La relevancia de los SPL y MI para la política de desarrollo

Department of Mechanical Engineering, Faculty of Engineering University of Peradeniya

Use of mechanical ventilation and air conditioning is becoming more prevalent in commercial and industrial sectors due to warm and humid outdoor conditions in most parts of the country. Such change in the use of energy for comfort is further supported by the requirements for clean air in working environments specified in relevant health and safety regulations. The common practice in maintaining required relatively comfortable indoor conditions is to use mechanical ventilation plus conditioning of air using conventional vapour compression refrigeration. Undesirable aspects of this technology are the use of environmentally harmful refrigerants and use of electricity that in many cases add a substantial running electricity bill. A more sustainable and low carbon alternative to vapour compression refrigeration based air conditioning would be to consider technologies that incorporate natural phenomena of cooling that use low-grade energy from industries or any other renewable source. Here, an evaporation and regeneration-based desiccant cooling system provide a satisfactory alternative for applications where indoor conditions are not very closely controlled.

This paper presents a study of a desiccant cooling system. The analysis is based on a software tool; TRNSYS, which enables detailed modelling of the heat and mass transfer process in a desiccant system, particularly the regeneration process and heat/ mass transfer process in desiccant wheel. The performance of a cooling solution is parametrically studied, where the regeneration energy to drive the cooling cycle is determined by examining the humidity ratio and temperature profiles for a year on an hourly basis. The results of the simulations, at different conditions, in an air dehumidifier, are used to propose an optimum coefficient of performance (COP) of the cooling system for a selected case study.

Comfort indoor conditions specified in ASHRAE standards, i.e., of 25ºC dry bulb temperature and 50% relative humidity were considered in the simulations as the desired indoor conditions. The results indicate that hot water storage at 100ºC via a heat exchanger can produce the thermal energy required to heat up the return air at 70ºC to regenerate the desiccant. The ventilation air flow rate is maintained at 20,000 kg/hr while the hot water flow rate required to produce the necessary energy of 250 kW is 1.2 kg/s. The cooling load met by the system is 120 kW and the calculated coefficient of performance of the desiccant cooling system is 0.48, which saves up to 40% in current electrical energy use of the application concerned.

This study makes it clear that use of low grade heat or renewable sources to drive the thermally activated component of a desiccant system have a number of benefits including reduction of peak demand and less energy consumption; i.e., a low carbon footprints. This work shows that a desiccant cooling concept could maintain satisfactory indoor conditions at a lower energy consumption level and presents a sustainable alternative to supplement industrial space cooling demands.

Proceedings of the Peradeniya University Research Sessions, Sri Lanka, Vol. 16, 24th _{November 2011} 36 e L e L e

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Study of Adsorption Isotherms for Methyl Red Removal using Activated Carbon Derived from Ormosia amazonica Seeds

B.A.A. Izzadheen, P.K.G.T. Shashinkamali, S.M.W.T.P.K. Ariyaratne and R. Shanthini

Department of Chemical and Process Engineering, Faculty of Engineering, University of Peradeniya

As an inexpensive alternative to charcoal-based activated carbon (CAC) in pollution control applications, several carbon-based materials have been studied. In this study, we researched the adsorption capacity of activated carbon derived from Ormosia

amazonica (OA) seeds in the removal of an organic dye, methyl red (MR). OA seeds are

found in the dry zone of Sri Lanka, almost free of cost.

OA seeds-based activated carbon (OASAC) was prepared in the laboratory using chemical methods. Batch equilibrium adsorption experiments were carried out using 0.7 g OASAC thoroughly mixed with 50 ml of synthetic MR solutions of initial MR concentrations varying in the range of 25 to 200 mg/L at pH 4.0. The adsorption equilibrium isotherm best fitting the equilibrium experimental data was chosen from among the most commonly used isotherms, namely, the Langmuir, Freundlich and the Tempkin isotherms. Another set of similar experiments were carried out with commercially available CAC. The results obtained with OASAC and CAC were compared in order to assess their relative adsorption capacities.

Batch equilibrium studies carried out with one sample showed that 100 min were adequate for equilibrium to be reached. A set of seven equilibrium liquid-phase and solid- phase concentrations were used to determine the isotherm parameters. Estimated correlation coefficients, given by adjusted R2, provided evidence for the adsorption of MR onto OASAC/ CAC being best explained by the Langmuir isotherm,

,

where qe (in mg/g) and Ce (in mg/L) are the equilibrium concentrations of MR in solid- phase and liquid-phase, respectively. The Langmuir adsorption capacity reflecting the maximum capacity of a monolayer adsorption, given by Qmax, was estimated as 5.425 mg/g for OASAC and 5.667 mg/g for CAC. The Langmuir adsorption coefficient, given by

KL, was estimated as 0.142 L/mg for OASAC and 0.180 L/mg for CAC.

The similarities found among the parameters reported above as well as in the estimated parameters of the reasonably fitting Freundlich and the Tempkin isotherms in this study, therefore, bear strong evidence for the adsorption performance of OASAC being comparable with that of CAC when it comes to MR removal. Therefore, we recommend the use of OASAC as a low-cost alternative to the relatively expensive CAC for the removal of dyes or colour from industrial effluents.

Proceedings of the Peradeniya University Research Sessions, Sri Lanka, Vol. 16, 24th _{November 2011}

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Microbial Fuel Cells with Ceramic and Earthen Plate Membranes for Rice Mill Wastewater