Experimental performance study of a proposed desiccant based air conditioning system

AbstractAn experimental investigation on the performance of a proposed hybrid desiccant based air conditioning system referred as HDBAC is introduced in this paper. HDBAC is mainly consisted of a liquid desiccant dehumidification unit integrated with a vapor compression system (VCS). The VCS unit has a cooling capacity of 5.27kW and uses 134a as refrigerant. Calcium chloride (CaCl2) solution is used as the working desiccant material. HDBAC system is used to serve low sensible heat factor applications. The effect of different parameters such as, process air flow rate, desiccant solution flow rate, evaporator box and condenser box solution temperatures, strong solution concentration and regeneration temperature on the performance of the system is studied. The performance of the system is evaluated using some parameters such as: the coefficient of performance (COPa), specific moisture removal and energy saving percentage. A remarkable increase of about 54% in the coefficient of performance of the proposed system over VCS with reheat is achieved. A maximum overall energy saving of about 46% is observed which emphasizes the use of the proposed system as an energy efficient air conditioning system

MAT-704: RESISTANCE OF CONCRETE INCORPORATING PORTLAND LIMESTONE CEMENT TO SULFURIC ACID

Concrete has long been the most popular choice for constructing key infrastructural elements such as sewer pipes, water treatment facilities, industrial floors and foundations. However, many field cases from all around the world have shown that concrete elements in these environments are severely damaged due to biogenic and/or chemical sulfuric acid attack. Since high alkalinity is required for the stability of the cementitious matrix, concrete is highly prone to acid attacks, which decalcify and disintegrate the hydrated cement paste to various levels based on exposure conditions and type of concrete. Numerous studies have been conducted to enhance the durability of concrete and understand the influence of key mixture design parameters on its resistance to sulfuric acid attack. Yet, there is dearth of information on the behaviour of a new type of cement in North America, which contains a high level (5 to15%) of interground limestone powder (portland limestone cement: PLC), under acidic attack. Hence, the aim of this study is to investigate the effect PLC with or without supplementary cementitious materials (SCMs) on the durability of concrete exposed to acidic attack. The study comprised 13 weeks (90 days) immersion of test specimens in 5% sulfuric acid solutions with pH in the range of 0.1 to 2.5. Physical and microstructural results reveal that PLC may improve the resistance of concrete to sulfuric acid attack, whereas the SCMs had a mixed effect on the results

Surface Treatments for Concrete Under Physical Salt Attack

Physical salt attack (PSA) is a key deterioration mechanism for concrete structures in contact with salt-rich media. Yet, procedures and techniques for protecting and repairing concrete affected by PSA are not adequately addressed in the technical literature. Therefore, in this study, three surface coatings of concrete were tested to determine their ability to withstand conditions stimulating to PSA. The treatments were selected to achieve either a single function such as acting as a membrane layer or hydrophobic agent, or combined pore blocking and water repelling functions. Coatings were applied on a concrete mixture typically used for residential foundations in Canada. Mass change was used as a measure to quantify the damage, in addition to microscopy and mineralogical analyses to elucidate the damage mechanisms. The results showed that the damage in deteriorating specimens was due to a combination of physical and chemical sulfate attacks. Also, epoxy and ethyl silicate were effective at protecting concrete from sodium sulfate damage while silane was not

Post-Cracking Behavior of Cementitious Composite Incorporating Nano-Silica and Basalt Fiber Pellets

Recently, fiber reinforced polymers (FRPs) have been increasingly used to reinforce concrete structures in harsh environments, due to their non-corrodible nature. Developing a nonferrous reinforcement system (corrosion-free system) for concrete using FRP bars along with discrete fibers is a promising option for exposed concrete structures in cold regions or marine environments. Incorporating highly efficient non-metallic fibers into any cementitious composite is capable of reducing bleeding, controlling shrinkage cracking, and improving toughness and impact resistance. Therefore, in this study, a new type of basalt fiber pellets with high tensile strength was investigated. This paper reports on the flexural performance of the basalt fiber-reinforced cementitious composite (BFRCC) compared to steel fiber-reinforced cementitious composite (SFRCC). The cementitious composite incorporated general use cement, slag and nano-silica. The key mechanical property determined was the post-cracking behavior in terms of residual strength, and toughness. Standard prisms (100 × 100 × 350 mm) were cast using basalt fiber pellets and steel fibers with three different dosages and tested after 28 days following the general guidelines of ASTM C1609 (Standard Test Method for Flexural Performance of Fiber-Reinforced Concrete). Analysis of results showed a high level of effectiveness of the basalt fibers to enhance the post-cracking behavior of specimens, as they behaved comparably or superiorly (first cracking, load-deflection relationship, and toughness) to counterpart specimens comprising steel fibers

MAT-705: IMPROVING THE EFFICIENCY OF ZINC SACRIFICIAL ANODES IN REPAIRED CONCRETE

Zinc sacrificial anodes are considered an effective and economical method to prevent the electrochemical corrosion of steel bars by providing cathodic current to bars, which can provide corrosion protection at low galvanic current densities in the range of 0.2 to 2 mA/m2. Sacrificial anodes are commonly used in RC structures particularly in bridge decks to mitigate a critical phenomenon that occurs in the original concrete beside the repaired patches, which is known as the ‘halo effect’. One of the key factors affecting the efficacy of zinc anodes is the resistivity of concrete or cementitious repair material in which these anodes are embedded. There is a general notion that the higher the electrical resistivity of concrete or repair material, the less likely that zinc anodes produce the target galvanic current for optimum protection of steel bars. However, no systematic data are available on the maximum allowable electrical resistivity of repair materials/concretes beyond which zinc anodes cannot properly function to prevent corrosion. The specific objective of this study is to explore the effect of concrete resistivity on the efficiency of zinc anodes at mitigating patch accelerated corrosion (halo effect). Concrete slabs were cast to simulate the patch repair technique in the field, and the main parameter in this research was changing the resistivity of the repair section in the slabs (5,000, 15,000, and 25,000 Ω-cm). Analysis of results shows a high level of effectiveness of the anode to prevent corrosion up to 20 weeks under a wetting-drying exposure

Assessment of Thermal Comfort in Operating Rooms Using PMV-PPD Model

Operating rooms (ORs) are the most critical and expensive sector of healthcare facilities. The air conditioning system is designed to provide a well-controlled indoor air quality (IAQ). This design guarantees a perfect infection control and a good thermal comfort of patient and operating staff.This paper aims to analyze and evaluate indoor thermal comfort at different cases to assign the proper inlet air temperature to the OR. The predicted mean vote (PMV) and the predicted percentage dissatisfied (PPD) models in accordance with ISO 7730 were used for this study.Field measurements were first carried out in an OR at Kafr El-Sheikh educational hospital to get the thermal environment parameters. These parameters are required to determine the thermal comfort indices namely (PMV & PPD). Four different cases of supplied air temperature 17.5, 18.5, 19.5 and 20.5oC were studied and compared through 105 measuring points distributed in the operating room. The PMV and PPD indices were computed at each case for three groups of medical staff: surgeons (metabolic rate equal to 120 W/m2), nurses and surgeon\u27s assistants (100 W/m2), anesthetists (70 W/m2).The results revealed that inlet air temperature has a minor effect on the air velocities and airflow patterns inside the OR at the same air change rate. For the current ventilation system, it is difficult to create a very comfortable work conditions for all operating staff at the same time due to their different thermal requirements. It was concluded that a supplied air temperature of 18.5oC provides almost comfortable conditions for all surgical staff

Optimization of CNFET Parameters for High Performance Digital Circuits

The Carbon Nanotube Field Effect Transistor (CNFET) is one of the most promising candidates to become successor of silicon CMOS in the near future because of its better electrostatics and higher mobility. The CNFET has many parameters such as operating voltage, number of tubes, pitch, nanotube diameter, dielectric constant, and contact materials which determine the digital circuit performance. This paper presents a study that investigates the effect of different CNFET parameters on performance and proposes a new CNFET design methodology to optimize performance characteristics such as current driving capability, delay, power consumption, and area for digital circuits. We investigate and conceptually explain the performance measures at 32 nm technologies for pure-CNFET, hybrid MOS-CNFET, and CMOS configurations. In our proposed design methodology, the power delay product (PDP) of the optimized CNFET is about 68%, 63%, and 79% less than that of the nonoptimized CNFET, hybrid MOS-CNFET, and CMOS circuits, respectively. Therefore, the proposed CNFET design is a strong candidate to implement high performance digital circuits