不同工质对大型联合收割机余热回收的热力学性能

Thermodynamic performance of waste heat collection for large combine harvester with different working fluids

为了协同收集农作物联合收割机缸套循环水和烟气2种品位的余热,该文采用LR6A3L型号的内燃机进行试验,获得了在全负荷变速情况下的余热特性参数;选取2 200和1 700 r/min这2个试验工况点,采用工质R123、R245fa、R152a、R600和水建立了单种工质和2种工质分别协同收集2种品位余热的数学模型,并进行了热力学性能分析。结果表明:采用单种工质收集2种余热时,相同条件下,采用工质R245fa单位换热量所产生的?损最小,分别为0.122和0.129 k W;采用R152a和R1232分别收集缸套循环水和烟气2种余热,在相同条件下,吸收单位热量所产生的?损最低,分别为0.156和0.154 k W,且换热后产生的温升最高。研究结果可为联合收割机余热即时干燥粮食提供参考。

With increasing energy crisis, energy conservation is imperative. Newly harvested grain without timely drying will cause germination, mildew and other issues. In China, a huge amount of grain is wasted by mildew and germination every year, just because grain has not been dried below the safe moisture in time. If the grain moisture content is timely reduced during the harvest, it can reduce the possibility of grain germination and mildew and extend the shelf life. However, in the operation of crop combine harvester, most of the energy released by fuel combustion is lost in the form of flue gas and cylinder circulating water residual heat, and only a little is used to do work. And the energy recovery potential is huge. In order to achieve the full utilization of energy, this paper conceives the use of waste heat from combine harvester to dry newly harvested grain instantly. For the combine harvester, the change of actual operation conditions will lead to the change of the waste heat, mainly including the jacket water and exhaust heat. In order to collect these 2 kinds of waste heat with different quality synergistically, the waste heat characteristics of the harvester engine are explored through the experiment with the LR6 A3 L type diesel engine. In this experiment, the parameters of the diesel engine waste heat under the condition of full load were obtained, which included output power, fuel consumption, jacket water flow, jacket water import and export temperature, exhaust gas flow, exhaust gas temperature, diesel engine speed, and so on. Based on the advantages of organic working fluid in recovery of waste heat under changing working conditions, R123, R245 fa, R152 a, R600 and water were selected, and 2 models of collecting the 2 grades of waste heat were built using the single working fluid and 2 kinds of working fluids among these 5 working fluids selected under 2 rotating speeds of 2 200 and 1 700 r/min respectively. Additionally, the thermodynamics analysis on each condition was performed. The results show that, for the single working fluid collecting the waste heat of combine harvester diesel engine, water, R600 and R152 a exhibit the biggest capacity to collect the waste heat, which is 106.66 and 92.12 k W under the 2 rotating speeds, and for R152 a, the temperature rise after the heat exchange is the highest and is 76.4 and 82.57 ℃ respectively for the 2 rotating speeds. The exergy loss per heat collected is the smallest and is 0.122 and 0.129 k W respectively for the 2 rotating speeds using R245 fa. For 2 kinds of working fluids collecting the 2 grades of waste heat, the 6 combinations of working fluids of R152 a and R123, R152 a and R245 fa, R600 and R123, R600 and R245 fa, water and R123, water and R245 fa are selected. And each combination can reach the maximum of the heat transfer under each condition, which is 106.89 and 92.2 k W respectively. For the combination of R152 a and R123, the exergy loss per heat collected is the smallest and is 0.156 and 0.154 k W respectively for the 2 rotating speeds. And the temperature rise after the heat exchange is the highest, and is 69.18 and 58.98 ℃ respectively for R152 a and R123 under 2200 r/min rotating speed, and 64.94 and 53.65 ℃ under 1700 r/min. These results will be helpful to the next work of drying the grain using the waste heat from combine harvester.