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[en] We consider a system model of a general finite-state machine (ratchet) that simultaneously interacts with three kinds of reservoirs: a heat reservoir, a work reservoir, and an information reservoir, the latter being taken to be a running digital tape whose symbols interact sequentially with the machine. As has been shown in earlier work, this finite-state machine can act as a demon (with memory), which creates a net flow of energy from the heat reservoir into the work reservoir (thus extracting useful work) at the price of increasing the entropy of the information reservoir. Under very few assumptions, we propose a simple derivation of a family of inequalities that relate the work extraction with the entropy production. These inequalities can be seen as either upper bounds on the extractable work or as lower bounds on the entropy production, depending on the point of view. Many of these bounds are relatively easy to calculate and they are tight in the sense that equality can be approached arbitrarily closely. In their basic forms, these inequalities are applicable to any finite number of cycles (and not only asymptotically), and for a general input information sequence (possibly correlated), which is not necessarily assumed even stationary. Several known results are obtained as special cases. (paper: classical statistical mechanics, equilibrium and non-equilibrium)
[en] A micro-channel is a common component in various fields, for example, micro-channel heat sink, compact heat exchanger, and lap-on-a-chip. In this study, we investigated the effects of surfactant on the bubble motion of nitrogen gas in a 510 μm x 470 μm rectangular micro-channel using a sodium dedecyl sulfate (SDS) surfactant. We selected different concentrations of SDS based on the surface tension of water (70 mN/m). The mole fraction of 1.9 mM and 3.71 mM show a surface tension of 60.29 mN/m and 50.62 mN/m, respectively. These will be expressed as Water 70, SDS 60 and SDS 50. More details including experimental facilities and procedure were described in Choi et al.'s previous work
[en] This paper focuses on optimal materials selection for microelectronic heat sinks to maximize the thermal, mechanical and electronic response based on electro-thermal heat transfer analysis using the Ashby approach. In this work, material indices have been developed for a number of properties of heat sinks supported by materials selection tables/graphs. It is found that aluminum based alloys/metals perform better than other available materials for microelectronic heat sinks.
[en] To evaluate the effect of the heat-sink phenomenon induced by artificial ascites on the size of the ablation zone during percutaneous radiofrequency (RF) ablation of the hepatic subcapsular area in an in vivo rabbit model. A total of 21 percutaneous rabbit liver RF ablations were performed with and without artificial ascites (5% dextrose aqueous solution). The rabbits were divided into three groups: a) control group (C, n = 7); b) room temperature ascites group (R, n = 7); and c) warmed ascites group (W, n = 7). The tip of a 1 cm, internally cooled electrode was placed on the subcapsular region of the hepatic dome via ultrasound guidance, and ablation was continued for 6 min. Changes in temperature of the ascites were monitored during the ablation. The size of the ablation zones of the excised livers and immediate complications rates were compared statistically between the groups (Mann-Whitney U test, Kruskal-Wallis test, linear-by-linear association, p = 0.05). One rabbit from the 'W' group expired during the procedure. In all groups, the ascites temperatures approached their respective body temperatures as the ablations continued; however, a significant difference in ascites temperature was found between groups 'W' and 'R' throughout the procedures (39.2± 0.4 .deg. C in group W and 33.4±4.3 .deg. C in group R at 6 min, p = 0.003). No significant difference was found between the size of the ablation zones (782.4±237.3 mL in group C, 1,172.0±468.9 mL in group R, and 1,030.6±665.1 mL in group W, p = 0.170) for the excised liver specimens. Diaphragmatic injury was identified in three of seven cases (42.9%) upon visual inspection of group 'C' rabbits (p = 0.030). Artificial ascites are not likely to cause a significant heat-sink phenomenon in the percutaneous RF ablation of the hepatic subcapsular region
[en] The present paper examines the optimization of triangular microchannel heat sinks. The impact of volume fraction of solid material and pressure drop on the maximum temperature of the microchannel heat sinks are investigated and their optimum operating conditions are compared. From the results, it is seen that increasing the side angle of the triangular microchannel, improves its performance. Furthermore, there is an appropriate agreement between the analytical and numerical results. Finally, the effect of degrees of freedom on the performance of microchannels is investigated. To accomplish this end, the triangular microchannels with the side angle of 60 degree have been chosen as it has the best performance compared to other microchannels. It is observed that the minimized maximum temperatures of optimized microchannel heat sinks with three degrees of freedom are 10% lower than the ones with two degrees of freedom
[en] High duty cycle operation of quantum cascade superlattice lasers with graded superlattice active regions is investigated with the goal of achieving high average optical power. The optical output power increases with pulse width and decreases with heat sink temperature. This behavior is explained on the basis of the laser core temperature oscillations during the pulsed, high duty cycle operation. Between 175 and 325 K heat sink temperature, optimum duty cycles vary from 10% to 1% and average power levels vary from 50 to 1 mW for various lasers used in this study. [copyright] 2001 American Institute of Physics
[en] Since the blanket First Wall (FW) of the International Thermonuclear Experimental Reactor (ITER) is subjected to a high heat and high neutron loads, it is one of the most important components. It composed of a beryllium (Be) layer as a plasma facing material, a copper alloy (CuCrZr) layer as a heat sink and type 316L authentic stainless steel (SS316L) as a structure material. The joining of the three different metals is the key issue to be solved. And more, the peak heat load was assumed to be 0.5 MW/m2 in the initial design of the FW, but it was changed to be up to 5 MW/m2 In Korea, the joining method has developed and it was proved through the several mock-up fabrication and high heat flux tests for confirming the joining integrity. Some of them were tested in the foreign facilities such as JEBIS at JAEA in Japan, TSEFEY at Efremov in Russia, and JUDITH at FZJ in Germany, and others were tested in our own facilities such as KoHLT-1 and -2. And finally, the 1st, recently. Therefore, the FW panel design has been changed for enhancing the cooling and ITER Organization will provide the proposed design. Qualification was passed, in which two 80x80x3 Be/Cu/SS mock-ups were tested under 0.625 and 0.875 MW/m2 heat fluxes for 12,000 cycles and then tested under 1.75 and 1.40 MW/m2 Currently, the 2 heat fluxes for 1,000 cycles at FZJ and SNL, respectively. Currently, the 2nd qualification program was started and the semi-prototype should be fabricated by the end of 2011 for testing under 5.0 MW/m2 heat flux for certain number of cycles. In order to prepare the semi-prototype, several fabrication methods should be developed through the fabrication and test with the several mock-ups. In the present study, small Be mock-up was fabricated as the first step for the preparation. It was fabricated according to the designs considering the currently modified design of the FW. In the present paper, the fabrication objectives, methods, results and related tests were introduced
[en] The thermal performance of a thermoelectric module in a thermoelectric cooling system with a heat sink is analytically and experimentally examined. The thermoelectric cooling system is composed of a thermoelectric module and two heat sinks. The thermal performance of a thermoelectric module (Seepel, Crystal) is analytically taken into account. The results show that COP (Coefficient Of Performance) of a thermoelectric module is reduced and the heat absorbed increases as the input voltage increases. The thermoelectric cooling system with 12V provides 73.3% lower COP and 46.7% higher heat absorbed compared to 5V, experimentally. The theoretical predicted result is in good agreement with the measured data.
[en] Highlights: • Experimental thermal measurements of optimal heat sinks. • Experimental heat sinks obtained by topology optimization. • Bi-material distribution in volume-to-point heat evacuation. - Abstract: For optimal tree-like heat conductive structures obtained numerically by topology optimization (TO), few experimental investigations exist in the literature to author’s knowledge. In this context, the present study deals with an experimental investigation of tree-like structures obtained by topology optimization (known also by bi-material volume-to-point problems). For a volume (of lower conductivity material) that is continuously generating heat, TO predicts tree-like structures (of higher conductivity material) to evacuate efficiently the amount of heat being generated. Experimental measurements were carried out on two tree-like structures using infrared thermography in order to test the validity of the developed numerical topology optimization approach. It is found that the experimental thermal measurements are in good agreement with numerical data obtained by TO, which was developed in this work by coupling the method of moving asymptotes (MMA) as optimization algorithm to the solid isotropic material with penalization (SIMP) as a bi-material distribution technique.