Enhanced temperature uniformity by tetrahedral laser heating

emperature profile on a spherical sample that is heated by laser beams in various geometries while processed in vacuum is analyzed. Sample heating by one or four laser beams was considered. An analytical expression was derived for directional sample heating cases. It suggests an enhanced temperature uniformity over the samples when heated with four diffuse laser beams arranged in a tetrahedral geometry. This was experimentally verified by heating a spherical stainless steel sample by laser beams. Both the calculated and experimentally determined temperature variations over the sample suggest that use of diffuse four beams arranged in tetrahedral geometry would be effective in reducing temperature variation to within 1 K. The enhancement in the temperature uniformity for four diffuse beams arranged in a tetrahedral geometry by a factor of 50 over a single focused beam is promising to accurately measure of thermophysical properties. This drastic improvement in temperature uniformity might even enable atomic diffusion measurements in the undercooled liquid states of the bulk glass forming alloys since Marangoni and gravity driven convection will be substantially reduced

Amplification efficiency and thermal stability of qPCR instrumentation: Current landscape and future perspectives

This is a final draft version of the publication following acceptance by the journal.Quantitative polymerase chain reaction (qPCR) is a method of amplifying and detecting small samples of genetic material in real time and is in routine use across many laboratories. Speed and thermal uniformity, two important factors in a qPCR test, are in direct conflict with one another in conventional peltier‑driven thermal cyclers. To overcome this, companies are developing novel thermal systems for qPCR testing. More recently, qPCR technology has developed to enable its use in point‑of‑care testing (POCT), where the test is administered and results are obtained in a single visit to a health provider, particularly in developing countries. For a system to be suitable for POCT it must be rapid and reliable. In the present study, the speed and thermal uniformity of four qPCR thermal cyclers currently available were compared, two of which use the conventional peltier/block heating method and two of which use novel heating and cooling methods

A tool for predicting heating uniformity in industrial radio frequency processing

Radio frequency energy is utilised for heating in a wide range of applications, particularly in the food industry. A major challenge of RF processing is non-uniform heating in loads of variable and angular geometry, leading to reduced quality and product damage. In the study, the specific effects of geometry on the heating profiles of a range of geometrically variable loads in an industrial scale RF system are analysed, and the understanding used to derive a general tool to predict heating uniformity. Potato was selected as a test material for experimental work; dielectric properties were measured using a 44mm coaxial probe. Analysis of simulated and experimental surface temperature profiles and simulated power uniformity indices indicates that the presence of vertices and edges on angular particles, and their proximity to faces perpendicular to the RF electrodes increases localised heating; faces parallel to the electrodes heated less than those faces perpendicular to them. Comparison of the same geometrical shape in different orientations indicates that overall power absorption uniformity can be better even when localised heating of edges is greater. It is suggested, for the first time, that the rotation of angular shapes within a parallel plate electric field can improve heating uniformity, and that this can be achieved through the design of bespoke electrode systems. A Euler characteristic based shape factor is proposed, again for the first time, that can predict heating uniformity for solid, dielectrically homogenous shapes. This provides industry with a tool to quickly determine the feasibility for uniform RF heating of different three dimensional shapes based on geometry alone. This provides a screening method for food technologists developing new products, allowing rapid assessment of potential heating uniformity and reducing the need for early stage specialist computational modelling

Experimental investigation of non-uniform heating effect on flow boiling instabilities in a microchannel-based heat sink

Copyright @ 2011 ElsevierTwo-phase flow boiling in microchannels is one of the most promising cooling technologies for coping with high heat fluxes produced by the next generation of central processor units (CPUs). If flow boiling is to be used as a thermal management method for high heat flux electronics it is necessary to understand the behaviour of a non-uniform heat distribution, which is typically the case observed in a real operating CPU. The work presented is an experimental study of two-phase boiling in a multi-channel silicon heat sink with non-uniform heating, using water as the cooling liquid. Thin nickel film sensors, integrated on the back side of the heat sinks were used in order to gain insight related to temperature fluctuations caused by two-phase flow instabilities under non-uniform heating. The effect of various hotspot locations on the temperature profile and pressure drop has been investigated. It was observed that boiling inside microchannels with axially non-uniform heating leads to high temperature non-uniformity in the transverse direction.This research was supported by the UK Engineering and Physical Sciences Research Council through grant EP/D500109/1

An efficient plate heater with uniform surface temperature engineered with effective thermal materials

Extended from its electromagnetic counterpart, transformation thermodynamics applied to thermal conduction equations can map a virtual geometry into a physical thermal medium, realizing the manipulation of heat flux with almost arbitrarily desired diffusion paths, which provides unprecedented opportunities to create thermal devices unconceivable or deemed impossible before. In this work we employ this technique to design an efficient plate heater that can transiently achieve a large surface of uniform temperature powered by a small thermal source. As opposed to the traditional approach of relying on the deployment of a resistor network, our approach fully takes advantage of an advanced functional material system to guide the heat flux to achieve the desired temperature heating profile. A different set of material parameters for the transformed device has been developed, offering the parametric freedom for practical applications. As a proof of concept, the proposed devices are implemented with engineered thermal materials and show desired heating behaviors consistent with numerical simulations. Unique applications for these devices can be envisioned where stringent temperature uniformity and a compact heat source are both demanded.Comment: 14 pages, 5 figure

Multi-Dimensional, Inviscid Flux Reconstruction for Simulation of Hypersonic Heating on Tetrahedral Grids

The quality of simulated hypersonic stagnation region heating on tetrahedral meshes is investigated by using a three-dimensional, upwind reconstruction algorithm for the inviscid flux vector. Two test problems are investigated: hypersonic flow over a three-dimensional cylinder with special attention to the uniformity of the solution in the spanwise direction and hypersonic flow over a three-dimensional sphere. The tetrahedral cells used in the simulation are derived from a structured grid where cell faces are bisected across the diagonal resulting in a consistent pattern of diagonals running in a biased direction across the otherwise symmetric domain. This grid is known to accentuate problems in both shock capturing and stagnation region heating encountered with conventional, quasi-one-dimensional inviscid flux reconstruction algorithms. Therefore the test problem provides a sensitive test for algorithmic effects on heating. This investigation is believed to be unique in its focus on three-dimensional, rotated upwind schemes for the simulation of hypersonic heating on tetrahedral grids. This study attempts to fill the void left by the inability of conventional (quasi-one-dimensional) approaches to accurately simulate heating in a tetrahedral grid system. Results show significant improvement in spanwise uniformity of heating with some penalty of ringing at the captured shock. Issues with accuracy near the peak shear location are identified and require further study

Multi-scale gapped smoothing algorithm for robust baseline-free damage detection in optical infrared thermography

Flash thermography is a promising technique to perform rapid non-destructive testing of composite materials. However, it is well known that several difficulties are inherently paired with this approach, such as non-uniform heating, measurement noise and lateral heat diffusion effects. Hence, advanced signal-processing techniques are indispensable in order to analyze the recorded dataset. One such processing technique is Gapped Smoothing Algorithm, which predicts a gapped pixel’s value in its sound state from a measurement in the defected state by evaluating only its neighboring pixels. However, the standard Gapped Smoothing Algorithm uses a fixed spatial gap size, which induces issues to detect variable defect sizes in a noisy dataset. In this paper, a Multi-Scale Gapped Smoothing Algorithm (MSGSA) is introduced as a baseline-free image processing technique and an extension to the standard Gapped Smoothing Algorithm. The MSGSA makes use of the evaluation of a wide range of spatial gap sizes so that defects of highly different dimensions are identified. Moreover, it is shown that a weighted combination of all assessed spatial gap sizes significantly improves the detectability of defects and results in an (almost) zero-reference background. The technique thus effectively suppresses the measurement noise and excitation non-uniformity. The efficiency of the MSGSA technique is evaluated and confirmed through numerical simulation and an experimental procedure of flash thermography on carbon fiber reinforced polymers with various defect sizes

Solar dryer with thermal storage and biomass-backup heater

An indirect type natural convection solar dryer with integrated collector-storage solar and biomass backup heaters has been designed, constructed and evaluated. The major components of the dryer are biomass burner (with a rectangular duct and flue gas chimney), collector-storage thermal mass and drying chamber (with a conventional solar chimney). The thermal mass was placed in the top part of the biomass burner enclosure. The dryer was fabricated using simple materials, tools and skills, and it was tested in three modes of operation (solar, biomass and solar-biomass) by drying twelve batches of fresh pineapple (Ananas comosus), with each batch weighing about 20 kg. Meteorological conditions were monitored during the dehydration process. Moisture and vitamin C contents were determined in both fresh and dried samples. Results show that the thermal mass was capable of storing part of the absorbed solar energy and heat from the burner. It was possible to dry a batch of pineapples using solar energy only on clear days. Drying proceeded successfully even under unfavorable weather conditions in the solar-biomass mode of operation. In this operational mode, the dryer reduced the moisture content of pineapple slices from about 669 to 11% (db) and yielded a nutritious dried product. The average values of the final-day moisture-pickup efficiency were 15, 11 and 13 % in the solar, biomass and solar-biomass modes of operation respectively. It appears that the solar dryer is suitable for preservation of pineapples and other fresh foods. Further improvements to the solar chimney design are suggested to avert reverse thermosiphoning at night or during periods of low insolation