements to the temperature non-uniformity inside the regenerator. Further, methods of using copper wire mesh filling at the hot end of the regenerator, and optimizing heat exchange tubes inside the aftercooler were studied to reduce the temperature non-uniformity.

Visualization experimental and numerical study on multiphase flow characteristics of main cryogenic heat exchanger in offshore liquefied natural gas industry chain

The deep-sea natural gas resources are safely and efficiently sent to the energy market through the offshore liquefied natural gas (LNG) industry chain, which provides a feasible idea for the utilization, development, storage and transportation of deep-sea natural gas fields. The offshore LNG industry chain includes production equipment (LNG-FPSO, LNG Floating Production Storage and Offloading Unit, also known as FLNG) and receiving equipment (LNG-FSRU, LNG Floating Storage and Regasification Unit). Due to the influence of sea conditions, the key cryogenic heat exchangers in LNG-FPSO and LNG-FSRU have the problem of insufficient heat transfer caused by uneven distribution of multiphase flow, which affects the performance index of liquefaction and gasification process. In this work, the visualization experimental device and numerical simulation model of falling film flow in LNG-FPSO and multiphase flow of intermediate medium in LNG-FSRU have been established, based on the sloshing platform system, camera and processing system, VOF two-phase flow model and dynamic grid technology. The measures are put forward to improve the offshore adaptability of multiphase flow in offshore LNG industry chain. When the anti-sloshing angle of the cover plate is 15°, the liquid fluctuation index (FI) is small and the anti-sloshing resistance is good. The optimal number of transverse anti-sloshing separators is 3, and the anti-sloshing partition number required for unit axial length is 7.5.