Radiating Surface Area Research Articles

Investigation on H2-fueled combustion characteristics and improvement of thermal performance in a micro-planar with arranged inlet-fins and bluff-bodies for micro-thermophotovoltaic

To improve the energy conversion and efficiency, a micro-planar with arranged inlet-fins and bluff-bodies is proposed for H2-fueled micro thermophotovoltaic system. Effects of inlet-fins and bluff-bodies setting and combustor dimensions on combustion properties, heat transfer and energy conversion are investigated and analyzed under various operating conditions. The results illustrate that the flame stability and heat transfer in combustion chamber with arranged inlet-fins and bluff-bodies are enhanced, where heat recirculation is formed and radiation temperature is boosted. According to the field synergy analysis, coupling effects of inlet-fins and bluff-bodies on burning and thermal process can be improved by the optimization of bluff-bodies setting, and the flow limit is also expanded. There is a balance of the burner dimensions effects on the augment of radiation surface area and the reduction of radiation temperature for micro power generation. Particularly, the micro-planar with La/L = 0.62 contributes to achieve a higher radiation density, and the highest electrical output Pe = 3.16 W is adopted in combustor C2-0.62 at mf = 6.751 × 10−5 kg/s. It is beneficial to promote energy output of micro-planar and the energy efficiency of micro-thermophotovoltaic system.

Numerical investigation of multi-nozzle ejector device with inclined nozzles for marine gas turbine

The high-temperature exhaust gases and the hot surfaces of the ejector device in marine gas turbines generate significant levels of infrared radiation. An appropriate nozzle structure can effectively lower the exhaust gas temperature and reduce the high-temperature radiation surface area, thereby minimizing external infrared radiation. In this study, a numerical simulation of the nozzle structure in the ejector device was conducted using computational fluid dynamics (CFD) methods. By investigating the orthogonal combinations of nozzle inclination angles and the number of nozzles, the temperature distribution and flow characteristics under different operating conditions were analysed. The results showed that as the nozzle inclination angle increased, the entrainment coefficient (Ce) and the temperature ratio at the inlet and outlet (Rt) initially improved but then worsened. Simultaneously, the pressure loss coefficient (Cpl) increased with the inclination angle. The CRITIC weight method was employed to objectively allocate weights to Rt, Ce, and Cpl, determining the optimal solution. The results indicated that Rt and Cpl had significant and similar weights. The optimal solution was found in Case 10 (α = 5°, x = 4), with corresponding evaluation indices of Ce=2.38, Cpl=11.45, and =0.68. This study's findings are of great importance for enhancing the performance of marine gas turbines and reducing external infrared radiation.

Assessing the Potential of Heat Pumps to Reduce the Radiator Size on Small Satellites

Future small satellites will demand high-performance on-board electronics, requiring sophisticated approaches to heat rejection beyond simply increasing the radiator surface area. An interesting alternative approach is to increase the surface temperature of the radiator, using a heat pump. In this study, calculations were carried out to compute the theoretical radiator size reduction potential enacted by having a heat pump as part of a satellite’s thermal management system. The practical likelihood of a ‘typical’ vapor compression cycle (VCC) heat pump satisfying theoretical requirements was considered. In agreement with theoretical calculations, employing a ‘typical’ VCC heat pump could either increase or decrease the required radiator surface area. The choice of heat pump and its design is therefore crucial. A heat pump with a large temperature lift is essential for satellite radiator cooling applications, with the coefficient of performance (COP) being less important. Even with a low COP, such as 2.4, a ‘typical’ heat pump providing a large temperature lift, close to 60 °C, could reduce the satellite’s radiator surface area by a factor close to 1.4. This is a significant potential reduction. The decision on whether to pursue this approach compared to alternatives, such as deployable radiators, should consider the relative complexity, cost, weight, size, reliability, etc., of the two options. The focus of this study is VCC heat pumps; however, the results provide performance targets for less mature heat pump technologies, e.g., caloric devices, which could ultimately be applied in space.

Using intelligent multi-objective optimization and artificial neural networking to achieve maximum solar radiation with minimum volume in the archetype urban block

Nowadays, with the rapid development of cities, the demand for efficient and renewable energy, particularly solar radiation, is growing. Thus, urban planners and designers should employ solar energy analysis as a requirement to propose efficient solutions. This research aims to determine the maximum annual solar radiation with the least volume in various patterns of urban blocks and convert solar radiation modeling and analysis from simulation to emulation for types of urban blocks. As a result, simulation approaches such as Multi-Objective Optimization and Artificial Neural Networking were presented to characterize the influence of different urban scales on solar access and reach the optimal dimensions of the block. In Kermanshah, different patterns of urban blocks were investigated for the study on the urban block scale. The height, direction, number of plots, and scales impact access solar radiation energy and optimize the block’s dimensions. A study of 34 different urban blocks found that the ideal size is roughly 100∗100 m, while the best height is between 10 and 15 meters. Furthermore, the findings of predicting the data training models revealed that three outputs, the rate of solar radiation absorption, volume, and area of the urban block, can be predicted with an R2 score of 98% using the research input variables. Thus, radiation absorption estimations utilizing AI algorithms can ultimately replace traditional approaches and time-consuming large-scale energy estimates. The ANN methodology outperforms other machine learning techniques in predicting the objective function, which contains the amount of solar radiation absorption, volume, and surface area, according to the results of this research. Also, this research demonstrates how a simulation technique based on NSGA-II and ANN algorithms may drastically decrease computation time and costs while predicting optimum states prior to getting a real sample.

Heat transfer performance and exergy analyses of MgO and ZnO nanofluids using water/ethylene glycol mixture as base fluid

Forced laminar convective heat transfer of MgO and ZnO nanofluids through flat tube automobile radiator was studied numerically using 0.25-3ć volume concentrations at Reynolds number ranges (250–1750) for both nanofluids. The results showed an increase in the convective heat transfer coefficient 13.76% and 17.1% at 3% concentration of ZnO and MgO nanofluids, respectively, relative to water/ethylene glycol mixture (50:50 by vol%.) as a base fluid. However, increasing the volume concentration caused an increase in the pumping power For same heat rejection of W/EG mixture, a reduction of about 4.15% and 3.1% in radiator surface area was obtained at 1% concentration of MgO and ZnO nanofluids, respectively. A decrease in total exergy destruction rate of 15.7% and 12.2% compared to the base fluid was obtained for 3 vol% of MgO and ZnO nanofluids, respectively, at Re = 1750.

Experimental investigation on premixed hydrogen/air combustion in varied size combustors inserted with porous medium for thermophotovoltaic system applications

Micro combustion stabilization is challenged by the large heat loss ratio, and the operating conditions are narrow because of the small combustor size. In this work, experimental tests combined with numerical simulations are carried out to investigate the premixed H2-air combustion with and without porous medium. The results indicate that the flame stabilization is greatly enhanced in the combustor with porous medium, and the wall temperature with porous medium is 188 K higher than that of the free flame in the tube with a length 22 mm, an outer diameter 7 mm and the wall thickness 0.5 mm. The appropriate porosity of porous medium is selected for each combustor to achieve a better thermal performance and high radiation temperature. With the increase of combustor diameter, the limitations in terms of inlet velocity and flame blowout are expanded and the radiation surface area is also increased for a higher energy output. The radiation temperature and surface area play important roles in the application of micro thermo-photovoltaic system. The combustor with a length 27 mm and an outer diameter 7 mm is able to achieve an optimal balance between the contingent negative variation of radiation surface area and radiation temperature, delivering an electrical power of 1.41 W with an efficiency 1.39% for the micro-TPV system with InGaAsSb PV cells when the H2 flow rate is 3.03 g/h and equivalence ratio Φ = 0.85.

Method for Producing Fine Liquid-Drop Systems in Ultrasound Fields

This study is devoted to theoretical research on two-stage fine spraying of liquids that consists of the primary formation of large drops under the effect of ultrasound on a thin liquid film and the secondary breakup of generated drops under the influence of a high-frequency acoustic field in an air-drop medium. A physical mechanism is revealed and a physicomathematical model is proposed for the breakup of drops, which makes it possible to determine the threshold levels of acoustic pressure for various drop sizes, properties of a sprayed liquid, and types of action. It is found that the most effective method of acoustic action is the sequence of different-frequency pulses at a high aerosol concentration (greater than 10 vol %), which creates conditions for intermode dispersion. It is shown that, under the effect of continuous single-frequency vibrations, the radiator power necessary for drop disintegration can exceed 550 kW. Under pulsed action, the required power decreases to 2 kW at a radiating surface area of 800 cm2.

Reliability and loading-following studies of a heat pipe cooled, AMTEC conversion space reactor power system

During the progress and development of the space technology, the space reactor power system (SRPS) is one of the best options for providing high power density, long-term life, light weight, and high reliability space power for civil or military space missions. The heat pipe cooled SRPS (HPS) equipped with the static conversion technology Alkali Metal Thermal-to-Electric Conversion units (AMTEC) has good inherent dynamic characteristic for frequent change load following of the space mission power, with high safety and reliability. This paper analyzed the system safety and reliability of an AMTEC conversion HPS, the load following characteristics of the AMTEC conversion and the HPS's performance in response to partial surface area loss of potassium heat pipe radiator. The results show the following. (1) As the external load resistance increases, the AMTEC thermoelectric conversion efficiency and electric power output both increase to the maximum, and then decrease. The maximum thermoelectric conversion efficiency and electric power output correspond to different critical external load values. The load following capacity of the AMTEC HPS exists only when the external load demands exceed a critical value. (2) When the potassium heat pipe radiator's surface area is partially lost because of the impact of a meteorite, the reactor thermal power, the AMTEC conversion efficiency and the electric power output also decrease, except the radiator temperature due to the radiator area loss. The waste heat rejection, the conversion efficiency and electric power output of the system decrease proportionally to the radiator's surface area loss. To ensure the safety and reliability of the SRPS, the reactor thermal power will run down after the loss of the radiator's surface area.

The influence of large foundation arrangement on underwater radiated noise of underwater vehicle engine compartment

Mechanical vibration is the main noise source of underwater vehicle. The foundation of the main power is an important pathway of mechanical noise. Large size foundation of the power not only affects the vibration transmitted from the power to the hull structure, but also affects the vehicle shell radiation area and radiation efficiency, thus affecting the radiation noise of underwater vehicle. Based on the study of the influence of the large size foundation arrangement on the radiated noise of underwater vehicles, two new types of foundation arrangement were proposed. The foundation could meet the requirements on the acoustic performance, and could greatly reduce the radiation surface area of the shell and reduce the radiated Sound Pressure. To the power compartment general layout and support function, three foundation layout schemes such as continuous style, large span style and bulkhead support style in the typical excitation of power equipment were designed. Further way, far field underwater radiation noise of the compartment was numerically calculated. The results show that bulkhead support style can effectively reduce underwater acoustic radiation of the compartment shell on the premise of the meet the weight control and impedance characteristics.

Investigations on Convective Heat Transfer Enhancement in Circular Tube Radiator Using Al2O3 and CuO Nanofluids

In this study, forced convective heat transfer inside a circular tube automobile radiator is experimentally and numerically investigated. The investigation is carried out using Al2O3 and CuO nanofluids with water as their base fluid. A single radiator circular tube with the same dimensions is numerically modeled. Numerical model is validated using the experimental study results. In the experimental study, Al2O3 and CuO nanofluids of 0.05% volume concentrations (ϕ) were recirculated through the radiator for the Reynolds number (Re) between 260 and 1560. The numerical investigation is conducted for the nanoparticle volume concentration from 0% to 6.0% and 260 < Re < 1560. The investigation shows an enhancement of convective heat transfer coefficient (h) with the increase in nanoparticle volume concentration and with the Reynolds number. A maximum enhancement of 38% and 33% were found for Al2O3 and CuO nanofluids of ϕ = 1% and Re = 1560. For the same cooling load of the radiator, the pumping power can be reduced by 8% and 10%, when Al2O3 and CuO nanofluids (ϕ = 0.8%) were used. Enhancement in convective heat transfer can be utilized to reduce the radiator surface area required. However, the addition of nanofluid results in an enhancement of density (ρ) and viscosity (μ) along with a reduction in specific heat capacity (Cp). Hence, the selection of nanoparticle volume concentration should consider its effect on the thermophysical properties mentioned earlier. It is found that the preferred concentration is between 0.4% and 0.8% for both Al2O3 and CuO nanofluids. In our investigations, it is observed that the convective heat transfer performance of Al2O3 nanofluid is better than the CuO nanofluid.

Directivity control of a graphene loudspeaker array using elementwise switching technique

Graphene is a promising material for thermoacoustic transducers because of its low heat capacity per unit area and easy fabrication process. In contrast to the conventional voice-coil loudspeaker, a small thermoacoustic loudspeaker can produce omnidirectional radiation even without enclosures. In addition, the sound level from a thermoacoustic loudspeaker is less sensitive to its radiating surface area, which makes it an ideal omnidirectional sound source in high frequency region. In this work, we present an elementwise switching control of a graphene loudspeaker array utilizing the advantages of thermoacoustic loudspeakers. With an array of 3D graphene transducers, a directivity is controlled by polarity switching of each element according to a pre-determined pattern. A single channel input signal is modulated into two different channel signals using a polarity inverter. Each graphene element is driven by the same signal with different sign, and the polarization pattern of the array forms a designated beam pattern. The proposed technique simplifies the control of beam patterns without using large number of independent channels, and hence, enables the construction of a high frequency driver with variable-directivity.

Effects of ultrasonic disintegration of excess sewage sludge.

Breaking down sludge floc (sonodyspergation effect) and destruction of the cell membranes of microorganisms forming floc is a direct effect of ultrasonic disintegration of sludge excess. This results in release of organic material by liquid sludge (the sonolysis effect). Desired technological effects of the disintegration are: to shorten the hydrolytic phase of fermentation, to increase the production of biogas (source of renewable energy) and an increased mineralization (stability) of fermented sludge. The presented study demonstrates research covering thickened excess sludge of various physicochemical properties, collected from nine municipal sewage treatment plants. The sludge was subjected to ultrasonic disintegration using three differently constructed disintegrators and different proportions of sonification area. Direct effects of disintegration were monitored and recorded using selected indicators describing changes in the properties of sludge and increase of substance dispersed and dissolved in the supernatant liquid to be filtered. Studies have demonstrated that those (direct) effects of ultrasonic disintegration depend on the physicochemical properties of the sludge (foremost the concentration of dry solids) that determine their variable susceptibility to the disintegration methods. The direct effects also depend on optimal process conditions (which consist of the construction of the ultrasonic disintegrator), the geometric proportions of the sonication area and the operating parameters of disintegration (which could be appropriately matched to the characteristics of sludge). The most preferable results were obtained for ultrasonic disintegration of sludge with a dry matter concentration C 0<4.2%. The highest effect of sonolysis-an almost 30-fold increase in the COD dissolved in the supernatant-was obtained for the sludge of lowest dry matter (C 0=2.0%), which was sonicated in a reactor with a short transducer of the largest radiating surface area, as well as the lowest ratio between this area and area of reactor. The best effects of disagglomeration of flocks have corresponded with the high value of power density U UD=880-900WL(-1).

Numerical Analysis on the Heat Transfer Characteristics of the Radiator in a Heating Room

Natural convective heat transfer is the most important means to supply heat load for resident building to keep necessary indoor air temperature in winter. To determine the surface convective heat transfer coefficient (CHTC) of a radiator is of primary importance to evaluate the heat flow within building interiors, and thereby to affect the thermal comfort and the overall energy consumption of a building. In this paper, a turbulent k-ε model is used to numerically analyze the heat transfer characteristics of a radiator used in a heating room in Lanzhou region of China. The results indicate that the averaged Nu number of radiator surface increases with increasing outer wall thermal conductivity, decreasing outdoor temperature and decreasing radiator surface area, respectively. And the outer wall thermal conductivity has weak influence on the local Nu number of radiator surface.

THE PECULIAR BALMER DECREMENT OF SN 2009ip: CONSTRAINTS ON CIRCUMSTELLAR GEOMETRY

We present optical and near-IR spectroscopic observations of the luminous blue variable SN 2009ip during its remarkable photometric evolution of 2012. The spectra sample three key points in the SN 2009ip lightcurve, corresponding to its initial brightening in August (2012-A) and its dramatic rebrightening in early October (2012-B). Based on line fluxes and velocities measured in our spectra, we find a surprisingly low I(H-alpha)/I(H-beta) ~ 1.3-1.4 in the 2012-B spectra. Such a ratio implies either a rare Case B recombination scenario where H-alpha, but not H-beta, is optically thick, or an extremely high density for the circumstellar material of n_e > 10^13 cm^(-3) The H-alpha line intensity yields a minimum radiating surface area of >~20,000 AU^2 in H-alpha at the peak of SN 2009ip's photometric evolution. Combined with the nature of this object's spectral evolution in 2012, a high circumstellar density and large radiating surface area imply the presence of a thin disk geometry around the central star (and, consequently, a possible binary companion), suggesting that the observed 2012-B rebrightening of SN 2009ip can be attributed to the illumination of the disk's inner rim by fast-moving ejecta produced by the underlying events of 2012-A.

Dirt analysis on the performance of an engine cooling system

This present work looked at the effect of sand blocking the heat transfer area of the radiator and its effect on the engine coolant through the conduct of experiments and a mathematical model developed. The results indicated that the percentage area covered resulted in a proportional increase of the inlet and outlet temperatures of the coolant in the radiator. The mathematically model developed also predicted the experimental data very well. Regression analysis pointed out that every 10% increase area of the radiator covered with silt soil resulted in an increase of about 1.7oC of the outlet temperature of the radiator coolant. Similarly, using mud as a cover material, 10% of the area covered of the radiator resulted in an increase of about 2oC of the outlet temperature of the radiator coolant. Statistical analysis pointed to the fact that the result obtained for mud, silt and the mathematical model were not significantly different. Thus, irrespective of the type of material that blocks the radiator surface area, the coolant rises proportional of the radiator covered.

Characterization and Water Activation Behavior of Tourmaline Nanoparticles

Tourmaline nanoparticles were prepared by using a wet mechanochemisty method. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results showed that the tourmaline grain size is in the range from tens of nanometers to several hundred nanometers. Through characterization by Fourier transform infrared spectroscope, it was found that the milled tourmaline had a better far infrared emitting performance due to the increase of radiation surface area. The structure change of liquid water clusters induced by the addition of tourmaline nanoparticles was observed by nuclear magnetic resonance (NMR). The results showed that the addition of tourmaline nanoparticles reduced the 17O NMR full width at half maximum intensity (FWHM) for treated water and the volume of water molecule clusters. The feature of activated water was enhanced with decreasing tourmaline nanoparticles size due to the cooperation of strong surface electric field and high far infrared emissivity. Moreover the activation time can be maintained at 480 h suggesting the potential application of tourmaline in wastewater treatment.

Edge electroluminescence of single-crystal silicon at 80 K: Structures based on a high-efficiency solar cell

The spectral, kinetic, and energy characteristics of edge luminescence of silicon light-emitting diodes (LEDs) with radiating surface area of 0.055 cm2 are studied at a temperature of 80 K over a wide range of pulsed currents. The LEDs are fabricated by cutting a high-efficiency solar cell. In contrast to a number of less effective silicon LEDs studied earlier, the external quantum efficiency of our LEDs at a fixed current at 80 K is higher than that at 300 K and its maximum value is about 0.4%. Despite the occurrence of Auger recombination, a record-high emissive power per unit surface area P = 0.2 W/cm2 is attained at a pulsed current of 12 A. It is shown that this record value is achieved largely because the mechanism of radiative recombination is changed at large currents. The conditions are analyzed under which the free-exciton luminescence is changed to electron-hole plasma luminescence.

Applying thermal imaging software to cattle grazing winter range

1. Metabolic demands of cattle grazing winter range may be over-predicted by models that do not account for animal behavior. Cattle may conserve energy and mitigate cold stress by short-term behavioral responses. 2. We solved the thermal balance equation for a revolving three-dimensional model using advanced thermal solution software to simulate unconstrained cattle during winter. This software, developed for inanimate objects, predicted energetic requirements within expected range of values. 3. Solar radiation and apparent surface area were instrumental in reducing energy requirements, especially on cold clear days, whereas wind velocity and ambient temperature had a lesser effect on well-insulated cows in good body condition.

A windowless VUV excilamp

An open windowless excilamp capable of operating on argon (λ ∼ 126 nm), krypton (∼146 nm), and xenon (∼172 nm) dimers is described. The lamp has a total radiating surface area of 23 × 23 = 529 cm2. At a total power of ∼0.8 W radiated through this area, the average output power density at λ ∼ 126 nm is ∼1.6 mW/cm2 at a distance of 2 cm from the emitting surface. A pulsed discharge between insulator-coated anode and thin wire cathode ensures a high efficiency of the proposed radiation source operating in the vacuum ultraviolet spectral range.

A high-power xenon dimer excilamp

A high-power sealed-off excilamp operating on xenon dimers excited by a barrier discharge and emitting in the vacuum ultraviolet spectral range (λ ∼ 172 nm) has been designed, constructed, and tested. The lamp comprises six quartz tubes (emitters) and has a total radiating surface area of 20 × 20 = 400 cm2. The average output power density radiated from the surface of each emitter exceeds 120 mW/cm2. The total output power of the excilamp immediately upon discharge ignition exceeds 50 W.