科研之友
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摘要
It is well acknowledged that the onset of natural convection have significant impacts on transient thermal conductivity measurement of liquids. Aiming at this drawback, a single-sided horizontal method based on the transient hot disk technique is proposed to perform more accurate measurements of liquids by suppressing natural convection during the tests. Theoretical solutions of this proposed single-sided method are deduced, and numerical simulations are applied to obtain quantified effects of natural convections. Some experiments are performed to verify the numerical settings. Water, glycol and methanol are analyzed numerically using both the traditional vertical orientation method and the single-sided horizontal method. Both temperature profiles and velocity profiles are recorded. It is found that the viscosity and the coefficient of thermal expansion of liquid samples are the key factors for the onset of natural convection. For single-sided horizontal method, the temperature boundary is 2 mm thinner and the maximum velocity is an order lower when testing water compared with the results from vertical method. Besides, the average temperature of the sensor recorded in single-sided horizontal method fits better with the standard value for all tested liquid samples. All of these analyses show that the proposed single-sided horizontal method can effectively suppress the onset of natural convection during the measurements.
