Thermo-fluid characteristics of fin-and-tube heat exchangers with various fin details for air conditioning applications

ABSTRACT The need for more efficient air conditioning systems requires an in depth understanding about the performance of its components. One of the key components in the air conditioning plant is the fin-and-tube cooling coil, which is investigated here. The main focus of the work is concerned with the analysis of fin-and-tube cooling coils having two classes of passive enhancement techniques known as corrugated and turbulated fins with particular reference of developing flow region. Initially, two-dimensional modelling was done to establish the scope of later three-dimensional modelling in terms of dominant variables, meshing strategies and convergence criteria. The results gave key insights into required modelling strategies needed for the more complex three-dimensional problem of the composite fin-and-tube cooling coil. Three-dimensional CFD modelling of fin-and-tube cooling coils having turbulated, corrugated and flat-fin geometries have been investigated with particular reference to the dry-hot arid climate. Five modelling approaches have been considered based on an isothermal fin-and-tube, periodic boundaries, conjugate heat transfer, tube-row temperature gradient and the effect of manufacturing defects. The last three approaches are novel contributions to this field of research. The influences of the key design parameters of fin pitch, fin material, and fin thickness have also been investigated parametrically for all fin types. To provide confidence in these models, experimental studies on these cooling coils were carried out to acquire data for comparison between the predicted and measured values of heat transfer and friction, and to investigate the effect of range of design conditions on the cooling coils performance. The detailed results of this work can be used to optimise the air-conditioning coil designs. The turbulated fin coil was found to give the highest values of Nusselt number at given friction factor followed by the corrugated fin coil. At a given pressure drop (dP = 52 N/m2 corresponding to 14, = 2.3 m/s), the heat transfer coefficient of the corrugated and turbulated fin coils was higher than that of flat fin by 16 % and 36 % respectively. For typical operating conditions, the corrugated and turbulated fin coils required core volumes of 19 % and 40 % less than that of flat fin coil respectively for the same performance. The cooling coils employing corrugated and turbulated fin geometries contribute significantly to the energy conservation and volume reduction of the air conditioning plant

Thermal performance of the chilled water spirally coiled finned tube in cross flow for air conditioning applications

AbstractThe thermal performance of spirally coiled finned tube in cross flow was investigated experimentally. The effects of curvature ratio, flow direction, fin pitch and flow rate of chilled water and air on thermal characteristics of spirally coiled finned tube have been studied. Six test sections with curvature ratios of 0.027, 0.03, 0.04, tube pitches of 18, 20, 30mm, and fin pitches of 33, 22, 11mm were used. The experiments were done using a pilot wind tunnel with air Reynolds number range 35,500–245,000. Innermost and outermost flow directions of chilled water with Reynolds number range 5700–25,300 have been investigated. The innermost flow direction has significant enhancement effect on the Nusselt number compared with outermost flow direction. The decrease of fin pitch enhances the Nusselt number on expense of pressure drop. Decreasing the curvature ratio increases air side Nusselt number on expense of pressure drop. A set of empirical expressions for predicting the friction factor and the Nusselt number for air flow across the spiral coils have been regressed based on the obtained data in the present experiments

Primary School Teachers’ Perspectives on ADHD in Alkadrow, Khartoum, Sudan

Background: Attention deficit hyperactivity disorder, which is a prevalent neurodevelopmental condition, commonly manifests during early childhood and has the potential to adversely affect an individual’s social, academic, and occupational performance in multiple settings. Students with ADHD may struggle with attention, focus, listening, and completing schoolwork. Additionally, they may exhibit restless or disruptive behavior in class and may have learning disabilities that affect their academic performance. The aim of this study was to explore the perspectives of primary school teachers on ADHD in Alkadrow, Khartoum, Sudan. Methods: A descriptive cross-sectional study was conducted in Alkadrow-Bahri locality, Sudan, over a period of three to six months in 2022. The study population included primary school teachers who had taught for at least one year and encountered at least one student with ADHD. A convenience sampling technique was used to select a minimum of 59 participants, and data were collected using a self-administered questionnaire with closed-ended questions. SPSS version 23 was used to analyze the data, including descriptive statistics and inferential statistics such as chi-square tests and logistic regression analysis. Results: The study had 59 participants, with the majority being female and in the age group of 41–45 years. The participants were mostly married and had obtained psychology courses, with a bachelor’s degree being the most common level of education. Many participants had over 20 years of teaching experience. Regarding the attitude toward attention deficit hyperactivity, most participants strongly agreed that they did have a negative/positive attitude toward it, and a majority agreed or were neutral toward ADHD. However, in the case of attention deficit hyperactivity, a significant percentage of participants disagreed or strongly disagreed with the statement. Conclusion: The study found that most participants had a negative attitude toward student referrals for medical care and believed that most symptoms of ADHD can be lowered by aging. Additionally, more than half strongly disagreed that punishment has a positive effect on ADHD

Prognostic model to predict postoperative acute kidney injury in patients undergoing major gastrointestinal surgery based on a national prospective observational cohort study.

Background: Acute illness, existing co-morbidities and surgical stress response can all contribute to postoperative acute kidney injury (AKI) in patients undergoing major gastrointestinal surgery. The aim of this study was prospectively to develop a pragmatic prognostic model to stratify patients according to risk of developing AKI after major gastrointestinal surgery. Methods: This prospective multicentre cohort study included consecutive adults undergoing elective or emergency gastrointestinal resection, liver resection or stoma reversal in 2-week blocks over a continuous 3-month period. The primary outcome was the rate of AKI within 7 days of surgery. Bootstrap stability was used to select clinically plausible risk factors into the model. Internal model validation was carried out by bootstrap validation. Results: A total of 4544 patients were included across 173 centres in the UK and Ireland. The overall rate of AKI was 14·2 per cent (646 of 4544) and the 30-day mortality rate was 1·8 per cent (84 of 4544). Stage 1 AKI was significantly associated with 30-day mortality (unadjusted odds ratio 7·61, 95 per cent c.i. 4·49 to 12·90; P < 0·001), with increasing odds of death with each AKI stage. Six variables were selected for inclusion in the prognostic model: age, sex, ASA grade, preoperative estimated glomerular filtration rate, planned open surgery and preoperative use of either an angiotensin-converting enzyme inhibitor or an angiotensin receptor blocker. Internal validation demonstrated good model discrimination (c-statistic 0·65). Discussion: Following major gastrointestinal surgery, AKI occurred in one in seven patients. This preoperative prognostic model identified patients at high risk of postoperative AKI. Validation in an independent data set is required to ensure generalizability

Rangelands attributes and productivity as affected by application of water harvesting techniques in Butana area

PowerPoint presentationDue to climatic changes, rainfall duration and annual amount of precipitation have changed in different ecological zones in Sudan including Butana area. Accordingly, plant species composition and land area productivity have declined in recent years. The study developed strategies that could enable livestock producers to better adapt to climate changes, while also assessing the impact of water harvesting techniques on soil health and rangeland productivity. The presentation includes tables of results and images of the rangeland sites

Thermal Performance Analysis of Low-GWP Refrigerants in Automotive Air-Conditioning System

The energy and exergy of low-global warming potential (GWP) refrigerants were investigated experimentally and theoretically. Refrigerants with a modest GWP100 of  ≤ 150 can be sufficient for bringing down emissions which were concerned for the automotive air-conditioning system. Three types of low-GWP refrigerants, R152a, R1234yf, and R1234ze(E), were examined with particular reference to the current high-GWP of R134a. The effect of different evaporating and condensing temperatures in addition to compressor speed was considered. The purpose was to bring a clear view of the performance characteristics of possible environment friendly alternatives of R134a. The analysis was carried out with compressor power, cooling capacity, coefficient of performance, exergy destruction, and exergy efficiency. It was noted that the total exergy destruction of R1234yf was reduced by 15% compared to that of R134a. The refrigerant R1234ze(E) has the highest energetic and exergetic performance compared with the other investigated refrigerants