Thermal-hydraulic Characteristics Research Articles

Thermal-hydraulic analysis of He-Xe gas mixtures in triangular rod bundle wrapped with different shaped wire wraps

Gas-cooled reactors employing a helium-xenon (He-Xe) gas mixture as the coolant are regarded as one of the most promising technologies for megawatt-scale space energy systems. One technical solution to achieve high power density, reduced mass, and a compact structure in gas-cooled space reactors is the use of fuel arranged in triangular bundles encased with wire wraps. Nevertheless, research on the flow and heat transfer characteristics of He-Xe gas within such configurations remains scarce. In order to enhance the heat transfer performance of He-Xe reactor cores, thermal–hydraulic simulation methods were employed using computational fluid dynamics (CFD) in order to investigate the thermal–hydraulic characteristics within a triangular rod bundle channel equipped with wire wraps. The study examined the impact of wire wrap structures on velocity and temperature fields, inter-subchannel mixing, and the distribution of hot spots. The findings indicate that the wire wrap structure has the effect of promoting transverse flow, inter-channel mixing and vortex formation. Conversely, this also gives rise to the issue of hot spots, particularly at the contact angles between the wire wrap and the fuel rod. At a wall heat flux of 91,477.3 kW m−2, the maximum temperature at the circular wire wrap hot spot can reach 1217 K, while the average wall temperature of the corresponding cross-section is only 770 K. Furthermore, the flow and heat transfer characteristics of three wire wrap geometries—circular, rectangular, and trapezoidal—were evaluated and compared across a Reynolds number range of 2.6 × 104 to 1.4 × 105. The findings indicate that the trapezoidal wire wrap configuration results in the lowest wall hot spot temperature and the smallest temperature inhomogeneity. Furthermore, an analysis of the heat transfer coefficients (Nusselt number) and thermo-hydraulic performance ratios (THPR) demonstrates that the trapezoidal wire wrap exhibits superior heat transfer performance compared to the other two geometries.

Thermal-Hydraulic Characteristics of an Earth Air Heat Exchanger: An experimental analysis

The pipe layout design has a great effect on the thermal-hydraulic characteristics of earth air heat exchanger (EAHE) systems. So, in the current study proposed four new buried pipe design configurations; low to high to low, high to low to high, spiral, and circular, in addition to the straight or uniform for comparison. These five configurations are tested and analyzed experimentally depending on the thermo-hydraulic performance for summer cooling requirements with variation of Re in the range of 18041 – 40843. The results show that changing the uniform design of the EAHE with fixed pipe length enhances both the heat transfer process and pressure loss values. At the same operating conditions, the circular design has the best performance compared to the other ones. For all pipe shapes, the cooling effect increases with the increase of air Re. The thermal- hydraulic performance of the circular design pipe is higher than that of the other pipe designs. The highest coefficient of performance (COP) average values that can be obtained at Re = 18041 is 3.05 for circular shape and enhances by 48.08 % compared to uniform shape. The effectiveness of EAHE with circular shape is improved by about 3.52 % compared to uniform shape at Re = 18041. Spiral design is optimum design based on the Nu value which reaches about 48 with enhancement 12.56% and 0.34 % compared to uniform and circular shapes respectively, at Re = 40843. The hydrothermal performance factor is highest in the case of circular shape with value about 21.9 at Re = 21257. By increasing Re, the drawbacks of the increasing in the total entropy generation are reflected negatively on the exergy efficiency. The specific cost of the circular shape at Re = 40843 is the optimum value by about 0.7 $/W. Spiral and circular shapes have a decrease of CO2 emissions less than uniform shape by percentage varied from 2.93 % to 13.84% for decrease in the Re from 21257 to 40843. It is concluded that using EAHE with four new shapes is highly efficient in increasing cooling capacity and energy consumption in buildings.

Thermal hydraulic performance and characteristics of a microchannel heat exchanger: Experimental and numerical investigations

Abstract This paper presents extensive fluid flow and Heat Transfer studies conducted through an experimental setup followed by a detailed three-dimensional (3D) numerical analysis of the same setup using a commercial package for computational fluid dynamics (CFD), known as CFD-ACE® for additive-manufactured counter-flow AlSi10Mg microchannel heat exchangers (MCHEs). A detailed 3D computational model of the experimentally tested MCHEs was built and analyzed using the commercial software CFD-ACE® for the same experimentally tested operating conditions. The computational model results are in good agreement with experimental data of tested MCHE within +2% to +7% and ~0% to -13.5% variation for cold and hot fluids for the entire set of design of experiments (DoEs). This percentage disagreement may be due to various factors, such as manufacturing deviation within tolerance, longitudinal conduction, variation in the thermal conductivity of the material after heat treatment, variation in environmental temperature, sensor deviation, and surface roughness of internal channels. Instead of Stainless steel (SST), AlSi10Mg was used because of its lower manufacturing cost because AlSi10Mg was lighter than SST, though its thermal conductivity is almost ~8-10 times more than that of SST. A higher thermal conductivity is not good for MCHEs because it leads to higher longitudinal conduction, which eventually degrades the performance of MCHEs in terms of effectiveness. MCHE effectiveness is also reduced by ~12% to 18% owing to longitudinal conduction from ideal effectiveness.

Numerical study on heat transfer of two-phase fluid in helical coil pipe under ocean condition

The thermal hydraulic characteristics and heat transfer of two-phase fluid in helical coil once-through steam generator under ocean conditions like rolling and heaving motions are studied numerically. A CFD model is established to analyze the effects of motion parameters like amplitude, period and rolling radius and the heat flux distribution are discussed. The analysis shows that the overall heat transfer decreases under ocean conditions, but the overall deterioration is limited, indicting the helical coil pipe has the stability for ocean conditions. The additional forces like Coriolis, centrifugal and inertial forces introduced by rolling motion are analyzed theoretically and the result shows it detorts the original two main vortexes responsible for high heat transfer due to its spiral geometry, making heat transfer fluctuates up and down periodically near the steady state value. As rolling height increases, the heat transfer is nonlinear due to the competition between Coriolis force and centrifugal and inertial forces. As rolling amplitude increases, the heat transfer variation increases and the local heat transfer deterioration is severely aggravated, indicating high rolling amplitude should be avoided as possible. Increasing rolling period makes heat transfer behavior more approximate to static case as gravity and centrifugal force due to spiral geometry is dominate. Under heaving motion, the overall heat transfer decreases, and increasing heaving amplitude and decreasing period make the fluctuation more severe.

Steady-state thermal–hydraulic analysis of an NTP reactor core based on the porous medium approach

Nuclear thermal propulsion (NTP) is a promising advanced technology which has attracted wide attention in recent years. The reactor core is an essential component of an NTP system and the corresponding thermal–hydraulic analysis is necessary. In this study, the porous medium approach was applied to the simulation of a two-pass NTP reactor core which consists of the porous prismatic cermet fuel elements. The thermodynamic property models of hydrogen and the fuel element materials were implemented, as well as the empirical correlations of the heat transfer coefficient and the friction factor. The three-dimensional simulation of a single fuel element was carried out and the results were compared against another code. The code-to-code comparison verified the applicability of the porous medium approach. The three-dimensional model of the two-pass NTP reactor core was established and the steady-state simulation was carried out. The distribution patterns of the parameters are determined by the thermal–hydraulic characteristics of the reactor core, including the nonuniform heat release, contact heat conduction and folded-flow scheme. The full-core heat-flow adaptability analysis is realized, which provides a reference for the thermal–hydraulic safety analysis of the NTP reactor.

Improved Heat Transfer Capabilities of Nanofluids—An Assessment Through CFD Analysis

AbstractConventional fluids used in fission‐based water‐cooled nuclear reactors have lower heat transfer coefficients (HTCs) and thermal conductivity, which has led researchers to explore high‐performance fluids that can enhance heat transfer in routine operation and prevent core meltdown in the case of accidents. It is important to investigate a wide range of fluids that can help designers improve thermal hydraulic characteristics, such as HTC, critical heat flux, and minimum departure from nucleate boiling ratio (MDNBR). In this study, the effectiveness of nanofluids in enhancing heat transfer parameters, including thermal conductivity and heat capacity, was investigated. Four different nanofluids (Al2O3–H2O, ZrO2–H2O, Ag–H2O, and Si–H2O) with pure water as the primary coolant in an HPR‐1000 nuclear reactor were compared using computational methods. Due to computational limitations, only the flow channel among four fuel rods with the highest power density in the core was simulated using Eulerian computational fluid dynamics. The results of this study show that silver water (Ag–H2O) nanofluid outperformed other nanofluids and pure water. It had a higher average HTC and MDNBR, with a 67.15 % and 45.23 % improvement, respectively, compared to pure water. The fuel rod wall temperature was also reduced by 28.5 K with Ag–H2O compared to water. Comparison of current simulated results with literature data shows a good agreement.

Steady and transient analysis on thermal hydraulic characteristic of helical coiled once-through steam generator of liquid metal fast reactor

A transient model for thermal–hydraulic characteristics of helical coiled once-through steam generator (HCOTSG) of liquid metal fast reactor was established based on global discrete grid method. The model meshed the liquid metal circuit and water-steam circuit. Meanwhile, unsteady heat conduction equations were built to accurately simulate coupled heat transfer between two sides. Four-equation drift-flux method was adopt for water-steam flow. Taking lead–bismuth fast reactor as example, thermal–hydraulic characteristics of HCOTSG were first calculated under steady conditions. It was found that heat flux distribution along steam generator is extremely uneven, and the difference between maximum and minimum wall heat flux reaches hundreds of times. Then, the transient response was simulated when inlet conditions of primary side were perturbed by step changes, and it was found that maximum wall heat flux increases from 1175.5 kW/m2 to 1365 kW/m2, increasing by nearly 16 %, when inlet lead–bismuth temperature step increases from 450°C to 480 °C.

Investigation of the thermal-hydraulic characteristics of SCO2 in a modified hybrid airfoil channel

The performance of printed circuit heat exchangers (PCHE) is critical to ensuring the efficiency and compactness of supercritical carbon dioxide (SCO2) Brayton cycle systems used in advanced nuclear energy. In order to improve the performance of the airfoil fin channel PCHE, the effect of the airfoil fin size on the channel performance is investigated and the effect of the airfoil fin arrangement parameters on the channel performance is analyzed by the Taguchi method. Particularly, a modified hybrid airfoil fin channel adapted to the changes in thermophysical properties of SCO2 is proposed. The results show that the heat transfer characteristics of the PCHE channel are enhanced and the flow characteristics are weakened with the reduction of the airfoil fin size, and the comprehensive performance firstly increases and then decreases. Taking the comprehensive performance of the channel as the optimization objective, the best combination of airfoil fin arrangement parameters is 2 mm for transverse spacing, 10 mm for longitudinal spacing, and 4 mm for staggered spacing. Compared with the traditional airfoil finned channel, the modified hybrid airfoil fin channel has significantly improved the comprehensive performance by 2.8%–13.2 %.

Numerical study on benchmark analysis of NACIE-UP facility with uniform and non-uniform power distribution

The NACIE-UP (NAtural Circulation Experiment-Upgrade) facility is located at the ENEA Brasimone Research Centre (Italy) and is designed to investigate the thermal–hydraulic properties of Lead-Bismuth Eutectic (LBE) within a wire-spaced assembly under uniform and non-uniform power distribution conditions. This benchmark exercise proposed by ENEA is based on previous experiment results, intending for development and validation of CFD/TH system code, stand-alone CFD simulation, etc. In this study, the thermal–hydraulic characteristics of Fuel Pin Simulator (FPS) are analyzed, which contains inlet bend and outlet section. ANSYS Fluent solver is applied with the COUPLE algorithm of RANS SSTk-ω model. Cheng&Tak correlation and computational conditions are implanted into Fluent in the form of UDFs. Moreover, calculations were performed for ADP10, ADP06 and ADP07. The results show that the RMSEs of ADP10SS1 and ADP10SS2 are 2.52 K and 3.69 K, 7.05 K and 8.48 K for ADP06SS1 and ADP06SS2, respectively, which indicate that the adopted models have good prediction ability for the temperature of the experimental conditions. Meanwhile, the heat transfer characteristics of different sub-channels and sections are investigated and compared with the correlations of Ushakov, Mikityuk, Kazimi and Carelli. The experimental and simulation values of the uniformly heated ADP10 are in good agreement with the correlations, while there is a large deviation for the non-uniformly heated ADP06. Therefore, it is necessary to develop new correlations for the heat transfer characteristics of LBE in wire-wrapped bundle. Above all, this study provides quantitative and qualitative analysis for verification and validation of CFD/TH system code and stand-alone CFD simulation.

Investigation of the Thermal Effects of MgO and ZnO Nanoparticles in a Pressurized Water Reactor Coolant with Computational Fluid Dynamics Model

When nanofluids are used as reactor coolants, they provide more effective heat transfer with their increase in thermal conduction properties. This plays an important role in energy production by increasing the efficiency of nuclear reactors. The present study delves into the thermal-hydraulic ramifications of utilizing nanofluids as coolants in the VVER-1000 nuclear reactor. Specifically, the thermal-hydraulic characteristics, encompassing parameters such as coolant temperature and departure from nucleate boiling ratio, were scrutinized in light of the incorporation of magnesium oxide (MgO) and zinc oxide nanoparticles. While performing these analyses, not only uranium but also thorium was used in the core as reactor fuel. Considering the emergence of thorium as a potential fuel material in nuclear technology, its inclusion in the fuel composition contributed to the originality of the research. With the addition of 0.2% MgO nanoparticles to a VVER nuclear reactor using 5% thorium dioxide (ThO2) fuel, the coolant temperature as a result of the channel flow was determined as 617.4 K (while 613.7 K for the light water). When employing thorium fuel (with an equivalent nanoparticle concentration), the maximum temperature exhibited an approximate increase of 3 deg compared to uranium fuel. With the addition of 0.2% MgO nanoparticles, the enthalpy value at the end of the channel was 1303.6 kJ/kg when using 5% ThO2 fuel, while the enthalpy value was determined as 1295 kJ/kg in 3.7% enriched UO2 fuel. As one of the most important results of the analysis, it was observed that the temperature value of the coolant increased when nanoparticles were used.

Enhanced heat transfer in sandwich heat transfer unit with metal foam: A numerical investigation

In this study, a novel configuration of a sandwich heat transfer unit (SHTU) is proposed, characterized by the partial filling of metal foam on both sides of the fin. The thermal–hydraulic characteristics of the SHTU are investigated numerically using the local non-equilibrium method and Forchheimer-Brinkman extended Darcy model, and compared with those of traditional flat plate-fin heat transfer unit (PHTU). The effect of geometrical parameters, mass distribution of fin and metal foam, and morphological parameters of metal foam on the characteristic of SHTU was explored. Compared to PHTU the Nusselt number of SHTU increases by 13.1% and 27.6%, while the friction factor increases by 6.2% and 33.1% at Reynolds numbers of 100 and 900, respectively. At a Reynolds number of 500, as the filling ratio increases from 0 to 0.95, the Nusselt number, friction factor, and comprehensive thermal performance enhancement increase by factors of 10, 20, and 3, respectively. When the foam fraction increases from 0.30 to 0.90, the thermal performance enhancement improves by 4–5 times within the investigated range. The impact of porosity (ε) and pore density (ω) on the performance of SHTU is not monotonic. The optimal ω was observed to be in the range of 15–20 PPI, while the optimal ε was found between 0.90–0.92.

Investigations on cooling heat transfer of CO2-based mixtures in a novel airfoil fin mini-channel at supercritical pressure

Thermal-hydraulic characteristics of three supercritical CO2-based mixtures (CO2/H2S, CO2/Xe and CO2/propane) in an airfoil fin (AFF) mini-channel adopted in the printed circuit heat exchanger (PCHE) under cooling conditions are comprehensively investigated through numerical simulations. The results show that the CO2/H2S mixture, which has higher critical temperature and larger critical pressure than the pure CO2, exhibits the greatest heat transfer performance among three mixtures. This advantage is particularly pronounced at relatively large Reynolds number, with small mass fraction of the H2S and under near-critical conditions. The overall friction loss of mixtures with the additive mass fraction smaller than 0.3 is comparable to that of the pure CO2. The heat transfer coefficient of the mixtures presents fluctuations during the cooling processes, and this goes against the stable and safe operation of the PCHEs. These fluctuations could be mitigated at relatively small mass flow rate and with small mass fraction of the additive. Three widely-recognized buoyancy criteria are employed to predict the onset of the buoyancy effects in the AFF channel, and the superior heat transfer of the CO2/H2S mixture could be attributed to the fiercer buoyancy effects. Considering the buoyancy effects, modified correlations for the flow and heat transfer of pure CO2 and the CO2-based mixtures in the novel mini-channel are proposed. The maximum deviations of the modified Nusselt number and fanning friction factor correlations are ± 25 % and ± 20 %, respectively.

Thermal-hydraulic characterization of a 50-kW medicinal-aimed aqueous homogeneous reactor (MAHR)

This paper analyses the thermal–hydraulic performance of a proposed 50-kW aqueous homogeneous reactor (AHR) aimed at producing Mo-99. The reactor thermal–hydraulic characteristics are analyzed using ANSYS-FLUENT software and Relap code, and the results are validated through experiments conducted by a prototypic cylindrical sector of the reactor vessel. Boundary conditions in the CFD simulation are set up based on Relap modelling, while CFD outputs are validated by experimental results achieved using the laboratory model. Then, various parameters, including coolant mass flow rate, first cycle pipe diameter, coolant outlet temperature, average fuel solution temperature, and the elevation difference between the reactor and heat exchanger, are optimized using the least-squares optimization method. Results demonstrate that the heat removal system provides sufficient cooling capacity to ensure stable operation of the proposed AHR core by preventing fuel solution overheating and, consequently, boiling (void formation) in the active fuel solution.

Performance evaluation of the SMART passive safety injection system against the SBLOCA scenario with the SMART-ITL facility

A set of system performance tests has been performed and the thermal-hydraulic behaviors were investigated for the passive safety injection system (PSIS) of the SMART design. Major thermal-hydraulic characteristics of core cooling in reactor coolant system and safety injection (SI) in PSIS were investigated using the SMART-ITL. The parametric effects of break size, break location and train number on the PSIS performance were discussed with the relevant SMART-ITL data. Compared with the 2.0 inch SI line break test, the 0.4 inch SI line break test has a milder change of system parameters. The pressure is reduced more quickly, the decrease of water level is slower and the break mass flow rate is higher during the pressurizer safety valve line break than during the SI line break. Major thermal-hydraulic parameters were compared among single, two and full train operation of the PSIS focusing on the effect of train number. It was shown that multiple trains of CMT and SIT were operated independently and the reactor vessel (RV) inventory increased proportionally with the addition of each train. Sufficient SI water was injected into the RV in a passive manner to cool down the reactor core efficiently during the full train test.

Effect of inclination on SB LOCA transient of a floating nuclear reactor in MARS-KS analysis using moving reactor model

As the imperative to reduce Green House Gas emissions grows within the maritime sector, nuclear power emerges as a promising solution. Especially, offshore floating nuclear power plants have garnered significant attention and development efforts from various institutions and nations. These types of reactors provide unique benefits such as extended refueling periods for advanced safety and exceptional mobility, facilitating access to remote regions. However, the external forces are induced by operating on a moving condition, that can impact the thermal–hydraulic characteristics of various hydraulic components in the entire reactor system. Addressing the safety issues of offshore floating reactors requires conducting thermal–hydraulic analyses under diverse oceanic motions. To achieve this objective, this study centered on analyzing accidents in an offshore floating reactor, specifically the BANDI-60, targeting the Small Break Loss of Coolant Accident induced by a double-ended guillotine break in the Direct Vessel Injection line. This study utilizes the system thermal–hydraulic code MARS-KS moving reactor model considering various tilting conditions and a BANDI-60 nodalization with a quarter-divided reactor pressure vessel and containment vessel volumes in the circumferential direction. The inclination conditions include static inclination along the x and y directions. Significantly, static inclination, particularly when the break aligned downward with the inclination direction, emerged as the most critical condition affecting reactor core integrity. Additionally, the containment vessel volume affects the equilibrium pressure after a break occurs, with smaller volume resulting in smaller peak cladding temperature values in static inclined conditions.

Design and analysis on the HP-PHRS for small modular lead-bismuth fast reactor

The heat pipe is an efficient heat-conducting element that can efficiently and passively transfer heat from a high-temperature heat source to a low-temperature heat source. It is widely used in the various industries. Based on high-temperature heat pipe technology, this paper designs a passive decay heat removal system for a small modular lead–bismuth fast reactor, and uses the system code ATHLET coupled with the heat pipe calculation module to calculate and analyze the thermal–hydraulic characteristics of the reactor under station black out accident.

Conjugate heat transfer analysis of helium–xenon gas mixture in tight rod bundles

Helium-xenon gas mixture (He-Xe) and tight rod bundles are widely used in gas-cooled space nuclear reactors. However, few studies have been conducted on the effects of pitch-to-diameter ratio (P/D) on thermal–hydraulic characteristics while considering conjugate heat transfer. This paper numerically investigated He-Xe heat transfer in a fuel-gas gap-cladding-coolant structure of tight rod bundles. The numerical model is validated using experimental data and the maximum error of wall temperature is less than 5 %. The results show that conjugate heat transfer significantly affects the heat transfer. The heat transfer coefficient without conjugate heat transfer is only 8.85 % of that with conjugate heat transfer in the quasi-triangular pipe. The decrease in P/D enhances the convective heat transfer and causes larger pressure drops. A new performance evaluation criterion (PEC) is presented considering the effects of heat transfer, pressure drop and volume. PEC first increases and then decreases with the increase in P/D and the best comprehensive performance occurs at P/D = 1.113. The analysis of the temperature difference in the viscous sublayer (y+ < 5) shows that the decrease in P/D enhances the turbulent effect of He-Xe and reduces the thickness of the viscous sublayer, resulting in the heat transfer enhancement. This study contributes to the optimal design of advanced space reactors.

Thermal-hydraulic characteristics analysis of unprotected accident and protection control strategy for helium-xenon cooled reactor system

The small modular helium-xenon cooled reactor has the advantages of simple and compact system structure, short construction cycle, light weight and small volume, which is very suitable for energy supply in remote area and small nuclear propulsion device. The research on accident characteristics and protection control strategies is very important to ensure the safe and reliable operation of the reactor system and mitigate the consequences of the accident. Therefore, the safety characteristics analysis program of helium-xenon cooled reactor system is developed based on Modelica language, and the transient verification of typical working conditions is carried out. The maximum relative error of the verification results was 7.91 %. Through the program, the unprotected transient conditions and corresponding protection control strategy transient conditions of external load loss accident, partial loss of heat sink accident, main valve accidental closing accident and Brayton unit efficiency step decline accident are simulated. The results show that the loss of all external loads will lead to rotation speed overspeed. The introduction of negative reactivity or bypass control can effectively control the rotation speed rise, but the introduction of negative reactivity is better than bypass control. Under unprotected control, the partial loss of the heat sink, the accidental closing of the main valve and the step down of the Brayton unit efficiency will all lead to the rapid decline of the rotation speed and mass flow rate, and there is a risk of the reactor temperature exceeding the limit. The rotation speed and mass flow rate can be effectively stabilized by load following to prevent the temperature exceeding the limit.

CorTAF-LBE: A full scale subchannel-level thermal-hydraulic characteristics analysis code for LBR core based on OpenFOAM

The lead-bismuth cooled fast reactor core adopts box-type design, and the fuel rod bundle is fixed by wrapping wires. The complex geometric structure of the fuel assemblies significantly affects the flow and heat transfer status of the liquid metal coolant. Building upon the open-source CFD platform, OpenFOAM, this work established conservation equations for liquid metal coolant, fuel rod thermal characteristic models, inter-wrapper coolant analysis models, and coupled heat transfer models, and developed the subchannel level thermal-hydraulic analysis code CorTAF-LBE for whole-core analysis of LBR core using the finite volume method. The wire-wrapped rod bundles internal flow and heat transfer experiments of lead-bismuth, carried out based on the THEADES and KYLIN-II circulation loops, were selected to perform verification and validation. The results match well with the experimental data and CFD fine-modeling prediction. The steady-state numerical simulation of three wire-wrapped rod bundle assemblies with inter-wrapper flow was carried out under normal operation condition. The temperature and pressure distributions of the coolant in each subchannel and inter-wrapper flow region, the temperature of cladding and other key thermal-hydraulic parameters were obtained. The role of the inter-wrapper coolant in heat removal from the fuel assemblies was revealed. The work in this paper has referential value for the optimization of lead-bismuth cooled fast reactor design and safety assessment during operation.

Experimental study on thermal-hydraulic characteristics of cryogenic plate-fin heat exchangers

Plate-fin heat exchangers (PFHEs) are used in diverse applications because of their superior capabilities. Recently, the demand for PFHEs has increased in cryogenic industries. Therefore, evaluating the thermal and hydraulic performances of PFHEs under cryogenic conditions is crucial for effectively designing them. In this study, the thermal–hydraulic characteristics of cryogenic nitrogen gas flowing through PFHEs were investigated experimentally. Two PFHEs with different fin geometries are used in this study. The hydraulic diameters of the PFHEs were 2.13 and 1.47 mm. The experimental ranges of the Reynolds and Prandtl numbers were 345–7800 and 0.72–0.75, respectively. From the experimental results, a heat transfer correlation based on the Diani correlation was derived in both turbulent and laminar regimes, with root mean square percentage errors of 0.68 and 6.9 % for the turbulent and laminar regimes, respectively. For hydraulic performance, the calculated pressure drop demonstrated good agreement with the experimental data, with a root mean square percentage error of 13 %.