Thermal Control Method Research Articles

Investigation on Active Thermal Control Method with Pool Boiling Heat Transfer at Low Pressure

In order to maintain a desirable temperature level of electronic equipment at low pressure, the thermal control performance with pool boiling heat transfer of water was examined based on experimental measurement. The total setup was designed and performed to accomplish the experiment with the pressure range from 4.5 kPa to 20 kPa and the heat flux between 6 kW/m2 and 20 kW/m2. The chosen material of the heat surface was aluminium alloy and the test cavity had the capability of varying the direction for the heat surface from vertical to horizontal directions. Through this study, the steady and transient temperature of the heat surface at different pressures and directions were obtained. Although the temperature non-uniformity of the heat surface from the centre to the edge could reach 10°C for the aluminium alloy due to the varying pressures, the whole temperature results successfully satisfied with the thermal control requirements for electronic equipment, and the temperature control effect of the vertically oriented direction was better than that of the horizontally oriented direction. Moreover, the behaviour of bubbles generating and detaching from the heat surface was recorded by a high-resolution camera, so as to understand the pool boiling heat transfer mechanism at low-load heat flux. These pictures showed that the bubbles departure diameter becomes larger, and departure frequency was slower at low pressure, in contrast to 1.0 atm.

Thermal error control method based on thermal deformation balance principle for the precision parts of machine tools

A new thermal error control method based on the thermal deformation balance principle is suggested to control the thermal error of a precision machine tool’s functional parts, which negatively affects processing precision. The compensation of the thermal expansion of metal by the thermal contraction of carbon fiber reinforced plastics (CFRPs), which has a negative linear expansion coefficient, lies behind this method. The metal structure is bonded with CFRP bandage and thermoelectric modules to achieve the temperature difference between the metal and the CFRP, thereby realizing the same thermal deformation. The heat transfer channel in the compensation system for thermal deformation is designed by the structural topology design method to distribute the heat evenly. Experimental and numerical simulation results show that the suggested approach reduces thermal displacement by 93% compared with the metal structure without the CFRP bandage. The suggested method can be applied to thermal deformation compensation for various high-precision equipment, including coordinate measuring machines, aerospace equipment, and optics and optical instruments.

The impact of non-chemical weed control methods and biopreparations on winter oilseed rape preparation for over-wintering and productivity

The current study was aimed to establish the impact of non-chemical weed control methods (thermal, mechanical andsmothering) and biopreparations on winter oilseed rape (Brassica napus L.) preparation for over-wintering and productivity under the conditions of the organic farming system. During the 2014–2016 period, a field experiment was conducted at the Experimental Station of Aleksandras Stulginskis University on Calc(ar)i-Endohypogleyic Luvisol (LVg-n-w-cc). The field experiment treatments were the following: Factor A – non-chemical weed control methods: 1) thermal (water steam), 2) mechanical (inter-row loosening), 3) smothering (self-regulation, sowing with narrow inter-rows); Factor B – application of biopreparations: 1) without application, 2) with application. During the period of autumn vegetation, in the smothering method plots, where the winter oilseed rape crop density was 1.5–2.4 times lower than that in the plots of thermal and mechanical weed control methods, the significantly highest aboveground mass of plant, number of leaves per plant, diameter of root collar, root area, total root length, root biomass of plant and leaf area of plant were determined, and in 2015 the highest chlorophyll index was measured in the leaves. In 2014 the application of biopreprations in the smothering method plots significantly increased the aboveground mass of plant (41.3%), the total root length (33.2%) and the root biomass of plant (28.0%). In 2004 the diameter of winter oilseed rape root collar depended on the leaf area of plant (r = 0.83, P < 0.05) and the root area of plant (r = 0.86, P < 0.05), and in 2015 it depended on the leaf area of plant (r = 0.89, P < 0.05), the root area (r = 0.99, P < 0.01), the total root length (r = 0.98, P < 0.01) and the root biomass of plant (r = 0.99, P < 0.01). Positive, strong and very strong, and statistically significant relationships were established between the leaf area of oilseed rape and the root area, the total root length and the root biomass of plant. In the spring of 2015, during the renewed oilseed rape vegetation stage, the highest crop density (98.0 units m–2) and over-wintering (96.0%) were obtained in the plots of the mechanical weed control method in combination with biopreparations. In the spring of 2016, different nonchemical weed control methods and biopreparations did not have any significant effect on the oilseed rape over-wintering and the crop density. In 2015, different non-chemical weed control methods did not have any significant influence on oilseed rape biometric parameters before harvesting. In 2016, in the smothering method plots a significantly lower mass of oilseed rape and the number of branches per plant were formed compared to those of other used treatments. The highest number of pods per plant was determined in the smothering method plots in combination with biopreparations. In 2015 biopreprations in the smothering method plots significantly increased the 1 000 seed mass, and in 2016 they increased the number of pods per plant, respectively 7.2 and 35.6%. In the droughty year of 2015, the significantly highest winter oilseed rape seed yield was recorded in the plots of the mechanical weed control method, and in the moist year of 2016, the highest yield was in the smothering method plots with biopreparations. In 2015 biopreprations significantly increased the oilseed rape seed yield in the plots of thermal and mechanical weed control methods, and in 2016 they increased the yield in the smothering method plots, respectively 43.4, 25.1 and 51.5%. In 2015 the winter oilseed rape seed yield depended on the crop density (r = 0.86, P < 0.05) and the plant height (r = 0.94, P < 0.01), and in 2016 it depended on the number of pods per plant (r = 0.98, P < 0.01) and the plant height (r = 0.85, P < 0.05).

Integrated system of non-contact thermal control of the units of self-contained locomotives

The stages of implementation of the integrated system of non-contact thermal control of the main units and systems of self-contained locomotives are considered. The developed techniques for assessing the technical state of sections of radiators, electrical machines, and high-pressure fuel equipment of self-contained locomotives using the thermal imaging control method are presented.

Design of thermal error control system for high-speed motorized spindle based on thermal contraction of CFRP

Among the thermal error sources of the high accuracy and efficiency machine tools, the thermal errors induced by the heat generated from running high speed motorized spindle is the crucial one. A new thermal error control method for motorized spindle is suggested, which is based on the thermal deformation balance principle. The essential idea of the method is to utilize the thermal contraction of Carbon Fiber Reinforced Plastic (CFRP) to restrain the thermal elongation of metal spindle housing. In the designed control system, the CFRP bars are uniformly distributed around the spindle housing, and the ThermoElectric Modules (TEMs) works as the heat pump which transfers the heat from spindle housing to CFRP bar. The experimental and numerical simulation results show that the suggested approach reduces 97% thermal displacement compared with the motorized spindle without the suggested thermal error control system. It is expected that the suggested method can also be applied to thermal error control for various cylindrical high-precision parts including aerospace equipment, optics and optical instruments.

Improvement of the internal light environment on the objects of transport infrastructure with aid of sun-protective devices

The article analyzes the problems of outdoor stationary sun-protective devices (S.P.D.) and their influence on the natural daylighting levels in the premises of civil objects of transport infrastructure under the hot and sunny climatic conditions of the environment. It is noted, that with clear sky, typical for the said climate, non-uniform luminance of the sky differs seriously from the luminance of standard overcast sky with diffused light, recommended by C.I.E. (Commission International D’Eclairage).A conclusion is made, that with clear sky conditions, a sun-protective devices in the form of stationary canopies (awninas) help to improve the lighting environment in the premises considered. This becomes possible due to reflected sun flow from the surfaces of SPD employed, as well as due to rise of a daylight factor values in farmost from windows zones of interiors, because of the increase of luminance factor values of the sky areas, observed from these zones. Thus, the SPD considered, in the hot and sunny climatic conditions are able not only to carry out their main function of passive method of solar radiation and thermal control in the interiors, but also to act as an efficient measure to improve lightning environment of the premises in question.

Control of electrical to thermal conductivity ratio for p-type LaxFe3CoSb12 thermoelectrics by using a melt-spinning process

In this work we improved the thermoelectric figure of merit ZT in a LaxCoFe3Sb12 (x = 0.80, 0.85, 0.90) skutterudite system by applying a conductivity ratio (electrical to thermal) control method based on the phonon-glass electron-crystal (PGEC) approach. Polycrystalline bulks of LaxCoFe3Sb12 were prepared by melt-spinning and subsequent spark plasma sintering. Based on the thermoelectric transport properties and microstructural analysis, we found that large amount of La-filler (x ≥ 0.9) in the LaxCoFe3Sb12 system is necessary to increase the conductivity ratio required to improve the thermoelectric properties in the LaxCoFe3Sb12 system. Resultantly, the maximum ZT value of 0.87 was obtained at 723 K in the heavily filled La0.9CoFe3Sb12. We discuss our results on the basis of the filling level dependence of the rattling effect and on the formation of the skutterudite single phase. We also confirm that a large amount of La-filling level is necessary to meet the electrical neutrality condition of the p-type LaxCoFe3Sb12 skutterudite system.

Determination of an acceptable comfort zone for apartment occupants in South Korea: An empirical analysis of cooling operation

Occupants of apartment blocks tend to wear less clothing and exhibit lower metabolic rates than occupants of other building types. Further, the use of air conditioning systems to maintain certain comfort levels within living spaces automatically generates financial cost.Therefore, in this study, an acceptable comfort range that differs from the conventional normative comfort range was established. A thermal comfort control method was designed to satisfy both the economic and comfort requirements, and experiments were conducted accordingly. Subsequently, empirical data on cooling were obtained via surveys and measurements and employed to derive regression equations for the thermal sensation vote, comfort sensation vote, and percentage dissatisfaction, which indicate occupant comfort. The derived regression equations were used to graph the comfort range, and the overlap region was plotted on a psychrometric chart to enable identification of an acceptable comfort zone.The suggested acceptable comfort zone, which applies to apartment blocks in Korea, is outside the conventionally recommended comfort zone and can satisfy various occupant preferences, contribute to reducing energy consumption, and facilitate maintenance of comfortable living environments.

Mathematical modeling of rotation effects on conjugate heat and mass transfer at a high-enthalpy flow around a spherically blunted cone at incidence

Some methods of thermal regime control for three dimensional flows around a body due to the simultaneous impact of body rotation around the longitudinal axis, mass ablative surface, and heat transfer flow in the body shell material are considered. The solution to the dual formulation allows us to take into account the impact of nonisothermal shell wall on the characteristics of heat and mass transfer in the boundary layer. The effect of the body rotation and the injection of cooler gas on the characteristics of heat and mass exchange in a thermal protection material is analyzed.

Entwicklung eines Applikationssystems zur selektiven, thermischen Unkrautbekämpfung in Reihenkulturen mit Pflanzenöl

The use of thermal weed control methods in row crops is currently not suitable for selective weed control because of insufficient precision. Flaming-, hot water-, superheated steam- or hot foaming units have the disadvantage to require a relatively large safety distance to the crop plant in order to avoid damages. The spray application of hot, vegetable oils from renewable raw materials should, in addition to high precision in the application, also enable an effective and environmentally friendly control of weeds even in the intra-row area. At the Institute of Agricultural Engineering at the University of Bonn, an application system was developed to investigate the harmful effectiveness of hot vegetable oils.

Analysis and Countermeasure Study on DC Bias of Main Transformer in a City

According to the December 2015 Guohua Beijing thermal power transformer DC magnetic bias phenomenon, the monitoring data of 24 hours of direct current is analyzed. We find that the maximum DC current is up to 25 and is about 30s for the trend cycle, on this basis, then, of the geomagnetic storm HVDC and subway operation causes comparison of the mechanism, and make a comprehensive analysis of the thermal power plant’s geographical location, surrounding environment and electrical contact etc.. The results show that the main reason for the DC bias of Guohua thermal power transformer is the operation of the subway, and the change of the DC bias current is periodic. Finally, of Guohua thermal power transformer DC magnetic bias control method is studied, the simulation results show that the method of using neutral point with small resistance or capacitance can effectively inhibit the main transformer neutral point current.

Study on Indoor Thermal Environment Control Based on Thermal Sensation Prediction

Currently the indoor thermal environment control is mainly conducted based on the set points given by room occupants or based on PMV, which might cause problems of unreasonable temperature setting and unsatisfied individual thermal preferences of room occupants. The indoor thermal environment control method based on thermal sensation expression can solve these problems. However, control based on thermal sensation expression might frequently interrupt room occupants’ concentrations on work because this method needs occupants to input their thermal sensations, when their comfortable temperature range changes with the differences of the metabolic rate, clothing level etc. In an attempt to solve this problems, a new indoor thermal environment control method is proposed, which is to collect occupants’ skin temperature measured by infrared imaging to estimate the occupants’ current thermal sensation and predict their future thermal sensations. This paper introduces the control method of the system based on thermal sensation prediction. The control method was verified by building the test-beds and conducting a series of experiments. Experiment results show that 98% of the evaluations are neutral/satisfied/very satisfied with this control system, which means the proposed indoor thermal environment control method based on thermal sensation prediction is feasible for actual application.

Neural networks and genetic algorithms for the evaluation of coatings thicknesses in thermal barriers by infrared thermography data

In the context of using non-destructive thermal control methods for the coatings thicknesses evaluation in thermal barriers. We have treated the laser-pulsed thermography data with the neural networks to model the relationship between the thermal response and the coating thickness. The algorithms based on the error gradient computation are used during the learning step. Indeed, the initial weights of the network found and the number of data processed facilitated the convergence of these algorithms. In this work we presented a neural network training method using pre-processing of data by principal component analysis(PCA) to optimize the number of network inputs and the genetic algorithm for the optimum initial weights determination in the network training by the back propagation algorithm. The two algorithms recombination allowed the thicknesses evaluation with deviations less than 5%.

Cross-Flaming Application for Intra-Row Weed Control in Maize

Abstract. Flame weeding is the most common thermal intra-row weed control method used in agriculture as an alternative to herbicides in heat-tolerant crops. Within the seventh framework program project “Robot fleets for Highly Effective Agriculture and Forestry Management” (RHEA), the University of Pisa was responsible for the development of an automatic machine for intra-row cross-flaming in maize ( L.). This study focused on the selection of a range of liquid petroleum gas (LPG) doses able to control weeds without affecting crop yields, for the basic calibration of the machine. Tests were conducted in 2012 and 2013 during the growing cycle of maize both in weed-free and real-field weedy conditions. Five biological LPG doses (0, 52, 65, 104, and 130 kg ha-1) were applied at different maize growth stages once (2- and 5-leaf) and twice (2-leaf the first time and 16 days after the first time). The response of maize and weeds to cross-flaming was evaluated in terms of grain yield, weed density after flame weeding, and weed dry biomass at harvest. Log-logistic models were used to describe the responses of different growth stages of maize and weeds to single and repeated applications of LPG doses. Overall response of maize yield to flame weeding was influenced by LPG dose, number of flame weedings, maize growth stage, and presence of weeds. The results of this study indicate that two cross-flaming treatments applied separately with an LPG dose ranging from 36 to 42 kg ha-1 can provide an acceptable level of weed control in maize, enough to ensure economically acceptable yields.

Influence of control logic on variation of indoor thermal environment for residential buildings

This study proposes an advanced thermal control method that employs artificial neural network (ANN) models for predictive and adaptive thermal control. Two predictive and adaptive control logic approaches were proposed to simultaneously control indoor temperature and humidity as well as predicted mean vote (PMV) in a residential building. Their thermal performance was analysed and compared with that of non-ANN-based counterparts to evaluate architectural variables such as envelope insulation and building orientation. A numerical computer simulation method was used for the tests after demonstration of its validity based on comparison with results of field measurement. Analysis results revealed that the proposed predictive and adaptive control methods conditioned the indoor temperature, humidity and PMV effectively. The periods during which each thermal factor was in a comfortable range increased, and overshoots and undershoots out of the targeted comfortable ranges were reduced when using the ANN model. The results demonstrate the functionality of the proposed method for variation in architectural variables and that the ANN model has the potential to be successfully applied to building thermal controls.

Opportunities of synergistically adjusting voltage-frequency levels of cores and DRAMs in CMPs with 3d-stacked DRAMs for efficient thermal control

Chip-Multiprocessors (CMPs) with 3D-stacked DRAMs is promising for solving the memory wall problem, but the high power density makes 3D ICs frequently operate at or near the thermal limit. System hot spot of a CMP with 3Dstacked DRAMs is usually in DRAMs that are in the layers farthest from the heat sink. Heat from DRAMs and cores are all accumulated in DRAMs. Therefore, existing thermal managements for 3D ICs all perform thermal control on cores only because lowering the power-level of cores can also lower DRAM access frequency. However, as the power consumption of single DRAM access increases with the number of DRAM stacks and the width of the vertical links, the instantaneous DRAM accesses may easily overheat the system. So, in addition to lowering the access frequency of DRAMs, reducing the power consumption per DRAM access is also crucial. In this paper, we characterize the thermal and performance behavior of the target architecture when the voltage and frequency levels of cores and DRAMs are synergistically controlled. We also evaluate the thermal and performance behavior of existing thermal control methods that can be applied to the target architecture. The insights provided by the characterizations presented in this paper are important for developing an effective thermal management policy for CMPs with 3D-stacked DRAMs. Our results show that, synergistically controlling the voltage-frequency levels of cores and DRAMs does achieve higher thermal efficiency than controlling cores only.

Researching the materials emissivity influence onto the thermal control method’s accuracy

The thermal imaging inspection is one of the main technical diagnostics development directions , allowing to control the thermal condition of equipment and structures without removing from the exploitation at an early stage of defects’ development, while reducing the technical inspection and defect detection costs. During thermal inspection essential is to pay a special attention to the analysis of the measurement errors occurred causes. One of the main issues we face with while calculating the temperature in compliance to the results of thermal imaging measurements, relates to the uncertainty in the assessment of the object’s surface emissivity. The effected study has been aimed onto researching the materials’ emissivity influence onto the thermal control method accuracy. The studies’ results demonstrate a significant impact of materials’ emissivity onto accuracy of temperature non-contact measuring method. Elaborated is the methodology of calculating the measurement uncertainty, due to the error in setting the coefficient emissivity. Results obtained can be used in various industries for more accurate actual temperature estimation for a real object.

A thermal boundary control method for a flexible thin disk rotating over critical and supercritical speeds

In practice a rotating flexible thin annular disk has to be operated at low speed, because three types of dynamic instabilities inevitably occur around critical and supercritical speeds, namely: aeroelastic, parametric and thermoelastic. The rotating disk is clamped and driven by a drive shaft attached to the disk inner edge. The external action of the flowing surrounding air causes the aeroelastic instability; a slider mass–damper–spring–friction moving load causes parametric instability; and disk/slider interface friction heat can cause thermoelastic instability. A thermal boundary control method is used to induce disk thermal membrane stresses utilizing drive shaft temperature increments to stabilize these dynamic instabilities. Fundamental investigations are made of disk temperature distribution, thermal stress, natural frequency, dynamic stability and steady state amplitude to validate and demonstrate the viability of the new control method. The thermal boundary control method offers valuable opportunities for rotating disk applications operating over critical and supercritical high speeds with high efficiency.

Smooth control of insulated gate bipolar transistors junction temperature in a small‐scale wind power converter

In wind power converters, the junction temperature of the power module is the crucial factor which affects its reliability. This study developed a comprehensive thermal management strategy to improve the operational reliability of a small-scale wind power converter. Firstly, the idea of thermal management that improves the reliability is introduced. Then, in order to smooth the temperature fluctuations, the adjustment law of the switching frequency and the strategy of the exterior thermal management have been investigated. A field-programmable gate array- based thermal management system consists of temperature-controlled oscillator and fan speed regulator as well as power resistor heating system was designed. Lastly, numerical simulation and experimental implementation were carried out to verify the correctness of the proposed thermal smooth control method.

Determination of criteria to find the quality of an electrical connection

A contact system is a nonredundant technical structure of electric railways that should provide uninterrupted power supply for railway vehicles. The failure of one part can lead to failure of the contact system. About 20% of damage to contact systems is due to inadmissibly high temperature at part of an overheated catenary. In this paper, normative indices are analyzed to determine the state of the terminal under operating conditions. The existing methods of thermal control are unable to determine the current heat state of an electric bolted connection with required accuracy. Heating control of electrical connections is suggested. To determine the state of the electrical connection, the factor of defectiveness due to heating is selected. As a result, criteria for determining the state of an electrical connection are obtained, which allows a methodology to be developed for monitoring the quality of an electrical connection.