Raya Al-Dadah

Experimental investigation of metal organic frameworks characteristics for water adsorption chillers

Adsorption cooling is a promising technology that can effectively utilise waste heat from many industrial processes for refrigeration and air conditioning. The choice of the adsorbent in this technology is vital to produce efficient and compact systems. Metal organic frameworks are new microporous materials with exceptionally high porosity and large surface area that can be used as adsorbents. This article experimentally investigates the characteristics of seven metal organic frameworks in terms of water adsorptivity compared to silica gel RD-2060. The adsorption characteristics were determined using an advanced gravimetric dynamic vapour sorption test facility. Results revealed that HKUST-1produced the highest water adsorption uptake with up to 95.7% increase compared to silica gel RD-2060 but showed deterioration in water adsorptivity with time. Throughout the temperature range tested, Fe-BTC has shown little hysteresis and produced up to 26.8% higher maximum water uptake value than silica gel RD-2060. These results highlight the potential of using certain metal organic frameworks materials to improve the efficiency of adsorption cooling systems; however, the thermal instability of some metal organic frameworks remains an issue that needs to be resolved.

A new set of correlations for EHD enhanced condensation heat transfer of tubular systems

Abstract An improved set of correlations for evaluating the heat transfer coefficient of EHD assisted condensation heat transfer for tubular systems is presented in this paper. The correlations were developed by curve fitting a wide range of experimental data and then optimising the empirical constants so that the percentage deviation is less than ±30%. The experimental data was classified in four categories: (I) condensation outside horizontal smooth tubes, (II) condensation inside horizontal smooth tubes, (III) condensation outside vertical tubes and (IV) condensation inside vertical tubes. The experimental data in each category included results obtained using various refrigerants and various electrode systems. The improved correlations were used to predict a total of 166 experimental data points. A comprehensive literature review of all available correlations for EHD assisted condensation heat transfer is also described in this paper. Two correlations that were identified to be simple were used to predict the above-mentioned data bank. These are the correlations of Choi and Reynolds and Didkovesky and Bologa. The Choi and Reynolds correlation was found to successfully predict heat transfer rates of condensation outside horizontal and vertical tubes and of condensation inside vertical tubes when high intensity electric field is applied. However, the Didkovesky and Bologa correlation was found to successfully predict only the results of condensation heat transfer outside vertical surfaces.

Exploitation of multiple sensor arrays in electronic nose

The Coupled Micro Resonator Array (CMRA) is a new type chemical sensor that has been developed to improve the performance of the electronic nose by increasing the number of sensors that can be used to detect specific odours. In the CMRA, an array of mechanically coupled micro mass balances, the mass of each micro mass balance can be determined by measuring the eigenfrequencies of the coupled array, with just a single input and output electrode. If the mass of each resonator is to be uniquely identified it is important that the changes in the eigenfrequencies are distinctive and that the eigenvectors of the system are stable against resonator mass changes. This paper models and evaluates the performance of an unsymmetrical yet balanced CMRA for individual resonator mass determination.

Investigation of activated carbon/ethanol for low temperature adsorption cooling

ABSTRACT Commercially available adsorption cooling systems use water/silica gel, water/zeolite and ammonia/ chloride salts working pairs. The water-based pairs are limited to work above 0°C due to the water high freezing temperature, while ammonia has the disadvantage of being toxic. Ethanol is a promising refrigerant due to its low freezing point (161 K), nontoxicity, zero ozone depletion, and low global warming potential. Activated carbon (AC) is a porous material with high degree of porosity (500–3000 m2/g) that has been used in wide range of applications. Using Dynamic Vapour Sorption (DVS) test facility, this work characterizes the ethanol adsorption of eleven commercially available activated carbon materials for cooling at low temperature of −15°C. DVS adsorption results show that Maxsorb has the best performance in terms of ethanol uptake and adsorption kinetics compared to the other tested materials. The Maxsorb/ethanol adsorption process has been numerically modeled using computational fluid dynamics (CFD) and simulation results are validated using the DVS experimental measurements. The validated CFD simulation of the adsorption process is used to predict the effects of adsorbent layer thickness and packing density on cycle uptake for evaporating temperature of −15°C. Simulation results show that as the thickness of the Maxsorb adsorbent layer increases, its uptake decreases. As for the packing density, the amount of ethanol adsorbed per plate increases with the packing density reaching maximum at 750 kg/m3. This work shows the potential of using Maxsorb/ethanol in producing low temperature cooling down to −15°C with specific cooling energy reaching 400 kJ/kg.

Development of Small-Scale Axial Turbine for solar powered Brayton Cycle

An efficient small scale turbine, which can operate at low mass flowrates, relatively low pressure ratios and moderately high temperatures, is needed for developing a Small Scale Brayton Cycle SSBC to generate power for domestic applications. Although research work was carried out to develop Brayton cycle however the effect of turbine design on the cycle efficiency was not considered. This work aims to develop a Small Scale Axial Turbine (SSAT) using 3D CFD simulations. Different design and operating conditions, for both turbine and cycle were investigated to identify the most efficient turbine for this application. Results showed that a turbine with rotor stagger angel of 30°, and rotor flow angel of -51.5°, pressure ratio of 3, and rotational speed of 17500rpm, a turbine efficiency of 83.89% and power output of 5.25 kW and cycle overall thermal efficiency 9.1%.

Novel adsorption system for cooling and power generation utilizing low grade heat sources

Adsorption cooling system is a promising technology that can be used to exploit the abundant amount of low grade heat sources such as solar energy, geothermal and waste heat from industrial processes. This technology can be more useful in the hot and developing countries where millions of people face annually the severe heat waves during summer and they still lack access to secure electricity grids, where adsorption system can be used to generate electricity as well as cooling in the same time. In this study, a novel four bed adsorption system is designed to generate cooling and electricity simultaneously. The system comprises mainly of two topping beds, two bottoming beds, two evaporators, condenser and expander (turbine). The topping beds are powered using the low grade heat source and utilizing AQSOA-Z02 (SAPO-34) zeolite (an advance adsorption material) and water, while the bottoming beds is powered by the heat recovered from the topping beds and utilizing Silica-gel and water. Results show that the overall system efficiency can be improved by 62%.

Passive enhancement of condensation heat transfer

Integral fin tubes are commonly used in the condensers of refrigeration, air conditioning and process industries especially where low surface tension fluids are used. In the last few decades, several three dimensional (3D) enhanced surfaces were developed for condensation heat exchangers. Also, several improvements were introduced to the standard integral finned tubes which resulted in a performance comparable to that of the 3D enhanced surfaces. Some of these improvements include optimisation of the fin specifications and the fin profile to make use of the surface tension and gravity forces, the use of ribs on the surface of the fins and the inclusion of drainage techniques. A review of the experimental and theoretical work used to augment the performance of integral finned tubes is presented in this paper. This is followed with a review of the 3D surfaces developed and a comparison between the integral fin tubes and the 3D surfaces. Performance in bundles and the effect of vapour shear are specific issues that were considered in the comparison.

Adsorption ice making and freeze water desalination using Metal Organic Framework materials

This work presents a novel adsorption system for producing ice and potable water using fresh and saline water as refrigerants and Metal Organic Framework material (CPO-27Ni) as adsorbent. In this work, an advanced technique of adsorption ice making integrated with vacuum direct freeze desalination is developed. The effect of fresh water specific volume in the evaporator and the performance of this system in terms of coefficient of performance (COP), specific daily production of ice (SDIP), slurry mixture (SDSP) and fresh water (SDWP) were experimentally investigated. The optimum COP was up to 0.205 whereas 10.5, 29.5 and 1.32 ton/day/ton of adsorbent for SDIP, SDSP and SDWP, respectively. The results are obtained at generation temperature of 95°C, antifreeze temperature of -1°C and fresh water of 450ml.

Development of micro-scale radial inflow turbine for organic Rankine cycle

This study describes the development of a micro-radial turbine for organic Rankine cycle powered by low temperature heat source. To achieve the aim, different working fluids with operating conditions were investigated to identify the most efficient turbine for low-grade heat source with temperature less than 85°C. In previous studies related to organic Rankine cycle analysis, the isentropic efficiency of the turbine was assumed constant, while in this work, the isentropic efficiency is calculated at different operating conditions for each working fluid. The ANSYSR17- CFX software is used to perform the three-dimensional computational fluid dynamic analysis of the radial-inflow turbine for a number of organic working fluids (R141b, R245fa and n-pentane) and different operating conditions. The real fluid properties using equations of state were employed and results showed that n-pentane has the highest performance for all operating conditions. The maximum total isentropic efficiency of turbine was about 80.15% with 5.119 kW power output and 10.34% cycle thermal efficiency.

Liquid nitrogen air conditioning system for domestic application

Current air conditioning systems consume significant amount of the electricity particularly during the peak period leading to significant fossil fuel energy consumption and carbon emissions. Thus there is a need to develop a new technology that consumes less energy and environmental friendly. Liquid nitrogen has been acknowledged as energy storage vector with high energy density. The current study investigates the feasibility of using the store cold energy in the form of liquid nitrogen to produce cooling and power for domestic building. A thermodynamic analysis of a combined cryogenic system fuelled by liquid nitrogen was carried out using Matlab integrated with Refprop software. Results showed that, using LN2 to meet the cooling demands at the peak period is feasible and promising. The proposed system recovered 81% of the energy stored in LN2 and with the current LN2 prices it achieved saving of 30% compared with the conventional AC system but the widespread of this technology can lead to further reduction of LN2 prices leading to significant savings of 81% and.