Ali Al-Alili

A review on desiccant coated heat exchangers

Fixed bed and rotatory desiccant systems have been widely studied and used for dehumidification; they suffer from decreasing sorption capacity as the desiccants temperature increases due to the released heat of adsorption. Desiccant coated heat exchangers overcome this limitation. Such heat exchangers are able to deliver combined heat and mass transfer between the process air and the working fluid. The process air can be cooled and dehumidified simultaneously by pumping cooling water/refrigerant in the desiccant coated heat exchanger. The desiccant coated heat exchanger has to be heated cyclically to regenerate the desiccant material. This article presents a review on the studies conducted on air-to-liquid desiccant coated heat exchangers. It summarizes various modeling approaches used to simulate the performance of desiccant coated heat exchangers as well as the experimental studies conducted to validate these models. It also reviews the current and potential applications of these heat exchangers. Current work in this field consists of experiments conducted on desiccant coated heat exchangers as standalone equipment (i.e. component level) as well as an integrated component into cooling and dehumidification systems (system level). The integration of desiccant coated heat exchangers in such systems was found to improve the coefficient of performance, leading to energy savings.

Experimental Investigation of a Desiccant Wheel Cycle

In hot and humid regions, removal of moisture from the air represents a considerable portion of the air conditioning load. Conventionally, air conditioning systems have to lower the air temperature below its dew point to accomplish dehumidification. Desiccant air conditioners offer a solution to meet the humidity and temperature requirements of buildings via decoupling latent and sensible loads. In this work, the performance of a new desiccant material is investigated experimentally. This desiccant material can be regenerated using a low temperature heat source, as low as 45°C. It also has a unique S-shape isotherm. The effects of the process air stream’s temperature and humidity, the regeneration temperature, the ventilation mass flow rate, and the desiccant wheel’s rotational speed on the cycle performance are investigated. ARI-humid conditions are used as a baseline and the moisture mass balance is maintained within 5%. The results are presented in terms of the moisture removal rate and latent coefficient of performance (COPlat). The results show a desiccant wheel’s COPlat higher than unity when it is coupled with an enthalpy wheel.Copyright

Optimization Study of a Hybrid Solar Air Conditioner

In order for the solar air conditioners (A/Cs) to become a real alternative to the conventional systems, their performance and total cost has to be optimized. In this study, an innovative hybrid solar A/C was simulated using the transient systems simulation (TRNSYS) program, which was coupled with MATLAB in order to carry out the optimization study. Two optimization problems were formulated with the following design variables: collector area, collector mass flow rate, storage tank volume, and number of batteries. The Genetic Algorithm (GA) was selected to find the global optimum design for the lowest electrical consumption. To optimize the two objective functions simultaneously, a Multi-Objective Genetic Algorithm (MOGA) was used to find the Pareto front within the design variables’ bounds while satisfying the constraints. The optimized design was also compared to a standard vapor compression cycle. The results show that coupling TRNSYS and MATLAB expands TRNSYS optimization capability in solving more complicated optimization problems.© 2013 ASME

Review of Solar Sorption Cooling Research in the MENA Region

This paper provides a brief overview of closed sorption cooling technologies, and highlights the research performed on them in the Middle East and North Africa region. The main findings are summarized and presented in tabulated and graphical forms. The reviewed studies are compared in terms of the working pair, the Coefficient of Performance, the normalized collector area, etc. The results show that the average cyclic Coefficient of Performance for the adsorption chillers was 0.41, whereas the average chiller Coefficient of Performance for the absorption chillers was 0.677.The research trends reveal that interest in solar sorption cooling was low in the 1980s and 1990s, and gradually increased during the 2000s. In addition, the most installed solar cooling system in the Middle East and North Africa region is utilizing absorption cycles.Copyright

Optimization of a Solid Oxide Fuel Cell and Gas Turbine Hybrid System

The low efficiency and high environmental impact of conventional power cycles are a major concern. The integration of solid oxide fuel cells (SOFCs) and gas turbines (GTs) has been proposed in the literature to increase fuel to power conversion. Parametric studies are usually conducted to identify suitable operating conditions for such integrated systems. However, parametric studies only consider the main effects of the design variables and do not provide information on the interactive effect of the design variables. In this study, a multi-objective optimization is performed to optimize the performance of a SOFC-GT hybrid system. The objective functions are system efficiency and total cost rate, including capital, operating, and environmental penalty costs. The design variables are selected based on sensitivity analysis to assess the effect of the variables on the objective functions. The performance of the SOFC-GT hybrid system is modeled in Aspen Plus, while MATLAB is used for multi-objective optimization. The multi-objective optimization solution is presented in terms of a Pareto frontier.Copyright