Thermal Resistance Factor Research Articles

The numerical analysis in heat transfer, fluid flow, and irreversibility of a pin-fin heatsink under the ultrasonic vibration with different transducer power assignment scenarios

The hydrothermal performance and entropy generation rate in a pin–fin heatsink were numerically investigated under different vibration transducer power distribution scenarios between 11 transducers located at 3 walls of the heatsink. Two cases were investigated; Case#A and Case#B which are different in 3 transducer locations on one wall of the heatsink. The highest convection coefficient (h) in Case#A was obtained for a variable power scenario, which escalated pressure drop (ΔP) by 91.94%. However, the highest h in Case#B was obtained for the constant power scenario. In addition, h, average temperature of CPU, and thermal resistance factor in Case#A are 5.84% higher than, 0.41% lower than, and 5.34% lower than those in Case#B. The PEC factor for Case#A is higher than unity (1.31) only under the constant power scenario, while the PEC of Case#B is higher than unity under different studied scenarios. Frictional irreversibility (Ṡfr) for Case#A was obtained as 1.45–74.56% higher than that for Case#B due to the swirl flow generated by the high-power transducers and creating the huge velocity gradients in Case#A. Nevertheless, the high flow mixing in Case#A leads to reducing the temperature gradients against Case#B, thereby thermal irreversibility (Ṡth) in Case#A is almost 7.05–19.69% lower than that of Case#B.

Numerical investigation of the effect of perforation inclination angle on the performance of a perforated pin-fin heatsink using two-phase mixture model

The numerical analysis of water/silver nanofluid (NF) flow in a perforated pin-fin heatsink (PFHS) is performed considering the nanoparticle concentration (φ) of 1% and seven different perforation inclination angles (γ). The configuration with the best hydrothermal performance and the lowest entropy generation rate at different values of Reynolds number (Re) is determined using the two-phase mixture technique. According to the results, the γs of 45º and -45º exhibit the highest heat transfer coefficient (h) and the lowest thermal resistance factor and mean CPU temperature at four studied Res of 500, 1000, 1500, and 2000. Consequently, the highest hydrothermal performance evaluation criterion (PEC) was obtained for the heatsink with γ of 45º followed by γ of -45º at Re of 500; the increase in Re reduced the PEC due to the pressure drop. PEC of the heatsink with γ of 45º was almost 11.06–16.63% higher than that with γ of 0º. In addition, γ of -15º and 45º provided the lowest frictional and thermal entropy generation rates (S˙fr and S˙th) at Re of 1500 and then 2000. S˙fr and S˙th for γ of 45º were 1401% and 97% lower than those for γ of 0º at Re=1500.

Numerical analysis of the magnetic field impact on hydrothermal characteristics of a microchannel heatsink with Fe3O4 ferrofluid and various pin-fin shapes

Enhancing the hydrothermal proficiency of thermal management devices by integrating active and passive heat transfer techniques is possible. Under magnetic field (MF), pin–fin heat sinks have rarely been studied in terms of frictional losses and coefficient of heat transfer (h). Here, with a nanoparticle concentration ratio of 2%, Fe3O4 ferrofluid flow inside a pin–fin heatsink was analyzed numerically considering various pin–fin shapes (rhumbas, squares, circles, and triangles) for absenteeism (WO) and attendance (W) of MF. In the results, the greatest and lowest gains for h were 13.12% and 8.8%, respectively, utilizing MF and Re = 200, for the circular and triangular heatsinks, which would be reduced to 5.36% and 2.41% by increasing Re to 500. In addition, h (and thermal resistance factor) in triangular configuration is 7.82–10.86% (and 4.98–8.68%) and 3.23–8.08% (1.94–6.22%) greater (and smaller) than that in the circular design under two scenarios of MF. Moreover, MF brings about a reduction of 1.86–0.60%, 1.61–0.46%, 1.71–0.54%, and 1.16–0.24% in Tm,CPU for the circular, square, rhumbas, and triangular configurations, respectively, within the Re range of 200–500. Although, when MF is present, pressure loss escalates by almost 6.39%, 4.97%, 3.60%, and 2.92% at Re numbers of 200, 300, 400, and 500 for each configuration, with the maximum pressure loss for triangular heatsink compared to the other arrangements. PEC factors at different Re numbers range from 1.51 to 1.87, suggesting an improved heatsink hydrothermal performance under MF impact compared to absenteeism of that. The highest/lowest PEC values at Re numbers 200 and 500 are associated with the rhumbas/triangular (1.871/1.782) and Triangular/square (1.547/1.496) configurations, respectively.

The Analysis effectiveness of heat rate in 1000℃ furnace by considering the dimensions of walls melting container

The metal smelting business is expanding, moving from combustion-based to electric-powered smelts. By adjusting the quantity of electrical power that enters the heater to be transformed into heat, the temperature of the melting chamber can quickly approach 1000°C. But if the thermal resistance is unable to slow down the rate of heat transfer from the smelting chamber to the outside, the temperature inside the smelting chamber can likewise fall quickly. If that keeps happening, the furnace machine's temperature of 1000°C cannot be reached, which makes the smelting process less than ideal. So that the temperature of the smelting chamber can be maximized, an examination of the thermal resistance factor is required in order to estimate the value of the thermal resistance on the wall. To obtain information on wall dimension fluctuation, the procedure involves gathering data from references and actual measurements of the furnace. Based on the findings, it was determined that the temperature of the environment had an impact on the heat resistance values measured. (T2 = 25.8°C), the melting chamber's temperature (T1 = 1000°C), the fire brick's thermal conductivity at k=4.78 J/s m° C, as well as the variation area and wall thickness the resultant resistance increases with increasing wall thickness. The highest resistance rating is 4.389R with a 150 mm wall thickness. Otherwise, the resistance is higher when a smaller portion of the wall is employed. On a 3600 mm2 wall area, the resistance value with the highest value is 2.905R. In order to increase the temperature of the smelting chamber, a furnace with wall dimensions that have a significant thickness value and a compact area can generate the best thermal resistance

THERMAL ANALYSIS OF LAMINAR WATER FLOW OVER A BACKWARD FACING CHANNEL WITH CARBON NANOPARTICLES

In the last few years, the thermo-hydraulic simulation of nanofluid flow bifurcation phenomena has become of great interest to researchers and a useful tool in many engineering applications. FVM has been employed in this article to numerically explore the laminar water flow over a backward facing channel with or without carbon nanoparticles (CN). The problem formulated in this paper has been solved by considering the effects of nanoparticle weight percentages (𝑤%), such as 0.00, 0.12, and 0.25 for different Reynolds number (𝑅𝑒). Nusselt number distribution (𝑁𝑢(𝑥)), coefficient of skin friction (𝐶𝑓), characteristics of pressure drop (Δ𝑝), velocity contours, static temperature, pumping power (𝑃𝑝) and thermal resistance factor (𝑅) have been investigated to know the behavior of thermo-hydraulic flow bifurcation phenomena. The present study shows that the surface temperature and coefficient of heat transfer can be reduced due to the effect of 𝑅𝑒 or w%. For different w%, it has been found that in the rise in the values of 𝑅𝑒 causes the increase of vortex length and as a result velocity gradient and Δ𝑝 arises. Furthermore, it has also been studied that the enhancement of 𝑅𝑒 causes the increaseof 𝑃𝑝 and Δ𝑝.

Hydrothermal analysis of water-Al2O3 nanofluid flow through a sudden expansion channel with intermediate step

This work presents the dynamic behavior of the laminar nanofluid hydrothermal flow through a sudden expansion channel with the variations in the normalized length, height, and pitch to width ratio of the intermediate step. The governing equations have been discretized by means of the finite volume method, and the SIMPLE algorithm has been applied to solve the system of algebraic equations. The effect of variations in the Reynolds number (Re), normalized height (B/C), normalized length (A/C), and step pitch-width ratio (A/B) on the enhancement of heat transfer have been studied. At various values of A/C, A/B and B/C, this work indicates that the average Nusselt number (Nuavg), thermal resistance factor (R), and performance number (PN) increase with the increase in Re. In the case of the hydrothermal flow phenomena, the configuration associated with B/C provides better results than the configurations associated with A/B and A/C. As an important outcome, we see that the presence of intermediate step enhances the average Nusselt number, and thermal resistance factor. This will become very much helpful for various realistic circumstances for triggering additional thermo-mechanical loads on the surface.

Thermal and economic analysis of preinsulated and twin-pipe heat network operation

This study focuses on the economic analysis of the heating network modernization by using preinsulated pipes and twin-pipes. The cost analysis is based on different type, diameter, and technological diagrams of different heating network pipe variants (from DN25to DN100) and various types of insulation. Net present value (NPV) analysis comparing a five variants of the heating network pipes (Case 0: Pipes with insulation PUR standard; Case 1: Pipes with insulation PUR plus; Case 2: Pipes with insulation PEX standard; Case 3: Twin-Pipes with insulation PUR; Case 4: Twin-Pipes with insulation PEX). The value of NPV, which is the highest (NPV = 7000 €, DN65, case 2 and NPV = 5200 €, DN50, case 4) among presented variants is the best choose to consider during the investment. Despite the higher prices of Twin Pipe system, they are more profitable due to shallow heat transfer losses. Heat losses are calculated for various heating networks, including preinsulated and twin-pipe heating networks. The remaining heat loss calculation is based merely on temperature levels and thermal resistance factors (in the ground), determined using the pipe dimensions and materials. It is found that the most cost-effective from an economic point of view is the use of TwinPipe system. These pipes are more expensive, but the heat losses that occurs during their use are much smaller compared to preinsulated pipes. Short return time of such an investment (6–7 years) with 100 m of pipe installed and positive NPV causes that this type of pipes is the best investment in the case of district heating networks. The results shown that Case 3 (PEX insulation) is more economicaly beneficial than Case 4 (PUR insulation).

Numerical determination of temperature distribution in heating network

This paper presents the determination of the heat losses of the pre-insulated pipe and twin pipe in the heating network. The paper compares the heat losses calculated by using the analytical solution (1D model) and numerical model (2D model) based on the Finite Element Method. The developed numerical model considered undisturbed ground temperature at various depths. Therefore, it allowed to study the effect of temperature distribution at various ground depths on heat losses in heating network. Various variants of insulation are considered including standard, plus and plus-plus types for pre-insulated tubes. The remaining heat loss calculation is based merely on temperature levels and thermal resistance factors (in the ground), determined by the pipe dimensions and materials. The differences in calculated heat losses by analytical and numerical model do not exceed 10%.

Study of the electrical properties of the thin film (SnO2 )1-X(Bi2O3)X Preparation by Vacuum evaporation system

In this study, bismuth element was added to the weight ratio of (0,1,3,5)% to tin element using powdered technology method. The thin film of (SnO2)1-X(Bi2O3)X have been prepared with a vacuum evaporation system and oxidized him in oven with temperature at 350° C for 30 min. Results (I-V) Characters with temperature showed that the thin film had a negative thermal resistance factor, while the results showed that the resistance value of the thin film increased from 1KΩ at (0%) to 7.5 KΩ at (5%). The thin film 's sensitivity to heat has also improved significantly. The energy activation decreased from 0,08eV at the addition (0%) to 0,03 eV at the addition of (3%)while increased to 0.087 eV at the addition of (5%) .

A wide band, low direct current drift, low noise preamplifier for a quadrupole mass spectrometer.

In order to measure the low current in the quadrupole mass spectrometer (QMS), we design a novel wide band composite trans-impedance preamplifier. The noise filtering components, which built in the feedback loop of the preamplifier, are designed to reduce the noise of two-stage amplifiers. By using the package with low thermal resistance factor, reducing the power consumption of preamplifiers and reducing the feedback resistance, the temperature drift of baseline signal is reduced. Compared with the traditional composite preamplifier, the novel preamplifier reduces maximum temperature drift amplitude and reduces root mean square of noise. At last, the environmental reliability of QMS detection was improved.

Effect of palm oil temperature on thermal losses of PTC sensor designed for overfill protection using current-voltage characteristic

Characteristic of positive temperature coefficient (PTC) sensor can be described using current-voltage curve which depends on thermal properties of medium. The PTC sensor for overfilling protection designed for palm oil (CPO) container cannot identify the medium liquid with high temperature and high viscosity due to the overlapping of current voltage curve. For this case, a signal of worst-case alarm is generated. This paper presents the effect of CPO temperature on thermal losses of the PTC sensor represented by thermal resistance factor between the sensor and the medium surrounding it. A type of EPCOS B59050D1100 PTC sensor was characterized in two mediums; CPO and still air, to simulate “full” and “empty” status. The sensor responds was then observed through the current-voltage curve at different temperature from 300 K to 360 K. The thermal resistance were then obtained from the modeling of current voltage curve, resulting the values of 125 K/W for CPO and 343 K/W for still air with 63.5% in difference between both mediums. Using proposed two points method, the effect of medium temperature on thermal resistance can be eliminated and reduced, where the Rw variation is less than 3.15% for palm oil and 4.5% for still air. This result is within the normal operation tolerance below 5% and can be used safely to determine the status whether the sensor is in still air or in palm oil medium.

Experimental and numerical study of effective thermal conductivity of cracked concrete

The pronounced decrease of Effective Thermal Conductivity (ETC) due to the cracking behavior of concrete changes the temperature profile in concrete structures, indirectly inducing the redistribution of thermal stresses. To study this phenomenon, a mini-scale numerical method within the framework of finite element method is proposed for both tensile and compressive cracked concrete and this method is applied to obtain quantitative relationships between tensile or compressive strain and ETC. Results show that (a) for tensile dominated failure, concrete ETC decreases by 23% during the plastic stage whereas little decrease is found at complete failure; (b) for compressive dominated failure, ETC decreases by 30% during the plastic stage, and then becomes stable afterwards. In the softening stage ETC linearly decreases with the increase of compressive strain; (c) it is the interfacial thermal resistances induced by the micro-cracks between aggregates and mortar rather than the macro-cracks that play the dominant role in this phenomenon; (d) concrete ETC becomes anisotropic when cracks appear. The experiments show that compressive cracked concrete's ETC vertical to cracks dramatically decreases by 20–25% at plastic drop stage and then becomes stable at the plastic steady stage. The numerical results are used to determine the interfacial thermal resistance factor in Wang Jiajun model. The proposed formulation provides results that are in excellent agreement with experiments.

Modelling steady-state thermal behaviour of double thermal network pipes

Optimal design and operation of district heating networks require accurate, but simple models to allow fast simulation. This paper describes the analytical derivation of such a model based on existing work regarding heat loss and dynamic temperature profile calculations in literature. The most important addition from this work is the incorporation and investigation of heat transfer from supply to return side in double pipes, something which is often (over)simplified in more commonly used models.The paper presents the mathematical derivations and the assumptions made in detail for the case of steady-state heat losses in double pipes. The resulting model is carefully examined in a parameter study, from which a number of interesting conclusions can be drawn. Firstly, the heat losses are found to be nearly independent of the mass flow rate in the range of mass flow rates usually encountered in thermal network pipes. The remaining heat loss calculation is simply based on temperature levels and thermal resistance factors, determined by the pipe dimensions and materials. Furthermore, it is found that heat losses from supply to return side should be incorporated in the analysis for better accuracy of the results, even more so with the increasing popularity of twin pipes with common insulation.

Analysis of the impact of thermal resistance of the roof on the performance of photovoltaic roof tiles

The paper explores the issues related to the impact of thermal resistance of the roof on the electrical parameters of photovoltaic roof tiles. The methodology of determination of the thermal resistance and thermal transmittance factor was presented in accordance with the applicable legal regulations and standards. A test station was presented for the purpose of measurement of the parameters of photovoltaic roof tiles depending on the structure of the roof substrate. Detailed analysis of selected building components as well as their impact on the design thermal resistance factor and thermal transmittance factor was carried out. Results of our own studies, which indicated a relation between the type of the roof structure and the values of the electricity generated by photovoltaic tiles, were presented. Based on the calculations, it was concluded that the generated outputs in the respective constructions differ by maximum 6%. For cells with the highest temperature, the performance of the PV roof tiles on the respective roof constructions fell within the range between 0.4% and 1.2% (depending on the conducted measurement) and amounted to 8.76% (in reference to 9.97% for roof tiles with the lowest temperature).

Effects of heat transfer characteristics between fluid channels and thermoelectric modules on optimal thermoelectric performance

Semiconductor thermoelectric generation technology has a promising application for waste heat recovery and is becoming a noticeable research field. This paper presents a mathematical thermoelectric generator (TEG) model applicable to engine exhaust gas heat recovery. This model considers the conduction along the heat exchanger and the contact thermal resistance of the exchanger plate between the fluid channel and the thermoelectric modules, which were neglected in a previous numerical analysis. Considering that there is an optimum module size corresponding to the maximum power output in a TEG system, the effects of heat transfer characteristics between the fluid channel and the thermoelectric modules on the optimal thermoelectric performance are investigated by using an engineering equation solver (EES) program. Numerical results show that there is a larger optimal area and a lower peak power when considering the conduction and contact thermal resistance factors mentioned above compared to traditional results, which are determined by considerably different factors such as internal heat transfer and temperature distributions. Moreover, an optimal thermal conductivity coefficient that corresponds to the peak power output exists when the conduction along the exchanger is considered. In the case when conduction along the exchanger is not considered, higher the thermal conductivity, the better is the thermoelectric performance. A thin-plate exchanger is recommended in the TEG system owing to its high power output. The optimal module area increases linearly, and the maximum power output exhibits an obvious decrease with an increase in the contact thermal resistance.

Effects of Sorbitan Monostearate and Monooleate on the Crystallization and Consistency Behaviors of Cocoa Butter

AbstractThe crystallization behavior of cocoa butter (CB) is the essential structuration issue in the development of chocolate products. An alternative to modify and control the crystallization patterns of CB in chocolate production is the incorporation of specific emulsifiers in their formulations. In this work, the effects of sorbitan monostearate (SMS) and sorbitan monooleate (SMO) in the crystallization and consistency behaviors as well as on the microstructure of CB were evaluated. CB samples at three different concentrations (0.5, 1.0 and 1.5 % w/w) of SMS and SMO were prepared and their main physical–chemical attributes determined. CB added with 1.5 % of SMS showed the largest effects with a sharp increase in the onset of the crystallization temperature (from 19.3 to 23.8 °C) and doubling the yield value (consistency) of pure cocoa butter. The classic two‐step isothermal crystallization behavior and morphology of CB were also modified with the addition of SMS. A possible explanation based on the solubility of SMS in an organic medium and its ability of self‐assembling was suggested as a mechanism for SMS performance in CB. SMS was considered as a potential crystal modifier for CB by changing its crystal structure and enhancing its thermal resistance—factors that favor the use of this emulsifier in the production of improved thermally stable chocolates.

Computer simulation of differential scanning calorimetry: influence of thermal resistance factors and simplex optimization of peak resolution

Computer simulation of differential scanning calorimetry: influence of thermal resistance factors and simplex optimization of peak resolution

Correction-Equivalent-Circuit Modeling of a Heat-Flux Differential Scanning Calorimetry Cell. Analysis of Thermal Resistance Factors and Comparison with Experimental Data

Correction-Equivalent-Circuit Modeling of a Heat-Flux Differential Scanning Calorimetry Cell. Analysis of Thermal Resistance Factors and Comparison with Experimental Data

Equivalent-circuit modeling of a heat-flux differential scanning calorimetry cell. Analysis of thermal resistance factors and comparison with experimental data

Equivalent-circuit modeling of a heat-flux differential scanning calorimetry cell. Analysis of thermal resistance factors and comparison with experimental data