Theoretical Analysis For Performances Of Carbon Dioxide Power Cycle And Experiment Research On The Heat Transfer Characteristics

With the shortage of energy and the worsening of environmental pollution,energy conservation,environmental protection and efficiency have become important topics for global scholars.In the field of power cycle,carbon dioxide,as an environmental and efficient working substance,has shown some advantages superior to water.Therefore,many scholars began to study the use of carbon dioxide instead of working fluid.In this paper,the carbon dioxide transcritical Rankine cycle and supercritical Bray cycle were adopted as the research object to analyse carbon dioxide cycle performance and heat transfer characteristics of the experimental study theoretically.In this paper,we study the Rankine cycle and the Braytom cycle based upon the carbon dioxide at first.Using Matlab to transfer the NIST Refprop’s database,the thermal efficiencies of two basic cycles were calculated respectively in the range of heat source temperature of 200 ~ 1000 ℃ and working pressure of 10 ~ 40 MPa.After data analysis,taking into account the actual project,we concluded that it’s benefit to use Braytom cycle when the heat source temperature is above 350 ℃.On the contrary,it is suitable for using Rankine cycle when below 350 ℃.For the thermal cycle with thermal carbon dioxide,the calculation results also show that the low temperature heat source should use Rankine cycle,while the high temperature heat source should choose Braytom cycle.Under the condition of the calculation of this paper,the conditional relation of heat source parameters is given when the two kinds of thermal cycles are equal.Based on the application of high temperature heat source,the law of thermodynamics was used to analyze the exergy loss of work,heat release,compression,endothermic and recuperation in the Brayton cycle of supercritical carbon dioxide.The results show that the heat loss,heat absorption and reheating process cause the largest exergy loss,while the exergy loss of the work and compression is low.That is,the heat transfer process is the weak link in the system.Finally,the experimental study on the heat transfer characteristics of supercritical carbon dioxide was carried out.With the increase of temperature,the heat transfer coefficient of supercritical initial zone rapidly increases.It reaches the peak when the temperature comes to the quasi-critical temperature.After that,it reduces drastically.At last,the heat transfer coefficient decreased gently in the main supercritical region.Enhancement of the working fluid pressure may be not beneficial to the development of the heat transfer.The curves of heat transfer coefficients at different pressures near the quasi-critical point cross each other.For most situation that heat transfer temperature above the point of the quasi-critical point,raising the pressure of the working fluid for heat transfer is very favorable.The heat transfer coefficient is greatly affected by the mass flow of working fluid and the flow of cooling water.