The Design And Performance Research Of Molten Salt Electrical Heating And Heat Exchange System

Molten salt is a kind of excellent heat transfer and heat storage medium, which has many advantages, such as wide temperature range, low steam pressure, large heat capacity, low viscosity, good thermal stability and low price. So molten salt has great application potential in the field of new energy and high temperature heating. Many domestic and international scholars have carried out some research work in high temperature molten salt flow and heat transfer. The research is mostly concentrated in simple structures and rarely in flow and heat transfer process inside the actual application equipment. The design of heat exchange systems for heat-conduction oil and steam systems is not suitable for molten salt systems obviously. In this paper, the author designed and studied a molten salt electrical heating and heat exchange system.Firstly, by adopting the method of thermodynamic calculation and numerical simulation, the molten salt melting and heating process was studied and a complete molten salt electrical heating system was designed. The structure of molten salt heating furnace with fins could guarantee molten salt in complete fusion within 4 hours under the heating power of 15 kW. With calculation and measurement of the pipe preheating element performance, the pipe preheating system was designed and manufactured, which could guarantee the temperature of each position inside pipe above molten salt melting point within 12 minutes under the heating element power of 60 W. Through water contrast experiment and numerical simulation of molten salt flow rate sensor, a low-cost flow rate sensor for molten salt was developed, and this flow rate sensor can effectively measure the pipe flow of molten salt.Secondly, a molten salt heat exchange system of gas heating was designed and built, and the dynamic characteristics of the system (including preheating stage and noamal operating stage) were studied. The designed preheating method could effectively increase the heat exchanger pipe wall temperature. The desired effect of preheating stage was achieved and the time of dynamic process was far less than the molten salt preheating time. The process of molten salt preheating is the main time bottlenecks of the preheating system. By establishing the numerical model of gas exchange system, the dynamic behaviour of system operation process was studied on mechanism combined with variable working conditions. The results obtained can provide reference for system operation control.Finally, molten salt flow and heat transfer characteristics in paddle heat exchangers (more general name of paddle dryers) was investigated by numerical simulation method. The heat transfer performance of 3 typical paddle-shaft structures in 3m2 paddle heat exchangers was compared, open hollow paddle-shaft structure transfers more heat than solid paddle-shaft structure and closed hollow paddle-shaft structure for the typical structure parameters and operation parameters. More factors like mechanical strength and manufacture cost should be taken into account, heat transfer optimization of molten salt in paddle heat exchangers is available and trade-off (between heat transfer and pressure drop or between temperature control and heat loss) is necessary.