Heat Conduction Resistance Research Articles

Enhancing orthogonal finishing machining of Ti6Al4V with laser-ablated tool geometry modifications

Finishing machining of Ti6Al4V, known for its high strength and heat conduction resistance, demands optimisation to achieve high-quality end products. This study explores modifying the chip contact length on the rake face and altering the flank face with a cavity to minimise process forces and temperatures while maintaining cutting edge integrity. The research validates the manufacturability of ultra-short pulsed laser-ablated tool geometry modifications, indicating potential for industrial scale-up. Extensive experimental evaluations under dry conditions assess the impact of tool modifications at various feed rates for planing and turning. Significant reductions in process forces and temperatures were observed with rake face modifications, particularly at a cavity distance of approximately 34 µm. Ideal performance was noted for feed rates between 0.035 and 0.045 mm for planing and 0.040 to 0.045 mm/rev for turning. Smoothed Particle Hydrodynamics (SPH) simulations employing a Johnson-Cook material model were used to analyse chip formation and to predict the process forces. These simulations revealed a clear change in the chip formation and lower process forces and temperatures. The SPH results closely matched experimental outcomes, with a discrepancy of less than 7 % in cutting forces for both tool types, although feed forces were underestimated by about 50 %. The effect of the tool modification is reflected accurately at the respective feeds.

Research of heat conductivity of quartz material

In the article the results of a study of heat conductivity and thermal resistance of quartz-containing materials were presented. The object of the study was a quartz mineral from the Aktas deposit, located in the Ulytau district of the Karaganda region. The initial size was a piece of quartz mineral measuring 5–10 mm, which was disassembled mechanically. To prepare the samples under study, quartz powder 0.2 mm thick, crushed by the electric pulse method, was used. Electropulse technology is one of the methods based on the influence of Yutkin, accompanied by the formation of a specially formed high-voltage pulsed electrical discharge inside a volume of liquid. The pulse discharge frequency of the electrohydropulse installation for grinding the mineral to the required fraction was f = 3 Hz, the pulse capacitor capacitance C = 0.4 μF, the pulse discharge voltage U = 18–37 kV. The samples under study were made in the following dimensions: width 100 mm, length 100 mm, height 25 mm. To evaluate the thermophysical properties of manufactured samples in a stationary mode, the ITP-МG4 “100” installation was used, which determines the heat conductivity and thermal resistance of materials for thermal insulation of industrial equipment and pipelines in accordance with GOST 7076, based on the thermoelectric method, and GOST 30256, based on the thermal probe method. As a result of the study, a graph of the temperature dependence of heat conductivity and thermal resistance of quartz-containing materials was obtained. Based on the results obtained, it was established that the thermophysical parameters of the sample containing quartz are lower compared to the sample consisting of cement.

Study on radar electronic module cooling by using diamond/copper composites

Diamond/copper composites are regarded as a new generation of heat dissipation materials because of their good thermal conductivity and matched thermal expansion coefficient to semiconductor materials. This study focuses on the thermal application study of the diamond/copper composite. A diamond/copper composite cooling module was designed to meet the requirements of thermal physical properties of an electronic device. The heat conduction resistance of diamond/copper substrate was calculated theoretically. It is found that the optimum thickness of diamond/copper substrate is about 0.34 times of the equivalent radius and improving the thermal conductivity of the substrate is more effective for heat dissipation when the thermal convective resistance is low. When the heat flux of the chip is 100 W/cm2, the temperature of the chip using diamond/copper composite as substrate is 4.84 °C lower than that using silicon aluminum alloy. The improvement effect increases about 5 °C when the heat flux increases by 100 W/cm2.

Tensile instability and limit strain behavior of explosion-welded steel/Al plate considering interface defect characteristics

Explosion-welded steel/Al composite plate has advantages of excellent conductivity, heat conductivity, light weight, and corrosion resistance. While the elongation of explosion-welded steel/Al composite plate can not been predicted by the traditional damage fracture theory. Establishing a new prediction model to analyze the deformation behavior of steel/Al composite plate are necessary. First, the deformation behavior and interface microscopic characteristics of explosion-welded steel/Al composite plate were analyzed using uniaxial tensile tests and SEM experiments, the result showed that wave structure, brittle phase, and microcrack existed at the interface layer of composite plate, the uniform elongation and elongation of steel/Al composite plates basically deviate linearly from the mixing law. Second, simulation models were established to analyze the effect of interface wave structure, brittle phase, and interface microcracks on the instability and fracture behavior of explosion-welded steel/Al composite plate. The interface wave structure could enhance the elongation of the composite plate, while the uniform elongation of the composite plate decreased with the increasing of brittle phase and microcrack. When f0 = 0.985, the predicted tensile strength through simulation is 258.94 MPa, which only has a difference of 1.9 MPa from the experimental value, when the length of the crack increases from 0.03 mm to 0.2 mm, the uniform elongation of the composite plate decreases by 92.52%. Finally, M−K theory considering the characteristics of interface defects was established to predict the tensile instability behavior of steel/Al composite plates. The instability behavior of the composite plate considering interface defects could be accurately described using the modified M−K theory when the height of the interface groove of the composite plate was Δta/Δts=ha/hs and Δta+Δts=0.5mm.

Exploring the water capture efficiency of covalently attached liquid-like surfaces.

The capture of moisture from the atmosphere through condensation has the potential to provide a sustainable source of water. Here, we investigate the condensation of humid air at low subcooling condition (11 °C), similar to conditions for natural dew capture, and explore how water contact angle and contact angle hysteresis affect the rates of water capture. We compare water collection on three families of surfaces: (i) hydrophilic (polyethylene oxide, MPEO) and hydrophobic (polydimethylsiloxane, PDMS) molecularly thin coatings grafted on smooth silicon wafers, which produce slippery covalently attached liquid surfaces (SCALSs), with low contact angle hysteresis (CAH = 6°); (ii) the same coatings grafted on rougher glass, with high CAH (20°-25°); (iii) hydrophilic polymer surfaces [poly(N-vinylpyrrolidone), PNVP] with high CAH (30°). Upon exposure to water, the MPEO SCALS swell, which likely further increases their droplet shedding ability. MPEO and PDMS coatings collect similar volume of water (around 5 l m-2day-1), both when they are SCALS and non-slippery. Both MPEO and PDMS layers collect about 20% more water than PNVP surfaces. We present a basic model showing that, under low heat flux conditions, on all MPEO and PDMS layers, the droplets are so small (600-2000 µm) that there is no/low heat conduction resistance across the droplets, irrespective of the exact value of contact angle and CAH. As the time to first droplet departure is much faster on MPEO SCALS (28min) than on PDMS SCALS (90min), slippery hydrophilic surfaces are preferable in dew collection applications where the collection time frame is limited.

Multifunctional nanocomposites integrate electromagnetic shielding, thermal, mechanical, and wear resistance properties

AbstractThe SiCnws/SiC nanocomposites were in situ synthesized by using nickel carbon foam as catalyst and skeleton. This technique has a series of advantages including simple operation, low cost, and high efficiency. Due to the excellent microwave absorption and thermal properties of SiCnws, SiCnws/SiC nanocomposites possess excellent electromagnetic shielding performance with a high SET value of 38.3 dB and good thermal properties with thermal conductivity of 13.77 ± 0.098 wm−1k−1 at room temperature. Meanwhile, the bending strength of the nanocomposites is 110.9 ± 7.7 MPa. The friction coefficient of nanocomposites is about 0.26 with a wear speed of about 67 um3/s. Therefore, the nanocomposites integrate many advantages including lightweight (2.0 g/cm3), excellent electromagnetic shielding, good heat conduction, high strength, and wear resistance.

S–CO2 heat transfer characteristics analysis in PCHE and vertical channel

Numerical simulations are applied to investigate supercritical carbon dioxide (S–CO2) and heat transfer characteristics in the case of uniform/nonuniform heating conditions in the straight vertical channel and printed circuit heat exchanger (PCHE). The proposed S–CO2 heat transfer correlation agrees well with the experimental values. Results show that high heat flux let S–CO2 heat transfer deterioration likely to occur. Heat transfer deterioration effect will be enhanced as S–CO2 is in area of the gas-like region. Heat transfer enhancement effect will be more significant when S–CO2 is in the area of the liquid-like region. The concept of total length is proposed which is the channel length affected by heat transfer deterioration and entrance effect together. The affected length is 55–70 times of the equivalent diameter in the case of 140 kW/m2 heat flux; the affected length is 85–125 times of the equivalent diameter in the case of 300 kW/m2 heat flux. Changes in dominance of h and λ of PCHE suggest that the convective heat transfer and heat conduction resistance strength of the fluid layer is changing. This study provides guidance for PCHE design and heat transfer enhancement.

Semi-analytical model for the heat conduction resistance of a single spherical condensate droplet

The evolution and heat transfer of a single spherical condensate droplet on a superhydrophobic surface (SHS) can be modeled by the droplet thermal resistance network. The calculation of the heat conduction resistance of a single spherical condensate droplet (Rd) is a fundamental problem in analyzing the droplet thermal resistance network. Till now, the majority of researchers have used Kim's formula to calculate Rd. However, the results from Kim's formula have errors above 85% compared to those from the CFD software (ANSYS Fluent). In this paper, we analyze the reason for inaccuracy of Kim's formula. Taking two-dimensional droplet heat conduction into consideration, we gain the theoretical temperature field function inside the condensate droplet by utilizing the conformal mapping. Basing on calculation of heat transfer rate through the droplet and ANSYS Fluent analysis, we put forward a new semi-analytical model to calculate Rd. We verify and find that the results from our new model have errors less than 13% compared to those from ANSYS Fluent. It means that our new semi-analytical model is more accurate than Kim's formula. We calculate the Rd proportion of the overall heat transfer resistance and find that the application of our model can obviously decrease heat transfer calculation errors for big droplets (r>16μm) with large contact angles (θ>120∘). The new semi-analytical model for the heat conduction resistance of a single spherical condensate droplet is promising in the sense that it might replace Kim's model to become a novel design criterion of enhanced heat transfer SHSs.

Wear Resistivity of Al7075/6wt.%SiC Composite by Using Grey-Fuzzy Optimization Technique

The application of SiC particulate reinforcement impact greatly for making aluminium matrix composite because of its superb heat conductivity, oxidation stability and high resistance to mechanical erosion. Present work based on dry sliding wear analysis of Al7075/6wt.%SiC composite fabricated by liquid state stir casting method. To acquire a productive wear rate, three major process parameters viz. load, sliding speed and covering sliding distance were compared at four different levels. ANOVA analysis showed that the probability rate of the load is less than 0.05 that revealed their significant factor. From the study, the highest GRG and GFG values are found 0.914 and 0.854, respectively, for the optimal operating parameters of 10 Newton load, 2 m/s sliding speed and 500-m sliding distance. Finally, it is revealed that the grey-fuzzy technique effectively authenticates the decision making of wear performance characteristics rather than a plain grey relational grade.

Integrating carbon fiber reclamation and additive manufacturing for recycling CFRP waste

There is a large amount of carbon fiber reinforced polymer (CFRP) waste generated annually, mainly due to the difficulty in recycling CFRPs. This work presents a novel additive manufacturing-based recycling approach that can be used to reclaim CFRP waste and to re-manufacture the carbon fiber into 3D printed composite parts. A trial of this idea was set up, in which carbon fiber was first reclaimed from CFRP waste using supercritical fluid and then mixed with Poly-Ether-Ether-Ketone to produce composite filaments. The filaments were then fed into a printer of fused deposition modeling (i.e., a 3D printing process) and the recycled CFRP parts were fabricated. The engineering application-oriented tests demonstrate that the reclaimed carbon fiber can modify the performances of 3D printed part effectively in terms of mechanical strength, electrical conductivity, heat conduction and wear resistance. This work illustrates that the additive manufacturing-based recycling approach offers a possible strategy to recycle CFRP waste and fabricate high-performance engineering parts with complex geometries, which are economical and environmentally friendly.

Composite Fouling Characteristics on Ni-P-PTFE Nanocomposite Surface in Corrugated Plate Heat Exchanger

Plate heat exchanger (PHE) has been widely used in energy transport fields for its high efficiency and compact structure. However, fouling is an intractable issue which reduces heat transfer efficiency and increases pressure drop. In this study, an experimental investigation on composite fouling characteristics of Ni-P-PTFE nanocomposite coating in corrugated PHE was conducted to evaluate the anti-fouling performance of this modified surface. The nanocomposite coating was prepared based on the stainless steel 304 plates through the electroless composite plating method. Clean tests and accelerated composite fouling tests were carried out, and the heat transfer and pressure drop performance of both the uncoated and coated plates was analyzed. Moreover, micro-structure of the surfaces and fouling deposits was mapped by scanning electron microscope. Compared to uncoated plates, the Ni-P-PTFE coated plates showed lower pressure drop by up to 15.8% and lower heat transfer performance by up to 17.6% at clean state. The smooth coating decreased the friction loss of the flow, while slightly increased the heat conduction resistance. The Ni-P-PTFE coated plates showed a significant anti-fouling performance, which decreased the fouling’s weight by 20.4% and the asymptotic fouling resistance by 28.2%, meanwhile reduced the pressure drop increment by 44.8%.

A Multiscale Theoretical Analysis of the Mechanical, Thermal, and Electrical Characteristics of Rough Contact Interfaces Demonstrating Fractal Behavior

The highly complex contact interface phenomena require analysis at different length scales ranging from nanometer up to nearly centimeter scales. When two nominally smooth surfaces are brought into contact, solid-solid interaction across their contact interface is confined at multiple protrusions (asperities) of various shapes, sizes, and heights. The deformation mechanisms encountered at the asperity level control the surface conformity, which, in turn, influences the transmission of traction, heat, and electric current across the contact interface. Thus, the multiscale roughness of real surfaces necessitates the advance of methodologies and contact models that bridge the spectrum of relevant length scales. Rough surfaces have been traditionally charac¬terized by statistical parameters, which cannot be uniquely deter-mined because they depend on the sampling interval and the resolution of the mea¬sur¬ing device. On the contrary, the scale-invariant parameters employed in fractal geometry provide an unbiased representa¬tion of the surface topography. This article provides an appraisal of the multiscale mechanical, thermal, and electrical characteristics of rough contact interfaces demonstrating fractal behavior. Theoretical treatments of elastic, elastic-plastic, and fully plastic deformation, heat conduction, temperature rise, and electrical contact resistance are presented for contact interfaces characterized by fractal geometry, providing a fundamental basis for developing multiscale thermo-electro-mechanics analytical treatments for contacting solid bodies.

The application of broken expanded polystyrene particles in thermal insulation coating material

Thermal insulation coating material is a kind of green thermal insulation material with high efficiency, which is used in the exterior wall of buildings and has many advantages such as strong sticking strength, low heat conductivity, flame retardancy and water resistance. The aggregates, main insulation components, play an important role in the thermal insulation coating material. Expanded polystyrene (EPS) particle is a good material, which can be used as an aggregate for its low thermal conductivity coefficient of 0.029 W/(m·K). Accordingly, by using the broken particles prepared from wasted expanded polystyrene, (EPS), the abandoned resources can be recycled and used again, resulting to the reduction of “white pollution” and cost. In the environment of establishing an economical social, it has huge significance and broad market prospects. Studies have shown that the broken expanded polystyrene particles and expanded perlite have the lowest thermal conductivity according to the weight ratio of 1:2.96. By using wasted expanded polystyrene particles and expanded perlite as aggregates, the thermal insulation coating material has good crack resistance, thermal insulation and compressive strength.

Thermal properties, permeability and compressive strength of highly porous accumulated ceramsites in the foundation of salt tank for concentrate solar power plants

Concentrated solar power (CSP) plants have a great potential for development, the key component of which is thermal energy storage (TES). In this article, thermostability, porous structure, heat conductivity, permeability and pressure resistance of accumulated ceramsites were researched. The effective thermal conductivity decreases from 0.129 to 0.098 W/mK with porosity of 71.6–78.9% while the average simulated values of absolute permeability for four cases have a wide range from 0.754 × 10−8 to 5.350 × 10−8 m2. The uniaxial compression experiment of accumulated ceramsites was carried out for the stress-strain property, whose curve decreases with the increase of porosity of accumulated ceramsites. The ceramsites is a feasible material for the foundation of the molten salt tank in CSP plants with its good thermal properties, low permeability and sufficient compressive strength, which are all related to porosity and particle size distribution.

Analysis of local thermal non-equilibrium condition for unsteady heat transfer in porous media with closed cells: Sparrow number

The local thermal non-equilibrium condition for a porous medium with closed cells under unsteady state heat transfer is analyzed. Although the fluid circulates in the closed pores due to the buoyancy effect, the volume averaged velocity for a closed pore is zero causing excluding of the continuity and momentum equations from the volume averaged governing equations. The volume averaged governing equations are non-dimensionalized by using the equilibrium thermal diffusivity and Sparrow number appears in the dimensionless governing equations automatically. The Sparrow number is interpreted as the equilibrium conduction thermal resistance to the convection thermal resistance for the entire domain. For the high values of Sparrow number (such as 1000), the convection heat transfer resistance is considerably smaller than the heat conduction resistance resulting in high possibility of the local thermal equilibrium. Dimensionless governing equations show that four dimensionless parameters as porosity, Sparrow number, solid (or fluid) dimensionless thermal capacitance and thermal conductivity play important roles on the prediction of the local thermal non-equilibrium state in a closed cell porous medium. A chart for the prediction of local thermal non-equilibrium is presented for Sparrow number of 1, 50, 100 and 500. Furthermore, a pore scale study for a closed cell porous medium with working fluids as water and air is performed. A good agreement between the pore scale and volume averaged results is observed. The obtained pore scale results support the results of the volume averaged parametric study and also the suggested chart for the prediction of local thermal non-equilibrium state.

Preparation and thermal‐insulating properties of Ce‐doped ZrO2 hollow fibers derived from a metaplexis template

AbstractZrO2 is an attractive thermal‐insulating material for high‐temperature applications owing to its low heat conductivity and corrosion resistance. The seed hair in metaplexis is a natural fiber with a hollow structure that endows it with outstanding thermal‐insulating properties. In this paper, we describe a procedure for preparing CeO2‐stabilized tetragonal ZrO2 hollow fibers obtained by imitating a metaplexis template. The metaplexis fibers were first immersed in a mixed solution of ZrOCl2 and Ce(NO3)3 to prepare the precursor fibers. The fibers thus produced were subsequently dried in vacuum and sintered under the standard atmospheric pressure in aerobic atmosphere at temperature values of 900, 1100, and 1300°C. The microstructures, phase composition, pore size distribution, and thermal conductivities of the fibers were investigated. Results showed that the Ce‐stabilized ZrO2 fiber inherited the hollow structure of the metaplexis, consequently exerting a significant effect on its thermal‐insulating properties. Compared to conventional ZrO2 fibers, the thermal conductivities of Ce‐stabilized ZrO2 fibers can decrease by approximately 12%‐24.3%.

Predicting the efficiency of CuO/water nanofluid in heat pipe heat exchanger using neural network

In this study, the CuO/water nanofluid was used to increase the performance of heat pipe heat exchanger. The results showed that the rise in the input power of the heat pipe leads to increase the wall temperature of the pipe, whereas augmenting the concentration of nanoparticles leads to reduce the wall temperature and decrease the temperature difference between the evaporator and the condenser. Using the nanoparticles increases the thermal conductivity of the base fluid and minimizes the temperature gradient within it. Therefore, the thermal power of the heat pipe increases and its resistance decreases. Also, the results showed that with increasing evaporation filling ratio, the resistance reduces (by Fr = 0.45) and then increases. Additionally, experimental data was compared with published data for the heat pipe in order to accurately evaluate the results obtained in this study. The results showed that the measured data are highly accurate. Also, the heat conductivity resistance equation was calculated based on the experimental data. In the next step, the model of neural networks was used to predict thermal performance, FR, the concentration of nanofluid and input power. The results showed that the network with an accuracy of 0.9938 is able to predict the heat transfer coefficient. A review of the predicted and experimental results for the verification part indicated that the residuals are scattered around the zero axis.

Heat Conductivity Resistance of Concrete Wall Panel by Water Flowing in Different Orientations of Internal PVC pipe

Green building technology and sustainability development is current focus in the world nowadays. In Malaysia and most tropical countries the maximum temperature recorded typically at 35°C. Air-conditioning system has become a necessity in occupied buildings, thereby increasing the cost of electric consumption. The aim of this study is to find out the solution in minimizing heat transfer from the external environment and intentions towards going green. In this study, the experimental work includes testing three types of concrete wall panels. The main heat intervention material in this research is 2 inch diameter Polyvinyl Chloride (PVC) pipe embedded at the center of the concrete wall panel, while the EPS foam beads were added to the cement content in the concrete mix forming the outer layer of the wall panel. Water from the rainwater harvesting system is regulated in the PVC pipe to intervene with the heat conductivity through the wall panel. Results from the experimental works show that the internal surface temperature of these heat resistance wall panels is to 3□C lower than control wall panel from plain interlocking bricks.

Thermal calculation of heat exchangers with simplified consideration of axial wall heat conduction

The usual thermal design and rating methods [1, 2] for heat exchangers neglect axial wall heat conduction in the separating walls and external shells of recuperators and in the solid matrix of regenerators. This may lead to undesirable undersizing. In this paper a simplified model is developed for the fast estimation of axial wall conduction effects in counterflow, parallel flow and mixed-mixed cross-flow recuperators. The dispersion model [3] is used to describe the performance deterioration of the exchanger with an effective fluid dispersion Peclet number for the correction of the heat transfer coefficients or mean temperature difference. The method is tested against analytical and numerical calculations for counterflow and parallel flow with good results. It is also shown how the method can be adapted to thermal regenerators and the related thermal calculation methods [1, 2]. An alternative approach is suggested for the consideration of lateral heat conduction resistance in the solid matrix.

Fire stability of carbon fiber reinforced polymer shells on the intermediate-scale

The fire stability of carbon fiber reinforced polymer (CFRP) shell structures was investigated using an intermediate-scale test setup. The shell specimens are representative of typical load-bearing CFRPs in modern civil aviation. The CFRP shell specimens were exposed to a fully developed fire with direct flame impingement to one side at a heat flux of 182kW/m2. Specimens were simultaneously loaded with constant compressive force equal to 40% of the ultimate failure load. CFRP shells and four different fire retarding configurations, using integrated protective layers, were investigated. Unprotected CFRP specimens failed after just 27s. Specimens with integrated protective layers with low heat conductivity and high burn-through resistance showed the most promising results. An integrated titanium foil decelerated the decomposition of the epoxy matrix and increased the time to failure by 68% compared to the unprotected CFRP shell.