Imaddin A. Al-Omari

Optimizing the tilt angle of solar collectors

Solar collectors need to be tilted at the correct angle to maximize the performance of the system. In this paper, the annual solar fraction of the system (the fraction of energy that is supplied by solar energy) is used as an indicator to find the optimum inclination angles for a thermosyphon solar water heater installed in northern and southern parts of Jordan. Calculations are carried out using the powerful computer program TRNSYS (Transient System Simulation). The system is assumed to operate with a daily hot water load of 150 l at 55°C flowing during the day according to the widely used Rand consumption profile. The results show that the optimum inclination angle for the maximum solar fraction is about φ+(0→10°) for the northern region (represented by Amman) and about φ+(0→20°) for the southern region (represented by the town of Aqaba). These values are greater than those for maximum solar radiation (which is commonly used as an indicator) at the top of the collector by about 5 to 8°.

Magnetic and structural properties of SmCo7−xCux alloys

We report the structural and magnetic properties of SmCo7−xCux, where x=0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.7. X-ray diffraction shows that these alloys from the disordered hexagonal TbCu7-type structure. For large values of x(x⩾0.8) the hexagonal TbCu7-type structure cannot be formed. X-ray diffraction on magnetically aligned samples show that these samples have uniaxial anisotropy. The lattice parameters (a and c) are dependent on the Cu concentration, and the unit cell volume is found to increase with x. The saturation magnetization decreases with x at both room temperature and 25 K. The Curie temperature increases with x for small values of x while it decreases with x for large values of x. A maximum value of TC=852 °C is found in these alloys.We report the structural and magnetic properties of SmCo7−xCux, where x=0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.7. X-ray diffraction shows that these alloys from the disordered hexagonal TbCu7-type structure. For large values of x(x⩾0.8) the hexagonal TbCu7-type structure cannot be formed. X-ray diffraction on magnetically aligned samples show that these samples have uniaxial anisotropy. The lattice parameters (a and c) are dependent on the Cu concentration, and the unit cell volume is found to increase with x. The saturation magnetization decreases with x at both room temperature and 25 K. The Curie temperature increases with x for small values of x while it decreases with x for large values of x. A maximum value of TC=852 °C is found in these alloys.

Effect of external magnetic field on the critical current in single and bifilar Bi-2223 tapes

We report on measurements of the critical current in a single and bifilar multifilamentary Bi-2223/Ag tapes, at 77 K, under various DC magnetic fields applied perpendicular to the tape plane. At low applied fields the bifilar tape exhibits higher critical current, as expected. However, above ∼50 G the situation is reversed, i.e., the critical current of the single tape is higher. These results are attributed to the different spatial distribution of the self-field in these two configurations. Our data and analysis imply that, in terms of critical current, the bifilar configuration has over advantage over the single tape configuration only in a limited range of external magnetic fields.

Dissipative behavior and γ-irradiation of silver-sheathed Bi1.8Pb0.4Sr2Ca2Cu3Ox tape

Abstract Dissipative mechanisms in Bi 1.8 Pb 0.4 Sr 2 Ca 2 Cu 3 O x tapes were investigated using magnetoresistance measurements and V – I characteristics. A considerable broadening of the resistive transition in applied magnetic field was observed up to a field of 0.5 T. The temperature and magnetic field dependence of the resistance R ( T , B ) were fitted to the Arrhenius relation and from which the magnetic field dependence of the pinning energy U 0 ( B )∼ B − α with α ≈0.9 was derived. The variations of the critical current densities J c with temperature and magnetic field before and after γ-irradiation were also studied. The temperature dependence of J c ( T ) was fitted to the relation J c ( T )∼(1− T / T c ) n with n =1.9 and discussed in terms of thermally activated flux flow (TAFF). However, J c ( B ) results were explained based on the weak links, grain boundaries, and Josephson junctions in which it shows a power law behaviour J c ( B )∼ B −0.5 . At relatively low temperatures and magnetic fields, the critical current density was increased with a γ-irradiation up to a dose of 100 MR.

Structural and Mössbauer spectroscopic studies of Fe0.7−xCrxAl0.3 alloys

Abstract Fe 0.7− x Cr x Al 0.3 alloys with x =0, 0.1, 0.2, 0.3 and 0.35 have been synthesized by arc melting and studied by X-ray diffraction and Mossbauer spectroscopy. All the samples studied were found to have single phase with body center cubic structure. The lattice parameter a , and hence the volume, were obtained from the X-ray diffraction patern and found to increase with increasing the chromium concentration. At room temperature Mossbauer studies show magnetic ordering for small values of x and paramagnetic behavior for large values of x under investigation. The Mossbauer spectra were analyzed considering a distribution of magnetic hyperfine fields for small values of x and two singlets were added for large values of x . During the fitting procedure, the relation between the hyperfine field and the isomer shift in the hyperfine field distribution was linear relation. The average hyperfine field and isomer shift as a function of chromium content x were found to decrease with increasing x . The results are explained in terms of local environmental effects on the hyperfine interactions.

AC-induced DC voltage in HTS coil

Abstract The interplay between AC and DC currents in a High- T c Superconducting (HTS) coil, made of multifilamentary silver-sheathed Bi-2223 tape, was investigated. We observed that the application of a small sinusoidal current in the frequency range of 50–500 Hz into the coil, while it is already carrying a DC current in the range of 16–22.5 A, caused an increase in the coil DC voltage. The DC voltage increment due to the AC signal is found to increase linearly with frequency and quadratically with amplitude. The DC voltage increment increases as the coil current grows towards its critical value of 22.2 A. This result may be important in some power applications such as fault current limiters (FCL) and superconducting magnet energy storage (SMES) based on HTS coils.

Effect of gamma irradiation on the transport critical current density of Tl2Ba2Ca2Cu3O10 tapes

Specimens of Tl2Ba2Ca2Cu3O10 tapes were prepared using the powder in tube method. The voltage-current (V - I ) characteristics were used to study the temperature and magnetic field dependence of the critical current density Jc(T,B). Obtained results confirmed the high sensitivity of the superconducting tape to the applied magnetic field and are explained based on the weak links and Josephson junctions between the grains. The temperature dependence of Jc was also derived and discussed in terms of the thermally activated flux flow (TAFF). The effect of gamma irradiation on the critical current density Jc(T,B) was also studied up to a gamma dose of 400 MR. Gamma irradiation was found to increase Jc at relatively low temperature and magnetic field ranges. Therefore, gamma irradiation is a useful method to improve the superconductivity of the Tl2Ba2Ca2Cu3O10 tapes.

Magnetic and structural properties of GdFe2-xTix alloys

Abstract We report the structural and magnetic properties of GdFe 2− x Ti x alloys, where x =0, 0.05, 0.10, 0.15, 0.20, 0.30. X-ray diffraction shows that these compounds form the cubic Cu 2 Mg type structure. The lattice parameter ( a ) and the unit cell volume ( V ) are found to increase with increasing Ti concentration. Magnetization measurements using a SQUID magnetometer show that all samples studied are magnetically ordered. We find that the saturation magnetization increases with x at room temperature and at 5 K. This is due to the replacement of magnetic iron by non-magnetic titanium which decreases the Fe sublattice moment.

The rotational magnetic process and effects of gamma-irradiation on vortex flux pinning in Tl-2223 at low temperatures

Magnetization vector measurements were carried out in a polycrystalline sample of Tl-2223 superconductor in fixed fields at low temperatures. Demonstrating the broad distribution in the vortex flux pinning, the vortex flux density B was seen to consist of two component: the rotational component BR turns rigidly with sample rotation and the frictional component BF stays at fixed angle F relative to the applied field H. The pinning torques per vortex were calculated as a function of H at constant temperature. The -irradiated sample shows an increase in pinning torque of ratio seven to one at temperatures 4.2 K and 25 K compared to an unirradiated sample; this is due to defects induced by the gamma irradiation.

Temperature dependence of vortex flux pinning with γ-irradiation in polycrystalline Tl-2223

Hysteresis loop measurements of superconducting polycrystalline samples of Tl-2223 were carried out at various temperatures. Using the magnetization remanence (MR) as measurement of the maximum vortex flux pinning at each temperature, our results reveal that the vortex flux pinning forces show two distinct behaviours of MR with temperature, a linear behaviour with t at high temperatures and an exponential behaviour with tβ at low temperatures, where t = (1-T/Tc) and β is constant of order 8. The effect of γ-irradiation shows six-fold enhancement in the vortex pinning over all temperatures up to Tc. This increase in the pinning forces is attributed to the induced defects introduced by the γ-irradiation. The same enhancement in the pinning forces at all temperatures implies constant defects induced by γ-irradiation.