The surface temperature during nucleate boiling was measured with a special thermocouple so designed as to measure the temperature of a small area and to have an extremely rapid response time. The surface temperature was found to drop occasionally 20" to 3OOF. in about 2 msec. during the boiling of water. This indicates a rapid extraction of heat during a short time interval. The significance of this observation is that i t provides a n important new clue to an understanding of nucleate boiling. A hypothesis is advanced to explafn these observations. full amplitude would not be observed in the extrapolation method. Where surface temperature have been measured directly either the measuring device was sensitive to such a large area that the temperature fluctuations averaged out, w the device had such a large time constant that the amplitude of the rapid fluctuations was damped out.
This investigation was initiated to
A P P A R A T U SThe measurement of the full amplitude of these temperature fluctuations of the heating surface reqnires a device capable of measuring the temperature of a relatively small area and of responding rapidly to temperature fluctuations. Also it must be associated with auxiliary equipment capable of recording these rapid tempera- ture changes. A thermocouple which comes close to meeting both of these requirements is described by Bendersky (4). This thermocouple measures the average temperature around a circle with a diameter of 0.005 in., and it has a microsecond response time. The thermocouple is fabricated from a wire and concentric tube, the tube being insulated from the wire by a thin oxide film. The thermocouple is made by polishing one end of the wire and tube, then applying a thin metal film, making electrical contact between the wire and tube. The temperature sensed by this thermocouple is the average temperature around the annulus between the wire and the tube, This thermocouple was press fitted into a strip of metal, and the thermocouple was machined flush with the top of the strip. A nickel plating, approximately 0.00005 in. thick, was vacuum deposited over the entire surface of the strip and the ends of the thermocouple. Details of this thermocouple are shown in Figure 1. The thermocouple was an Alumel wire in a Chromel P tube and the metal strip was Nichrome V. Nichrome V was selected because it matched the physical properties of the Chromel P closely. Later in the program the nickel plating was removed, and the entire surface, including the end of the thermocouple, was polished with 150 grit abrasive paper. This polishing action insured a relatively uniform surface over the entire strip. It formed the thermal junction between the Alumel wire and the Chroniel tube of the thermocouple bv carrying metal divers over the edqes of the insulation layer separating
The effect of proximal rigid boundaries on the motion and damage capabilities of spark bubbles is investigated by means of a qualitative photographic study. It is determined that an axially symmetric bubble collapsing nonhemispherically against a solid boundary can form a liquid jet which impinges against the solid boundary, but the jet has little or no damage capability. Observations of the toroidal minimum volume and associated damage to the boundary in the form of circular dents on indium indicate a pressure pulse damage mechanism.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.