Heat Transfer Coefficient Profiles Research Articles

Heat transfer and flow analysis of a novel particle heater using CFD-DEM

CFD-DEM coupled simulations of a unique gravity-fed particle heater are performed. Physical and heat transfer properties of the solid particles and walls are varied to determine their relative impact on the local heat transfer coefficient along the heater surfaces. The varied parameters are the coefficient of restitution, particle-particle and particle-wall friction coefficients, particle size distribution, normal spring constant, particle conductivity, particle specific heat, and the numerical lens radius. The local heat transfer coefficient increases when the local void fraction along the heater surface decreases. In addition to analyzing thermal performance, flow instabilities are also identified under certain conditions. The outlet particle flow oscillates when the top of each heater is rounded. For heaters with sharp top edges, the local heat transfer coefficient and void fraction profiles change dramatically. The sharp corners remove the particle stagnation point, and the particles adhere to the surface better which increases the heat transfer.

Experimental heat transfer results and flow visualization of horizontal Near-Saturated liquid nitrogen flow boiling in uniformly heated circular tube under Earth gravity

This study investigates 1-ge horizontal flow boiling of liquid nitrogen with a near-saturated inlet along a circular tube of dimensions 8.5-mm inner diameter and 680-mm heated length. Experiments are conducted using a payload developed for eventual parabolic flight experiments. The operating parameters varied are mass velocity of 406.76–1572.77 kg/m2s, inlet quality of −0.05 to −0.01, and inlet pressure of 336.29–493.07 kPa. High speed video recordings are presented to explain two-phase flow structure and regime transitions which are visualized through a transparent tube in a visualization section situated downstream of the heated tube. Recognized flow patterns are bubbly, plug, slug, stratified annular, and annular. Heat transfer results are presented and discussed in terms of flow boiling curve trends, streamwise wall temperature profiles, streamwise heat transfer coefficient (HTC) profiles, and average HTCs. Previous HTC correlations are evaluated against the measured HTC data, of which two are identified for superior accuracy in predicting cryogen data. Finally, this study confirms the reliability and readiness of the payload for subsequent parabolic flight experiments intended for acquisition of microgravity data.

Effects of heating configuration and operating parameters on heat transfer and interfacial physics of microgravity flow boiling with subcooled inlet conditions – Experiments onboard the International Space Station

This study is part of the Flow Boiling and Condensation Experiment (FBCE), a collaborative effort between the Purdue University Boiling and Two-Phase Flow Laboratory (PU-BTPFL) and the NASA Glenn Research Center. The FBCE fitted with the Flow Boiling Module (FBM) was launched to the International Space Station (ISS) in August 2021 and experiments were successfully performed from February to July 2022 to amass a large microgravity-flow-boiling database. This study is focused on heat transfer and flow visualization of microgravity flow boiling of n-Perfluorohexane in a rectangular channel of 5.0 mm height, 2.5 mm width (heated), and 114.6 mm length, with subcooled inlet conditions. High-speed-video photography is utilized to present flow patterns and temporal interfacial behavior. Heat transfer results are presented in the form of flow boiling curves and both parametric curves and streamwise profiles of wall temperature and heat transfer coefficient. Firstly, the parametric effects of mass velocity (199.4 – 3200.0 kg/m2s), inlet subcooling (0.2 – 46.0°C), and inlet pressure (124.2 – 176.7 kPa), on the aforementioned aspects are assessed for double-sided heating to establish them for a microgravity environment. Of these three parameters, mass velocity and inlet subcooling mostly determine the microgravity flow boiling behavior, while inlet pressure plays an insignificant role. Flow patterns for double-sided heating are more complex than those for single-sided heating due to interaction between the two vapor layers. Vapor interaction is minimized at high subcoolings and high mass velocities due to strong condensation offered by the subcooled bulk liquid layer separating them. Despite the different flow patterns, both single- and double-sided heating generally result in similar parametric trends and local heat transfer coefficients for similar operating conditions. Flow instabilities manifest as temporal flow anomalies and temperature oscillations, and their severity increases with increasing boiling number. Secondly, the effects of heating configuration are analyzed by comparing and contrasting several aspects of single- and double-sided heating data. The heat fluxes at which onset of nucleate boiling degradation (ONBD) and critical heat flux (CHF) occur are distinctly different for single- and double-sided heating. There exists a threshold inlet subcooling demarcating the dominance of flow acceleration and condensation effects in vapor removal from the near-wall region and replenishment of fresh liquid for boiling. Above the threshold, condensation from the near-wall region is dominant and single-sided heating yields higher heat fluxes, and below it, acceleration is dominant and double-sided yields higher heat fluxes. At mass velocity in the range of 200 – 2400 kg/m2s, the threshold inlet subcooling lies in the approximate range of 20 – 30°C (corresponding inlet quality of roughly -0.40 – -0.20).

Slip and radiative effect on magnetized CNTs/[formula omitted] hybrid base nanofluid over exponentially shrinking surface

In current research, the physical characteristics of the laminar steady boundary layer flow of CNTs/ C2H6O2+H2O hybrid base nanofluid across a permeable exponentially contracting surface along the influence of magnetic force, heat radiation, and velocity slip of the first order have been examined. The effect of magnetic field stability analysis on the hybrid-based nanofluid flow of CNTs with thermal radiation was not previously explored for the numerous solutions, which is the originality of the current work. The partial differential equations (PDEs) controlling the model were transformed to ordinary differential equations (ODEs), and then the ODEs were solved using the three-stage Lobatto IIIa numerical approach in the MATLAB program. For different nanofluids constituted of SWCNTs and MWCNTs as nanoparticles and C2H6O2+H2O as the hybrid base nanofluid, the impacts of changes in the values of various parameters on temperature, velocity, heat transfer, and skin friction coefficient profiles were explored. Tables and figures illustrate numerically and quantitatively the outcomes. In addition to the effects of outputs, there are two solutions within the range of suction parameter. In addition, the parameter ∅ has a diminishing influence on heat transfer rate and skin friction coefficient in the first solution, resulting in a decrease in the surface drag force and heat transfer rate. Moreover, the selection of nanoparticle kinds has a substantial effect on the cooling/heating processes and stream function. Finally, a linear temporal stability analysis was performed to classify the stable solution among the dual solutions.

Viscoelastic boundary layer analysis of constant surface temperature plate embedded in saturated porous media

AbstractMathematical models and numerical solutions of Williamson fluid flow under influences of various boundary conditions provide important support to experimental studies in the solar energy field. Therefore, the present study is concerned with the effects of forced convection of the viscoelastic boundary layer on a horizontal plate embedded in saturated porous media subjected to constant surface temperature. The study explores the profiles of shear stress, velocity, temperature, and heat transfer coefficient. The governing equations in nondimensional forms are obtained by using a model of Darcy–Forchheimer–Brinkman and finally are solved numerically by using bvp4c with MATLAB package. The results of the numerical solution show an insignificant rise in the distribution of the velocity boundary layer and shear stress profile as the Darcy parameter is increased, while a decrease in the temperature and Nusselt numbers are found. On the other hand, as the viscoelastic parameter is increased, the Darcy parameter shows a reverse response. Finally, insignificant increases in profiles of boundary layer velocity, temperature, shear stress, and Nusselt number are observed at high values of the Forchheimer number.

Heat transfer and interfacial flow physics of microgravity flow boiling in single-side-heated rectangular channel with subcooled inlet conditions – Experiments onboard the International Space Station

This study is the culmination of a long-term collaborative effort between researchers from the Purdue University Boiling and Two-Phase Flow Laboratory (PU-BTPFL) and the NASA Glenn Research Center to investigate gravitational effects on flow boiling and flow condensation. The science and design concepts for this large-scale effort were initiated in 2011 and included several studies detailing various aspects of two-phase fluid physics in both Earth gravity and microgravity, culminating in construction of the large-scale experimental facility named “Flow Boiling and Condensation Experiment (FBCE)”. The experiment was launched to the International Space Station (ISS) in August 2021. Following the successful installation of FBCE, equipped with the Flow Boiling Module (FBM), onboard the ISS and completion of several safety checks, flow boiling experiments were performed for five months from February 2022 until July 2022. This resulted in a large flow boiling database covering broad ranges of operating parameters and heating configurations spanning several research objectives. This study investigates microgravity flow boiling of n-perfluorohexane with subcooled inlet in a single-side-heated rectangular channel of dimensions 114.6-mm heated length, 2.5-mm heated width, and 5.0-mm height. Key operating parameters investigated are mass velocity (199.90 – 3200.13 kg/m2s), inlet subcooling (0.10 – 45.76°C), and inlet pressure (113.30 – 164.29 kPa). Images and image sequences acquired via high-speed-video are presented to elucidate the interfacial flow physics. To analyze and explain the effects of various parameters in microgravity, heat transfer results are presented as flow boiling curves, streamwise profiles of wall temperature and heat transfer coefficient, and parametric trends of local and averaged heat transfer coefficient. Mass velocity and inlet subcooling significantly influenced most of the aforementioned aspects of flow boiling, whereas effects of inlet pressure were comparatively insignificant. Although the data and observed flow physics might be different, the parametric effects and trends in microgravity are similar to vertical upflow in Earth gravity. Some cases, especially low mass velocities, high heat fluxes, and large degrees of inlet subcooling, experienced temporally anomalous flow behaviors caused by two-phase flow instabilities manifesting as flow reversals and resulted in deviations in overall trends. Severe thermodynamic non-equilibrium is observed throughout the channel. Overall, FBCE's ISS experiments were successful for subcooled inlet with single-sided heating of rectangular channel, and the collected data well established the various effects on flow boiling physics in highly controlled long-term microgravity conditions.

Optimising integrated heat spreaders with distributed heat transfer coefficients: A case study for CPU cooling

Increasing power densities of modern CPUs has led to regions of high temperature on the semiconductor die which can lead to performance and reliability problems. In this case study, the effect of imposing a non-uniform heat transfer coefficient profile across the convective surface the CPU's integrated heat spreader was investigated as a potential enhanced cooling concept. A finite element model of a copper heat spreader of 40 × 40 mm2 area and 2.5 mm thickness with a centred 13 × 13 mm2 heat source at 100 W/cm2 heat flux was considered to approximate typical modern high-powered CPUs. Both uniform and Gaussian distributions of the heat transfer coefficient were then considered. For the latter, both single and multi-objective Genetic Algorithm optimisation were carried out for three source temperature objectives; average temperature, maximum temperature and maximum temperature difference. The analysis showed that the multi-objective optimisation strategy produced the best overall heat transfer coefficient distribution, with almost 5 K reduction in both the maximum temperature and temperature gradient across the heat source compared with a uniform heat transfer coefficient distribution.

Compressibility Correction to Models for Hypersonic Turbulent Boundary Layers

A compressibility correction for models is proposed, and it explicitly takes the effects of high Mach numbers and wall-cooling into account. The correction is validated by a recent set of direct numerical simulation databases with and without pressure gradient. The proposed compressibility correction is based on the correspondence between eddy viscosity in compressible and incompressible turbulence, which shows that the standard models estimate incorrect values of eddy viscosity in the near-wall region of a hypersonic turbulent boundary layer with a cold wall. For a range of Mach numbers between 2.5 and 14, and wall-to-recovery temperature ratios between 0.18 and 1, the correction collapses the eddy viscosity profiles on the incompressible data and predicts significantly improved velocity, temperature, skin friction, and wall heat transfer coefficient profiles. The present approach is independent of the eddy viscosity definition and Reynolds stress model, and it can be implemented easily in any model by modifying the closure coefficients of the production and destruction in the equation. Furthermore, the formulation is completely local and is disabled as the effects of compressibility disappear.

Optimization of thermal barrier coating performance and durability over a drive cycle

A methodology to thermo-mechanically optimize a piston thermal barrier coating over a full drive cycle was established. The optimization objective was to minimize the heat transfer to the engine wall while maintaining structural integrity of the coating. Over 800 candidate materials were investigated and the optimization required more than one million non-road transient drive cycle calculations; real materials were investigated to ensure a realizable result and the existence of thermal and mechanical properties. High computational efficiency was achieved using a recently developed analytical heat transfer technique for multilayer engine walls. An uncoupled approach was utilized for the optimization, wherein the gas temperature and heat transfer coefficient profiles from a fully coupled and calibrated baseline model over the 20-min drive cycle were employed. The coating/piston interface temperature was constrained to be below the maximum piston service temperature limit. The durability was assessed using a recently developed analytical coating delamination framework for engine in-cylinder coatings based on the energy release rate when a crack forms. Results are presented for a mechanically unconstrained optimization and for cases constrained to three fixed levels of drive-cycle maximum energy release rate, and also constrained by the individual material’s toughness. The best-performing coating materials identified were verified using the fully coupled system-level model, which compared well to the uncoupled predictions. A study on the effect of adding a sealing layer to some high-performing, but porous, coatings showed a reduction in fuel consumption benefit and an increased exhaust temperature over the cycle, but the system still outperformed the uncoated case. The results of the study elucidate the importance of including engine performance and mechanical failure considerations in thermal barrier coating design.

Flow visualization, heat transfer, and critical heat flux of flow boiling in Earth gravity with saturated liquid‐vapor mixture inlet conditions – In preparation for experiments onboard the International Space Station

This study investigates flow boiling of n-Perfluorohexane with saturated two-phase mixture inlet in a rectangular channel of dimensions 114.6 mm heated length, 2.5 mm width, and 5 mm-height. The experiments were performed as part of the Mission Sequence Testing of the Flow Boiling and Condensation Experiment's (FBCE) Flow Boiling Module (FBM) in the vertical upflow configuration in Earth gravity using the same experimental system that was launched to the International Space Station (ISS) in August 2021. The operating parameters varied are heating configuration (single- and double-sided), mass velocity (380–2400 kg/m2s), inlet quality (0.011–0.519), and inlet pressure (120–179 kPa). High-speed video photographs are presented to explain the two-phase flow patterns within the channel's heated length. Flow patterns are constituted by low-density and high-density fronts moving along the channel, with the high-density fronts gradually reducing in length due to evaporation. Heat transfer results in terms of flow boiling curves, streamwise wall temperature profiles, streamwise heat transfer coefficient profiles, and average heat transfer coefficients are presented and trends discussed. CHF data from the present experiments are combined with prior databases to compile a consolidated FBCE-CHF database for saturated inlet to expand the ranges of operating conditions and include other flow orientations in Earth gravity. Experimental CHF trends are also discussed. The interfacial lift-off model shows a good CHF predictive accuracy evidenced by a mean absolute error of 11.97% for this consolidated database after constraining it to mass velocities greater than or equal to 500 kg/m2s. Finally, this study confirmed reliability of the upcoming ISS experiments for saturated inlet conditions and the collected Earth-gravity data will be compared to ISS microgravity data.

Numerical Results on Slip Effect over an Exponentially Stretching/Shrinking Cylinder

An investigation is conducted to study the flow and heat transfer on stagnation point over an exponentially stretching/shrinking cylinder filled with nanofluid in the presence of slip at the boundary. By using the appropriate exponential similarity transformation, the governing equations are converted into nonlinear ordinary differential equations and then solved computationally using bvp4c in Matlab software. The results of skin friction coefficient, heat transfer coefficient, velocity and temperature profiles on slip parameter, curvature parameter, nanoparticles as well as nanoparticle volume fraction parameter are presented graphically. The presence of slip and curvature parameters cause the region of dual solutions to expand and at once enhance the heat transfer rate at the surface but somehow the heat transfer rate at the surface decreases rapidly when cylinder is shrunk. The aim of this paper is to investigate the effect of slip parameter on nanofluid as well as on the stretching/shrinking surface. The new findings of the effects of skin friction and heat transfer coefficient on different nanoparticles and nanoparticle volume fraction were discussed. Since there are dual solutions in the flow characteristics, we carry out a stability analysis to verify which solution is in a stable state and can be realized physically.

Numerical Study of the Temperature Effects on Heat Transfer Coefficient in Mini-Channel Pin-Fin Heat Sink

Pin-fins are frequently used to increase the heat transfer surface and promote turbulent motion, which improves the devices cooling process by enhancing heat dissipation, as in hydrogen fuel cells applications. The application has burst out this last decade and became vital in several industrial devices. The present study is a numerical investigation of flow and heat transfer in rectangular mini-channels (RMC) and pin-fin heatsinks (PFHS). The pin-fins have a diamond shape arranged in segregated disposition (corrugated channel). In order to adequately calculate the heat transfer coefficient within this complex thermal system; several parameters, such as mass flow rate, geometry dimensions, heat flux and reference temperature are extensively examined. The importance in way the reference temperature was calculated was highlighted. A correct estimation of the heat transfer coefficient led to a better optimisation of the cooling process performances. The aim of this study was to elaborate a technique to correctly estimate the temperature difference between the cooler fluid and the heat sink wall, leading to a better approach for heat transfer coefficient estimation. For this purpose, an approach with variable reference temperature (VRT) has been adopted in the calculation of the wall-fluid temperature difference. Flow field and heat transfer are analysed qualitatively (visualisations of sensible zones) and quantitatively (profiles of heat transfer coefficient, heat flux, wall and fluid temperatures...). The numerical procedure has been validated by experimental measurements. The results showed that the proposed approach to calculate the reference temperature leads to a better presentation of the heat transfer coefficient. In addition, new fit function was involved, in particular the variation of the averaged heat transfer coefficient against Reynolds number.

Experimental heat transfer results and flow visualization of vertical upflow boiling in Earth gravity with subcooled inlet conditions – In preparation for experiments onboard the International Space Station

Since 2012, researchers at the Purdue University Boiling and Two-Phase Flow Laboratory (PU-BTPFL) and NASA Glenn Research Center have been collaborating on a long-term effort to study flow boiling and condensation in microgravity. The ultimate goal has been to develop the Flow Boiling and Condensation Experiment (FBCE) for the International Space Station (ISS). Based on the findings from prior flow boiling experiments both at different orientations in Earth gravity and onboard parabolic flights simulating short durations of microgravity, a final refined experiment design, construction, and operating procedure have been arrived at for long-duration microgravity flow boiling experiments onboard the ISS. This study investigates flow boiling of n-Perfluorohexane with subcooled inlet in a rectangular channel of dimensions 114.6 mm heated length, 2.5 mm width, and 5 mm height. These pre-launch experiments (Mission Sequence Testing) were conducted in vertical upflow orientation in Earth gravity using the same experimental rig that was launched to the ISS in August 2021. The various operating parameters varied are heating configuration (single- and double-sided), mass velocity (180 – 3200 kg/m2s), inlet subcooling (+0 – 32 °C, encompassing both highly subcooled and near-saturated inlet conditions), and inlet pressure (119 – 191 kPa). High-speed video flow visualization images are presented to explain the two-phase interfacial physics within the channel's heated section. Heat transfer results in terms of flow boiling curves, streamwise profiles of wall temperature and heat transfer coefficient, and averaged heat transfer coefficients are analyzed and parametric effects elucidated. Severe temporal thermodynamic equilibrium is observed for near-saturated inlet at very low velocities. Nucleate boiling degradation starts at larger heat fluxes for single-sided heating than double- sided at low mass velocities with highly subcooled inlet, and conversely at high mass velocities with near-saturated inlet. Nucleate boiling degradation can be delayed to higher heat fluxes by highly subcooling the inlet and increasing mass velocity. The entire local heat transfer coefficient profiles are degraded at higher heat fluxes for near-saturated inlet, but only the downstream part for highly subcooled inlet. This study also confirmed reliability of the upcoming ISS experimental data for subcooled inlet conditions and the collected Earth-gravity data will be used for comparison against the ISS data.

Numerical Study of Variable Viscosity and Thermal Conductivity on Natural Convection Flow along a Vertical Flat Plate with Pressure Work and Heat Conduction

A heated vertical flat plate in the presence of heat generation is an extremely significant technological issue, and many academics have studied this sort of problem. A vertical plate submerged in a fluid with varying viscosity will be used in this research to investigate the effects of variable viscosity and thermal conductivity on heat generation free convection flow. The boundary layer equations in this section are two-dimensional, laminar, and unstable. The fundamental governing equations are turned into non-dimensional governing equations by using the necessary variables. Using the Crank-Nicolson implicit finite-difference technique, these equations are solved numerically. Viscosity and thermal conductivity are temperature-dependent properties of a viscous, incompressible fluid. Variations in the study's numerous parameters will reveal and compare the velocities, temperatures, local skin friction, and local heat transfer co-efficient profiles. There will be a comparison between the current numerical data and previously reported data findings. Besides that, we'll compare our current work numbers to those of past released publications. Graphs and tables will be used to display the findings for a variety of key physical characteristics.

Fluid catalytic cracking process and apparatus for maximizing light olefin yield and other applications

In petroleum refining industry, external catalyst cooler is a key device in FCC units processing heavy residue feedstock. In this study, a new heat transfer intensification method was proposed for FCC external catalyst coolers, which aims to increase their bed-to-wall heat transfer coefficient by enhancing the internal solids mixing and thus the particle renewal on heat tube surface by a double-distributor design. To validate this idea, a large cold model with similar heat tube design and heat transfer mechanism to industrial catalyst coolers was built. Heat transfer coefficient and axial profiles of particle concentrations were measured under different operating conditions. The experimental results proved the feasibility of this heat transfer intensification idea. Higher bed-to-wall heat transfer coefficient, smaller fluidizing gas usage and higher adjustment flexibility are realizable in the new catalyst cooler. It is also learned from this study that uniform gas distribution, limited wall effect, good fluidization state are necessary to achieve good heat transfer performance in FCC external catalyst coolers. An effective height was speculated from the axial tube wall temperature distributions, within which the heat transfer intensification of the new catalyst cooler is effective. This effective height is also found to rise with increasing superficial gas velocity.

Numerical Analysis of Mixed Convection Flow Past a Symmetric Cylinder with Viscous Dissipation in Viscoelastic Nanofluid

Research on the nanofluid becomes trending amongst researchers especially in the industrial and engineering field due to its important and extensive applications. Therefore, the present study aims to investigate numerically the impact of viscous dissipation conducted by sodium carboxymethyl cellulose (CMC-water) nanofluid containing copper nanoparticles at room temperature with convective boundary conditions (CBC). The Tiwari and Das model was selected in this study and the transformed boundary layer equations for momentum and energy subject to the appropriate boundary conditions were numerically solved by employing numerical scheme, namely the Keller-box method. The results were analysed in detail and presented graphically for the velocity, temperature, skin friction coefficient as well as the heat transfer coefficient. The obtained results indicated that there was no significant effect for velocity and temperature profiles when values of Eckert number increased. However, it is significant for skin friction and heat transfer coefficient profiles. In the meantime, the thermal conductivity of the fluid may increase by increasing the concentration of nanofluid.

A review paper on heat transfer and flow dynamics in subsonic circular jets impinging on rotating disk

A review of the most important findings for jets impingement on rotating target is presented, the focus is on the heat transfer and flow dynamics in these jets. These jet configurations are encountered in many industrial applications. A significant number of research studies dealing with computational and experimental studies are reviewed. Different parameters are found to influence the flow and enhance mass and energy transfer in several heat configurations such as; Reynolds number (Re), nozzle geometry, spacing between jet exit and the impinging plate, jet impinging angle and the flow regime at the jet exit. There are a few studies that deal with heat transfer of a flow impinging on a rotating disk due to complexity of the flow structure and the challenges to conduct in-depth experimental investigation. Most studies present profiles of heat transfer coefficients, mean velocity and turbulence rates of the impinging flow. Many researches have reported that the LES can predict heat transfer and flow field data for different impinging angles to study the feedback mechanism between the nozzle and the plate.

Completion Effects on Diagnosing Multistage Facture Treatments with Distributed Temperature Sensing

Summary Distributed temperature sensing (DTS) is a valuable tool to diagnose multistage hydraulic fracture treatments. When a stage interval is shut in, the clusters that take more fluid during pumping warm up more slowly. Therefore, the fluid volume injected into each cluster can be quantitatively interpreted by numerical inversion of the warm-back temperature behavior. This general concept assumes that the different warm-back behavior is controlled by only the injected fluid volume; however, recent observations of DTS data indicate that completion configurations significantly influence the warm-back behavior. This paper investigates the completion effects on the DTS interpretation. In ideal conditions, when a stage is fractured, the upstream stage intervals should show an almost uniform temperature that is close to the injected fluid temperature. This is due to the high fluid velocity of injected fluid in the wellbore, and the upstream intervals have not been perforated (noncommunicating intervals), so the only heat transfer is heat conduction between the wellbore fluid and the surrounding reservoir. But the field DTS data show considerably irregular variations in temperature along the upstream stage intervals. These variations are caused by the completion effects. The nonuniform temperature profile is caused by different heat transfer behavior induced by completion hardware along the production casing string, such as joints, clamps, and blast protectors, and by the sensing cable location in the cement, as well as the cement quality. Because the varying heat transfer behavior impacts the warm-back behavior as well as the temperature profile, the completion effects need to be considered in DTS interpretation. A method of DTS interpretation considering the completion effects to diagnose multistage fracture treatments was developed. Because the heat transfer between a wellbore and a reservoir depends on the overall heat transfer coefficient describing heat conduction through the completion in a forward model, this parameter needs to be tuned all along the wellbore. To calibrate the completion effect, the temperature inversion is conducted using the temperature measured at a stage interval that is upstream of a stage interval currently being treated. Because the interpreted stage interval is not perforated at that time, the thermal behavior at the noncommunicating interval is governed by only the heat conduction through the completion environment. Once the effective values of the overall heat transfer coefficient are estimated along the interpreted stage interval, they can be assumed to be constant physical parameters. Then, the fluid volume distribution is interpreted by using the effective overall heat transfer coefficient profile along each interval. This study provides a field application of the developed interpretation method. The new interpretation method provides more accurate diagnosis of fracture treatments by DTS interpretation.

Development of an Instrumented Test Tool for the Determination of Heat Transfer Coefficients for Die Casting Applications

In the case of casting processes with permanent molds, there is still a relatively pronounced lack of knowledge regarding the locally prevailing heat transfer between casts and mold. This in turn results in an insufficient knowledge of the microstructure and the associated material properties in the areas of the casting component close to the surface. Therefore, this work deals with the design and evaluation of a test tool with an integrated sensor system for temperature measurements, which was applied to obtain a time-dependent heat transfer coefficient (HTC) during casting solidification. For this purpose, the setup, design and computational approach are described first. Special attention is paid to the qualification of the multi-depth sensor and the calculation method. For the calculations, an inverse estimation method (nonlinear sequential function) was used to obtain the HTC profiles from the collected data. The developed sensor technology was used in a test mold to verify the usability of the sensor technology and the plausibility of the obtained calculation results under real casting conditions and associated temperature loads. Both the experimental temperature profiles and the HTC profiles showed that, in the evaluated casting series, the peak values determined were close to each other and reached values between 6000 W/(m2·K) and 8000 W/(m2·K) during solidification.

Electrothermal transport via copper nanoparticles in a microchannel propagated by peristalsis

This communication investigates the simultaneous impact of the magnetic field, heat absorption and mixed convection in electroosmotically induced peristaltic flow of copper particles in the blood. The two-phase flow model is used in the microchannel with flexible walls. The thermal features of nanofluids are studied using copper nanoparticles. The Poisson–Boltzmann equation is employed to accommodate the electrical double layer in the microchannel. With Debye–Hückel, lubrication and long wavelength approximations, the problem becomes non-dimensional. Exact solutions have been calculated for velocity, stream function, pressure rise, pressure gradient and heat transfer coefficient and temperature profile. Impact of different embedded parameters on flow properties is graphically illustrated. It is found that the electroosmotic parameter strongly effects the velocity profile and bolus formation. Also, the decreasing behavior of temperature is presented, which clarifies the nanofluid as a cooling agent. The results show an increment in peristaltic pumping with rise in mixed convection while it decreases with magnetic field. Furthermore, a comparative study of pure blood and copper blood is conducted. The obtained results may be suitable in the peristaltic pump modulation for the efficient operation of a variety of industrial, biomedical and drug delivery systems in the microfluidic device.