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Abstract This paper addresses three main subjects in supercritical heat transfer: (1) difference in thermal characteristics between upward and downward flows; (2) effect of simulating flow channel shape; (3) evaluation of the existing supercritical heat transfer correlations. To achieve the objectives, a series of experiments was carried out with CO2 flowing upward and downward in a circular tube with an inner diameter of 4.57 mm and an annular channel created between a tube with an inner diameter of 10 mm and a heater rod with an outer diameter of 8 mm. The working fluid, CO2, has been regarded as an appropriate modeling fluid for water, primarily because of their similarity in property variations against reduced temperatures. The mass flux ranged from 400 to 1200 kg/m2 s. The heat flux was varied between 30 and 140 kW/m2 so that the pseudo-critical point was located in the middle of the heated section at a given mass flux. The measurements were made at a pressure of 8.12 MPa, which corresponds to 110% of the critical pressure of CO2. The difference between the upward and downward flows was observed clearly. The heat transfer deterioration was observed in the downward flow through an annular subchannel over the region beyond the critical point. Several well-known correlations were evaluated against the experimental data, and new correlations were suggested for both a tube and an annular channel.

Nowadays, wave energy plays an important role in renewable energy resource. In over thirty years, researches in wave energy converter system (WEC) have been deployed and carried out. This paper presents a design of wave energy converter using 5 cylinders combining with hydraulic power take-off system in order to convert the mechanical energy from ocean wave to electricity, or another useful and usable source. The WEC uses ordered 5 cylinders to represent the motion of the floating buoy under the wave elevation. The design and specification of the WEC system are presented. Buoy and wave interaction mathematical model is built and the hydraulic mathematical model is also presented. The system performance test is implemented and the result is shown.

In this study, numerical simulations and performance evaluation has been carried out to investigate performance characteristics of air-type high pressure piston pump. ANSYS and CFX were applied for analyzing the structure and flow behavior of air-type high pressure piston pump, respectively. The performance evaluation of high pressure piston pump was performed experimentally, the results were compared with simulation. It was found that the freezing phenomenon was improved by 20% and the pressure fluctuation decreased by 50%, compared with the previous pump.

In this study, heat transfer and thermal performance of a periodically dimple-protrusion patterned surface have been investigated to enhance energy-efficiency in compact heat exchangers. The local heat transfer coefficients on the dimple/protrusion walls are derived using a transient TLC (Thermochromic Liquid Crystal) technique. The periodically patterned surface is applied to the bottom wall only or both the bottom and top walls in the test duct. The ratio of dimple (or protrusion) depth to duct height is 0.25, and the ratio of duct height to dimple (or protrusion) print diameter is 1.15. The Reynolds number is tested in low range values from 1000 to 10000. On the single-side patterned walls, various secondary flows generated from the dimple/protrusion coexist. The vortices induced from the upstream affect strongly on the downstream pattern. For the double-side patterned wall case, vortex interaction affected by the opposite wall enhances highly the heat transfer. The heat transfer augmentation is higher in the lower Reynolds number due to the effective vortex interactions. Therefore, the performance factor considering both heat transfer enhancement and pressure loss increases with decreasing the Reynolds number.

This study investigates the relationship between violent conflict, food price, and climate variability at the subnational level. Using disaggregated data on 113 African markets from January 1997 to April 2010, interrelationships between the three variables are analyzed in simultaneous equation models. We find that: (i) a positive feedback exists between food price and violence - higher food prices increase conflict rates within markets and conflict increases food prices; (ii) anomalously dry conditions are associated with increased frequencies of conflict; and (iii) decreased rainfall exerts an indirect effect on conflict through its impact on food prices. These findings suggest that the negative effects of climate variability on conflict can be mitigated by interventions and effective price management in local markets. Creating environments in which food prices are stable and reliable, and markets are accessible and safe, can lower the impacts of both climate change and conflict feedbacks.

The Energy Information Administration (EIA) of the U.S. Department of Energy has projected net electricity generation through 2040 for ten selected countries and the world. These ten countries including China and the U.S. are projected to produce 70% of the world electricity generation. Some of the past projections by EIA have been rated too conservative. Using a simple experience curve, we produce alternative projections for comparison. Our projections are significantly higher for eight out of the ten countries. Utilities operating in these eight countries may need to reexamine their plan for future net electricity generation.

Abstract A polymer-based flexible pulsating heat pipe (FPHP) as a flexible heat spreader was developed, and a series of experiments were conducted to evaluate the thermal performance and the long-term reliability of the FPHP. The FPHP consisted of a multilayer laminated film and a low-density polyethylene (LDPE) sheet. HFE-7000 was used as the working fluid, and the width, length, and thickness of the FPHP were 53.4 mm, 85.5 mm, and 1 mm, respectively. To minimize the permeation of non-condensable gases (NCGs) in a lateral direction, the heat-sealed flanges were covered with the indium coating. Owing to the indium-coated flanges, the long-term reliability of the FPHP drastically increased. The lifetime of the FPHP was defined to evaluate the long-term reliability. The FPHP had a lifetime of 18.2 days in the acceleration test environment, which was equivalent to 306 days in a standard atmosphere and 17 times longer than the previous polymer-based PHP. The FPHP had the thermal resistance of 2.41 K/W, which is 37% lower than that of the copper reference sample in a vertical orientation. Under bending conditions as well as in a horizontal orientation, the FPHP still operated well as a PHP, but the thermal resistance increased slightly. The fabrication method of the FPHP is effective in minimizing the permeation of NCGs in a lateral direction and can pave the way for fabricating a thin flexible heat spreader that has high flexibility, high thermal performance, and long-term reliability.

Abstract This paper presents numerical optimization results for the thermal and effective efficiencies of a solar air heater duct as a function of various roughness geometries on the heated plate. A methodology for the prediction of thermal and effective efficiency of the SAH has been developed on the basis of heat transfer and friction factor correlations. Among the roughness geometries considered, the discrete multiple V-shaped rib results in the best thermal and effective efficiencies over the entire range of design conditions. This work also addresses the scope for future research in the area of roughened SAH ducts and will be helpful for researchers investigating new artificial shapes for SAH ducts to enhance the heat transfer.