Resistance Network Method Research Articles

Analysis and Experiment of Thermal Field Distribution and Thermal Deformation of Nut Rotary Ball Screw Transmission Mechanism

This study designs a differential dual-drive micro-feed mechanism, superposing the two “macro feed motions” (“motor drive screw” and “motor drive nut”) using the same transmission of “the nut rotary ball screw pair” structure. These two motions are almost equal in terms of speed and turning direction, thus the “micro feed” can be obtained. (1) Background: Thermal deformation is the primary factor that can restrict the high-precision micro-feed mechanism and the distribution of heat sources differs from that of the conventional screw single-drive system owing to the structure and motion features of the transmission components. (2) Discussion: This study explores the thermal field distribution and thermal deformation of the differentially driven micro-feed mechanism when two driving motors are combined at different speeds. (3) Methods: Based on the theory of heat transfer, the differential dual-drive system can be used as the research object. The thermal equilibrium equations of the micro-feed transmission system are established using the thermal resistance network method, and a thermal field distribution model is obtained. (4) Results: Combined with the mechanism of thermal deformation theory, the established thermal field model is used to predict the axial thermal deformation of the differential dual-drive ball screw. (5) Conclusions: Under the dual-drive condition, the steady-state thermal error of the nut-rotating ball screw transmission mechanism increases with the increase in nut speed and composite speed and is greater than the steady-state thermal error under the single screw drive condition. After reaching the thermal steady state, the measured thermal elongation at the end of the screw in the experiment is approximately 10.5 μm and the simulation result is 11.98 μm. The experimental measurement result demonstrates the accuracy of the theoretical analysis model for thermal error at the end of the screw.

In situ monitoring of flip chip package process using thermal resistance network method and active thermography

Flip chip technology has been used extensively in microelectronic packaging due to the high density, fine spacing, smaller size. However, the size and spacing of the solder bumps are decreasing gradually, defect detection is getting more and more difficult. Thus, the growing demand for high reliability has generated considerable attention on the importance of defect inspection. This paper proposes an in-situ infrared thermography monitoring method with in situ monitoring system bases on modified thermal resistance network model that added the phase transition for the non-destructive analysis of packaging process. The different defects, such as missing bump and pad, missing bump, and bridge are inspected with an accuracy of up to 90 % based on in situ monitoring system. The maximum error between the model and the experiment is 27.6 %, while the minimum error is 13.6 %. The experiment results show that the max temperature of missing bump and pad, missing bump is 35.43 °C and 6.13 °C higher than normal, and the bridge is 0.44 °C lower than normal, respectively. The maximum amplitude by the Fourier transform is used to inspect due to the max temperature of normal and bridge are indiscernible, the results show that the bridge is 4 lower than normal. The model and experimental results show that the in-situ infrared thermography monitoring method is effective for detecting defects in high density electronic devices. The proposed method of in situ monitoring is expected to provide a new strategy for next generation of three-dimensional heterogeneous integrated chips defect inspection.

Multi-scale collaborative design method for macroscopic thermal optimization and mesoscopic woven structure of hypersonic vehicle’s TOCMC leading edge

A new thermal protection design method for hypersonic vehicle’s leading edge is proposed, which can effectively reduce temperature of the leading edge without additional cooling measures. This method reduces the leading-edge’s temperature by the multi-scale collaborative design of the macroscopic thermal optimization and the mesoscopic woven structures of Three-dimensional Orthogonal Woven Ceramic Matrix Composites (TOCMC). The macroscopic thermal optimization is achieved by designing different mesoscopic woven structures in different regions to create combined heat transfer channels to dredge the heat. The combined heat transfer channel is macroscopically represented by the anisotropic thermal conductivity of TOCMC. The thermal optimization multiple linear regression model is established to optimize the heat transport channel, which predicts Theoretical Optimal Thermal Conductivity Configuration (TOTCC) in different regions to achieve the lowest leading-edge temperature. The function-oriented mesostructure design method is invented to design the corresponding mesostructure of TOCMC according to the TOTCC, which consists of universal thermal conductivity prediction formulas for TOCMC. These universal formulas are firstly derived based on the thermal resistance network method, which is verified by experiments with an error of 6.25%. The results show that the collaborative design method can effectively reduce the leading edge temperature by about 12.8% without adding cooling measures.

Comparative study of two quick-analysis models for frozen startup of high-temperature heat pipes

The alkali-metal high-temperature Heat Pipe (HP) is the common component connecting the reactor core and energy conversion device in Heat Pipe cooled Reactor (HPR). Due to the particularity of the working medium, the frozen startup of HP makes a great influence on the startup process of HPR system. In this paper, two quick-analysis models, the Improved Thermal Resistance Network (ITRN) method and the Pseudo Wick Thermal Conductivity (PWTC) method have been investigated and compared. The simulations of a sodium HP in a typical experiment are carried out by two methods in COMSOL. For simulation speed, the convergence time of a single HP using the quick-analysis models is about tens to hundreds of seconds depending on the computing equipment. The convergence of PWTC is 26.7% faster than that of ITRN. For simulation accuracy, except for the inevitable error near the flat-front, the relative error of ITRN is less than 6.94% and the relative error of PWTC is less than 8.24%. The maximum effective error of ITRN method is 34.84 K, while that of PTWC method is 58.21 K at the initial stage of startup. The TTransition = 651 K in PWTC is lower than the Texp. = 710 K in the experiment and the TTr = 701 K in ITRN, which affects the accuracy at the initial stage of startup. The error will decrease gradually in the thawing front advancing stage. For simulation analysis, some inherent defects and targeted model improvements of the two models are proposed. Through the detailed comparative study in this work, researchers can easily apply the appropriate model according to the specific requirements and avoid the defects during the simulation process.

Machine learning and computational fluid dynamics based optimization of finned heat pipe radiator performance

This study integrates machine learning, genetic algorithm and computational fluid dynamics to explore the influence of geometry on the finned heat pipe radiator performance. It also proposes an optimal geometry that enhances the heat transfer of the radiator significantly. Firstly, orthogonal test were designed, coupled the thermal resistance network method and the CFD method to model the finned heat pipe heat sink. The analysis of variance yielded the following qualitative conclusions: the height, number and thickness of the fins had different effects on the heat source temperature in descending order; the heat source temperature decreased with increasing number and thickness of the fins and increased slightly with increasing height. Secondly, a prediction model of the heat source temperature under different heat source distributions was built using four MLAs. The artificial neural network was chosen as the optimal model by comparison. The model was analysed with correlation analysis, SHAP and PDP analysis and consistent conclusions with the orthogonal test were obtained. Finally, GA was used to obtain the optimal geometric structure. The results showed that the heat source temperature was reduced to 41.75 °C and the heat sink mass was only 0.2231 kg when the number of fins was 18, the length was 38 mm, and the thickness was 0.6 mm. This solution decreased the heat source temperature by 8.7% and the heat sink mass by 18.42% compared with the optimal solution from the orthogonal test. This study demonstrated the advantages of machine learning methods in computational fluid dynamics.

Dynamic axial and radial temperature prediction of multi-plate frictional wet clutches in vehicle transmissions with the thermal resistance network method

Dynamic axial and radial temperature prediction of multi-plate frictional wet clutches in vehicle transmissions with the thermal resistance network method

Thermal-oxidation coupled analysis method for unidirectional fiber-reinforced C/SiC composites in air oxidizing environments below 1000 °C

The thermal analysis method for unidirectional fiber-reinforced C/SiC composites (C/SiC-UFRC) in air oxidizing environment below 1000 °C is developed, including a mathematical theoretical model and a finite element model. The mathematical model (MM) is established by combining the thermal resistance network method and the oxidation kinetics theory. The influence of oxidation characteristics on C/SiC-UFRC axial thermal conductivity is firstly introduced into MM, which provides a reference for the theoretical calculation method of C/SiC-UFRC axial thermal conductivity under oxidation conditions. The finite element model (FEM) is constructed on the representative volume element (RVE) of C/SiC-UFRC and the numerical heat transfer method. The FEM numerically simulated the microstructure in the oxidation process and firstly be applied to study the effects of oxidation on the micro temperature field and heat transfer of C/SiC-UFRC. Through the mutual confirmation of MM and FEM, the prediction of thermal conductivity of CMC in air oxidation environment is verified. The effects of oxidation time, oxidation temperature and random distribution of initial cracks are investigated to reveal their influences on the heat transfer behavior of C/SiC-UFRC.

Simulation of dry screw vacuum pumps based on chamber model and thermal resistance network

Current simulation for dry screw vacuum pumps fails to reflect the influence of heat transfer and component thermal deformation due to the lack of an effective simulation path. This paper proposes a novel simulation method based on the chamber model and thermal resistance network method, which integrally considers the influence of leakage, heat exchange as well as components’ temperature and deformation. First, the working process of dry screw vacuum pumps was analyzed and simplified to introduce the chamber model and thermal resistance network method. In detail, the chamber model was employed to predict the gas pressure and temperature in working chambers, and the thermal resistance network was introduced to simulate the component temperature by assuming rotors and casing only performing axial temperature distribution. Next, the detailed construction processes of the chamber model and thermal resistance network were presented. A simulation procedure was developed based on the iterative solution of the chamber model and thermal resistance network. Further, a specific case with detailed simulation setup, solution process, and experimental verification was given for a test dry screw vacuum pump. The results showed that the proposed simulation method performed a better agreement with the experimental pumping speed curve than the previous isothermal model and could effectively predict the component temperature under different inlet pressures and rotation speeds. Finally, the simulated results were further discussed to reveal the gas temperature, component deformation, and leakage process in dry screw vacuum pumps. The conclusions obtained could effectively guide the design and development of dry screw vacuum pumps.

Fault prediagnosis of power electronic devices in urban new energy system

The new energy system with low environmental load will more and more reflect its superiority in urban design and planning. The state monitoring of power electronic devices used for power conversion in new energy system is of great significance to the stable operation of the whole city. The failure mechanism and aging evolution process of IGBT modules are studied, and the failure types of IGBT devices are judged. An algorithm based on the thermal sensitive electrical parameter method and thermal resistance network method was proposed to identify aging types. Firstly, a healthy junction temperature model of IGBT based on the initial loss of turn-off was established in the double-pulse platform based on experimental data. Secondly, a thermal resistance network model of IGBT was established based on the datasheet. Finally, the accelerated aging of IGBT was carried out through the existing accelerated aging experimental platform of IGBT in the laboratory, and the aging parameters were imported into the above two models. The results show that the output results of the thermal resistance network model and the thermal parameter model are affected by the aging type, which provides a new solution for the aging type research of IGBT, and is of great value for the application of new energy system.

Heat transfer performance of the rectangular heat sinks with non-uniform height thermosyphons for high power LED lamps cooling

The rectangular heat sinks with non-uniform height thermosyphons are proposed for high power light emitting diode (LED) lamps cooling in this study. The combined thermal resistance network and finite volume method is developed to reveal the heat transfer mechanism. The simulated results show good agreement with experimental data with relative errors of 2.14–2.69% at heating powers of 12–20 W. In comparison with type-a thermosyphon heat sink, the thermal resistance of type-b thermosyphon heat sink offers 8.47–9.91% higher due to thicker thermal boundary layer between air and thermosyphon fins in the intermediary region, whereas the thermal resistance of type-c thermosyphon heat sink offers 7.26–9.07% lower because of better free stream among thermosyphon fins in the intermediary region. The maximum heat transfer rate of type-a, type-b and type-c thermosyphon heat sinks are 19 W, 17 W and 22 W in regard to the temperature threshold of 85 °C, respectively. This paper provides guidelines for the design of high power LED lamps cooling.

Numerical model and optimization strategy for the annealing process of 3D coil cores

Three-dimensional (3D) coil core is one kind of transformer iron core that is made of grain-oriented electrical steel. This material should be annealed before use because of the residual stress generated inside the silicon steel strip during production. The temperature evaluation of the 3D coil core is important to its annealing quality, but this temperature cannot be measured easily and the prediction method is seldom mentioned in the open literature. A numerical model, which considers the anisotropic heat conduction inside the 3D coil core and convection and radiation heat transfers inside the furnace, is built to link the temperature of furnace with the temperature of 3D coil core. Monte Carlo method is used to calculate the view factors between surfaces in the furnace. Thermal radiation resistance network method is used to obtain radiant heat flux. A computational fluid dynamics model is established to predict the convection heat transfer coefficient. The finite volume method is used to solve the anisotropic conduction inside the 3D coil core, wherein radiant heat flux and convection heat transfer coefficient serve as boundary conditions. The model considers the effects of size, position, location, orientation, and number of 3D coil cores on the temperature evolution. Onsite experiments verify that this digital model is precise in practical application, and the typical simulation error is less than ±2.5%. A straight forward optimization strategy is proposed on the basis of the digital model. The onsite experiments also show that the optimization method can effectively shorten the annealing time and increase the efficiency of the annealing process. Making a near real-time prediction and keeping 3D heat transfer features are the advantages of the present method.

Calculating the effective thermal conductivity of gray cast iron by using an interconnected graphite model

A new theoretical model of gray cast iron taking into account a locally interconnected structure of flake graphite was designed, and the corresponding effective thermal conductivity was calculated using the thermal resistance network method. The calculated results are obviously higher than that of the effective medium approximation assuming that graphite is distributed in isolation. It is suggested that the interconnected structure significantly enhances the overall thermal conductivity. Moreover, it is shown that high anisotropy of graphite thermal conductivity, high volume fraction of graphite, and small aspect ratio of flake graphite will cause the connectivity effects of graphite to more obviously improve the overall thermal conductivity. Higher graphite volume fraction, lower aspect ratio and higher matrix thermal conductivity are beneficial to obtain a high thermal conductivity gray cast iron. This work can provide guidance and reference for the development of high thermal conductivity gray cast iron and the design of high thermal conductivity composites with similar locally interconnected structures.

Review of IGBT Junction Temperature Extraction and Estimation Methods

IGBT is widely used in photovoltaic power generation, aerospace, electric vehicles, ships and other power electronic equipment due to its advantages such as simple driving, high power level, low power consumption, and good thermal stability. As the core component of power electronic equipment, IGBT has always been a major concern for manufacturers and users. Excessive temperature is considered to be the main cause of IGBT failure. In order to meet the needs of high reliability in these applications, it is important to manage and control the temperature of the IGBT. Therefore, how to estimate or measure the junction temperature of IGBT is the focus of research on IGBT reliability. This article introduces several published methods for measuring junction temperature, focuses on the Temperature sensitive electrical parameters (TSEP) method and thermal resistance network method, and conducts experimental verification through the IGBT double-pulse test platform. Trying to provide help for future junction temperature detection work.

On the steady posture of conical spindle distribution used in ball piston pump

Conical spindle distribution is a new type of hydraulic pump distribution, its steady working conditions refer to a stable position of the shaft and lubrication state under constant operating condition, which directly influences the hydraulic pump efficient and reliable work. In this paper, the Reynolds equation of the tapered flow field is used to establish the lubrication model. The static pressure boundary condition of the distribution pair is obtained by the hydraulic resistance network method. The finite difference method is employed to solve the model. The static and dynamic lubricating performances including the shaft eccentricity and the distribution gap height are obtained by solving the model with a numerical method. Accordingly, the influences of structural parameters and operating parameters on the steady state are investigated, and an experimental test rig is built to validate the model. The experimental results show that the model can predict the higher working pressure which leads to higher distribution gap and eccentricity; the higher the rotational speed is, the smaller the distribution gap and the eccentricity will become, which provides theoretical support for further guidance of the distribution design.

Glassy carbon cladding structure with elongated SiCnw reinforced carbon foam insert

In this study, glassy carbon cladding structure with elongated SiCnw reinforced carbon foam insert (GC-CF/SiCnw) is prepared by slow Polymer Infiltration Pyrolysis (PIP) method. It is tested that the density of the structure reaches 0.6362 g cm−3 while the open porosity reaches 0.8% and total porosity reaches 52.6%. The SEM images show the obvious boundary between the inner and outer parts. In addition, the structure exhibits excellent mechanical properties, its compressive strength reaches 6.6 MPa, and the specific strength reaches 10.3877 MPa g−1 cm−3. Considering the fracture mechanism, the four-stage different force composition in the fracture process is significantly different from the traditional material, reflecting the influence of the excellent structural design of the material on the mechanical properties. Moreover, the structure exhibits excellent high temperature insulation properties. As the temperature increases from 293 K to 1273 K, the effective thermal conductivity increases from 0.215 W m−1K−1 to 0.587 W m−1K−1. Considering the thermal insulation mechanism, the reflection of thermal radiation from the dense and smooth GC shell and the scattering of thermal radiation from the SiC nanowires greatly reduces the transmission of thermal radiation. Besides, the temperature field index diagram under steady-state heat conduction as a heat-source temperature of 1200 K is obtained by thermal resistance network method.

Heat transfer mathematical model for a novel parabolic trough solar collecting system with V-shaped cavity absorber

Solar heat utilization in medium temperature range (80–250℃) has attracted more and more attentions in the field of building and industry energy conservation. A heat transfer model for a novel parabolic trough solar collecting system with V-shaped cavity absorber is established based on the thermal resistance network method. Experimental validation was performed in different weather conditions to investigate the calculation accuracy of the proposed model. The analysis results demonstrate that the model calculation error mainly lies in the influence of wind speed deviation and the difference between the theoretical and actual temperature rise rate with the sudden changes of solar direct normal irradiation (DNI). By carrying out bias correction, the model calculated results were perfectly consistent with the experimental results. Based on the proposed model, the effects of different environmental factors on the outlet temperature and collecting efficiency were compared, and the comparison results can be used to correct the proposed model in different weather and environmental conditions, which make the proposed heat transfer model more reliable to the practical operation situation. As a result, the proposed model may provide a theoretical basis for the operation optimization of the solar collecting system.

Static performance of the aerostatic journal bearing with grooves

Aerostatic bearings are widely employed in precision machines due to their properties of low friction, low heat conduction, and long-life operation. In this work, static performance of the journal bearing with rectangular grooves is investigated numerically. The effect of geometrical parameters such as axial groove length [Formula: see text], circumferential groove length [Formula: see text], orifice diameter df, groove depth gh, misalignment angles [Formula: see text] and [Formula: see text] on the load capacity [Formula: see text], stiffness [Formula: see text], and gas flow rate [Formula: see text] are analyzed systematically. The resistance network method (RNM) is utilized to solve the Reynolds equation required in the analysis. Performance parameters including pressure distribution P, load force [Formula: see text], stiffness [Formula: see text], and gas flow rate [Formula: see text] are examined in the simulations. It is revealed from the simulations that the proper value of axial groove length [Formula: see text] to obtain a better static performance varies from 1/8 to 1/2 when df varies between 0.11 and 0.29 mm, respectively. Therefore, a larger load force and stiffness can be obtained if [Formula: see text] is chosen to be 1/4, when diameter of the bearing orifice df equals 0.17 mm. It is also suggested that [Formula: see text] be chosen from the range of 1/6 and 1/3 to obtain a better static performance and a smaller gas flow rate. [Formula: see text] decreases with an increase in df when [Formula: see text] is set to be 1/8. However, the load force [Formula: see text] increases with an increase in df when [Formula: see text] varies from 3/8 to 1/2. [Formula: see text] has a significant influence on the changes of [Formula: see text] with df when [Formula: see text] is set to be constant. Therefore, df should be selected according to [Formula: see text] for an optimal design. The increase of misalignment angle [Formula: see text] leads to an increase in the load force [Formula: see text]. [Formula: see text] has little influence on the load force [Formula: see text]. Misalignment angles [Formula: see text] and [Formula: see text] have little influence on stiffness [Formula: see text] and gas flow rate [Formula: see text]. Therefore, it is preferable if [Formula: see text] is larger than 0 rad.

The velocity distribution of a cutting microchannel plate based on the resistance network method

Velocity distribution has a very important influence on the performance of microchannel devices. In this paper, a cutting microchannel plate was proposed, and the velocity distribution was investigated based on the resistance network method. The results showed that the asymmetric cutting microchannel plate had the most uniform velocity distribution. Finally, the optimal results were further confirmed via ANSYS Fluent simulation and the heat and mass transfer efficiencies were also investigated. Taken together, the present findings provide direct evidence that uniform velocity distribution results in the higher performance of microchannel devices.

Thermal-hydraulic analysis of a new conceptual heat pipe cooled small nuclear reactor system

Abstract Small nuclear reactor features higher power capacity, longer operation life than conventional power sources. It could be an ideal alternative of existing power source applied for special equipment for terrestrial or underwater missions. In this paper, a 25kWe heat pipe cooled reactor power source applied for multiple use is preliminary designed. Based on the design, a thermal-hydraulic analysis code for heat pipe cooled reactor is developed to analyze steady and transient performance of the designed nuclear reactor. For reactor design, UN fuel with 65% enrichment and potassium heat pipes are adopted in the reactor core. Tungsten and LiH are adopted as radiation shield on both sides of the reactor core. The reactor is controlled by 6 control drums with B4C neutron absorbers. Thermoelectric generator (TEG) converts fission heat into electricity. Cooling water removes waste heat out of the reactor. The thermal-hydraulic characteristics of heat pipes are simulated using thermal resistance network method. Thermal parameters of steady and transient conditions, such as the temperature distribution of every key components are obtained. Then the postulated reactor accidents for heat pipe cooled reactor, including power variation, single heat pipe failure and cooling channel blockage, are analyzed and evaluated. Results show that all the designed parameters satisfy the safety requirements. This work could provide reference to the design and application of the heat pipe cooled nuclear power source.

Investigation of Effective Thermal Conductivity for Ordered and Randomly Packed Bed with Thermal Resistance Network Method

In the present paper, the effective thermal conductivities of Li4SiO4-packed beds with both ordered and random packing structures were investigated using thermal resistance network methods based on both an Ohm’s law model and a Kirchhoff’s law model. The calculation results were also validated and compared with the numerical and experimental results. Firstly, it is proved that the thermal resistance network method based on the Kirchhoff’s law model proposed in the present study is reliable and accurate for prediction of effective thermal conductivities in a Li4SiO4-packed bed, while the results calculated with the Ohm’s law model underestimate both ordered and random packings. Therefore, when establishing a thermal resistance network, the thermal resistances should be connected along the main heat transfer direction and other heat transfer directions as well in the packing unit. Otherwise, both the total heat flux and effective thermal conductivity in the packing unit will be underestimated. Secondly, it is found that the effect of the packing factor is remarkable. The effective thermal conductivity of a packed bed would increase as the packing factor increases. Compared with random packing at similar packing factor, the effective thermal conductivity of packed bed would be further improved with an ordered packing method.