Experimental results on two-phase heat transfer enhancement in microstructured corrugated plate heat exchangers

ABSTRACT

The thermohydraulic effect of microstructuring of the heat transfer surfaces of plate heat exchanger was studied experimentally. The aim of this enhancement strategy is to raise the heat transfer coefficient for the evaporation and condensation of the refrigerant in a vapor compression cycle up to the same level as typical single-phase heat transfer coefficients, when water is used as a secondary fluid. This would result in a better overall heat transfer performance. Titanium herringbone corrugated plates with no microstructure, micro-bump structures created by press rolling and femtosecond-laser-produced microstructures were studied. At first studies of the microstructured plates were performed in a visualization setup using 380 × 380 mm corrugated plate segments. Heat transfer and pressure drop were measured for liquid single-phase flow and evaporation with low vapor quality (x < 0.1). For the single-phase situation, the heat transfer coefficient of the microstructured plates dropped up to 5%, depending on the mass flux, while the pressure drop is not affected. For the evaporation situation, the heat transfer coefficient increased by about 25%, while the pressure drop stayed unchanged within the measurement uncertainty range. A second set of experiments was performed in an industrial-sized vapor compression cycle using R134a with a 100 kW plate evaporator and a 150 kW plate condenser. The microstructured plates gave a very moderate increase of less than 10% in heat transfer within the condenser, but a strong increase of about 40% in the evaporator as compared to the smooth plates.

KEYWORDS:

• Plate heat exchanger
• heat transfer enhancement
• microstructured surface
• evaporation
• condensation