Yuto Takeuchi

Quasi-steady nucleate boiling and its life caused by large stepwise heat input in saturated pool liquid He I☆

Abstract Quasi-steady nucleate boiling on a horizontal cylinder in liquid He I caused by large stepwise heat input, whose height was far beyond the value corresponding to the steady critical heat flux, was investigated. It was confirmed that quasi-steady nucleate boiling exists with a certain life at the state corresponding to the point on the extension of the steady nucleate boiling curve. The correlation to express the life for the step heat input was given as a function of quasi-steady nucleate boiling heat flux. Another correlation to express the total energy transferred to the liquid from the cylinder surface before the end of quasi-steady nucleate boiling for a step heat input was also derived. It was made clear that this correlation is applicable not only to step heat input but also to the heat input which increases exponentially at first and then keeps constant (exponential step heat input). Namely, it is possible by using the correlation to predict the time when the quasi-steady nucleate boiling terminates after the addition of step and exponential step heat inputs.

Preliminary design of high temperature lithium-lead blanket with SiC cooling panel

A high temperature lithium-lead blanket, which can be made within a limited extrapolations of present technology, has been proposed. The blanket structure is based on F82H as vessel material, and Pb-17Li as breeder. SiCf/SiC cooling panel is inserted between them to achieve high temperature extraction of Pb-17Li while maintaining F82H under allowable temperature limit. Neutronic analysis using ANISN code has been conducted to assess tritium breeding capability, shielding performance, and nuclear power generation. Heat transfer for the Pb-17Li streams has been calculated considering MHD pressure loss to be acceptable. Temperature distribution in the F82H vessel and SiCf/SiC cooling panel has been calculated using ANSYS Version 10.0. The results show that the maximum temperature of the F82H does not exceed 550 °C with He flow velocity of 60 m/s. The thermal-hydraulic evaluations of heat transfer media based on the experimental data shows that the overall heat transfer coefficient between SiC and Pb-17Li in the blanket is estimated to 650-800 W/m2K.

Hydrogen Production from Biomass using Nuclear Fusion Energy

Hydrogen deserves of a future energy medium in terms of global environmental issues and fossil resource constraints. This study intends to examine the feasibility of hydrogen production process by nuclear fusion heat. This process potentially provides hydrogen at significantly better efficiency than other proposed reaction such as electrolysis from renewable source with little CO2 emission, and is formulated as (C6H10O5)n+mH2Orarr6nH 2+6nCO-n814 kJ. The experimental result at 1273 K showed complete gasification of cellulose, and hydrogen was obtained at the conversion efficiency of respectively 40 percent of material and 50% of heat. A concept of a reactor and fusion-hydrogen plant is presented

Natural convection heat transfer from a horizontal cylinder in liquid sodium: Part 2: generalized correlation for laminar natural convection heat transfer

Abstract Rigorous numerical solution of natural convection heat transfer, from a horizontal cylinder with uniform surface heat flux or with uniform surface temperature, to liquid sodium was derived by solving the fundamental equations for laminar natural convection heat transfer without the boundary layer approximation. It was made clear that the local and average Nusselt numbers experimentally obtained and reported in part 1 of this paper were described well by the numerical solutions for uniform surface heat fluxes, but that those for uniform surface temperatures could not describe the angular distribution of the local Nusselt numbers and about 10% underpredicted the average Nusselt numbers. Generalized correlation for natural convection heat transfer from a horizontal cylinder with a uniform surface heat flux in liquid metals was presented based on the rigorous theoretical values for a wide range of Rayleigh numbers. It was confirmed that the correlation can describe the authors’ and other workers’ experimental data on horizontal cylinders in various kinds of liquid metals for a wide range of Rayleigh numbers. Another correlation for a horizontal cylinder with a uniform surface temperature in liquid metals, which may be applicable for special cases such as natural convection heat transfer in a sodium-to-sodium heat exchanger etc. was also presented based on the rigorous theoretical values for a wide range of Rayleigh numbers. These correlations can also describe the rigorous numerical solutions for non-metallic liquids and gases for the Prandtl numbers up to 10.

Estimation of Kapitza conductance effect on steady and transient boiling heat transfer in He I based on Kapitza conductance results in He II

Abstract Kapitza conductance in steady and transient boiling heat transfer on a horizontal 0.2-mm diameter test wire was estimated based on the measured Kapitza conductance value for the same surface in He II. The He II experiments performed are for liquid temperatures ranging from 1.8 to 2.1 K under atmospheric pressure, and the He I experiments of the steady and transient heat transfer caused by exponential heat inputs are for the periods ranging from 0.2 ms to 10s under saturated conditions at liquid temperatures ranging from 2.2 to 4.2 K, and subcooled conditions for the subcooling of 1.0 and 2.0 K at atmospheric pressure. The Kapitza conductance in He I is higher for higher saturation temperatures but little dependent upon heat flux, liquid subcooling, and heat input increasing rate. The temperature drop due to the Kapitza conductance for the wall superheat becomes more significant with the increase in heat flux and in saturation temperature. It was confirmed that the Kapitza conductance in He I can be estimated correctly based on the Kapitza conductance value for the same surface in He II.

Natural convection heat transfer from horizontal rod bundles in liquid sodium. Part 2: Correlations for horizontal rod bundles based on theoretical results

Natural convection heat transfer from horizontal rod bundles in Nxm × Nym arrays (Nxm, Nym = 5–9) in liquid sodium was numerically analyzed for three types of the bundle geometry (in-line rows, staggered rows I and II). The unsteady laminar two-dimensional basic equations for natural convection heat transfer caused by a step heat flux were numerically solved until the solution reaches a steady state. The PHOENICS code was used for the calculation considering the temperature dependence of thermophysical properties concerned. The surface heat fluxes for each cylinder were equally given for a modified Rayleigh number, Rf, ranging from 0.0637 to 63.1 (q = 1×104 to 7×106 W/m2). Sx/D and Sy/D for the rod bundle, which are the ratios of the distance between center axes on the abscissa and the ordinate to the rod diameter, respectively, were ranged from 1.6 to 2.5 on each bundle geometry. The spatial distribution of Nusselt numbers, Nu, on horizontal rods of a bundle was clarified. The average value of Nusselt number, Nuav, for three types of bundle geometry with various values of Sx/D and Sy/D were calculated to examine the effect of the array size, S/D and Rf on heat transfer. The bundle geometry for the higher Nuav value under the condition of Sx/D×Sy/D = 4 was examined by changing the ratio of Sx/Sy. A correlation for Nuav for the three types of bundle geometry above mentioned including the effects of Sx/D and Sy/D was developed. The correlation can describe the theoretical values of Nuav for the three types of bundle geometry in Nxm × Nym arrays (Nxm, Nym = 5–9) for Sx/D and Sy/D ranging from 1.6 to 2.5 within 10% difference.

High Temperature Operation of LiPb Loop

Abstract By introducing an induction heater and combination of a compact heat exchanger and a helium loop as a cooler, high temperature operation of lithium-lead loop at Kyoto University was performed successfully. After modification of thermal insulation, reasonable temperature distribution was obtained and sufficient effective heating power of 2.7kW and heating efficiency of 40% was demonstrated without concern about overheating of downstream of the high temperature section. As a result, observed highest temperature is 926°C and 4 hours continuous operation above 900°C was achieved.

Development of high temperature SiC/SiC composite intermediate heat exchanger for He and LiPb

In order to develop a compact intermediate heat exchanger which is applicable for high temperatures above 900°C, assuming HTGR (high temperature gas cooled reactor), a heat exchanger module made of SiCf/SiC composite has been designed, fabricated and tested with LiPb-He double loop. The heat transfer from liquid metal to gas has been measured, and heat transfer of ≫1.3kW and reasonable heat exchange performance are obtained with 10cm × 10cm × 3cm test module. The results also show that the heat transfer from the IHX module to fluid is predominant in overall heat transfer coefficient.

Natural convection heat transfer from horizontal rod bundles in liquid sodium. Part 1: Correlations for two parallel horizontal cylinders based on experimental and theoretical results

Natural convection heat transfer coefficients on two parallel horizontal test cylinders in liquid sodium were obtained experimentally and theoretically for various setting angles, γ, between vertical direction and the plane including both of these cylinders’ axes, over the range of 0°–90°. Both test cylinders are 7.6 mm in diameter and 50 mm in heated length with the ratio of the distance between each cylinder axis to the cylinder diameter, S/D, of 2. Theoretical equations for laminar natural convection heat transfer from the two horizontal cylinders were numerically solved for the same conditions as the experimental ones. The average Nusselt numbers Nu on the cylinders obtained experimentally were compared with the corresponding theoretical values on the Nu versus modified Rayleigh number Rf [= Gr*Pr2/(4 + 9Pr1/2 + 10Pr)] graph. The experimental values of Nu for the upper cylinder are about 20% lower than those for the lower cylinder at γ = 0° for the range of Rf tested here. The value of Nu for the upper cylinder becomes higher and approaches that for the lower cylinder with the increase in γ over the range of 0°–90°: the values for each cylinder agree with each other at γ = 90°. The values of Nu for the lower cylinder at each γ are almost in agreement with those for a single cylinder. The theoretical values of Nu on two cylinders except those for Rf < 4 at γ = 0° are in agreement with the experimental data at each γ with the deviations less than 15%. Correlations for two cylinders were obtained as functions of S/D and γ based on the theoretical solutions. A combined correlation for multi-cylinders in a vertical array based on the correlations for two cylinders was developed. The values by the correlation agree with the theoretical solution for the multi-cylinders for Rf ranging from 4.7 to 63 within 10% difference.

Hydrogen production from biomass using high temperature nuclear heat

Abstract The paper proposes a conceptual design of hydrogen production system with unused biomass wastes and steam generated from high temperature nuclear power systems including fusion reactor. A reaction of interest is expressed as a formula, (C6H10O5)n + nH2O => 6nH2 + 6nCO, which is accompanied by a large quantity of endothermic reaction. Basic experiments have been made of thermal decomposition of cellulose, specimen as biomass resource, with the aid of high temperature steam of 1000 deg C heated by an infrared image furnace. The endothermic quantity was evaluated from a numerical model in which measured temperatures are employed. The numerical results for endothermic quantity agreed well with the theoretical value of 816 kJ/mol. To discuss the technical feasibility of the present process, the conceptual design of a hydrogen production reactor system of heat exchanger type was made with the numerical results and heat transfer correlations for helium and steam flow. The present biomass based process, producing both electricity and more hydrogen than other processes such as water or steam electrolysis using an equivalent quantity of heat source, is characterized as an efficient hydrogen production method using nuclear thermal energy, which simultaneously contributes to reduce biomass wastes.