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[en] Trombe Walls and solar chimneys are examples of passive solar air heating systems. However, the airflow and thermal efficiency characteristics of this type of system are not well understood, and partly for this reason, they are not commonly utilised. This paper reports on an experimental investigation into buoyancy-driven convection in a test rig designed to simulate the operation of a passive solar collector. The test rig comprised a vertical open-ended channel, approximately 1a square, heated from one side. The channel depth could be varied from 20mm to 110mm, and heating inputs varied from 200W to 1000W. Temperatures and airflow rates were measured and recorded, to characterise both steady-state and transient performance. The principal findings are: 1. Time constants (for heating)ranged typically between 30 and 70 minutes. 2. Flow regimes were mainly laminar (Reynolds number varing from ∼500 to ∼4000, depending on heat input and channel depth. 3. The thermal efficiency (as a solar collector and the heat transfer coefficient were functions of heat input, and were not depended on the channel depth. 4. The mass flow rate through the channel increased bath as the heat input increased and as the channel depth increased. The paper presents these findings and discusses their implications in more detail.(Author)
[en] The investigation purpose an experimental study of the natural convection flow. This study simulates the fires evolving in a free and unlimited environment then in interaction with their material surrounding. The fires met such as in the forests in the oil fields and in the tower blocks create a thermal plume which extends in space. The pollutants transported by the fires flows threaten the inhabitants health and cause a natural imbalance of the environment. In reality the thermal plume generated by these fires undergone the influence of the neighbouring walls. Indeed, the walls which surround it are heated by thermal radiation thus creating a thermosyphon flow which interacts with the plume. According to former work, the researchers [16, 20] noticed that the fires can be simulated by a hot source heated by Joule effect. For that, we studied the thermal plume flow generated by a hot rectangular source placed in a free then in a semi-confined environment. To better understand the development mechanisms of the free fire flow and in interaction with surrounding, we simulated these phenomena at the laboratory. In a first time we studied a thermal plume generated by a rectangular source heated uniformly by Joule effect. In a second time the same source is placed at the entry of a vertical canal which its the two Duralumin walls are heated at a constant temperature. The visualization by laser plane enables us to follow the vertical evolution of the flow for two studied configurations. Using hot wire anemometry, we explored the thermal and dynamic field of the flow. In order to better describe the fine structure of the flow, we analyzed the spectra of temperature fluctuations
[en] This paper presents an experimental investigation on the heat transfer characteristics of a vertical flat thermosyphon (VFT). Several tests were performed to assess the effects of filling ratios, hydraulic radius, working fluid, and aspect ratio (Le/4HR) at a vertical orientation on the heat transfer characteristics of the VFT. It was found that the filling ratios and hydraulic radius affect heat flux: while the aspect ratios of VFT increased, the heat flux decreased. In addition, the working fluid changed from water and ethanol to R123 as the heat flux increases
[en] Carbon steel is a sturdy but inexpensive material and is preferred to copper or stainless steel wherever a lower cost is desirable. However, carbon steel-water combination is known to be incompatible for heat pipes due to generation of non-condensible gases during operation. The life time of the carbon steel-water heat pipe was tested based on the Arrhenius model using accelerated life-test scheme. Mass generation of the non-condensible gas was estimated by measuring axial temperature distribution of the heat pipes. The test was conducted with 8 heat pipes and 2 thermosyphons with 1.2-m length and 2.54-cm outer diameter in an elevated temperature range, 165∼250 .deg. C. From the test results, the heat pipe with a chemical retardant added in the working fluid exhibited about 5 years of life time, which was much longer than the one without the additive.
[en] The R3B-Glad superconducting Magnet provides the field required for a large acceptance spectrometer, dedicated to the analysis of Reactions with Relativistic Radioactive ions Beams. In the framework of the FAIR Project to GSI and within NUSTAR physics program, the technical study started in 2006, and the engineering design is undertaken. One main feature of this butterfly-like magnet with graded, tilted and trapezoidal racetrack coils is the active shielding. It makes it possible to decreasing the field by two orders of magnitude within a 1.2 m length, despite the large opening on the outlet side of the magnet (around 0.8 square meters). The fringe field is lower than 20 mT in the target area beside the entry, while the main field is larger than 2 teslas, out of 2 m length. The other principal characteristics are as follows: first, a high level of magnetic forces (300 to 400 tons per meter), with little place to block the coils, requiring a very specific mechanical structure; then, the magnet protection system that is based on an external dump resistor, coupled to a strong quench-back effect, to prevent any damage of the coils which could be caused by the 24 MJ of stored energy; lastly, the indirect cooling of the cold mass with a two-phase helium thermosyphon. The overall size of the conical cryostat will be around 3.5 m long, 3.8 m high and 7 m broad. (authors)
[en] The present study shows the experimental and modeling results of the cooling system using nanofludic loop thermosyphon. The experimental results show that nanofluid is not effective for small scale cooling system. The heat transfer performance is not much improved with the current small scale loop system comparing with the convectional water based loop system. In this study, various effects of nanofluids such as the concentration, the kind of particle, host fluid, and heat capacity and so on were investigated. With nanofluid as the working fluid, the flow instability was improved at a certain concentration
[en] Unlike existing models the operation of heat pipes (TT), using approximation of laminar flow of steam from the evaporator to the condenser [1-3], the model of the relaxation re-work bench press in TT . Experiments in which such a regime is observed. Submitted's mathematical model of this regime and a description of the functioning of the TT in this mode. The possible advantages of the relaxation regime is realized modifying heat pipe, use-forming relaxation mode and shows its great effectiveness.
[en] Experimental investigations were carried out to study heat transfer characteristics of titanium (commercially pure titanium, TA2)/water two-phase closed thermosyphon (Ti/H2O TPCT). Experiments of copper/water (Cu/H2O) TPCT with same dimension and manufacturing process had also been performed for contrast. Experimental results show that there are no remarkable differences of heat transfer coefficients in evaporator (he) between the two kinds of TPCTs, whereas surprisingly the experimental results of heat transfer coefficient in condenser (hc) of Ti/H2O TPCTs are about 2-3 times more than that of Cu/H2O TPCTs, moreover the Nusselt's theoretical correlation based on laminar filmwise condensation is not suitable for simulating the hc of Ti/H2O TPCTs. Experimental results and theoretical analysis of surface free energy difference between condensate and solid surface indicate that the mixed condensation mode with dropwise and filmwise condensation coexisting on titanium surface result in the higher hc for Ti/H2O TPCTs. Experiments on condensation mechanism of titanium surface are ongoing to further validate the point.
[en] During the outage(overhaul) of the CANDU plant, there is a period when the coolant is partially drained to the reactor header level and the coolant is cooled and depressurized by Shutdown Cooling System(SDCS) other than PHTS pump. In the postulated accident of the loss of SDCS-the PHTS pump failure, the primary coolant system should be cooled by the alternate heat sink using the thermosyphon pheonomenon(TS) through the steam generator(SG) This study was aimed at verification and analyzing the core cooling ability of the TS. And the sensitivity analysis was done for the number of SGs used in the TS. As an analysis tool, RELAP5/CANDU was used