William Hamburgen

Warm Water Cooling

The production of hypothermia by surface cooling is a well-established and documented subject. This type of hypothermia is used in a wide variety of operations in neurological and cardiovascular surgery. The technique for inducing surface cooling as described in most publications on the subject is fairly well standardised. Premedication of these patients varies with authors and their anaesthetic techniques. Phenothiazines, in particular chlorpromazine, are commonly used. Anti-sialogogues, atropine or hyoscine are given and the patients anaesthetised by techniques usually practised in the particular centre. Maintenance may be by controlled or spontaneous respiration, though the former is often preferred. Volatile anaesthetics, mainly halothane or ether, are added to the gases. Cooling may be between blankets, in a bath or in a cabinet. The last-named method has many advantages, but owing to the apparatus required is not widely used. Water is the commonest surface coolant, and it is with its use that this study is concerned. The common factor in all the techniques detailed above is the use of cold water. Some authors take 6°C. as their temperature, others prefer iced water. The pattern of cooling with cold water is constant. Initially oesophageal, rectal and pharyngeal temperatures show little change. The skin temperature falls at once, as might be expected, and rapidly goes on falling to near that of the water. After 10 to 15 minutes the deep temperatures begin to fall, the oesophageal and pharyngeal leading the rectal. When cooling is stopped, by removing the patient from the bath, or warming the blankets, the “after-drop” sets in. The deep temperatures fall a further 2” to 4” as the cold peripheral tissues of the body “shell” are warmed from within. The rectal temperature is the last to fall to the desired level. Although widely used, this technique seems to suffer from several disadvantages. The peripheral tissues become extremely vasoconstricted, no matter what vasodilators are used. Metabolic acidosis is a well-known complication of hypothermia, even by extracorporeal methods. The greater the cooling of the peripheral tissues, the greater the acidosis, both from vasoconstriction and

Boiling binary mixtures at subatmospheric pressures

The authors present a study of boiling binary mixtures of water with methanol or 2-propanol at subatmospheric pressures. Liquid-phase equilibrium vapor pressures, binary phase equilibrium thermodynamic properties, heat transfer characteristics, and the critical heat flux (CHF) condition are determined for saturated pool boiling from a localized heat source while varying the concentrations of methanol and 2-propanol in water. The heat source is an upward-facing copper surface submerged in a laterally confined, finite pool. Low-pressure boiling of aqueous mixtures provides a means of removing high heat fluxes while maintaining low surface temperatures. Small additions of alcohol to water increase the CHF condition above that of pure water. Higher concentrations of alcohol begin decreasing the CHF condition to that of the pure alcohol. While single-component correlations using mole weighted binary liquid thermodynamic properties have been shown to predict ideal binary mixture boiling behavior, they are unsuccessful in predicting the characteristics of aqueous mixtures. The significance of the results obtained to the use of binary coolants for electronics cooling applications is discussed.<<ETX>>

Photoetched clad with embedded heatpipes for mobile electronics

Aluminum-cored clads offer attractive properties for constructing thin, lightweight cases and other thermal management structures for mobile electronics. Additional possibilities open up when the clad is modified by a two-step photoetching process. The focus of this paper is a free-convection cooled structure with small heat-pipes embedded within channels etched into a 0.6 mm thick stainless-steel clad aluminum plate. We performed experiments and simulations for both this novel embedded heat-pipe structure and conventional spreader-plate designs. We applied a Percent of Envelope Power (PEP) steady-state heat-transfer metric to compare their performance, and found that this and other similar metrics may be equivalent when average temperatures can be accurately determined. Our results demonstrate that photoetched clads with embedded heatpipes and engineered air gaps have the potential to significantly enhance mobile electronic device cooling and allow higher point-load power inputs without increasing product thickness or the maximum surface temperature to which users are exposed.