In this work, a detailed analysis and thermal modeling for temperature prediction of a stand-alone photovoltaic module is performed. The study aims to present precise estimation of module ...temperature, since it is an important parameter for power output calculation. Hence, the required data were collected via experiments. Accounting for all heat transfer mechanisms, and following model validation, a proposed algorithm was implemented to investigate heat transfer from the module to its surrounding and predict different layers’ temperature. Results indicate that accurate energy distribution and temperature prediction was achieved by the adopted thermal model, only about 16% of the received energy is converted to electrical power while the rest is released by heat. Moreover, the proposed simulation algorithm provided one of the best results in comparison to literature models, achieving an R2 of 0.963 and a MAE of 1.883, which is very close to the best overall model by King at R2=0.973 and MAE=1.663. Additionally, two new models for module temperature prediction were proposed. After testing on new data, the explicit model provided a reasonable first approximation attaining an adjusted R2 of 0.97 and a MSE of 3.505, and an accurate implicit model, achieving a MSE of only 1.268.
Maintenance of a homeostatic body core temperature is a critical brain function accomplished by a central neural network. This orchestrates a complex behavioral and autonomic repertoire in response ...to environmental temperature challenges or declining energy homeostasis and in support of immune responses and many behavioral states. This review summarizes the anatomical, neurotransmitter, and functional relationships within the central neural network that controls the principal thermoeffectors: cutaneous vasoconstriction regulating heat loss and shivering and brown adipose tissue for heat production. The core thermoregulatory network regulating these thermoeffectors consists of parallel but distinct central efferent pathways that share a common peripheral thermal sensory input. Delineating the neural circuit mechanism underlying central thermoregulation provides a useful platform for exploring its functional organization, elucidating the molecular underpinnings of its neuronal interactions, and discovering novel therapeutic approaches to modulating body temperature and energy homeostasis.
Low temperature district heating (DH) system gives easier access to the renewable energy as heat sources and improves the heat distribution efficiency. From the exergy point of view, low DH supply ...temperature also better matches the exergy demand of space heating and domestic hot water. It is more beneficial to operate district heating system under lower temperature level for the heat-sparse area where the distribution losses accounts for a large proportion in the total heat supply. In this study, the actual performance of a case ultra-low temperature district heating (ULTDH) system in Denmark was investigated based on long-term measurements. The system combines the central heat pump and local boosters, while the impact of such configuration on the overall system performance was analysed. The energy, exergy and economy performances of the case system were compared to medium temperature district heating system (MTDH) and low-temperature district heating system (LTDH). The results show that the LTDH system without supplementary heating has the highest energy and exergy efficiency. While the ULTDH system has better performance compared to the MTDH system in energy, exergy and economy due to substantial savings from the distribution heat loss.
•A case ULTDH network for low-heat-density area was measured for long term.•The ULTDH system was analysed from energy, exergy and economy aspects.•The impact of using renewable energy source and local boosters was analysed.•The performance was compared with MTDH system (70/40 °C) and LTDH (55/25 °C) system.
Abstract
A solar pond technology employs a layer of salinity gradient to prevent heat loss due to convection from the lower convective zone. Thus, the energy received from solar radiation is stored ...in a lower convective zone. The thickness of various zones significantly affects the behaviour of solar pond temperature. In this present study, a transient numerical investigation is conducted to evaluate the impact of depths of different zones on the performance characteristics of solar pond. The variation in maximum temperature and maturation period under the influence of non-convective zone and lower convective zone thickness is discussed. The energy obtained from a solar pond significantly depends on various losses associated with the zones. Thus, an assessment of conduction and ground heat loss is presented for the variation in thickness of zones. An attempt is also made to study the effect of thickness of zones on the temperature of the lower convective zone. It is found that the configuration of a smaller thickness of LCZ and a higher thickness of NCZ yields maximum LCZ temperature.
Abstract
The current architectural preference for the recess of windows is in line with the forefront of the building facade. The recess of a window has consequences for: solar loads, heat loss, and ...risk of outside condensation. This paper presents an analysis of these issues in relation to variations in recess depth and differences in orientation of the window. The solar load in buildings is highly influenced by the depth of the window recess, depending on the orientation. Solar gains both contribute to heating the building during the heating season, but also to overheating in other periods. The latter being especially important for other buildings than residential buildings. This is analysed for different window orientations and size (height and width) as wells as the recess depth. Recess depth also influences the overall heat loss though the facade and window and is analysed through detailed calculations. Last, but not least, condensation on the external face of modern low energy windows causes a serious issue regarding visual comfort in the mornings during periods with clear weather and low outdoor temperatures. Analyses of the recess depth influence on the outside condensation risk is presented. The issues regarding the recess depth for facade windows is analysed using dynamic simulations of different window and recess depths in different orientations in combination with 2D static calculations of the overall heat loss coefficient for the total window and facade construction in typical highly insulated facade constructions.
The influence of wall heat loss on the emission characteristics of ammonia-air swirling flames has been investigated employing Planar Laser-Induced Fluorescence imaging of OH radicals and Fourier ...Transform Infrared spectrometry of the exhaust gases in combustors with insulated and uninsulated walls over a range of equivalence ratios, ϕ, and pressures up to 0.5 MPa. Strong influence of wall heat loss on the flames led to quenching of the flame front near the combustor wall at 0.1 MPa, resulting in large unburned NH3 emissions, and inhibited the stabilization of flames in the outer recirculating zone (ORZ). A decrease in heat loss effects with an increase in pressure promoted extension of the fuel-rich stabilization limit owing to increased recirculation of H2 from NH3 decomposition in the ORZ. The influence of wall heat loss resulted in emission trends that contradict already reported trends in literature. NO emissions were found to be substantially low while unburned NH3 and N2O emissions were high at fuel-lean conditions during single-stage combustion, with values such as 55 ppmv of NO, 580 ppmv of N2O and 4457 ppmv of NH3 at ϕ = 0.8. In addition, the response of the flame to wall heat loss as pressure increased was more important than the effects of pressure on fuel-NO emission, thereby leading to an increase in NO emission with pressure. It was found that a reduction in wall heat loss or a sufficiently long fluid residence time in the primary combustion zone is necessary for efficient control of NH3 and N2O emissions in two-stage rich-lean ammonia combustors, the latter being more effective for N2O in addition to NO control. This study demonstrates that the influence of wall heat loss should not be ignored in emissions measurements in NH3-air combustion, and also advances the understanding of previous studies on ammonia micro gas turbines.
A Joule heater made of emerging 2D nanosheets, i.e., MXene, has the advantage of low‐voltage operation with stable heat generation owing to its highly conductive and uniformly layered structure. ...However, the self‐heated MXene sheets easily get oxidized in warm and moist environments, which limits their intrinsic heating efficiencies. Herein, an ultrathin graphene skin is introduced as a surface‐regulative coating on MXene to enhance its oxidative stability and Joule heating efficiency. The skin layer is deposited on MXene using a scalable solution‐phased layer‐by‐layer assembly process without deteriorating the excellent electrical conductivity of the MXene. The graphene skin comprises narrow and hydrophobic channels, which results in ≈70 times higher water impermeability of the hybrid film of graphene and MXene (GMX) than that of the pristine MXene. A complementary electrochemical analysis confirms that the graphene skin facilitates longer‐lasting protection than conventional polymer coatings owing to its tortuous pathways. In addition, the sp2 planar carbon surface with a low heat loss coefficient improves the heating efficiency of the GMX, indicating that this strategy is promising for developing adaptive heating materials with a tractable voltage range and high Joule heating efficiency.
An impermeable graphene skin strategy applied on MXene enhances the durability and almost doubles the heating efficiency of MXene heating units. This skin layer features the hydrophobic sp2 carbon structure on the surface and the tight and tortuous pathway inside the layer, which impede the permeation of water molecules and regulate the heat loss from the film surface.
•A mathematical model was developed and validated to estimate the nighttime heat loss.•Annual performances based on the typical meteorological year data were carried out.•Variations in number of ...supplying days and heat gain were analyzed in detail.•Variations in monthly and annual nighttime heat loss were presented.•Influence of set temperature to annual performance was presented and discussed.
Loop thermosyphon (LT) is usually introduced to overcome the freezing and corrosion problems associated with the conventional solar water heating (SWH) system. Compared with the conventional SWH system, the LT-SWH system possesses a lower nighttime heat loss because of the thermal diode property of loop thermpsyphon but bigger daytime heat loss because of the secondary heat exchange. However, the effect of above interaction to the system performance is rarely reported based on long-term running. In this study, based on the typical meteorological year data of Fuzhou city, annual performances of above two systems, including the effective number of supplying days, effective heat gain and nighttime heat loss, are comparatively analyzed under two different operational modes. Variations of above mentioned variables with the increment in the set temperature are discussed. The results indicate that, under the discontinuous heating mode, the effective numbers of supplying days of SWH system and LT-SWH system are 139 and 153, respectively. While the numbers of days are respectively 168 and 173 under the continuous heating mode. The SWH system possesses an expected bigger nighttime heat loss ratio with an average annual value of 15.07% corresponding to 6.15% for the LT-SWH system. Particularly, for the LT-SWH system, the different relative magnitudes of heat loss coefficients functioning at different times leads to a smaller temperature drop at night and also a smaller temperature rise at the subsequent day. It generates an unanticipated results that corresponds to the same month from November to April, the two systems have the approximate effective heat gain. The set temperature significantly influences the relative magnitudes of annual effective number of supplying days and annual effective heat gain, the superiority of LT-SWH system gradually diminishes and even reverses with the increment in the set temperature. The bigger daytime heat loss dominating the dominance is responsible for that transition. Combining with a longer static payback period, it is conditional to substitute the conventional SWH system with the LT-SWH system, especially when the water temperature on demand is high.
•Analyzing the effect of hydrogen on methane explosions.•Explosion characteristics of a premixed combustible gas in a 20-L spherical device.•A four-step combustion-mechanism model based on the CFD ...code GASFLOW-MPI.•Numerically simulating the methane/hydrogen explosion process.
The addition of hydrogen to methane changes its deflagration characteristics and increases the combustion rate. However, studies on the effect of hydrogen on methane deflagration remain insufficient. Therefore, based on the CFD code GASFLOW-MPI, a four-step combustion-mechanism model was established for methane/hydrogen mixtures. The deflagration characteristics of a premixed combustible gas in a 20-L spherical device was numerically simulated using a methane/hydrogen/air equivalence ratio of 1 and hydrogen addition in the range of 0–50%; subsequently. The results were compared with experimental data. The four-step methane/hydrogen combustion-mechanism could effectively reproduce the methane/hydrogen deflagration process on considering the heat losses. With an increase in hydrogen addition, the laminar burning velocity increases, and the deflagration duration reduces. It decreases the explosion heat loss and increased the maximum deflagration pressure. Under adiabatic simulation, the maximum deflagration pressure decreased with an increase in hydrogen addition, in contrast with the experimental results. This indicates that the heat-loss effect of the methane/hydrogen/air-mixture deflagration process should not be ignored. Moreover, the heat loss during the methane/hydrogen/air-mixture deflagration was mainly caused by thermal radiation. Thus, the influence of the thermal-radiation and convective heat-transfer mechanisms should be considered in the numerical simulations of methane/hydrogen/air-mixture deflagration.
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