Variation Of Temperature Profile Research Articles

Assessment and outlook of variable retort temperature profiles for the thermal processing of packaged foods: Plant productivity, product quality, and energy consumption

Thermal processing has been used for packaged foods for many years and remains one of the most common and safe processes to preserve foods and extend their shelf life. Advances in thermal processing in the last two decades have helped maintain its relevance in international food trades. In this study, we aimed to gain a better understanding of thermal food processing using variable retort temperature profiles (VRTPs). VRTPs were assessed to optimize processes, either by ensuring high quality level or minimizing the operating process time. Based on the research results, VRTPs could improve quality retention; however, the improvement was not sufficient to be detectable by consumers and to justify implementation of VRTPs at the industrial level. Our general assessment provided a preliminary guide for processors to discover real opportunities for VRTPs, e.g., increased productivity by reducing operating process time and energy consumption.

Evaluation of the bandwidths and spatial resolutions achievable with near-infrared observations of Venus below the cloud deck

We identified potential atmospheric windows with which to study the Venusian surface on the nightside and calculated the approximate scattering footprint as would be seen by a prospective aerial mission. The emission from the surface, its scattering through the atmosphere, and the emission from the atmosphere were calculated from the surface to various heights beneath the cloud deck. We explored the effects of different sensor altitudes, varying surface emissivity, variation in elevation causing changes in surface temperature, and variations in the temperature profile, on the possible surface viewing atmospheric windows. The effects of surface emissivity and surface elevation dominated, and those of sensor altitude and variation in temperature profile are relatively small. The prospective windows are largely expanded versions of previously identified windows that have been exploited by satellites and ground-based observation with an additional window centered at 1.27 μm. Any mission that exploits the improved visibility beneath the cloud decks should make use of 0.7–1.0, 1.1, and 1.27 μm windows, as these provide a comprehensive ability to extract information about the surface. We explored the effect of sensor altitude and surface elevation on the scattering footprint. The scattering footprint beneath the cloud deck varies from ~15 to 5 km depending on wavelength at our nominal altitude of 40 km, a significant improvement over the 50–100 km footprint for orbiting satellites. Lowering the sensor altitude only mildly reduces the scattering footprint, as most scattering is caused by the dense lowermost atmosphere. Increased surface elevation reduces the scattering footprint. We concluded that regions elevated above the mean planetary radius represent the best targets as these have the greatest amount of the electromagnetic spectrum identified as surface viewing atmospheric windows and the smallest scattering footprint. These windows have the potential to elucidate questions about the composition and redox state of the surface of Venus, even for low emissivity materials (e.g., fine-grained hematite at ε~0.5), which have important implications for the evolution of the planet.

Long range intensity fluctuations on the Chukchi continental shelf measured during the year-long Canada Basin Acoustic Propagation Experiment 2017

Analysis of one-year-long broadband transmissions from five deep water sound sources recorded on shelf during the Canada Basin Acoustic Propagation shows strong azimuthal variability. Broadband chirp signals (140–325 Hz) transmitted every 4 h were received on spatially distributed receiver arrays on the Chukchi shelf from October 2016 through 2017. Here, we present spatial, temporal, and azimuthal correlations by four receiver arrays with source-receiver distances ranging from 228.6 to 524.4 km in a cross-the-shelf orientation. Temporal fluctuations in received field are related to water column variability for each source-receiver pair. Received signals from the same source to each receiver on the shelf, separated from 15.8 to 49.63 km in “along-the-shelf” direction show large intensity fluctuation. This is related to the turbulence that signals have experienced in their path. Temporal and spatial variations of temperature profiles were measured on the shelf, however, from deep water sources to the shelf break region, there is little information. Analysis are conducted for three time zones, from fully frozen seas, transition from full ice, and ice-free conditions. The parabolic equation model is used to report the propagation of field for the ice-free condition. Limitations of the acoustic modeling due to spatially under-sampled input environmental parameters are discussed. [Work supported by ONR-322 OA.]Analysis of one-year-long broadband transmissions from five deep water sound sources recorded on shelf during the Canada Basin Acoustic Propagation shows strong azimuthal variability. Broadband chirp signals (140–325 Hz) transmitted every 4 h were received on spatially distributed receiver arrays on the Chukchi shelf from October 2016 through 2017. Here, we present spatial, temporal, and azimuthal correlations by four receiver arrays with source-receiver distances ranging from 228.6 to 524.4 km in a cross-the-shelf orientation. Temporal fluctuations in received field are related to water column variability for each source-receiver pair. Received signals from the same source to each receiver on the shelf, separated from 15.8 to 49.63 km in “along-the-shelf” direction show large intensity fluctuation. This is related to the turbulence that signals have experienced in their path. Temporal and spatial variations of temperature profiles were measured on the shelf, however, from deep water sources to the shelf ...

Experimental and numerical study on the influence of critical 3D printing processing parameters

In the present work the temperature profile variations generated in rectangular specimens built using the Fused Deposition Modeling (FDM) process, at different printing speeds and orientations, were investigated. The temperature recordings were achieved by the integration of temperature sensors throughout the 1st and/or 21st building layer of the specimens. The experimental results show that the temperature values inside the specimen re-main above the glass transition temperature (Tg) even at the end of the fabrica­tion process. Higher values were obtained when increasing the printing speed and decreasing the printing path. The experimental results were compared to the corresponding ones derived by simulation of the thermal diffusion problem via Finite Element Analysis. The calculated maximum temperature values were in good agreement with the experimentally recorded ones.

Experimental demonstration of the thermodynamic advantage of modular heat storage system for a variable-temperature input

Storage acts as an inseparable component of the heat accumulation process using an inherently intermittent and variable source such as solar heat. Sensible thermal storage often is chosen over the other options owing to its operational simplicity and lower response time. In the current study we propose a novel method of designing the sensible heat storage system which can provide significantly better energetic and exergetic efficiency particularly under variable temperature profile for the input flow as compared to the conventional single tank storage. Through small scale laboratory experiments, we demonstrate the proof of concept for the proposed modular multi-tank storage against a low temperature input flow having prescribed temperature variations. We observe that for both charging and discharging, the modular storage holds a distinct thermodynamic advantage due the thermal segregation as well as the appropriate sequencing of the use of different tanks based on heat transfer argument. The concept of modular thermal storage can remarkably enhance the flexibility of plant operation and improve the energetic and exergetic efficiencies of the storage.

Influence of the Temperature Effect on the Lateral Distribution of the EAS Electron Component

The sensitivity of the lateral distribution of the EAS electron component to variations in the atmospheric temperature profile is investigated. An approach developed by the authors on the basis of the variational theory of sensitivity is used to solve the problem. The differential sensitivity coefficients of the lateral distribution of EAS electrons to variations in the temperature profile are obtained for the first time. A method of adjusting a ground-based EAS array’s data for the temperature effect is proposed.

The asymptotic solution of the ion-damped acoustic-gravity wave equation

In his classic work Hydrodynamics, Horace Lamb devoted a significant amount of effort to the mathematical analysis of atmospheric waves, i.e. waves in a compressible medium under the influence of a local gravitational field and a variable temperature (and hence sound speed) profile. In so doing, he derived equations for both the divergence and the curl of the velocity field, yielding expressions of considerable mathematical beauty and complexity. Eight decades later, Derek Moore and Edward Spiegel extended Lamb’s analysis to include an arbitrary external applied force in the equations of motion. By a suitable choice of such force, the governing wave equations for a wide variety of Lorenz force/Coriolis force-induced wave motions can be derived. However, they chose to investigate the radiation field resulting from the application of a concentrated vertical force. In so doing, they were able to utilize an important theorem by James Lighthill concerning the asymptotic radiation field from a source with compact support, using the concept of a wavenumber surface. This paper has two main components: the first is to extend the work of Moore and Spiegel to ion-damped acoustic-gravity waves in the ionospheric F-region, based on the seminal work of C. H. Liu and K. C. Yeh. The second part is a consequence of the first: the corresponding wavenumber surface becomes complex, and so Lighthill’s method has to be modified to account for the effects of this. Furthermore, a significant inconsistency in the formulation of the physical problem by Liu and Yeh has been corrected and the corresponding derivations have been reformulated. Some graphical information has also been provided in special cases to illustrate the comparative effects of damping on the asymptotic behaviour of the acoustic-gravity radiation field. A final feature of the paper is that the equations derived are very general and can provide the basis for investigation of more realistic atmospheric temperature profiles in future work.

Numerical Simulation of MHD Peristaltic Flow with Variable Electrical Conductivity and Joule Dissipation Using Generalized Differential Quadrature Method

In this paper, the MHD peristaltic flow inside wavy walls of an asymmetric channel is investigated, where the walls of the channel are moving with peristaltic wave velocity along the channel length. During this investigation, the electrical conductivity both in Lorentz force and Joule heating is taken to be temperature dependent. Also, the long wavelength and low Reynolds number assumptions are utilized to reduce the governing partial differential equations into a set of coupled nonlinear ordinary differential equations. The new set of obtained equations is then numerically solved using the generalized differential quadrature method (GDQM). This is the first attempt to solve the nonlinear equations arising in the peristaltic flows using this method in combination with the Newton-Raphson technique. Moreover, in order to check the accuracy of the proposed numerical method, our results are compared with the results of built-in Mathematica command NDSolve. Taking Joule heating and viscous dissipation into account, the effects of various parameters appearing in the problem are used to discuss the fluid flow characteristics and heat transfer in the electrically conducting fluids graphically. In presence of variable electrical conductivity, velocity and temperature profiles are highly decreasing in nature when the intensity of the electrical conductivity parameter is strengthened.

Predicting combustion characteristics in externally heated micro-tubes

This study employs a simplified analytical model to obtain qualitative predictions of transitions between non-adiabatic combustion regimes found in non-catalytic tubular micro-flow reactors, i.e. normal stable flames, flames with repetitive extinction and ignition (FREI), and weak flames that are stabilized by wall heat transfer. Assuming large activation energy for single-step kinetics, a comparison of exact solutions for constant and variable wall temperature profiles reveals that while a non-zero wall temperature gradient introduces a temperature lag, it has no impact on the structure of the flame solution itself. This result is significant as it establishes a link to quenching characteristics within heated micro-tubes, and further facilitates a simplified micro-flow reactor analysis. Predictions for sweeps of wall temperatures are combined to S-curves, which allow for a combustion regime classification for a given combination of micro-flow reactor geometry and mixture properties. A variation of parameters such as tube diameter or mixture stoichiometry yields predictions of shifts in regime transitions, thus providing insights on interactions between heat transfer and first order effects of chemical kinetics. A comparison to experimental data illustrates that the theoretical framework, – within inherent limitations, – captures qualitatively correct trends that reflect experimental observations, thus providing valuable insights for micro-flow reactor design and operation.

Design and Evaluation of a Multidirectional Thermal Flow Sensor on Flexible Substrate

The development and the corresponding evaluation of a multidirectional thermal flow sensor are presented in this work. The sensor was fabricated on a flexible substrate, allowing for new applications, since it provides the possibility of installation in nonplanar surfaces such as pipelines. Furthermore, the sensing elements are not in direct contact with the fluid, which increases the device reliability, extends its application range, and allows the noncontact monitoring of fluids. This was achieved by utilizing the substrate as a protective layer between the sensing elements and the fluid under measurement. The operation principle is based on the determination of the flow-induced temperature profile variations. A dedicated experimental setup was designed and used for the device evaluation. Both flow velocity value and direction were successfully extracted, while the results were consistent with the predicted theoretical values. A single-layer back propagation neural network that correlates the sensors’ readouts to the angle of rotation was implemented, which leads to a mean absolute direction estimation error in the order of 2.7 degrees independent to the training procedure datasets.

Numerical simulation of a simplified, transient, 2D, non-reactive heat transfer model of a lab-scale fixed-bed pyrolysis reactor

Pyrolysis of agro-industrial residues can be used to produce alternative liquid fuels to reduce consumption of fossil fuels. To study these biomass pyrolysis processes, experimentation and numerical simulations are commonly compared. For the latter, thermophysical properties of biomasses and proper thermal models of pyrolysis reactors are required in numerical simulations. This paper presents values for the specific heat capacity, density, and thermal conductivity of Colombian Coffee Husk, as well as a simplified non-reactive heat transfer model of a lab-scale, fixed-bed pyrolysis reactor. The thermal conductivity was determined by combining the axial rod method with transient temperature measurements and an inverse problem solution. CH properties values determined were 1.62 kJ/kg K, 1390 kg/m3, and 0.19 W/mK. To test the validity of the reactor’s thermal model simulation, temperature profiles results were compared with results from an experimental study employing a pyrolysis reactor with the same characteristics. Variations of temperature profiles in time were compared and good agreement between numerical and experimental results was observed for temperatures lower than pyrolysis temperatures (300–400 °C), validating the simplified model. Temperature differences above 300–400 °C were expected as chemical reactions were not included in the numerical model.

Heat transfer and water migration in loess slopes during freeze–thaw cycling in Northern Shaanxi, China

Migration of heat and water during freeze–thaw cycling has always been one of the significant topics in frozen soil mechanics. This paper first carries out field tests in the heartland of Loess Plateau, i.e., Northern Shaanxi, China, on the water migration and heat transfer in loess slopes during freeze and thaw. Results indicate that the water content within a certain depth shows sudden increase during freezing, while it tends to be more uniform after thawing, strongly depending on the variation of temperature profile over depth. When modeling heat and water migration in seasonal frozen ground, two characteristic curves, i.e., soil freezing curve and water retention curve, were incorporated in an improved Harlan model. The modified Richards’ equation and a nonlinear heat conduction equation considering ice-water phase change were both included. As for the effect of freeze–thaw cycling, laboratory tests were carried out to investigate how the coefficients of heat and water conductivity vary with both the degree of saturation and freeze–thaw cycles, based on which empirical models for loess were derived. A large-scale model test on the loess slope with the gradient of 1:0.75 was carried out to verify the rationality of the proposed model. Comparison of calculated curves and test data shows that the proposed method well describes the migration of both heat and water during cyclic freeze and thaw.

Multi Objective Dynamic Optimization Study of Butylated Urea Formaldehyde Resin Process in a Batch Reactor

Butylated urea formaldehyde (BUF) is a key intermediate for manufacturing paint and coating. The quality of BUF resins can be measured in terms of the concentration of free formaldehyde in the BUF resins and the extent of butylation. We in this work present an optimal control study to obtain minimum free formaldehyde concentration and minimum butanol concentration at the end of the batch operation. Reactor temperature is used as the manipulated variable and optimum temporal reactor temperature profiles are obtained using control vector parameterization approach. The two aforementioned criteria are observed to be mutually conflicting and hence the multi-objective optimal control problem is solved in this work yielding the pareto optimal curve showing the trade-off solutions of the MOO problem. Such pareto optimal curve helps the operator to choose an operating condition for a desired operation.

Otolith shape differences between ecotypes of Icelandic cod (Gadus morhua) with known migratory behaviour inferred from data storage tags

Otolith shape can be used to identify ecotypes of the Icelandic cod (Gadus morhua) stock. The use of data storage tags has increased our knowledge of the stock structure of Icelandic cod. The profiles of tagged cod reveal different migratory strategies. This has led to the definition of two ecotypes within the cod stock. Frontal ecotypes reside in deep waters during feeding season and express a highly variable temperature profile associated with thermal fronts, while coastal ecotypes stay in shallow waters all year round. In this study, the data storage tag profiles were analysed with cluster analysis, which revealed the existence of an intermediate behaviour that expresses a variable depth profile and feeding migration that is both shorter in time and not as deep. The main objective was to develop a morphological key based on otoliths to distinguish the ecotypes. The shape of the otoliths was extracted with shape measurements and fast Fourier transforms. A discriminant function analysis indicated a difference in morphology between the ecotypes, resulting in successful classification.

Self-Consistent Electrothermal Modeling of Passive and Microchannel Cooling in AlGaN/GaN HEMTs

AlGaN/GaN high electronic mobility transistors (HEMTs) are highly promising for power and RF electronics due to large bandgap and high breakdown voltage. However, the thermal bottlenecks associated with the elevated temperatures in the device at high power density presents significant barriers in achieving the full potential of these HEMTs. Embedded cooling solutions have been explored for these devices for the efficient thermal management of extreme heat fluxes and hotspots. This involves conductive, convective, and evaporative cooling methods located closer to the electrically active regions of the device. Developing simulation tools that can guide thermal-mechanical-electrical co-design are necessary for implementation of the embedded cooling solutions. We present self-consistent electrothermal models for AlGaN/GaN HEMTs to study the passive and embedded microchannel cooling. In the case of passive cooling, we develop a fully compact electrothermal model that is computationally very efficient and provides high-fidelity results. The model can capture the spatial variation of temperature profile in the device and can predict the temperature-dependent drain current variation among the various fingers in a multifinger HEMT. We then explore the potential of liquid cooling of a multifinger AlGaN/GaN HEMTs using microchannels embedded in the substrate. A 3-D computational fluid dynamics (CFD) model of the device is coupled with the compact dc current model. Our analysis shows that the self-consistency effects on power and temperature remain significant even for the high flow rates in microchannels. Predictive capability of the “standalone” CFD models of AlGaN/GaN HEMTs can be limited unless they are self-consistently coupled with the electrical models.

Geometric Mean of Fin Efficiency and Effectiveness: A Parameter to Determine Optimum Length of Open-Cell Metal Foam Used as Extended Heat Transfer Surface

High porosity open-cell metal foams have captured the interest of thermal industry due to their high surface area density, low weight, and ability to create tortuous mixing of fluid. In this work, application of metal foams as heat sinks has been explored. The foam has been represented as a simple cubic structure and heat transfer from a heated base has been treated analogous to that of solid fins. Based on this model, three performance parameters namely, foam efficiency, overall foam efficiency, and foam effectiveness have been evaluated for metal foam heat sinks. Parametric studies with varying foam length, porosity, pore density, material, and fluid velocity have been conducted. It has been observed that geometric mean of foam efficiency and foam effectiveness can be a useful parameter to exactly determine the optimum foam length. Additionally, the variation in temperature profile of different foams heated from one end has been determined experimentally by cooling these with atmospheric air. The experimental results have been presented for open-cell metal foams (10 and 30 PPI) made of copper/aluminium/Fe–Ni–Cr alloy with porosity in the range of 0.908–0.964.

Effect of thermal asymmetries on the entropy generation analysis of a variable viscosity Couette–Poiseuille flow

The influence of viscous dissipation on forced convective heat transfer and entropy generation rate in the conduction limit for a variable-viscosity flow between asymmetrically heated parallel plates is studied in an analytical framework consistent with perturbation method. The study considers a flow of Newtonian fluid under the simultaneous action of an applied pressure gradient and an axial movement of the upper plate. The present study emphasizes on the effect of dissipative heat produced by the movable upper plate as well as viscous heating generated due to applied pressure gradient on the underlying thermo-hydrodynamic transport. A few non-dimensional parameters such as dimensionless upper plate velocity, degree of asymmetry parameter and Brinkman number have been defined and their influential role on the variation of temperature profile, the Nusselt number and entropy generation number has been discussed in detail. The study shows that the variation of Nusselt number exhibits an unbounded swing, which, in turn, leads to appearance of the point of singularities at some cases of asymmetrical plate heating. Finally, the source of appearance of point of singularities has been discussed in view of the energy balance, and from the second-law analysis of thermodynamics.

A model for the biochemical degradation of inosine monophosphate in hake (Merluccius merluccius)

ATP-derived products are typically used as early indicators of fish quality loss during storage. In this work, we explore different biochemical routes that are potentially relevant in contributing to nucleotide degradation in hake (Merluccius merluccius). A major motivation of this study is to get more insight on the biochemical degradation mechanisms of nucleotide catabolites in hake muscle at fish storage and transport conditions. This requires the identification of its relevant pathways.To that purpose, different degradation routes proposed in the literature are considered and a mathematical model for the degradation process is derived. First order kinetics are assumed for all the reactions and temperature dependence is taken into account through the Arrhenius equation. Unknown model parameters, namely activation energies and pre-exponential Arrhenius coefficients, are estimated via fitting to experimental data. From the estimation results, relevant routes are identified. The kinetic study is performed on sterile fish juice to avoid coupling with microbial degradation mechanisms or possible interferences of the food matrix that might hide biochemical interactions.The proposed scheme adequately describes biochemical changes in nucleotide catabolites under variable temperature profiles. It also reveals a pathway which at least seems relevant for nucleotide degradation in hake.

Influence of pulsation in thermo-mechanical analysis on laser micro-welding of Ti6Al4V alloy

The pulse parameters of laser heat source have a definite effect on the weld joint structure. However, the complexity in parameter selection increases many folds with reduction in geometric dimensions of the specimen. Hence, an attempt has been made to investigate the laser microwelding of 500µm thick Ti6Al4V alloy in butt joint configuration using pulse Nd:YAG laser. The influence of laser scanning speed and pulse energy is analyzed to produce a defect-free joint. High peak power is actually dampen by pulsation of laser cratered to use in microwelding process. The feasible range of process parameters like laser scanning speed of 3–7mm/s and peak power of 1–5kW produces high quality weld joint using other favorable conditions that mainly diminishes the formation of oxides in welding of titanium alloy. A sophisticated numerical model is always beneficial to capture the thermo-mechanical behavior under differential influence of process parameters. A 3D finite element based sequentially coupled thermo-mechanical model is developed by considering the pulse mode of heat flux. There is considerably variation in temperature profile using actual pulse mode of heat flux as compared to average laser power. Typical hourglass heat source for over penetrated weld is developed for the simulation of microwelding process. Large-displacement theory is considered to predict the weld-induced distortion for laser microwelding process. The computed results are well agreed with experimentally measured values and show the robustness of the present numerical model used for micro scale welding process.

Investigation of thermal control for different SOFC flow geometries

A dynamic solid oxide fuel cell (SOFC) model is used to investigate the effects of different flow arrangements, as well as those of non-uniform air flow across channels, on temperature profile and thermal gradients under transient and steady state response. A high performance multi-input multi-output feedback controller has been developed to minimize SOFC spatial temperature variations during changes in power demands for different flow patterns. Numerical results show that the controller would result in negligible temperature variations for the modified cross-flow arrangement proposed here, even for large changes in the power drawn. The combination of a high performance controller and design modification results in a more uniform temperature profile at steady state nominal conditions, and modest variations in temperature profile, from the nominal, for ±15% change in power. Similarly, non-uniform air flow rate decreases the temperature gradient as well as maximum temperature across the cell, though its effect is less pronounced in the closed loop response.