Coolant Outlet Temperature Research Articles

Verification of the WWER-1200 reactor dynamic model consisting of one-fuel unit adjacent to two coolant units

As modern control systems engineering imposes limits on mathematical models of control objects, further development, and verification of the mathematical models suitable for power control system synthesis of nuclear power facilities is an ongoing problem. This article deals with the low-order dynamics model with lumped parameters of the Russian-designed pressurized water reactor, as well as its verification with experimental data from the full-size simulator of the WWER – 1200 nuclear reactor within two tests related to changing the position of Group 12 of CPS CR and changing the inlet coolant temperature. This model was created as a MATLAB S-function lv.2 model because of its capability to handle any type of signal. Within this approach, the equation describing the coolant heating process is represented as a «two well-stirred tanks in series» model. The article demonstrates the upside of the given approach in comparison with the conventional approach, where the average temperature of the coolant is determined as an arithmetic mean of inlet and outlet coolant temperatures, respectively, on the basis of the test with a sudden change of the reactor inlet coolant temperature. In the frequency domain, the authors carry out stability analyses of the given model in a state-space form in relation to different external disturbances. Conclusions about the suitability of the given model as a fifth-order control object for parametric synthesis of a controller for the power control system of a nuclear power facility are drawn.

Hybrid mechanistic and neural network modeling of nuclear reactors

An accurate and efficient model is the foundation for dynamic characteristics analysis and control design of nuclear reactors. Nevertheless, the widely-used mechanistic models of nuclear reactors inevitably have some deviations from the actual reactors due to inaccurate model parameters and model assumptions. This paper proposes a hybrid mechanistic and neural network modeling method for nuclear reactors to eliminate or minimizing these deviations. The high-efficiency point reactor kinetics model was adopted as the mechanistic reactor core model, and the simulation results obtained using the commercial program RELAP5 were taken as the reference operational data, based on which the reactivity feedback in the mechanistic model that is difficult to be accurately determined during reactor operations was calibrated using a genetic algorithm optimized BP neural network. Dynamic simulation results of a Generation III large pressured water reactor under three typical reactivity change transients show that the core power and outlet coolant temperature obtained with the hybrid model match much better with the reference results than those of the mechanistic model, demonstrating that the hybrid modeling method can improve the accuracy of the mechanistic reactor model effectively. This study can provide a valuable reference for accurate and efficient modeling of complex systems.

Neutronic and thermal-hydraulic calculations under steady state and transient conditions for a generic pebble bed fluoride salt cooled high-temperature reactor

Here, we develop multiphysics coupled neutronics/thermal-hydraulics models for a recently available generic Fluoride-salt-cooled High-temperature Reactor (FHR) at equilibrium core burnup conditions with reactivity control mechanisms. We utilized the pebble bed reactor transient tool KP-AGREE with multigroup homogenized cross-sections generated by the continuous energy Monte Carlo neutron transport code Serpent to simulate transient events for an FHR. Comparing global reactor parameters and safety characteristics between Serpent and published results to standalone neutronic calculations in KP-AGREE verifies our initial conditions for our transient models. This work explores three separate transients: a loss of flow accident, an overcooling accident, and a total control rod withdrawal accident. The boundary conditions of these scenarios come from either transient benchmark definitions of a gas-cooled pebble bed reactor or transient analysis of a similar FHR design. For the loss of flow accident, our predicted peak fuel and coolant outlet temperatures show a similar response to published values, albeit slightly higher, with differences between values attributed to our modeling assumptions. The overcooling transient simulation predicts a 52 K temperature increase in the maximum fuel kernel temperature and an approximately 32.6% increase in total core power due to the negative coolant temperature feedback of the FHR design. Our control rod removal transients predicted a 235 K increase in maximum fuel kernel temperature and a 107.5% increase in total core power. For all transient cases, the fuel temperature remained significantly lower than the temperature limit, but coolant outlet temperatures for the reactivity-initiated accident exceeded external core material temperature limits.

Benchmarking FFTF LOFWOS Test# 13 using SAM code: Baseline model development and uncertainty quantification

The development and deployment of advanced reactors, such as the sodium-cooled fast reactor (SFR), relies on sophisticated modeling tools to ensure the safety of the design under various transients. The predictive capability of these advanced modeling tools requires validation to garner trust in supporting the licensing of the advanced reactors. For this reason, the International Atomic Energy Agency (IAEA) initiated a coordinated research project (CRP) in 2018 for the analysis of the Fast Flux Test Facility (FFTF) Loss of Flow Without Scram (LOFWOS) Test #13.In this study, we present and discuss the benchmarking efforts of the modern system code SAM on the FFTF LOFWOS Test #13. The SAM baseline model was developed according to the benchmark specification, which included a detailed core model with reactivity feedback. Generally, good agreement was observed between the baseline results and benchmark measurements; however, discrepancies persisted, particularly in predicted fuel assembly coolant outlet temperatures. Utilizing the baseline model, uncertainty quantification (UQ) and sensitivity analysis (SA) were conducted with the assistance of various statistical learning and machine learning methods, including kernel density estimation, Gaussian processes, and Sobol indices. Following the baseline model prediction and UQ and SA results, we discuss the reasons for the simulation discrepancies and propose further improvements to the model. This benchmarking effort adheres to the best-estimate plus uncertainty approach and can serve as a valuable example for supporting risk-informed licensing of advanced reactors.

Thermal-hydraulic CFD simulation of PWR 5 × 5 bowing fuel assembly

To investigate the effect of fuel assembly bowing on coolant flow and heat transfer, three-dimensional thermal–hydraulic characteristics of 5×5 bowing fuel assembly are investigated using CFD simulation. The effects of different bowing sizes (1 mm and 2 mm) on the coolant thermal–hydraulic characteristics under three patterns of bowing shapes (C-shape, S-shape, and W-shape) of fuel assembly are revealed. The results show that in case 6 bowing of the fuel assembly reduces the average coolant outlet temperature by 0.37 k. Compared with normal conditions, the pressure, velocity, and temperature of the corner channel and the side channel are more affected by bowing than the middle channel. The research has reference value for fuel assembly design.

Hybrid concentrator photovoltaic/membrane distillation system for potable water production using new fabricated PS/ZIF_L membrane

A hybrid system is proposed to use solar energy as a heating source for the membrane distillation unit. Concentrating photovoltaic needs an efficient cooling system to manage the excess thermal load. Two microchannel heat sinks were proposed to keep the cells from thermal degradation and simultaneously transfer the excess thermal energy to the membrane distillation unit. The results showed a maximum coolant outlet temperature of 59 °C, which is adequate for the membrane distillation unit. A new composite electrospun nanofibrous membrane was successfully synthesized to reduce unfavorable membrane wettability. First, ZIF-L nanoparticles were synthesized and characterized to prove successful preparation, then used as a nanofiller with polystyrene as the polymer membrane matrix for the first time. SEM, XRD, FTIR, static water contact angle, membrane thickness, and porosity were introduced to prove nanofillers' successful preparation and encapsulation. The antiwetting phenomenon was proven by the measured contact angle of 160°. Furthermore, the fabricated membrane was tested experimentally on a lap scale direct contact membrane distillation unit with a productivity of about 4 kg/m2 h and 18 ppm water quality at 55 °C hot water temperature. Also, the introduced membrane outperformed the productivity of the commercial PVDF membrane at all examined operating conditions.

Performance analysis of a new mechanical superheat coupled-orc refrigeration system with thermoelectric conversion

This paper proposes a new refrigeration and energy conversion system, namely Expander Mechanical Overheating-Organic Rankine Cycle (EMO-ORC) system. Compared with the existing carbon dioxide (R744) refrigeration system, the new system can not only improve the coefficient of performance (COP) of the system and reduce the discharge pressure, but also effectively recover the waste heat of the system, and convert it into electrical energy. Simulation were conducted to compare its system performance with R744 refrigeration system (with heat exchanger), at the same time, the effect of different factors on the performance of new system is analyzed. The results demonstrate that, at the same evaporation temperature and gas cooler outlet temperature, compared with the system (with heat exchanger), the COP of the new system increased by 8.2% and 8.9% on average, respectively. And the discharge pressure decreased by 0.88% and 0.79%, respectively. In the given superheat degree range, compared with the system(with heat exchanger), the COP of the new system is increased by 4.5% on average, and increased by 10.2% at the highest level. Under the most given working conditions, the cooling capacity of new system is higher than that of the system (with heat exchanger), and the power consumption is lower than that of the system (with heat exchanger). In the new system, the narrow point temperature difference and the outlet temperature of the first stage gas cooler have a greater impact on the COP, with the increase of both, the COP of the new system increases by 5.6% and decreases by13.7%, respectively.

Numerical analysis and optimization of a novel photovoltaic thermal solar unit improved by Nano-PCM as an energy storage media and finned collector

An increment in temperature will deteriorate the efficiency of photovoltaic systems dramatically. The application of a cooling mechanism can reduce the operating temperature and perform a better operation. Therefore, in this research, a nanoparticle-based phase change material (PCM) layer is combined with finned collectors as the condenser for higher electricity generation in photovoltaic/thermal (PV/T) collectors. The temperature distribution of the PCM layer in both solid and fully melted phases are poked to identify the effect of the Nano-PCM layer on the mentioned system efficiency. Afterward, a big data collection is created and employed to introduce a deep learning model to tune and find the best network. Ultimately, the gilt-edged network is optimized using LINMAP, TOPSIS, as well as Shannon entropy decision makings and Gray Wolf Optimization (GWO), Bat algorithm (BA), Particle swarm optimization (PSO), and Biogeography-based optimization (BBO) techniques. The results indicated that the maximum thermal efficiency values are obtained at wind speed values less than 2 m/s and DNI higher than 950 W/m2. Considering their mentioned impacts on thermal efficiency, this variable of the renewable unit changes by 10–24%. Moreover, the optimal condition reveals the optimum melted PCM, the coolant outlet temperature, and the electrical efficiency of 6.497 kg, 37.72 °C, and 13.92%, respectively. It is concluded that compared with the traditional systems, enhancement in electrical efficiency can be achieved by Nano-PCM layer utilization as cooling media.

Thermodynamic performance and the exergy destruction of the transcritical CO2 two-stage compression and ejector expansion direct cooling ice making system

The transcritical CO2 direct cooling technology was used for the first time in the indoor venues of the 2022 Beijing Winter Olympic Games. The technology has a series of advantages, such as compact structure, uniform ice temperature, energy saving and environmental protection. In order to further reduce the power consumption and improve the performance, two-stage compression and low-pressure ejector direct cooling ice making system (TCLES) and two-stage compression and intermediate-pressure ejector direct cooling ice making system (TCIES) are studied. The performance of the systems is simulated by constructing a one-dimensional thermodynamic model. The impacts of the gas cooler pressure, gas cooler outlet temperature, evaporation temperature and intermediate pressure on these systems are considered. It is showed that TCLES and TCIES have their own advantages when the system is without and with heat recovery, and found that two-stage compression improves the system performance more than the ejector when only the cooling performance is considered. On this basis, conventional exergy and advanced exergy analysis of both systems are carried out. Advanced exergy analysis shows that exergy destruction can be avoided mainly in low-pressure and high-pressure compressors of both systems. Besides, the influence of gas cooler pressure on exergy destruction characteristics is discussed. When controlling the gas cooler pressure at 9.0 MPa, the avoidable endogenous exergy destruction of compressors and ejector is reduced by a maximum of 4.14% and 13.92% for TCLES and reduced by a maximum of 16.15% and 28.04% for TCIES.

Next generation of ejector-supported R744 booster systems for commercial refrigeration at all climates

The pernicious effects of synthetic refrigerants on different environmental aspects leave natural refrigerants as the only alternative for vapour compressions systems. Among natural refrigerants, CO2 (R744) has become the preferred choice for commercial refrigeration at almost any location and climate. However, efficient R744 refrigeration systems for warm climates have a great level of complexity, implementing technologies such as mechanical subcooling or ejector that increase the investment costs. The goal of the novel hybrid configuration presented in this work is to simplify ejector-supported R744 commercial refrigeration systems while maintaining all the benefits of the ejector implementation in transcritical operation mode. Moreover, utilization of a low-pressure accumulator layout in the subcritical mode removes all the practical challenges related to the booster layout operating at low ambient temperatures. This solution is based on: (i) MT and LT compressor suction groups, (ii) non-superheated MT evaporation with increased evaporation temperature, and (iii) ejector utilization throughout the year. The ejector is actively operated as a high-pressure-control device at elevated ambient temperatures ('summer mode'), while it is passive and acts as a check-valve at lower ambient temperatures ('winter mode'). The experimental campaign performed proved that this novel system configuration is more energy efficient than booster systems with parallel compressors at any condition, improving the COP by around 40 % at the most extreme gas cooler outlet temperatures tested, i.e., 40 °C (summer mode) and 10 °C (winter mode).

Experimental study on rapid cold start-up performance of PEMFC system

The cold start-up of a proton exchange membrane fuel cell is considered one of the main factors affecting the commercialization of fuel cell vehicles. In this study, an automotive fuel cell system was designed and tested for cold start-up at low temperatures. In the absence of PTC (Positive Temperature Coefficient) heating device, the stack was directly loaded to generate heat, which provided the cold start-up characteristics of system at low temperatures. Cold start-up process and purging control strategies were analyzed at −20 °C and −30 °C. It was found that the fuel cell system could produce 50% power in 25 s at −20 °C, the coolant temperature's heating rate was 0.78 °C/s, the coolant outlet temperature could reach 20 °C within 40 s and no apparent low voltage of single cell occurred. While, the cell close to the end plate had low cell voltage and reverse polar phenomena throughout the −30 °C cold start-up process. The heating rate of the coolant temperature was 0.44 °C/s, and the temperature of coolant outlet reached 20 °C within 90 s. The purging time ranged from 180 to 260 s according to the voltage drop value of stack and the ohmic resistance of stack was 360–470 mΩ after the high-volume air purging at different tests. After 30 cold start-up tests, the rated point performance of the stack declined by about 1%, and the consistency of cell voltages did not change significantly. Future work will focus on optimizing cold start-up strategy and speeding up purging time to minimize the performance impact of the cold start-up.

High-fidelity neutronics and thermal-hydraulics analysis of helical cruciform fuel based on small modular FHR

Fluorine High-temperature Reactor (FHR) is a novel reactor type without water-cooling, but with a high outlet temperature. Small Modular FHR is convenient for modular assembly and transportation. Therefore, it is suitable for remote and water shortage areas to provide efficient and clean nuclear energy. The neutronics and heat transfer of the fuel are the key issues when the small modular FHR has high thermal power output. This research proposes the fuel – TRISO (TRi-ISOtropic) particles dispersed in Helical Cruciform Fuel (HCF). HCF can be self-supported in radial direction, no additional grid-spacers are required, which can decrease the pumping power and improve the efficiency of the reactor system. For small modular FHR, it can be disassembled, transported, and assembled better without grid-spacers and simplifying the core structure. The heat transfer capacity of the coolant also could be further improved because of the special structure of HCF. Based on the Monte-Carlo particle transport code MCNP, the neutronic characteristic from the assembly to the whole core of FHR is studied. By obtaining the fission power distribution in near-critical condition, the thermal-hydraulics of the single most heated HCF and 7 bundle HCF in the heated assembly are calculated. In order to preliminary analyze the thermal-hydraulics of the whole core scale, the thermal-hydraulics analysis of porous media is carried out for 1/6 core. The isotropic resistance tensor and thermal equilibrium porous model have been introduced with reasonable approximation, and porous resistance relation has been carried out. The radial power peak factor is 1.185 and the axial power peak factor is 1.435 in near-critical condition, which proves the arrangement of the HCF and the control rods can flatten the power distribution effectively. The average temperature of the coolant outlet in the active region of the core is 974.44 K, and the average temperature of the upper plenum outlet is 972.85 K. High coolant outlet temperature can ensure effective supply of high-temperature process heat. And the highest temperature of the fuel is 1271.49 K, which is lower than the limitation 1573 K. The parameters of this research can supply the neutronics and thermal-hydraulics references for further FHR design.

Liquid Cooling Flow Field Design and Thermal Analysis of Proton Exchange Membrane Fuel Cells for Space Applications

Proton exchange membrane (PEM) fuel cells are a promising technology with many features, including having a high energy density, efficiency, lightness, and producing energy directly instead of storing it. PEM fuel cells are currently used in mobile vehicles, military applications, portable systems, stationary systems, and air-independent propulsion systems for sea and space. Elimination of the cooling problems associated with PEM fuel cells in space applications is of great importance to produce more efficient systems. With this motivation in mind, this study examined PEM fuel cell elements and cooling flow channel design for space applications. The effect of the designed flow channel on the PEM fuel cell temperature distribution was investigated. Five different PEM fuel cell cooling channels were designed and modeled computationally, and the most suitable cooling channel design was selected based on the thermal analysis. While modeling the PEM fuel cell, space environment operating conditions, pure reactant supply (oxygen and hydrogen), electrochemical reaction in the membrane, physical properties of liquid coolant, physical properties of fuel cell elements, and heat transfer in the fuel cell were considered. The temperature distribution obtained as a result of the thermal analysis was examined, and it was seen that the PEM fuel cell cooling channel design was successful in maintaining the operating temperature of the PEM fuel cell. According to the data obtained, the cooler inlet temperature is approximately 40°C and the cooler outlet temperature is approximately 75°C in flat serpentine design. These values were obtained as a result of the analysis made with a mixture of 50% ethylene glycol and 50% water selected as the liquid coolant. As a result, a fuel cell can be formed by producing a fit bipolar plate with the analyzed PEM fuel cell cooling flow channel design, and current density and homogeneity can be determined by applying single-cell performance tests to the fuel cell.

The Influence of Thrust Chamber Structure Parameters on Regenerative Cooling Effect with Hydrogen Peroxide as Coolant in Liquid Rocket Engines

Liquid rocket engines with hydrogen peroxide and kerosene have the advantages of high density specific impulse, high reliability, and no ignition system. At present, the cooling problem of hydrogen peroxide engines, especially with regenerative cooling, has been little explored. In this study, a realizable k-epsilon turbulence model, discrete phase model, eddy dissipation concept model, and 10-step 10-component reaction mechanism of kerosene with oxygen are used. The increased rib height of the regenerative cooling channel causes the inner wall temperature of the engine increases, the average temperature of the coolant outlet decreases slightly, and the coolant pressure decreases. The overall wall temperature decreases as the rib width of the regenerative cooling channel increases. However, in the nozzle throat area, the wall temperature increases, the average coolant outlet temperature decreases, and the coolant pressure drop increases. A decrease in the inner wall thickness of the regenerative cooling channel results in a significant decrease in the wall temperature and a small increase in the average coolant outlet temperature. These findings contribute to the further development of the engine with hydrogen peroxide and can guide the design of its regenerative cooling process.

Comprehensive Performance Analysis and Correlation Fitting of R744 and Its Mixture Used in Refrigeration and Heat Pump Systems

Abstract In this paper, the performance of R744 and R744/R170 mixed refrigerants in refrigeration and air source heat pump systems is studied by the simulation method. The change trend of coefficient of performance (COP), refrigeration/heat capacity, power consumption with discharge pressure, and the ratio of R744 is analyzed. In addition, optimal parameters of the system are discussed in detail with the change of evaporation temperature, outlet temperature of the gas cooler, and different proportions of R744. The results show that when the discharge pressure is 8–12 MPa, there is a critical ratio of R744. When the ratio of R744 is less than the critical ratio, the optimal pressure of the system increases with the increase of the ratio of R744, and when the ratio of R744 is higher than critical ratio, the optimal pressure of the system decreases with the increase of the ratio of R744. The change trend of COP with the ratio of R744 is first decreasing and then increasing, the optimal discharge temperature of the system increases with the increase of the ratio of R744, and the change trend of optimal discharge pressure with the ratio of R744 is first increasing and then decreasing. In addition, when the evaporation temperature is 233–253 K and the gas cooler outlet temperature is 308–318 K, the average optimal pressure and temperature of R744/R170 (25/75) are 11.64% and 8.06% lower than R744, respectively. And it is the most suitable refrigerant to replace R744. Finally, the optimal performance parameter correlations of R744, R744/R170 (25/75), R744/R170 (50/50), and R744/R170 (77.6/22.4) under the given conditions are fitted through the simulation data.

Energetic and entropy analysis of a novel transcritical CO2 two-stage compression/ejector refrigeration cycle for shipboard cold chamber

The adverse effects of global warming and climate change require critical measures for marine refrigeration technology because of its impact on GHG emissions. A novel transcritical CO2 two-stage compression/ejector refrigeration cycle for shipboard cold chamber is proposed in this research. A comparative analysis was conducted between the basic transcritical CO2 two-stage compression cycle and the cycle equipped with a two-phase ejector considering the COP. Meanwhile, the refrigeration cycle was analyzed using entropy analysis to elucidate the distribution of irreversible losses in each component of the two-stage compression/ejector refrigeration cycle, and the effects of system parameters such as the evaporating and gas cooler outlet temperatures as well as the intermediate and discharge pressures on the cycle were investigated. The results showed that the ejector had the largest power capability loss, accounting for 26.95 % of the overall system, which is followed by the low pressure compressor with 26.06%. The COP of basic and ejector system significantly increase as the gas cooler outlet temperature and intermediate pressure decrease as well as the evaporating temperature increases. Furthermore, the entropy production of the system components decreases gradually with increasing evaporating temperature, with the greatest reduction in the ejector. In addition, the entropy production of the two-phase ejector remains constant with the increase of the high pressure side discharge pressure and gas cooler outlet temperature.

Long-term performance evaluation of CO2 heat pump water heater under different discharge pressure control strategies

CO2 heat pump water heater has raised considerable attention as an environmentally efficient technology for hot water production. However, after long-term operation, the deterioration of component performance will not only directly cause system performance degradation, but also lead to a deviation of discharge pressure from the actual optimum under different discharge pressure control strategies, further resulting in additional performance loss. So far, the additional performance loss in the long run has not been in-depth investigated. In this study, based on a validated system model of CO2 heat pump water heater with component performance degradation factors, the long-term additional loss of system performance under eight different discharge pressure control strategies are compared. The results reveal that additional performance loss in the long-term operation can be significant under certain control strategy and working conditions. As for the investigated system, the control strategy with the parameter group of ambient and gas cooler outlet temperatures is favorable for application under the nominal operating condition with long-term degradation of heat exchangers, and the average additional loss of COP (coefficient of performance) can be decreased to 0.62%. As for the compressor degradation, the optimal refrigerant charge management strategy is preferred with an average COP loss as low as 0.05% under certain working conditions. In facing with year-round performance degradation, the control strategy with the parameter group of evaporating temperature and gas cooler outlet temperature shows better robustness, since the average additional annual performance loss can be reduced to only 2.52%.

Thermodynamic performance evaluation of an ejector-enhanced transcritical CO2 parallel compression refrigeration cycle

A parallel compression cycle is one efficient approach to improving the transcritical CO2 refrigeration cycle performance. This paper proposes a modified parallel compression transcritical CO2 refrigeration cycle with an ejector and a sub-cooler to further enhance the cycle performance. The thermodynamic analyses based on the energetic and exergetic analyses are conducted, and the influences of the parameters, including discharge pressure, flash pressure, gas cooler outlet temperature, and evaporation temperature, are discussed. The particle swarm optimization method is used to get the optimal discharge pressure and flash pressure and the temperature reduction in the sub-cooler with respect to the maximum COP. The performance comparisons between the conventional cycle and the modified cycle are presented. The results illustrate that the maximum improvements in COP and volumetric refrigeration capacity reach 15.8% and 17.1%. The utilization of the ejector and sub-cooler could reduce the optimal flash pressure by 16.4–33.0% and the compressor displacement by 11.4% compared with the conventional cycle. The ejector plays a dominant role in performance improvement at a high gas cooler outlet temperature. The exergy destruction analysis shows that the first-largest system exergy destruction ratio of 31.5% in the ejector-enhanced cycle is caused by the gas cooler, and its second-largest exergy destruction is generated in the two parallel compressors instead of the expansion valves in the conventional cycle.

Experimental analysis of a transcritical heat pump system with CO2 refrigerant

Today, it is seen that increasing environmental pollution is getting ahead of the increasing energy need. Therefore, more environmentally friendly and more economical refrigerants are needed. In this context, carbon dioxide appears as a natural refrigerant in cooling systems and heat pump (HP) systems, and it has been widely used in recent years. In this study, a single-stage heat pump system with a CO2 refrigerant, with a transcritical cycle, has been experimentally studied. The system is designed as a water-to-water heat pump. The performance of the system has been determined experimentally. In the system, capillary pipes with a diameter of 2.00 mm and two different lengths are used. It is aimed to create different evaporation pressures with two capillary tubes. The first capillary tube is 2.40 m long and the second is 1.20 m long. Gas cooler pressures, gas cooler and evaporator cooling water mass flow rates were kept the same for both cases. A certain gas charge was made and measurements were made for both cases. Thermodynamic analysis and comparison of the system were made. In the short capillary tube system, it was observed that the COPHP value was 7.2% higher, the CO2 mass flow rate increased by 9.1% to achieve the same gas refrigerant pressure value, and the power consumption in the compressor decreased by 1.8%. In addition, the gas cooler outlet temperature, the evaporator outlet temperature and the change in ambient temperatures, as well as the exergetic destruction and exergetic efficiencies in the system and system components are presented in figures with EES.

Characteristic analysis of natural circulation residual heat removal in small reactor

In order to study the characteristics of small helium-xenon cooled nuclear reactor that only relies on natural circulation to remove residual heat after shutdown, this paper carries out geometric and physical modeling of helium-xenon cooled nuclear reactor, and uses CFD to simulate the process of natural circulation residual heat removal. Variation laws of the hot spot temperature on the surface of fuel cladding and the mass flow of helium-xenon mixed gas under different working conditions are calculated, and the transient characteristics of temperature, flow and other related parameters in the system loop are analyzed. The calculation results show that during the natural circulation residual heat removal process, the overall change trend of the hot spot temperature on the surface of the fuel cladding, the average temperature of the primary coolant and reactor outlet temperature first rises to the highest value and then decreases, and the mass flow of helium-xenon mixed gas shows an exponential decay trend; Increasing the initial mass flow of helium-xenon mixed gas and reducing the residual heat of the reactor core can reduce the maximum hot spot temperature on the surface of the fuel cladding. The relevant research results provide a useful reference for the optimal design of natural circulation residual heat removal of helium-xenon cooled nuclear reactor.