A TRANSIENT NUMERICAL MODEL FOR SENSIBLE FIXED-BED REGENERATOR IN HVAC APPLICATIONS

Peer Reviewe

TRANSIENT ANALYSIS AND OPTIMIZATION OF FIXED-BED REGENERATORS FOR HVAC APPLICATIONS

Air-to-air energy exchangers (AAEEs) recover energy from the exhaust airstream to precondition the supply airstream into buildings. In a fixed-bed regenerator (FBR), a type of AAEE, energy from the exhaust airstream is stored in the exchanger over a period; then, the energy is transferred to the supply airstream flowing through the same exchanger in the next period. Due to the storage and release of energy in consequent periods, the temperature and humidity of the airstreams at the outlet of the FBR vary with time. This variation poses difficulties for experimental testing and effectiveness evaluation of the FBR because of the slow response of sensors. The primary goal of this thesis is to develop and validate transient numerical models to accurately predict the transient characteristics of FBRs (sensible and desiccant-coated) and their sensors (temperature and humidity). A numerical model consisting of an exchanger model and sensor models is developed to capture the transient characteristics of FBRs and their sensors. The developed model is validated using experimental results and can distinguish the actual FBR performance from the performance that is measured by the sensors in an experiment. The results show that the configuration of the FBR, and the sensors’ location influence the measurement of the outlet air properties and, thus, the calculated effectiveness (effectiveness error). In addition, for the desiccant-coated FBRs, the effectiveness error depends on the operating condition of an experiment. This thesis also provides recommendations to improve North American testing standards (ASHRAE 84 and CSA C439-18) for FBRs. The results show that measurement requirements in the testing standards are conservative and can be relaxed for many designs and operating conditions. Furthermore, this thesis provides insights on optimizing sensible FBRs considering their transient characteristics

Enhancing the mechanical properties and formability of low carbon steel with dual-phase microstructures

In the present study, a special heat treatment cycle (step quenching) was used to produce a dual-phase (DP) microstructure in low carbon steel. By producing this DP microstructure, the mechanical properties of the investigated steel such as yield stress, tensile strength, and Vickers hardness were increased 14, 55, and 38%, respectively. In order to investigate the effect of heat treatment on formability of the steel, Nakazima forming test was applied and subsequently finite element base modeling was used to predict the outcome on forming limit diagrams. The results show that the DP microstructure also has a positive effect on formability. The results of finite element simulations are in a good agreement with those obtained by the experimental test

Modeling the Chlorine Gas Dispersion in the Water Treatment Plant

An issue rose for industrial safety and successful address of crisis involves quick and pragmatic decision that would reduce losses and accidents. This will become practical when in addition to studying of past accidents the industrial executives create the necessary readiness to face risks through precise estimation of the consequences of eventual accidents. The present research concerns modeling the consequences of chlorine gas dispersion in the wastewater installations. The transfer of knowledge and information in this study were gained from modeling the dispersion of chlorine in the water treatment plants, useful for managers and executives. Detection and specifying the risks of chlorine for the public and especially the staff and those residing near the water treatment plant, would result in the appropriate action against this lethal substance, which is the subject of this study. Identification of risks related to foreign agents and their negative impacts on water treatment plants containing chlorine tanks is among the objectives of this study. The modeling and accurate specification of the scope and level of danger created following the dispersion of chlorine was done using the PHAST software, which allowed a clear identification of danger zones created by the dispersion of Chlorine. This text reports the radius of areas affected by chlorine dispersion as well as the results of different conditions after running the model for variable physical and process conditions, and given their availability, these results can be compared with each other

A transient numerical model for desiccant-coated fixed-bed regenerators and compensation for transient sensor errors

This is an Accepted Manuscript of an article published by Taylor & Francis in Science and Technology for Build Environment on 06-January 2022, available at: https://doi.org/10.1080/23744731.2021.2017236Natural Science and Engineering Research Council (NSERC), Tempeff North America Inc., Winnipeg, Canada (Project No: 533225-18), ASHRAE.Peer ReviewedDesiccant-coated fixed-bed regenerators (FBRs) can achieve high effectiveness due to high ratio of energy transfer area to volume, and therefore, they are favourable air-to-air energy recovery exchangers for HVAC systems. However, unlike other types of energy recovery exchangers, the air properties (i.e., temperature and humidity) at the outlet of FBRs vary with time. The variations in outlet airflow properties can cause errors in measurements because the measurements include the FBR and sensors transient responses. In this paper, a numerical model is developed to evaluate the performance of desiccant-coated FBRs and their transient operation. The model consists of an exchanger model (FBR model) and sensor (temperature and humidity) models to distinguish the actual performance of the FBR alone from the measured performance, which includes both the FBR and the sensor's response. The model is validated with experimental measurements and available results in the literature. The model can decouple the measured response of the FBR and sensors to predict the FBR performance. This paper's main contribution is an insight into the complex heat and mass transfer processes in desiccant-coated FBRs and measurement sensors. The results of this paper could be used to provide practical recommendations for humidity measurements of different types of desiccant-coated FBRs developed for HVAC applications. Furthermore, the measurement requirements in the current testing standards (ASHRAE 84 and CSA C439-18 standards) for FBRs are examined. Recommendations from this paper could be implemented in future versions of these standards

Experimental Investigation on Thermo-Hydraulic Performance of Triangular Cross-Corrugated Flow Passages

National Science and Engineering Research Council (NSERC), Tempeff North America Inc., Winnipeg, Canada, (Project No: 533225-18)Peer ReviewedHeat exchangers made of corrugated flow passages generally have better thermo-hydraulic performance compared to parallel flow passages. The corrugation angle (), corrugation pattern, and the ratio of depth to pitch (hch/Pch) are critical geometrical parameters influencing the heat transfer and pressure drop in corrugated flow passages. This paper experimentally investigates heat transfer and pressure drop characteristics of triangular-shaped cross-corrugated flow passages for the range of 25°<<75° and 0.13<hch/Pch<0.36. Experiments are performed using representative compact heat exchangers in a small-scale test facility. This study also reports the effects of plate geometry on heat transfer and pressure drop and provides correlations for the average Nusselt number and friction factor. A detailed comparison of test data with relevant literature is also presented. Results of this study will be useful to manufactures and designers for developing high-performance heat exchangers

Synthesis and Effects of 4,5-Diaryl-2-(2-alkylthio-5-imidazolyl) Imidazoles as Selective Cyclooxygenase Inhibitors

Objective(s)In recent years highly selective COX-2inhibitors were withdrawn from the market because of an increased risk of cardiovascular complications. In this study we were looking for potent compounds with moderate selectivity for cox-2. So, four analogues of 4, 5-diaryl-2-(2-alkylthio-5-imidazolyl) imidazole derivatives were synthesized and their anti-inflammatory and anti-nociceptive activities were evaluated on male BALB/c mice (25-30 g). Molecular modeling and in vitro COX-1 and COX-2 isozyme inhibition studies were also performed. Materials and Methods2-(2-Alkylthio-5-imidazolyl)-4,5-diphenylimidazole compounds were obtained by the reaction of benzyl with 2-alkylthio-1-benzylimidazole-5-carbaldehyde, in the presence of ammonium acetate. Spectroscopic data and elemental analysis of compounds were obtained and their structures elucidated. Anti-nociception effects were examined using writhing test in mice. The effect of the analogues (7.5, 30, 52.5 and 75 mg/kg) against acute inflammation were studied using xylene-induced ear edema test in mice. Celecoxib (75 mg/kg) was used as positive control.ResultsAll four analogues exhibited anti-nociceptive activity against acetic acid induced writhing, but did not show significant analgesic effect (P< 0.05) compared with celecoxib. It was shown that analogues injected 30 min before xylene application reduced the weight of edematic ears. All analogues were found to have less selectivity for COX-2 in comparison to celecoxib. ConclusionInjected doses of synthesised analogues possesses favorite anti-nociceptive effect and also has anti-inflammatory effects, but comparing with celecoxib this effect is not significantly different. On the other hand selectivity index for analogues is less than celecoxib and so we expect less cardiovascular side effects for these compounds

Development of a Small-Scale Test Facility for Effectiveness Evaluation of Fixed-Bed Regenerators

National Science and Engineering Research Council, Tempeff North America Inc., Winnipeg (Project No:533225-18).Peer ReviewedFixed-bed regenerators (FBR) transfer heat (and moisture) between supply and exhaust air streams in heating, ventilating and air conditioning (HVAC) systems to reduce building energy consumption. This paper presents a new small-scale testing facility to evaluate the performance (i.e. sensible effectiveness) of FBRs for HVAC applications. The major contributions of this paper are: development of a new small-scale experimental facility and methodology for testing FBRs, quantification of uncertainties, and verification of small-scale test data over a large range of FBR design conditions. A numerical model and two well-known design correlations are used to verify the results and testing methodology. The advantages of small-scale testing are that it requires low volume of conditioned airflow, has low uncertainty, requires less exchanger material and has a low cost per test. Moreover, the small-scale testing methodology of FBR would benefit heat exchanger manufacturers to perform detailed sensitivity studies and optimize the exchanger performance over a wide range of design and operating parameters prior to the fabrication of full-scale exchangers

Transient sensor errors and their impact on fixed-bed regenerator (FBR) testing standards

This is an Accepted Manuscript of an article published by Taylor & Francis in Science and Technology in Build Environment on 14 December 2020, available at: https://doi.org/10.1080/23744731.2020.1846428.National Science and Engineering Research Council (NSERC), Tempeff North America Inc., Winnipeg, Canada, (Project No: 533225-18)Peer ReviewedFixed-bed regenerators (FBRs) are a favorable option for energy recovery in building HVAC systems due to their high sensible effectiveness. Unlike other types of energy recovery exchangers, the air temperature at the outlet of FBRs varies with time, which creates challenges when measuring the outlet temperature and effectiveness of FBRs since the actual outlet air temperature will include the transient response of the FBR and the temperature sensor. In this article, a validated numerical model of FBRs that takes into account the sensor response is used to quantify the temperature and effectiveness errors that result due to sensors’ response characteristics over a wide range of design parameters. The main contributions of this article are the practical recommendations for the temperature measurement for different types of FBRs developed for HVAC applications. The recommendations presented in this article could be implemented in future versions of the current standards (ASHRAE 84 and CSA C439-18 standards) for performance testing of air-to-air energy exchangers

Validation of an individualized home-made superficial brachytherapy mold applied for deep nonmelanoma skin cancer

Background: This study was conducted to evaluate the effect of brachytherapy (BT) customized mold [Condensation silicone elastomer (ProtesilTM)] and its thickness on the dose distribution pattern of deep nonmelanoma skin cancers (NMSC). Materials and methods: Four blocks of mold material were constructed in 5, 10, 15, and 20 mm thickness and 100 × 100 mm2 area by a plastic cast. The high dose rate (HDR) plus treatment planning system (TPS) (Version 3, Eckert &amp; Ziegler BEBIG Gmbh, Berlin, Germany) with a 60Co source (model: Co0.A86, EZAG BEBIG, Berlin, Germany) as an high dose rate brachytherapy (HDR-BT) source was used. Solid phantom and MOSFETTM and GAFCHROMICTM EBT3 film dosimeters were used for experimental dosimetry of the different thicknesses (up to 20 mm) of BT customized mold. Skin dose and dose to different depths were evaluated. Result: The TPS overestimated the calculated dose to the surface. Skin dose can be reduced from 250% to 150% of the prescription dose by increasing mold thickness from 5 mm to 20 mm. There was a 7.7% difference in the calculated dose by TPS and the measured dose by MOSFET. There was a good agreement between film dosimetry, MOSFET detector, and TPS’ results in depths less than 5 mm. Conclusion: Each BT department should validate any individualized material chosen to construct the customized surface BT mold. Increasing the mold thickness can treat lesions without overexposing the skin surface. Superficial BT can be recommended as an appropriate treatment option for some deep NMSC lesions (up to 20 mm) with pre-planning considerations employing thicker molds