Моя профессиональная капьепа

Ahmad Yaxshimurodov Asror o’g’li
Secondary school №16 of the Department of Public Education of Pastdargom district, Samarkand region.
Eldor Turdiyev Nasriddinovich
Secondary school №126 of the Department of Public Education of Pastdargom district, Samarkand region
Azimjon Hamdamov Muzaffar o’g ’li
Tashkent Institute of Irrigation and Agricultural Mechanization Engineers Bukhara branch, 200100, Uzbekistan.
Название публикации: «DETERMINATION OF THE THERMAL DIFFU SIVITYOF AQUEOUS SOLUTIONS OF METHANOL IN AN EXTENDED RANGE OF TEMPERATURE BY A LASER-INDUCED THERMAL GRATING TECHNIQUE»
Abstract: Experimental thermal diffusivity data are presented for aqueous solu-tions of methanol in the temperature range 295-335 К. The thermal diffusivity measurements were performed using a laser-induced thermal grating technique at atmospheric pressure. The aqueous solutions studied have weight fractions of 20, 40, 60, and 80% methanol. Because of the small temperature rise (AT < 0.2 K) in the thin sample (sample thickness d = 0.5 mm) during the measurements and the very short measuring time of a few milliseconds, the influence of free convection is negligible. The results converted to thermal conductivity show very good agreement with the experimental data in the literature.
Keywords: aqueous solutions, diffraction, laser-induced thermal grating, methanol, mixtures, thermal conductivity, thermal diffusivity
INTRODUCTION
For many technical processes, the exact knowledge of transport properties is very important whenever heat transfer must be evaluated. However, there are many fluids and fluid mixtures for which few accurate trans-port property data exist [1]. As working fluids, aqueous solutions of alcohols are widely used in the chemical and foodstuffs industries. But their thermal diffusivity and conductivity have rarely been studied experimentally. Assal et al. [2] measured the thermal conductivity of the mixtures of alcohols with water with a hot-wire technique at atmospheric pressure and in the temperature range 300-345 K.
This paper describes an experimental investigation of the thermal diffusivity of aqueous solutions of methanol at amospheric pressure and over an extended range of tem-perature, from 295 to 335 K. The measurements were carried out using a laser- induced thermal grating tech-nique, which is an absolute optical method and can be applied to all transparent or semitransparent liquids and their mixtures.
MEASUREMENT
TECHNIQUE
AND
EXPERIMENTAL APPARATUS
The theory and the experimental setup of the laser-induced thermal grating technique have been described in detail in the literature [3-7]. Figure 1 shows the principle of this measurement technique.
A pulsed laser beam of wavelength A_h = 488 nm is split into two beams of equal intensity with a beamsplitter. Subsequently, the two beams intersect each other at an angle 0 in the sample of thickness d and generate a spatially periodic intensity distribution during a light pulse (0 < t < t_h). By absorbing the light intensity, a spatially modulated, time - dependent temperature field (i.e., a tran-sient thermal grating) is induced that corresponds to the intensity distribution in the interference
region. After a heating light pulse (t > t_h).), the thermal grating decays due to heat conduction in the sample. For t > t_h, one obtains the temperature fluctuation in the modulation direction of temperature (x direction)
ST( x ,t )= AT ( t ) с о s qx = A T ( t_h) e x p[ — (t —t_h)/'T]COS qx, (1) where AT ( t) is the maximum amplitude of the transient periodic temperature field, A T ( t_h) the value of AT ( t )at t = t_h,z, the relaxation time of AT ( t ), and q the modulus of the grating vector,