喉管与喷嘴截面积比对射流式鱼泵输送性能及鱼损的影响

为探究喉管与喷嘴截面积比对射流式鱼泵输送性能及鱼损的影响规律,该文设计了喉管与喷嘴截面积比分别为1.75和3的射流式鱼泵,以鲫鱼为试验对象进行鱼类输送试验,获得了不同喉管与喷嘴截面积比射流式鱼泵的输送能力及单位质量能耗,并采用表观损伤统计、解剖和血清指标检测等方法分析了射流式鱼泵喉管与喷嘴截面积比对鲫鱼损伤的影响。研究结果表明:在相同被吸流体流量工况下,喉管与喷嘴截面积比较小的射流式鱼泵输送鱼类能力较强,且单位质量能耗较低。试验中喉管与喷嘴截面积比为1.75的射流式鱼泵输送鱼类能力达到1913kg/h,而单位质量能耗仅为1.51 kW?h/t。鱼类损伤的主要类型是局部鳞片少量脱落(轻度损伤),约占所有过泵鱼类的10%。在相同被吸流体流量下,喉管与喷嘴截面积比较小的射流式鱼泵中鱼类轻度损伤率较高,而喉管与喷嘴截面积比对重度损伤率影响较小;喉管与喷嘴截面积比较大的射流式鱼泵在输送过程中对少数鲫鱼肝脏造成的损伤较严重;而不同喉管与喷嘴截面积比射流式鱼泵输送过程均会对鲫鱼肾脏造成影响,但是这种影响在24 h内可以恢复到未过泵时的水平。综合考虑输送能力及鱼损情况,喉管与喷嘴截面积比为1.75的射流式鱼泵更适合鱼类输送。研究结果可为射流式鱼泵推广应用提供支持并可作为其优化设计的参考。

Influence of sectional area ratio of throat to nozzle on transportation capacity and fish injury in jet fish pumps

Fish have been an important human food source for a long time. In recent years, the development of high tech fisheries such as large-scale deep-water cages has led to a dramatic increase in the global supply from capture fisheries. However, traditional methods of fish transport by heavy lifting in a fish container are energy-intensive and result in great fish loss. Fish pumps have been developed as an efficient substitute for aquaculture to transfer the fish using less energy intensive systems and fewer losses that preserve the fish freshness. According to the operating principle, fish pumps can be classified as impeller fish pumps, pressure/vacuum fish pumps, and jet fish pumps. The impeller fish pumps have a special design to adapt to fish transport and the high-speed rotating impeller provides high transport capacity of fish but results in high fish mortality and injury rates. The water-ring vacuum-pump drives utilize vacuum and high-pressure regions which treat the fish more gently but lower capacities because of the discontinuous operations during suction and discharge stage. In the jet fish pump, the primary flow goes into a suction chamber via an annular nozzle and then creates a suction force on the secondary flow carrying the fish. The fish-water mixture then flows through the nozzle, throat and diffuser and is finally pumped out. Among these fish pumps, jet fish pump has the highest comprehensive properties giving consideration to transport capacity and mortality rate. Typical jet fish pump is composed by a suction duct, a primary duct, an annular nozzle, a suction chamber, a throat and a diffuser. The area ratio is the ratio of the throat sectional area to the annular nozzle sectional area and is a key parameter in a jet fish pump. In present paper, jet fish pumps with different area ratios (1.75 and 3) were designed and a series of experiment were conducted to study the transportation performance of jet fish pumps and relative injuries of Carassius auratus. The experiment results showed that the jet fish pump with smaller area ratio had a higher transportation capacity in the same secondary flow rate operation condition. The difference of transportation capacity caused by area ratio increased as the rise of secondary flow rate and the maximum transportation capacity difference reached 748 kg/h in the experiment. Moreover, the jet fish pump with smaller area ratio had lower energy consumption per unit mass in the same secondary flow rate operation condition. The difference of energy consumption per unit mass caused by area ratio increased as the rise of secondary flow rate and the maximum transportation capacity difference reached 1.31 kW?h/t. In the experiment, the external injuries of fish were classified as mild and severe injuries, and the main type external injury was mild injury. The severe injury rates caused by jet fish pumps with different area ratios showed no significant difference. Yet, the fish transported by the jet fish pump with smaller area ratio had a higher mild injury rate. The organs and serum of Carassius auratus were also checked. The transportation process of jet fish pumps affected the liver of fish and this influence was more significant when fish were transported by the jet fish pump with a bigger area ratio. The kidney of fish was also influenced but it could recover in 24 h after the transportation of jet fish pumps. Considering the transportation capacity and fish injury rates, the jet fish pump with smaller area ratio was more suitable for fish transportation. Consequently, the main contribution of our work is to demonstrate the influence of jet fish pump area ratio on the transportation performance and fish injuries caused. More importantly, the present paper provides guidelines for optimizing jet fish pumps considering transportation performance of jet fish pumps and injuries of fish.