Experimental study of Liquid-Liquid direct contact heat exchanger

—Part 1 Evaporation Rate of n-Pentane—

Abstract

Liquid-liquid direct contact heat exchangers have many advantages over conventional multi-tubular type exchangers from the point of view of area of heat exchange and scaling. However, the mechanism of liquid-liquid direct contact heat exchange is so complicated that many experimental researches are going on.
Hot water and n-Pentane are mixed and exchanged each other in a acrylic cylinder, 40 mm dia. and 220 mm height, of our experimental apparatus.
It is the main object of our research to observe flooding phenomenon of n-Pentane from the cylinder since research reports about the flooding phenomenon are very rare and a portion of liquid n-Pentane still exists in hot water at higher temperature than its boiling point. The evaporation rate of n-Pentane is an important scale of exchanged heat flux between hot water and n-Pentane.
We have found evaporation rate of n-Pentane (evaporated n-Pentane/injected n-Pentane) from the measurement of flooding n-Pentane. From the measurement results, the evaporation rate (λ) is expressed by superheated temperature (ΔT_W) of hot water and the mass flow rate (φ=n-Pentane/hot water) . Equation of the rate is obtained as follow;
λ=1-exp{-[ΔT_w-(10∅+2.0)/16∅^0.6]} where ΔT_W = T_l-T_b
T_l: Inlet hot water temperature (K) . T_b : Boiling temperature of water and n-Pentane mixture (K) . φ : Mass flow rate (n-Pentane/hot water) .
The equation is in accord with the experimental results in all superheated temperature region at hot water flow of 8.33×10^-6 (m³/s) . And it differs about 5-10% at hot water flow of 16.7×10^-6 (m³/s) . The experimental equation can be adopted to estimate evaporation rate, and the experimental process is acceptable to observe the flooding phenomenon in Liquid-Liquid Direct Contanct Heat Exchange.