Titanium Cooling Coils for Surface Ship Applications

Abstract

High machinery space temperatures and generally inadequate ventilation air cooling in many Navy ship machinery compartments influenced a David Taylor Research Center (DTRC) decision to reevaluate seawater cooling coils as a principal means of compartment cooling. Earlier Navy designed and fabricated copper-nickel seawater coils had suffered numerous reliability problems due to fouling, corrosion, and erosion and, thus, were removed from ship use. Advanced plate-fin and integral fin cooling coil designs were evaluated as a means of improving reliability and thermal performance of the previous Navy seawater cooling coils. Math models were developed to analyze the effects of (1) seawater and air temperature, (2) seawater and air flow rates, and (3) coil material on thermal performance. Unique fabrication techniques were assessed for both coils to allow fabrication using titanium in place of copper-nickel for all seawater-wetted components. Finally, various cooling coil waterbox de signs were evaluated to improve the seawater flow patterns and thus reduce fouling and increase component reliability. Results showed that both cooling coil designs can satisfactorily handle cooling requirements of machinery spaces on existing and future class ships without the need for large increases in air conditioning capacity. Furthermore, both seawater coil designs can be fabricated from titanium by modifying fabrication techniques used in the previous design. The recommended general design approach, as concluded from the study, can be summarized as follows: 1 Increase air velocity across the coil to maximize thermal performance; 2 Increase seawater flow rate in the tubes and water-box to prevent biofouling accumulation; 3 Limit the compartment ventilation air to only that amount needed for life support; 4 Provide a small chilled water coil in the compartment for latent heat removal and; 5 Utilize titanium as the seawater-wetted component material to increase reliability over the copper-nickel coil previously used.