Experimental Study Of LNG Cold Energy Thermoelectric Generation

Under the background of the environmental and energy problems increasingly serious,as a clean and efficient energy sources,the natural gas has been employed more and more widely.Therefore,more and more attention has been paid to the research of the cold energy recovery and recycle in the process of natural gas utilization as well.Due to the production and consumption of natural gas is very big,then this part of cold energy released also cannot be ignored.And recycling this part of the cold energy,can not only reduce the energy loss,avoid the extra energy consumption,but also reduce the impact on the environment.Semiconductor thermoelectric generation is a way of all-solid-state energy conversion,recovering energy in this way,especially for such medium and low temperature waste heat,have the advantages of no noise,no wear,no leakage of medium,small volume,light weight,easy to use,as well as almost not limited by the amount of LNG vaporizer and gasification quantity while applied to the LNG cold energy recovery.Therefore,this way can be readily applied to various occasions.In this paper,thermoelectric generation technology was applied to cold energy recovery.The experimental apparatus of the cryogenic thermoelectric generation performance test and cold energy thermoelectric generation was designed and set up.The performance of thermoelectric generation under the condition of low temperature and the impact of various conditions on it were investigated.And influence law of the boiling heat transfer on thermoelectric generation was also studied.In order to measure the performance of thermoelectric generation under the condition of low temperature and applied to the cold energy recovery and utilization,this article designed and set up the low temperature performance test platform.Low temperature performance of thermoelectric module was tested.The impact of the hot and cold side temperature,load pressure,interface materials and other factors on the thermoelectric module was obtained.The experimental results show that increasing thermoelectric module load pressure under the condition of low temperature can improve the performance of the thermoelectric module.But the best load pressure is about 1.1 MPa to 1.5 MPa.Promoting the temperature of thermoelectric module hot side can significantly improve the performance of the thermoelectric module.When the temperature difference between hot and cold side of the thermoelectric module was 43 ℃,the maximum output power of 0.28 W can be attained,and the maximum conversion efficiency can reach to 0.38 %.Seebeck coefficient and electrical resistivity would reduce with the decrease of average temperature of the thermoelectric module,but on the contrary the thermal conductivity would increase as thermoelectric module under the condition of low temperature.And ZT value of the module cut down with temperature decrease,in low temperature the value is 1/10 of that in room temperature.Graphite paper is more appropriate for reducing the thermal contact resistance under the condition of low temperature.With the purpose of combining the boiling heat transfer of natural gas with thermoelectric generation and applying it to real cold energy recovery,take the liquid nitrogen as the cold source and air as the heat source,this paper designed and built the experimental system of cold energy thermoelectric generation.The experimental study of thermoelectric properties of the cold energy thermoelectric generator has been carried out.The influence law of the liquid nitrogen boiling heat transfer on thermoelectric generation characteristics been acquired,too.The experimental results show that as the gasification of liquid nitrogen,the flow channel area divided into liquid phase region,two-phase region and gas phase region,which are mainly liquid phase region and two-phase region When the liquid nitrogen flow is larger,the temperature difference between the hot and cold side and the open circuit voltage increases gradually along the flow direction.However,as flow is small the length of the gas phase region is greater than the liquid phase region and the two-phase region,the temperature difference between hot and cold side and the open circuit voltage are decrease first and then increase.But the increase amplitude of the open circuit voltage is smaller due to the effect of material properties.In addition,with the increase of liquid nitrogen flow,maximum output power of the generator increase obviously.As flow is 125 SLPM,maximum output power of the system reached to 0.14 W.At the end of the paper points out that the hot and cold side temperature difference is far less than it between cold and heat source and poor performance of the thermoelectric module at low temperature are the key factors to restrict cold energy thermoelectric generation properties.