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Seawater desalination has emerged as an important source of fresh water.Low-temperature multi-effect distillation (LT-MED) is one of main methods of seawater desalination.LT-MED desalination system is commonly divided into forward feed configuration,backward feed configuration,parallel feed configuration and mixed feed configuration.The concentration ratio of seawater of mixed feed configuration can be higher than other configurations and the spray density of which is easily designed in a reasonable range which are important for operation.Based on the mass and energy conservation,the mathematical model of a mixed feed LT-MED desalination system with thermal vapor compressor (TVC) was established,in which the temperature losses were considered caused by the boiling point elevation (BPE) of sea water and the flow pressure drop when steam flow through tube bundle,demisters and pipelines.The property parameters of seawater were considered as the functions of temperature and concentration.And the property parameters of fresh water and saturated steam were considered as the functions of temperature.A computer program was carried out to solve the model.The calculation was based on the system with a rated water production of 3500 t/d.Taking actual operation into account,many factors impacting on the system performance were analyzed which included the entrained steam position of TVC,the heating steam temperature of the first effect,the motive steam parameters of TVC,and the position ofpreheater.The results show that when the entrained steam position of TVC is at the effect just behind the mixed feed position,GOR reaches the maximum value and the total area of evaporators reaches the minimum value which is benefit to reduce the water cost.The impact of motive steam parameters of TVC on GOR is greater than on total area of evaporators and it is better to increase the parameters of motive steam for reducing the cost of water.For reducing the water cost it is also better to put preheater at the position before the entrained steam position of TVC.