Transient Free Convection Mass Transfer of Second-grade Fluid Flow with Wall Transpiration

The study of mass transfer in the non-Newtonian fluid is essential in understanding the engine lubrication, the cooling system of electronic devices, and the manufacturing process of the chemical industry. Optimal performance of the practical applications requires the appropriate conditions. The unsteady transient free convective flow of second-grade fluid with mass transfer and wall transpiration is concerned in the present communication. The behavior of the second-grade fluid under the influence of injection or suction is discussed. Suitable non-dimensional variables are utilized to transform the governing equations into non-dimensional governing equations. A Maple solver “pdsolve” that is using the centered implicit scheme of a finite difference method is utilized to solve the dimensionless governing equations numerically. The effects of wall injection or suction parameter, second-grade fluid viscoelastic parameter, Schmidt number, and modified Grashof number on the velocity and concentration profiles are graphically displayed and analyzed. The results show that with increasing wall suction, viscoelastic parameter, and Schmidt number, the velocity and concentration profiles decrease. Whereas, the velocity profiles show an opposite tendency in situations of wall injection. The wall suction has increased the skin friction and also the rate of mass diffusion in the second-grade fluid.

“Low Cost" Negative Pressure Wound Therapy for Acute and Chronic Wounds Healing - About 3 Cases

Background: Negative pressure wound therapy (NPWT) is an alternative to standard treatment of acute wounds (such as traumatic or post-operative wounds) but also in that of chronic wounds (such as ulcers or stage 3 and 4 pressure ulcers). However, the exorbitant cost of VAC (vaccum assisted closure) devices for our limited resources health facilities, and their unavailability led us to opt for a "low cost" solution using wall suction and disposable materials readily available in all surgical departments. Materials and methods: After surgical debridement in 3 patients with both acute and chronic lesions evolving in septic environment, we replaced polyurethane foam by that from surgical scrub brushes, the tubing and its suction port by nasogastric tube, the hydrocolloid for the protection of wound edges by tulle gras (vaseline gauze), the adhesive film ensuring sealing by an incise drape, and the therapy unit by wall suction and exudates collection bottle. We cut up the foam to make it correspond to the wound, in size and depth, and then, using straight forceps, we create a tunnel in it, large enough to allow the introduction of the nasogastric tube. We then carefully place the foam in the wound. After that, we proceed to application of incise drape to cover foam dressing and connect the end of the probe to wall suction system via suction bottle. Therapy is initiated by setting vacuum gauge to a continuously delivered negative pressure of -125 mmHg.Results: The size of all wounds reduced considerably and rapidly with the installation of budding granulation tissue which appeared as early as the first dressing change enabling subsequently the best possible conditions for directed healing or coverage procedures (skin graft or flaps). The healing was obtained for all our patients.Conclusions: In this "low cost" NPWT, the negative pressure produced by wall vacuum promotes effective management of acute and chronic wounds, including complex ones, by rapidly "producing" good quality granulation leading to healing, while reducing the cost of therapy, the number of dressings and the length of hospital stay.Trial registration: Retrospectively registered

Comparing the effectiveness of negative-pressure barrier devices in providing air clearance to prevent aerosol transmission

Purpose To investigate the effectiveness of aerosol clearance using an aerosol box, aerosol bag, wall suction, and a high-efficiency particulate air (HEPA) filter evacuator to prevent aerosol transmission. Methods The flow field was visualized using three protective device settings (an aerosol box, and an aerosol bag with and without sealed working channels) and four suction settings (no suction, wall suction, and a HEPA filter evacuator at flow rates of 415 liters per minute [LPM] and 530 LPM). All 12 subgroups were compared with a no intervention group. The primary outcome, aerosol concentration, was measured at the head, trunk, and foot of a mannequin. Results The mean aerosol concentration was reduced at the head (p < 0.001) but increased at the feet (p = 0.005) with an aerosol box compared with no intervention. Non-sealed aerosol bags increased exposure at the head and trunk (both, p < 0.001). Sealed aerosol bags reduced aerosol concentration at the head, trunk, and foot of the mannequin (p < 0.001). A sealed aerosol bag alone, with wall suction, or with a HEPA filter evacuator reduced the aerosol concentration at the head by 7.15%, 36.61%, and 84.70%, respectively (99.9% confidence interval [CI]: -4.51–18.81, 27.48–45.73, and 78.99–90.40); trunk by 70.95%, 73.99%, and 91.59%, respectively (99.9% CI: 59.83–82.07, 52.64–95.33, and 87.51–95.66); and feet by 69.16%, 75.57%, and 92.30%, respectively (99.9% CI: 63.18–75.15, 69.76–81.37, and 88.18–96.42), compared with an aerosol box alone. Conclusions As aerosols spread, an airtight container with sealed working channels is effective when combined with suction devices.