Circumferential Temperature Research Articles

Thermo-hydraulic analysis of direct steam generation in a 500 m long row of parabolic trough solar collector using Eulerian two-fluid modeling approach

Direct steam generation (DSG) in the parabolic trough solar collectors is a potential alternative for economic and performance improvement of the solar thermal system. This process comprises the preheating, evaporation, and superheating of water/steam in the solar collectors. The modeling and simulation of the evaporation section are challenging because of the complex physics associated with the boiling phase change process. This work describes the Eulerian two-fluid modeling of the once-through mode of the DSG process in solar collectors. The interfacial interactions between phases have been modeled using the appropriate empirical correlations. The experimental data from the Spanish DISS test facility is used to validate the numerical model. Further, the 3-D thermal–hydraulic investigation of DSG in a 500 m long solar collectors' row has been performed for operating pressures of 60 bar and 100 bar; inlet mass flow rates of 0.4 kg/s and 0.6 kg/s; DNI of 750 W/m2 for the solar time at 12:00 h and 13:00 h. It has been observed that the maximum absorber temperature is reduced by 27 % at 60 bar and 20 % at 100 bar operating pressure when the inlet mass flow rate increases from 0.4 kg/s to 0.6 kg/s. Similarly, the maximum circumferential temperature difference reduces by 12 % and 14 %, respectively. Moreover, the fluid temperature, steam quality, absorber temperature distributions, fluid velocity, and pressure loss under the subjected boundary conditions have been summarized.

Redesign of a Disc-on-Disc Computer Numerical Control Tribometer for a Wide-Range and Shudder-Resistant Operation

The paper presents a redesign of the custom disc-on-disc-type tribometer intended for the experimental characterization of the friction and wear of automotive dry clutch friction lining. The redesign is aimed at expanding the operating range at which the machine is not sensitive to shudder vibrations. This is achieved through a set of hardware and software upgrade measures. First, the natural frequency of the normal load-generation linear axis of the machine is increased by enlarging its bending stiffness and reducing the suspended mass. The former is realized by replacing the single, two-axial force/torque piezoelectric sensor with a set of three three-axial piezoelectric force sensors, adding a set of stiff linear guides, and reducing the lengths of the cantilevers of lateral forces acting on the linear axis guide system. The latter is accomplished by reducing the overall dimensions of the cooling disc and redesigning the thermal insulation components. The shudder sensitivity resistance is further reduced through individual normal force-readings-based adjustment of parallelism between friction contact surfaces and the increase in the stiffness of eccentrically positioned water-cooling pipes. Finally, the stability of the coefficient of friction and, consequently, the wear process are boosted by adjusting the control routines to minimize the circumferential and/or radial temperature gradients. These adjustments include the introduction of a clutch lock-up interval at the end of the clutch closing cycle, a minimum cooling delay inserted between two closing cycles, and maximum normal force demand of the clutch torque controller. The performance gain of the upgraded tribometer is demonstrated through a study of the dry clutch friction plate static wear experimental characterization for a wide range of operating conditions.

Rapid 2-Dimensional prediction of supercritical CO2 heat transfer behaviors in inclined tubes based on deep learning

At present, there is a dearth of empirical correlations for the prediction of the inclined supercritical heat transfer. Considering the shortage of the rapid prediction method in the initial design stages for the supercritical fluid heat exchanger with inclined tubes or under inclined conditions, a 2-Dimensional rapid prediction method based on the numerical method combining deep learning method was proposed to reconcile the accuracy and the efficiency of the inclined supercritical heat transfer behaviors prediction. In order to train the deep learning model, 200 numerical cases with 520,000 data were conducted. After that, 7 new cases were chosen to analyze the inclined heat transfer behaviors and validate the current model. The results were indicative of a significant circumferential inner wall temperature difference in the inclined supercritical heat transfer. The temperature difference was larger when the inclined angle was closer to 90°, even though the circumferentially averaged temperature is smooth and acceptable. This potential temperature difference would not only cause large thermal stress which may accelerate fatigue failure, but also increase the risk of over-temperature. Fortunately, the current deep learning model could predict the 2D temperature distribution of these new cases with the max absolute relative error of 16.60%. Therefore, the circumferential inner wall temperature distribution of the inclined supercritical CO2 heat transfer could be evaluated during the initial heat exchanger design. Moreover, the trained model and the relative files are available at Supplementary materials.

Cooling performance of the hot-rolled seamless steel tube with different jet forms

The jet form is closely related to the cooling strength and uniformity of steel tubes, which is the first consideration in the design of quenching equipment. A reasonable choice of jet form will improve product quality and reduce production costs. In this study, the heat transfer behavior of different jet forms is discussed. Two jet forms are considered: planar jet and annular jet. Besides, the size of the steel tube is also an important variable in this simulation. The remaining parameters are fixed values. The axial and circumferential temperature distributions of the steel tube were obtained. The results showed that the annular jet has better performance on cooling intensity and cooling uniformity. The cooling performance of the two jet forms are almost the same when the steel tube size is smaller than 50 mm. As the planar jet quenching equipment is simple to manufacture, low in cost, and convenient in site application, so the planar jet can be considered when the diameter is small.

Improving the Heat Transfer Performance of the Tower Molten Salt Solar Receiver With the Novel Folded Flow Tubes

Abstract The molten salt has been widely used in concentrated solar power generation as an effective high-temperature heat transfer and heat storage working fluid. However, due to the concentrating characteristic of the tower receiver, the solar flux distribution of the molten salt receiver is extremely non-uniform, and thus the circumferential non-uniform heat flux has a prominent effect on the heat transfer performance and reliability of the traditional solar molten salt receiver tube (TRT). In this contribution, in order to solve above problems, we propose some novel folded flow tubes (NFTs), which add a partition in the tube and seal the top with end cap so that the inflow and outflow of the fluid can only proceed from the same cross section. Then, we apply the binary nitrate (solar salt) as a heat transfer fluid, which is a mixture of 60% sodium nitrate and 40% potassium nitrate. First, we analyze some effects such as flow parameters, structure, and heat flux loading direction on the convective heat transfer performance of the NFTs. The results show that the circumferential temperature difference of NFTs is about 17–92 K lower than that of TRT, and the molten salt temperature distribution is more uniform accordingly. Moreover, the heat transfer coefficient is increased about 88.37–122.85%, which can provide a guidance for the structural optimization of practical solar molten salt receivers to improve the heat transfer performance and reliability.

Numerical and experimental study on thermal performance and thermal stress of molten salt receiver during preheating

Due to the high thermal stress, the evacuated molten salt tower receiver is prone to safety problems during the daily preheating, but there is relatively little research on it, especially on on-site receivers. In this study, the preheating performance of a lab-scale receiver is experimentally investigated first, and the influence of several operating or environmental factors on its thermal performance is obtained. The experimental results indicate that the tube front side always reaches the wall temperature requirement of salt circulation before the tube back side. Then, the numerical model of the receiver tube based on the finite volume method and 2D thermoelastic method is established and verified. Finally, by applying the numerical model to an on-site receiver, the influence of extreme environmental conditions on the preheating performance of the on-site receiver are obtained. It is found that the minimum and maximum thermal stresses occur at 90° and 180° of the outer wall, respectively, and the thermal stress is determined by the circumferential temperature gradient. The equivalent thermal stress first increases and then decreases during preheating, and the maximum equivalent thermal stress reaches within the first few minutes. Compared with the windless condition, the maximum equivalent thermal stress under strong wind (10 m/s) is reduced by 20.5%. The maximum equivalent thermal stress is linearly related to the ambient temperature, and it decreases by 6 MPa for every 10 °C increase in ambient temperature.

Effect of pulsation parameters on the spatial and temporal variation of flow and heat transfer characteristics in liquid metal cross flow the in-line tube bundle

Liquid metal has a broad application prospect in tube bundle heat exchangers because of its excellent thermal conductivity. However, conventional in-line tube bundle arrangements often exhibit limited secondary flow, so new methods are urgently needed to improve heat transfer. The topic of this paper is to combine two methods, liquid metal cross flow tube bundle and pulsating flow, to improve the heat transfer performance in-line tube bundles. Firstly, the applicability of the model was validated through experimental data from existing literature, encompassing overall flow dynamics, heat transfer performance, and circumferential pressure distribution around the tubes. Subsequently, numerical simulations are conducted involving liquid metal cross flow in-line tube bundles at varying pulsating frequencies, amplitudes, and Reynolds numbers. Circumferential pressure distributions and temperature profiles for individual tubes were analyzed and compared. The amplitude of reduction in thermal resistance compared to the no-oscillation condition increases gradually from a minimum of 8 % in the first row to a maximum of 40 % in the third row, while the reduction in the rear row of tubes is similar to that of the third row. Remarkably, a reversal in the trend of thermal resistance for the first three rows of tubes under pulsating flow were observed, contrasting conventional flow except for the case with an amplitude of 0.1. By analyzing the local transient flow field distribution near single tube and the corresponding circumferential heat transfer performance, the influence of the vortex evolution characteristics on the heat transfer performance at different phases of the pulsating velocity is revealed, which transient Nu is up to three times that of flow with no pulsating. Finally, a series of coherence analyses reveal that as frequency rises, turbulence exhibits a richer spectrum of small-scale vortex structures, intricately linked to enhanced energy cascade efficiency. Amplitude augmentation intensifies velocity fluctuations, particularly at high amplitudes, resulting in substantial energy peak amplification. The integrated heat transfer performance PEC factor varies in the range of 1.25 to 1.51 for all the conditions simulated in this paper, which indicates that the liquid metal coupled pulsating flow approach can significantly increase the comprehensive performance of the tube bundle heat exchangers. These findings hold significant promise for advancing heat exchanger design and enhancing thermal efficiency, with implications for various engineering applications.

Numerical analysis of coupled flow and heat transfer in primary and secondary sides of double-side heating once-through steam generator with helical tubes

The inner tubes of double-side heating once-through steam generator (OTSG) with helical tubes are spiral channels, and the secondary fluid is heated on both sides, effectively improving the heat transfer efficiency. The spiral structure makes its flow heat transfer characteristics different from straight tube type OTSG. This article establishes a numerical model of Euler two-phase flow in double-side heating OTSG with helical tubes to analyze its velocity distribution, volume fraction distribution, and temperature distribution. The results show that the fluid spirally rises in the secondary flow passage, the velocity of two phases increases rapidly after vaporization, the slip ratio is greater than 1, the steam volume fraction on the wide side is higher than that on the narrow side, and the steam volume fraction presents a spiral distribution on the wall. The non-uniform circumferential steam volume fraction leads to the wall dryout first at the wide edge, and the wall temperature also presents a spiral distribution. The dryout position temperature rises 40.13 K along the Z direction, and the temperature gradient is 5.26 K/mm. The circumferential temperature rises 44.46 K, and the temperature gradient is 15.11 K/mm.

Numerical and experimental analysis of air-cooled Lithium-ion battery pack for the evaluation of the thermal performance enhancement

The main objective of this study is to assess the thermal performance of an air-cooled Lithium-ion battery pack. This involves analyzing the heat dissipation characteristics and temperature distribution within the battery pack at different operating conditions. Here, the thermal performance of the battery pack is evaluated numerically and experimentally. The experimental platform allows adjusting numerous control factors, like air velocity (0.5 to 2.0 m/s), air temperature (282.0 to 315.0 K), and battery pack discharge rate (0.5 to 2.5C). The temperature distribution is studied in longitudinal and transverse directions of the battery pack and circumferentially for a cell. The numerical simulations involve the solution of Shear Stress Transport (SST) k- ω model-based Navier-Stokes (N-S) equation using the ANSYS FLUENT R19.2 software. The numerical results were found to closely match the experimental findings with maximum error to be within 3.12%. The evaluation parameters used to assess the thermal performance of BTMS are maximum temperature(Tmax), maximum temperature difference (∆Tmax), average temperature (Tavg.), and standard deviation of the temperature σT within the battery pack. The numerical and experimental analyses show a reduction in both the maximum and mean temperature of the battery pack and improved temperature uniformity, with the increase in air velocity, lowering the discharge rate and decreasing the ambient temperature. The correlation between air inlet velocity and temperature drop is stronger at higher discharge rates than lower discharge rates. The effect is due to high heat transfer coefficient and uniform air distribution at high velocities, less heat generation and more time to dissipate heat at low discharge rates, and lower temperature of air at cold ambient conditions. The reduced temperatures and temperature uniformity minimizes the occurrence of localized hotspots within the battery pack. Further, for any given air inlet temperature, an increase in temperature is observed parallel to the direction of airflow. Under severe operating conditions, the inlet-to-discharge temperature difference reached a maximum of T = 22.14 K whereas, under mild conditions, it dropped to T = 0.21 K. The circumferential temperature non-uniformity of cells lying in high-temperature zone of the battery pack reduces with increasing velocity. The work presented here can help in the identification of potential hotspots and design better cooling strategies for the battery pack at different operating conditions.

Numerical investigation on heat transfer characteristics of S−CO2 in equal-section inclined tubes

The heat transfer characteristics of are investigated at different inclination angles (15°, 30°, 45°, 60°, and 90°) and pressures (p = 8, 9, and 10 ). It is found that the model can more accurately predict the heat transfer of in horizontal tubes. When is large, the top surface temperature will rise sharply. It is due to the gas-like film weakens the thermal absorption efficiency and impedes the fluid in the core region from taking up thermal in the near-wall area, resulting in severe heat transfer deterioration. The buoyancy criterion shows that the buoyancy and the gas-like film thickness decrease as the inclination angle increases, which effectively improves the heat transfer performance in the top area and weakens the heat transfer deterioration phenomenon. Affected by the critical temperature and the peak of specific heat, the bulk temperature also increases when the pressure increases. In the region of = 45° to 315°, raising the pressure is accompanied by higher circumferential wall temperature, whereas in contrast to the change in

Research on Low-Carbon, Energy-Saving Sintering Process with Uniform Temperature for Drill Bits

A low-carbon and energy-saving sintering process with uniform temperature distribution has been developed to address several issues associated with the sintering of drill bits in medium-frequency furnaces, namely, the large circumferential temperature differences, uneven heating of the mold, and low energy utilization. Theoretical calculations indicated that the output energy of the conventional drill bit sintering process was 12.7 kW·h, with an energy loss of 8.84 kW·h. The low-carbon sintering process achieved an output energy of 4.2 kW·h, with an energy loss of only 0.26 kW·h. Consequently, the energy utilization rates for the two processes were 30.4% and 93.8%, respectively. It was observed through the experiment that when sintering 76/49 mm drill bits at insulation temperatures of 900 °C and 1080 °C, the circumferential temperature differences in the mold were 43.7 °C and 48 °C, respectively, in the conventional drill bit sintering process. In contrast, the circumferential temperature differences in the mold were reduced to 8.7 °C and 11.3 °C, respectively, in the low-carbon and energy-saving sintering process with uniform temperature. This indicates that the average circumferential temperature difference in the mold can be reduced by 81.61% at 900 °C and by 76.46% at 1080 °C, leading to improved drill bit quality.

Modeling of a Rotary Adsorber for Continuous Capture of Indoor Carbon Dioxide

Removing indoor CO2 as a pollutant via solid sorbents is a promising solution to maintaining acceptable indoor air quality while minimizing the energy consumption of ventilation. Compared to fixed-bed and fluidized-bed configurations, which require at least two beds to allow for continuous operation, a rotary adsorber is more compact and suitable to be integrated into the ventilation systems of buildings. In the present study, a regenerative rotary adsorber based on temperature swing adsorption was modeled to investigate continuous CO2 capture in an indoor environment. The governing equations of heat and mass transfer processes associated with the capture were established and coded in ANSYS Fluent software. The spatiotemporal variations of CO2 concentration and temperature in gas and solid phases within the rotary adsorber were obtained. The key findings are: (1) adjusting the speed mainly affects circumferential concentration and temperature distribution, but has little impact on axial concentration and temperature; (2) Increasing desorption inlet flow rate has little impact on adsorption outlet concentration, but significantly decreases desorption outlet concentration; (3) Raising desorption inlet temperature can increase both adsorption and desorption outlet average concentrations; (4) Reducing the volume proportion of the desorption sector will slightly increase adsorption outlet concentration and slightly decrease desorption outlet concentration, but barely affects average adsorption and desorption outlet temperatures.

Investigation of parabolic trough collector receiver with U-pipe exchanger using a numerical approach: Towards temperature non-uniformity optimization

In this work, a numerical study of the heat flux and temperature distribution for a parabolic trough collector absorber with an internal U-pipe tube exchanger is carried out using SolTrace and ANSYS Fluent software. The effect of solar flux and temperature non-uniformity on the system performance related to the focal distance is investigated. It was noticed that the highest circumferential temperature gap of about 105 °C occurs at the medium of the absorber (0.9 m). Moreover, for the focal distances of 0.18 m, 0.19 m, and 0.2 m, the outlet water temperatures are increased to 328.8, 329.01 and 328.89 K, respectively. For these distances, the highest thermal efficiencies of about 69, 70 and 71%, respectively, are reported. Furthermore, the promising proposed approach to investigate the receiver performance combines simulation results and correlations between variables. Indeed, a strong negative correlation of −0.65 between thermal efficiency and focal distance is noticed. Thus, thermal efficiency correlates positively with maximum temperature gap, inlet–outlet temperature gap, flow rate, and outlet temperature in decreasing order with correlation coefficients of 0.64, 0.59, 0.38, and 0.32, respectively. Additionally, the simulation study emphasizes the importance of relating optimum temperature uniformity and thermal efficiency for optimizing the system performance.

Numerical Investigation into the Temperature Profile of a PHWR Channel Containing a Disassembled Fuel Bundle During a Postulated Accident Condition

A reactor core overheats due to decay heat generated in the fuel when an effective cooling medium is unavailable, such as in a loss-of-coolant accident combined with a loss of emergency core coolant. If the heat generated is not effectively dissipated, then at extreme temperatures, the structural strength of the bundle assembly may deteriorate, leading to slumping of fuel elements onto the inner wall of the pressure tube. It is essential to examine the temperature behavior of the channel containing fuel pins in a disassembled state in order to comprehend the impact of further thermally induced deformations in the channel during postulated accident conditions. Capturing the temperature of channel components at each circumferential position from experiments is extremely difficult; thus, a modeling tool is necessary to obtain a thorough circumferential temperature profile. This paper presents a numerical study that aims to study the temperature distributions in a 1-m-long pressurized heavy water reactor (PHWR) channel containing a disassembled fuel bundle. The channel geometry and the boundary conditions implemented were obtained from the experiment. A temperature profile for each channel element at every circumferential and axial location was obtained. A thorough comparison of the predicted and the reported experimental values was performed, and it was found that the predicted temperature behavior of the channel was consistent with the experimental data. Further simulations with different fuel element configurations and decay powers may be carried out; in addition, the results obtained may be used for coupled thermal-mechanical and thermal-mechanical-chemical simulations.

Forced convection heat transfer characteristics of aviation kerosene in a horizontal tube under electric field

The electrohydrodynamic (EHD) technique can considerably improve the performance of aviation heat exchangers. In this study, the forced convection heat transfer characteristics of aviation kerosene in a horizontal wire-tube structure under electric field were investigated. The influences of positive and negative high voltages on the heat transfer in test section were compared. Key factors affecting EHD heat transfer enhancement, such as fuel inlet temperature, mass flow, heat flux and operating pressure were explored. Furthermore, the cause of electrode corrosion was investigated using Scanning Electron Microscope (SEM) and Energy Disperse Spectroscopy (EDS). The experimental results showed that the circumferential temperature distribution of the test section was uneven owing to buoyancy in the absence of electric field. As the applied voltage increased, temperature heterogeneity decreased. Negative voltage improved the heat transfer more effectively than positive voltage. The electric field enhanced the heat transfer of high-temperature fuel more effectively. In the charge injection mechanism voltage range, the numerical simulation results were more similar to the negative voltage experimental results. The heat transfer enhancement ratio was reduced by an increase in the fuel mass flow and operating pressure. A higher heat flux led to a more substantial buoyancy effect, which inhibited the electric field force effect. Finally, the corrosion rate of positive high voltage electrode was the highest, resulting in rapid loss of metal elements from the electrode surface.

Novel three-dimensional simplified numerical simulation method of a compact precooler for hypersonic precooled air-breathing engine

The revolutionary thermal cycle of precooled air-breathing engines has led to the application of a compact tubular precooler. A novel three-dimensional simplified numerical simulation method for a compact tube precooler is proposed. The unique aspect of this method is the integration of low-dimensional design method of the precooler with three-dimensional simulation technique. The method includes a segmented model to discretize the precooler into sub-precoolers, with corresponding performance calculation programs for circumferential uniform and non-uniform airflows in the circumferential direction. The heat transfer and pressure drop are then simulated using a combination of the distributed heat source method and porous model. The developed method was verified with previous experiments, and showed good agreement. In addition, the flow and heat transfer characteristics of the precooler were investigated under both circumferential uniform and non-uniform inlet conditions. The results show that the radial total temperature distortion intensity at the outlet of the precooler is 0.087 and 0.073 under uniform and non-uniform inlet conditions, respectively. Additionally, the intensity of circumferential total temperature distortion increases from 0.004 under uniform inlet conditions to 0.029 under non-uniform inlet conditions. Overall, this method provides an accurate evaluation of the precooler during the engineering design phase.

Heat transfer deterioration and circumferential wall temperature inhomogeneity in a helically coiled tube carrying supercritical water: An intensive numerical simulation

Analysis of the flow and heat transfer characteristics of supercritical water (SCW) become complicated by the extensive changes in the physical properties of SCW near its pseudo-critical line and by the secondary flow stemming from the buoyancy and centrifugal force in a helically coiled tube (HCT). To address the heat transfer deterioration (HTD) of SCW in HCTs, we investigated the distribution of circumferential wall temperatures and heat transfer coefficients of SCW in a vertical HCT under the HTD condition via numerical simulation. Wall temperature was highest on the inner side, and the local heat transfer coefficient was the lowest. With increasing heat flux, the wall temperature of each circumferential position around the tube rose, while the inner wall temperature rose the most. To explain the mechanism of HTD, the rapid decrease of the specific heat and thermal conductivity near the inner side played a certain role in deteriorating the heat transfer. Further, the buoyancy effect, and the thermal acceleration effect could be used to quantitatively assess the HTD condition. The threshold values of the dimensionless number Bu describing buoyancy effect and the dimensionless number Ac describing thermal acceleration effect were found to be 3.0 × 10−6 and 1.28 × 10−6, respectively. The concept of circumferential wall temperature inhomogeneity (CWTI) was used to quantify differences in local wall temperature around the HCT. CWTI significantly increased with increasing heat flux. At low heat flux levels (qw = 300–700 kW m−2), the CWTI decreased at first, and then increases. When the heat transfer deteriorated with increasing heat flux, the trend of CWTI reversed. These results indicated that differences in circumferential wall temperature became larger under HTD conditions. Increasing pressure reduced the physical property changes in the HCT, leading to more uniform wall temperatures and a smaller CWTI. Under a constant ratio of heat flux to mass velocity, increasing the mass velocity weakens the heat transfer and even triggers HTD. In contrast, increasing pressure suppresses HTD.

Experimental investigation on flow boiling heat transfer characteristics of water and circumferential wall temperature inhomogeneity in a helically coiled tube

Helically coiled tubes (HCTs) have been widely used in chemical industry and nuclear engineering because of its compact structure and excellent heat transfer performance. This paper designed and built an experimental platform to study the flow boiling heat transfer (FBHT) of subcritical water with high temperature and high pressure in an HCT. The results showed that the wall temperature on the inner side is higher and it gradually decreases when moving to the outer side along the circumferential direction. The variation law of circumferential wall temperature inhomogeneity (CWTI) under different pressures, mass velocities, heat fluxes and vapour qualities was obtained. The distribution of circumferential wall temperature varies greatly in the single-phase region while it varies slightly and is relatively uniform in the two-phase boiling region. As the vapour quality increases, the CWTI decreases first, and maintains at a low value when the vapour quality is about 0.0 ∼ 0.9. When the vapour quality reaches about 0.9, the CWTI increases rapidly. When the vapour quality is less than 0.5, the heat flux and mass velocity have little effect on the CWTI. When the vapour quality is larger than 0.5, reducing the heat flux or increasing the mass velocity can effectively reduce the CWTI. In addition, the flow pattern of two-phase boiling flow in the HCT is divided into four regions, namely bubble flow, slug flow, annular flow and mist flow, and the transition vapour quality xt1 = 0.2, xt2 = 0.5 and xt3 = 0.93 are respectively selected according to the sudden abrupt change of the wall temperature or the differential pressure. Finally, the existing FBHT correlations are collected and evaluated and the calculation accuracy needs to be improved for more accurate calculation. Therefore, a new FBHT correlation with better accuracy is proposed for calculating the heat transfer coefficient of two-phase flow boiling in the HCT.

Thermal Analysis of a Modular Permanent Magnet Machine under Open-Circuit Fault with Asymmetric Temperature Distribution

A modular permanent magnet machine is composed of several stator modules, and the three-phase winding of each module can be controlled independently. The novel modular permanent magnet machine has good abilities in terms of fault tolerance when the machine is exposed to fault conditions. The current of each phase is different and will result in uneven loss distribution in each phase. Heat transfer occurs in the circumferential direction and temperature distribution will be asymmetric in the circumferential direction. This paper proposes a 3D finite element thermal model to accurately calculate the rise in temperature under open-circuit conditions for modular permanent magnet machines. When two modules are in operation, the machine can output rated torque. When one module is in operation and the temperature is 150 °C, the output torque is 0.76 times the rated torque. The temperature of the machine under the one-phase open-circuit condition with a zero-temperature-difference control strategy will be 0.8 °C lower than that with a minimum copper loss control strategy. Finally, a prototype with three stator modules is manufactured and the calculation results are validated by experimental test. It holds great significance for the accurate calculation of a machine with asymmetric temperature distribution in the circumferential direction.

Numerical Investigation on Heat Flux Variation in Fuel Bundle Over Fully Voided Concentric Channel of IPHWR Under Severe Accidental Scenario

Abstract A steady-state thermal analysis is performed on a fully voided channel of an Indian pressurized heavy water reactor (IPHWR) by providing variable heat flux inputs of 800 W/m2, 1500 W/m2, 2500 W/m2, 3500 W/m2, and 4500 W/m2 for evaluating the numerical results of temperature distributions in pressure tube (PT) and calandria tube (CT) at concentric scenarios using a numerical approach. The top to bottom temperature difference of PT and CT is found to be 0.57% and 3.31%, respectively, for 800 W/m2 input heat flux, and this variation decreases to 0.015% and 0.05%, respectively, for 4500 W/m2 input heat flux, thus pointing out that increasing the heat flux leads to the decreased top to bottom temperature difference. Also, the temperature distribution pattern is found to be similar for all the input heat fluxes, and for a particular heat flux, the change in circumferential temperature is found to be negligible. The boiling phenomenon starts at 2500 W/m2, and the volume fraction of moderator vapor increases as the heat flux is increased, the average density of moderators inside the enclosure decreases, and continuous variation in film thickness is also observed with respect to time for a particular heat flux value. The results also showed that the moderator acted as an effective heat sink for higher heat input rates.