Entropy Production Method Research Articles

Hydraulic loss analysis of turbodrill blade cascades based on entropy production theory

Turbodrill is a kind of high-temperature resistant downhole motor which is commonly used in drilling deep and high-temperature wells. It belongs to multi-stage axial flow turbomachinery. There are complex flow losses in turbodrill blade cascades, but conventional flow-loss evaluation methods cannot obtain the location of losses in cascades. The entropy production method constructs the relationship between flow field parameters and flow losses, so the location where flow losses generate can be obtained, which is commonly used to analyze the flow losses in various flows. In this paper, entropy production method is used to obtain the magnitude and position of hydraulic losses in turbodrill blade cascades. The single passage calculation model of three-stage stator and rotor is established, and CFD method is employed to compute the flow field parameters at different viscosities and rotary speeds. Different kinds of entropy production rates and values are calculated. Finally, the total flow loss calculated by entropy production method is compared with that calculated by pressure difference method, and the contrastive result is very similar, which indicates the correctness of entropy production method. The results show that the high entropy production regions are mainly located near the walls and the position changes with variations in rotary speed and viscosity, and the stator entropy production value is always lower than that in rotor. In addition, when the fluid viscosity is low, the main types of entropy production are turbulent entropy production and wall friction entropy production, while when the fluid viscosity is high, the main types of entropy production are direct entropy production and turbulent entropy production. Furthermore, the rotary speed variation has a greater impact on turbulent entropy production and wall friction entropy production compared to viscosity change, while the viscosity change has a greater impact on direct entropy production than the variation rotary speed. This paper introduces entropy production method into flow losses analysis for turbodrill, presenting a new approach for studying flow losses and providing a reference for improving turbodrill design.

Energy loss evaluation of a radial inflow turbine for organic Rankine cycle application using hierarchical entropy production method

To evaluate the location and main sources of energy loss in radial inflow turbines for organic Rankine cycle application, this study proposed a hierarchical entropy production method, which is superior to the traditional pressure drop method. The method includes three levels: local entropy production, split of turbine total entropy production, and split of component entropy production. The energy loss of the radial inflow turbine under design condition and different pressure ratios is presented. The results indicate that the high-entropy production zone is primarily located at the stator trailing edge and the rotor tip clearance. The proportion of turbulent entropy production and wall entropy production in the total energy loss of the turbine is about 77% and 20%, respectively. Among the components of the radial inflow turbine, the energy loss of the rotor and diffuser is the highest, accounting for 71.9% and 13.6% of the total entropy production of the turbine, respectively. However, the stator and rotor have higher volume average entropy generation rate and area average entropy generation rate. The high-entropy production region is mainly located in the stator outlet zone and the rotor tip zone. When the pressure ratio increases from 3 to 5, the turbine efficiency decreases by 13.44%. The pressure ratio has a significant effect on the turbulent entropy production of the rotor. This method can provide insight into the energy loss characteristics of radial inflow turbines for organic Rankine cycle applications.

Optimization of a radial inflow turbine rotor with splitter blades based on entropy production theory and artificial neural network

The radial inflow turbine is the core component of the organic Rankine cycle, and the application of splitter blades is an effective way to reduce its flow loss. It is helpful to study the energy loss characteristics of radial turbines with splitter blades and the optimal geometrical parameters of splitter blades for further improving their aerodynamic performance. In this paper, an optimization framework based on the combination of back-propagation neural network and non-dominated sorting genetic algorithm II is developed. Considering the turbine efficiency as the objective, the geometric parameters of splitter blades, including relative length of the blade, relative distance of the leading edge, circumferential offset, and outlet angle of the blade, are optimized. In addition, the entropy production method is used to locate and quantitatively evaluate the energy loss of the radial turbine with the optimal splitter blades. The results indicate that the genetic algorithm optimized back-propagation neural network model can accurately predict turbine efficiency with a maximum deviation of 2.47 %. In addition, the optimal geometrical parameters of the splitter blade are related to the turbine geometry. In this case, the optimal splitter blade has a relative blade length of 0.639, a relative leading edge distance of 0.3, a circumferential offset of 0.442, and an outlet angle of 38°. Compared with the original turbine, the efficiency of the radial turbine with optimal splitter blades increases by 4.65 %. The total entropy production of rotor and turbine is reduced by 33.3 % and 44.1 % respectively by the installation of optimal splitter blades. Compared with the case without splitter blades, the turbine with the optimal splitter blades can achieve higher efficiency at a flow rate 40 % higher than the design value, and it expands the efficient working range of the turbine by 60 %. This work can provide guidance for the optimization design of radial inflow turbines.

Modelling the mechanics of 32 T REBCO superconductor magnet using numerical simulation

High-temperature REBCO superconducting tapes are very promising for high-field magnets. With high magnetic field applications there are high electromechanical forces, and thus a concern for mechanical damage. Due to the presence of large screening currents and the composite structure of the tape, the mechanical design of these magnets is not straightforward. In addition, many contemporary designs use insulated winding. In this work, we develop a novel two-dimensional axi-symmetric finite element tool programmed in MATLAB that assumes the displacement field to be within a linear elastic range. The stack of pancakes and the large number of REBCO tape turns are approximated as an anisotropic bulk hollow cylinder. Our results agree with uni-axial stress experiments in the literature, validating the bulk approximation. Here, we study the following configuration. The current is first ramped up to below the critical current and we calculate the screening currents and the forces that they cause using the minimum electromagnetic entropy production method (MEMEP) model. This electromagnetic model can now take insulated magnets into account. As a case study, a 32 T REBCO superconductor magnet is simulated numerically. We perform a complete mechanical analysis of the magnet by including the axial and shear mechanical quantities for each pancake, unlike in previous work where only radial and circumferential quantities were focused on. The effect on mechanical quantities without the screening current is also calculated and compared. It is shown that including the screening current-induced field strongly affects the mechanical quantities, especially the shear stress. The latter may be a critical quantity for certain magnet configurations. Additionally, in order to overcome high stresses, a stiff overbanding of different materials is considered and numerically modelled, which significantly reduces the mechanical stresses. The finite element-based model developed is efficient in calculating the mechanical behaviour of any general superconductor magnet and its devices.

Variations on the models of Carnot irreversible thermomechanical engine

Abstract The JETC Conference held in Salerno (June 12–17, 2023) was the opportunity to honor the two centuries anniversary of the booklet publication of Sadi Carnot. The paper reports on a selective review summarizing the evolution of the ideas and concepts proposed by Carnot. We consider mainly: a. The Carnot cycle relative to thermomechanical engine, b. The concept of efficiency (Carnot efficiency), c. The forms of energy (thermal energy or heat, Q, and mechanical energy or work, W), d. The concept of entropy, rediscovered and completed by Clausius. We show the importance of the energy conversion irreversibilities that started to be considered more recently by two methods, namely, the ratio method and the entropy production method. The second approach provides more significant results from a global point of view, also with more local modeling (cycle process modeling). Some examples are given that illustrate the proposal: Carnot cycle in endo-irreversible or exo-reversible configuration, Chambadal modeling, Curzon–Ahlborn modeling. More generally, the modeling is done in the frame of FTT (Finite Time Thermodynamics), FST (Finite Speed Thermodynamics), or FDOT (Finite physical Dimensions Optimal Thermodynamics). Preliminary conclusions and perspectives are proposed.

Evaluating hydraulic dissipation in a reversible mixed-flow pump for micro-pumped hydro storage based on entropy production theory

The promotion of renewables improves energy security but degrades the electricity quality and grid stability. This paradox can be resolved by enlarging the capacity of pumped hydro storage. Although high-head hydropower resources have been exhausted, untapped low-head resources are ideal alternatives and are utilized for micro-pumped hydro storage. Instead of the miniaturized pump-turbine or pump as turbine, we apply a low-head reversible mixed-flow pump (RMFP), which can efficiently fulfil both storage and generation requirements in microgrids without complicated guide vanes. To enhance the efficiency of the RMFP in two reverse directions simultaneously, high-hydraulic dissipation zones associated with deformed flows and unreasonable structural parameters must be investigated. This study introduces entropy production theory into computational fluid dynamics numerical simulation to evaluate hydraulic dissipation under the rated discharge in both pump and turbine modes of the RMFP. Refined mesh and validation from the energy characteristics experiment demonstrate the accuracy of the numerical scheme. The head loss assessed by the entropy Production method is compared with the predictions of the pressure drop method, and its precision exceeds 7%. In pump mode, entropy production in the volute constitutes the largest proportion (43%), followed by that in the runner (35%). However, in turbine mode, the largest proportion of the total entropy is generated in the runner (45%), followed by that in the draft tube (33%). The dissipation in the runner is bound up with the secondary flows over the blades. Backflow occurs on the suction surface near the leading edge; however, across different spans, flow separation occurs on the suction surface near the trailing edge. The requests for blade modification are opposite in pump and turbine modes. Significantly, hydraulic dissipation of the draft tube concentrates within its 0.5D2 segment upstream. The dissipation there is bound up with the transport of two types of vortex ropes. The originality lies in evaluating hydraulic dissipation and explaining the high-dissipation zone with the specific unsteady secondary flows in pump and turbine modes of an RMFP.

Numerical investigation of no-load startup in a high-head Francis turbine: Insights into flow instabilities and energy dissipation

The presented paper numerically investigates the internal flow behaviors and energy dissipation during the no-load startup process toward a Francis turbine. Passive runner rotation is implemented through the angular momentum balance equation accompanied by dynamic mesh technology and user defined function. Three phases of rotational speed are identified: stationary, rapid increase, and slow increase. Head exhibits a monotonic decrease, rapid rise and fall, and eventual fluctuation. Flow rate shows quasi-linear increase. The pressure fluctuations in the vaneless region are primarily dominated by the frequencies induced by Rotor-Stator Interaction and a broad frequency range below 50 Hz, and below 30 Hz in the draft tube. Runner inlet experiences positive to negative incidence angles, causing intense flow separation and unstable structures. Draft tube exhibits large-scale recirculation and evolving vortex structures. Energy loss analysis based on the entropy production method highlights the runner and draft tube as primary contributors. The energy loss within the runner exhibits an initial increase, subsequent decrease, and then a rise again during the stationary and rapid speed increase phases. While the draft tube shows a rapid increase during the phase of rapid speed increase. Turbulent fluctuations significantly contribute to entropy production loss, with trends matching total entropy production. Maximum energy loss locations correspond to runner inlet and draft tube wall, emphasizing the importance of unstable flow and vortex generation. This study establishes foundational insights into unstable hydrodynamics and energy dissipation modes during hydraulic turbine no-load startup, paving the way for further research.

Performance improvement of a double-suction centrifugal pump for water supply system based on energy loss analysis and cavitation behaviour prediction

ABSTRACT To gain a comprehensive understanding of the energy dissipation of a double-suction pump, analysing the energy loss of its various components is necessary. However, the liquid temperature in the double-suction pump remains almost constant, using the entropy production or dissipation method to evaluate energy loss is difficult. The traditional analysis method based on pressure drop cannot quantify the internal energy changes in each component. To solve this problem, a pressure energy loss evaluation approach is developed on the basis of the pressure drop theoretical analysis and numerical prediction, and the effects of cavitation on the energy loss are investigated. The structure of the volute casing is improved to enhance the performance based on energy loss analysis and cavitation behaviour prediction. The results show that the energy loss efficiencies for the suction casing, impeller, and volute casing are 0.55, 4.6, and 5%, respectively, at the design flow rate. The proportion of energy loss in the impeller and volute casing increased with a decrease in NPSHa. The RNG k–ε and k–ω turbulence models are chosen for the numerical simulation, and the numerically predicted results are verified experimentally.

Design method based on a new slip-diffusion parameter of centrifugal pump for multiple conditions in wide operation region

Centrifugal pumps are widely used in industrial production, agricultural irrigation, water transportation, energy storage pump station and ocean engineering, and the development prospect of centrifugal pump is to work in a wide operation region with high efficiency. In this work, the achievement of high-efficiency operation for multiple conditions in a wide operation region is strenuously realized by a new design method from the perspective of flow mechanism analysis and theoretical derivation. A new dimensionless slip-diffusion parameter Φ on consideration of the slip effect and diffusion effect in impeller is proposed. On the basis of the new parameter Φ, a new design method of centrifugal pump is established to improve the pump efficiency for multiple conditions in a wide region. Two centrifugal pumps with different specific speeds of 102 and 127 are designed to validate the proposed design method. When the slip-diffusion parameter Φ ≈ 0.677, the centrifugal pump can achieve the maximum average efficiency for multiple conditions. For Φ < 0.677, the pump efficiency rapidly drops at the high flow rate region. For Φ > 0.677, the pump efficiency rapidly drops at the low flow rate region. Two centrifugal pumps are numerically simulated to obtain the flow pattern, and the entropy production method is used to analyze the relationship between flow field and energy performance of the pumps. Entropy production mainly appears at the blade suction side and the impeller outlet. For different flow rates, the total entropy productions of pumps with Φ ≈ 0.677 are always the minimum.

Performance prediction and optimization of hydrogenation feed pump based on particle swarm optimization – least squares support vector regression surrogate model

Due to high power consumption and low energy efficiency of the hydrogenation feed multistage pump, conducting structural optimization design and reducing energy losses for this pump is necessary. In this study, an optimization method based on the particle swarm optimization (PSO) algorithm and least squares support vector regression (LSSVR) surrogate model is proposed. The head and efficiency are taken as the optimization objectives of the multistage pump, and the optimization design of the two impellers is carried out. Through the optimization of the surrogate model, the head and efficiency of the multistage pump are increased by 3.99% and 2.91%, respectively. It is found that the optimized impeller has more stable flow characteristics than original impeller. Further, the entropy production method is introduced to analyze the energy loss of pump. The result shows that the pump optimized by PSO-LSSVR surrogate model can reduce 9% energy consumption under nominal flow rate. It is attributed to the inhibitory effect of the optimization scheme on the horseshoe vortex at leading edge and the wake vortex at trailing edge of impeller. This study provides a new idea for the optimization design of high efficiency and low energy consumption of multistage centrifugal pumps.

The Splitter Blade Pump–Turbine in Pump Mode: The Hump Characteristic and Hysteresis Effect Flow Mechanism

This study focuses on the splitter blade pump–turbine as the research object to analyze the problems of hump characteristics and the hysteresis effect. We simulated the operation of the pump condition with small opening of the guide vane, analyzed the hydraulic loss by using the entropy production theory and entropy wall function, and investigated the study of internal flow transfer characteristics. In this paper, it was first verified that the maximum error of the energy loss calculated by the pressure method and the entropy production method was less than 6% for the working zone. From the quantified energy loss results, a significant instability feature was observed in the 0.65 QBEP–0.9 QBEP operating interval, accompanied by the phenomenon of the non-overlapping of the characteristic curves. The results show that the hump characteristic with hysteresis effect also exists in the splitter blade pump–turbine. The percentage of energy loss in the hump zone is in descending order of runner, guide vanes, spiral casing, and draft tube, but this changes again at low flow rates. By analyzing the high-entropy production region, it was found that the high-hydraulic-loss region is mainly distributed at the trailing edge of the long blade in the vane-less space, which is different from the traditional runner.

Numerical investigation of energy loss distribution in the cavitating wake flow around a cylinder using entropy production method

The wake flow of a circular cylinder is numerically investigated by Large Eddy Simulation (LES) combined with the Schnerr–Sauer cavitation model. By comparing entropy production in the presence or absence of cavitation, the energy loss distribution in the wake flow field of a cylinder is explored, shedding light on the interactions between multiscale vortex systems and cavitation. The comparative results reveal that, under non-cavitating conditions, the energy loss region in the near-wake area is more concentrated and relatively larger. Energy dissipation in the wake flow field occurs in regions characterized by very high velocity gradients, primarily near the upper and lower surfaces of the cylinder near the leading edge. The influence of cavitation bubbles on entropy production is predominantly observed in the trailing-edge region (W1) and the near-wake region (W2). The distribution trends of wall entropy production on the cylinder’s surface are generally consistent in both conditions, with wall entropy production primarily concentrated in regions exhibiting high velocity gradients.

Fluctuation characteristics induced by energetic coherent structures in air-core vortex: The most complex vortex in the tidal power station intake system

The air-core vortex is the most complex vortex in the intake system of tidal power stations. Nearly all power plants prohibit the operation of units with air-core vortices, as these vortices not only contain air but also induce significant inflow fluctuations that can potentially lead to significant damage to the units. The current understanding of the fluctuation characteristics and mechanisms induced by energetic coherent structures in the air-core vortex flow is very limited. To address this, the coupled level-set and volume-of-fluid large-eddy simulations are conducted to investigate the energetic coherent structures that cause power output fluctuations. Two critical frequencies have been identified in the energy spectra of the velocity field: the air-core vortex meandering frequency and the shear vortex shedding frequency. The level and trend of the spectrum density at low frequencies are determined by the large-scale energy structure represented by the air-core vortex. The shear vortices are initially formed from a shear separation layer that eventually evolves into streamwise vortices downstream. When the air-core vortex enters the pipe, it breaks up and merges with the near-wall coherent structures. The enhanced velocity and pressure fluctuations, induced by air-core vortices and coherence structures, are analyzed using the turbulent kinetic energy transport equation, revealing that the production term dominates the development of turbulent kinetic energy. Moreover, the diffusion term is responsible for transferring energy through the evolution of turbulent structures. The energy loss induced by fluctuations is investigated using the entropy production method. We find that the direct dissipation of entropy production is mainly induced by air-core vortices, while the side-wall coherent structures in the pipe contribute to the turbulent dissipation.

Study on the energy loss characteristics of ultra-low specific speed PAT under different short blade lengths based on entropy production method

With the increasing attention to micro-hydro power, the PAT has a broad prospect in micro-hydro power generation because of its low cost and simple structure. The ultra-low specific speed pump as turbine (USSPAT) is widely used in remote areas to realize micro-hydro power generation because of its advantages, such as high output power under a small flow rate. However, the output power of USSPAT is closely related to the length of the short blade. Therefore, this paper optimizes the design of USSPAT and selects four groups of short blades for the numerical simulation of energy loss characteristics of the USSPAT based on entropy production theory. Unlike other fluid machinery, the entropy production of USSPAT increases with the flow rate increase, so it has certain limitations to measure the energy loss of USSPAT under different flow rates simply by entropy production method. Therefore, the power loss number is defined in this paper to characterize the energy loss characteristics of PAT at different flow rates. The energy loss in the impeller is always the largest under all flow rate conditions, but at 0.4Qdes, the energy loss in the chamber is the largest. The length of the short blade mainly causes the change of entropy production in the downstream region at large flow rates. In contrast, at small flow rates, the entropy production in the upstream region changes the most. In addition, it is also found that the determination of the optimal Rs can effectively suppress the incident loss in the impeller inlet and the high wall shear in the local regions. As a result, to improve the performance of the USSPAT, it is necessary to consider the length of short the blade as an essential parameter. This study not only reveals the energy loss characteristics of the USSPAT, but also provides a new perspective for optimizing the USSPAT structure.

Characterization of flux pump-charging of high-temperature superconducting coils using coupled numerical models

Flux pumps provide a promising solution for contactless charging of high-temperature superconducting (HTS) coils, eliminating the need for bulk current leads and reducing the heat burden for the cryogenic system. Characterizing the nonlinear effects of an HTS coil charged by a flux pump and understanding the dynamics of the charging process is essential for promoting the practical application of flux pumps. Numerical models provide a fast and cost-effective way of achieving this. In this study, we propose a methodology for coupling HTS coil and flux pump models using an electrical circuit, resulting in reduced computation costs. We validate the effectiveness of our approach against the experimental results of an HTS coil charged by a dynamo-type flux pump. Specifically, we obtain the voltage produced by the HTS dynamo using a 3D model based on the minimum electromagnetic entropy production method and apply this voltage to the load HTS coil using a formulation finite-element method model coupled via an electrical circuit. The simulated charging current shows good agreement with experimental observations, validating our modeling strategy. The results demonstrate that the flux flow state in the HTS coil is the primary factor limiting the charging performance of the HTS dynamo as the charging current approaches the coil’s critical current. Furthermore, based on the simulation, we demonstrate that, when using flux pumps, it is advisable to leave a margin between the operating current and the critical current of the coil. Overall, our approach has the potential to be applied to HTS coils charged by any device.

Study on the Energy Loss Characteristics of Shaft Tubular Pump Device under Stall Conditions Based on the Entropy Production Method

This study aimed to reveal the energy loss characteristics of each part of the shaft tubular pump device (STPD) under stall conditions. Numerical simulations were conducted by using the SST k-ω turbulence model with curvature correction, and the reliability of the simulation results was verified by a model test. The entropy production method was used to evaluate and visualize the energy loss. The results show that turbulent entropy production (TEP) is the main source of energy loss in each component of the STPD, and the TEP increases significantly with the deterioration of stall. The energy loss in the impeller is mainly concentrated near the shroud and hub, while in the guide vanes it is mainly concentrated near the shroud and suction surface of the blades. In addition, with the deterioration of stall, the energy loss in the inlet of the impeller and guide vanes increases significantly. Influenced by the backflow from the impeller, there is a significant amount of energy loss at the outlet segment of the inlet passage, and the location of the high-energy-loss region is consistent with the backflow region. Affected by the flow separation vortex at the tail of the guide vanes, the energy loss in the outlet passage is mainly concentrated at the inlet segment.

Investigation of energy dissipation mechanism and the influence of vortical structures in a high-power double-suction centrifugal pump

The extensive applications of double-suction centrifugal pumps consume a considerable amount of energy. It is urgent to reveal the detailed energy dissipation generation and find the critical factor for pump performance enhancement. In this investigation, the internal flow field of a double-suction centrifugal pump was obtained by solving the Reynolds averaged Navier–Stokes equations. The entropy production method was utilized to calculate and visualize irreversible energy dissipation. The Omega vortex method was utilized to identify vortical structures and determine the temporal and spatial relationship between entropy production and vortices. The results indicate that the entropy production in the main flow regions was critical in hydraulic loss, accounting for 54%–71% of the loss, and turbulent dissipation in the main flow regions of the impeller and volute casing dominated the variation of pump efficiency. The near-wall entropy production in the impeller positively correlated with the flow rate, but the impact was insignificant in volute casing. Although the suction chamber contributed minimally to the hydraulic loss, the backflows at the impeller inlet were relieved near the ribs, and the dissipation at the impeller inlet was reduced when the blade leading edges passed the ribs. By adopting Omega vortex identification, wake vortices, separation vortices, and their interactions were determined to correlate strongly with hydraulic loss in volute channels and near cutwaters. Furthermore, these vortices were influenced by the back flows from the impeller sidewall gaps. Additionally, this study can also provide the foundational principles for the optimal design of this type of pump.

Study of Energy Loss Characteristics of a Shaft Tubular Pump Device Based on the Entropy Production Method.

The unstable flow of a shaft tubular pump device (STPD) leads to energy loss, thereby reducing its efficiency. The aim of this study is to investigate the distribution pattern of energy loss in STPDs. This paper reveals that the two components with the highest proportion of energy loss are the impeller and the outlet passage. Furthermore, turbulent entropy production is the primary cause of energy loss. Due to the wall effect, the energy loss in the impeller mainly occurs near the hub and shroud. Additionally, the presence of a tip leakage vortex near the shroud further contributes to the energy loss in the region near the shroud. This results in the energy loss proportion exceeding 40% in the region with a volume fraction of 14% near the shroud. In the outlet passage, the energy loss mainly occurs in the front region, with a volume fraction of 30%, and the energy loss in this part accounts for more than 65%. Finally, this study reveals the locations of the vortex in the STPD under different flow-rate conditions, and when the distribution of energy loss is visualized, it is found that the energy loss occurs high in the vortex regions.

Energy loss and pressure fluctuation characteristics of coastal two-way channel pumping stations under the ultra-low head condition

The ultra-low head condition is a unique condition of the coastal two-way channel pumping stations, but the quantitative research on its hydraulic characteristics still needs to be improved. The entropy production method with computational fluid dynamics and the high-frequency pressure fluctuation test were employed to analyze the pumping device's internal energy loss and pressure fluctuation. The results show that the primary source of energy loss of the two-way channel pumping device under the ultra-low head condition is the turbulent dissipation caused by the velocity fluctuation of the impeller and guide vane, in which there are large irregular high entropy production areas on the pressure surface of the impeller and in the impeller channel. The high-frequency pressure fluctuation in the pumping device is mainly concentrated near the impeller, and the amplitude under the ultra-low head is 3.5 times the amplitude under the design head. Due to the dynamic and static interaction between the impeller and the guide vane, the frequency domain components of the pressure fluctuation at the outlet channel bell mouth are complex. Under the ultra-low head condition, the pressure fluctuation degree is intensified, the energy loss of each part is greater, and the low-frequency resonance should be prevented.

On the turbulent heat fluxes: A comparison among satellite-based estimates, atmospheric reanalyses, and in-situ observations during the winter climate over Arctic sea ice

The surface energy budget is crucial for Arctic sea ice mass balance calculation and climate systems, among which turbulent heat fluxes significantly affect the air–sea exchanges of heat and moisture in the atmospheric boundary layer. Satellite observations (e.g. CERES and APP-X) and atmospheric reanalyses (e.g., ERA5) are often used to represent components of the energy budget at regional and pan-Arctic scales. However, the uncertainties of the satellite-based turbulent heat fluxes are largely unknown, and cross-comparisons with reanalysis data and in-situ observations are limited. In this study, satellite-based turbulent heat fluxes were assessed against in-situ observations from the N-ICE2015 drifting ice station (north of Svalbard, January–June 2015) and ERA5 reanalysis. The turbulent heat fluxes were calculated by two approaches using the satellite-based ice surface temperature and radiative fluxes, surface atmospheric parameters from ERA5, and snow/sea ice thickness from the pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS). We found that the bulk-aerodynamic formula based results could better capture the variations of turbulent heat fluxes, while the maximum entropy production based estimates are comparable with ERA5 in terms of root-mean-square error (RMSE). CERES-based estimates outperform the APP-X-based ones but ERA5 performs the best in all seasons (RMSE of 18 and 7 W m−2 for sensible and latent heat flux, respectively). The air–ice temperature/humidity differences and the surface radiation budget were found the primary driving factors in the bulk-formula method and maximum entropy production (MEP) method, respectively. Furthermore, errors in the surface and near-surface temperature and humidity explain almost 50% of the uncertainties in the estimates based on the bulk-formula, whereas errors in the net radiative fluxes explain more than 50% of the uncertainties in the MEP-based results.