The heat losses are mainly affects on the performance of cavity receiver of solar concentrator. In this paper, the experimental and numerical study is carried out for different heat losses from cylindrical cavity receiver of 0.35 m cavity diameter and 0.55 m opening diameter with wind skirt. The total and convection losses are studied experimentally to no wind conditions for the temperature range of 60 °C to 80 °C at 0°, 25°, 50°, 75° and 90° inclination angle of cavity receiver .The experimental set up mainly consists of cylindrical cavity receiver which is insulated with glass wool insulation to reduce the heat losses from outside surface.. The numerical analysis was carried out with Fluent Computational Fluid Dynamics (CFD) software, to study connective heat losses for no wind condition. The numerical results are compared with experimental results and found good agreement with maximum deviation of 13%. The effect of inclination angle of cavity receiver on total losses & convection losses shows that as the inclination angle increases from 0o to 90o, both losses decreased due to decreased in convective zone into the cavity receiver. The effect of operating temperature of cavity shows that as the temperature of cavity receiver increases, the total and convective losses goes on increasing. The present results are also compared to the convective losses obtained from M. Prakash. The convective loss from M. Prakash shows nearest prediction to both experimental and numerical results.

The experimentation is carried out to examine the influence of receiver aperture/opening ratio (receiver’ s aperture diameter to the maximum diameter ratio, d/D), glass cover thickness and inclination angle of cavity receiver on its collection efficiency for various flow rates of ordinary water as a working fluid. Experimental tests have been conducted at lower incident energy, i. e., at lower cavity wall temperatures (less than 200 ° C). The aperture ratio examined encompasses values as 0. 46, 0. 6, 0. 7, and 0. 93 for water flowing at flows of 0. 8, 0. 65, 0. 5, and 0. 4 LPM that corresponds to Reynolds numbers (Re) of 1880, 1525, 1175, and 938, respectively. The glazing thicknesses of 6, 4, and 2 mm were provided at an aperture. A Modified cavity-type receiver is made inclined at angles 90° , 60° , 45° , and 30° (with 90° as down-facing receiver opening and 30° as close to sideway-facing of receiver opening). The tests have been conducted for cavity surface temperatures ranging from 90° to 180 ° C. It is observed that an aperture ratio of 0. 6 demonstrates maximum receiver performance for the values of Reynolds number studied, while the receiver performance exhibited reducing trend with reduction in receiver tilting angle from 90° to 30° .

Reliable detection of life under rubble and collapsed buildings after disasters like earthquake or air raid is the most important issue in life-detection process. In this paper, the performance of microwave life-detection system (MLDS) based on a continuous wave (CW) radar is analyzed from different aspects such as penetration depth, sensitivity, and total harmonic distortion (THD) of the output signal. A novel quadrature receiver as an appropriate architecture for the MLDS, and harmonic radar system as an alternative structure are proposed in order to resolve the well-known null point issue and improve the sensitivity of the system. Results show that by using these structures in the MLDS, the null points can be completely removed and hence the chance of detecting a trapped victim under the rubble can be improved considerably. Moreover, by using the harmonic structure, the received power in some distances away from the MLDS can be improved by 3 dB compared to that of the conventional systems. By examining different frequencies, 1. 15 GHz (L-band) is found to be the most appropriate carrier frequency because of deeper penetration of about 5 meters in the rubble and 7 percent improved output signal THD compared to the previously designed X-band radars for the MLDS.

In this paper, the effect of using four different types of inserts in cavity receiver tube of solar power tower to improve heat transfer and reduce non-uniform temperature distribution is investigated. Numerical simulation is performed in three dimensions and the effect of inserts configurations, position inside receiver tube, pitch and thickness of insert and the effect of non-uniform heat fluxon the Nusselt number, friction factor and temperature of outer surface of receiver tube are investigated. The flow is incompressible, steadystate, turbulent and the Reynolds number is in the range of 8000 to 20000. Numerical simulation results for four types of inserts: twisted-tape, wavy-tape, helical-tape and louvered-tape show that wavy-tape compared to the other three types, has the higher Nusselt number and the lower average temperature of receiver tubesurface. The Nusselt number of the wavy-tape is increased by 1.8%, 2% and 3.2% relative to the louvered-tape, twisted-tape and helical-tape, respectively and 10% relative to the receiver tube without insert. By increasing the insert thickness and decreasing the insert pitch, the Nusselt number increases and average temperature of receiver tubesurface decreases. Investigating the insert position in three cases: close to the non-uniform heat flux wall, the middle of the tube and close to the insulation wall show that by increasing the distance of insert from non-uniform heat flux wall, the mixing of hot and cold fluids flow is better and the temperature distribution is more uniform.Therefore, the best position to place insert is the farthest distance from the non-uniform heat flux wall.

Objective: Comparison of interaural attenuation between insert receiver made button receiver and Standard earphone. Design: Quasi-experimental survey. Place and date: Department of audiology, School of Rehabilitation Sciences IUMS 1999-2000. Subjects: Foutry 20-25 years old, male students with bilateral normal hearing. Results: 1) IA Obtained with insert receiver at frequencies 250, 500, 1000 and 2000 Hz was greater than those produced by standard earphone specially there will be reducing of IA difference between insert receiver and earphone of frequency increases. 2) Average IA values become larger for air–conduction by standard earphone as frequency increase. 3) There was no significant correlation between frequency and mean IA obtained by insert receiver. Conclusion: Since our insert receiver is easily available, cheap, convenient to use and less prone for masking dilemma than standard earphones using it as insert receiver is desirable. Audiologists can use them to solve masking dilemma.    

In this manuscript, a solar cavity packed with the thermoelectric generator modules has been investigated numerically. The hot plate of TEG modules makes the inner surface of the cube, and the cold plate is the outside the cavity, under natural convection. The TEG modules are electrically in series. The solution algorithm using the equations of heat transfer and generated power of TEG modules is developed via MATLAB and simulated under various non-concentrated irradiation levels. The variation of generated power in solar thermoelectric cavity shows that increasing of the solar irradiance caused increasing the growing rate of the generated power. The radiation varies from 700 to 1200 W/m2, and the generated power is increased from 0. 26 mW to 10 mW in the side of TEGs and up to 30 mW in the bottom of TEGs. The evaluation of aperture size indicates although the generated power of fully open cavity is 2. 25 times higher than the generated power in 0. 05×0. 05 m2 aperture size cavity, its efficiency is 46% lower than the small aperture cavity. Heat transfer analysis of cavity depicts that 91% of heat transferred by conduction in the cube surfaces. Only 6% and 3% of input energy are lost by re-radiation and convection through the aperture, respectively.

Accurate calculation of pressure distribution in the impeller cover side cavity is the key to predict the axial force of centrifugal pump. The existing calculation models almost does not involve the prediction of cavity pressure when the radial clearances of different sealing rings are matched with the diameter of different balance holes. On the basis of the original prediction model of pump cavity pressure, a mathematical model of pressure distribution of impeller cover side cavity with different radial clearance of sealing ring and the diameter of balance hole was established by introducing potential head correction coefficient and flow proportional coefficient. In order to improve the calculation accuracy of rotation coefficient for rear pump cavity, the balance aperture length ratio and the rotation undetermined coefficient were introduced in the calculation equation of original rotation coefficient. A test bed for pressure and leakage was designed and established, and the pressure of impeller cover side cavity and balance hole leakage was systematically tested when the radial clearance of sealing ring and the diameter of balance hole were different. Experimental results showed that the radial clearance of rear sealing ring and the diameter of balance hole had different effects on the radial pressure gradient of pump cavity. The diameter of balance hole had little effects on the pressure of the front pump cavity. When the clearance of the front and rear sealing rings were the same, the pressure of rear pump cavity was generally higher than that of the front pump cavity. For the equilibrium chamber liquid, increasing the diameter of balance hole could relieve the pressure, and increasing the radial clearance of sealing ring could increase the pressure. Combined with the test data, the potential head correction coefficient, the rotation undetermined coefficient and the flow proportional coefficient of different specific areas were calibrated, with a specific solution equation. In this study, the reliability of the proposed pressure mathematical model for impeller cover side cavity was verified by three cases. The results showed that the theoretical prediction value was more consistent with the actual measured value, proving that the proposed mathematical model had high accuracy and universality.

Introduction: Marginal seal in class V Cavities and determining the best restorative material to decrease microleakage of them is very important in operative dentistry.Objective: To evaluate the microleakage of class V cavity preparations restored with three different types of resin composite and resin Modified glass Ionomer.Materials and Methods: Two class V cavities were prepared in buccal surface of 32 recently extracted premolar teeth.The occlusal margin of each restoration was on enamel and the gingival margin on dentin. Teeth were randomly assigned to four groups of 8 teeth and restored as follows: Group I: microhybrid resin composite (Z250); Group II: nano composite (supreme); Group III: Flowable composite (3M); Group IV: resin Modified glass Ionomer (vitremer). In all groups, the manufacture instructions were strictly followed. All teeth were immersed in 50% Silver Nitrate during 4 hours and developing solution for 8 hours after thermocycling. The teeth were longitudinally sectioned and observed under a stereomicroscope. The degree of dye penetration was recorded and analyzed with the kruskal-wallis and mann-whitney test.Results: There was no evidence of microleakage on the enamel margins in any groups. When the margins were in dentin, vitremer and flowable composite had the less and the most level of microleakage in dentinal margine respectively (p<0.05). There was no significant differents in other groups of dentinal margin.Conclusion: Vitremer has an efficterness role and flawable composite has a weakness role in reducting microleakage of dentinal margin.