PLATE HEAT EXCHANGERS FOR OCEAN THERMAL ENERGY CONVERSION

Abstract

Ocean Thermal Energy Conversion (OTEC) utilizes the temperature difference between the warm surface seawater and cold deep ocean water to generate electricity. The heat exchanger in an OTEC power plant is significant as it exchanges a large quantity (nearly 40-50 times of the gross power) of heat energy due to the low thermal efficiency of the power cycle. Nearly 30-40% of the total cost of the plant should be allotted to this single component. For the present, 1-MW OTEC plant plate heat exchangers are used both as an evaporator and a condenser. This paper reports a Computational Fluid Dynamics (CFD) investigation for a dimple plate heat exchanger. The analysis uses the Log Mean Temperature Difference Method (LMTD) in all its calculations. Whilst the shell side flow highly resembles the flow over a rough or wavy plate, the tube side passage in these represents the flow over short hexagonal tube banks with the flow across the sectional areas between the hexagons having the shape of a benzene ring. The CFD code employed is Fluent 5 using the Re-Normalization Group (RNG) turbulence model and the two-layer zonal model for near wall areas on the shell side. For tube side flow, the normal k-ε turbulence model is used with a turbulent Prandtl number of 0.63 suggested for flow in tube banks by the literature.