Experimental and numerical studies on heat transfer enhancement for air conditioner condensers using a wavy fin with a rectangular winglet

Journal of Mechanical Science and Technology - The air side thermal performance of wavy fins with rectangular winglets are studied using experimental and numerical methods. The following parameters...     

Enhancement of uranium extraction from seawater using chromic-acid-treated amidoxime adsorbent prepared by simultaneous irradiation grafting technique

Enhancement of uranium extraction from seawater using chromic-acid-treated amidoxime adsorbent was studied. Chromic-acid-treated amidoxime fibers were synthesized based on the simultaneous irradiation grafting method at a low temperature. Low-density polyethylene (LDPE) fibers were treated with chromic acid for up to 90 minutes. After the treatment, the fibers were submerged in 60:40 acrylonitrile:methacrylic acid monomer by volume and irradiated with 40 kGy γ-ray. The maximum grafting efficiency of about 90% occurred at 20 minutes of acid treatment time, as a significant enhancement of 30% compared to the literature-reported value of about 70%. When submerged in shallow seawater with an average temperature of 30 °C for 4 weeks, the amidoxime adsorbent exhibited the adsorption capacity of 2.06 g-U/kg-adsorbent, which was 37% higher than the literature-reported value. These significantly increased grafting and adsorption efficiencies were attributed to the increased surface area of chromic-acid-etched LDPE fibers. Moreover, for the submersion up to 8 weeks, the adsorption increased to 2.15 g-U/kg-adsorbent. The adsorption capacity was evaluated to reduce to about 65% after eight cycles of repeated usage. Uranium concentrations in Thailand's seawater collected at various depths and locations were analyzed using inductively coupled plasma-mass spectrometry (ICP-MS) to be about 3 ppb everywhere.     

Experimental and numerical study on heat transfer and flow characteristics in an alternating cross‐section flattened tube

An experimental and numerical study on convection heat transfer of water flowing through an alternating cross‐section flattened (ACF) tube are investigated in this paper. The thermal‐fluid characteristics were evaluated by numerical simulation. The test run conditions covered a mass flux of 200 to 800 kg m^?2 s^?1, a heat flux of 10 kW/m², and an inlet temperature of 40°C. The results showed that the Nusselt number increased with the increase in mass flux. Moreover, the heat transfer was also affected by the flow characteristics. Vortices were formed at the curved wall, and their intensities were increased along the flow direction. It was also found that the heat transfer and pressure drop were larger than that of the circular tube. However, the thermal performance was greater than the pressure loss penalty. The comparison results showed that the ACF tube had better performance than the circular tube. Further, the details of heat transfer, flow resistance, and fluid behavior were investigated and discussed in this study.     

Troubleshooting HF Alkylation Units

Good design criteria, an excellent clean‐up and the best knowledge with regard to the philosophy of operation allows a fast start‐up and a reduction of the time to reach the designed steady‐state conditions in the alkylation units. Presented are the findings after starting‐up three new alkylation units as well as the difficulties encountered and their possible solutions.