A series of multiple-effect evaporators is to be used for evaporating 400,000 kg water per day from a salt solution. The total initial cost for the first effect is $18,000 and each additional effect costs $15,000. The life period of the evaporators is estimated to be 10 years and salvage or scrap value at the end of life period is assumed to be zero. A straight-line depreciation method is used in the optimization analysis. Fixed charges are 15% yearly based on the first cost of equipment. Steam costs $1.50/100 kg. Annual maintenance charges are 5% of the initial equipment cost. All other costs are independent on the number of effects. The series will be operated 300 days per year. If steam company is related to the number of effects as =0.85 N, where N is the V. number of effects. Determine the optimum number of effects for minimum annual cost.