Research On Rankine Cycle Based Hydraulic Retarder Thermal Management System

A hydraulic retarder operates in the manner of converting the kinetic energy of axle into the retarder oil heat energy completely.To the conventional hydraulic retarder thermal management system,the oil temperature is managed by the engine cooling system.As the limited engine cooling system cooling capacity,the hydraulic retarder oil heat power cannot be too high,making the hydraulic retarder torqure performance is affected.From the perspective of waste heat recovery,the largest heat energy of hydraulic retarder working fluid can reach up to 500 kW,which has a certain revovery potential.Organic Rankine Cycle(ORC)uses phase change heat transfer,which has a better heat transfer efficiency than single phase heat transfer.And by controlling the operation of the ORC system,we can control the temperature of heat source.Moreover,as a promising technology for low and medium-grade heat recovery,ORC has advantages of high thermal efficiency,simple structure,as well as low maintenance costs.Based on theses,we proposed a novel hydraulic retarder thermal management system utilizing ORC technology.In the system,hydraulic retarder oil temperature is managed by using ORC technology,which achieves a more accurate temperature control.At the same time,recovery of hydraulic retarder oil heat energy can be achieved,without affecting the hydraulic retarder braking performance.And some key problems are studied.From oil heat generation mechanism heat balance equations,the main influencing factors of the hydraulic retarder oil temperature are analyzed.Based on the working oil viscosity-temperature and density-temperature characteristics,the retarder baking torque performance under different oil temperature is obtained by using CFD numerical simulation method.And the oil temperature value when the braking torque tends to be stabilized is obtained.From the retarder working oil waste heat quantity and quality point of view,combining with exergy analysis mechod,and heat transfer reate and the temperature change of the retarder oil under the typical working condition are obtained.Analysis of different blade front lean angles and oil inlet and outlet structure arrangements are conducted.A scheme of hydrodynamic retarder-ORC thermal management system is proposed,thermodynamic models of the system are established,and the optimal organic working fluid of the ORC is selected.According to the environmental condtions,dry and wet property,flammability,suitable temperature range and thermosphysical properties of the different organic working fluids,six primary fluids of R123,R11,R245 ca,R245fa,R141 b and R365 mfc are primary selected.By selecting a typical retarder heat source condition and extreme heat source conditions,considering the system condition adaptability,thermodynamic performance,equipment degree of perfection of the thermodynamics,as well as heat transfer area of the evaporator,the performances of the different working fluid systems are compared and analyzed.The results show that the R245 ca has a better adaptability and the heat transfer area of the evaporator is smaller under the typical heat source condition,while R365 mfc behaves better in the exergy destruction rate and exergy efficiency.In the cases of extreme heat source,R245 ca evaporation area is smaller,whiles R365 mfc performs better in other aspects.Considering all the factors,R245 ca is finally chosen as the optimal organic working fluid of the ORC subsystem.The working parameters of ORC have important influence on the performance of the system.Therefore,evaporating pressure,condensing temperature,evaporator pinch point temperature difference(PPTD)and degree of superheat are analyzed.Results show that,increasing evaporating pressure or reducing condensing temperature can significantly improve the system thermal efficiency and exergy efficiency,meanwhile,an increasing evaporating pressure makes the evaporator heat transfer area first increase and then decrease,and a decreasing condensing temperature makes the area decrease slightly.PPTD does not affect the system thermal efficiency and exergy efficiency,but will obviously change the evaporator heat transfer area.And the increase of superheated degree makes the thermal efficiency and exergy efficiency decrease slightly.In the ORC based hydraulic retarder thermal management system,the ORC subsystem needs to be regulated to make the oil achieve the appropriate target temperature,aiming to meet the requirements of hydraulic retarder braking performance.For this reason,two kinds of temperature control methods are proposed,that is,a given temperature control and variable temperature control for the retarder oil temperature at the outlet of the evaporator.By comparing the two methods from the aspects of temperature regulation result,parameter adjustment mode and the influence on the system,it is found that,under the appropriate operating parameters,both two kinds of temperature regulation can achieve the target temperature adjustment,and the latter is simpler,and has a higher thermal efficiency.However,retarder oil temperature could not adjusted too high,since high temperature will deteriorate the oil lubrication and sealing performance.The hydraulic retarder test bench is built,and reliability of the CFD numerical simulation results is verified by testing the partial torque temperature characteristics of the retarder.At the same time,through a reasonable program design and component selection,using constant temperature oil tank simulating of hydraulic retarder heat source conditions,the ORC based hydraulic retarder thermal management system prototype bench is setup.The reliability of the temperature control model is verified by experiments.Meanwhile,the influence of heat source mass flow rate is analyzed experimentally.Finally,by testing the expander,the characteristics of the load torque,relationship between loas torque and evaporating pressure,and impacts of load torque on the system are studied.