Measurement and prediction of heat transfer coefficient on ammonia flow boiling in a microfin plate evaporator

• Thermal characteristics of microfin plate evaporators are investigated.
• Longitudinally- and laterally-finned heat transfer surfaces are used and compared.
• Mechanisms of heat transfer enhancement by using microfin are discussed.
• Effects of mass flux, heat flux, channel height, and saturation pressure are discussed.
• Modified empirical correlations to predict heat transfer coefficient are developed.

Thermal characteristics of ammonia flow boiling in a microfin plate evaporator are experimentally investigated. Titanium microfin heat transfer surface is manufactured to enhance boiling heat transfer. Longitudinally- and laterally-microfined surfaces are used and those performances are compared. Heat transfer coefficient of microfin plate evaporator is also compared with that of plain-surface plate evaporator. The effects of mass flux, heat flux, channel height, and saturation pressure on heat transfer coefficient are presented and discussed. The experiments are conducted for the range of mass flux (5 and 7.5 kg m−2 s−1), heat flux (10, 15, and 20 kW m−2), channel height (1, 2, and 5 mm), and saturation pressure (0.7 and 0.9 MPa). Heat transfer coefficient is compared with that predicted by available empirical correlations proposed by other researchers. Modified correlations using Lockhart-Martinelli parameter to predict heat transfer coefficient are developed and they cover more than 87% of the experimental data.