Design of Cross Flow Heat Exchanger Using Performance Charts

The manuscript reviews the various steps involved in the design of a cross flow heat exchanger. Performance charts describing the thermal performance of the heat exchanger in terms of dimensionless parameters are used to develop the preliminary design of the heat exchanger. The preliminary design involves choosing the required number of heat exchanger passes, the required number of transfer units (NTU) and the capacity rate ratio for a given heat transfer application. These dimensionless parameters account for material, flow and thermal characteristics of the heat exchanger. In addition, NTU accounts for heat exchanger size, flow configuration and the type of heat exchanger. Since the preliminary design accounts for all the major characteristics of the heat exchanger, this approach is beneficial in optimizing the heat exchanger during the design phase. Performance charts indicate that indefinitely increasing the surface area (or NTU) does not increase the rate of heat transfer. There exists a threshold limit beyond which increasing the surface area adds no benefit to the heat exchanger. Instead, it just adds weight, material and cost of the heat exchanger. It must be noted that an undersized heat exchanger for a given application may not deliver the required heat transfer and while an oversized heat exchanger will increase the capital cost. Hence, it is very important to choose the right parameters during design of a heat exchanger. From the preliminary design, the detailed design for the heat exchanger can be readily extrapolated. The benefits of using performance charts in the design of a cross flow heat exchanger are described in the manuscript

Membrane Assisted Simultaneous Extraction and Derivatization with Triphenylphosphine of Elemental Sulfur in Arabian Crude Samples by Gas Chromatography/Mass Spectrometry

Determination of trace level elemental sulfur from crude oil samples is a tedious task. Recently, several gas chromatographic methods were reported in which selective triphenylphosphine derivatization of sulfur was used to form triphenylphosphine sulfide. Direct quantitation of elemental sulfur from crude oil requires an efficient sample preparation method. This paper describes how simultaneous extraction derivatization of elemental sulfur was performed for the first time using porous hollow fiber membrane. A thick (0.25 um pore size; 1550 μm wall thickness; and 5500 μm inner diameter) hollow fiber membrane filled with triphenylphosphine (dissolved N-methylpyrrolidone) is used as a solvent bar. The solvent bar is tumbled freely in the crude oil sample; the elemental sulfur was extracted and derivatized. Finally, the derivatized sulfur was analyzed by gas chromatography/mass spectrometry. Various experimental conditions of solvent bar microextraction (SBME) were optimized to achieve higher extraction. The linear range was established between 1 and 50 μg/mL, while a squared regression coefficient was found to be 0.9959 μg/mL. Relative standard deviation (RSD) was below 10%. Relative recoveries were calculated for SBME in crude oil samples and were in the range between 98.2% and 101.2%

Management of Extremity Venous Thrombosis in Neonates and Infants: An Experience From a Resource Challenged Setting

We aimed to evaluate the outcome of different treatment modalities for extremity venous thrombosis (VT) in neonates and infants, highlighting the current debate on their best tool of management. This retrospective study took place over a 9-year period from January 2009 to December 2017. All treated patients were referred to the vascular and pediatric surgery departments from the neonatal intensive care unit. All patients underwent a thorough history-taking as well as general clinical and local examination of the affected limb. Patients were divided into 2 groups: group I included those who underwent a conservative treated with the sole administration of unfractionated heparin (UFH), whereas group II included those who were treated with UFH plus warfarin. Sixty-three patients were included in this study. They were 36 males and 27 females. Their age ranged from 3 to 302 days. Forty-one (65%) patients had VT in the upper limb, whereas the remaining 22 (35%) had lower extremity VT. The success rate of the nonsurgical treatment was accomplished in 81% of patients. The remaining 19% underwent limb severing, due to established gangrene. The Kaplan-Meier survival method revealed a highly significant increase in both mean and median survival times in those groups treated with heparin and warfarin compared to heparin-only group (P < .001). Nonoperative treatment with anticoagulation or observation (ie, wait-and-see policy) alone may be an easily applicable, effective, and a safe modality for management of VT in neonates and infants, especially in developing countries with poor or highly challenged resource settings

Latitude gradient influences the age of onset of rheumatoid arthritis : a worldwide survey

The age of onset of rheumatoid arthritis (RA) is an important outcome predictor. Northern countries report an age of RA onset of around 50 years, but apparently, variability exists across different geographical regions. The objective of the present study is to assess whether the age of onset of RA varies across latitudes worldwide. In a proof-of-concept cross-sectional worldwide survey, rheumatologists from preselected cities interviewed 20 consecutive RA patients regarding the date of RA onset (RAO, when the patient first noted a swollen joint). Other studied variables included location of each city, rheumatologist settings, latitudes (10A degrees increments, south to north), longitudes (three regions), intracountry consistency, and countries' Inequality-adjusted Human Development Index (IHDI). Data from 2481 patients (82% females) were obtained from 126 rheumatologists in 77 cities of 41 countries. Worldwide mean age of RAO was 44 +/- 14 years (95% CI 44-45). In 28% of patients, RA began before age 36 years and before age 46 years in 50% of patients. RAO was 8 years earlier around the Tropic of Cancer when compared with northern latitudes (p <0.001, 95% CI 3.5-13). Multivariate analysis showed that females, western cities, and latitudes around the Tropic of Cancer are associated with younger age of RAO (R (2) 0.045, p <0.001). A positive correlation was found between the age of RAO and IHDI (r = 0.7, p <0.01, R (2) 0.5). RA often begins at an early age and onset varies across latitudes worldwide. We postulate that countries' developmental status and their geographical and geomagnetic location influence the age of RAO.Peer reviewe

Understanding Shale Petrophysics Helps in Drilling Stable Boreholes: Case Studies

Abstract Drilling stable boreholes in shale formations can be a very challenging task when water-based drilling fluids are used. The interactions between water phase in drilling fluids with shale rocks cause different drilling problems such as shale swelling and dispersion. The extent to which a shale sample swells or disperses depends on the clay content of the shale. Some types of clay have more swelling tendency while others have more dispersion tendency. Therefore, identifying the type of clay present in a shale rock is very important for developing drilling fluids capable of mitigating shale drilling problems. Gama ray data is a powerful tool to predict the clay mineralogy, determine shale reactivity and, as a result, predict the rock response when contacted by drilling fluids. Using petrophysical properties to characterize shale can help determine the appropriate drilling fluid and shale inhibitor to be used. The spectral gamma ray log has been used to determine the proportion of the radiation coming from potassium, uranium and thorium. The ratio of K/Th is utilized to identify clay mineralogy for different shale formations. In addition, formation density log data was utilized with neutron log to give more accurate information about lithology. The objective of this study is to discuss how petrophysics data of shale formations can be utilized to improve and optimize drilling practices to achieve the ultimate goal of enhanced wellbore stability. Depending on clay content, different shale formations have different responses when exposed to drilling fluids and, therefore, it is of high importance to characterize the shale formation to develop the appropriate drilling fluid.</jats:p

Novel Method and Apparatus for Sticking Fluid Performance Evaluation

Abstract Drilling fluid is the life line of safe and economic drilling operation to explore oil and gas resources from the earth's crust. However, it is also the root cause of various mud related drilling problems such as shale-drilling fluid interactions, borehole instability, loss of circulation, differential pipe sticking, etc. Differential sticking is one of major drilling problems that is very common when passing through a sticking prone high permeable zone. It is one of the major items of non-productive time that increases the total drilling cost dramatically, especially if there is a delay in recovering a stuck pipe. Moreover, delay or inability in recovering a stuck pipe may lead to other drilling problems leading to abandonment or side tracking of a well. Hence, every step should be taken to recover a stuck pipe as soon as possible. One of the most effective strategy for quick recovery of a stuck pipe is the use of a highly efficient and rapidly acting spotting fluid to damage, degrade and destroy mudcake-pipe sticking bonds as quickly as possible to release the stuck pipe easily from the mudcake matrix. This dictates quick laboratory evaluation of various spotting fluids available to identify the best spotting fluid for a particular mud and mudcake composition. As the chemistry of the mud additives and the deposited mudcake materials influence the performance of a spotting fluid, it is highly recommended to evaluate the de-bonding, degrading and destructive potential of a spotting fluid for a particular mudcake composition to select the superior and reject the inferior. However, there is no API or any other industry method that can be used for quick screening of various spotting fluids available to the industry to select the most efficient one for a particular stuck pipe rescue operation. This paper describes a dedicated operating software driven novel laboratory method for quick screening and reliable prediction of the performance of various spotting fluids to demonstrate the suitability of the method and test apparatus for oil and gas field application. Experimental results indicate that the newly developed method and test apparatus can consistently and precisely predict the performance of various spotting fluids and mudcake compositions to select the most suitable spotting fluid for a particular rescue operation. It provides useful guidelines and a practical decision making tool for the drilling and mud engineers and the consultants for quick and easy recovery of stuck pipe from the mudcake matrix. The method and apparatus will also play an important role in the development of a new generation of high performance spotting fluids to overcome current and future challenges associated with differential pipe sticking problems.</jats:p

The postauricular fasciocutaneous flap with an adipofascial extension: A case report

AbstractIntroductionA complex defect on the anterior surface of the ear requires flap cover; such as the postauricular skin flap. The postauricular skin flap has never been used with an adipofascial extension.Presentation of caseA 5-year old boy was involved in a car accident resulting in an exposed cartilage of the upper part of the right ear. The defect was covered with a post-auricular fasciocutaneous flap with an adipofascial extension. The adipofascial part of the flap was covered with a skin graft.DiscussionThe adipofascial extension serves two purposes: Firstly, it allows easier primary closure of the donor site. Secondly, it is less bulky and hence it does not observe the definition of the ear cartilage.ConclusionOur case is the first case reported in literature using the post-auricular fasciocutaneous flap with an adipofascial extension