THEORITICAL STUDY FOR COMPACT LIQUID DESICCANT DEHUMIDIFIER / REGENERATOR SYSTEM
Air may be dehumidified when it is brought into contact with a suitable liquid desiccant. Different types of liquid desiccants are available in the market and the application of the proper desiccant in hot humid climates would improve the dehumidification effectiveness. The driving potential for a dehumidification process is the difference in the pressure of the water vapor in the air and the water vapor saturation pressure corresponding to the airdesiccant solution interfacial temperature and concentration of water above the desiccant. The vapor pressure of a liquid desiccant is a function of its temperature and concentration. Among the various desiccants available, lithium chloride, lithium bromide, calcium chloride, and triethylene glycol have received much attention. The present study aims to evaluate numerically the performance of the proposed liquid desiccant dehumidifier system that utilizes calcium chloride solution as a liquid desiccant. The performance parameters for the air dehumidifier were the reduction ratio of the air humidity ratio and the dehumidifier effectiveness. Several benchmarks were carried out under the following operating conditions: The cooling water temperature (10 o C-18 o C), desiccant solution temperature (26 o C-33 o C), air flow rate (3.4-6 l/s), air inlet temperature (38 o C-51 o C), air inlet humidity ratio (21-25 gw/kgda), desiccant solution mass flow rate (0.04-0.13 kg/s), desiccant solution to air mass flow rate ratio (10-26), heating water temperature (42 o C-51 o C), and desiccant solution concentration (20% -45%). The results show that the humidity ratio at the exit from the dehumidifier decreases with increasing the desiccant solution concentration and with decreasing of the desiccant solution temperature. The desiccant solution moisture content decreases with increasing of the desiccant solution temperature and mass flow rate, but it decreases with decreasing of the air inlet humidity ratio. Also, the air temperature leaving the dehumidifier decreases with increasing the desiccant solution concentration and the air inlet humidity ratio, but it decreases with decreasing of the desiccant solution temperature. The desiccant solution temperature decreases with increasing the desiccant solution concentration and with decreasing both of the desiccant mass flow rate and the cooling water temperature, but it is not affected with the air inlet humidity ratio. The desiccant solution moisture content gain increases with increasing each of the desiccant solution concentration, the air inlet humidity THEORITICAL STUDY FOR COMPACT LIQUID DESICCANT DEHUMIDIFIER/REGENERATOR SYSTEM Vol. 3, No. 11, Dec. 2008 353 ratio and the air mass flow rate. It also increases with decreasing desiccant solution mass flow rate and temperature. Also the results show that both of the dehumidifier reduction ratio of the air humidity ratio and the effectiveness increase with the increase of the heating water temperature, the desiccant solution mass flow rate, the desiccant solution to air mass flow rate ratio and the desiccant concentration. Both the reduction ratio of the air humidity ratio and the effectiveness of the dehumidifier decrease with the increase of the cooling water temperature, the desiccant solution temperature and of the air flow rate. The performance parameters were almost unaffected with the inlet air temperature. The dehumidifier reduction ratio of the air humidity ratio slightly increases with the increase of the inlet air humidity ratio, but the dehumidifier effectiveness is almost unchanged with the increase of the inlet air humidity ratio.
Performance characterisation of liquid desiccant columns for a hybrid air-conditioner
Use of liquid desiccant-vapor compression hybrid system is encouraged for low humidity applications. The liquid desiccant is primarily used to further dehumidify the supply air. In the present study, by using psychrometric equations and liquid desiccant property data, heat and mass transfer analysis for the dehumidifier and regenerator columns in counter flow configuration has been carried out. The simulation of the columns corresponds to low solution to air (S/A) flow ratio where precooled air gets dehumidified in the absorber while preheated air is used for regeneration of the solution. A detailed study of the performance characteristics for the absorber and regenerator columns confirms the requirement of the desiccant loop for additional dehumidification of the conditioned air. This need develops the main motive towards the concept of hybrid air conditioning.
Evaluation of CuAl2O4 as an Oxygen Carrier in Chemical-Looping Combustion
The chemical-looping combustion (CLC) process is a novel solution for efficient combustion with intrinsic separation of carbon dioxide. The process uses a metal oxide as an oxygen carrier to transfer oxygen from an air to a fuel reactor where the fuel, or gasification products of the fuel, reacts with the solid oxygen carrier. In this work, copper(II) aluminate (CuAl2O4) was assessed as a potential oxygen carrier using methane as fuel. The carrier particles were produced by freeze–granulation and calcined at 1050 °C for a duration of 6 h. The chemical-looping characteristics were evaluated in a laboratory-scale fluidized-bed reactor in the temperature range of 900–950 °C during 45 alternating redox cycles. The oxygen carrier exhibited reproducible and stable reactivity behavior in this temperature range. Neither agglomeration nor defluidization was noticed in any of the cycles carried out at 900–925 °C. However, after reactivity tests at 950 °C, soft agglomeration and particle fragmentation were observed. Systematic phase analysis of the Cu–Al–O system during the redox cycle was carried out as a function of duration of reduction and oxygen concentration during the oxidation period. It was found that the CuAl2O4 is reduced to copper(I) aluminate (CuAlO2; delafossite), Cu2O, and elemental Cu. The CuAlO2 phase is characterized by slow kinetics for oxidation into CuO and CuAl2O4. Despite this kinetic limitation, complete conversion of methane with reproducible reactivity of the oxygen carrier is achieved. Thus, CuAl2O4 could be a potential oxygen carrier for chemical-looping combustion.