scholarly journals An Improved LPTN Method for Determining the Maximum Winding Temperature of a U-Core Motor

Energies ◽  
2020 ◽  
Vol 13 (7) ◽  
pp. 1566
Author(s):  
Bin Li ◽  
Liang Yan ◽  
Wenping Cao
Keyword(s):  
Heat Flux ◽  
Heat Source ◽  
Heat Dissipation ◽  
Temperature Drop ◽  
Maximum Temperature ◽  
Heat Sources ◽  
Heat Generator ◽  
Thermal Network ◽  
Lumped Parameter ◽  
Flux Change

In a traditional lumped-parameter thermal network, no distinction is made between the heat and non-heat sources, resulting in both larger heat flux and temperature drop in the uniform heat source. In this paper, an improved lumped-parameter thermal network is proposed to deal with such problems. The innovative aspect of this proposed method is that it considers the influence of heat flux change in the heat source, and then gives a half-resistance theory for the heat source to achieve the temperature drop balance. In addition, the coupling relationship between the boundary temperature and loading position of the heat generator is also added in the lumped-parameter thermal network, so as to amend the loading position and nodes’ temperature through iterations. This approach breaks the limitation of the traditional lumped-parameter thermal network: that the heat generator can only be loaded at the midpoint, which is critical to determining the maximum temperature in asymmetric heat dissipation. By adjusting the location of heat generator and thermal resistances of each branch, the accuracy of temperature prediction is further improved. A simulation and an experiment on a U-core motor show that the improved lumped-parameter thermal network not only achieves higher accuracy than the traditional one, but also determines the loading position of the heat generator well.

scholarly journals Pool Boiling of Nanofluids on Biphilic Surfaces: An Experimental and Numerical Study

Nanomaterials ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 125
Author(s):  
Eduardo Freitas ◽  
Pedro Pontes ◽  
Ricardo Cautela ◽  
Vaibhav Bahadur ◽  
João Miranda ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Numerical Model ◽  
Heat Dissipation ◽  
Numerical Study ◽  
Pool Boiling ◽  
Temperature Drop ◽  
Surface Cooling ◽  
Average Temperature ◽  
Gold Silver

This study addresses the combination of customized surface modification with the use of nanofluids, to infer on its potential to enhance pool-boiling heat transfer. Hydrophilic surfaces patterned with superhydrophobic regions were developed and used as surface interfaces with different nanofluids (water with gold, silver, aluminum and alumina nanoparticles), in order to evaluate the effect of the nature and concentration of the nanoparticles in bubble dynamics and consequently in heat transfer processes. The main qualitative and quantitative analysis was based on extensive post-processing of synchronized high-speed and thermographic images. To study the nucleation of a single bubble in pool boiling condition, a numerical model was also implemented. The results show an evident benefit of using biphilic patterns with well-established distances between the superhydrophobic regions. This can be observed in the resulting plot of the dissipated heat flux for a biphilic pattern with seven superhydrophobic spots, δ = 1/d and an imposed heat flux of 2132 w/m2. In this case, the dissipated heat flux is almost constant (except in the instant t* ≈ 0.9 when it reaches a peak of 2400 W/m2), whilst when using only a single superhydrophobic spot, where the heat flux dissipation reaches the maximum shortly after the detachment of the bubble, dropping continuously until a new necking phase starts. The biphilic patterns also allow a controlled bubble coalescence, which promotes fluid convection at the hydrophilic spacing between the superhydrophobic regions, which clearly contributes to cool down the surface. This effect is noticeable in the case of employing the Ag 1 wt% nanofluid, with an imposed heat flux of 2132 W/m2, where the coalescence of the drops promotes a surface cooling, identified by a temperature drop of 0.7 °C in the hydrophilic areas. Those areas have an average temperature of 101.8 °C, whilst the average temperature of the superhydrophobic spots at coalescence time is of 102.9 °C. For low concentrations as the ones used in this work, the effect of the nanofluids was observed to play a minor role. This can be observed on the slight discrepancy of the heat dissipation decay that occurred in the necking stage of the bubbles for nanofluids with the same kind of nanoparticles and different concentration. For the Au 0.1 wt% nanofluid, a heat dissipation decay of 350 W/m2 was reported, whilst for the Au 0.5 wt% nanofluid, the same decay was only of 280 W/m2. The results of the numerical model concerning velocity fields indicated a sudden acceleration at the bubble detachment, as can be qualitatively analyzed in the thermographic images obtained in this work. Additionally, the temperature fields of the analyzed region present the same tendency as the experimental results.

Analytical Formulation for the Temperature Profile by Duhamel’s Theorem in Bodies Subjected to an Oscillatory Heat Source

2005 ◽  
Vol 129 (2) ◽  
pp. 236-240 ◽  
Author(s):  
Jun Wen ◽  
M. M. Khonsari
Keyword(s):  
Finite Element Method ◽  
Heat Flux ◽  
Heat Source ◽  
Temperature Profile ◽  
Rectangular Domain ◽  
Temperature Fields ◽  
Heat Sources ◽  
Point Heat Source ◽  
Analytical Formulation ◽  
Analytical Technique

An analytical technique is presented for treating heat conduction problems involving a body experiencing oscillating heat flux on its boundary. The boundary heat flux is treated as a combination of many point heat sources, each of which emits heat intermittently based on the motion of the flux. The working function of the intermittent heat source with respect to time is evaluated by using the Fourier series and temperature profile of each point heat source is derived by using the Duhamel’s theorem. Finally, by superposition of the temperature fields over all the point heat sources, the temperature profile due to the original moving heat flux is determined. Prediction results and verification using finite element method are presented for an oscillatory heat flux in a rectangular domain.

scholarly journals Induction Motor Thermal Analysis Based on Lumped Parameter Thermal Network

2020 ◽  
Author(s):  
Pedro Cabral ◽  
Amel Adouni
Keyword(s):  
Thermal Analysis ◽  
Induction Motor ◽  
Operating Conditions ◽  
Heat Sources ◽  
Thermal Network ◽  
Iron Losses ◽  
Lumped Parameter ◽  
Proposed Model ◽  
Industry Applications ◽  
Different Temperatures

Many industry applications required the use of the induction motors. In such envirenement the electrical machines are facing of many stressed operating conditions. One of the critical creteria which decide the choice of the induction motor is the thermal behaviour under different mode operation. In this paper a study of the thermal behavior of an induction motor is presented. In order to predict the temperature in the different machine components, a model based on the lumped parameter thermal network   has been developed. The geometry of the machine and the thermal properties of its various components are used to express the developed model. The joule and the iron losses are considering as the inputs. The proposed model is implemented and tested using MATLAB software. It is a simple model which could predict rapidly the different temperatures. Keywords: Induction motor, Thermal analysis, Lumped parameters thermal network, Modeling, Heat sources

Causes of the 1985-2014 Surface Warming over the Sanjiangyuan Region of the Tibetan Plateau from the Perspective of Energy Transport

2020 ◽  
Author(s):  
Yinglin Tian ◽  
Deyu Zhong
Keyword(s):  
Heat Flux ◽  
Tibetan Plateau ◽  
Heat Source ◽  
Energy Transport ◽  
Longwave Radiation ◽  
Warming Trend ◽  
The Tibetan Plateau ◽  
Heat Sources ◽  
The South ◽  
Downward Longwave Radiation

<p>The Tibetan Plateau (TP), known as the “World Roof”, has significant influences on hydrological and atmospheric circulation at both regional and global scale. As the Sanjiangyuan Region (SJY) supplies water resources to the adjacent river basin and the TP could exert strong thermal forcing on the atmosphere over Asian monsoon region, adequate understand of the climate change over this region and its underlying mechanisms is of great importance. Based on gridded data provided by China Meteorological Administration (CMA), a continuous warming trend higher than that over elsewhere in China has been observed over the TP during 1985-2014, especially in the cold season (0.69 K/decade) and over the SJY (1.0 K/decade). On the basis of ERA interim reanalysis datasets, this paper analyzed the factors facilitating this warming trend in the SJY from the perspective of energy transport. At first, the local processes involved were investigated by calculating partial temperature changes using the surface energy budget equation. Then the horizontal convection of heat was quantified by summing the heat flux across the boundaries of the SJY. Finally, a Lagrangian heat source diagnostic method was developed to identify the major heat source. As the results indicating, among all the local heat sources, the enhanced downward longwave radiation reflected to surface air and the increasing upward longwave radiation emitted by warmer land surface were responsible for the pronounced surface air warming. However, the changes in surface sensible and latent heat fluxes had a reduced warming effect on the surface air. As for the non-local horizontal heat sources, rising horizontal heat flux from the south, west and east boundaries into the SJY contributed to the higher surface temperature of the SJY. In winter season, the heat flows stemmed from the South Himalayan vein into the SJY played a dominant role. Moreover, the higher the temperature over the SJY was, the more inclined this heat source was to Nepal.</p>

scholarly journals Effect of phase change materials on heat dissipation of a multiple heat source system

Open Physics ◽  
2019 ◽  
Vol 17 (1) ◽  
pp. 797-807
Author(s):  
Kai Yu ◽  
Yao Wang ◽  
Yanxin Li ◽  
Jakov Baleta ◽  
Jin Wang ◽  
...  
Keyword(s):  
Heat Source ◽  
Phase Change ◽  
Heat Pipe ◽  
Phase Change Materials ◽  
Heat Dissipation ◽  
Experimental Tests ◽  
Equilibrium Temperature ◽  
System Structure ◽  
Heat Sources ◽  
Lower Temperature

AbstractThis paper experimentally investigates heat dissipation of a heat pipe with phase change materials (PCMs) cooling in a multiple heat source system. Two heat sources are fixed at one end of the heat pipe. Considering that a heat sink cannot dissipate all the heat generated by two heat sources, various PCMs are used due to a large latent heat. Different materials in a container are wrapped outside of the middle heat pipe to take away the heat from the evaporation section. The experimental tests obtain temperature data of heat source, evaporation section, and energy storage characteristics of PCMs are also determined under constant and dynamic values of the heat source powers. It is found that under this multiple heat source system structure, the phase change material RT35 maintains temperature variations of the evaporation section at a lower temperature and shortens the required time to reach the equilibrium temperature under a heating power of 20 W.

Plastic Dissipation and Temperature Field around a Steady Running Crack

2006 ◽  
Vol 324-325 ◽  
pp. 895-898
Author(s):  
Wen Bo Luo ◽  
Ting Qing Yang
Keyword(s):  
Temperature Field ◽  
Heat Source ◽  
Plastic Zone ◽  
Temperature Rise ◽  
Heat Dissipation ◽  
Crack Tip ◽  
Maximum Temperature ◽  
Growth Speed ◽  
Density Distribution Function ◽  
Plastic Dissipation

Temperature field is formed due to heat dissipation when material is subjected to irreversible deformation. In this paper, the heat dissipation in the crack-tip plastic zone was considered. By considering the propagating crack-tip plastic zone as a running heat source and constructing a reasonable heat source density distribution function, the temperature field around a steady running crack was obtained. It is shown that temperature rise is dependent on the crack growth speed and the material parameters. The maximum temperature rise reaches to >50 oC in our example calculations for a steady running crack in PMMA.

Thermo-Electro-Mechanical Refrigeration Based on Transient Thermoelectric Effects

1999 ◽  
Author(s):  
Andrew Miner ◽  
Arun Majumdar ◽  
Uttam Ghoshal
Keyword(s):  
Heat Flux ◽  
Figure Of Merit ◽  
Temperature Drop ◽  
Maximum Temperature ◽  
Pulsed Current ◽  
Thermoelectric Cooler ◽  
Thermoelectric Effects ◽  
Mechanical Element ◽  
Intermittent Contact ◽  
A Tec

Abstract This paper introduces the concept of a thermo-electro-mechanical cooler (TEMC), which modifies a traditional thermoelectric cooler (TEC) by using intermittent contact of a mechanical element synchronized with an applied pulsed current. Using Bi2Te3 as the thermoelectric material, it is predicted that the maximum temperature drop across a TEMC may be as much as 35 percent higher than that of a TEC in low heat flux applications. This effectively increases the figure of merit by a factor of 1.8.

scholarly journals Deferred Cooling System for Desert Climates

2020 ◽  
Vol 12 (2) ◽  
pp. 168781401988805
Author(s):  
MF El Bedaiwy ◽  
MS El Morsi ◽  
MA Serag-Eldin
Keyword(s):  
Heat Dissipation ◽  
Cooling System ◽  
Temperature Drop ◽  
Weather Data ◽  
Maximum Temperature ◽  
Air Cooling ◽  
Ambient Conditions ◽  
Thermodynamic Cycles ◽  
Radiation Exchange ◽  
Equipment Sizing

The paper presents the design of a novel heat rejection system suitable for desert climates where daytime temperatures are typically high, nighttime cooling through sky radiation exchange is highly effective, and freshwater is scarce. Desert climates also feature high solar energy intensities during daytime, which can be exploited to power thermodynamic cycles. However, such cycles reject heat during operation, and daytime temperatures are too high for employing air cooling whereas scarcity of freshwater limits the applicability of evaporative cooling. We propose a system that defers dissipation of heat rejected during daytime operation to nighttime when ambient conditions are much more favorable for heat dissipation to the atmosphere. The paper presents the proposed design, its method of operation, and its implementation in a solar-driven ice-making plant in Upper Egypt. A mathematical model was developed to predict system performance and support decision-making over equipment sizing. It was used to simulate the performance of the deferred cooling system over a week. Using weather data collected at New Cairo (30.02 °N latitude, 31.5 °E longitude) in April 2017, the model demonstrated that the system could achieve a maximum temperature drop of 16 °C, which corresponds to a cooling of 47 MJ/m2/night.

Cutting Tool Temperature Analysis in Heat-Pipe Assisted Composite Machining

2007 ◽  
Vol 129 (5) ◽  
pp. 902-910 ◽  
Author(s):  
Jie Liu ◽  
Y. Kevin Chou
Keyword(s):  
Heat Flux ◽  
Finite Element ◽  
Heat Source ◽  
Heat Pipe ◽  
Heat Dissipation ◽  
Cutting Tool ◽  
Advanced Materials ◽  
Chemical Vapor Deposition Diamond ◽  
Rake Face ◽  
Coating Failure

Machining of advanced materials, such as composite, encounters high cutting temperatures and rapid tool wear because of the abrasive nature of the reinforcement phases in the workpiece materials. Ultrahard coatings, such as chemical vapor deposition diamond, have been used for machining such advanced materials. Wear of diamond-coated tools is characterized by catastrophic coating failure, plausibly due to the high stress developed at the coating-substrate interface at high temperatures because of very different elastic moduli and thermal expansion coefficients. Temperature reductions, therefore, may delay the onset of the coating failure and offer tool life extension. In this study, a passive heat-dissipation device, the heat pipe, has been incorporated in composite machining. Though it is intuitive that heat transfer enhanced by the heat pipe may reduce tool temperatures, the heat pipe will likely increase heat partitioning into the tool at the rake face, and complicate the temperature reduction effectiveness. A combined experimental, analytical, and numerical approach was used to investigate the heat-pipe effects on cutting tool temperatures. A machining experiment was conducted and the heat-source characteristics were analyzed using cutting mechanics. With the heat sources as input, cutting tool temperatures in machining, without or with a heat pipe, were analyzed using finite element simulations. The simulations encompass a 3-D model of a cutting tool system and a 2-D chip model. The heat flux over the rake-face contact area was used in both models with an unknown heat partition coefficient, determined by matching the average temperature at the tool-chip contact from the two models. Cutting tool temperatures were also measured in machining using thermocouples. The simulation results agree reasonably with the experiment. The model was used to evaluate how the heat pipe modifies the heat transport in a cutting tool system. Applying heat-pipe cooling inevitably increases the heat flux into the tool because of the enhanced heat dissipation. However, the heat pipe is still able to reduce the tool-chip contact temperatures, though not dramatically at current settings. The parametric study using the finite element analysis (FEA) models shows that the cooling efficiency decreases as the cutting speed and feed increase, because of the increased heat flux and heat-source area. In addition, increasing the heat-pipe volume and decreasing the heat-pipe distance to the heat source enhances the heat-pipe cooling effectiveness.

scholarly journals Effect of Perforation Shapes on the Heat Transfer Characteristic of Perforated Fins

2019 ◽  
Vol 8 (4) ◽  
pp. 1394-1400
Keyword(s):  
Heat Transfer ◽  
Heat Dissipation ◽  
Temperature Drop ◽  
Transfer Characteristic ◽  
Maximum Temperature ◽  
Shape Modification ◽  
Flow Area ◽  
Cross Sectional ◽  
Enhancement Of Heat Transfer ◽  
Different Shapes

A large number of engineering applications required rapid heat dissipation from its surface. This is achieved by the use of the fins i.e. increasing the surface area. Enhancement of heat transfer and reduction in the weight is the major criteria for designing the fins. The main objective of this project is to enhance the heat transfer through the use of perforated fin. A large number of study have been conducted on shape modification by cutting some material from fins to make holes, cavity, slots, groves or channel through the fin body to increase flow area. A rectangular fin of dimension 100 mm. x 200 mm. x 2 mm. and area of perforation is 100 mm2 was selected. The number of perforation was varied from 20, 28, 36 and 44. It was found that maximum temperature drop occurred with 44 perforations. With the same fin with 44 perforation, temperature drop and heat transfer was analysed for different shapes (circular, square, oriented square, pentagon and elliptical) of perforation. I was found that in case of different shape of perforation with same cross sectional area, weight is nearly reduced by 28.42 % for elliptical perforation (a/b>3) was most effective in which 32.20 % more temperature drop and maximum average heat flux as compared to other perforation shape.

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