Mohammad Shakir Nasif

Modeling of Air to Air Enthalpy Heat Exchanger

The thermal performance of a Z-shaped enthalpy heat exchanger utilizing 45-gsm Kraft paper as the heat and moisture transfer surface for heating, ventilation, and air conditioning (HVAC) energy recovery is experimentally investigated through temperature and moisture content measurements. A mathematical model is developed and validated against the experimental results using the effectiveness-NTU method. In this model the paper moisture transfer resistance is determined by paper moisture permeability measurements. Results showed that the paper moisture transfer resistance is not constant and varies with moisture gradient across the paper. Furthermore, the model is used to predict the heat exchanger performance for different heat exchanger flow configurations. The results showed that higher effectiveness values are achieved when the heat exchanger flow path width is reduced. Temperature and moisture distribution in the heat exchanger is also studied using a computational fluid dynamics package (FLUENT). To model the moisture transfer through the porous materials a nondimensional sensible–latent effectiveness ratio was developed to obtain the moisture boundary conditions on the heat exchanger surface.

Computational fluid dynamics simulation of blood flow profile and shear stresses in bileaflet mechanical heart valve by using monolithic approach

Bileaflet mechanical heart valves (BMHVs) are widely used to replace diseased heart valves. However, patients may suffer from implant complications, such as platelet aggregation and damage to blood cells, which could lead to BMHV failure. These complications are related to the blood flow patterns in the BMHV. A three-dimensional computational fluid dynamic (CFD) model was developed to investigate blood hydrodynamics and shear stresses at different cardiac cycles. A user-defined function (UDF) code was developed to model the valve leaflet motion. This UDF updates the tetrahedral mesh according to the location of the valve leaflet, which enables modeling of complicated moving geometries and achieves solution convergence with ease without the need to adjust the relaxation factor values. The agreement between the experimental and numerical results indicates that the developed model could be used with confidence to simulate BMHV motion and blood flow. Furthermore, valve leaflet and valve pivot were found to be continuously exposed to shear stresses higher than 52.3 Pa which according to previous research findings may cause damage to blood platelets.

Numerical simulation of two-phase flow regime in horizontal pipeline and its validation

Purpose: The purpose of this paper is to investigate oil-gas slug formation in horizontal straight pipe and its associated pressure gradient, slug liquid holdup and slug frequency. Design/methodology/approach: The abrupt change in gas/liquid velocities, which causes transition of flow patterns, was analyzed using incompressible volume of fluid method to capture the dynamic gas-liquid interface. The validity of present model and its methodology was validated using Baker�s flow regime chart for 3.15 inches diameter horizontal pipe and with existing experimental data to ensure its correctness. Findings: The present paper proposes simplified correlations for liquid holdup and slug frequency by comparison with numerous existing models. The paper also identified correlations that can be used in operational oil and gas industry and several outlier models that may not be applicable. Research limitations/implications: The correlation may be limited to the range of material properties used in this paper. Practical implications: Numerically derived liquid holdup and holdup frequency agreed reasonably with the experimentally derived correlations. Social implications: The models could be used to design pipeline and piping systems for oil and gas production. Originality/value: The paper simulated all the seven flow regimes with superior results compared to existing methodology. New correlations derived numerically are compared to published experimental correlations to understand the difference between models. © 2018, Emerald Publishing Limited.

Experimental data for the slug two-phase flow characteristics in horizontal pipeline

The data presented in this article were the basis for the study reported in the research articles entitled “Statistical assessment of experimental observation on the slug body length and slug translational velocity in a horizontal pipe” (Al-Kayiem et al., 2017) [1] which presents an experimental investigation of the slug velocity and slug body length for air-water tow phase flow in horizontal pipe. Here, in this article, the experimental set-up and the major instruments used for obtaining the computed data were explained in details. This data will be presented in the form of tables and videos.

Numerical Investigation of Slug Characteristics in a Horizontal Air/Water and Air/Oil Pipe Flow

In the present work, the transition from stratified flow to slug flow regime for air-water and air-oil two-phase flow was simulated and analysed numerically. The simulation was carried out by numerically solving a three dimensional (3D) implicit unsteady volume of fluid (VOF) model. Typical slug characteristics, such as slug length, slug translational velocity, and slug frequency were determined. The numerical results were validated by comparison with experimental results and a reasonable agreement with an error less than 8.7% was achieved. Moreover, the results from the proposed model were compared to the results obtained from three empirical correlations for the two-phase slug flow and it demonstrated a good agreement. The simulation results demonstrated that for the same boundary conditions, the characteristics in terms of slug initiation and slug growth were strongly affected by the fluid properties. The simulation results also show that for air-oil flow, the pressure drop, slug translational velocity, and slug frequency values were less than in air-water flow by 2.9%, 14.3%, and 7.9%, respectively.

Hydrocarbon Fire and Explosion’s Safety Aspects to Avoid Accident Escalation for Offshore Platform

Offshore platforms are never 100% secure from fire hazard despite of using advanced technology. Hydrocarbon fire and explosion accidents are among commonly reported incidents in the oil and gas process-related activities. In April, 2015, PEMEX-operated oil platform caught fire—45 injured and four died. Accidents such as Piper Alpha have recorded greatest loss of human live on offshore platform in history. A total of 167 persons perished victim of the tragedy confluence of design flows, human error, and bad luck. Saving lives and property in such disaster is extremely a challenging job for engineers. Hydrocarbon fire and explosion produce extreme pressure and temperature, which cause fatalities and structural damages at large scale within a fraction of time. The experimental studies are restricted due to limited facilities available for fire and explosion testing for offshore structure. In previous studies, individual structure member was tested, which cannot represent the behaviour of the entire structure. Therefore, structural safety is always being a main issue to prevent property damage or least-obtained safe evacuation before structural collapse. To understanding the behaviour of structural modelling techniques allow to study the possible behaviour of the platform. These techniques entirely depend on personal experience and modelling practice adopted in oil and gas sector. Therefore, simulation should be verified by a full-scale experimental study on combined structural members. The standard experimental studies should be conducted and data should be easily available after testing for validation for future simulation and to overcome lack of date issues.

Numerical Validation of Two-Phase Slug Flow and its Liquid Holdup Correlation in Horizontal Pipeline

The transition of one flow regime into another is a very common phenomena in pipeline networks, which can be potentially hazardous for the structural integrity of the pipeline. Literature review showed that there is almost no reported detail investigation of transitional flow whereby the fluid constituents change from one regime to another especially slug transition. Most of the open research papers focused on slug flow regime and its liquid holdup in horizontal pipelines and channels have been carried out on experimental test rigs. The objective of this study is to explore oil-gasoil vapor slug transition and its liquid holdup in a 3.15 inch diameter horizontal straight pipe. The abrupt change in gas/liquid velocities, which causes transition of flow patterns is analyzed using incompressible Volume of Fluid (VOF) method, along with Piecewise Linear Interface Construction (PLIC) technique to capture the sharp front of segregated gas-liquid interface. Slug liquid holdup derived from the present numerical model is compared to existing experimental correlations in the literature.

Numerical Simulation of the Transient Development of Slug Flow in Horizontal Pipes

Slug flow regime in two and multi-phase flow in pipes is a complicated flow phenomena representing challenge in the design of the piping system. In the present work, water/air two phase flow was modeled and simulated as 3 dimensional, transient, and incompressible flow using Volume of Fluid technique in STAR-CCM+ software. The simulation was conducted to predict and evaluate the air-water slug flow in a horizontal pipe with 0.16 m diameter and 7 m long. The superficial velocities for both phases were extracted from Baker chart slug zone. The results were validated against experimental bench marking referenced in Baker chart and the proposed VOF technique shows a good capability in simulating the development of the slug flow regime. This model could be utilized for simulation of various two phase flow regimes.

Numerical Study on Fluid Structure Interaction of Slug Flow in a Horizontal Pipeline

It is well-known that when slug flow occurs in pipes it may result in damaging the pipe line. Therefore it is important to predict the slug occurrence and its effect. Slug flow regime is unsteady in nature and the pipelines conveying it are indeed susceptible to significant cyclic stresses. In this work, a numerical study has been conducted to investigate the interaction between the slug flow and solid pipe. Fluid Structure Interaction (FSI) coupling between 3-D Computational Fluid Dynamic (CFD) and 3-D pipeline model code has been developed to assess the stresses on the pipe due to slug flow. Time – dependent stresses results has been analyzed together with the slug characteristic along the pipe. Results revealed that the dynamic behavior of the pipelines is strongly affected by slug parameters. The FSI simulation results show that the maximum stresses occurred close to the pipe supports due to slug flow, where the pipe response to the exerted slug forces is extremely high. These stresses will subsequently cause fatigue damage which is likely reduce the total lifetime of the pipeline. Therefore a careful attention should be made during the design stage of the pipeline to account for these stresses. The system has been investigated under multiple water velocities and constant air velocity, the maximum stress was obtained at the water velocity of 0.505 m/s. Moreover, when the water velocity is increased from 0.502 to 1.003 m/s the maximum stress magnitude is decreased by 1.2% and when it is increased to 1.505 m/s the maximum stress is diminished by 3.6%.

Effect of Air to Air Fixed Plate Enthalpy Energy Recovery Heat Exchanger Flow Profile on Air Conditioning System Energy Recovery

Fixed plate enthalpy heat exchanger which utilizes permeable material as heat and moisture transfer surface has been used as an energy recovery system to recover sensible and latent heat in HVAC systems. The heat exchanger effectiveness is affected by the air flow profile. It is well known that counter flow configuration provides highest effectiveness, however, in real applications, it is not possible to implement a counter flow configuration, as both inlet and outlet ducts of the two flow streams are located on the same side of the heat exchanger. Therefore, several quasi-counter-flow heat exchanger designs including Z-shaped, L-shaped, Z-shaped opposite flow configurations are proposed in this research and their effect on energy consumed by an air conditioning cooling coil has been investigated, where each of the proposed heat exchanger is incorporated in an air conditioning cooling coil model. The modeled cooling coil energy consumption and energy recovered by the heat exchangers are evaluated under Kuala Lumpur weather conditions. It has been found that an air conditioner coupled with L-shaped heat exchanger recorded up to 20% increase in energy recovery in comparison with Z-shaped oposite and Z-shaped heat exchanger.