A general solution is presented for the temperature rise produced by the absorption of a scanning Gaussian laser beam in a solid target. In normalized coordinates, the temperature rise is found to depend only on the ratio of the scan speed to the rate of heat diffusion in the solid and the ratio of the beam radius to the absorption depth. For slow scan speeds the solution simplifies to the steady-state approximation in which the power input is balanced by heat conduction into the solid. For fast scan speeds the solution approaches the energy density limit in which the temperature rise is proportional to the integrated beam intensity. For highly absorbing materials the solution simplifies to the surface absorption approximation. The general solution demonstrates the conditions under which each approximation can be used. Similar solutions are found for the related case of pulsed exposure by a stationary beam. The solution is demonstrated experimentally by exposing thermal paper with a CO2 laser.

Temperature distributions produced by scanning Gaussian laser beams.

Stretchable Helical Architecture Inorganic-Organic Hetero Thermoelectric Generator

Results from an experimental study on the rapid measurement of thermal conductivity of chemical vapor deposited (CVD) diamond films are presented. The classical thermal comparator method has been used successfully in the past for the measurement of thermal conductivity of bulk materials having high values of thermal resistance. Using samples of known thermal conductivity, a calibration curve is prepared. With this calibration curve, the comparator can be used to determine thermal conductivity of unknown samples. We have significantly modified and extended this technique for the measurement of materials with very low thermal resistance, i.e., CVD diamond films with high thermal conductivity. In addition to the heated probe, the modified comparator employs a thermoelectric cooling element of increase conductive heat transfer through the film. The thermal conductivity measurements are sensitive to many other factors such as the thermal contact resistances, anisotropic material properties, surrounding air currents and temperature, and ambient humidity. A comprehensive numerical model was also developed to simulate the heat transfer process for the modified comparator. The simulations were used to develop a numerical calibration curve that agreed well with the calibration curve obtained from our measurements, The modified method has been found to successfully measure the thermal conductivity of CVD diamond films.

Thermal Conductivity Measurement Of CVD Diamond Films Using A Modified Thermal Comparator Method

This work examines the thermal transfer through porous media by means of measurement of the effective thermal conductivity and modelling of the structural parameters. While most of the work is of a general nature, the porous media in focus are pigment plus latex binder systems as used for paper coatings. As such, the application field of thermal effects in printing is discussed. At first the use of a dynamic measurement method for the thermal conductivity of porous coating pigment binder systems in the form of tablets is evaluated. In addition, a Lumped Parameter Model is developed to analyse the measured thermal conductivities in terms of the material volume fractions and their structural configuration. The model therefore uses two independent structural parameters instead of porosity alone as the governing parameter. This enables a discussion following modelling approaches adopting parameter modelling and structural modelling. A combination of both is used to discuss the solid-solid connectivity of pigment binder systems. It is shown by the model parameter of pigment connectivity that a disruption of the pigment packing already at low concentrations of binder occurs related to surface and colloid chemistry factors which cause the binder to accumulate first at pigment nodal points. The analysis of different pigment binder systems shows that, due to the presence of two interacting solid phases, the effective thermal conductivity cannot be modelled by using porosity and pore structure alone, but also requires the additional parameter of dual solid phase connectivity. It is proposed, therefore, that a combination of pore structure analysis and thermal conductivity measurement can be used to identify and parameterise subtleties in interactive particulate systems. For the application of toner fusing in electrophotography it is shown that a thermally insulating coating layer leads to a concentration of the fusing energy on the surface, thus aiding the fusing/adhesion development of the toner while shielding the base paper from undesired heating. In the heatset web-offset drying process, an insulating precoating in combination with liquid barrier properties can lead to a similar shielding of the base paper and thus helps to maintain an even moisture profile effectively reducing the waving/fluting tendency.

Heat transfer through porous multiphase systems measurement, modelling and applications in printing of coated papers

The measurement device 10 according to the invention comprises a heat source 14 connected to a cold source 15 by two solid copper bars 12, 13 aligned along the same axis OX in order to have an adjustable air gap 16 and each provided with thermocouples 21 disposed along their length. The method for measuring the thermal resistance of a sample 11 consists in making a constant heat flux flow in the bars and in the sample, in plotting the curve representing the development of temperature along each bar, the resulting curve being formed from two parallel straight-line segments corresponding to the two respective bars; in measuring the distance which separates the two straight-line segments along the axis (OX); and in converting this distance into an equivalent length of one of the bars in order to obtain the value of the thermal resistance of the sample.

Method and device for measuring the thermal resistance of a sample such as in particular an electronic circuit component

A new thermal conductivity cell is described which can be used to measure the bulk thermal conductivity and the thermal contact resistance of paper and other thin‐film materials. The cell incorporates a hydraulic piston which can apply pressures up to 1700 psi to the sample which is situated between the optically flat end faces of two brass columns. By measuring the thermal resistance of paper samples of various thicknesses, it is demonstrated that a pressure of 1700 psi effectively eliminates the thermal contact resistance. By comparing measurements at zero and maximum applied pressure, both the bulk conductivity and the contact resistance can be calculated. This is illustrated with several types of paper. In all cases, there is a qualitative correlation between the measured contact resistance and the surface roughness of the sheet. The technique can also be used for thin polymer films, and for layered structures such as the ink donor films used in thermal transfer printing.

D. J. Sanders

Papers

Measurement of thermal conductivity and contact resistance of paper and thin‐film materials