FIELD OF THE INVENTION

The invention generally relates to a method for measuring thermal properties of solids and more particularly relates to a method for estimating thermal diffusivity of dielectric solids based on the non-dimensional velocity (NDV).

BACKGROUND OF THE INVENTION

Thermal diffusivity is a thermo-physical parameter of paramount importance while addressing issues relevant to thermal design/management and control in real world applications. It appears as a constant of proportionality in the Fourier’s equation, for the conduction of heat in presence of non-stationary temperature field. The physical meaning of thermal diffusivity is associated with how fast heat diffuses in solid when temperature in changing with time. The direct knowledge of thermal diffusivity is required in the modelling of cooling and heating of machinery, heat sinks or spreaders and heat resistant coatings and indirect information of thermal diffusivity is useful in non-destructive depth profiling of surface modified metals, the curing of reaction-moulding resins and potentially in the in-situ quality control of manufactured metal sheet.

Thermal diffusivity measurement requires measurement of several quantities and requires several measurements. In 18th century, Angstrom introduced ‘periodically varying temperature wave’ in semi-infinite solid of small cross-section for measuring thermal conductivity of metallic solid. In 19th century, King measured thermal diffusivity and thermal conductivity of solid based on measurement of velocities of sinusoidal temperature waves of two different input frequencies. For dielectric solids, Debye explained the relationship between thermal conductivity and volumetric specific heat capacity based on velocity of phonon and mean free path.

The challenge in measurement of thermal diffusivity in dielectric solid is it requires measurement of several quantities inside the solid and its neighbor medium. Therefore, in order to eliminate the number of measuring quantities and their measurements, there exists a need to provide a method for estimating thermal diffusivity. Traditional optical methods like thermal lensing, interferometric technique, IR technique, Photothermal beam deflection technique, Dew-film boundary translatory motion techniques, etc., involving the number of measuring quantities related to either sample or/ and neighbor medium.

For example, interferometric technique required the knowledge related to sample like refractive index, thickness, thermo-optic coefficient, surface finishing, optical wedge etc. For example, Dew-film boundary translatory motion technique requires the data related to ambient, like ambient-humidity, ambient-temperature and excitation/input temperature and dew point temperature. In IR technique, using IR camera based method, requires reflection parameter from the sample surface, temperature profile inside the solid can be measured directly from which fitting the data with model thermal diffusivity of solid is estimated.
The present invention provides one such method that a moving isothermal surface/ moving feature with unique non-dimensional velocity (NDV) exhibited inside the sample is utilized to estimates thermal diffusivity of dielectric solids.

OBJECT OF THE INVENTION

The primary object of the present invention is to measure the thermal diffusivity of dielectric solids by exploring the properties of Non-dimensional velocity (NDV).

Another object of the present invention is to provide a module based on direct method to measure thermal diffusivity of dielectric solids by relating its spatial and velocity quantities without measuring its temperature.

Yet another objective of the present invention is to solve the problem of obtaining several measurements to compute thermal diffusivity of dielectric solids.

Yet another object of the present invention is to visualize the thermal diffusivity inside a solid during heat flow by using IR camera.

Other objects and advantages of the present invention will become apparent from the following description taken in connection with the accompanying drawings, wherein, by way of illustration and example, the aspects of the present invention are disclosed.

SUMMARY OF INVENTION

The present invention relates to a method to measure thermal diffusivity of dielectric solid by exploring the Non-dimensional velocity (NDV) of ‘selective color band’ recorded by using IR Camera.

The main embodiment of the present invention is that for the prescribed transient thermal excitation, the evolution of temperature profile is coded as movement of several color bands and the position, NDV, and velocity of particular color band is governed by diffusivity of solid.

In the present invention, image input is provided by IR camera; for reference-solid the position of selective color band, and its thermal diffusivity is calibrated. Utilizing the said data the color, the location and velocity of samples under test is measured through image processing.

Another embodiment of the present invention is the extraction of the IR images from the recorded video and applying the basic image processing techniques to estimate thermal diffusivity of sample under test.

Other objects and advantages of the present invention will become apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood after reading the following detailed description of the presently preferred aspects with reference to the appended drawings:

Figure 1: shows solids with no colour band at initial condition;

Figure 1a) shows the test-sample 1;

Figure 1b) shows reference solid;

Figure 1c) shows test sample-2, the dimension of all solids are identical, and equal to 10mm X 10mm X 150mm and all are at uniform temperature which is equal to ambient temperature Ti, represented as (101);

Figure 2 shows solids with colour band captured by IR Camera after thermal excitation at time t1 seconds;

Figure 2a shows test-sample 1;

Figure 2b shows reference solid;

Figure 2c shows test sample-2.

Figure 3 shows only segmented interface colour band of interest at time t1 seconds in all solids.

Figure 3a) shows test-sample 1;

Figure 3b) shows reference solid ;

Figure 3c) shows test sample-2;

Figure 4 shows isometric view of Figure 3;

Figure 5 shows image processing for reference solid, figure 5a) represent gray-level image of reference-solid, figure 5b) represent segmented image and figure 5c) represent binary conversion which is the location of segment of interest;

Figure 6 shows the processed image of location of unique interface of colour band of interest in different solids.

Figure 6a, 6b and 6c shows location of unique interface of colour band in test-sample-1 at (104), The said colour band location in reference solid at (105), The said colour band location in test sample-2 at (106).

DETAILED DESCRIPTION OF THE INVENTION

These and other features and advantages of the present invention may be incorporated into certain embodiments of the invention and will become more fully apparent from the following description or may be learned by the practice of the invention as set forth hereinafter. The present invention does not require that all the advantageous features and all the advantages described herein be incorporated into every embodiment of the invention.

The present invention relates to a method to estimate thermal diffusivity of dielectric solids by exploring the properties of Non-dimensional velocity (NDV). The method paves a new way for direct measurement of thermal diffusivity of dielectric solid by relating its spatial and velocity quantities without measuring its temperature. The present method also solves the problem of obtaining several measurements to compute thermal diffusivity of dielectric solids.

In the present invention the IR camera indicate the spectrum of isothermal surface at different instant of time, and different color bands indicates different and unique temperature. In the present invention, the heat flow inside the solids are captured by IR camera and indicate the spectrum of isothermal surface at different instant of time, and different color indicates, corresponding temperature gradient.

In the present invention, the thermal diffusivity of dielectric solid is measured by the procession of moving element which is indicated by a moving spectrum of colors.

The IR camera indicate the spectrum of isothermal surfaces at different instant of time and different color bands indicates, corresponding temperature bands of similar temperature.
In the present invention the thermal diffusivity of solid is estimated by exploring non-dimensional velocity of ‘selective color band’ which is recorded by IR camera. For the prescribed transient excitation, the evolution of temperature profile is coded as ‘movement of color bands’. The position, NDV and velocity of a particular color band is governed by diffusivity of solid. The position of color band and thermal diffusivity of reference solid is calibrated and using the same color, the location and velocity of sample under test is captured by IR camera. The images are extracted from the recorded video and basic image processing techniques are applied such as segmentation and partial area effect to achieve sub-pixel resolution of position, and velocity of selective color band in both test-sample and reference sample to estimate thermal diffusivity of sample since the color band is not sample dependent so thermal diffusivity of several samples can be measured simultaneously.

The present invention provides a method to compute diffusivity of dielectric solids using Non-dimensional velocity (NDV). Non- dimensional velocity is used in boundary layer theory and also to define the law of the wall. The Non-dimensional velocity (NDV) is obtained by the following steps:

Let be the one-dimensional temperature distribution in homogeneous semi-infinite bulk-solid that results, after a time lapse of seconds. If is the thermal diffusivity of the solid, in the absence of sources/sinks of heat inside its surfaces, the heat conduction in such sample is governed by the partial differential equation
0 = x < 8, t > 0 (1)
Using chain rule the above equation can be written as,

(2)

(3)
where, v is velocity of isothermal surface.

Using exact solution in non-dimensional form with standard initial and boundary condition the solution of equation (1) is

(4)
where, (5) and
(6)
On solving equation (3), using exact solution, we get velocity and thermal diffusivity of the solid as follows:

?=x/2t (7)

(8)

Re-arrange equation (8)

NDV= (9)

NDV can also be obtained from the equations 4, 5 and 6. NDV can be written as inverse form of exact solution mentioned in equation (10). The unique moving isothermal surface TB due to step temperature excitation of T0 at x=0, with initial temperature Ti.

(10)

Under step temperature excitation, different isothermal surface have unique NDV. All isothermal surface undergoes migration with different position dependent speed. Since different isothermal surface moves with different position dependent speed, so for the given instant of time, a unique isothermal surface with NDV is separated, and measure its speed and location to estimate thermal diffusivity.

In the present invention, for a step-temperature excitation, heat flow in solid is recorded using IR camera. The different colors bands in the IR image indicate different temperature. i.e., isothermal surfaces can be coded by different color band using IR image.
The video is recorded using IR camera indicate a motion of color bands at different instant of time; originated at x=0 moved at different locations with different color at different instant of time.

The thermal diffusivity of solid is obtained by measuring the velocity and position of both reference solid, and sample-solid. Using equation (11) thermal diffusivity of solid is obtained

Using equation (8) thermal diffusivity for test-solid-sample 1 and reference-solid-sample can be written as,

Diffusivity of test-solid-sample 1= (11)

Where, v1 is velocity of selective color band in solid under test, and x1 is its location at a given time t1 seconds.

Thermal diffusivity of reference solids = (12)

Where, v2 is velocity of selective color band in reference solid, and x2 is its location at a given time t1 seconds.

In the above equations are equated since NDV is same then,

Thermal diffusivity of sample-solid 1 is given by

(13)

where, v1 and v2 are velocities of selective interface of color band measured in test sample-solid 1, and reference-solid 1 respectively.

Similarly, for test- sample 2 thermal diffusivity is given by

(14)

Where, v3 is velocity of selective interface of color band in solid under test 2, and x3 is its location at a given time t1 seconds.

Utilizing the proposed method, during heat flow inside the solid can be visualized by any of the following technologies.

Dew-film boundary translatory motion technique,
Using IR technique, and
Interferometric technique.

In interferometric technique, when the solid is subjected to one-dimensional heat flow indicated by the moving fringes and each moving fringe represents a unique temperature.

In IR method the moving color band represents a motion of band of unique temperatures.

In dew-film boundary translator motion technique the moving optical mark results from condensation of water-vapour’ for the estimation of thermal diffusivity.

The moving feature inside the solid is captured by using IR camera. By image Processing or interferogram processing thermal diffusivity can be obtained without measuring actual temperature.

In the present method, the properties of Non-dimensional velocity (NDV) is explored to estimate thermal diffusivity of dielectric solid. The Non-dimensional velocity (NDV) is a constant and independent of solid.

The numerical value of Non-dimensional velocity (NDV) is unique, time invariant and independent of sample. Utilizing the said properties, the measurement of diffusion-problem is converted into measurement of spatial location/ distance and velocities of both reference-solid and solid-sample under study. Under tailored experimental conditions, the numerical value of NDV is identical for both reference solid and sample solid (under test). Therefore, the method relates to diffusivities of reference-solid and sample-solid with its velocities and spatial quantities.

NDV concept can be utilized to measure thermal diffusivity of solid using Interferometric technique, IR technique, Dew-film boundary translatory motion technique and any technique which exhibits a moving feature resulting from transient heat flow.

The procedure to obtain thermal diffusivity is of the proposed method is given below:

Conduct experiment to obtain an Input image with Colour bands using IR camera for sample-solids and reference solid.
Read the images using appropriate tool (e.g. Matlab).
Convert them into gray scale.
Crop according to area of interest.
Apply Segmentation method to obtain the unique interface of colour band of interest in different solids shown in figure 6.
Apply Partial area effect to obtain the velocity and spatial location of the image.
Using equation (13) to calculate Thermal diffusivity of sample-solid1under test and equation (14) is utilized to estimate diffusivity of sample solid2 respectively.

Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the invention.

We Claim:
1) A method for estimating thermal diffusivity of solids based on the non-dimensional velocity, wherein the method comprising:

a) providing a test sample of solid and a reference solid;
b) capturing heat flow in the said solids using IR camera under step-temperature excitation;
c) calibrating the position of color band and thermal diffusivity of reference solid by extracting and processing the image obtained from said IR camera;
d) capturing the location and velocity of said sample of solid by said IR camera using the same color band of said reference solid; and
e) obtaining the spectrum of isothermal surface at different instant of time and different color to estimate thermal diffusivity of said sample of solid.

2) The method as claimed in claim 1, wherein the thermal diffusivity of dielectric solid is directly measured by relating its spatial and velocity quantities without measuring its temperature.

3) The method as claimed in claim 1, wherein different color bands in the IR image indicate different temperature.

4) The method as claimed in claim 3, wherein the color band is independent of sample solid and enables measurement of several samples simultaneously.

5) The method as claimed in claim 1, wherein the images are extracted from the recorded video and basic image processing techniques are applied such as segmentation and partial area effect to achieve sub-pixel resolution of position, and velocity of selective color band in said solids to estimate thermal diffusivity of sample of solid.

6) The method as claimed in claim 1, wherein by using suitable heating element, the thermal difusivity of more samples are measured simultaneously.