DOUBLE PERFORATED IMPINGEMENT PLATE (DPIP) IN SHELL-AND-TUBE HEAT EXCHANGER

This paper presents a solution to a chronic problem causing repeated tube failure at shell-and-tube heat exchangers. The problem is related to fouling process on tubes surface which accumulates downstream the impingement plate at exchanger inlet nozzle within the first tube rows due to low velocity and vortices production. In fouling services, the suspended deposits, fouling, accumulates on tubes surface downstream the impingement plate causing under-deposit corrosion and raising tubes surface temperature due to lack of cooling accelerating fouling process. Under fouling corrosion attacks tubes and causes repeated tube failure costing a lot of money in terms of material, maintenance and production losses. Normal practice of extending tubes life and delaying their failure is to upgrade the tubes metallurgy. So this paper objective is to present an economical solution option through modifying the impingement plate in shell-and-tube heat exchangers where impingement plate is recommended by Tubular Exchanger Manufacturers Association, TEMA. The impingement modification is to replace the solid conventional impingement plate with double spaced plates having offset holes, called Double Perforated Impingement Plate (DPIP). The objective of this work can be met through simulate and compare shell side inlet flow distribution around the conventional and modified impingement plate, DPIP, and insuring of enhancing the flow pattern distribution at the area behind impingement plate. Since experimental work in flow investigation can be time consuming and costly, computational fluid dynamics, CFD, fluent software was implemented as a cost effective helpful tool to conduct the simulation and comparison purpose. The modified impingement plate, DPIP, will destroy vortices created behind the conventional plate retarding fouling accumulation principal. DPIP will enhance shell side flow distribution downstream the impingement plate and stop fouling accumulation on the tubes to prevent under-deposit corrosion

Global patient outcomes after elective surgery: prospective cohort study in 27 low-, middle- and high-income countries.

BACKGROUND: As global initiatives increase patient access to surgical treatments, there remains a need to understand the adverse effects of surgery and define appropriate levels of perioperative care. METHODS: We designed a prospective international 7-day cohort study of outcomes following elective adult inpatient surgery in 27 countries. The primary outcome was in-hospital complications. Secondary outcomes were death following a complication (failure to rescue) and death in hospital. Process measures were admission to critical care immediately after surgery or to treat a complication and duration of hospital stay. A single definition of critical care was used for all countries. RESULTS: A total of 474 hospitals in 19 high-, 7 middle- and 1 low-income country were included in the primary analysis. Data included 44 814 patients with a median hospital stay of 4 (range 2-7) days. A total of 7508 patients (16.8%) developed one or more postoperative complication and 207 died (0.5%). The overall mortality among patients who developed complications was 2.8%. Mortality following complications ranged from 2.4% for pulmonary embolism to 43.9% for cardiac arrest. A total of 4360 (9.7%) patients were admitted to a critical care unit as routine immediately after surgery, of whom 2198 (50.4%) developed a complication, with 105 (2.4%) deaths. A total of 1233 patients (16.4%) were admitted to a critical care unit to treat complications, with 119 (9.7%) deaths. Despite lower baseline risk, outcomes were similar in low- and middle-income compared with high-income countries. CONCLUSIONS: Poor patient outcomes are common after inpatient surgery. Global initiatives to increase access to surgical treatments should also address the need for safe perioperative care. STUDY REGISTRATION: ISRCTN5181700

Simple and clear approach to industrial boiler circulation analysis

Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.Circulation in industrial boiler is the continuous supply of water to the boiler heated tubes in order to sustain steady steam output without overheating tubes. Adequate circulation occurs when there is sufficient flow of water into tubes for adequate cooling. In natural circulation industrial boiler system the rate of flow in the circulation system is governed by flow resistances and differences in density between downcomer tube circuits and heated riser circuits. Control of these resistances allows adequate flow of water to parallel circuits. Adequate water flow through the boiler's heat absorbing circuits is necessary to cool the tubes. To insure proper boiler circulation, a simple, clear and comprehensive approach will be described in this paper covering all aspects in boiler circulation analysis. The analysis will detail all boiler circulation circuits explaining all forces imposed on them including thermosyphon as well as friction forces.ej201

Influence of Boiler Load Swing Rates on Effective Stresses of Drum Boiler Riser Tubes

In this paper, different rates of steam flow (swing rates