Rapid Heat Exchange Research Articles

Establishment of compact processes

In order to realize sustainable development, it is anticipated that industrial structure, social and technical systems based on large-scale production at concentrated sites must be changed in the near future. Establishment of highly controllable compact processes with high speed reaction is desired to realize distributed production with multi-purpose low-volume production. Integration of high-pressure micro-engineering and supercritical fluid has received considerable attention as a core technology for compact processes. To realize the technology, basic developments for high-pressure micro-engineering such as rapid heat exchange and precise temperature control were firstly needed, and then process developments on basic engineering followed. As applications of compact processes, organic synthesis under supercritical water is discussed, and inorganic synthesis and an innovative coating process using supercritical carbon dioxide are also described.

Polymer Chemistry in Microfluidic Reaction System

Polymer synthesis requires strict control of reaction conditions such as temperature, reaction time, and mixing of reagents. Microfluidic reaction systems enable efficient mixing and rapid heat exchange. Moreover, laminar stream in a microfluidic channel enables control of the resulting shape of a molecule. This article reviews the use of microfluidic technology in the field of polymer chemistry. First, conformational aspects of polymers in microfluid are summarized. Next, the techniques for linear and branched polymer synthesis are described. We also describe the potential use of microreaction system for polymer particle and membrane synthesis. A description of how it would be possible to use this technology to prepare larger quantities of polymer compounds is also given.

Thermal inactivation profiles of Mycobacterium avium subsp. paratuberculosis in lamb skeletal muscle homogenate fluid

Mycobacterium avium subsp. paratuberculosis ( MAP) causes Johne's disease in livestock and there is a debate about its role in humans in chronic inflammatory bowel disorders such as Crohn's disease, but the relationship remains unproven. Nevertheless livestock health authorities in many countries aim to lower the prevalence of this infection to reduce potential contamination of the human food supply. MAP may occur in bovine milk and data on thermal inactivation suggest pasteurisation is an effective process. Recently MAP has been identified in skeletal muscle of cattle and sheep but there are no data on its thermal inactivation in these substrates. In this study the inactivation of MAP was studied in a fluid homogenate of lamb skeletal muscle at temperatures previously identified as being relevant to cooking processes applied by domestic consumers. A PCR thermocycler was used to ensure accurate temperatures and rapid heat exchange, while radiometric culture was used to ensure sensitive detection of viable MAP for determination of D and z values. Among the two predominant strains of MAP, S and C, D 55 ranged from 56 to 89 min, D 60 was 8 to 11 min, D 65 was 26 to 35 s while D 70 was 1.5 to 1.8 s. Values for z were 4.21 C° for the S strain and 4.51 C° for the C strain. At temperatures of 65–70 °C, MAP appeared to be less heat tolerant in skeletal muscle fluid than in previous reports using milk as the medium. The total thermal exposure of MAP during baking of a sample of 16 leg-of-lamb roasts in domestic ovens was determined to result in more than 20 log reductions in most cases, that is the product was microbiologically safe. Based on the models used in this study, there is a low probability of survival of MAP provided that red meat is cooked to recommended standards.

Constructing the Phase Diagram of an Aqueous Solution of Poly(N‐isopropyl acrylamide) by Controlled Microevaporation in a Nanoliter Microchamber

AbstractThis paper describes a poly(dimethylsiloxane) (PDMS)‐based microfluidic platform for constructing the phase diagram of poly(N‐isopropyl acrylamide) (PNIPAM) in aqueous solution. The PNIPAM solution was delivered into a nanoliter chamber through the main microchannel. An osmotic pressure difference was established between the chamber and the control microchannel by flowing a high‐concentration salt solution in the control microchannel. Controlled evaporation of water resulted in increasing concentration of PNIPAM. A phase diagram of PNIPAM was built by measuring the cloud points at different concentrations, with a minimum point at ≈40 wt.‐%. The microfluidic platform has the advantages of low sample consumption and rapid heat exchange rates, and allows studying viscous polymer solution.magnified image

Effect Of Palm Cooling On Reducing Heat Strain In Resting Hyperthermic Subjects

Exposure to a non-compensable heat stress environment results in hyperthermia and risk of heat illness. In many military situations cooling methods are limited. One proposed method of personal cooling involves heat extraction from the palm using a device called the Rapid Thermal Exchanger (RTX). The palm is proposed as an efficient site for heat loss because of the many arteriovenous anastomoses allowing rapid heat exchange. PURPOSE: The present study evaluates whether the RTX reduces heart rate (HR), core temperature (Tes), mean skin temperature (Tsk), mean body temperature (Tb) and thermal/discomfort sensations in hyperthermic subjects passively seated in a hot, dry, environment. METHODS: Ten male subjects (mean ± SD; ht, 178.6 ± 5.3 cm, wt 74.8 ± 12.4 kg, age 25 ± 5yr, VO2 pk 57.3 ± 10.1 ml/kg/min−1) wearing military fatigues and MOP gear walked on a treadmill (3.8 mph, 4% grade) in a hot environment (42.2 ± 0.5°C, RH 37 ± 1%) until Tes reached 38.8°C (time 33.3 ± 10.5min). They then sat for 50 minutes in a semi-recumbent position with either no cooling (NC) or palm cooling (RTX: 10°C, flow rate 2.5 L/min, without negative pressure). Heat extraction from the palm during RTX trials was measured by direct calorimetry. RESULTS:TableWith RTX, Tes, Tsk, and Tb were significantly lower than NC from 15-50 minutes and thermal sensation was significantly lower from 30-50 minutes. CONCLUSION: Palm cooling with RTX reduced thermal strain in passive, hyperthermic subjects. With an average heat extraction of 37.1 ± 11 W the cooling capacity of RTX is modest compared to other published methods. However, in some military conditions (e.g. soldiers seated in a hot armored vehicle) RTX may extend field duration and reduce heat strain. Supported by DARPA W911NF-06-1-0025.

Similarity Solution of Laminar Axisymmetric Jets With Effect of Viscous Dissipation

Abstract In this work the similarity solution of the thermal boundary layer for a laminar axisymmetric jet with viscous dissipation is derived and solved numerically, using a fourth-order Runge-Kutta method. The results are compared with the existing solutions, in which viscous dissipation is neglected. After that the effects of Reynolds and Prandtl numbers of the incoming hot jet on the temperature profile of the jet is investigated. It is seen that inclusion of viscous dissipation term results in a more rapid heat exchange between the incoming jet and quiescent fluid than the case where the viscous dissipation term is neglected. Also, it is observed that by increasing the Reynolds and Prandtl numbers of the jet, the heat penetrates better in locations near the symmetry line, whereas in locations farther from the symmetry axis the penetration is less.

Influence of packaging material on bread characteristics during ageing

AbstractOne of the priorities of today's bread‐making industry is to find suitable packaging solutions to satisfy the peculiar requirements of bread, mostly appreciated by Italian consumers for its crispy crust. The packaging material should allow for both rapid heat exchange with the environment and water vapour evaporation to prevent condensation inside the package. Perforated orientated polypropylene (OPP) films are currently the best materials available for satisfying the industry's requirements. Recently, our group demonstrated that bread wrapping with perforated films is efficacious against bread contamination. The aim of this work was to verify whether these types of films could also influence the trend of phenomena related to product ageing. In particular, variations in the moisture inside the loaf during storage and their influence on changes in crumb softness were investigated. Three OPP films and one double‐layer film bag with different hole size characteristics were chosen for this study and their performances were compared with those of a paper bag. Because of the considerable differences in the hole size characteristics, the films showed very different barrier effects to water evaporation. The C250 OPP film (hole mean diameter = 0.54 mm and density = 21.4 holes/cm2) played an interesting role in modulating moisture variations. Wrapping bread in this film enabled both crust crispness and crumb softness to be maintained during 48h of storage. Such performances cannot effectively be obtained by using alternative industrial bread packaging materials, such as paper bags. Copyright © 2006 John Wiley & Sons, Ltd.

What makes hydromagmatic eruptions violent? Some insights from the Keanakāko'i Ash, Kı̄lauea Volcano, Hawai'i

Volcanic eruptions at the summit of Kı̄lauea volcano, Hawai'i, are of two dramatically contrasting types: (1) benign lava flows and lava fountains; and (2) violent, mostly prehistoric eruptions that dispersed tephra over hundreds of square kilometers. The violence of the latter eruptions has been attributed to mixing of water and magma within a wet summit caldera; however, magma injection into water at other volcanoes does not consistently produce widespread tephras. To identify other factors that may have contributed to the violence of these eruptions, we sampled tephra from the Keanakāko'i Ash, the most recent large hydromagmatic deposit, and measured vesicularity, bubble-number density and dissolved volatile content of juvenile matrix glass to constrain magma ascent rate and degree of degassing at the time of quenching. Bubble-number densities (9×10 4–1×10 7 cm −3) of tephra fragments exceed those of most historically erupted Kı̄lauean tephras (3×10 3–1.8×10 5 cm −3), and suggest exceptionally high magma effusion rates. Dissolved sulfur (average=330 ppm) and water (0.15–0.45 wt.%) concentrations exceed equilibrium-saturation values at 1 atm pressure (100–150 ppm and ∼0.09%, respectively), suggesting that clasts quenched before equilibrating to atmospheric pressure. We interpret these results to suggest rapid magma injection into a wet crater, perhaps similar to continuous-uprush jets at Surtsey. Estimates of Reynolds number suggest that the erupting magma was turbulent and would have mixed with surrounding water in vortices ranging downward in size to centimeters. Such fine-scale mixing would have ensured rapid heat exchange and extensive magma fragmentation, maximizing the violence of these eruptions.

On the high heat flow in the Nankai Trough area—a simulation study on a heat rebound process

A concentration of high heat flow (as high as 120–160 mW/m 2) has been observed in the Nankai Trough, off southwest Japan, where the Philippine Sea plate (Shikoku Basin) is subducting beneath the Japanese landmass. We interpret this high heat flow in the subduction zone as being caused by the recovery of conductive heat flow to the theoretically expected value for the young Shikoku Basin lithosphere after cessation of hydrothermal heat exchange through sediment. The thickening sedimentary cover suppresses the rapid heat exchange between basement and sea water, whereas the topmost part of the basement allows a hydrothermal circulation within it to pump up heat from the hot plate to the sediment cover. We propose to call this process “heat rebound”. Numerical simulation shows that significant heat flow recovery can occur and is largely influenced by the sedimentation rate. We believe that the high heat flow in the Nankai Trough is one of the heat rebound cases. However, rapid sedimentation in the trough also indicates that heat flow recovery expected by the simulation is not large enough to explain the trough high heat flow by the heat rebound process only.

Pillow lavas and the Leidenfrost effect

Field observations of the formation of pillows by hot, de-gassed lava entering the sea have proved that their generation involves the underwater exposure and movement of incandescent material. This is made possible by the Leidenfrost effect, the phenomenon whereby film boiling replaces the usual nucleated boiling above a certain temperature, thereby forming an insulating sheath of vapour around any sufficiently hot body immersed in a liquid. Only on cooling below a certain temperature (defined here as the Nukiyama temperature) will rapid heat exchange occur between water and hot, gas-free lava. Near the surface, this could produce phreatic explosions and extensive clouds of steam.

An Explosive Reactor Possibility

The Nuclear Regulatory Commission has commissioned a study to test a newly proposed hypothesis which may show how steam explosions of containment-shattering proportions could develop as a result of core-melt accidents, and that there might be a far greater likelihood of such an event than was previously believed. An explosion sometimes results from an extremely rapid heat exchange when a large amount of molten material is plunged into a large volume of colder liquid. The sudden transfer of heat energy from the hot liquid to the cold liquid is accompanied by the development of a pressure wave, the force and magnitude of which are determined largely by the quantities of the liquids involved and the rate of energy release. If the hypothesis proves valid, the risk involved in continuing to operate the 50 or so commercial reactors in the U.S. may be so great as to require their immediate shutdown. It might also require a halt in construction in reactors of current design, a shift to a different kind of reactor technology, or a complete redesign of light-water-reactor safety systems. (MU)

Alleged Specific Effects of High-Frequency Fields on Biological Substances

VARIOUS claims for the demonstration of specific electric actions of high-frequency fields on biological substrates, that is, non-thermal effects dependent on wave-length, have already been refuted1. Attenuation of some bacterial toxins exposed to 1·9–3·7 m. fields, under conditions which appeared to eliminate the influence of the heat developed, seemed nevertheless to indicate the existence of such an athermal action (Szymanowski and Hicks2). Subsequent negative results with different bacteria, etc., led these authors3 to suspect that their previous results might have been due to an undetected local rise of temperature, although a selective heating of small dispersed particles (bacteria, micellae, macromolecules) is improbable because of the rapid heat exchange with the medium4.