Determination of view factors by contour integral technique

This paper presents the application of contour integral technique to derive the diffuse radiation view factor expressions (analytical) for elements of nuclear reactor fuel bundle. The cases considered are: (i) view factor between two cylindrical rods of equal diameter and finite length, (ii) view factor between two cylindrical rods with interference by another rod and (iii) view factor between a cylindrical rod and a non-concentric cylindrical enclosure. The contour integral method is significantly more accurate than the area-integration method. The view factor results based on the analytical expressions derived for these finite length geometries are compared with that of the exact expressions available in the literature for infinite length. It is observed that the use of infinite length approximations in finite length cases can lead to significant errors. (C) 200

Analytical expressions for configuration factor between cylindrical surfaces in rod bundle geometry

Contour integral technique has been applied to obtain expressions for diffuse radiation configuration factor for cylindrical geometries in a nuclear reactor fuel bundle. The cases studied are: (i) view factor between two cylindrical rods/tubes of different diameter and equal finite length, (ii) view factor between two cylindrical rods with interference from a third rod and (iii) view factor between a cylindrical rod and a concentric cylindrical enclosure, of equal finite lengths. In the literature, contour integral technique has been stated to appreciably be the more precise method than the area integration method. Present configuration factor results of finite length geometries have been compared with that of exact algebraic expressions available in the literature for infinite length. It was observed that the length of the geometry influences the configuration factor results considerably and use of infinite length approximations in finite length cases can lead to significant errors. (C) 2010 Elsevier B.V. All rights reserved

Experimental investigations on heat transfer and frictional characteristics of a turbulator roughened solar air heater duct

An experimental investigation has been carried out to study the heat transfer coefficient and friction factor by using artificial roughness in the form of specially prepared inverted U-shaped turbulators on the absorber surface of an air heater duct. The roughened wall is uniformly heated while the remaining three walls are insulated. These boundary conditions correspond closely to those found in solar air heaters. The experiments encompassed the Reynolds number range from 3800 to 18000; ratio of turbulator height to duct hydraulic mean diameter is varied from, e/D(h) = 0.0186 to 0.03986 (D(h) = 37.63 mm, and e = 0.7 to 1.5 mm) and turbulator pitch to height ratio is varied from, p/e = 6.67 to 57.14 (p = 10 to 40 mm). The angle of attack of flow on turbulators, alpha = 90 degrees kept constant during the whole experimentation. The heat transfer and friction factor data obtained is compared with the data obtained from smooth duct under similar geometrical and flow conditions. As compared to the smooth duct, the turbulator roughened duct enhances the heat transfer and friction factor by 2.82 and 3.72 times, respectively. The correlations have been developed for area averaged Nusselt number and friction factor for turbulator roughened duct. (c) 200

Experimental investigations on decay heat removal in advanced nuclear reactors using single heater rod test facility: Air alone in the annular gap

During a loss of coolant accident in nuclear reactors, radiation heat transfer accounts for a significant amount of the total heat transfer in the fuel bundle. In case of heavy water moderator nuclear reactors, the decay heat of a fuel bundle enclosed in the pressure tube and outer concentric calandria tube can be transferred to the moderator. Radiation heat transfer plays a significant role in removal of decay heat from the fuel rods to the moderator, which is available outside the calandria tube. A single heater rod test facility is designed and fabricated as a part of preliminary investigations. The objective is to anticipate the capability of moderator to remove decay heat, from the reactor core, generated after shut down. The present paper focuses mainly on the role of moderator in removal of decay heat, for situation with air alone in the annular gap of pressure tube and calandria tube. It is seen that the naturally aspirated air is capable of removing the heat generated in the system compared to the standstill air or stagnant water situations. It is also seen that the flowing moderator is capable of removing a greater fraction of heat generated by the heater rod compared to a stagnant pool of boiling moderator

Evaluation of contribution of thermal radiation in transferring decay heat to the moderator, in case of 18 rod bundle facility, simulating advanced nuclear reactors

case of heavy water moderated nuclear reactors, the decay heat of a fuel bundle can be transferred to the moderator available outside calandria vessel. Radiative heat transfer accounts for significant amount of total energy exchange from the fuel bundle during LOCA (loss of coolant accident) situation. In order to simulate one channel of an advanced reactor comprising 54 nuclear rods of 3.5 m length, scaling analysis has been used to scale it down to an 18 rod bundle facility of 1 m test length. The experimental analysis, in order to examine the contribution of energy transfer by thermal radiation and natural convection in removing decay heat of fuel/heater rods using moderator as a heat sink, is presented. It focuses mainly on the role of moderator in removal of decay heat, for situation with air alone in the annular gap between pressure tube and calandria tube coupled with flowing and standstill/boiling moderator situations. Four experimental tests have been presented in this paper. It is seen that, 80% of heat energy is transferred from the heater bundle of rods to the enclosing pressure tube by means of radiation mode, out of this 20-45% of energy is carried away by the moderator. It depends mainly on the resistances involved in the heat flow path and the test set up conditions. (C) 2015 Elsevier Ltd. All rights reserved