Chapter 61 - Local heat transfer in liquid and gas - liquid systems agitated by concave disc turbine

Abstract

This chapter discusses local heat transfer in a liquid and a gas–liquid system agitated in the vessel equipped with baffles and concave disc turbine. On the basis of the measured profiles of the heat transfer coefficient along the vessel wail, the chapter formulates the equations, which enable to describe both the distributions and averaged values of these coefficients for a liquid and gas–liquid system. The effects of aeration through the free surface of the agitated liquid and by means of the gas sparger on the intensity of the heat transfer process are also analyzed. The measurements are carded out by means of the computer aided an electrochemical method where the diffusion current ld proportional to the local mass transfer coefficients κA was measured. Local heat transfer coefficients α(anal) are calculated on the basis of the assumed analogy between mass and heat transfer processes. The effect caused by the developing of the concentration profile in the liquid laminar boundary layer can complicate the measurements of local transfer coefficient which are conducted using the small electrodes. If the size of the electrode is considered as not sufficient to eliminate entrance effect then the result of the measurement should be corrected by means of the experimentally determined calibration factor ρ.