•A performance-enhanced parabolic trough solar receiver is manufactured.•Indoor heat loss experiment based on heat equilibrium method is conducted.•Outdoor thermal efficiency experiment is carried ...out in two-axis tracking platform.•The heat loss of new receiver is reduced by around 28.0%.•The thermal efficiency of new receiver is effectively raised by 1.6–4.9%.
Parabolic trough collectors (PTCs) are the most mature way to harvest high-temperature heat source and widely applied in solar thermal utilizations. Parabolic trough solar receivers as the heat-collecting elements (HCEs) are the key parts of PTC, but face with a knotty problem that is exploding radiative heat loss under high operating temperature, which exerts a significantly negative role on the overall performance of the PTC system. For effectively reducing the heat loss and improving the thermal performance of solar receiver, a structurally optimized HCE with an inner radiation shield was proposed, designed, and manufactured. Furthermore, the indoor heat loss and outdoor thermal efficiency testing were carried out in the Institute of Electrical Engineering, Chinese Academy of Sciences (IEECAS) to validate comprehensive thermal performance of the proposed HCEs. The results show that the radiation shield plays an effective role in reducing the heat loss and improving the thermal efficiency. The heat loss of the proposed HCE is significantly reduced by 28.0% compared to the conventional HCE at the absorber temperature of 550 °C. And the proposed HCE possesses superior performance at high operating temperature and low solar irradiance. In the case of inlet temperature of 350 °C and solar irradiance of 600 W/m2, the thermal efficiencies of proposed HCE and conventional HCE are 49.4 and 51.8% respectively, and the thermal efficiency of the proposed HCE is effectively enhanced by 4.9%.
Little is known about the phylogenetic variation of avian evaporative cooling efficiency and heat tolerance in hot environments. We quantified thermoregulatory responses to high air temperature (
) ...in ∼100-g representatives of three orders, namely, the African cuckoo (
, Cuculiformes), lilac-breasted roller (
, Coraciiformes) and Burchell's starling (
, Passeriformes). All three species initiated respiratory mechanisms to increase evaporative heat dissipation when body temperature (
) approached 41.5°C in response to increasing
, with gular flutter observed in cuckoos and panting in rollers and starlings. Resting metabolic rate and evaporative water loss increased by quantitatively similar magnitudes in all three species, although maximum rates of evaporative water loss were proportionately lower in starlings. Evaporative cooling efficiency defined as the ratio of evaporative heat loss (EHL) to metabolic heat production (MHP) generally remained below 2.0 in cuckoos and starlings, but reached a maximum of ∼3.5 in rollers. The high value for rollers reveals a very efficient evaporative cooling mechanism, and is similar to EHL/MHP maxima for similarly sized columbids which very effectively dissipate heat via cutaneous evaporation. This unexpected phylogenetic variation among the orders tested in the physiological mechanisms of heat dissipation is an important step toward determining the evolution of heat tolerance traits in desert birds.
Solar steam generation is emerging as a promising technology, for its potential in harvesting solar energy for various applications such as desalination and sterilization. Recent studies have ...reported a variety of artificial structures that are designed and fabricated to improve energy conversion efficiencies by enhancing solar absorption, heat localization, water supply, and vapor transportation. Mushrooms, as a kind of living organism, are surprisingly found to be efficient solar steam‐generation devices for the first time. Natural and carbonized mushrooms can achieve ≈62% and ≈78% conversion efficiencies under 1 sun illumination, respectively. It is found that this capability of high solar steam generation is attributed to the unique natural structure of mushroom, umbrella‐shaped black pileus, porous context, and fibrous stipe with a small cross section. These features not only provide efficient light absorption, water supply, and vapor escape, but also suppress three components of heat losses at the same time. These findings not only reveal the hidden talent of mushrooms as low‐cost materials for solar steam generation, but also provide inspiration for the future development of high‐performance solar thermal conversion devices.
Mushrooms can, surprisingly, enable efficient solar steam generation (≈78% under 1 sun illumination), as their natural structures possess the excellent properties of light absorption, thermal management with minimized heat loss, efficient water supply, and vapor escape.
•A downward air jet is used to suppress natural convection from a near-vertical wall.•The jet lowers convective heat loss by ∼30% at the top of the wall, near the jet.•There is a ∼20% reduction in ...heat loss in the laminar-turbulent transition zone.•The concept could be applied to reduce heat loss from solar-thermal receivers.
Concentrating solar power (CSP) plants encounter inefficiencies at all stages of electricity generation. Convection from the solar-thermal receiver is a significant mode of heat loss in CSP systems, and is challenging to mitigate. This study investigates the reduction of convection losses by using a planar jet that disrupts the buoyant flow arising from the heated surface of an external CSP receiver. An isothermal flat plate with a height of 1.8 m was used to model the receiver, and a planar jet air curtain with a nozzle thickness of 3 mm was introduced near the upper edge of the wall. A computational fluid dynamics model was first validated and subsequently implemented to conduct a parametric study on the heat transfer from the isothermal plate with an air curtain varying four parameters: jet speed, jet angle, plate temperature and plate inclination. The results showed that the air curtain generates a stagnation zone adjacent to the wall which successfully reduces local convective heat losses. The effectiveness of an air curtain is defined here as the relative reduction in the local heat loss due to the air curtain, compared to the case of natural convection alone. A local maximum of 31.2% effectiveness is achieved in the stagnation zone below the jet outlet for a vertical wall with a jet speed of 2.5 ms−1 and jet angle of 45∘. The air curtain effectiveness at the stagnation region was found to decrease with increasing jet speeds, whereas the effectiveness increased near the laminar-to-turbulent transition region with increasing jet speed. Smaller air curtain angles relative to the wall resulted in lower effectiveness. A 45∘ air curtain on a vertical wall can offer performance benefits that are similar in magnitude to inclining a wall from the vertical. A higher wall temperature was accompanied by better effectiveness near the jet outlet, particularly in the stagnation region, while lower wall temperatures produced higher effectiveness further from the jet. Therefore, an air curtain can be used to reduce convective heat losses locally from a heated flat surface, including potentially when applied to CSP receivers.
A paraffin phase-change material (PCM) was entrapped by poly(methyl methacrylate) microcapsules that were loaded into plaster panels at high concentrations; these were used to build a model house. ...The PCM-plaster-lined and reference model houses were equipped with measuring instruments and heated during the daytime, to test their heat storage abilities in the studied wintertime conditions. A meteorological station collected the irradiation and outer temperature data; meanwhile, the external wall, internal wall, air, ceiling, and floor temperatures were measured using thermoelements. Electric energy consumption during heating was also recorded. Both houses were regulated by a controlled indoor temperature during daytime, followed by night-time free cooling. This regulation facilitated the complex evaluation of the heat-storage capabilities and their effects on the dynamic thermal behaviour and energy consumption of the PCM-plaster-lined and reference model houses. The PCM-plaster-lined model house exhibited a significantly lower temperature fluctuation; however, its energy demand exceeded that of the reference house, because its average internal temperature level was substantially higher during the test period. The global heat loss coefficient was estimated in a quasi-equilibrium state for the entire house. The heat loss was ~6.8% higher in the PCM-plaster-lined house, owing to the higher inner temperatures during the day. However, the heat loss coefficient in the PCM-plaster-lined house was ~7.8% lower, suggesting that latent heat storage can be economically used to maintain a constant inner temperature.
•Phase change material plaster lined model house was compared with a reference house.•Controlled indoor conditions in daytime with nighttime free cooling were applied.•PCM plaster lined model house showed significantly lower temperature fluctuation.•The heat loss was higher in PCM plaster lined house due to higher inner temperature.•Global heat loss coefficient in the PCM plaster lined house was lower by about 7.8%.
Design of efficient, downsized piston engines requires a thorough understanding of transient near-wall heat losses. Measurements of the spatially and temporally evolving thermal boundary layer are ...required to facilitate this knowledge. This work takes advantage of hybrid fs/ps rotational coherent anti-Stokes Raman spectroscopy (HRCARS) to measure single-shot, wall-normal gas temperatures, which provide exclusive access to the thermal boundary layer. Phosphor thermometry is used to measure wall temperature. Measurements are performed in a fixed-volume chamber that operates with a transient pressure rise/decay to simulate engine-relevant compression/expansion events. This simplified environment is conducive for fundamental boundary layer and heat transfer studies associated with engine-relevant processes. The thermal boundary layer development and corresponding heat losses are evaluated within two engine-relevant regimes: (1) an unburned-gas regime comprised of gaseous compression and (2) a burned-gas regime, which includes high-temperature compression and expansion processes. The time-history of important boundary layer quantities such as gas / wall temperatures, boundary layer thickness, wall heat flux, and relative energy lost at the wall are evaluated through these regimes. During the mild unburned-gas compression, Tcore increases by 30 K and a thermal boundary layer is initiated with thickness δT ~ 200 μm. Wall heat fluxes remain below 6 kW/m2, but corresponds to ~6% energy loss per ms. In the burned-gas regime, Tcore resembles adiabatic flame temperatures, while Twall increases by 16 K. A thermal boundary layer rapidly develops as δT increases from 290 to 730 μm. Energy losses in excess of 25% occur after flame impingement and slowly decay to ~10% at the end of expansion. Measurements also resolve thermal mixing of fresh- and burned gases during expansion, which yield strong temperature reversals in the boundary layer. Findings are compared to canonical environments and demonstrate the transient thermal boundary nature during engine-relevant processes.
Introduction. During construction of underground facilities, architectural, finishing and installation works begin before the completion of the main structures. At that time, there is no permanent ...heating network connection and therefore temporary heat sources must be used to ensure compliance with the works technology. The lack of specific information about the required capacity of such sources makes it impossible to forecast the financial costs, which is essential for contractors. The purpose of the study is to determine the specific value of heat energy consumption for heating underground stations, construction of which is carried out by open method, depending on different outdoor temperatures, construction completion, depth of station installation, as well as the construction volume of the station. Materials and methods. Heat flows have been calculated by means of mathematical modelling of a stationary thermal regime. Analyses of calculation results and normative data have been performed in accordance with the provisions of probability theory and mathematical statistics. Calculation of coefficients and loads are carried out according to generally accepted equations and laws of heat and mass exchange. Climatic data and material parameters are taken according to current normative documents. Results. The values of specific thermal performance of open-cut metro stations depending on space-planning and design solutions, composition of external envelopes, as well as the stage of construction completion (including the presence or absence of backfill) are calculated. Estimated rate of heat energy consumption for temporary heating of open cut metro station is 3.87 Gcal/(1,000 m 3 · month). Conclusions. Temporary heating norms (amount of heat energy) for open-circuit metro stations have been proposed. Heat costs for ensuring the specified air parameters, referred to a unit volume and required for construction and installation works inside the stations during the heating period, are determined.
Photothermal therapy usually requires a high power density to activate photothermal agent for effective treatment, which inevitably leads to damage to normal tissues and inflammation in tumor ...tissues. Herein, we rationally design a protein‐binding strategy to build a molecular photothermal agent for photothermal ablation of tumor. The synthesized photothermal agent can covalently bind to the thiol groups on the intracellular proteins. The heat generated by the photothermal agent directly destroyed the bioactive proteins in the cells, effectively reducing the heat loss and the molecular leakage. Under a low power density of 0.2 W cm−2, the temperature produced by the photothermal agent was sufficient to induce apoptosis. In vitro and in vivo experiments showed that the therapeutic effect of photothermal therapy can be efficiently improved with the protein‐binding strategy.
A protein‐binding molecular photothermal agent was developed for photothermal therapy. In vitro and in vivo experiments demonstrated that the heat generated by the photothermal agent directly destroyed the intracellular bioactive proteins and induced apoptosis under low power density laser irradiation. The therapeutic effect can be efficiently improved with the protein‐binding strategy.
Animals living in the extremely cold environment, such as polar bears, have shown amazing capability to keep warm, benefiting from their hollow hairs. Mimicking such a strategy in synthetic fibers ...would stimulate smart textiles for efficient personal thermal management, which plays an important role in preventing heat loss and improving efficiency in house warming energy consumption. Here, a “freeze‐spinning” technique is used to realize continuous and large‐scale fabrication of fibers with aligned porous structure, mimicking polar bear hairs, which is difficult to achieve by other methods. A textile woven with such biomimetic fibers shows an excellent thermal insulation property as well as good breathability and wearability. In addition to passively insulating heat loss, the textile can also function as a wearable heater, when doped with electroheating materials such as carbon nanotubes, to induce fast thermal response and uniform electroheating while maintaining its soft and porous nature for comfortable wearing.
A textile with excellent thermal insulation capability, mimicking the porous structure of polar bear hair, is fabricated by a “freeze‐spinning” technique to continuously spin silk fibroin solution into aligned porous fibers. Doped with electroheating materials, this type of textile is beneficial for personal thermal management, thermal stealth in military applications, and wearable electronics.
Whether whole body heat loss and thermoregulatory function (local sweat rate and skin blood flow) are different between summer and autumn and between autumn and winter seasons during exercise with ...different air flow in humid heat remain unknown. We therefore tested the hypotheses that whole body sweat rate (WBSR), evaporated sweat rate, and thermoregulatory function during cycling exercise in autumn would be higher than in winter but would be lower than in summer under hot-humid environment (32 C, 75% RH). We also tested the hypothesis that the increase of air velocity would enhance evaporated sweat rate and sweating efficiency across winter, summer, and autumn seasons. Eight males cycled for 1 h at 40% V̇o
in winter, summer, and autumn seasons. Using an electric fan, air velocity increased from 0.2 m/s to 1.1 m/s during the final 20 min of cycling. The autumn season resulted in a lower WBSR, unevaporated sweat rate, and a higher sweating efficiency compared with summer (all
≤ 0.05) but WBSR and unevaporated sweat rate in autumn were higher than in winter and thus sweating efficiency was lower when compared with winter only at the air velocity of 0.2 m/s (All
≤ 0.05). Furthermore, evaporated sweat rate and core temperature (
) were not different among winter, summer, and autumn seasons (All
> 0.19). In conclusion, changes in WBSR across different seasons do not alter
during exercise in a hot humid environment. Furthermore, increasing air velocity enhances evaporated sweat rate and sweating efficiency across all seasons.
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