Warm-up Process Research Articles

Temperature Compensation Method for Raster Projectors used in 3D Structured Light Scanners.

Raster projectors are commonly used in many various measurement applications where active lighting is required, such as in three-dimensional structured light scanners. The effect of temperature on the raster projector, in some conditions, can lead to significant deterioration of the measurements performed with such a scanner. In this paper, the outcomes of several experiments concerning the effects of temperature on raster projectors are presented. The described research is focused on the thermal deformations of projected images caused by common thermal effects observed in projectors: those caused by the warming-up process and changes in ambient environmental temperature. A software compensation method is also presented. It is suitable for implementation in any existing measurement method that uses raster projectors. The results of performed verification experiments show that the developed compensation method can decrease the thermal drift of the projected images by up to 14 times in the ambient temperature range °C.

DecaWave Ultra-Wideband Warm-Up Error Correction

In the field of indoor localization, ultra-wideband (UWB) technology is no longer dispensable. The market demands that the UWB hardware has to be cheap, precise, and accurate. These requirements lead to the popularity of the DecaWave UWB system. The great majority of the publications about this system deal with the correction of the signal power, hardware delay, or clock drift. It has traditionally been assumed that this error only appears at the beginning of the operation and is caused by the warm-up process of the crystal. In this article, we show that the warm-up error is influenced by the same error source as the signal power. To our knowledge, no scientific publication has explicitly examined the warm-up error before. This work aims to close this gap and, moreover, to present a solution, which does not require any external measuring equipment and only has to be carried out once. It is shown that the empirically obtained warm-up correction curve increases the accuracy for the two-way ranging significantly.

A new automatic machine learning based hyperparameter optimization for workpiece quality prediction

Workpiece quality prediction is very important in modern manufacturing industry. However, traditional machine learning methods are very sensitive to their hyperparameters, making the tuning of the machine learning methods essential to improve the prediction performance. Hyperparameter optimization (HPO) approaches are applied attempting to tune hyperparameters, such as grid search and random search. However, the hyperparameters space for workpiece quality prediction model is high dimension and it consists with continuous, combinational and conditional types of hyperparameters, which is difficult to be tuned. In this article, a new automatic machine learning based HPO, named adaptive Tree Pazen Estimator (ATPE), is proposed for workpiece quality prediction in high dimension. In the proposed method, it can iteratively search the best combination of hyperparameters in the automatic way. During the warm-up process for ATPE, it can adaptively adjust the hyperparameter interval to guide the search. The proposed ATPE is tested on sparse stack autoencoder based MNIST and XGBoost based WorkpieceQuality dataset, and the results show that ATPE provides the state-of-the-art performances in high-dimensional space and can search the hyperparameters in reasonable range by comparing with Tree Pazen Estimator, annealing, and random search, showing its potential in the field of workpiece quality prediction.

Study of structural and optical properties of the thermochromic silver and copper tetraiodomercurates (Ag2, Cu2) HgI4 ceramics

Powders of silver (Ag2HgI4) and copper (Cu2HgI4) tetraiodomercurates were synthesized by a simple co-precipitation method. Their phase transition behavior was investigated by differential scanning calorimetry, X-ray diffraction (XRD), as well as diffuse reflectance to determine its reversibility and stability during heating–cooling cycles. Calorimetry showed a sharp transition at 51 °C when heating, and at 40 °C when cooling for Ag2HgI4 samples. For Cu2HgI4 samples in the first cycle, one peak was observed when heating at 69.6 and 49.7 °C when cooling. However, in these samples, the first peak splits into two peaks when heating during the second and third cycles (67.5 and 57.8 °C), indicating a probable loss of crystallinity. XRD and diffuse reflectance showed that the transition starts almost since the beginning of the warming-up process and is more evident around 40 °C for Ag2HgI4 and around 60 °C for Cu2HgI4. The energy bandgap indicates that Ag2HgI4 and Cu2HgI4 behave differently during the transition. Copper tetraiodomercurate follows almost the same path for heating than for cooling. Its reversible thermochromic and superionic properties are promising for several applications and open the possibility of using them as inclusions in smart composite systems.

Advantages of using a cooler bypass in the low-pressure exhaust gas recirculation line of a compression ignition diesel engine operating at cold conditions

The low efficiency of the after-treatment systems during the cold start period of the internal combustion engines leads to excessive pollutant emissions levels. To reduce the nitrogen oxide emissions at these conditions, it could be necessary to use the high- and low-pressure exhaust gas recirculation strategies, even operating at low temperatures. This article evaluates the impact of using a low-pressure exhaust gas recirculation cooler bypass in a Euro 6 turbocharged diesel engine running under cold conditions (–7 °C). A new compact line fitted with a bypass system for the cooler is used with the aim of accelerating the engine warm-up process as compared to the original low-pressure exhaust gas recirculation line. The system is evaluated following two strategies, first performing exhaust gas recirculation without bypass and then performing exhaust gas recirculation bypassing the cooler. The results show that the activation the low-pressure exhaust gas recirculation from the engine cold start leads to a significant nitrogen oxide emissions reduction. Moreover, the bypass activation leads to increase the engine intake temperature, reducing the engine warm-up time and the CO emissions due to better combustion efficiency. However, the activation of the low-pressure exhaust gas recirculation at low temperatures could produce condensation and fouling deposits on the engine components affecting their life span. These phenomena are visualized using endoscope cameras in order to identify the condensation time and the final conditions of the elements. In addition, a chemical analysis of some condensates collected during the experiments and a comparison versus other species found in the literature is presented.

Upper-body vibration as part of warm-up: its effect on throwing velocity in elite adolescent handball players

Purpose The purpose of this study was to examine the acute effects of 40-Hz upper-body vibration at two different amplitudes, added to the warm-up process, on throwing velocity in elite adolescent handball players.

Transient Thermal Behaviors of Ultra-Supercritical Steam Turbine Control Valves During the Cold Start Warm-Up Process: Conjugate Heat Transfer Simulation and Field Data Validation

Abstract Transient thermal behaviors of ultra-supercritical steam turbine control valves during the cold start warm-up process of steam turbine systems were comprehensively studied using conjugate heat transfer (CHT) simulation. The geometrical configurations and boundary conditions used in simulation were identical to the field setup in a thermal power plant. The simulated temperature variations were first validated using measurements by the flush-mounted thermocouples inside the solid valve bodies. The CHT simulation implementing the shear stress transport (SST) turbulence model demonstrated good agreement with the field data, and the overall numerical errors were below 10%; however, the numerical errors of the simulation, which used empirical heat transfer coefficients at the fluid–solid interfaces, reached 40%. The determined temperature differences between the cold valve bodies with the hot steam flow decreased significantly. Specifically, the temperature differences along the inner wall surfaces of the valve bodies decreased to less than 50 °C. Further investigation of the transient heat flux distributions and Nusselt number distributions confirmed that the unsteady flow behaviors, such as the alternating oscillations of the annular wall-attached jet, the central reverse flow and the intermediate shear layer instabilities, enhanced the fluid–solid heat convection process and thus contributed to the warming up of the solid valve bodies.

Research on Control Algorithm of Proton Exchange Membrane Fuel Cell Cooling System

The proton exchange membrane fuel cell (PEMFC) is taken to be the ultimate technical direction of vehicle power. Cooling system is a key component which directly affects the fuel cell performance, reliability and durability. For the purpose of keeping accurate temperature control under dynamic loads and achieving rapid warm-up control during cold-start, a 35 kW PEMFC’s cooling system dynamic model is established and validated by experiments firstly. According to the simulation results, the model can well be fitted to the actual system. Then an integrate separate PID (Proportional-Integral-Derivative) algorithm and cooling fan prestart strategy is proposed. The result shows that it can effectively reduce the temperature overshoot under dynamic loads. In view of the thermostat mechanical characteristics tend to cause large temperature fluctuation during warm-up process, a thermostat control strategy is proposed to reduce the temperature fluctuation from 7.5 °C to 0.4 °C.

Quantitative evaluation of the plutonium proliferation resistance

The mathematical model presented in (Kulikov et al. 2018) can be used for the quantitative evaluation of the plutonium proliferation resistance. This requires the warm-up process of an implosion nuclear explosive device (NED) with a different structure to be analyzed with respect to various heat removal conditions and the option to be identified in which the NED remains operational for the longest time possible. The fraction of the 238Pu isotope with which, even in this case, the NED will prove to be operational only for quite a short time can be regarded as sufficient for the plutonium with such composition to be considered a proliferation resistant material. The purpose of the paper is to evaluate in quantitative terms the content of 238Pu in plutonium for ensuring its proliferation resistance and to identify the factors which influence significantly this evaluation. The data, procedures and findings from earlier works on the topic, as well as the authors’ own estimates and calculations were used for the study. It has been shown that the important factors involved in the plutonium proliferation resistance evaluation are the NED technology level and the required NED lifetime. Depending on the required lifetime, tougher requirements can be introduced with respect to the 238Pu content both from the standpoint of low-technology and high-technology NEDs. With a lifetime of five hours taken as the guide-mark (a NED is unlikely to be finally assembled, transported and used for such a short time), it is only plutonium containing 55% of 238Pu that can be considered a proliferation resistant fissile material.

Computational model and physical and technical factors determining the plutonium proliferation resistance

Since the closed nuclear fuel cycle suggests that plutonium is extracted from irradiated fuel and is recycled in nuclear reactors as part of the loaded fuel, proliferation resistance of fissile materials (plutonium) is becoming a problem of a practical significance. It is important to understand to what extent the physical and technical properties of fissile materials are capable to prevent these from being diverted to nonenergy uses. This paper considers the term ”proliferation resistance” from a physical and technical point of view with no measures taken for the physical protection, accounting and control of nuclear materials. Thus, proliferation resistance of plutonium means that it is technically impossible to fabricate a nuclear explosive device (NED) of the implosion type due to the overheating of the device’s components and the resultant NED failure. The following conclusions have been made. The assessment of the plutonium proliferation resistance is not justified where it relies on the analysis of an implosion-type NED excluding the use of modern heat-resistant and heat-conducting chemical explosives (CE) which are inaccessible. Consideration of the asymptotic temperature profile in the NED components is not justified enough for the development of plutonium proliferation resistance recommendations. No options enabling the slowdown of the NED warm-up process have been exhausted for analyzing the physical and technical factors that determine the proliferation resistance of plutonium. The assessment of the plutonium proliferation resistance is not justified where it relies on the analysis of an implosion-type NED excluding the use of modern heat-resistant and heat-conducting chemical explosives (CE) which are inaccessible. Consideration of the asymptotic temperature profile in the NED components is not justified enough for the development of plutonium proliferation resistance recommendations. No options enabling the slowdown of the NED warm-up process have been exhausted for analyzing the physical and technical factors that determine the proliferation resistance of plutonium. General conclusion. The underlying rationale in a fundamental monograph by Dr. G. Kessler proved to be insufficiently valid, which has led to an unfounded inference as to the status of the plutonium proliferation resistance. The development of the procedures used and other factors taken into account are expected to increase the requirements to the content of the 238Pu isotope in plutonium for ensuring its proliferation resistance.

Oceanic methane hydrate utilization system design and reservoir scale numerical modeling

In recent years, the exploration and utilization of methane hydrate from permafrost and off-coast regions has become a very hot topic. Aiming at its potential as a vast energy resources in future use, the current study is focused on the low emission extraction and utilization system for oceanic methane hydrate and its economic and technological feasibility. In this study, recent real extraction tests in both China and Japan in 2017 are firstly discussed and compared, where the challenges in production period and production rate are explained. In those tests, depressurization method is used to dissociate the methane hydrate for gas production form the unconsolidated reservoir layers below the seabed. Based on the conditions of Japan, a systematic utilization system is proposed for oceanic methane hydratewhich is consisted of extraction system, power generation system, Carbon Capture and Sequestration (CCS) system and hot fluid injection system. Vertical well systems are adopted in this design and the strategic warming up process is used before depressurization extraction, so as to obtain optimal production rate of methane gas. The inclusion of CCS makes it possible to utilize methane hydrate with very low carbon emission. It is estimated that the electricity price obtained by this system can be comparable with the current civil electric price in Japan if the production rate is around 1.0×105 m3/d. Also in this study, the real extraction scenarios and possible strategies of Nankai Trough in Japan and Shenhu Area in China are re-visited and discussed by numerical models. It is found that the only depressurization or thermal stimulation method have the problems of wellbore deformation, pressure problem and energy efficiency problems, while combined strategic modes show the possibility of long-term continuous production. For the basic dissociation parameter analysis, the conditions near the equilibrium curve show higher production rate, which is due to higher initial reservoir temperature. Such results indicate the importance of heat supply inside the reservoir layer as the methane hydrate dissociation is endothermic. It is shown that with the increase of reservoir pressure, such temperature effects become more critical as the optimal initial temperature increases according to equilibrium curve. This results support the system design with strategic warming-up process in a sister well during methane hydrate extraction. In addition, the effects of reservoir layer thermal management, hot reservoir fluid flow effects on the dissociation behaviors are analyzed in this study. For vertical well analysis, the production rates under different permeability parameters show the same trend with real production, which in turn help confirm the in-lab permeability tests. Horizontal well simulation show the importance of overburden and under burden. If the confining layers are less permeable, the production rate becomes higher due to the limited intrusive water flow from the confining layers. In sum, this study summarized the advantages and disadvantages of oceanic methane hydrate extraction/utilization methods and put forward a low-carbon emission system. It is hoped that this study will contribute to the future development of both production prediction and real extraction tests.

A study on the fire behaviors of 18650 battery and batteries pack under discharge

In order to have a better understanding of the fire behaviors of lithium-ion battery (LIB) and batteries pack under discharge, a series of fire tests were conducted. The fire behaviors of LIB were characterized by parameters including the flame photographs, surface temperature, mass loss, radiative heat flux and hydrogen fluoride (HF) mass flow. The results indicate that the number of batteries will affect the fire behaviors of LIB. Pack with larger number of LIB possesses a faster temperature rise, a higher peak heat flux and total radiative heat, leading to a quicker thermal runaway. Additionally, the discharging treatment also has a significant impact on LIB. It can accelerate the warming-up process, increase the fire risks of LIB, decrease the combustion efficiency of LIB and reduce the radiative heat. This is the result of the heat generation during discharge and the more reactive materials inside the battery under discharge. Besides, the HF generated during tests is discussed in the paper to note the toxicity of the released gases in LIB fire.

Important interaction of chemicals, microbial biomass and dissolved substrates in the diel hysteresis loop of soil heterotrophic respiration

Increasing the emission of carbon dioxide by heterotrophic respiration (Rh) might lead to global warming. However, issues remain on how Rh responds to changing temperatures, especially with respect to the hysteresis loop in the relationship between Rh and temperature at the daily scale, along with elucidating the underlying mechanisms. We investigated hysteresis loop by measuring Rh in subtropical forest soil at the daily scale (12 h for warm-up (6–30 °C) and cool-down processes (30–6 °C), respectively) using continuous temperature variation and high resolution of measurements over a 56-day incubation period. The ratios of R20 and Q10 between warm-up and cool-down were calculated as the characteristics of diel hysteresis. We measured chemical (pH, conductivity, oxidation-reduction potential), microbial biomass and dissolved substrate (carbon and nitrogen) parameters to explain variation of diel hysteresis. Rh was strongly dependent on temperature, with a clockwise hysteresis loop of Rh between the warm-up and cool-down daily processes. The average value of R20 [at a reference temperature of 20 °C] during the whole incubation period under the warm-up process was significantly higher (46.05 ± 0.96 μgC g−1 d−1) than that under the cool-down process (14.74 ± 0.03 μgC g−1 d−1). In comparison, the average value of Q10 under the cool-down process (5.27 ± 0.2) was significantly higher than that under the warm-up process (1.66 ± 0.02). Redundancy analysis showed that the interaction effects of soil chemical, microbial biomass, and dissolved substrate parameters explain most variation of diel hysteresis: 98% variation in R20 and 93.5% variation in Q10. Compared with the weak effect of chemistry parameters on the diel hysteresis, the sole and interactive effects of microbial biomass and substrate were more important, especially their interaction. Interactions of chemical, microbial biomass, and dissolved substrate parameters dominated the variation in diel hysteresis of Rh with temperature, especially the interaction of microbial biomass and dissolved substrate. Of note, Q10 during the warm-up process might be overestimated when using the highly fitted temperature-dependent function of cool-down period. Furthermore, using a constant value of Q10 (Q10 = 2) in carbon cycle models might be an important source of uncertainty.

Optimal Control Strategy for Series Hybrid Electric Vehicles in the Warm-Up Process

To address the problems of low efficiency and high fuel consumption during the cold start and warm-up processes of internal combustion engines, a series hybrid electric vehicle was selected as the research object and two optimal control strategies were designed. A bench test was performed to determine the following: (a) the influence of engine coolant temperature on effective thermal efficiency; and (b) the relationship between engine operating conditions and coolant temperature increase rate. On the basis of the test results, two sets of warm-up process optimization control strategies were designed using a dynamic programming method and a fuzzy control method based on equivalent consumption minimization strategy (ECMS). The test results show that the fuzzy control method for the coolant temperature can effectively shorten the time required to warm up the engine, and the energy consumption of warm-up process can be reduced by nearly 10% through the dynamic programming method.

Modeling and analysis of the process of polymeric film cooling on the drum with a liquid cooling agent

Using the developed mathematical model, we performed an analysis of the process of cooling an extruded polymeric film on the drum with inner cooling. Dependence of average and local temperatures of a polypropylene film and the drum’s shell under condition of drum’s settling under stationary thermal mode was studied. It was shown that temperature difference between the surface of the shell and the refrigerant in the drum at film cooling can reach 40–65 °C and higher, which affects intensity of cooling of a polymeric film. With an increase in the minimum thickness of a film and (or) a decrease in its velocity, the influence of drum’s warm-up on the intensity of film cooling increases. Ignoring the drum’s warm-up process can lead to the insufficient cooling of a polymeric film and thus, to a decrease in its quality. The developed mathematical model could be used to analyze the process of cooling of not a film only, but also of other roll polymeric materials, obtained both by extrusive and rolling-calender method.

An investigation on a diesel jet’s ignition characteristics under cold-start conditions

The diesel engine is widely regarded as a critical power source for transportation vehicles, construction machinery vehicles, and military-equipment due to its advantages of significant horse power, higher fuel efficiency, greater reliability. However, diesel engines do suffer from ignition issues in extremely cold environments. Ignition characteristics during the start-up process directly impact both the start-ability and emission levels of the diesel engine. In this study, various optical diagnostics, such as Mie scattering, shadowgraphy method, and high-speed imaging, were applied to investigate the spray’s vapor and liquid phases as well as the initial flame development, while an optical constant volume chamber was used to observe the in-cylinder condition. During the experiments, the ambient temperature, injection pressure, and fuel temperature was varied in a large range to simulate different stages of the cold-start or warm-up processes. The results show that the penetration of the spray’s liquid and vapor phases, flame lift-off length, and ignition delay all observably increase with a decrease in the ambient density, ambient temperature, and fuel temperature. Furthermore, the chemical process is the dominant factor for ignition at a low ambient temperature. A low ambient temperature may lead to a misfire due to the separation between the spray’s vapor phase and the expected initial flame location. Additionally, a low ambient density could lead to misfires due to the low heating capacity of the ambient gas. The study results also show that the injection pressure does not significantly influence the ignition delay or the flame lift-off length, but a higher pressure could result in a lower ignition success rate due to over-mixing of the air-fuel. Additionally, the fuel temperature significantly influences the ignition, which advances the initial ignition time 0.1ms with every increase of 10°C under an ambient temperature of 535°C.

Production strategy for oceanic methane hydrate extraction and power generation with Carbon Capture and Storage (CCS)

Methane hydrate (MH) is one well-known promising energy resources, which has been proved to exist widely around the world and in large amount. Though there are several proposals for efficient utilization system of MH, challenges still remains in the production enhancement. In this study, a new strategic production model is proposed for oceanic MH extraction and offshore power generation with Carbon Capture and Storage (CCS). The batch type design is facilitated with vertical well system and warm-up process, which is executed before and during the continuous gas extraction from MH reservoir. The system includes a methane gas extraction system, power generation system and CO2/H2O injection system. The re-injection of hot water/CO2 sustains the sensitive heat for the dissociation extraction process in a typical strategic production lifecycle. Numerical simulation shows that this design is possible to enhance the long-term gas production. Thermal balance and sensitive heat supply are proved to be of special importance for production rate. The analysis of power generation and CCS system show a general efficiency of 40% for this design. The selection of amine use, the effect of injection conditions and the feasibility of the proposed extraction/generation system are also discussed into detail in this study.

Numerical analysis of high-temperature proton exchange membrane fuel cells during start-up by inlet gas heating and applied voltage

This paper investigates the start-up or warm-up process of a high-temperature proton exchange membrane fuel cell (HT-PEMFC) from room temperature to a desired temperature of ∼180 °C. The heating strategy considered in this study involves an initial heating of the HT-PEMFC by a process referred to as inlet gas heating to a temperature above 100 °C. After the fuel cell reaches above 100 °C, a voltage is applied, where electrochemical reaction heating is expected to contribute to the heating process. Thus, a numerical transient non-isothermal three-dimensional model is derived to mimic the start-up process. Operational parameters such as anode inlet temperature, cathode inlet temperature, applied voltage and voltage application temperature are varied and their effects on the maximum temperature in the membrane electrode assembly (MEA) and temperature difference in the MEA are studied. Firstly, the distribution of temperature along the channel length indicates an increase of temperature during gas heating and as the voltage is applied at the voltage application temperature, the temperature increases at the centre of the MEA due to exothermic reactions. The two-dimensional temperature distribution indicates a temperature difference between the centre of the MEA and the regions below the bipolar plate where the temperature is relatively lower. Considering the whole start-up process with respect to time, the temperature difference exists throughout the process. This will be the key focus in the parametric study. The parametric study indicates that the inlet gas temperatures, applied voltage and the voltage application temperature affect the maximum temperature in the MEA and most importantly, the temperature difference in the MEA. This can cause thermal stresses to build-up if the increase rate of temperature difference is excessive. Setting the applied voltage high (thus, lower current density) is necessary to reduce the increase rate of temperature difference.

Unsteady flow behavior of a steam turbine control valve in the choked condition: Field measurement, detached eddy simulation and acoustic modal analysis

Abstract The unsteady flow behavior of a steam turbine control valve in the choked condition, which occurs during the warming-up process of a steam turbine, was studied through complementary techniques, including field measurements of the valve spindle’s vibration behavior, detached eddy simulation (DES) of the unsteady flow field, and acoustic modal analysis of the valve chamber. Three peak frequencies at St = 0.044, St = 0.17, and St = 0.59 were identified from field measurements of the vibration behavior. Subsequently, the unsteady flow fields in the control valve were determined from DES and then analyzed using the state-of-the-art data-driven proper orthogonal decomposition (POD) method and cross-correlation analysis, which extracted the dominant unsteady flow behavior in relation to the valve spindle’s vibrations. The findings demonstrated that the valve spindle’s lateral force fluctuations at St = 0.019 occurred due to the alternating oscillations of the annular wall-attached jet, which resulted from the first two POD modes occupying 25% of the turbulent fluctuation energy. The valve spindle’s axial force fluctuations at St = 0.043 were attributed to the synchronous oscillations of the annular wall-attached jet, which resulted from the third, fourth, and fifth POD modes occupying 15% of the turbulent fluctuation energy. Finally, through acoustic modal analysis that compared the pressure fluctuations extracted from the DES results, the axial acoustic mode in the valve’s cavity at St = 0.19 was found to be associated with the valve spindle’s axial force fluctuations at St = 0.174, while the first circumferential acoustic mode of the valve diffuser at St = 0.61 was found to be associated with the valve spindle’s lateral force fluctuations at St = 0.62. This confirmed the potential coupling between the acoustic mode pattern and pressure fluctuation pattern. These complementary techniques were demonstrated to be effective methodologies for the flow-induced vibration behavior and intensive acoustics in valves.

Development of large scale unified system for hydrogen energy carrier production and utilization: Experimental analysis and systems modeling

The world's largest class hydrogen energy carrier production, storage, and utilization system has been operated in order to obtain basic data for practical use of the system using renewable energy. In this system, an alkaline water electrolyzer is combined with hydrogenation reactors to produce methylcyclohexane (MCH). Since electrolyzer behavior directly affects hydrogenation reaction, behaviors of the 150 kW class water electrolyzer against fluctuating electricity inputs were experimentally investigated. The cell stack voltage and hydrogen flow rate changed following temporal changes of the input current, whereas the temperature response was slow due to the large heat capacity of the system. Hydrogenation reactors performance using the hydrogen from the electrolyzer are reported. Then, based on the experiment data, a numerical simulation model for the electrolyzer was developed, which predicts the experimental result using fluctuating electricity very well. Furthermore, using the simulator, the heat utilization from the hydrogenation reaction for the electrolyzer warm-up process was investigated.