Thermoelectric Junctions Research Articles

EFFECTS OF COOLING AND WARMING OF THE COMMON CAROTID ARTERIES ON THE BRAIN AND TYMPANIC MEMBRANE TEMPERATURES IN THE RABBIT

The thermal change in the hypothalamus, the thermoregulatory center, of the experimental animals has been usually measured by use of a thermocouple or a needleformed thermistor inserted through the skull and the brain parenchyma. However, these procedures may be unsuitable for a longterm, observation of the body temperature because the insertion of the thermodes causes considerably widespread damage of the brain tissues, particularly the hypothalamus. Recording the intracardiac, rectal and muscular temperatures of the rabbit by means of the thermistor equipped on the apex of the venous catheter or of the metal-needle, Yasuda (1-3) of this laboratory has reported the influence of various pyrogenic substances on the temperature. Using the same technique, Takashima (4) has compared the effects of pyrogenic substances in the intact and the liver-damaged rabbits. There exist some reports on the tympanic membrane temperature. Benzinger (5) has chosen the tympanic membrane of a human for the measurement of internal body temperature as close as feasible to the hypothalamic heat center. He has introduced 36-gauge twin wires of copper and constantan into the external auditory canal and has placed the thermoelectric junction of the wires at the tympanic membrane. But little work has been done to study the correlation between the brain temperature and the tympanic membrane temperature. The present experiments have been designed to determine whether the tympanic membrane temperature changes in parallel with the hypothalamic temperature or not. In these experiments a decline of the tympanic membrane and brain temperatures was produced by cooling the common carotid arteries or by the administration of some hypothermic agents. An elevation of the temperature was produced by the carotid warming or by the administration of pyrogenic substances. Moreover, the influences of the carotid cooling and warming on behaviors, respiration, blood pressure and heart rate were studied.

Fabrication of Miniature Thermocouples for uhf Acoustic Detectors

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Some problems in the development of a commercial thermoelectric refrigerator

Two basic problems in the development of a thermoelectric refrigerator are the construction of a cooling unit, consisting of the thermoelectric junctions, and the optimization of the complete refrigerator design to make best use of the thermoelectric material. It is essential for the unit to achieve good thermal contact with the cooling chamber and to have good electrical contact across the p and n semiconductor bars forming each junction. A simple but accurate method for measuring the junction resistance is shown, and the relative merits of various methods of forming the cooling unit are discussed. The heat balance equations for a refrigerator are given which include the cooling fin system, and the method of optimization of the design is noted.

Measurement of the electrical resistance of metal-thermoelectric semiconductor contacts

Small contact resistance in thermoelectric junctions relative to the volume resistance is an important factor in the efficiency of the thermoelectric element. A systematic study of different bonding techniques requires a sensitive measuring method. Several methods are discussed and a four-terminal bridge method is described in detail. This method allows one to measure contact resistances of the order of 1 microΩ∗ with an accuracy of ± 5 per cent. Measurements on nickel-plated and unplated soldered junctions of doped Bi 2Te 3 with copper having a contact resistance of 10 microΩ showed no rectification, but a variation of almost 100 per cent in contact resistance around the periphery of the junction.

Cascading of Peltier Couples for Thermoelectric Cooling

The cooling of a single thermoelectric junction is limited to a certain temperature difference by the inherent properties of the elements used. Altenkirch gave a theoretical treatment of the single couple and showed a way to overcome the limitation on cooling by using a number of thermocouples in thermal cascade. Such an arrangement was constructed by Turrettini and shown to work. A simplified form of Altenkirch's theory is presented and a form of cascade which is simpler and more efficient than that of Turettini is described and experimental results are given. A two-stage cascade of elements limited to 11°C cooling as a single couple reached 15°C cooling while rather heavily loaded by lack of adequate thermal insulation. A good agreement with theory is obtained for the behavior of this cascade. It is shown that such a cascade is in theory more efficient than a single couple under all circumstances.

A 4 pi-radiometer.

Total radiated heat loss and average surface temperature of living bodies have heretofore required laborious computation from numerous local measurements. The present study introduces the blackbody principle for this objective. Shieldless surface receivers have been designed, and built from identical and symmetrical sets of thermoelectric foil junctions, which were then made different only in their power to absorb or reflect radiation. By means of thermal shunting, they have been rendered stable against air motion up to 8 m/sec. A cavity, when uniformly lined with such receivers, will integrate the measurements of radiated output into every direction of space, permitting a direct recording of the total. The receivers have been developed specifically for application to the human gradient calorimeter now under construction. However, since the laws of radiation apply to cavities of any size or shape, the proper function of blackbody radiometry could be experimentally verified with a smaller number of receivers in a body of 8×8×16 cu. in. The 4π-measurement is practically independent of location, size, or shape of the emittent source. The sensitivity is 76 μv/cal./sec. Full response is attained within 2.4 sec.

An expansion method of measuring the Peltier coefficient

When a current is passed through the wires of a thermoelectric junction the alteration in temperature at the junction produces a change in length over and above that produced on the resistance heating effect. An expression for this change in length is developed in terms of the Peltier coefficient and other properties of the metals forming the couple. The experimental arrangement is such as to eliminate the resistance heating effect.

SKIN TEMPERATURE AND BASAL METABOLISM DURING FASTING

In a previous paper, the skin temperatures of normal children measured with the thermo-electric junction were presented and discussed. The present study presents skin temperature measurements and basal metabolism determinations of four children with idiopathic convulsions, obtained before and during therapeutic fasts of seven to fourteen or more days. Comparisons were made of the heat production, the temperature of the skin, the pulse rate and the blood pressure, in an attempt to estimate the quality and quantity of the changes which take place during fasting. The blood chemical changes in these children, showing the diminution in the glycogen reserve and the onset of a compensated acidosis, have been reported in an earlier communication.¹ The ages of these four children varied from 11 to 13½ years. Physical examination and exhaustive laboratory tests failed to show any abnormality other than poor posture. But for the history of convulsive attacks, they would

The Thermal Effect of Vapours on Rubber

This Paper relates to the heating of rubber when suddenly immersed in various vapours. It describes the method of measuring the thermal changes by means of thermoelectric junctions and gives the results obtained with benzene, pyridine, ammonia and water-vapour. The effect is compared to that of water-vapour on cellulose.

Societies and Academies

LONDON. Physical Society, March 26.—Dr. A. Russell, vice-president, in the chair.—Prof. A. W. Porter and F. Simeon: The change of thermal conductivity with fusion. The change in question was determined for mercury and for sodium by finding the temperatures at different points of a cylinder of ttie metal contained in a glass tube. The ends of the cylinder were maintained at such temperatures that the metal was liquid half-way down its length, the remaining part being solid. The temperatures were taken by means of thermo-electric junctions inserted in narrow tubular depressions which had been formed in the glass tube by forcing a knitting needle down into the locally heated glass. The ratio of the thermal conductivity for solid and liquid was estimated from the slope of tangents drawn to the temperature-curve on each side of the melting point. The values of these ratios are of the same order as the ratio of the corresponding values of the electrical conductivities. The mean value for mercury is 3.91, and for sodium 1-31.—Dr. J. A. Fleming: An instrument for the optical delineation and projection of physical curves such as hysteresis, resonance, and characteristic curves. This instrument is designed for projecting on to a screen or photographing on a plate such curves as magnetic hysteresis, resonance, or characteristic curves which can be performed slowly, or are non-periodic or non-repetitive.—Dr. P. Phillips and J. Rose Innes: The stability of some liquid films. The authors give a simple method of calculating the equilibrium form of a thin film which is a surface of revolution. They then consider the stability for certain kinds of displacement of three classes of such films, viz., the sphere, the cylinder and the catenoid. The mathematics used is quite elementary throughout and the treatment is rigorous.—Prof. A. W. Porter and E. Talbot Paris: A demonstration of the green-flash of the setting of an artificial sun. A large disc of card mounted so that it can be slowly rotated has a hole, 1 in. in diameter, cut in it about 2 in. from the periphery. This is covered with red gelatine films, and is illuminated from behind so as to form an artificial sun. The front of the disc is covered with white Bristol board and is moderately' illuminated by a lamp in front. This sun is viewed through a rectangular aperture (4 in. wide) in a blackened board, the lower edge of the aperture serving as the horion. When the disc is rotated the artificial sun sets and green afterimages are obtained of characters varying according to the amount that the eye has been exposed to the bright sun. If the sun is not viewed until immediately before the complete setting the after-image represents simply the disappearing segment to which it is due. The authors claim that this phenomenon is what is often described as the green-flash at sunset, though they are ready to admit that other (but probably rarer) phenomena also go under the same name.

The Change in Thermal Conductivity of Metals on Fusion

The change in question was determined for mercury and for sodium by finding the temperatures at different points of a cylinder of the metal contained in a glass tube. The ends of the cylinder were maintained at such temperatures that the metal was liquid half-way down its length, the remaining part being solid. The temperatures were taken by means of thermoelectric junctions inserted in narrow tubular depressions which had been formed in the glass tube by forcing a knitting needle down into the locally heated glass. The ratio of the thermal conductivity for solid and liquid was estimated from the slope of tangents drawn to the temperature-curve on each side of the melting point. The values of these ratios are of the same order as the ratio of the corresponding values of the electrical conductivities. The mean value for mercury is 3.91, and for sodium 1.31. A summary list is given of other data concerned with fusion.

TEMPERATURE OF THE CONJUNCTIVA

I. EARLIER METHODS OF MEASUREMENT Other students, appreciating the probable importance of this subject, have attempted similar measurements, but all of them were made with some modification of the mercurial thermometer. One form of this which attracted considerable attention was suggested by Galezowski. It had a flat bulb small enough to pass easily beneath the lid, and the tube extended 8 or 10 cm. at right angles to the bulb; but the glass of the bulb was so thin that the least pressure of the lid produced a rise of the mercury, and of course constant readings were imposssible. II. THE THERMO-COUPLE The thermo-couple is also called the thermo-electric junction, or thermal If two strips of metal of unequal conducting power are soldered together, the line where they meet is of course a junction. If the free ends of these two strips are connected, and then if the line

Liquid Air—Production and Applications 1

IN the former of these papers the author details experiments showing the trustworthiness of a German silver platinum couple to measure temperatures in the neighbourhood of those of liquid air and liquid and solid hydrogen. The electric resistance of metals is an unsafe guide at very low temperatures, and the manipulation of gas thermometers involves much time and care. A thermo-electric junction would be much more convenient if trustworthy. That it is trustworthy the experiments go to show, but only within limits. If the constants of the formula for interpreting the observations be determined at temperatures between 90½° and 123½° abs., the formula will then give the temperature of solid hydrogen at low pressure as 15°.27 abs., whereas if the constants be deduced from experiments at a lower temperature, 20½° to 77½°, the interpretation formula then makes the temperature of solid hydrogen at low pressure 1¾° lower, i.e. 13°.5 abs., which the author considers more correct. Bearing in mind that at this very low temperature a difference of 1¾° is equivalent to a difference of 37° at the ordinary temperature, we see that the method has no confirmatory value, and can itself be trusted only over the range for which it has been verified by the careful use of gas thermometers. If, therefore, helium be procured in sufficient quantity for liquefaction or solidification, its lower temperatures, possibly within 5° of the absolute zero, will have to be ascertained by the low-pressure helium thermometer. For ranges of temperature over which its indications can be verified, the thermo-electric junction thermometer will have a useful sphere of work in saving the inconvenience of employing gas thermometers. Among important cautions given by the author is a warning that junctions made with soft solder are affected by the low temperature. The junctions should be made with hard silver solder, and the indications at the temperature of liquid oxygen compared before and after exposure to the temperature of liquid hydrogen, to see whether there has been any change produced. A German silver platinum junction was employed, but as the result of his experience the author recommends German silver gold.

On the thermo-electric junction as a means of determining the lowest temperatures

The inconvenience of using the gas thermometer at very low temperatures and the failure of platinum and other metal-resistance thermometers within 30° or 40° of the absolute zero, led me some years ago to consider the experimental behaviour of the thermo-electric junction at the lowest temperatures. My special object at the time the experiments were made was to have a further confirmation of the melting point of hydrogen, and also of the lowest temperature reached on exhausting solid hydrogen, other than that I had found by means of the hydrogen gas thermometer. The results have remained unpublished, because my intention has always been to extend them to other thermo-electric combinations. Not having been able to accomplish this project, they are now abstracted as affording useful information in this field of investigation, and as furnishing a general confirmation of my previous investigations. A German-silver platinum couple was selected as likely to give the most uniform results at low temperatures, although subsequent experiments have led to the conclusion that it would have been better to have replaced the platinum by gold. As regards resistance thermometers, I have shown that gold is more reliable than platinum at temperatures near the boiling point of hydrogen. The difficulties of the investigation were considerable: it had to be carried out at the time in the neighbourhood of the machinery producing the liquefied gases required in the investigation, namely, oxygen, nitrogen, and hydrogen, so that the zero of the delicate galvanometer employed did not remain quite constant. To remedy this I inserted a rocking make-and-break in order to get the readings of each observation at both ends of the scale. In the process of removing one difficulty another presented itself, through the development of small but appreciable thermo-electric currents in the rocker. Precautions had to be taken against these and at all other metal junctions against similar small thermo-electric currents, and it was even found necessary to have a correction on account of the resistance box, inserted in the circuit to bring large readings within the limits of the scale. The galvano­meter and resistance box were inserted in the German-silver branch of the couple, the points of junction of the copper leads with the German-silver ends of the couple being insulated and placed close together within a vacuum test-tube packed with cotton wool to ensure equality of temperature.

I. On the temperature variation of the thermal conductivity of rocks

§1. The experiments described in this communication were undertaken for the purpose of finding temperature variation of thermal conductivity of some of the more important rocks of the earth’s crust. § 2. The method which we adopted was to measure, by aid of thermoelectric junctions, the temperatures at different points of a flux line in a solid, kept unequally heated by sources (positive and negative) applied to its surface, and maintained uniform for a sufficiently long time to cause the temperature to be as nearly constant at every point as we could arrange for.

Note on the Thermal Effect of Pressure on Water

I have just seen in the Comptes Rendus (June 27) an account of some experiments, on this subject, made by M. Galopin in the laboratory of Professor Pictet. As the effects obtained by him seem to be somewhat greater than my own experiments had led me to expect, I was induced to repeat my calculations with the view of trying to account for the difference. Unfortunately, M. Galopin's work is confined to 500 atmospheres, a pressure which lies a little beyond the range of my experiments ; so that no very trustworthy comparison can be made. M. Galopin's results have one advantage over those of the direct experiments of the same kind which I made, inasmuch as he was able to use ordinary thermometers, while I employed thermo-electric junctions, in measuring the rise of temperature by compression. But they have a corresponding disadvantage, in the fact that mine were obtained instantaneously (by means of a dead-beat galvanometer) and required no correction; while his had to be corrected for the heat-equivalent of his apparatus to an amount not easy to estimate with accuracy.

VII. On the measurement of the heat produced by compressing liquids and solids

In the year 1885 Messrs. Creelman and Crocket (‘Edinburgh Roy. Soc. Proc.,’ vol. 13. p. 311), under Professor Tait’s supervision, performed a series of experiments on the heat produced by the compression of various substances. Their method was briefly as follows:— For the application of the pressure, the same apparatus which we describe and figure later was used. A thermo-electric junction of insulated nickel and iron wires was fixed between the leather washers and a sufficient length of wire coiled away inside the gun to allow the junction to be drawn out at the top and a specimen attached to it.

2. On the Application of Angström's Method to the Conductivity of Wood

This was an account of a series of experiments made in the Natural Philosophy Laboratory of the University, to test the applicability of Angström's method of periodic variations of temperature to the determination of low conductivity. The wood was cut into discs of a standard thickness, and these were very tightly secured together, after the interposition of copper-iron thermo-electric junctions (of very fine wire). One series of discs was cut parallel, the other perpendicular, to the fibre. The results were obtained very easily, and accorded satisfactorily with those obtained by more laborious methods.

I. Experiments made to determine surface-conductivity for heat in absolute measure

The experiments described in this paper were made in the Physical Laboratory of the University of Glasgow, under the direction of Sir William Thomson, during the summer of 1871. A set of similar experiments were made in 1865 ; but being merely preliminary, carried on by different individuals, and embracing only a limited range of temperatures, it is thought unnecessary to allude further to them here. A copper ball, 2 centimetres radius, having a thermo-electric junction at its centre, was suspended in the interior of a double-walled tin-plate vessel which had the space between the double sides filled with water at the atmospheric temperature, and the interior coated with lamp-black. The other junction was in metallic contact with the outside of the vessel, and the circuit was completed through the coil of a mirror galvanometer. One junction was thus kept at a nearly constant temperature of about 14° Cent., while the other had the gradually diminishing temperature of the ball.

V. On the thermal effects of fluids in motion—temperature of bodies moving in air

An abstract of a great part of the present paper has appeared in the ‘Proceedings,’ vol. viii. p. 556. To the experiments then adduced a large number have since been added, which have been made by whirling thermometers and thermo-electric junctions in the air. The result shows that at high velocities the thermal effect is proportional to the square of the velocity, the rise of temperature of the whirled body being evidently that due to the communication of the velocity to a constantly renewed film of air. With very small velocities of bodies of large surface, the thermal effect was very greatly increased by that kind of fluid friction the effect of which on the motion of pendulums has been investigated by Professor Stokes.