Performance of a single-effect desalination system operating with different tube profiles and materials

In this paper, the effects of tube materials and profiles on the thermal performance of a single-effect evaporator have been investigated. Three different types of tube profiles, such as, single-fluted aluminum tube, smooth Cu–Ni (90–10) tube and corrugated Cu–Ni (90–10) tube have been used for the design of the evaporator. Simulated seawater with variable concentrations (25,000–35000 ppm) has been used as feed. A series of experiments under different operating conditions has been conducted. The effects of the operating variables on the production rate, performance ratio, specific heat transfer area and overall heat transfer co-efficient of the evaporator have been investigated. Flashing effect has been found to have a significant impact on the performance ratio of the system. The lowest specific heat transfer area has been found for the corrugated Cu–Ni (90–10) tube profile. The system performance ratio tends to decrease with the increase of the saturation temperature in the evaporator. The system can yield product water with average concentrations of 15–20 ppm. A numerical model of the system has been developed. A non-equilibrium analysis of the evaporator has also been made. The experimental and predicted results obtained from simulation show good agreement with the actual plant performance.

The following conclusions can be made from the experimental and simulation results of a singleeffect desalination system described in this paper. 1. Heating medium flow rate and temperature variations have significant effect on the thermal performance of the system. An increase in flow rate and temperature increases the performance ratio, overall heat transfer coefficient and decrease in specific heat transfer area. 2. Preheating of the feed water yields better performance. With the increase of degree of super- Experimental overall HTC (W/m K) Predicted overall heat transfer co-efficient (W/m K) heat of the feed water, flashing effect becomes prominent. When flashing occurs, the performance ratio improves considerably for all of the three tube-profiles used in the evaporator. 3. Corrugated copper–nickel (90–10) tubeprofile shows improved performance compared to single-fluted aluminum and smooth copper– nickel (90–10) tube profiles. This may be attributed to the fact that the corrugated profile improves heat transfer performance both inside and outside of the tube and also allows turbulence of the feed water as it flows through the tube. 4. Smooth copper–nickel (90–10) profile shows better performance than single-fluted aluminum. This may be attributed to a lower thickness of the copper-nickel profile compared to aluminum.