[en] Short communication

[en] The heat line, as defined by Kimura and Bejan does not involve, explicitly, a reference temperature for the energy converted by the flow. As a result different flow patterns may be obtained for the same physical problem. In this paper the heat function is re-defined and the temperature of the cold wall, in natural convection flow problem inside cavities, is used as reference temperature. The heat function, as defined here, is also written in a generalized coordinate system and is employed to visualize the heat flow in some natural convection problems inside irregular cavities. (author)

[en] The papers deals with a numerical 3D study of natural convection in a finned Rayleigh-Be nard (RB) cubical enclosure. A single fin with a thickness of 10 pour cent of the cavity side (and a height of 50 pour cent ) is placed vertically on the bottom hot wall at T_H. The working fluid is air with Prandtl number Pr = 0.71 and the Rayleigh number (Ra) varies from 10³ to 10⁵. The solid-to-fluid thermal conductivity ratio (k_R) was fixed at R_K = 7000, corresponding to a metal of high conductivity. The top wall is at the temperature T_C < T_H and the remaining four surfaces are insulated. Inside the RB enclosure, the flow structure and the temperature distribution are presented in terms of mean velocity vector plots and isotherm plots. The effects of the Rayleigh number on the mean heat transfer rate through the cold wall are presented and discussed. A correlation between the averaged Nusselt number through the top wall and Ra is proposed

[en] Cotton tents are frequently used in the army and disaster relief. Because of the special structure of the cotton tent, its heat preservation and heat insulation performance is poor in the summer. In order to improve the rest environment of soldiers, experimental studies on improving the internal thermal environment of tents by natural ventilation were done at Tianjin in the summer. The thermal environment parameters of tents with different natural ventilation schemes were recorded and analyzed. The experimental results show that the natural ventilation plays a certain role in adjusting thermal environment of tents. (paper)

No abstract available

[en] Highlights: •Experimental and numerical investigations on expansion tank dynamics are reported. •Investigations on natural circulation loop (NCL) performance are presented. •Role of expansion tank in loop single-phase NCL dynamics has been investigated. •A model has been proposed for expansion tank dynamics. •Role of expansion tank in hysteresis observed experimentally is explained. -- Abstract: Expansion tank is an important component of all single-phase natural circulation loops. The tank serves the twin purposes of venting the air out during the loop filling and accommodation of the swells and shrinkages of the loop fluid during the transient. In the present study, experimental investigations have been carried out in a rectangular single-phase natural circulation loop to bring out the role of expansion tank in loop dynamics. The results on loop stability and transient behavior are discussed. The experimental investigations show that there is significant amount of heat exchange between the main loop fluid and the expansion tank fluid. First, the results of experimental studies are presented. The different flow regimes observed in these experimental investigations are discussed. Next, a model is presented for taking into account the heat exchange between the main loop fluid and the expansion tank fluid. Finally, the model is applied to simulate the dynamic behavior of different single-phase natural circulation loops. The investigations carried out in this study have helped in resolving the issue of hysteresis observed in these loops.

[en] It may be stated that for the calculation of the heat transfer coefficients for natural convection cooling of large-diameter finned surfaces it is necessary to take in consideration the effects of the fin length, fin material and of the azimuthal angle around the cylinder. The present results replace earlier less accurate correlations gained from the same measurements. The new, better correlation was elaborated with the aid of the improved method of evaluation of multiple parameters of a measurement matrix of multiple dimension (one dimension for each parameter), rendering the sum of the squares error a minimum at the same time for the complete matrix. 5 references

[en] To increase the capacity of decay heat removal of a LMR system that uses a natural air circulation cooling, feasibility of heat transfer enhancement has been studied for a planar air channel by introducing a new channel configuration using radiation-convection structures of compact heat transfer surface. For the new channel configuration, the heat transfer mechanism has been investigated and design guides for the radiation-convection structure have been developed based on the investigation results. Following the developed design guides, a new radiation-convection structure has been also devised. Analysis of the air channel cooling with the new radiation structures revealed substantial heat transfer enhancement and the feasibility of the heat transfer enhancement with the new channel configuration design has been confirmed. (orig.)

No abstract available

[en] Short communication