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M EASUREMENTS of mean velocity, spread rate, and merging point location were made to investigate the flowfield generated by four identical jets of air in a square configuration, issuing from axisymmetric nozzles in a common end wall and mixing with the ambient air. The effect of stagnation pressure ratios as well as the nozzle spacings on the flowfield behavior were investigated. The effect of nozzle configurations was also studied. The results show that the nature of the mean velocity profile as well as the mean velocity decay are unaffected by the pressure ratio. The nozzle spacing effect on the mean velocity decay is only marginal. The four jets interact with axis switching at the midpoint between them, which implies better mixing. ContentsIt is well known that the multijet has many advantages over a single jet. The advantages include better mixing and noise reduction. 1 Recently, many investigators have used a non circular nozzle 2 (triangular, elliptic, etc.) to improve the jet mixing process. The elliptic jets were shown to be capable of entraining large amounts of surrounding fluid relative to that entrained by a circular jet. 3 The main advantage for using these geometries is the axis-switching phenomenon. However, the fabrication of such geometrical shapes is somewhat difficult. The circular nozzle fabrication is easier, and an attempt was made to identify the advantage of the multijet (good mixing) and the noncircular jet (axis switching) by keeping the four nozzles in a square configuration, with the arrangement as shown in Fig. 1. The nozzle exit diameter d e was 4.2 mm, and the nozzle spacings S were chosen as S = 12, 16, 18, and 22 mm. The nozzles' axes were aligned parallel to the Xaxis of the three-dimensional traversing system. The stagnation pressure was varied from 1.25 to 2.5 atm. The total pressure in the jet was measured by a three-hole pressure probe of 0.3 mm i.d. All measurements were made in the X-Y plane at two positions in the Z direction. The total pressure reading was taken from the axis of the top jet or the symmetric axis between the two base jets to the distance at which the mean velocity became zero in the Y direction. This step was repeated at several positions downstream (up to 5Qd e ) from the nozzle exit plane.The mean velocity profiles in the X-Y plane of the top jet at x/d e = 18.5 is shown in Fig. 2. Earlier measurements 4 of single and triple jets also appear on the plot for comparison.The center line mean velocity u n decay of the top jet as a function of the stagnation pressure ratio P&/PQ is presented in Fig. 1. As shown, the jet velocity decay as well as the potential core length have a fairly weak dependence on the

A humidification-dehumidification (HD) solar desalination unit was designed. It seems to be suitable to provide drinking water for population or remote arid areas. Solar water and solar air collectors were designed to provide the hot water and air to the desalination chamber. The desalination chamber was divided into humidifier and dehumidifier towers. The circulation of air in the two towers was maintained by the forced convection. Theoretical and experimental works were done at different environmental conditions. A mathematical model was formulated, in which the thermodynamic relations were used to study the flow, heat and mass transfer inside the humidifier and dehumidifier. Such a technique was performed in order to increase the unit performance. Heat and mass balance was done and a set of governing equations was solved using the finite difference technique. The solar intensity was measured along the working day during the summer and winter months and a comparison between the theoretical and experimental results were performed. The average accumulative productivity of the system in November, December and January was ranged between 2 to 3.5 kg / m 2 day while the average summer productivity was found between 6 to 8 kg/m 2 day in June and 7.26 to 11 kg/m 2 day in July and August. 2 ‫الفصل‬ ‫نفس‬ ‫من‬ ‫وأغسطس‬ ‫يوليه‬ ‫شھور‬ ‫ل‬ ‫خ‬ .

Membrane distillation is a hybrid process in which the separation process is based on both thermal potential and membrane characteristics. However, some technical challenges such as thermal boundary layer builds up (temperature polarization) resulted in low mass flux. In this study, the direct contact membrane distillation is equipped with corrugated feed channel to create fluid mix for mass flux improvement. A lab scale flat sheet membrane distillation is assembled with corrugated feed channel to suppress the thermal boundary layer in the vicinity of the membrane wall. The flat sheet PTFE-membrane of a pore size of 0.45 μm and porosity 65% is considered in the present study. The effect of feed channel gap height has been investigated at different values of flow rate, feed temperature, and feed salinity.The experiments showed that the corrugated feed channel has a dominant effect of improving of the mass flux and the thermal efficiency rather than gap height and operating conditions. The experimental results showed the water flux and thermal efficiency of the corrugated feed channel module is 44% and 33% higher than the original module respectively. NomenclatureA: Membrane area, m 2 Cp: Specific heat capacity of fluid (J kg −1 K −1 ) LHv: Latent heat of vaporization of water (J kg −1 ) Nm: Water flux (kg m −2 s −1 ) EE: Energy efficiency (%) T: Temperature (°C) m: Mass flow rate ( kg/sec.)

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