| Cylindrical silos have important applications in national defense,such as on-board silos and underground silos.There are precision equipment in the silos,hence an efficient thermal control system is required to maintain the internal temperature at approximately 20 ?.Meanwhile,the infrared stealth of the silos is an important prerequisite for the safety of related equipment.Therefore,we have done the following work in these two aspects.The idea of applying a liquid coil thermal control system to the on-board silos was proposed.The model of the liquid thermal control system(L-TCS)was designed,constructed and experimentally verified.Then,this system and the traditional gas thermal control system(G-TCS)were compared through simulation and engineering calculation.It was found that under stable operation,the pressure drop in the G-TCS mainly comes from the heat exchanger,while the pressure drop in the L-TCS mainly comes from the main part.The flow energy consumption of the G-TCS is 21.8 times that of the L-TCS.The heat loss of the L-TCS and the G-TCS are mainly from the main part,and the difference between the systems in total heat loss is small.Due to the difference in flow energy consumption,the energy efficiency of the L-TCS is 11.6,10.3 and 3.8 times that of the G-TCS in spring,summer and winter,respectively.Accordingly,the L-TCS can save energy by 93.2%,88.7%and 71.3%in spring,summer and winter,respectively.In addition,the L-TCS is superior to the G-TCS in all three seasons in terms of spatial uniformity and temporal stability of the target surface temperature field.In the un-loaded starting,the L-TCS is better in control of the inner surface temperature of the silo while the G-TCS is better in control of the air temperature inside the silo.However,neither system can start up within 5 hours.Adding a fan in the L-TCS allows it to start up within 2 hours.The on-board silos are often on the move,thus their surroundings change frequently.As a result,the traditional passive infrared stealth technology is difficult to achieve a continuous infrared stealth effect on them.An infrared stealth cold plate system for the on-board silos that isolates the silos from the outside environment was proposed and designed.The system dissipates heat to the ambient air,so that its temperature follows the ambient air temperature,thereby reducing the temperature difference between the outer surface of the silo and the land surface to achieve dynamic infrared stealth.The infrared stealth effects under different volume flow rates were simulated and analyzed.It was found that in summer,without the cold plate,the maximum value of the temperature difference between the outer surface of the on-board silo and the land surface in a day(?Tmax)is 28.1 ?;while with the cold plate,when the volume flow rate is 1.694 m3/h,?Tmax reduces to 9.3 ?.In winter,without the cold plate,?Tmax is 6.2?,and ?Tmax dosen't change much with the cold plate.However,the cold plate with just a volume flow rate of 0.906 m3/h can eliminate hot spots on the joints between the side surface and end surfaces.An L-TCS applied to the underground silos was proposed and designed.The model of the system was established and the rationality of setting the soil circumferential side to adiabatic in the model was verified.It was found that,without the L-TCS,in summer,the maximum temperature difference of the target surface can reach 11.9 ?,and the maximum deviation from 20 ? is 9.3 ?.In winter,the maximum temperature difference of the target surface is 16.9 ? and the maximum deviation from 20 ? is 26.5 ?.After the application of the L-TCS,in summer,the temperature range of the target surface is compressed to 19.3?20.0 ?;in winter,it is compressed to 19.1?19.7 ?.Moreover,it was found that the flow consumption is only 0.64 kW·h,and heat consumption is the main part of the total energy consumption in a day.The total energy consumption is 70.96 kW h and 101.54 kW·h in summer and winter,respectively.In addition,an energy saving strategy consisting of a 60.55 m2 solar collector and a 1.87 m3 hot water tank was designed to meet the heat consumption.The exposed surface of the silo and the surrounding soil surface are at the same level,and covering a thin layer of soil can make its infrared emissivity consistent with that of the surrounding soil surface.However,it is difficult to maintain the silo surface and the soil surface at the same temperature.The first reason is that the cover of the silo and the soil are different in thermophysical properties,thus the silo surface and the soil surface have different thermal response to the same environmental conditions.The second reason is that the temperature inside the silo needs to be maintained at approximately 20 ? to ensure the normal operation of equipment inside,while the temperature of the surrounding soil changes periodically.Base on these analyses,we designed an infrared camouflage cloak composed of an imitative layer and an insulation layer from top to bottom.The imitative layer is used to imitate the thermal response characteristics of the soil to the surrounding environment.The insulation layer is used to weaken the influence of the internal temperature field of the silo on the lower boundary of the imitative layer.Then,the composite material composed of alumina powder and silicone rubber was selected as the imitative layer material,and the volume fraction of alumina powder was determined to be 3.18%to make its thermal inertia consistent with that of the soil.Through simulations,it was found that the thickness of the imitative layer does not need to be greater than its thermal penetration depth to achieve a good infrared camouflage effect,and the absence of the insulation layer may result in hot spots on the silo surface in winter and affect the infrared camouflage effect.The thickness of each layer in the cloak was optimized in two steps,and the optimized thicknesses of the imitative layer and the insulation layer are 22 cm and 4 cm respectively.Before application of the optimal cloak,the maximum temperature differences between the average temperatures of the silo surface and the soil surface temperatures both appear at 17:00,and are 1.59 ? and 1.92 ? in summer and winter respectively.After application of the optimal cloak,the maximum temperature differences both appear at 14:00,and are 0.31 ? and 0.21 ? in summer and winter respectively.The designed infrared camouflage cloak can achieve passive infrared camouflage for underground silos in all-weather and full-time. |
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