Optimization of baffle spacingon heat transfer, pressure drop and estimated price in a shell-and-tube heat exchanger

In this paper for a given heat duty, study of the effects of baffle spacing on three parameters mentioned above is considered in a STHX with single segmental baffles and staggered tubes layout in Iran, Arvand petrochemical. A program in EES (Engineering Equations Solver) software is used for this purpose to solve governing equations; moreover, Aspen B-JAC and HTFS+softwares are used for considering estimated total price. At first the simulated results obtained from this program is compared to the experimental data for two cases of baffle spacing. The effects of baffle spacing are considered from 4 to 24 inches over overall heat transfer coefficient (OHTC) to pressure drop ratio (U/Δp ratio). The results show that U/Δp ratio is low when baffle spacing is minimum (4 inches) because pressure drop is high; however, heat transfer coefficient is very significant. And in this case estimated total price increases 7 percent. Then with the increase of baffle spacing, pressure drop rapidly decreases and OHTC also decreases, but the decrease of OHTC is lower than pressure drop, so (U/Δp) ratio increases. After increasing baffles more than 12 inches, variation in pressure drop is gradual and approximately constant and OHTC decreases; Consequently, U/Δp ratio decreases again. If baffle spacing reaches to 24 inches, STHX will have minimum pressure drop, but OHTC decreases, so required heat transfer surface increases and U/?p ratio decreases. After baffle spacing more than 12 inches, variation of both estimated price and shell side pressure drop is negligible. So optimum baffle spacing is suggested between 8 to 12 inches (43 to 63 percent of inside shell diameter) for a sufficient heat duty, low cost and low pressure drop. © IDOSI Publications, 2012

Design and implementation of a sliding-mode controller for digital low-dropout/linear regulators

This paper presents an approach to utilize of sliding-mode (SM) controller in digital low-dropout/linear regulators. Various design aspects, including the extraction of the regulator state-space model and sliding coefficients by considering the hitting, existence, and stability conditions are described. Moreover, the freeze control block is introduced as a solution to compensate the high frequency chattering phenomenon of SM, resulting in reduction of switching losses. In order to verify the statements, a quasi digital low-dropout/linear regulator (QDLDO) is implemented in a discrete form on a PCB. The circuit consists of the proposed current-mode current feedback amplifier (CFA)-based SM controller and switchedmode PMOS array driven by a bidirectional serial shift register, which is controlled by the SM controller. The results reveal that the controller detects the load changes rapidly, and eliminates the output limit-cycle oscillation, providing a robust and stable output voltage.Peer ReviewedPostprint (author's final draft

Impact of solar energy application on warming, health caring and pollution prevention in Iran

Abstract: Solar energy is cited as a clean alternative to fossil fuels. Solar panels generate energy without producing ambient pollution. Therefore, there is no argument that pure solar energy is a clean, green energy source. The result in the present paper shows that by using renewable energy special sun light energy, considerable amounts of Greenhouse polluting gasses are avoided. The use of conventional energy in factories and vehicles in has been a major source of pollution health hazards. These hazardous pollutants, such as suspended particle, heavy metal, organic matter and carbon monoxide (CO) adversely affect health. Although solar energy has significant environmental benefits in comparison to the fossil fuel, some problems has be seen in this way. The important advantage is related to the reduced CO2 emission and air pollution prevention and it can be said this method for producing energy which has some economic benefit. The supplies of the fossil fuels used to generate much of its shrink, the cost of this energy is increasing worldwide. Solar energy allows human to generate its own energy in cheap way. To the best of our knowledge, the comparison of two categories of energy and investigation in the benefits of solar energy as a new way in Iran are investigated to prevent our environmental and natural sources