Plate heat exchangers are used in Ocean Thermal Energy Conversion plants, dairy unit and lube oil cooling plants where a small D T is available for transfer in the system. They are widely preferred because of their compactness, surface area temperature approach upto 1° C. Absolute heat exchanger cleanliness is essential for the performance of these exchangers.

The design of these heat exchangers is such that it cannot tolerate any fouling buildup since the gap between successive plates is only around 3.7 mm. Absolutely there is no data on the performance of these heat exchangers for seawater applications where they are susceptible to biofouling and corrosion product accumulation.

A prototype test system has been developed to investigate the effects of flow, temperature regimes, fouling thickness, and biomass and corrosion products on the heat transfer efficiency using the OTEC thermal cycle as a model. Logarithmic mean temperature difference method (LMTD) is commonly applied for plate heat exchangers. The test system has been designed to operate at velocities ranging from 0.2 to 1.2 m/s, which are the normal operating velocities of these heat exchangers. The channel width has been designed at 5 mm, which is maximum permissible gap for these heat exchangers. The system is fitted with sensors for measuring temperature of plates on the warm and cold legs. A chiller with a 15-ton capacity is used for generating cold water at 6° C for the heat transfer studies. The fouling data obtained is further correlated with real time data obtained with the heat exchangers to serve as a reckoner for the performance of the exchangers at a given duty and fouling thickness.

From- http://www.nio.org/; P. Sriyutha Murthy, S. Syed Jahan, D. Soundarajan, Raju Abraham, K.Sudharshan and R. Venkatesan, National Institute of Ocean Technology, Velachery-Tambaram main road, Pallikarnai Post, Chennai- 601 302, Tamil Nadu, INDIA