Semitransparent Wall Research Articles

Performance analysis of a concentrated direct absorption solar collector (DASC) with nanofluids using computational fluid dynamics and discrete ordinates radiation modelling (CFD-DORM)

This study utilises computational modelling to investigate the application of thermal nanofluids in direct absorption solar collectors (DASC), including the effect of optical and thermal properties on the prediction of thermal energy production. A single-phase, computational fluid dynamics (CFD) model has been used to understand the hydrothermal behaviour of nanofluids operated at high temperature. A non-gray discrete ordinate radiation model (DORM) was coupled to the CFD to capture the dependence of optical parameters on the bulk temperature variation. In order to increase the robustness of the numerical modelling approach, the extinction coefficient of the solar participating media, including the reflective and transmissive behaviour of the semitransparent wall, were taken into consideration. Results show that the exergy efficiency is lower when using fully diffusive conditions at the semitransparent wall as opposed to fully specular conditions. Overall, exergy efficiency decreases with the Nusselt number, Nu, (until Nu=10∼12), although it increases with non-dimensional irradiation. When modelling with temperature-dependent as opposed to temperature-independent properties of the working fluid, the Carnot efficiency was found to vary by 0.67% to 3.30%. Additionally, a correlation between the hydraulic entrance length and Reynolds number, Re, (in the range Re<1,000) has been established and this can be applied for the further hydrothermal analysis. This study serves as a basis for future numerical modelling of any volumetric solar receiver that takes into account the various key system performance indicators of the solar participating media.

2D waveguides: asymptotics of eigenvalue induced by a window in a semitransparent separating wall

Two-dimensional quantum waveguides with common semitransparent wallare considered. It is assumed that there is a small window in the separat-ing wall. It leads to the appearance of an eigenvalue below the continuousspectrum. Semitransparent wall is introduced as a potential supported bya hypersurface. We use the method of asymptotic expansions of boundaryproblems solutions. It allows us to obtain the main term of the asymptoticsexplicitly

Investigation of thermal adiabatic boundary condition on semitransparent wall in combined radiation and natural convection

Two thermal adiabatic boundary conditions arise on the semitransparent window (wall made of glass material) owing to the fact that whether semitransparent window allows the energy to leave the system by radiation mode of heat transfer or not. It is assumed that the energy does not leave by the conduction mode of heat transfer, due to the low thermal conductivity of semitransparent material. This does mean that the semitransparent window may behave as only conductive adiabatic or combined conductive and radiative adiabatic In the present work, the above two thermal adiabatic boundary conditions have been investigated for natural convection in a cavity, whose left vertical wall has been divided into upper and lower parts in the ratio 4:6. The upper section is a semitransparent window, while the lower section is an isothermal wall at a temperature of 296 K. A collimated beam is irradiated on the semitransparent window with values 0, 100, 500, and 1,000 at an azimuthal angle 135°. The cavity is heated from the bottom by convective heating with free stream temperature 305 K and heat transfer coefficient 50 While the right wall is also isothermal at the same temperature as of lower left wall and the upper wall is adiabatic. All walls are opaque for radiation except the semitransparent window. The results reveal that the dynamics of both the vortices inside the cavity change drastically with irradiation values and also with the boundary conditions on the semitransparent window. The temperature and Nusselt numbers increase many folds inside the cavity for combined conductive and radiative adiabatic condition than only conductive adiabatic condition on the semitransparent window.

Fixed Beam Broadband Leaky Wave Antenna

A linear leaky-wave antenna with a fixed beam, containing a waveguide with a semitransparent narrow wall made of metal cylinders and a prism with constrained refraction of 15 metal waveguides, is proposed and studied using numerical simulations based on the finite element method in the Ansys HFSS software product. A compact three-channel waveguide power divider in the E-plane is proposed and investigated. Using numerical simulation, the characteristics of an antenna array containing a divider and three linear leaky wave antennas with prisms are investigated. It is shown that in a frequency band of more than 15%, the efficiency of the antenna array surface is more than 0.65.

Analytical Technique for Synthesizing a Leaky-Wave Antenna with a Semitransparent Wall of Metal Cylinders

We have developed an analytical technique for synthesizing a leaky-wave antenna in the form of an irregular hollow rectangular metal waveguide with a narrow wall in the form of an array of circular metal cylinders using an approximate expression for the reflection coefficient of a plane wave from a fine-periodic lattice of circular metal cylinders and the dispersion equation for a waveguide with a partially transparent wall. As an example of the application of this technique, two leaky-wave antennas are synthesized: with a uniform and sinusoidal distribution of the field amplitude along the antenna. We have performed electrodynamic modeling of synthesized antennas using the finite element method. For a synthesized antenna with a uniform amplitude distribution, the results of a numerical experiment are compared with the results of measurements of an experimental sample in the centimeter wavelength range.

Synthesis and Analysis of an Leaky Wave Antenna with a Semitransparent Wall of Metal Cylinders

Abstract—The article considers problems of synthesizing and analyzing a leaky wave antenna in the form of an irregular hollow rectangular metal waveguide with a narrow wall in the form of a array consisting of round metal cylinders. The cross section method, an approximate expression for the reflection coefficient of a plane wave from an array of round metal cylinders with small period, and the dispersion equation for a waveguide with a partially transparent wall are used to solve the problem of synthesizing a given linear front with a given amplitude distribution. As an example, the laws of change in the period of the arrangement of cylindrical conductors and their distances to the opposite narrow wall of the waveguide are found in order to achieve a linear leaky wave antenna with a uniform distribution of the amplitude of the zero spatial harmonic along the waveguide. Using the finite element method, a linear antenna and an antenna array of six linear leaky wave antennas were electrodynamically simulated.

Mathematical modelling of conjugate laminar and turbulent heat transfer in a cavity: Effect of a vertical glazed wall

A numerical analysis of the laminar and turbulent natural convection combined with surface thermal radiation in a square cavity with a glazed wall is presented. The enclosure is composed of one left vertical isothermal wall, two horizontal adiabatic walls, and one right vertical partially semitransparent wall (clear glass sheet). Different values of the aspect ratio of the right vertical glazed wall (A=0.15,0.25,0.5,0.75,1.0) are analyzed, and the incoming solar irradiation (G) over the glass is varied from 0 to 750 W/m2 at intervals of 150 W/m2. Three different case studies were considered based on the position of the clear glass sheet on the right wall: (a) located at bottom side/Case 1 (C1), (b) located at the middle side/Case 2 (C2), and (c) located at the upper side/Case 3 (C3). The numerical solution was carried out using an in-house code based on the finite volume method. The numerical code was validated against experimental data for the turbulent natural convection problem. A comparison between the predicted and measured dimensionless vertical velocity, temperature profiles and local and average Nusselt numbers are presented, obtaining good agreement. Results show that convective heat transfer increases from about 70 to 250 as the aspect ratio increases from 0.15 to 1.0, for all solar radiation intensities, and all cases of turbulent flow. Also, radiative heat transfer decreases as the aspect ratio and solar radiation increase, which implies that it could become lower than convective heat transfer for some aspect ratio values set. When a laminar flow regime is considered, lower average convective and radiative heat transfer rates are obtained regarding the case of turbulent flow. In general, they are between 2.0<Nuconv<7.5 and 2.0<Nurad<13.5 for all cases under analysis. Finally, a set of correlations for the total Nusselt number were obtained for turbulent conjugate heat transfer.

Analysis of Combined Natural Convection and Radiation Heat Transfer in a Partitioned Rectangular Enclosure with Semitransparent Walls

In this paper, we present a two-dimensional numerical analysis of the conjugate natural convection and radiation heat transfer in a double-space enclosure with two semitransparent walls. Two kinds of boundary conditions are considered, the first being the isothermal process of the opaque wall, and the other the incidence of a constant radiation flux in the left semitransparent wall. The renormalization group k–ε model is adopted to simulate the turbulent flow in the enclosure. To compute the radiation heat transfer in a semitransparent medium, the discrete ordinates model is used. We compare the behaviors of enclosures with single and double semitransparent walls and determine the difference in the results obtained for semitransparent and opaque partitions. The results indicate that a semitransparent partition facilitates a reduction in the heat loss or obtains a higher temperature distribution. The transmittance of a semitransparent wall has a great effect on the thermal and flow characteristics in an enclosure. The change of wall temperature is found to be significant when the thermal conductivity values range from 0.05 to 0.5 W/(m·K), and to be small when ranging from 0.5 to 10 W/(m·K). These conclusions are helpful for green design and energy saving in solar buildings.

Subsurface Laser Engraving Techniques for Scintillator Crystals: Methods, Applications, and Advantages

Pixelated scintillators are commonly used for gamma radiation detection in PET scanners. Dimensions, surface treatment, and reflector thickness affect the resolution and sensitivity of the detector and increase the signal to noise ratio. Pixel arrays fabrication is laborious and expensive, while by including nonscintillating material the active area of the detector is reduced. This process can be simplified and improved by the application of subsurface laser engraving techniques, where a grid of laser-induced microcracks form semitransparent walls inside the scintillator. Conceptual development of such patterns including simulations and photometric measurements is presented as a proof that pixelation without the application of external reflectors is possible, liberating pixel size and shape and allowing detector-specific patterns to be created. To demonstrate this, a case study of a hexagonal grid of pixels of 1.4 mm $^{2}$ size on LYSO monolithic scintillators is proposed and results presented. Depth of interaction is also implemented on same size pixels, through different approaches. Advantages, concerning sensitivity, packing fraction, and cost effectiveness are discussed, supporting the viability of the process as an alternative to conventional pixelated array fabrication techniques which combines advantageous characteristics of both monolithic and pixelated scintillators.

Thermal performance of a room with a double glazing window using glazing available in Mexican market

A thermal evaluation of a four configurations of double glass window (DGW) coupling to a room is presented. The DGW consists of two vertical semitransparent walls separated by a 12mm air gap. The effect of varying the ambient temperature and the incident solar radiation in the warm climate conditions in México is analyzed. Numerical simulations were conducted for four configurations; Case 1: clear glass+air gap+clear glass (Reference); Case 2: clear glass+air gap+absorbent glass; Case 3: clear glass+air gap+Low-e glass; and Case 4: clear glass+air gap+reflective glass. Optical transmittance and specular reflectance were measured individually and in one sample piece for each case. The results showed that Case 4 reduces the heat flux to the indoors by up to 73%, with respect to Case 1. Moreover, Cases 2 and 3 had a similar behavior, obtaining a reduction of indoor heat flow close to 33.5% with respect to Case 1. Case 4 is the best option for energy savings in a warm climate, where it is possible to save up to $20.29 USD per kWh per year, in comparison to Case 1. In addition, the payback period for Case 4 is 3.7years. Therefore, the use of reflective double pane window is highly recommended in Mexican warm climates.

Ah, Wilderness!

Ah, Wilderness!

Thermal evaluation of a Room coupled with a Double Glazing Window with/without a solar control film for Mexico

The thermal evaluation of a Room (R) coupled with a Double Glazing Window (DGW) with/without solar control film (SCF) under warm and cold climate conditions of an extreme weather of Mexico is presented. The right vertical wall of the room is partially adiabatic and contains the DGW. The DGW consists of two vertical semitransparent walls: glazing-1 facing the room, and glazing-2 facing the external environment. The SCF is attached to glazing-1 for cold climate condition, or attached to glazing-2 for warm climate condition. During one day, hourly simulations of the R-DGW were done using an in-house code based on the finite volume method. Three cases were defined to analyze the R-DGW system: Case C1 corresponds to the R-DGW without SCF; Case C2 and C3 correspond to the R-DGW with SCF for warm and cold climate conditions, respectively. For warm climate condition the use of a SCF is highly recommended, since the Case C2 was able to reduce ≈62% of the energy gains with respect to Case C1. When the solar control coating in double glass window is used for cold climate condition (case C3), the average temperature inside of the room is similar to the case C1.

المشربیة ...... الجدار الشفاف الفاصل بین العام والخاص

Islamic architecture present a various useful details and elements through an aesthetic vision providing a properfunction and merges in homogeneity with the surrounded built environment.Al Mashrabeyia (In Arabic) where is drinking water jars are kept, or Al Mashrafeyia (in Arabic) which it’s functionsimulating the terrace, is a witness of the architect’s creativity to create a semi transparent wall gives vision from insideto outside the space in parallel to keeping an inner proper privacy.Al Sehiemy house at Mamlouki Cairo includes a perfect study models of geometrical treatments used to shape thetransparent walls.

Thermal energy storage and losses in a room-Trombe wall system located in Mexico

A thermal evaluation of a R-TW system (room with a Trombe wall) is presented. Hourly climatic data of the coldest and the warmest days of 2014 was used to assess the behavior of the R-TW in two cities of Mexico with cold climate (Huitzilac and Toluca). The simulations were done with an in-house code based on the Finite Volume Method. It was found that thermal energy losses through the semitransparent wall are about 60% of the solar radiation incident on the system (Gsol). Despite of the thermal losses, the system gets enough energy to keep the air inside the room with a temperature above 35 °C. For both cities during the coldest day, the maximum energy stored is about 109 MJ and during the warmest day is about 70 MJ. This energy is supplied from the storage wall to the air inside the room during periods without insolation.

Computational fluid dynamics for thermal evaluation of a room with a double glazing window with a solar control film

The thermal analysis of a Room (R) coupled with a Double Glazing Window (DGW) with/without solar control film (SCF) for warm and cold climate conditions of Mexico City is presented. The right vertical surface of the room is considered partially adiabatic and with a DGW. The DGW consists of two vertical semitransparent walls: glazing-1 facing the room, and glazing-2 facing the external environment; there is a SCF attached to glazing-1 for cold climate condition, or glazing-2 for warm climate condition. During one day, the hourly simulations of the R-DGW were done in an in-house code based on the finite volume method. To carry out the thermal analysis of the R-DGW, three cases were defined: Case C1 corresponds to the R-DGW without SCF; Case C2 and C3 correspond to the R-DGW with SCF for warm and cold climate condition, respectively. For warm climate condition the use of a SCF is highly recommended, since Case 2 reduces the amount of energy gained in ≈67.7% compared to Case 1. When using the SCF on the R-DGW for cold climate condition case C3, the average temperature inside of the room is similar to case C1.

Unsteady-RANS simulation of conjugate heat transfer in a cavity with a vertical semitransparent wall

A numerical study of the unsteady conjugate heat transfer for a square cavity with a semitransparent (glass) wall is presented. The cases with or without solar control film on the semitransparent wall were studied from 8:00 to 18:00h. This wall interacts with the environment through the incident solar radiation and the outdoor air temperature, which were considered changing over the time. URANS (Unsteady Reynolds Averaged Navier–Stokes) model together with the model of Low-Reynolds number turbulence k–w were solved using the finite volume method. The results show flow patterns from multicellular to unicellular in different times for each case as result of the temperature in the semitransparent wall. Moreover, at approximately 9:00am, the solar control film increased the air temperature inside the cavity up to 10°C compared to the air temperature when the solar control film is not used. The cavity with solar control film has a lower period of time with a multicellular flow than the cavity without film. When the solar control film is used, the average heat flux due to convection and radiation represents 45% and 55%, respectively of the interior heat flux (qint). On the contrary, when the solar control film is not used, the heat flux due to radiation represents 70%.

Thermal performance of a double pane window using glazing available on the Mexican market

A numerical study of a double pane window (DPW) with three types of commercial glass available in Mexican market is presented. The DPW consist of two vertical semitransparent walls separated by an air gap. The effect of varying the gap width (b) between glasses, the room temperature and the incident solar radiation is analyzed. Simulations were conducted for three configurations; case 1: clear glass + air gap + clear glass; case 2: clear glass + air gap + absorbent glass; and case 3: clear glass + air gap + reflective glass. Optical transmittance and specular reflectance of each case were measured. Two climatic conditions were analyzed, warm and cold climate. The results showed that, in order to increase or reduce the indoor heat gains, from b ≥ 0.02 m, the heat fluxes remains almost constant for both climate conditions. For cold climate, the case 1 reached the highest energy savings (∼10.5 and ∼28.5% higher than cases 2 and 3, respectively), however in warm climate it had the worst behavior (∼105 and ∼177% higher than cases 2 and 3, respectively). Finally, considering the case 1 as reference, the case 3 had the best combined energy saving ($17.64 USD-kWh/year) and case 2 presents a combined energy saving of $7.16 USD-kWh/year. Therefore is highly recommended the use of reflective double pane window, like to case 3, in Mexican warm and cold climates.

Use of P-1 model with the additional source term for numerical simulation of ultraviolet radiation in a photoreactor

Radiation distribution in a photoreactor with multiple mediums is solved by the P-1 model. The UV lamp is included in the computational domain. An additional source term method is presented to describe the generation of UV light, which can avoid the use of analytical lamp emission model at the lamp surface. The boundary condition for incident radiation at the semi-transparent wall between adjacent mediums has been derived to link the P-1 equations in adjacent mediums, which enables the present model to adapt to the photoreactor with complicated structure. The predicted incident radiation agrees well with the experimental data in literature. The effects of absorption coefficient, scattering coefficient and phase function of lamp plasma on the radiation distribution are discussed in detail.

Casimir Force in a One-Dimensional Cavity with Quasimode

We calculate the Casimir force between a perfect reflective wall and a semitransparent wall in the laser cavity. Using the Fox—Li quasimode theory to describe the electromagnetic field in the laser cavity, the vacuum energy and the Casimir force are calculated. We compare our results to the force in the ideal situation and find it smaller in the dissipative cavity. We also find that the Casimir force decreases with the increase of the wall-wall distance and the decay rate of the quasimodes in the laser cavity.

Thermal analysis for a double pane window with a solar control film for using in cold and warm climates

Abstract A numerical study in a double pane window (DPW) with solar control film (SCF) for warm and cold climates is presented. The DPW consists of two vertical semitransparent walls: glazing-1 facing the room, and glazing-2 facing the external environment and exposed to solar radiation; there is a SCF attached to glazing-1 for cold climate, or glazing-2 for warm climate. The effect of varying the separation distance (b) between the glasses, room temperature and the incident solar radiation is analyzed. To carry out the thermal analysis of the DPW, three cases were defined: Case C1 corresponds to the DPW with SCF; Case C2 corresponds to the DPW and Case C3 corresponds to single glazing window. It was found that in order to reduce or increase heat gains toward the inside environment, the optimal distance between the glasses was b > 6.0 cm for both climate conditions. For warm climate the use of a SCF is highly recommended, since the Case 1 reduces the amount of energy gained within 52% compared to Case 2. When using the SCF on the DPW for cold climate, the amount of energy gain through the system reduces 10% respect to the case C2.