FORM 2
THE PATENT ACT 1970
&
The Patents Rules, 2003
PROVISIONAL / COMPLETE SPECIFICATION (See section 10 and rule 13)
1. TITLE OF THE INVENTION
"Method and Apparatus for Thermal Conductivity Testing/'
2. APPLICANT
(a) NAME : Larsen and Toubro Ltd.
(b) NATIONALITY.: Indian Company, registered under the provisions of the
Companies Act, 1956
(c) ADDRESS : L&T House, Ballard Estate, Maharashtra State, India.
3. PREAMBLE TO THE DESCRIPTION

PROVISIONAL
The following specification describes the invention.

COMPLETE
The following specification particularly describes the invention and the manner in which it is to be performed.



Title
Method and Apparatus for Thermal Conductivity Testing
Technical Field
The present invention relates to the field of thermal conductivity testing. More particularly this invention relates to an apparatus for testing thermal conductivity of a low thermal conductive ceramic sleeve.
Background and Prior Art
The determination of thermal conductivity of ceramic material has been the subject of extensive study and research efforts. The accepted standard method of test of thermal conductivity of ceramic material utilizes Lee's Disc Method. The apparatus working on Lee's Disc Method which uses a steam as a heating medium and maximum temperature achieved on one side of ceramic disc is 100°C. The Lee's Disc Method can be described as follows.
The sample used to measure the thermal conductivity using the Lee's Disk method is in the form of a disk whose thickness, x, is small relative to its diameter, D. Ignoring heat losses from the edge of the disk, the heat transfer, Q, across the thickness of the sample is given by


Where k is the thermal conductivity, A is the cross-sectional area of the disk and (T2-T1) is the temperature difference across the sample.
Method
The thin polymer sample is placed between two brass plates in conjunction with a heat source. Because of the very low thermal conductivity of the polymer compared with that of brass (approximately 3 orders of magnitude), the temperature of Brass Plate
(1) can be assumed to be very close to that of one surface of the polymer
sample. Similarly, the temperature of Brass Plate (2) can be assumed to
approach that of the other surface of the sample. In this way the
temperature difference across the sample, (T2-T1) can be measured.
At equilibrium, heat entering the Brass Plate (2) equals the rate of heat loss due to cooling. The heat loss can be determined by measuring the cooling rate at the equilibrium temperature T1 (with the Brass Plate
(2) covered with a pad of insulation as in Figure 3 below). If the disk

cools at a rate of then the rate of heat loss is given by:
Where m is the mass of the brass plate and Cp is the heat capacity of brass.


Drawbacks of Prior Art
1. Use of steam as heat source reduces capacity to heat the sample up to desired temperature.
2. Use of steam causes corrosion of the metallic discs thus reducing the life of the apparatus.
3. Assumptions taken are less close to actual situation with steam as heat source.
4. The rate of heating is slow & less efficient with steam as heat source.
Objective of the Present Invention
The main object of the invention is to check thermal conductivity of a low thermal conductive ceramic sleeve at high temperature.
Another object of the present invention is to overcome the difficulties that have occurred in a prior art method.
The foregoing objects of the invention are accomplished and the problems and shortcomings associated with prior art techniques and approaches are overcome by the present invention as described bellow in the preferred embodiment.
This invention is illustrated in the accompanying drawings, through out which like reference letters indicate corresponding parts in the various figures.
Description of the Drawing of the Present Invention


Figure 1 is the block diagram of the testing apparatus.
Apparatus and Working
The apparatus of the present invention is illustrated in figure 1 of the accompanying drawing. The apparatus of the present invention comprises of:
1. Upper and lower metal discs (1);
2. Ceramic sample (2);
3. Resistance coil (3);
4. Upper and lower enclosures of cerawool (4);
5. Metallic box (5);
6. Thermocouples (6);
7. Switches (7);
8. Indicators (8)
The upper & lower disc (1) is used to transmit the heat from resistance coil (3) to sample (2) & heat from sample (2) to itself. It is the ceramic sample (2) whose thermal conductivity has to be determined. Resistance coil (3) is the heating coil of metal used for raising the temperature of metallic disc (1). Upper & lower enclosures (4) of insulating material e.g. thermoglass/cerawool which are used to avoid heat transfer to atmosphere. Metallic Box (5) is the outer box which houses the metal discs (1), sample (2), enclosure (4) & resistance coil (3). Upper & lower thermocouples (6) used to measure the temperatures of the two metallic discs (1). Switches (7) used for putting on & off the heat source. Indicators (8) used for showing the readings.


Working of the Present Invention
The test sample of appropriate size e.g. 23mm diameter and 3-7 mm thick is heated between two metal discs (1) of same diameter as that of the sample (2). Whole arrangement is enclosed between upper and lower enclosure (4) made of high temperature withstanding bricks. Lower enclosure (4) has facility to hold metal discs (1) and sample (2) and provision for insert of thermocouples (6) and upper enclosure (4) has facility to hold heating coil and provision for insert of thermocouples (6). Control panel is provided with one temperature indicator controller for upper disc (1) and temperature indicator for lower disc (1). The upper disc (1) is heated with coil with preset temperature of 600°C. The temperature of the upper and lower disc (1) is measured continuously with the help of thermocouples (6) inserted in the metal discs (1). The whole system is kept on stand with enclosure of Cerawool (4) to avoid heat transfer to atmosphere. The heating is facilitated by means of single phase power supply to heating coil through control panel where heating is controller based on preset temperature. The heating is continued till steady temperature is attained. The steady state temperature of the lower disc (1) is noted.
Calculation





Where,
k=Thermal Conductivity (Cal - Sec-1. cm-1. °C-1)
K= Thermal Conductivity (W/m-K)
M= Weight of lower disc (gms)
S= Specific heat of metal of lower disc
(Cal gm-1 °C-1)
dq/dt = Rate of cooling of lower disc (°C - Sec-1)
d= Thickness of the sample (cm)
a= Area of the sample (cm2)
q1= the steady state temperature of upper disc, °C
q2= the steady state temperature of lower disc, °C
Procedure for dq/dt
The lower disc (1) was heated 10 °C higher than the steady temperature by direct heating, the source of heating was removed after heating and allows the disc to cool; the temperature of the lower disc (1) was measured after every 30 sec till the temperature attains 10°C lower to the steady state temperature. The graph of temperature vs. time was plotted and the slope (dq/dt) was measured at the steady state temperature.


Graph

The foregoing objects of the invention are accomplished and the problems and shortcomings associated with prior art techniques and approaches are overcome by the present invention described in the present embodiment.


Detailed descriptions of the preferred embodiment are provided herein; however, it is to be understood that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure or matter.
The embodiments of the invention as described above and the methods disclosed herein will suggest further modification and alterations to those skilled in the art. Such further modifications and alterations may be made without departing from the spirit and scope of the invention; which is defined by the scope of the following claims.
Advantages of the Present Invention
1. Use of resistance coil as heat source enables to heat the sample up to desired temperature.
2. As we use resistance coil as heating medium this increases the life of the apparatus compared to corrosive steam medium as heat source.
3. The assumptions taken are closer to actual situation resistance coil as heat source.
4. Higher rate of heating is obtained by using resistance coil as heating medium.
5. The efficiency of measurement increases by use of this apparatus.


We claim
1. Apparatus for thermal conductivity testing comprising of, upper and lower metal discs (1); ceramic sample (2); resistance coil (3); upper and lower enclosures of cerawool (4); metallic box (5); thermocouples (6); switches (7); indicators (8); the upper & lower disc (1) is used to transmit the heat from resistance coil (3) to sample (2) & heat from sample (2) to itself, it is the ceramic sample (2) whose thermal conductivity has to be determined, resistance coil (3) is the heating coil of metal used for raising the temperature of metallic disc (1), upper and lower enclosures (4) of cerawool which are used to avoid heat transfer to atmosphere, metallic Box (5) is the outer box which houses the metal discs (1), sample (2), enclosure (4) & resistance coil (3), upper & lower thermocouples (6) used to measure the temperatures of the two metallic discs (1), switches (7) used for putting on & off the heat source. Indicators (8) used for showing the readings.
2. Method for thermal conductivity testing using apparatus as claimed in claim 1, wherein, the test sample of 23mm diameter and 3-7 mm thick is heated between two metal discs (1) of same diameter as that of the sample (2), whole arrangement is enclosed between upper & lower enclosure (4) made of high temperature withstanding bricks, lower enclosure (4) has facility to hold metal discs (1) and sample


(2) and provision for insert of thermocouples (6) and upper enclosure (4) has facility to hold heating coil and provision for insert of thermocouples (6), control panel is provided with one temperature indicator controller for upper disc (1) & temperature indicator for lower disc (1), the upper disc (1) is heated with coil with preset temperature of 600°C, the temperature of the upper and lower disc (1) is measured continuously with the help of thermocouples (6) inserted in the metal discs (1), the whole system is kept on stand with enclosure of cerawool (4) to avoid heat transfer to atmosphere, the heating is facilitated by means of single phase power supply to heating coil through control panel where heating is controller based on preset temperature, the heating is continued till steady temperature is attained, the steady state temperature of the lower disc (1) is noted.
3. Method for thermal conductivity testing using apparatus as claimed in claim 1 and method claim in claim 2; wherein d0/dt is measured by direct heating of the lower disc (1), 10 °C higher than the steady temperature then the source of heating was removed after heating and allowed the disc to cool; the temperature of the lower disc (1) was measured after every 30 sec till the temperature attains 10°C lower to the steady state temperature.


4. Method and apparatus for thermal conductivity testing, substantially as hereinabove described in the specification with reference to the accompanying drawing.

Abstract
The present invention relates to the method and apparatus of the thermal conductivity testing consisting of upper and lower metal discs (1); ceramic sample (2); resistance coil (3); upper and lower enclosures of cerawool (4); metallic box (5); thermocouples (6); switches (7); indicators (8).
The present invention refers to an apparatus that check thermal conductivity of a low thermal conductive ceramic sleeve at high temp i.e. 600°C.