The present research studies experimentally the effect of the ratio of the centurial hollow on the average of laminar convective heat transfer and the thermal gradation of the thermal boundary layer of three square flat plates. An experimental set-up was made for this purpose containing basically three uniformly Aluminum flat plates of a centurial hollow representing (0.25,0.5,0.75) of the entire surface area of each plate. Each of the three plates were heated by a constant heat flux for a rang of Rayleigh number of (5.62x105≤Ra≤1.67x106).The study showed that increasing the hollow ratio causes to increase the average of convective heat transfer by increasing the average Nusselt number, and the increasing average from a ratio to another decreases by the increases of the hollow ratio. The increasing between the two surfaces at (m=0.25&m=0.5) reached (39.6%) and for (m=0.5&m=0.75) was less than that and reached (29.2%).The increase average between the biggest and smallest hollow ratio was (78%).The study also showed that the maximum thermal gradation was on the out side edge of the plates and increases with the increase of Rayleigh number and the hollow ratio.
The direct sequence (DS) spread spectrum communication technique is widely regarded as one of the most effective methods of mitigating the effects of a repeating jammer in military communications systems. The proposed system coupled DS with multiple frequency shift keying (DS/MFSK). It is comprised of a transmitter and a receiver. Non-coherent demodulation is examined, as are the spreading sequences in question. The effect of AWGN and Rayleigh fading channels on the proposed approach's bit error rate (BER) is examined. The investigation demonstrates that even with an 8 dB signal-to-noise ratio, superior outcomes can be achieved; this study's suggested endeavor is to create a novel transceiver system built on the DS/MFSK modular architecture. MFSK modulation prevents multiple-access interference, while DS is typically employed to boost system efficiency across erratic fading. Test results show that reliability on the AWGN channel decreases a little while reliability is greatly enhanced by Rayleigh fading. Moreover, notable improvements in bandwidth efficiency are achieved.
WMAN (wireless metropolitan area network) technology is based on the IEEE 802.16 air interface standard suite, which provides the wireless technology for fixed and nomadic data access. WMAN employs orthogonal frequency division multiplexing (OFDM), and supports adaptive modulation and coding depending on the channel conditions. The objective of this paper is to study the performance of the IEEE 802.16d WMAN physical layer under Nakagami model as a Multi-path and frequency-selective fading channel beside the additive white Gaussian noise (AWGN) and Doppler. Finally, we compared it with the Rayleigh fading model. The transmission bit rate, Probability of Error ( ) and estimated SNR have been compared under single/multi path propagation conditions.
A Numerical study has been conducted to clarify the effect of the buoyancy forces on the thermal development through a horizontal annulus sector heated with constant surface temperature. The study includes the solution of governing equations for the flow and heat transfer of different sections along the channel. Theoretically these governing equations were reduced to four, which are continuity equation, radial and tangential momentum equations, axial momentum equation and vorticity equation in which the variables were the temperature, vorticity, stream function and axial velocity. These equations were reduced to dimensionless equations in which Rayleigh, Prandtl and Reynolds numbers were presented. They were numerically solved by using the marching process explicit finite difference method and Gauss elimination technique. Numerical results for annulus sector heated by constant surface temperature for different values of Rayleigh numbers and total sector angles and diameters ratio were obtained and represented by stream function contours and isotherms and circumferential distribution of local Nusselt number. Also the results include the values of friction factor and average Nusselt number for the pure forced convection. Comparisons are made between the computed results and the analytical or numerical results available in the literature, for all cases compared, satisfactory agreement is obtained. The results include a survey of annulus sector surface in many sites of channel flow, whereas it is apparent that the buoyancy force causes the secondary flow to behave non uniformly at the entrance and then the average heat transfer will increase with the increasing both of diameter ratio and total annulus sector angles. A correlation relationship is extracted to find an average change of Nusselt after the stability of the flow in the fully developed region for the studied ranges of annulus sector angles and diameters ratio.
Laminar natural convection heat transfer and fluid flow due to the heating from below at variable heat source length inside two dimensional enclosure has been analyzed numerically in this study. The enclosure has filled with air as a working fluid. The vertical inclined walls of the enclosure are maintained at lower temperature while the remaining walls are insulated. The value of Rayleigh number from (1x103 ≤ Ra ≤ 4x104), the inclination angle at (γ = 0o, 22.5o , 45o ) and dimensionless heat source length at ( S = 1 and 0.5 ). The continuity, momentum and energy equations have been applied to the enclosure and solved by using finite difference method. The results showing that the average Nusselt number increases with the increasing of the heating source length and decreases with the increasing in an inclination angle of the vertical walls.
Natural convection heat transfer in two-dimensional region formed by constant heat flux horizontal flat tube concentrically located in cooled horizontal cylinder studied numerically. The model solved using the FLUENT CFD package. The numerical simulations covered a range of hydraulic radius ratio (5, 7.5, and 10) at orientation angles from (0o up to 90o). The results showed that the average Nusselt number increases with hydraulic radius ratio, orientation angles and Rayleigh number. As well as enhancement ratio for Nusselt number at orientation angle 90o and hydraulic radius ratio 7.5 equal 24.87%. Both the fluid flow and heat transfer characteristics for different cases are illustrated velocity vectors and temperature contours that obtained from the CFD code. The results for the average Nusselt numbers are compared with previous works and show good agreement.
Serial Concatenation Convolutional Codes (SCCCs) encoder is built using a serial concatenation of two Recursive Systematic Convolutional (RSC) encoders, separated by an interleaver. These two RSC encoders depending on the trellis termination criteria are software implemented and the performance of each one of them is analyzed under different conditions and circumstances. The output data from the encoder are multiplied by an amplitude matrix (AM) at the transmitter side and the Inverse of Amplitude Matrix (IAM) at the receiver side. The reliability estimation, log-likelihood algebra, and soft channel outputs for Soft Output Viterbi Algorithm (SOVA) are examined. Then the modified Viterbi metric that incorporates a-priori information used for SOVA decoding is derived. A low memory implementation of the SOVA decoder is presented. The iterative SOVA for SCCCs is described with illustrative examples. The behavior of the SCCCs encoder-decoder scheme is tested under different circumstances with AM and without AM at the AWGN and Rayleigh fading channels with unlike frame sizes (FS) and constraint length (K). The results show that the performance of system with AM outperforms the other conventional system that worked without AM.