Abstract On icy worlds, the ice shell and subsurface ocean form a coupled system—heat and salinity flux from the ice shell induced by the ice-thickness gradient drives circulation in the ocean, and ...in turn, the heat transport by ocean circulation shapes the ice shell. Therefore, understanding the dependence of the efficiency of ocean heat transport (OHT) on orbital parameters may allow us to predict the ice-shell geometry before direct observation is possible, providing useful information for mission design. Inspired by previous works on baroclinic eddies, I first derive scaling laws for the OHT on icy moons, driven by ice topography, and then verify them against high-resolution 3D numerical simulations. Using the scaling laws, I am then able to make predictions for the equilibrium ice-thickness variation knowing that the ice shell should be close to heat balance. The ice shell on small icy moons (e.g., Enceladus) may develop strong thickness variations between the equator and pole driven by the polar-amplified tidal dissipation in the ice; in contrast, the ice shell on large icy moons (e.g., Europa, Ganymede, Callisto, etc.) tends to be flat due to the smoothing effects of the efficient OHT. These predictions are manifested by the different ice-evolution pathways simulated for Enceladus and Europa, considering the ice freezing/melting induced by ice dissipation, conductive heat loss, and OHT as well as the mass redistribution by ice flow.
The foam-structured reactor is one which has hitherto been regarded as of great potential for industrial applications in the field of solar thermochemistry. The utilization mode of ceramic foam has, ...generally, a significant impact on energy conversion and storage efficiency. This study establishes a numerical model, coupled with computational fluid dynamics and dry reforming of methane reaction kinetics, to find the optimal structural parameters of the ceramic foam. A local thermal non-equilibrium model coupled with the P1 approximation has been developed to address the heat-transfer problems, and the non-Darcy flow effect has been considered to calculate the momentum dissipation in the porous zone. Based on ample simulation examples, the effects of porosity and foam cell size on the reaction temperature, surface heat loss, thermal efficiency, CH4/CO2 conversion, H2/CO yield, carbon deposition, and solar-to-chemical efficiency are illustrated in detail. The results indicate that using the ceramic foam with high porosity and large cell size is able to attain the best thermochemical characteristics, of which the validity can be assured, insofar as the various operating conditions in this study are concerned. Furthermore, as compared to the best single-layer structure, the application of the optimized double-layer foam structure is a more effective solution, which is able to further improve the energy storage efficiency by a remarkable 9.23%.
•The significance of foam structure to thermochemical characteristics is revealed.•CFD coupled with DRM kinetics determines reactor characteristics.•Ceramic foam with high porosity and large cell size refines system performance.•The optimized structure could yield efficiency gains of 10–28%.•Double-layer structure further improves energy storage efficiency by 9.23%.
•High power efficiency and a large amount of DH were achieved by the new proposed system.•The most suitable working fluids for the ORC and HP were butane and ammonia, respectively.•The unit exergy ...cost of product of the system was 33.97 $/GJ, the SIC was 325.94 $/kW, and the PBP was 0.48 years.•The ORC evaporator and the HP condenser accounted for the largest proportion of the total system exergy destruction.•Based on sensitivity analysis, multi-objective optimization was applied in the system.
Waste-to-energy (WTE) technology is regarded as the most promising way to deal with municipal solid waste because it has the advantages of saving land area and reducing the emission of pollutants. However, the electrical efficiency of WTE combined heat and power plant is low. One factor that leads to such result is the large heat loss of the boiler exhaust gas. Besides, the amount of high-temperature steam used for power generation decreases because a part of high-temperature steam is used to provide district heating (DH), resulting in a low electricity output. In this study, a novel combined organic Rankine cycle (ORC) and heat pump cycle (ORC-HP) system is analyzed. The waste heat of the exhaust gas is recovered by the ORC and generates mechanical work to drive the HP system, which absorbs the waste heat of low-temperature and low-pressure vapor for the DH. Considering the environmental compatibility, different organic working fluids are compared to select a suitable working fluid for the combined system. Comprehensive thermodynamic and exergoeconomic analyses are performed to identify the effects of different parameters on combined system. And the economic benefits of the system are considered from the perspective of the investment payback period (PBP). Furthermore, based on sensitivity analysis, multi-objective optimization analysis was applied in the combined system to determine the optimal working conditions. The results indicate that butane and ammonia are the most suitable working fluids. Sensitivity analysis results show that for SIC, the evaporator pressure of ORC and the superheat degree of HP evaporator have a greater impact, and for ORC-HP system efficiency, the evaporator temperature of HP, the superheat of HP evaporator and ambient temperature have a greater impact. Optimization results show that, the optimal PBP and the specific investment cost (SIC) of the new combined system are 0.48 years and 325.94 $/GJ. After optimization, SIC reduces from 333.15 $/GJ to 325.94 $/GJ, with a 2.2% reduction and the product unit cost of DH reduces to 33.97 $/GJ.
Heat flux dissipated by the buried warm-oil pipeline causes the accelerated and potentially irreversible permafrost thaw.
The mean annual heat flux exponentially decreases with increasing insulation ...thickness, while have a logarithmical increase with the increase of the thermal conductivity of insulation material.
Two-phase closed thermosyphons (TPCTs) can be an excellent strengthen measures to mitigate permafrost thaw by increasing the heat extraction on an average 0.5 W/m2.
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•The amount of heat dissipated by a warm oil pipeline was quantified.•Heat flux exponentially decreased with the increase of the thermal resistance.•Insulation material cannot protect permafrost degradation in the service life.•Thermosyphons largely increase heat extraction by a daily average of 0.5 W/m2.
Permafrost degradation negatively affects the thermal stability of northern infrastructure. The quantification of heat loss through a buried oil pipeline is imperative to determine the thermal interaction between the pipe and underlying permafrost. However, the magnitudes and patterns of heat flux have not been studied methodically. This study quantifies how lateral and vertical heat fluxes from a buried warm oil pipeline increase the permafrost thawing rate and promote talik (i.e., bodies or layers of unfrozen ground in permafrost areas) development in subarctic regions by employing a three-dimensional conductive heat transfer model. In addition, the sensitivities of daily and annual heat fluxes to insulation thickness and its thermal conductivity were determined. Simulated results indicate that the heated oil pipeline acts as a heat source with the maximum daily heat flux of 6.7 W/m2 and maximum annual heat flux of 4.3 W/m2. The mean annual heat flux exponentially decreases with increasing insulation thickness, while has a logarithmical increase with the increase of the thermal conductivity of insulation material. For an insulated (0.04-m thickness) oil pipeline, a fast-growing talik initiates and enlarges laterally and vertically over time. By contrast, two-phase closed thermosyphons can be used as a remedying measure to mitigate the accelerated permafrost thaw around a buried oil pipeline. Thermosyphons increase the lateral daily heat flux by an average of 0.5 W/m2 and lower mean annual soil temperature at depth by an average of 2 °C. Within the context of climate warming, we expect that talik beneath the oil pipeline will enlarge faster than previously estimated in the coming decades due to the adverse effects of the subsurface water flow. The net founding of our results is applicable to improve the engineered design and assess the vulnerability of the oil pipeline in cold regions.
For proper use of a new or a long time period operated boiler equipment, it is necessary to evaluate the effectiveness of its work, which is characterized by a coefficient of efficiency (efficiency). ...Its calculation requires greater accuracy as even tenths of its value can influence the decision on an application of one or the other boiler equipment kind or on a choice of the equipment producer. All the efficiency components can be determined experimentally (according to parameter chart of boiler equipment in operation) by means of modern instrument base, the exeption is the value of the heat losses from heated boiler surfaces into the environment or from the external cooling boiler surface. In the literature there are no information and recommendations on the choice of methods for this value determining. And for the small-capacity boiler equipment there are no even indicative figures. To solve this problem, it is necessary to study all the factors that affect the desired value, as well as methods for determining it. The results of experimental studies of the operation of the small-capacity boiler equipment allow us to identify the relationship between the amount of heat loss from the heated boiler surfaces to the environment, the thermal power value and the equipment surface area. Based on the obtained results, graphical and analytical dependencies are developed to determine the heat loss from the heated boiler surfaces to the environment.
The North Atlantic and Europe experienced two extreme climate events in 2015: exceptionally cold ocean surface temperatures and a summer heat wave ranked in the top ten over the past 65 years. Here, ...we show that the cold ocean temperatures were the most extreme in the modern record over much of the mid-high latitude North-East Atlantic. Further, by considering surface heat loss, ocean heat content and wind driven upwelling we explain for the first time the genesis of this cold ocean anomaly. We find that it is primarily due to extreme ocean heat loss driven by atmospheric circulation changes in the preceding two winters combined with the re-emergence of cold ocean water masses. Furthermore, we reveal that a similar cold Atlantic anomaly was also present prior to the most extreme European heat waves since the 1980s indicating that it is a common factor in the development of these events. For the specific case of 2015, we show that the ocean anomaly is linked to a stationary position of the Jet Stream that favours the development of high surface temperatures over Central Europe during the heat wave. Our study calls for an urgent assessment of the impact of ocean drivers on major European summer temperature extremes in order to provide better advance warning measures of these high societal impact events.
To improve energy efficiency and give more access to renewable energy sources, low-temperature district heating (LTDH) is a promising concept to be realized in the future. However, concern about ...Legionella proliferation restricts applying low-temperature district heating in conventional systems with domestic hot water (DHW) circulation. In this study, a system with decentralized substations was analysed as a solution to this problem. Furthermore, a modification for the decentralized substation system were proposed in order to reduce the average return temperature. Models of conventional system with medium-temperature district heating, decentralized substation system with LTDH, and innovative decentralized substation system with LTDH were built based on the information of a case building. The annual distribution heat loss and the operating costs of the three scenarios were calculated and compared. From the results, realizing LTDH by the decentralized substation unit, 30% of the annual distribution heat loss inside the building can be saved compared to a conventional system with medium-temperature district heating. Replacing the bypass pipe with an in-line supply pipe and a heat pump, the innovative decentralized substation system can reduce distribution heat loss by 39% compared to the conventional system and by 12% compared to the normal decentralized substation system with bypass.
•The system of decentralized substations can realize low-temperature district heating without running the risk of Legionella.•Decentralized substations help reduce the distribution heat loss inside the building compared to conventional system.•A new concept that can reduce the return temperature for district heating is proposed and analysed.
The first decade of the 21st century was characterized by a hiatus in global surface warming. Using ocean model hindcasts and reanalyses we show that heat uptake between the 1990s and 2000s increased ...by 0.7 ± 0.3W m−2. Approximately 30% of the increase is associated with colder sea surface temperatures in the eastern Pacific. Other basins contribute via reduced heat loss to the atmosphere, in particular, the Southern and subtropical Indian Oceans (30%) and the subpolar North Atlantic (40%). A different mechanism is important at longer timescales (1960s–present) over which the Southern Annular Mode trended upward. In this period, increased ocean heat uptake has largely arisen from reduced heat loss associated with reduced winds over the Agulhas Return Current and southward displacement of Southern Ocean westerlies.
Key PointsHeat uptake increased in the Southern, Atlantic, and Indian OceansThe increase of 0.5–1 W/m2 in ocean heat uptake is enough to explain the hiatusTropical Pacific SST is not the only way to change global ocean heat uptake
•Proposed an alternative low-e film installation approach—elevating it from window-pane to reduce thermal transmittance of window.•Experimentally and theoretically studied the thermal insulating ...performance of the elevated low-e assembly.•The optical and mechanical properties of this assembly were proved to be desirable.
To minimize the heat loss through single-pane windows, we investigate the effects of elevating low-emissivity (low-e) film from glass pane. With an insulating air gap, not only heat conduction but also radiative thermal transfer can be suppressed. The thermal transmittance is reduced from 5~7 W/(m2K) to less than 2.8 W/(m2K). The water condensation resistance is enhanced. The visual transmittance and haze are satisfactory. The structural resilience of the hollow structure is excellent.
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