基于ORC的柴油机排气余热回收蒸发器传热特性试验与数值分析

EXPERIMENT AND NUMERICAL ANALYSIS OF HEAT TRANSFER PERFORMANCE OF DIESEL ENGINE EXHAUST HEAT RECOVERY EVAPORATOR BASED ON ORGANIC RANKINE CYCLE(ORC)

针对某款柴油机排气余热能量,试制一种板翅式蒸发器并建立热力学模型,通过柴油机排气余热台架试验数据验证模型的准确性与有效性,分析有机朗肯循环(ORC)R245fa工质流量与柴油机排气流量的匹配关系及对蒸发器传热特性和ORC性能的影响。结果表明:在各转速满载工况下,工质流量可在有效工作区间内连续变化,而不必局限于某一指定流量,在该区间内蒸发器及ORC输出净功率和热效率均能保持较好的热力性能;蒸发器传热能力主要受工质影响,在低转速小流量时,蒸发器效能和传热单元数较高,但蒸发器传热系数和传热面积的乘积(UA)和回收的排气能量较低,限制了ORC在低转速一般工况下的应用,在高转速大流量时,传热单元数较低,但UA值和排气余热能量较高,可回收较多的排气余热能量。

According to the exhaust heat energy of a certain diesel engine,a plate-fin evaporator was established based on the organic Rankine cycle(ORC)and the thermodynamic model of the evaporator was established. The accuracy of the model was verified by the diesel engine waste heat recovery bench test data,then the matching relationship of the ORC working fluid R245fa mass flow rate and diesel engine exhaust mass flow rate was analyzed and its influence on evaporator heat transfer performance and ORC performance was studied. The results show that the working fluid mass flow rate can be continuously changed within an effective working range under the full load condition of the diesel engine each speed,and it was not limited to a specified mass flow rate. In each effective working range,the evaporator,ORC net output power and thermal efficiency can be maintained at a good thermal performance;The heat transfer capacity of the evaporator was mainly affected by the working fluid,at low engine speed and small mass flow rate,the evaporator efficiency and the number of transfer units were high,while the product of heat transfer coefficient and effective area for heat transfer(UA)and the recovered exhaust energy were lower,which limited the general operating condition of the ORC at low speed;at high engine speed and large mass flow rate,the number of transfer units were low,but the UA value and exhaust heat energy were higher,and more exhaust heat energy can be recovered.