Study On Heat Transfer In Dense Fluidized Granular Target

Accelerator Driven Sub-critical System(ADS)can effectively transmute nuclear waste,and spallation target is one of the key components of ADS.In the study of ADS,the concept of dense granular target(DGT)was proposed by Institute of Modern Physics,Chinese Academy of Sciences.Dense granular target is a relatively novel target design scheme.Solid particles are used as spallation material and cooling medium as well.The beam interacts with particles by spallation reaction to release neutrons.The temperature rise of particles in the target is not only related to beam current,but also closely related to particle velocity and environmental conditions.Controlled nuclear fusion is one of the effective ways to solve future energy problems.The International Thermonuclear Experimental Reactor(ITER)project has been launched internationally,in which high-flux neutron sources are required to conduct radiation damage experiments on fusion structural materials.With the support of ADS pilot project and ITER neutron source project,the research team has carried out research on the Compact Materials Irradiation Facility(CMIF).CMIF refers to the experience of ADS dense granular target and adopts the design of chute beryllium granular target.Both ADS target design and CMIF target design need to consider the beam and target coupling problem as well as the efficiency of remote heat transfer.The study on heat transfer of dense granular system is one of the keys to solve the above problems.At present,the research on heat transfer of dense granular target system mainly focuses on simulation calculation.Various heat transfer models have been established,but the experimental research on heat transfer of dense granular flow is relatively few.Therefore,the heat transfer experiment of particles has quite important in both engineering and theoretical value.The main research contents include:(1)The granular flow heating device of moving bed was built,and the heat transfer of high-temperature granular flow was experimentally studied by contact and noncontact temperature measurement,so as to obtain the average heat transfer coefficient of different particles under different working conditions,and the comparison was made with the Bauer two-zone heat transfer model.The results showed that the heat transfer of moving bed was consistent with the Bauer two-region model.With the increase of contact time,the average heat transfer coefficient of particle moving bed decreases.The average heat transfer coefficient of particle moving bed increases with the increasing of particle thermal conductivity and gas thermal conductivity.The experimental results were consistent with the results of Schlünde's empirical formula.(2)CMIF is a Be(d,xn)neutron source driven by a 50 MeV@10 mA continuous wave(CW)deuteron beam with a granular chute target.Beryllium particles are used as both targets and thermal removal media.In this paper,the chute target of beryllium particles is studied by discrete element method.The stability of granule chute flow is studied.The relationship between radiation conditions and beam target parameters is studied.With the decrease of beam spot,the thermal density increases.At the same time,numerical simulation of flow granular heat transfer was carried out for the chute target system being operated in a helium environment(1atm).The maximum temperature rise of particles was about 550 K.Finally,the heat removal for the backplate and also irradiation damage were investigated.(3)Based on the concept of granular chute target,a CMIF cold prototype was designed and established.The design scheme of the key parts of the prototype is described briefly.Meanwhile,off-line experiments were carried out on some key parts of the prototype,including chute flow experiment,heat exchange experiment and longterm stability experiment.CMIF cold prototype currently run 120 hours without failure.