Plate Temperature Research Articles

A direct numerical simulation study for confined non-isothermal jet impingement at moderate nozzle-to-plate distances: Capturing jet-to-ambient density effects

A direct numerical simulation (DNS) campaign is deployed for a series of confined downward oriented, non-isothermal turbulent impinging jet configurations. A baseline Reynolds number of 9960 is obtained through a precursor DNS pipe flow simulation (Reτ=505). Three jet temperature configurations (confinement height to nozzle diameter of three) enter a cylindrical domain that share ambient and impingement plate temperatures (298.15K). The range of jet temperatures are crafted such that the ratio of inlet to ambient density varies from unity to 0.52, showcasing the effect of density disparity on flow characteristics such as core collapse, radial mixing of momentum and energy, near-wall stagnation behavior, wall-jet profiles, and large-scale vortical structures. Surface quantities provided include mean radial heat flux and wall-shear stress profiles, and heat flux histograms at select radial stations. Results showcase increased radial normal stresses for higher temperature jets that support increased mixing, resulting in large-scale recirculation structures that are smaller, while retaining similar normalized radial wall profiles for shear stress, heat flux and pressure. Radial plots for wall shear stress and Nusselt number showcase strong radial decay as compared to previous configurations that share similar jet and ambient temperatures. For the 373.15 K case, a Gaussian-like histogram for heat fluxes at the impingement plate transitions to a log-normal profile as radial distances increase. In contrast, the 573.15 K configuration displays a bi-modal heat flux characteristic at the impingement plate, and in similar manner to the moderate temperature counterpart, transitions to a log-normal profile at larger radial distances.

Evaluation of high-speed aircraft thermal management system based on spray cooling technology: Energy analysis, global cooling, and multi-objective optimization

With the increase in aircraft speed, the aerodynamic heating on the aircraft wall has become one of the key factors restricting flight safety. Although passive thermal protection can solve the thermal protection problem of the aircraft body, there will always be some heat transferred into the cabin. And the temperature of the cabin interior environment and cabin wall increases, which reduces safety. The spray cooling system with R134a as a coolant can reduce the cabin wall temperature to 275 K, and the temperature drop rate can reach 1.05 K/s, so that the cabin cooling needs can be realized. The refrigeration system is used to connect the spray system with the fuel loop to form the closed-air spray cooling heat management system of the aircraft. The refrigeration system and the tandem radiator are optimized according to the genetic algorithm. After repeated iterations with different design parameters, the exergy efficiency and COP of the refrigeration system can reach 80 % and 2.36, and the pressure loss and the bottom plate temperature of the microchannel heat exchanger are 0.98 Mpa and 313 K, respectively. According to the analysis of the efficiency of the heat management system, the ejector efficiency, the energy efficiency ratio (EER) of the total system, and the required primary fluid flow rate, the required primary flow rate is at least 0.0027 kg/s to drive the thermal management system, EER of high-speed aircraft thermal management system can reach 15.62 %, exergy efficiency of the refrigeration system and the ejector efficiency can reach 44 % and 1 4% respectively.

Build Plate Heating and Cooling Technique Using Peltier Element for Fused Filament Fabrication

In fused filament fabrication, the adhesion force between the build plate and the target object must be strong enough during operation. It is, however, an obstacle to detaching the object after printing. The adhesion force heavily depends on the temperature of the build plate. This work suggests controlling the temperature of the build plate using the Peltier module that alters the heat flow direction. The modified build plate replaces the factory-equipped build plate of a commercial fused filament fabrication machine. The experimental results show that the modified build plate leads to 16.6 °C, approximately 9 °C less than the ambient temperature, even with 23.9–27.1% less total energy consumption than the primary build plate.

Re-examination of thermo-mechanical buckling and postbuckling responses of sandwich plates with porous FG-GPLRC core

The current study re-examines compressive postbuckling and thermal postbuckling responses of porous sandwich plates resting on an elastic foundation. The core of the sandwich plates is made of porous graphene platelets reinforced composite (GPLRC). Compressive postbuckling of the porous sandwich plates under uniaxial compression at elevated temperature and thermal postbuckling of the same plates under uniform thermal loading are studied. The GPLRC core is made of multilayers, and each layer may have different values of porosity coefficient to obtain a piecewise functionally graded (FG) pattern. The Young’s moduli along with the shear modulus of the porous GPLRC core are estimated through a generic Halpin–Tsai model in which the porous nature of the material is taken into consideration. The material properties of the metal face sheets and the porous GPLRC core are assumed to be temperature dependent. The governing equations for the postbuckling of the porous sandwich plates reinforced by GPLs are established based on the Reddy’s third order shear deformation theory (TSDT). In the modeling, we also consider the von Kármán nonlinear strain–displacement relationships, the plate-foundation interaction and the thermal effect. A two-step perturbation approach is utilized in solving the postbuckling problem. Numerical studies are performed to compare the results obtained from the present model and the equivalent isotropic model (EIM). The results confirm that the EIM is not suitable for analyzing buckling and postbuckling of porous plates.

A CFD-based approach on thermohydraulic performance evaluation and optimisation of the wavy corrugated curved channel solar air heater

ABSTRACT The present paper addresses the optimisation of geometrical design and flow parameters of the curved channel solar air heater (SAH). The prominence on heat transfer enhancement, absorber plate temperature, turbulence and thermo-hydraulic performance factors by changing the design and geometrical input parameters such as height, length and width has been thoroughly discussed. In addition, the consequences of amplitude and wavelength of wavy corrugated curved passage SAH are also studied. Here, the effects of different flow and geometrical parameters viz., Reynolds number ( 2000 ≤ R e ≤ 24000 ) , length ( 1 ≤ L ≤ 5 m ) , width ( 0.1 ≤ W ≤ 1 m ) , height ( 0.010 ≤ h ≤ 0.05 m ) , wavelength ( 0.025 ≤ λ ≤ 0.125 m ) and amplitude ( 0.004 ≤ α ≤ 0.024 m ) are investigated and presented at the optimum values on the basis of outlet air temperature and thermo-hydraulic efficiency. Finally, a wavy corrugated surface in the curved channel SAH can expand the heat transfer coefficient to a greater extent in comparison to the smooth wavy curved channel SAH.

Experimental investigation on incipient boiling in narrow closed gaps with water

This research deals with characterization of the Onset of Nucleate Boiling (ONB) in an enclosed narrow gap system containing a stationary liquid. In the experimental system, subcooled water at atmospheric pressure is confined between two parallel vertical rectangular copper plates. One of the plates is heated electrically and the opposite one is cooled with an external water-cooling system, maintaining its constant temperature.The experimental gaps explored in this research are: 5 mm, 3 mm, 0.9 mm and 0.5 mm. In each gap, several experiments are performed with a different controlled cold plate temperature. Various heat transfer mechanisms are observed (convection, transition and conduction), depending on the gap size. In the convection regime, the results are in good agreement with a correlation from the literature. In the gap 0.5 mm wide, the heat transfer occurs by conduction through the water, whereas for the gap 0.9 mm wide, single-phase experiments show a “transition” heat transfer regime. The onset of nucleate boiling (ONB) is detected as the point at which the heat transfer coefficient behavior changes dramatically, and is revealed also by visualization of the experimental channel. The wall superheat and the heat flux are evaluated at ONB.An analytical model is developed, based on the [1] correlation and on the experimental values of the heat transfer coefficient. A good agreement for the ONB heat flux prediction is achieved with the model, whereas the ONB superheat is over-estimated, except for the really narrow, 0.5 mm, gap.

Development and validation of a general two-fluid thermal-hydraulic analysis code for reactors with plate-type fuel assemblies

A general two-fluid thermal-hydraulic analysis code, TTHAC-PFA (Two-fluid Thermal-Hydraulic Analysis Code for reactors using Plate-type Fuel Assemblies), has been developed. The code was developed on basis of the fundamental governing equations. Reasonable mathematic and physical models for parallel rectangular channels and fuel plates have been built up to meet the command of the safety analysis for plate-type fuel reactors. The coolant distribution is conducted on basis of the pressure drop equation theory. Normal subchannel approach is adopted in the code. Fortran language is adopted. The RA-6 experiment is used to evaluate the heat transfer models. The max deviation of the simulations from the measured value is about 5.7 °C. Then, experiments on two-phase flow pressure drop are adopted to validate the code. Approximately 97% of the data points are within ±20% of the deviation range. In addition, CARR (China Advanced Research Reactor) is adopted as the benchmark for normal condition validation. Flow distribution validation and temperature profile validation are conducted. The flow validation presents negligible mean discrepancy and the temperature differences are within the scope of 6 °C. All validations are in good agreement, which indicates the developed code meet the requirements of analyzing thermal-hydraulic characteristics for parallel rectangular channels in reactors. Furthermore, TTHAC-PFA is applied to the investigate channel blockage accident occurred in the CARR. The mass flow is redistributed among channels due to the obstruction. In the obstructed channel and two nearby channels, the coolant temperatures increase a lot. The coolant temperature in the obstructed channel rises by 60 °C. In the rest of the channels, the coolant temperatures decrease with the increase of coolant flow. Besides, the two fuel plates, which form the blocked channel, are asymmetrically cooled due to flow maldistribution. The temperature difference between the cladding on both sides of the fuel plate can reach 40 °C. As a result of partial blockage, the cladding temperature on the side of the blocked channel rises by 63 °C. During the blockage accident, the plate temperature is under the melting temperature. The results indicate the significance of studying the effects of the adjacent channels near the obstructed channel for reactors with plate-type fuel elements.

Heat transfer enhancement in array of impinging jets by a row of pin-fins on dead fluid zone

BackgroundImpinging jet is one of the most effective practice techniques used in many industrial applications and thermal treatments which is one of its main applications in gas turbine blades. Therefore, in the past decades, many studies investigated the effects of impinging jets on the flow and thermal characteristics. In the present work, a row of pins has been employed to enhance the heat transfer rate by disturbing the dead fluid zone between the impinging jets. MethodsA row of impinging jets with 10 mm diameter has been considered for cooling a heated flat surface. The pin fins with 2.0 mm diameter and 1.0 mm height were exactly placed between the jets. A silicon heater supplied the uniform heat flux of 2500 W/m2 on the target surface. The temperature of the target plate was exactly measured by an IR(infrared) camera. The effects of pin-fins in the middle distance of the jets on velocity distribution and thermal field have been carried out for two jets Reynolds numbers of 10,000 and15000 and two jet-to-surface spacing (H/D = 1.0, 2.0). Significant findingsThe present experimental and numerical results confirm that the dead fluid zone between jets can efficiently disappear by applying a row of pins at the middle distance of the jets. Results showed that at H/D = 1.0, by the presence of a row of pins in the dead fluid zone, the averaged Nusselt number on the dead fluid zone increases from 29.47 to 37.95 to 44.43 and 43.73 for Reynolds numbers of 10,000 and 15,000 respectively.

Best Practice of Striving Energy Sustainability in a Hot Press Machine for Clutch Facing Manufacture

A facing clutch manufacturer in Surabaya, Indonesia, PT. X uses 20 hot press machines to produce the facings. The required heating process is provided by heat transfer oil (HTO), which is heated by natural gas burned in a heater. PT. X wants to reduce its natural gas consumption. The assessment started with checking the insulation on the piping system, measuring the temperature in the hot press machines, and measuring the HTO flow rate. The insulation in the piping system is in good condition. From the measurement, it was found that the HTO flow rate is adequate and fits the need of the heating process. Another finding is that the surface temperature of the lower plate in shaft no. 4 is the lowest than in the other shafts. The existing (asbestos) insulation from the lower bed in shaft no 4 to the hydraulic component is only 3 mm thick. This is not enough to prevent heat loss from the bed in shaft no. 4. The new 18-mm asbestos replaced the old asbestos. The replacement shows that the temperature at the mold surface at shaft no. 4 increased from 162.6°C to 170.9°C on average for MC-02 and from 166.7°C to 173.1°C on average for MC-03. Another achievement obtained is that the natural gas consumption was reduced by around 7.3% or 39 MMBtu/month, or equivalent to reducing 0.312 metric tons of CO2 per month. This is a simple effort to use less energy to protect our environment.

Emergency heater based on gas-fired catalytic combustion infrared technology: Structure, evaluation and thermal response

Deaths caused by extreme cold occur frequently, emergency heating needs to be greatly enhanced. In present work, a porous media catalytic combustion emergency heater was designed with a self-developed 1% Pt/Al2O3·SiO2 catalyst. Some evaluation indicators of the natural diffusion heater (including thermal efficiency, combustion efficiency, ignition temperature, cold start performance, combustion plate temperature uniformity, and infrared wavelength distribution) were established experimentally. According to the results, the catalyst possesses high activity (T50 = 397.2 °C and T90 = 463.2 °C) and nanoscale loading uniformity. Controlling the gas flow rate at 1 L/min can achieve the 21.56% thermal efficiency and 99.90% combustion efficiency. The heater can be preheated successfully at 120 °C and its cold start limitation is −30 °C. The infrared energy peak wavelength range (3–10 μm) is matched to the absorption ranges of the human skin and common textiles. Besides, real-person heating was tested in the apparent temperature (AT) region of −14.8–12.4 °C. Subjects' skin temperatures, subjective thermal sensations, and optimization suggestions were collected, and the relationship between mean skin temperature and AT was modeled, which revealed the efficient heating capacity. Therefore, this paper opens up great prospects for practical emergency heating and evaluation method for alleviating the cold-stricken heating problems.

Temperature Evolution and Heating Rates of Biomass undergoing Ablative Pyrolysis

The ablative reactor may be employed to enable fast pyrolysis to produce bio-oil from relatively large-sized biomass samples. Ablation mainly involves direct compressive force and conductive heat transfer between a hot surface and the biomass materials. Temperature evolution and heating rates are important operating factors in the biomass thermal conversion process. In this work, experimental and analytical investigations were carried out for different vertical dimensions of the biomass samples (2-20mm) and hot plate temperatures (400-550°C). It was shown that the thermal characteristics of the biomass were mainly affected by the transient conditions. It was observed that volatile release occurred during the transient heat transfer periods. It was found that at the maximum hot plate temperature of 550°C, the highest heating rate that could be achieved by ablation was more than 600°C/min.

Heat transfer performance assessment for precise accelerated control cooling of the hot heavy clad plate

In this study, the heat transfer characteristics are estimated to determine the internal temperature distribution of the hot heavy clad plate from the measured surface temperature prior to the accelerated control cooling process. The temperature prediction accuracy is verified by the advanced inverse heat transfer method (A-IHTM). It is found that the plate temperature distribution can be considered with the quasi-equilibrium state within the temperature deviation rate of 0.1 °C/s. The results have been also verified through a comparison with an analytical method over time, using dimensionless surface temperature. The comparison yielded a standard deviation of 0.027 and root mean squared error (RMSE) of 0.0574 in dimensionless temperature, indicating that the numerical method is a viable option for accurately predicting the temperature distribution in the hot heavy clad plate during the accelerated control cooling process. The internal temperature distribution of the heavy plate changes non-linearly. This phenomenon is defined as the “heat capacity effect” considering the enthalpy change. With the heat transfer characteristics, the cooling process of heavy clad plate could be controlled within finish cooling temperature deviation of 14.7 °C, cooling rate deviation of 0.7 °C/s. Also, the cooling control accuracy for the finish cooling temperature can be improved by 12.6 % with the satisfied mechanical property of heavy clad plate for corrosion resistance.

Impact of in Situ Heat Treatment Effects during Laser‐Based Powder Bed Fusion of 1.3343 High‐Speed Steel with Preheating Temperatures up to 700 °C

For laser‐based powder bed fusion (PBF‐LB) of high carbon steels, preheated build platforms can reduce thermal stresses and crack formation inside the generated material. Furthermore, the heat distribution during PBF‐LB is affected by laser energy input and heat transfer into the surrounding area. Depending on the preheating temperature and the thermal conditions during PBF‐LB, thermal gradients and different thermal exposure times of the manufactured layers can lead to in situ heat treatment effects. As a result, gradients in microstructures and properties are observed in the manufactured material. The effects are investigated on AISI M2 high‐speed steel (1.3343). Specimens are manufactured at platform preheating temperatures between 200 and 700 °C. Base plate and surface temperatures in the building layer are monitored by thermocouples and pyrometry. Local variations in the material microstructure and properties are determined and the effects of temperature distribution on microstructure and hardness are discussed.

Geometry Controlled Oscillations in Liquid Crystal Polymer Films Triggered by Thermal Feedback.

Light-induced oscillatory behavior of liquid crystal polymer network (LCN) films has been demonstrated by several researchers in the past decade. Similarly, oscillations in LCN films under constant thermal stimulus have been reported recently, although the mechanism and the factors that govern the oscillatory behavior are not well understood. In this work, we study the dynamics of self-sustained oscillations exhibited by LCN films under a constant thermal stimulus through experiments and simulations. Geometrically asymmetric films such as a right triangle and an equilateral triangle are obtained from a twisted nematic square film. A multiphysics computational framework using the finite element method is developed to simulate the oscillatory behavior of the LCN films kept on a hot plate. The framework accounts for a coupling between heat transfer and mechanical deformations during the oscillations. Small temperature fluctuations (≈ 1 °C) coupled with gravity induced torque are shown to drive the oscillatory behavior at a specific plate temperature. We show for the first time that self-sustained oscillations can also be achieved in symmetric shapes, such as square films, by creating a thickness tapering between two opposite edges. The frequency of the oscillations is found to be in the range of 0.5 to 2.5 Hz for different geometries studied. The oscillation temperature depends on the mean thickness, size, and thickness profile of the films. As a possible application, we demonstrate a thermally actuated optical chopper using the oscillatory response of the films.

Heat Transfer Enhancement of Microchannel with Jets and Ribs

In this paper, we propose a new microchannel heat sink with ribs and jets, which can not only increase the heat transfer performance but also improve the fluid flow in the microchannel. The effects of different shapes of ribs and inlet aspect ratios on the performance evaluation criteria at various Reynolds numbers are discussed. At an inlet Reynolds number of 3000, the maximum temperature of the modified microchannel heat sink is 8.78% lower than that of the smooth microchannel, and the performance evaluation criteria is increased by 0.94. Under the same conditions, the bottom plate temperature difference of the hydrofoil rib microchannel jets is 3.4% lower than that of the cylindrical rib microchannel jets; and the triangular-shaped ribs increase the heat transfer and cause greater pressure loss penalty due to the formation of a larger swirl zone in the back area. The jet inlet parameters can effectively improve the heat transfer coefficient of the microchannel. In terms of the heat transfer capability and the uniformity of the bottom plate temperature, the hydrofoil rib microchannel with jets has the best heat dissipation effect when the jet inlet parameter is .

Heat Transfer Analysis of Core Melt Contact with a CANDU Calandria

In a severe accident in a CANDU reactor, disassembly of the core could produce a bed of coarse debris at the bottom of the calandria that would eventually transition into a pool of molten corium. During this process, it may be possible for small amounts of molten core material to contact the calandria wall. The transient heat flow through a calandria wall suddenly contacted by molten Zr or corium is analyzed with a finite element model. Ablation of the wall at its inner surface and the temporary increase in heat flux through its outer surface are calculated for various boundary conditions. Model calculations are compared to observations of the ablation and temperature of a stainless steel plate sprayed by prototypic corium in the Cesium Aerosol Generation-4 or CAGE-4 experiment.

Effect of Process Parameters on Electrodeposition Process of Co-Mo Alloy Coatings

Plating bath composition, temperature, current density, and pH have a great influence on the properties of a Co-Mo alloy coating. However, these conclusions are obtained from the perspective of test results. Most of the factors that affect the properties of the coating operate by interfering with the electrodeposition process. Therefore, it is of great significance to study the kinetics of the electrodeposition process. To further study the influence of process parameters on the deposition process of Co-Mo alloy coatings, cyclic voltammetry (CV), scanning linear voltammetry (LSV), and electrochemical impedance testing (EIS) were used to study the deposition kinetics of Co-Mo alloy coatings. The results show that with the increase in sodium molybdate content in the plating solution, more Mo elements are involved in the deposition process. At the same time, a higher Mo element content can reduce the dissolution of the coating as the anode and improve the service life of the coating, but too high a Mo element content will lead to cracks on the surface of the coating. The deposition temperature will affect the processes of reduction deposition and oxidation dissolution of the coating. The pH of the plating bath will directly affect the reduction reaction process of MoO42− ions in the plating bath. With the increase in the pH value, the reduction reaction rate of MoO42− ions decreases, and the cathodic reduction reaction current density decreases. At the same time, the peak current density of anodizing decreases with the decrease in the pH value of the plating solution, indicating that the alkaline plating solution has an inhibitory effect on the plating dissolution process.

Experimental investigation of thermal storage integrated indirect solar cooker with and without reflectors

Environmental degradation, harmful gas emissions, and the increase in prices of fuel and electricity are the main driving forces behind the need for more effective utilization of renewable energy. In the present study, indirect solar cooking system with a flat plate collector integrated with a phase change material was designed, constructed and experimentally tested. Comparative study was conducted on the performance of the solar cooker with and without reflectors. Four plane reflectors on each side of the collector were used to enhance the solar insolation falling on the collector while stearic acid is used as PCM in the thermal storage unit. Daily average enhancement of 42.3% on the reflected solar radiation was found with four reflectors. The result showed that the maximum average absorber plate temperature, maximum outlet water temperature, maximum energy and exergy efficiency of FPC with and without reflectors are found to be 130 °C, 103.65 °C , 79%, and 48% and 92 °C, 71 °C, 63%, and 42% respectively.The overall system efficiency of the indirect solar cooker was found to be 19.04%. The utilization efficiency and characteristic boiling time of the cooker was found to be 22.3% and 15.7 min/kg.

A simplified core catcher model for the containment code AC2/COCOSYS

In Generation 3+ NPPs such as EPR or WWER-1200 the ex-vessel core catcher presents a key component of the severe accident mitigation concept. A simplified core catcher model in the containment code COCOSYS (part of AC2 code package) is developed to consider core melt retention and cooling phenomena in core catchers for containment simulations. The model enables the characterization of the corium in the core catcher including processes in the corium conditioning phase (melting of sacrificial material in the core catcher, oxidation of metallic components, possible layer flip) and the long-term cooling phase (evolution of long-term corium pool bulk temperature and changes in physical state). The core catcher model is based on the existing molten corium / concrete interaction (MCCI) model in COCOSYS with additions for melt retention within water-cooled structures and input data can be adapted to simulate various core catcher design features of e. g. NPPs with EPR or WWER.The current state of the model, including basic assumptions, calculation methods, simplifications, and two application examples are outlined. The recalculation of the water-cooled basemat test OECD WCB-1 shows that the experimental data regarding e. g. the ablation of the sacrificial concrete on top of the water-cooled basemat, corium pool temperature and heat fluxes at water-cooled interfaces can be adequately reproduced by the COCOSYS simulation, when using empirical data for the heat transfer, including the MCCI phase. These empirical heat transfer data agree well with findings obtained from recent analytical work on MCCI tests. However, the model does not predict high local bottom plate temperatures as observed in the WCB-1 test due to a restriction of the model to quasi-steady state processes. The second calculation example demonstrates the current modelling features when applied to an axisymmetric geometry of a reactor-scale core catcher. With view to reactor-scale, the model is ready for a further verification, like e.g. comparison with other analytical core catcher approaches.

Analysis on influencing factors of asphalt pavement icing and establishment of icing prediction model

At present, the prediction of the icing occurrence for asphalt pavement will take a lot of time, and data are relatively discrete. In this study, the heat transfer equation of phase transition was deduced based on theory of heat transfer and ice–water phase transition, and icing prediction model of pavement was also established through finite element software. The results show that the icing time and rutting plate temperature of indoor experiment are close to simulated results, which verifies effectiveness of prediction model. On this basis, when other factors remain unchanged, the lower ambient temperature and higher the wind speed will accelerate speed of road icing, but the degree of speeding up speed of road icing will reduce. The reduction of depth of accumulated water can also accelerate speed of road icing, but the degree of speeding up speed of road icing first increases and then decreases.