Analysis of thermal effects in packed bed liquid desiccant dehumidifiers
Abstract An analysis of the performance of a packed bed liquid desiccant dehumidifier is presented. The enthalpy and material balance equations written over a differential height of the bed incorporate the effect of the heat of dilution of the desiccant liquid, the liquid—air interface temperature and the fraction of the evolved heat that is accounted for in the air stream. Numerical results obtained are discussed in terms of the physical and operating parameters of the system.
Analysis of an integrated absorption/liquid desiccant air conditioning system
Abstract This paper presents an analysis of an integrated absorption cooling machine with a water heat-driven liquid desiccant dehumidifier for air conditioning systems. The waste heat recovery unit operates between the condenser of the absorption machine and the liquid absorbent regenerator. A mathematic model for the liquid desiccant unit is described and the governing equations are solved. The model is applied to the dehumidifying chamber (DHC) and the regeneration chamber (RGC) in a coupled mode. Results showed that the cooling water temperature and the transfer potentials are the controlling factors affecting the DHC while the mass transfer potential and the absorbent air mass ratio are dominant in the RGC. For a 42°C/31°C DBT/WBT outside air, the integrated system has an estimated overall COP of 1.21 for a supply of hot water at 140°C fed to the generator and a cooling water supply at 30°C. This COP is 50% higher than the COP for the absorption chiller alone (0.81). The overall COP is higher than that for a double effect absorption machine if the outside air conditions and the cooling water effects are taken into consideration. Moreover, a LiBr-H 2 O solution is used at both ends of the system, which would reflect some savings in both capital and running cost of the air conditioning unit.
A high performance dehumidifier for solar desiccant cooling systems
An advanced-design, one-tenth scale dehumidifier for use in residential solar desiccant cooling systems has been built and tested. The new dehumidifier was designed using a parallel-passage geometry, where air flows through channels formed by walls coated with fine-ground silica gel desiccant. This concept has a high heat and mass transfer effectiveness and promises to double the coefficient of performance of the desiccant cooling system to 1.1 kW cooling output/kW thermal input. The parallel-passage design was found to have very low pressure drop, typically 20 Pa (.08 in. water) at design conditions. The low fan power required to drive such low pressure drop components indicates that electrical COP's in the range of 8.0-8.2 kW cooling output/kW electrical input are possible. Results to be presented include parametric studies of the effect of conditions such as temperature and humidity and design parameters such as desiccant particle size and channel spacing on dehumidifier performance.