Papers by Keyword: Thermal Diffusivity

Abstract: An investigation of solidification process of as-cast ADC12 aluminum alloy in sand molds with different pouring conditions by temperature field was discussed in the present study. The ADC12 aluminum alloy was investigated in quarzt sand mold and chromite mold using sodium silicate binder with hardening by CO₂ gas under atmospheric and low vacuum conditions. Mechanical properties results indicated that a chromites mold under low vacuum condition has the optimal value. Thermal diffusivity was determined by finite difference method. The maximum thermal diffusivity was obtained in a chromite mold under low vacuum condition and correspondence to the minimum solidification time field.

Abstract: Recently the physical model for the temperature field generated by thermophysical single-probe sensor in a shape of planar disc has been derived. The model accounts cylindrical sample having final radius and infinite length. The prototype of measuring electronics RTA was build that operates with auto balancing bridge. For the measurements the single-transition method is used. While the measurement error of the temperature response measured by thermocouple was 1% at the height of temperature response 1°C, the sensitivity of the measurement with the automatically balanced bridge is better and the signal to noise ratio is improved about 10 times. The measuring electronics was tested for measuring the temperature response using a single-sensor. This sensor generates the heat pulse and sense the temperature response in the same time. The next advantage is that the temperature response to the generated step-wise pulse is much smaller and it can be reduced to the level of 1-8° C compared to stationary method like guarded hot plate method. The effect of the temperature field generated by the probe is much smaller, which in the case of measurement of porous materials at the presence of moisture is beneficial, as the resulting redistribution of moisture under the created temperature gradient is negligible. There were derived basic models for the evaluation of this type of experiment. The probe should be in form of full cylinder or an annulus. The derived temperature function counts the outer and inner diameter of annulus. Putting the inner radius to zero we get the solution for full circle probe, so the model is universal. The model counts also the heat losses from the outer surface of the sample, when the time of measurement exceed the time when the penetration depth of generated heat pulse rich the outer radius of sample. The estimated output parameters from single measurement are the thermal conductivity, thermal diffusivity and specific heat. The heat transfer coefficient is additional parameter fitted as free parameter of the model.

Abstract: Temperature wave method is a quasi-stationary method for measuring thermal diffusivity of a substance. Method of plane temperature waves is a derivative of temperature wave method based on the notion of applying heat flux to first side of a sample and measuring temperature fluctuation on the second side of a sample. Changing temperature wave frequent allows us to enter adiabatic regime. Considering that phase of heat flux is known, the only parameter to be measured is phase of temperature changes on the second side of a sample relative to the phase of heat flux, which (in adiabatic regime) gives us thermal diffusivity.

Abstract: Mannitol is an alcoholic sugar that is commonly used in the food industry. It is a white, odorless crystalline powder. Its melting temperature is about 168 °C. It is possible to be used also for the accumulation of energy in the heat exchangers based on oils. On its basis is sold a product PlusICE A164 of company PCM Products Ltd. (T = 164 °C, c_p = 2.42 kJ.K^-1 kg^-1). Thermal properties of the material in both, solid and liquid phase were investigated for this purpose in terms of potential applications. Temperature dependence of thermal parameters (thermal diffusivity, thermal conductivity, and specific heat) were determined using a transient (step-wise) method. Fractal model of heat transport was used for the determination of thermal parameters. This model is independent on the geometry and on the type of the sample heating, and includes heat losses too. The experiment confirms the phase change temperature about 168 °C.

Abstract: The texture in illite-based ceramics was introduced by spreading a large number of thin layers of a wet plastic mass one on top of the other. The basal planes of the plate-like illite crystals are predominantly oriented parallely with the direction of spreading. The samples were fired at different temperatures ranging from room temperature up to 1100 °C with a heating rate of 5 °C/min, then freely cooled and measured at room temperature. We determined Young modulus (E), thermal diffusivity (a) and relative dimension changes (Δl/l₀) in two directions: parallely to the basal planes (a subscript ||) of the illite crystals and perpendicularly to these planes (a subscript ⊥). It was found that the ratio E_|| / E_⊥ ≈ 2.9 and a_|| / a_⊥ ≈ 2.0 up to 900 °C. Above 900 °C, the values of E and a increase due to sintering, and the differences between the values measured in the two directions decrease. In the case of the thermal diffusivity these differences do not disappear even after firing at the temperature of 1200 °C.

Abstract: Computer aided cooling curve analysis (CACCA) is an online prediction tool for the determination of solidification characteristics of metals or alloys. The results of CACCA can be used to accurately determine latent heat and solid fraction needed for modeling of the solidification process. Newtonian and Fourier analysis techniques adopt a data base line fitting technique to the first derivative curve for calculation of the solid fraction and latent heat of solidification. This paper describes the theoretical and experimental procedures involved Newtonian and Fourier analysis techniques with reference to an Al-22% Si alloy. The correlations between the solid fraction and temperature/time for the alloy were determined.

Abstract: The electronic modules are complex ensemble of electronic components having terminals (PIN) connected by solder joints on dedicated metallic surfaces (PAD) parts of conductive interconnection structure realized on rigid or flexible dielectric substrate having different core materials. The reliability of the electronic modules could be considered as expression of solder joints functionality (SJF) relating to working conditions and unique defined by their electrical, mechanical and thermal properties. These properties are in close connection with the solder joints microstructures, result of the soldering Process temperature gradient action over the trinomial solder alloy Paste, Pin and Pad. Consequently the solder joints quality can be correctly evaluated taking into consideration not only the severally intrinsic parameters of the trinomial elements Pin-Pad-Paste characterized by specific thermophysical properties (ThP), but also interrelate the complex reaction at the interface between them and interdependence with the soldering Process parameters.In the paper, will be analyzed the influencing factors of manufacturing processes, the most important assembling defects at macro and micro level, their causes relating to specific ThP and processes at interfaces Pin-solder joints-Pad, it will be identify the Key Process Input Variables (KPIV) and propose a structural model for assembling processes, 4P Soldering Model, as an useful tool in engineering of electronic product in order to assure the assumed goal for assembling stage.

Abstract: Pt-SnO₂ ceramics were prepared via solid-state route from a mixture of powders of (100-x) SnO₂.x Pt (0≤ x wt %≤ 1). The samples were then sintered at 600, 800 and 1000 °C for 3 hours. The resulting samples were then characterized using Laser Flash Apparatus (LFA) for determining thermal diffusivity (α ) value. The measurements of α were carried out at room temperature up to 400 °C with the intervals of 50 °C. Experimental results showed that thermal diffusivity value is in the range of 5.0×10^-7m²s^-1 - 3.0×10^-6m²s^-1. We also show that larger grain size increases the thermal diffusivity of the ceramic. Data concerning the effects of additive amount, pore content, and temperature were also reported.

Abstract: The main thermal and morphology properties of novel thermally conductive polymeric materials are studied in this work. Novel thermally conductive materials can be used as heat-releasing materials in LED-lamps.

Abstract: The epoxy composites with high thermal conductivity for metal-core printed circuit board (MCPCB) can be prepared by varnish coating and a hot press method. Alumina filler of plate-like shape was used as primary micro-filler, while plate-like alumina filler, h-BN, a-BN and s-BN filler were used for blending into the plate-like alumina filler as the secondary filler. Results showed that the secondary fillers a-BN and s-BN loaded epoxy composites have higher thermal conductivity than alumina filler single-loaded composites. Also, BN filler has high thermal conductivity, but h-BN filled epoxy composite has lower thermal conductivity than alumina filled epoxy composite. The decrease of voids in epoxy composite are very important, and the filler shape and surface modification is also necessary to achieve high thermal conductivity in epoxy composite for MCPCB