Amir A. Al-Haddad

Prediction of heat transfer coefficient in pulsating flow

Abstract A general empirical correlation has been developed for prediction of the heat transfer coefficient in a heating process for steady and pulsating flow of air through a rigid circular pipe. The pulsating frequency (5–60 Hz) was in sine form, and a combined dimensionless number composed of the Reynolds number and a dimensionless flow frequency was used to correlate thermal behavior with flow parameters. A critical value of 2.1 × 10 5 for the combined dimensionless number was noticed. Below this value no significant improvement was obtained. The correlation was found to be general and valid for steady and pulsating turbulent flow heat transfer.

Experimental Investigation of the Performance of Two-Stage Evaporative Coolers

Experiments have been conducted to investigate the thermal effectiveness and the air-side pressure drop of single- and two-stage evaporative coolers. Two different configurations of the two-stage evaporative cooler have been tested. The first one uses an external cooling tower to cool the water required to precool the air in the indirect water-to-air precooler. In the second design the cooled water in the direct-contact evaporative cooler is used as the cooling medium in the air precooler. Tlie variables considered are packing thickness, mass flow rate of water to the precooler, and mass flux of water irrigating the packing. The data obtained indicate that the thermal effectiveness of the two-stage evaporative cooler with a cooling tower is high compared to that of the system without a cooling tower, which in turn is superior to that of the single-stage, direct-contact evaporative cooler. Increasing the mass flow rate of water to the air precooler improves the effectiveness of the two-stage evaporative co...

Thermal and hydraulic performance of a modified two-stage evaporative cooler

The thermal and hydraulic performance of a modified two-stage evaporative cooler is evaluated. Variables considered are the mode of operation, packing thickness, mass flow rate of the water flowing to the precooler, and the mass flux of water flowing over the packing media. The effectiveness of the system increased with the increase of the mass flow rate of water flowing to the precooler, decreasing the mass flux of water flowing to the packing, and with the increase of the packing thickness. The effectiveness of the system with structured packing was higher than that with sheathy leaf base or natural fiber packing.

Homopolymerization of 4‐propionoxybenzoic acid: A kinetic study

A kinetic study of the synthesis of poly(4-oxybenzoate) by melt-step growth polymerization using para-propionoxybenzoic acid is reported. The polycondensations obey second-order kinetics, irrespective of whether the reaction was catalyzed or uncatalyzed. Breaks are observed in the kinetic plots, suggesting the presence of different kinetic regimes during the course of the reaction. An elaborate kinetic model that presupposes precipitation of oligomers predicts two-stage kinetics as well as breaks in the rate plots and fits experimental data well throughout the course of the reaction and the performance of two transesterification catalysts are estimated. No isokinetic temperature is displayed for the transesterification reaction. Activation energy values for catalyzed reactions are found to be higher than the uncatalyzed reaction, indicating that entropy factors drive the reaction to completion.

Estimation of inorganic and organic pollutants in Kuwait groundwaters used in irrigation: a study after the gulf war

Kuwait was invaded on August 2, 1990. Around 700 oil wells were destroyed during the Iraqi aggression. Many septic tanks and drainage systems were destroyed. One of the major concerns following the Iraqi invasion is the possibility of ground water contamination. A study of underground water in Kuwait during the period June to December 1993 with regard to irrigation is presented. Water from four different aquifers were analysed for organics and inorganics. A hydrochemical study of these waters indicated that water from (Su‐123), (E‐15) and (PW‐1OL) are suitable for irrigation. The boron concentration in these plants is less than 1 ppm, making it suitable for sensitive and semisensitive crops. Nickel and vanadium are the major inorganics found in crude oil. No appreciable rise in the concentration of these elements was observed. The concentration of polyaromatic hydrocarbons (PAH) and total organic carbon (TOC) is found to vary from 0.01 to 0.07 ppm and 0.21 to 0.9 ppm. PAH is found to vary with location while TOC is found to vary with time.

Copolyesterification between poly (butylene terephthalate terephthalic acid and hydroquinone diacetate: a Kinetic analysis.

Abstract The kinetics of liquid crystalline copolyester synthesis via melt transesterification between poly(butylene terephthalate) (PBT), terephthalic acid (TA) and hydroquinone diacetate (HQDA) is examined. Two different copolyester compositions PBT30/(HQDA+TA) 70 and PBT 50/(HQDA+TA) 50 mol% ratio were synthesized. The ratio of HQDA to TA was kept constant for all the reactions. The copolyesters were synthesized via melt polycondensation route at 265°C, 275°C and 285°C using two different transesterification catalysts, zinc acetate and dibutyl tin oxide. A key postulation assumed in this work is that the reaction originates between TA and HQDA to form a dimer which slices PBT chain. The copolyesterification rate constant for a system containing butylene glycol a more nonpolar moiety compared to ethylene glycol in poly(ethylene terephthalate) has been determined. The activation energy values for the different copolymer systems has also been determined. The rate constants for the uncatalyzed and catalyzed copolyesterification reaction and the activation energy values for the reaction have been determined.

Kinetics of copolyesters of poly(butylene terephthalate), hydroquinone diacetate and terephthalic acid: A simple rate model for catalysed synthesis in melt.

Abstract Considerable literature exists on the structural organisation of thermotropic liquid crystalline aromatic copolyesters. Majority of these copolyesters are synthesised via the copolymerisation route, which helps in tailoring the characteristic properties to the predecided values. Another major advantage of copolymerisation is that it helps in conferring specific chemical properties to the major component present in the system. Synthesis of aromatic polyesters using bromo, chloro, methyl and methoxy substituted hydroquinones have been reported, to lower the melting temperatures relative to the unsubstituted polyesters. These polyesters have applications in fabricating thermally stable high strength fibres and moulding resins with unusual properties. An understanding of the melt polyesterification kinetics is a must to economise on the process productivity and to improve the polymer properties. There is no published literature on the melt polyesterification kinetics of PBT, HQDA and TA. Kinetic investigation of copolymerisation between PET and 4-acetoxy benzoic acid (PET/OB) did not reveal precipitation of poly (4-oxybenzoate). Here we explore the kinetics of a three component system, wherein many parallel reactions take place simultaneously. Homopolymerisation between HQDA and TA lead to a rigid rod system. The work was carried out with the following objectives: (1) To identify plausible routes to simplif the kinetics of a three component system; (2) To determine the kinetic order with respect to the homopolymers of HQDA and TA as well as the copolymers of PBT, HQDA and TA; (3) To predict the rates of acetic acid generation during the homopolymersiation and copolymerisation reactions and (4) To check whether precipitation constitutes an added complication, as observed in the earlier study on one component 4-acetoxy benzoic acid system.

Chemical Kinetics of a two component phase segregated system. A simple rate model

Considerable research has been performed on polymeric systems that exhibit liquid crystalline or mesomorphic behavior. The principal reason for this effort was that these materials might be developed as ultrahigh strength materials. Jackson and Kuhfuss from Tennessee Eastman demonstrated that liquid crystalline behavior existed in copolymers based on poly(ethylene terephthalate) (PET) and para-hydroxy benzoic acid (ABA). However, intricate details pertaining to the polyesterification kinetics have remained unexamined. Transesterification reactions between poly(ethylene terephthalate) PET, and acetoxybenzoic acid (ABA) were conducted using the melt polymerization technique to understand the transesterification kinetics of a phase segregated system. The transesterification kinetics of two compositions PET 20/80 (ABA) and PET10/90 (ABA) have been studied at 260, 275, 290 and 305°C using dibutyl tinoxide (0.1 mole percent) as a catalyst. Homopolymerization of acetoxy benzoic acid was also studied at similar temperatures and catalyst concentration. In the present experimental work moles of acetic acid found experimentally is computed using a standard procedure. The rate constant k is determined. The role of the catalyst is also evaluated.

Chemical kinetics of a two component phase segregated system. A simple rate model

Abstract Considerable research has been performed on polymeric systems that exhibit liquid crystalline or mesomorphic behavior. The principal reason for this effort was that these materials might be developed as ultrahigh strength materials. Jackson and Kuhfuss from Tennessee Eastman demonstrated that liquid crystalline behavior existed in copolymers based on poly(ethylene terephthalate) (PET) and para-hydroxy benzoic acid (ABA). However, intricate details pertaining to the polyesterification kinetics have remained unexamined. Transesterification reactions between poly(ethylene terephthalate) PET, and acetoxybenzoic acid (ABA) were conducted using the melt polymerization technique to understand the transesterification kinetics of a phase segregated system. The transesterification kinetics of two compositions PET 20/80 (ABA) and PET10/90 (ABA) have been studied at 260, 275, 290 and 305°C using dibutyl tinoxide (0.1 mole percent) as a catalyst. Homopolymerization of acetoxy benzoic acid was also studied at similar temperatures and catalyst concentration. In the present experimental work moles of acetic acid found experimentally is computed using a standard procedure. The rate constant k is determined. The role of the catalyst is also evaluated.

H2S pollution : A Gulf War problem. Prediction of Henry's constant for H2S under simple experimental conditions

One of the major concerns after the Iraqi invasion was the possibility of air pollution due to the presence of many volatile contaminants emitted from sewage tanks and pipeline. Hydrogen sulfide (H2S) was one of the major contaminants and was a common cause of complaint from the residents in the Ardiya district in Kuwait. In this study an effort was made to develop an apparatus for the estimation of Henrys constant (H) for H2S. The accuracy of this instrument was counter checked with respect to published data. The experiments could be reproduced with a maximum error of 10%. The experiments were performed between 20–40°C. Henrys constants for the sewage water were found to be 600, 720 and 905 atm/mole at 20, 30 and 40°C. The values were compared to the literature values and were found to be on the higher side, indicating a need for remedial measures.