Explore the vast range of titles available.

While the role of long‐term sea ice decline in shaping Arctic climate change is well‐established, the contribution of short‐term sea‐ice variability remains insufficiently explored. Here we present observational evidence that since 2007, sea ice fluctuations in Arctic marginal ice zone have remained at a high level. The annual‐mean daily variability of sea ice concentration rose by 11.4%, with high‐variability days becoming more frequent, especially in summer and autumn. Composite analyses reveal enhanced net heat uptake in summer (+11.9%) and greater ocean‐to‐atmosphere heat release in winter (+45.3%), both of which intensify after 2007. Causal analyses reveal a feedback, with higher sea ice variability being closely linked to and reinforced by anomalous net heat fluxes. These findings highlight the increasing short‐term variability of the Arctic sea‐ice and its key role in regulating local air–sea heat exchange.

Shallow lakes (<2 m depth) of Central Asian, receiving strong solar radiation and low precipitation, are sensitive to atmospheric forcing because of their low heat capacity, yet their under‐ice thermal conditions remain poorly investigated. We conducted the first complete ice season monitoring of Lake Ulansu (Ulansuhai, Wuliangsuhai), revealing unique thermal behavior. The lake was salinity stratified (<3‰), stabilizing the lower water layer and allowing the water temperature to reach 10°C before break‐up. The solar radiation absorbed by the water (Qsw) drove the water–ice heat flux, with approximately 82% of Qsw returning to the ice base, facilitating a rapid shift from convective mixing to stable stratification. These findings provide key insights into the thermal regimes of Central Asian shallow lakes, informing climate models and ecological assessments for more than 10,000 similar lakes in the region.

A key challenge in lake ice modeling is quantifying the heat flux from water to ice. In shallow Central Asian lakes, where the seasonal ice cover mainly consists of columnar congelation ice, sunlight penetration enables strong interactions between ice and water. The evolution of ice cover in Lake Ulansu (Ulansuhai, Wuliangsuhai) in northern China was investigated via the High‐resolution Thermodynamic Snow and Ice (HIGHTSI) model. Atmospheric forcing was provided by calibrated ERA5 reanalysis data, and the initial freeze‐up dates were identified from remote sensing observations. A new parameterization of the water–ice heat flux (Fw), which is suitable for shallow lakes, was proposed as Fw = aQsw + b, where Qsw represents the solar heating of water and a and b are fitted coefficients. The model showed high correlations (>0.9) and low errors (<5 cm for ice thickness; <2°C for ice temperature) with respect to field observations. Throughout the ice season, long‐ and shortwave radiation promoted ice growth and melting, respectively. Surface melting and sublimation accounted for 9.5% and 9.8%, respectively, of the total ice decay, and the water–ice heat flux Fw = −17.5 ± 13.0 W m−2 was critical for simulation accuracy. Furthermore, despite the shallow depth, the lake released over 100 W m−2 of heat into the atmosphere for 2 days after break‐up. These findings highlight the climatic sensitivity and support sustainable water resource management of more than 10,000 shallow lakes in Central Asia.

Various enhancement techniques are proposed in the literature to alleviate heat transfer issues arising from the low thermal conductivity of the phase change materials (PCM) in latent heat thermal energy storage systems (LHTESS). The identified techniques include employment of fins, insertion of metal structures, addition of high conductivity micro/nanoparticles, micro-encapsulation, macro-encapsulation and cascaded PCMs arrangement. However, these conventional techniques tend to reduce the storage capacity as they generally add additional components/materials into the storage medium. On the other hand, if techniques such as direct contact heat exchange, ultrasonic vibration, electrohydrodynamics and movable PCM are employed, the storage volume would remain unaffected. Hence, the said techniques seem to have gained importance in PCM research in recent times. Although several review papers elaborating conventional techniques are available, none can be found on the aforementioned alternative class. Driven by the current scenario, this review paper intends to summarize past research on alternative heat transfer enhancement techniques employed for LHTESS. The critical analysis of the potential of each technique in enhancing the phase change heat transfer rate and their practical applicability are presented. Further, the present review evaluates relative merits/demerits and challenges/issues/limitations of these techniques to provide guidelines for future research.

Many energy systems demand heat transfer at high temperatures to keep up with high demand for power, so high‐temperature material that can perform and last under these harsh conditions is needed for heat exchangers. The engineering requirements for these high‐temperature heat exchanger material call for high thermal conductivity, high resistance to fracture, high resistance to creep deformation, environmental stability in environments associated with the application, and high modulus of elasticity while maintaining low cost to make and maintain. Naturally, ceramics are a good solution for this endeavor. In the past, high‐temperature heat exchangers made from ceramics have been used. We provide examples of ceramics in relevant heat exchange applications and provide motivation where additive manufacturing (AM) can improve efficiency. AM for the relevant material is under development, and we provide insight on the AM of ceramic materials and examples of AM heat exchangers keeping cost in mind. The motivation of the review paper is to provide a framework for material and manufacturing selection for high‐temperature heat exchangers for AM to keep up with the demand for better efficiency, better material, better manufacturing, and cost moving forward with AM technology in high‐temperature ceramic heat exchangers. High temperature heat exchangers may be designed from ceramics to achieve higher performance, and various materials and manufacturing techniques can help achieve highly efficient high temperature systems.

Large pelagic fishes often dive and surface repeatedly as if they were airbreathers, raising a question about the functions of these movements. Some species (e.g., bigeye tuna, ocean sunfish) apparently alternate foraging in deep cold waters and rewarming in shallow warm waters. However, it is unclear how prevalent this pattern is among species. Blue sharks are the widest-ranging pelagic shark with expanded vertical niches, providing a model for studying foraging–thermoregulation associations. We used electronic tags, including video cameras, to record the diving behaviour, muscle temperature, and foraging events of two blue sharks. During repeated deep dives (max. 422 m), muscle temperature changed more slowly than ambient water temperature. Sharks shifted between descents and ascents before muscle temperature reached ambient temperature, leading to a narrower range (8 °C) of muscle temperature than ambient temperature (20 °C). 2.5-h video footage showed a shark catching a squid, during which a burst swimming event was recorded. Similar swimming events, detected from the entire tag data (20 − 22 h), occurred over a wide depth range (5 − 293 m). We conclude that, instead of alternating foraging and rewarming, blue sharks at our study site forage and thermoregulate continuously in the water column. Furthermore, our comparative analyses showed that the heat exchange rates of blue sharks during the warming and cooling process were not exceptional among fishes for their body size. Thus, behavioural thermoregulation linked to foraging, rather than enhanced abilities to control heat exchange rates, is likely key to the expanded thermal niches of this ectothermic species.

A region of physical realizability of two- and multiflow heat transfer has been constructed in the space of thermodynamic indicators: heat load, energy dissipation, and thermal conductivity coefficient. The boundary of this region is achievable in a counterflow displacement heat exchanger, provided the conditions placed on the flows’ heat capacities are observed. Using the concept of thermodynamic equivalence of a two-flow heat exchanger and a multiflow system, the requirements for an optimal heat exchange system have been formulated. It is shown that the dependencies of the cold and hot flows’ temperatures on the heat load in an equivalent heat exchanger constructed using the suggested algorithm determine the total number of two-flow cells in the system, their heat loads, the heat transfer coefficients, entropy production, and the structure of the contacts. In this case, each hot flow in an optimal system can be in contact with several cold ones, and each cold flow can contact several hot ones. Cases of flow state phase variation have been considered. Limitations placed on the temperatures of all or part of the flows at the inlet and outlet of a heat exchange system have been taken into account. An algorithm has been suggested for selecting free parameters of flows, their heat capacities, boundary temperatures, and distribution of contact surfaces.

Currently used TEG modules have low efficiency of about 5%. The energy generated by the TEG module depends on the temperature difference between the module surfaces. Heat exchange between the heat source and the module surface takes place through the contact between two rough solid surfaces. This creates contact resistance. It can be reduced by using a substance filling the empty spaces between the contact surfaces and applying pressure. During the tests, the efficiency of electricity generation with a thermoelectric generator was measured (TEG) at various pressure forces. The tests were carried out at a pressure force of 250 N, 500 N, 750 N and 1000 N. The selected values of pressure do not exceed the limit value arising from the thermoelectric generator (TEG) design. A copper element constituting the heat source was heated in a furnace. Next, it was pressed at an adequate force to the generator, which was placed on a water cooler. The impact of conductive materials placed between the faces of the heat source and the TEG on the generation of electricity was examined. At low forces, the use of a thermal pad as an intermediary substance does not result in improved heat transfer in the heat source—TEG generator system. Better filling of voids is provided by thermally conductive paste due to its properties.

In the present research paper, the thermal performance of helical ground air heat exchanger (HGAHE) has been experimentally analyzed under Saharan climate conditions during summer season. A flexible PVC pipe with a diameter of 0.06 m and a length of 30 m has been arranged as a helical-coil layout to design the HGAHE, and it is inserted into a borehole of 5 m depth. The study acknowledges that a drop as high as 11.0 °C in air temperature can be achieved with an air velocity of 10 m s −1 and an inlet air temperature of 38 °C. The study also revealed that, by incrementing the air velocity from 10 to 20 m s −1 , the heat exchange rate of the HGAHE system increases by 158% after 3 h of operation time; however, the efficiency of the HGAHE decreases by 21.51%. Moreover, thermal performance derating factor (TPDF) increments with increasing the operation time and air velocity. After 3 h of operation time, the highest TPDF is attained as 0.27 with a velocity of 20 m s −1 , whereas the lowest TPDF is observed as 0.14 for a velocity of 10 m s −1 .

In this paper, the important role played by the local air-sea heat exchange in the east–west oscillation of the Western Pacific subtropical high (WPSH) on the sub-seasonal scale is revealed. First, the east–west oscillation index is defined for the WPSH using the relative vorticity field. The index can well characterize the sub-seasonal east–west oscillation of the WPSH, and it has a significant sub-seasonal cycle of 10–30 days. During the westward events, there is a cold sea surface temperature (SST) anomaly in the WPSH and its west side at the early stage of westward WPSH extension, and the cold SST anomaly makes the low-level atmosphere relatively stable, which is conducive to the generation of abnormal anticyclone, and then leads to the westward extension of the WPSH. During the westward WPSH extension, the convective activity is further suppressed; therefore, the water vapor evaporation and the cloud cover are reduced, and the net heat flux received by the ocean surface increases, eventually leading to the rise of SST. At the late stage of the westward extension, the continually enhanced warm SST causes instability of the low-level atmosphere, weakens the abnormal anticyclone, and then leads to the eastward retreat of the WPSH. Thereafter, the enhanced convective activities causes the increase of latent flux and cloud cover in the atmosphere, as well as the decrease of solar radiation flux. As a result, the warm SST anomaly weakens. The situation is the opposite for the eastward events. During the eastward or westward movement of the WPSH, beside the influence of the air-sea interaction in the WPSH region, the northward and northwestward propagation of the OLR anomaly in the tropical Indian Ocean and the Western Pacific respectively, and the SST anomaly in the equatorial western Pacific also have some influence on the WPSH east–west movement. The process of air-sea interaction is similar in the early and late summer, but the intensity of each meteorological factor is stronger in the early summer than that in late summer, which indicates that the air-sea interaction is more obvious in the early summer.