Tikrit Journal of Engineering Sciences

This paper presents design and analysis of a single phase multilevel inverter by optimizing both switching angles and DC link voltage of a cascaded inverter. The switching angles and dc link voltage are chosen such that to minimize the total harmonic distortion of the output voltage. The main power devices are switched only once per cycle , so that to overcome the switching loss problem, as well as electromagnetic interference (EMI) problem, a method is given to determine the optimum value of the switching angles and the value of the dc link voltage. Theoretical analysis and simulation of a single phase 5-level cascaded inverter are introduced with a wide range of modulation index.

The mathematical model for the two interacting tanks system was derived and the dynamic behavior of this system was studied by introducing a step change in inlet flow rate. In this paper, the analysis of the interaction loops between the controlled variable (liquid level) and manipulated variable (inlet flow rate) was carried out using the relative gain array. Also decoupling technique is applied to eliminate the effect this interaction by design suitable decouplers for the system. The results show that the gain of each loop is cut in half when the opposite loop is closed and the gain of other loop changes sign when the opposite loop is closed. The decoupling method show that the liquid level of tank one is constant when the second inlet flow changes and to keep the liquid level of tank two constant the first inlet flow must be changed.

In present work tubular shaped fiber reinforced composites were manufactured by using two types of resins ( Epoxy and unsaturated polyester) and separately reinforced with glass, carbon and kevlar-49 fibers (filament and woven roving), hybrid reinforcement composites of these fibers were also prepared. The fibers were wet wound on a mandrel using a purposely designed winding machine, developed by modifying an ordinary lathe, in winding angle of 55 for filament. A creep test was made of either the full tube or specimens taken from it. Creep was found to increase upon reinforcement in accordance to the rule of mixture and mainly decided by the type of single or hybridized fibers. The creep behavior, showed that the observed strain tends to appear much faster at higher temperature as compared with that exhibited at room temperate. The creep rate also found to be depending on fiber type, matrix type, and the fiber /matrix bonding. The creep energy calculated from experimental observations was found to exhibit highest value for hybridized reinforcement.

To define the biological features of phytoplankton in Mosul Dam Lake, monthly samples were collected along a year from September 2003 to August 2004. Consisting thermal stratification and turn over periods from four locations in the main lake and another location in the regulating lake. Total numbers of algae reached 2300 cell/ml in the main lake and 1100cell/ml in the regulating lake. Bacillariophyta were dominant with a maximum number of 1400 cell/ml in autumn. Chlorophyta were dominant in autumn also with 550 cell/ml. Ten genus of Chlorophyta were appeared in this water body: Cosmarium, Chlorella, Spirogyra, Scendesmus, Pediastrum, Tetraedron, Quadrigula, Ankiseradosm, Pandorina, and Straurastrum. Seven genus of Bacillariophyta were noticeable. Some genus of Cyanophyta was recorded as Aphanocapsa. In addition some Euglenophyta spp. were occurred in the main lake and the regulating lake also. On the basis of these algae abundance, the lake is undergoing cultural Eutrophication. It has passed in mesotrophic state (the middle trophic state of Eutrophication). Some genera which were appeared are the indication of eutrophic state. Total plate count bacteria ranged from 400-1700 cell/ ml in the main lake and 200- 950 cell/ml in the regulating lake were also recorded. Coliform bacteria were founded with most probable number reached 460 cell/100ml in the main lake and 150 cell/100ml in the regulating lake. Therefore, the lake water is classified as moderate pure and considering a good source of raw water supply with all treatment units and safe for swimming and recreational uses.

This paper presents practical study to improve the indication COP of a vapor compression refrigeration cycle in instrumented automobile air conditioner by designing internal heat exchanger and installing it in the vapor compression refrigeration cycle. Two cases of vapor compression refrigeration cycle were taken in this paper: the first case is that the vapor compression refrigeration cycle without internal heat exchanger and in the second case the vapor compression refrigeration cycle with heat exchanger ; in these two cases, the temperature at each point of a vapor compression refrigeration cycle, the low and the high pressure ,the indoor temperature and the outdoor temperature were measured at each time at compressor speed 1450 rpm and 2900 rpm for each blower speed 1, blower speed 2 and blower speed 3. The refrigerant fluid was used in the vapor compression refrigeration cycle without IHE and with IHE is R134a.

The recycling of wood chippings, an industrial waste product, has a potential use in the production of a lightweight concrete. In modern countries, the low cost and the proximity of supply makes this material a good candidate for local building applications. This study aims to examining the ability of enhancing of a wood fibre lightweight concrete strength by reinforcing it with lathe scrap from lathe industry. Specimens have been casted, compressive and split tensile strengths were measured in addition to the wet and dry weight as per relevant British standard specifications. The wood chippings are saturated with a water for 24 hours, this is to prevent chippings from sorption the water of the mixture. Test results indicate that addition of waste fibre from lathe enhances the strength markedly and in the same time increases the weight.

The majority of high voltage gapped silicon carbide lightning arresters on transmission and sub transmission systems have been in service for over 10 years. A testing program is required that can accurately and efficiently determine the condition of these high voltage arresters. The essential theory of silicon carbide arresters was investigated, focusing particularly on arrester construction, performance and the unique characteristics of high voltage arresters. The effectiveness of available testing procedures was then evaluated and a set of tests selected, based on their expected performance, their ability to assess all facets of arrester behavior, the ease with which they could be completed in the available laboratory and their possible application to in-field testing. The testing program implemented consisted of a series of procedures including the lightning impulse sparkover voltage test, power frequency sparkover voltage test, power frequency withstand test, AC and DC leakage current measurements, 5 kV insulation resistance test, and finally a non-standard current impulse test. The tests were performed on a set of 6 arresters rated at 33 and 132 kV and a set of 5 arrester sections. The results of the investigation verified the effectiveness of the selected procedure with a consistent and accurate assessment of arrester condition obtained for all arresters under test. All arresters exhibited satisfactory performance in the selected tests, indicating that high voltage gapped silicon carbide arresters are more durable than those used on distribution systems.

In this study, Different basis [NaOH and KOH] of variable concentration are used to reactivate Anion exchangers employing different schemes .The Laboratory results showed large improvement in efficiency of these exchangers ( i.e operating time was increased from 12 to 42 hours ) . The results of this work showed that the environmental load (waste water) can be reduced greatly when using the proposed regeneration scheme.

An experimental compression refrigeration system performance study was presented in this research depending on the change of the capillary tube length and by using (R134a). The tests were done for three capillary tube lengths (80,100,120cm) and changing mass flow rate for each length. Their values were (2 6g/s) with capillary tube diameter (2mm). The results showed that the (COP) decreases by (38.14%) as the mass flow rate increases from (2 6g/s), and by (6.65%) as the capillary tube length increases from (80- 120 cm). At (L=80Cm) the (COP) value will be greater than it’s value at (L=120Cm) for lowest mass flow rate, while it’s values converge for all lengths at high mass flow rate .Also it was declared that (COP) will decrease as the condenser temperature increases for all lengths. The study showed that the compressor compression power increases as the condenser temperature increases by (68.36%), and increases as the capillary tube length increases by (9.54%) with convergence value at (100 cm) and (120 cm) . This study showed also that sub-cooling temperature stays constant at low flow rates, and decreases at higher flow rates by (34.35%). Through this study was found best length used in refrigeration cycle at lowest mass flow rate (2.78 g/s) is (80Cm) which will give highest performance and lowest compression power, and at high mass flow rate (5.83 g/s) found the length (100Cm) will give highest performance and lowest compression power.

The research focus on using the aeration process as means for water recarbonation after lime-soda softening. The results indicated that aeration efficient for recarbonation of three water samples with different characteristics. The lime-soda softening increased the (pH) values of the three samples to reach (10.08,10.39,10.54) respectively. The aeration decreased these (pH) values to (8.26,8.36,8.23) respectively within (60)minutes. The depression was related to the convert of the hydroxide and carbonate of the sample to the bicarbonate form by CO2 gas absorbed from the air bubbles. The absorption efficiencies were (30.9,31.0,24.7)% for the three samples respectively. The research also determined the value of (pH) at which the softened sample is saturated with calcium carbonate . These values for the three samples were (8.30,8.39,8.44) respectively. Accordingly the Langer saturation index for each sample have a positive value. The samples is at supersaturation condition with calcium carbonate for all samples. Therefore the aeration period needed to obtain the saturation state at which the sample is stable was determined to be (58.8,59.1,55.2)minutes for the three samples respectively.