US3148531A

US3148531A - Method and apparatus for thermal analyses

Info

Publication number: US3148531A
Application number: US261237A
Authority: US
Inventors: Alice M Stoll; Lambert R Munroe
Original assignee: Individual
Current assignee: Individual
Priority date: 1963-02-26
Filing date: 1963-02-26
Publication date: 1964-09-15
Anticipated expiration: 1981-09-15

Description

Sept. 15, 1964 M. STOLL ETAL 3,148,531.

METHOD AND APPARATUS FOR THERMAL ANALYSES Filed Feb. 26, 1963 2 Sheets-Sheet 1 T POWER SUPPLY SWITCH RECORDER IN VEN TORS ALICE M. STOLL LAMBERT R. MUNROE Sept. 15, 1964 s' ro ETAL 3,148,531

METHOD AND APPARATUS FOR THERMAL ANALYSES Filed Feb. 26, 1963 2 Sheets-Sheet 2 k PYROMETER IN E E -w l I I 10 s ETZ RECORDER FLAME U I TQ; our

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| 3 i T3 L;? J W s F /g 3 INVENTORS X a ALICE M. STOLL l LAM ERT R. MUNROE L BY Fig-

r I I ATTORNEY United States Patent 3,148,531 METHUD AND APPARATUS FOR THERMAL ANALYSES Alice M. Stoll, Spring Vaiiey, and Lambert R. Munroe, Ambler, Pa, assignors to the United States of America as represented by the Secretary of the Navy Filed Feb. 26, 1963, Ser. No. 261,237 Claims. (CI. 73-15) (Granted under Title 35, US. Code (I952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to method and apparatus for determining the thermal properties of lightweight, thin fabrics or textiles which are proposed or contemplated for use in garments worn in air and space vehicles.

The speeds and altitudes now attainable or expected in existing and contemplated high performance air and space vehicles has further extended mans environmenal demands, He may be subjected to ambient temperatures that vary to wider extremes, and untoward exposure to flames from more volatile and high energy fuels. For example, following an airplnae crash, the pilot may have to escape through an envelope of fuel flames. Notwithstanding all of the precautions taken in vehicle design to insure a safe and tolerable environment for man, his flying garments or space suit still remain his last and most fundamental protection against temperature extremes and flame exposure. Government procurement of fabrics or textiles which will serve well under such severe thermal conditions has heretofore been impaired because no reliable and precise method or apparatus was available for assimilating these conditions with any degree of reproducibility and then imparting them on the various thin fabrics or materials proposed by the textile industry. Testing techniques and apparatus known in the prior art are incapable of yielding the accurate and consistent results which permit the evaluations and fair comparisons of these thin materials as contemplated by the present invention.

Accordingly, it is an object of the present invention to provide a novel method and apparatus for accurately determining thermal properties of thin fabrics and other materials and with which lightweight textiles containing new heat-resistant, nonflammable synthetic fibers may be compared as to their thermal diffusivity, conductivity and flame destruction temperature.

Another object of the invention is to provide a new and improved method and apparatus for determining the transient heat transfer properties of single or multi-layer fabrics during flame exposure, in which multi-layer fabrics may be selected from a wide variety of combinations in materials and structural arrangements, and in which the fabric is uniformly exposed to a desired flame intensity for a predetermined duration, and in which the measured parameters are suitable for direct thermodynamic analysis and comparison.

Still another object of the invention is to provide method and apparatus for predicting the physiological effect on living skin protected by thin fabrics under severe thermal environments.

A further object of the invention is to provide a method and apparatus for measuring thermal properties of materials subjected to a reproducible thermal environment, which method can be carried out easily and rapidly without degrading the accuracy of results, and which apparatus is of relatively simple construction and is inexpensive to maintain.

Various other objects and advantages will appear from the following description of one embodiment of the invention, and the most novel features will be particularly "ice pointed out hereinafter in connection with the appended claims.

In the drawings:

FIG. 1 is a mechanical and electrical schematic representation of one embodiment of the apparatus of the present invention;

FIG. 2 is a fragmentary schematic representation of the apparatus taken along the line 22 of FIG. 1;

FIG. 3 represents a more detailed electrical circuit diagram of the apparatus of FIG. 1;

FIG. 4 is a graphical representation of a typical timing sequence for the apparatus as established in the electrical circuit of FIG. 3;

FIGS. 5a, 5b, and 50 represent enlarged cross-sectional views of different combinations and arrangements of material specimens to be tested in the invention; and

FIG. 6 is a graphical correlation of thermal diflusivity and temperature-time history for various materials.

In the illustrated embodiment of the invention, the apparatus shown in FIGS. 1 and 2 is set up for flame destruction temperature tests, and so will be first described in connection therewith. In the situation where a pilot flees from a flaming crash area, his garments may inflame or melt and adhere to his skin. To evaluate fabrics as to these properties, the flame characteristics and exposure time is postulated. The invention then provides method and apparatus for carrying out the flame destruction tests in the laboratory, based on these postulations, on various fabric specimens.

As best seen in FIG. 1 with the enlargement in FIG. 2, the apparatus is in a deenergized start or FLAME-OUT position with a thin fabric or specimen S held securely in a specimen holder 10 which in turn is removably mounted on an elongated carriage, indicated generally by the numeral 11. The carriage 11 rests in a generally horizontal plane and is slidable along its length on a support means not shown from the FLAME-OUT position illustrated to a FLAME-IN position where the specimen S is directly in a flame region. The holder 10 is particularly adapted for performing flame destruction temperature tests because it simply supports the specimen S without any backing. Other specimen holders such as shown in FIGS. 5a, b and c are adapted to be substituted for the flame destruction test holder 1% when transient heat transfer properties of a specimen are being determined, as disclosed hereinbelow.

The carriage 11 is positioned over a burner 12, such as a Meker or Bunsen type which is adjustable to provide a steady-state, uniformly distributed circular flame. A carriage spring 14 secured at one end of the carriage 11 urges the latter to the FLAME-OUT position. The armature of a solenoid operated motor 13 when energized drives the carriage 11 in the opposite direction against the force of the spring 14 until the carriage 11 is in the FLAME-IN position and the specimen S is directly over the burner 12.

Prior to a test exposure of the specimen S it is important that the flame be uniform and in a desired steadystate condition of temperature and heat generation. To assist in accomplishing this, the burner 12 is connected through a flow meter 16 and manually adjustable control valve 17 to a fuel supply 18 such as propane-propylene gas. With the carriage 11 in the FLAME-OUT position, the flame will impinge upon the lower surface of a high temperature resistant window 19, made of transparent mica or the like, which is supported in a carriage cross member 21. Thus, the flame can be easily viewed while adjusting for a desired flame condition. The window 19 also prevents the flame so formed from projecting upward through the carriage 11 while the specimen S is out of the flame. A thermocouple T may be added on the lower side of the holder 10 adjacent to the specimen S to provide a record representative of flame temperatures during the flame exposure, and a thermocouple T may be added on the upper surface of the specimen S to provide a check of flame destruction temperatures. Appropriate terminals are provided on the holder 10 for making connections to a high speed time-temperature recorder 33.

When the motor 13 is energized and positions the specimen S over the burner 12, an arm 22 projecting from the carriage 11 engages and actuates an electric switch 23 such as a Micro-switch and Whose function is explained hereinbelow. The carriage 11 further includes a rigid extension 24 for supporting a solenoid operated motor 26 whose armature is drivingly connected to guillotinetype slidable flame cut-off shutter 27. When the motor 26 is deenergized, the shutter 27 is urged totally out of the flame region irrespective of the carriage 11 position by a shutter spring 28. The flame cutting edge of the shutter 27 defines a semicircular notch 29 equal to the flame diameter thereby approaching instantaneous flame cut-ofl when the shutter 27 traverses over the burner 12.

Measurement of the flame destruction temperature of the specimen S is accomplished by a tilted mirror 31 positioned directly over the burner 12 which reflects the radiant energy from the specimen S to a radiation detecting head 3-2 whose output is connected to the time-temperature recorder 33. An optical filter 34 on the head 32 blocks all visible Wavelengths to provide only measurements of the temperature of the upper surface of the specimen S during flame contact at its lower surface. A rotary solenoid operated motor 36 electrically connected to the switch 23 positions a radiation cut-off shutter 37 out of the radiant energy path when the carriage 11 has moved the specimen S into the flame region. A spring 38 urges the shutter 37 in front of the radiation head 32 when the motor 36 is deenergized.

this position, the carriage arm 22 causes the switch 23 to close and energize the radiation shutter motor 36. The shutter 37 moves to provide an unobscured view by the head 32 of the upper surface of the specimen S. At the position b, the timer contact 47 closes to energize the shutter motor 26 thereby blocking further flame impingement to the under surface of the specimen S. At the position 0, the timer contact 44 opens to deenergize both

motors

13 and 36 and allows

springs

14 and 33 to urge the carriage 11 and the shutter 37, respectively, to the FLAME-OUT position. The flame shutter 27 is urged by the spring 28 back to its start position and the

timers

43 and 46 are automatically reset when the manual switch 41 is opened. During the interval when the specimen S is in the flame, the temperature on the upper surface of the specimen S is measured by the radiation head 32 and thermocouple T on the recorder 33.

It is contemplated that in most flame temperature destruction tests the temperature measured at the instant of total penetration of the flame through the garment is of more interest than a temperature rise measurement. In these instances the time interval a-b is set at some amount which will not interfere with flame impingement until after penetration.

In addition to flame temperature destruction testing, the invention is also useful in determining the transient heat transfer properties of very thin fabrics. A better understanding and appreciation of this portion of the invention will be obtained from a preliminary thermodynamic anaylsis of transient heat transfer through twolayer Walls.

An equation for transient heat flow through a twolayer wall has been expressed by Griflith and Horton in Proceedings of the Physical Society (London), vol. 58, page 481 et seq, 1946, as follows:

The electricity for operating the

motors

13, 26 and 36 obtains from a power supply 39 through a manually operated switch 41 and a timer unit 42, shown in more detail in FIG. 3. In the steps and operations of the invention, there are three distinct events, two of which are predetermined and set into the timer unit 42. These events are graphically illustrated in FIG. 4 wherein the time point a represents the instant when the manual switch 41 is closed and the specimen S moves from the position shown in FIG. 1 to the FLAME-IN position. At the time point b, the flame cut-off shutter 27 blocks the flame from the specimen S, and at the time point c, the specimen S is removed from the flame to the FLAME-OUT position. The time interval ac is determined by an adjustable timer 43 and its normally closed contact 44 which opens at expiration of the time set; and the time interval ab is determined by an adjustable timer 46 and its normally open contact 47 which closes at expiration of the time set.

A flame temperature destruction test sequence should now be apparent. In the FLAME-OUT position shown in FIG. 1, and with the specimen S secured in the holder 10, a desired flame exposure time a-b is set on the timer 46, and a time interval a-c is set on the timer 43 at some slightly greater value. The flame from the burner 12 is also adjusted for the desired steady-state condition by the adjustment of the valve 17 and the burner 12. The apparatus is now ready for test.

When the manual switch 41 is closed at time point a, the

timers

43 and 46 are started and the carriage motor 13 is energized through the normally closed contact 44 thereby driving the specimen S into the fiarne region. At

m/D z wherein subscripts 1 and 2 refer to the adjacent exposed and base layers, respectively,

The factor 7 in Equation 1 represents:

kgS k1S kgS2 wherein k thermal conductivity, and S volume specific heat (specific heat dcnsity).

Equation 2 differs from Griffith and Hortons equation only to the extent of What may be a more precise mathematical procedure.

The mathematical constant A obtains from Now, for a particular set of constant test conditions wherein the thermal properties of a constant base layer are known, and the heat flux H, exposure time t, and thickness x and a are preselected, the diflusity D of the exposed layer can be plotted against the base layer temperature rise U for various combinations of thermal conductivity k, and volume specific heat S A curve so plotted is shown in FIG. 6. t should now be apparent that the diffusivity D of any material used as the exposed layer can be determined directly from the temperature rise U of the constant base layer so long as the test conditions are the same as those used in plotting the curve of FIG. 6.

FIG. 50 illustrates a transient heat transfer test arrangement for a single-layer specimen S, the thicknesses c and x appropriately identified. The thermocouple T represents the means for measuring the temperature rise in the base layer. As in the flame temperature destruction tests, thermocouple T serves as a flame temperature check during FLAME-IN positioning. FIGS. 5a and 5b illustrate the thickness parameters or and x for two differ.- ent materials S and S with and without an air space therebetween. The invention thus contemplates the measurement of the average diffusivity of any combination of materials so long as the aforementioned test conditions remain the same as used for plotting the curve as shown in FIG. 6.

Procedures for carrying out direct transient heat transfer determinations are substantially the same as described above for flame temperature destruction tests except that the radiation head 32 is not used. Instead, a temperature is measured in the base layer by the thermocouple T Referring again to FIG. 50, the specimen S is secured beneath a rigid base layer 48 of known thermal properties. The thermocouple T is imbedded in the layer 48 a known distance from the interface between the base layer 48 and the specimen S, hence the parameters of x and a as defined in Equation 1 are known. The thermocouple T is included merely for observing flame conditions during exposure of the specimen S. Additional thermocouples, such as T at the interface, may be situated at other points of interest.

After establishing a desired flame condition, the manual switch 41 is closed. The specimen S then moves over the flame region for the preset time during which the thermocouple T will sense and transmit to the recorder 33 the temperature rise U as it occurs. This temperature rise U is then correlated on a curve such as shown in FIG. 6 for directly determining the diffusivity D of the specimen S without extensive computations such as discussed in connection with Equation 1.

It is further contemplated that the base layer 48, FIGS. 5a, 5b and 50, may be chosen with thermal properties similar to living skin in order that test conditions closely approximating those of a pilot wearing a garment made of specimen S or S and S" may be obtained.

It should now be apparent that the present method and apparatus provide a very rapid means for empirically determining the thermal properties of various materials, particularly very thin fabrics and textiles. No extensive mathematical computations are involved. The invention is capable of assimilating a variety of actual thermal environments, at the same permitting these environments to be reproduced with a high degree of accuracy. The invention is particularly applicable to direct determinations of the destruction temperature of thin materials, their heat transfer characteristics, and their insulation effect when air spaces are placed between layers thereof. Moreover, the presently disclosed method and apparatus permits analyses of thermal properties of materials in contact with living tissues. Such data are of inestimable value in solving physiological problems concerning heat flow into living skin where temperatures at shallow depths cannot otherwise be accurately measured.

It will be understood, of course, that various changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated in order 6 to explain the nature of the invention, may be made by those skilled in the art Within the principle and scope of the invention as expressed in the appended claims.

What is claimed is:

1. A method for rapidly determining the transient heat transfer properties of thin fabrics, comprising the steps of:

mounting the fabric on a base of known thermal properties,

establishing a uniform steady-state flame of known heat flux,

exposing the outer side of the fabric to direct contact with said flame,

measuring the temperature rise in said base at a known distance from the interface of said fabric and base during the flame exposure, and

removing the fabric from exposure after expiration of a predetermined time;

whereby the temperature rise so measured is a direct function of the thermal diffusivity of the fabric.

2. A method for rapidly determining the transient heat transfer properties of thin material, comprising the steps of:

mounting the material on a base of known thermal properties,

exposing the outer side of the material to direct contact with a uniform flame for a predetermined duration, and

measuring the temperature rise in said base at a known distance from the interface of said material and base during the flame exposure;

whereby the temperature rise so measured is a direct function of the thermal diffusivity of the material.

3. A method for rapidly determining the transient heat transfer properties of thin materials, comprising the steps of:

mounting the material on a base of known thermal properties,

exposing the outer side of the material to a flame, and

measuring the temperature rise in said base at a known distance from the interface of said material and base during the flame exposure.

4. Apparatus for determining thermal properties of thin fabrics, comprising:

a burner for establishing a uniform steady-state flame of known heat flux,

a carriage slidable relative to said burner in a horizontal plane selectively over the flame,

a holder supported in said carriage and formed to secure a specimen of fabric thereto,

a first spring-return electric motor drivingly connected to said carriage for normally positioning said carriage so that said specimen is out of said flame until energized,

a flame shutter slidable in said carriage for selectively blocking the flame from said specimen irrespective of the position of said carriage,

a second spring-return electric motor drivingly connected to said flame shutter for normally positioning said shutter out of the blocking position until energized,

a radiation responsive means positioned for measuring the temperature on the upper side of the specimen when positioned in said flame region by said carriage,

a radiation shutter positioned for selectively blocking the radiation from said specimen,

a third spring-return electric motor drivingly connected to said radiation shutter for normally positioning said radiation shutter in a blocking position until energized,

first switch means positioned relative to said carriage and electrically connected to said third motor for energizing the latter when said specimen is positioned in the flame region,

first automatic-reset timer means electrically connected to said first motor and said first switch for energizing said first and third motors for a predetermined time interval,

second automatic-reset timer means electrically connected to said second motor for maintaining electrical energy thereto for a time duration not greater than the time interval set on said first timer means, and

second switch means electrically connected between a power supply and said first and second timers for selectively energizing said timers.

5. Apparatus as set forth in claim 4 wherein said holder further comprises:

a base made of a material having thermal properties similar to living skin and formed to secure the specimen thereunder for flame exposure, and

a thermocouple imbedded in said base at a known distance from the interface of said base and said specimen.

6. Apparatus for determining thermal properties of thin material comprising:

a burner for establishing a uniform steady-state flame of known heat flux,

carriage slidable relative to said burner in a horizontal plane selectively over the flame and formed to secure a specimen of material thereto,

a first electric motor drivingly connected to said carriage for normally positioning said carriage so that said specimen is out of said flame until energized,

a second electric motor drivingiy connected to said flame shutter for normally positioning said shutter out of the blocking position until energized,

a third electric motor drivingly connected to said radiation shutter for normally positioning said radiation shutter in a blocking position until energized,

first timer means electrically connected to said first motor and said first switch for energizing said first and third motors for a predetermined time interval,

second timer means electrically connected to said second motor for maintaining electrical energy thereto for a time duration not greater than the time interval set on said first timer means, and

7. Apparatus as set forth in claim 6 wherein said carriage further comprises:

8. Apparatus for determining thermal properties of thin materials, comprising:

a burner for establishing a uniform steady-state flame of known heat flux,

a. carriage slidable relative to said burner in a horizontal plane selectively over the flame and formed to secure a specimen of material thereto,

a first electric means drivingly connected to said carriage for normally positioning said carriage so that said specimen is out of said flame until energized,

a second electric means drivingly connected to said flame shutter for normally positioning said shutter out of the blocking position until energized,

a temperature responsive means positioned on the upper side of the specimen,

first timer means electrically connected to said first motor for energizing the latter for a predetermined time interval,

switch means electrically connected between a power supply and said first and second timers for selectively energizing said timers.

9. Apparatus as set forth in claim 8 wherein said carriage further comprises:

a base made of a material having thermal properties similar to living skin and formed to secure the specimen thereunder for flame exposure.

10. Apparatus for determining thermal properties of thin material, comprising:

a burner,

a carriage slidable relative to said burner selectively over the flame and formed to secure a specimen of material thereto,

a temperature responsive means positioned for measuring the temperature on the upper side of the specimen when positioned in said flame region by said carriage,

first timer means operatively connected to said carriage for positioning said specimen in the flame for a predetermined time interval,

second timer means operatively connected to said flame shutter for positioning said shutter in the flame after a time duration not greater than the time interval established by said first timer means, and

References Cited in the file of this patent UNITED STATES PATENTS Kime Sept. 4, 1951 Hager July 24, 1962 fer, N.Y., D. Van Nostrand Co., Inc, 1957, pp. 5 and 6.

Claims

10. APPARATUS FOR DETERMINING THERMAL PROPERTIES OF THIN MATERIAL, COMPRISING: A BURNER, A CARRIAGE SLIDABLE RELATIVE TO SAID BURNER SELECTIVELY OVER THE FLAME AND FORMED TO SECURE A SPECIMEN OF MATERIAL THERETO, A FLAME SHUTTER SLIDABLE IN SAID CARRIAGE FOR SELECTIVELY BLOCKING THE FLAME FROM SAID SPECIMEN IRRESPECTIVE OF THE POSITION OF SAID CARRIAGE, A TEMPERATURE RESPONSIVE MEANS POSITIONED FOR MEASURING THE TEMPERATURE ON THE UPPER SIDE OF THE SPECIMEN WHEN POSITIONED IN SAID FLAME REGION BY SAID CARRIAGE,