Performance Of Desiccant Cooling System Research Articles

Investigation of a Wheel Liquid Desiccant Cooling System Performance via ANSYS CFX

A liquid desiccant cooling system is an alternative air-conditioning system with significant energy-saving potential. This system is commonly used in the industrial sector, such as in dehumidifiers. The key component of the liquid desiccant cooling system is its dehumidification performance. Therefore, a study on a liquid desiccant dehumidifier has been conducted to predict its performance using computational fluid dynamics analysis. In these simulations, the effects of the temperature of the liquid desiccant and the velocity of air flow on the absorption process between the liquid desiccant and air were studied. The same applies to the velocity profile, which helps determine the airflow pattern within the dehumidifier. The model was constructed using ANSYS FLUENT and Autodesk Inventor. The model is the rotary desiccant wheel dehumidifier which was used to dehumidified the air.. ANSYS CFX was used for simulating the velocity profile to achieve the airflow pattern in the dehumidifier. The volume of fluid was selected as the multiphase method for the second simulation process. The temperature and mass fraction of water were monitored within the air during the counterflow simulation between the liquid desiccant and the air. The liquid desiccant chosen for this study was LiCl. The simulations were conducted at specific air velocities, and the behavior within the dehumidifier was observed. The analysis results revealed that the air entering the rotary desiccant wheel dehumidifier experienced a drop in velocity after passing through the desiccant wheel in the middle. Additionally, turbulence occurred after the air passed through the wheel and the dehumidifier’s wall. Based on these findings, the design of an optimal dehumidifier and the selection of an appropriate air velocity for cooling can be carried out.

Performance analysis of desiccant cooling system using polyacrylic acid sodium salt desiccant wheel

The adsorbent material has an important role in the improvement of desiccant cooling system performance. Super Desiccant Polymer (SDP) is chosen in this work as a sophisticated desiccant material characterized by excellent adsorption capacity and durability. The mathematical correlations of adsorption isotherm on SDP surface, adsorption heat and water diffusivity coefficient are used to model the SDP desiccant wheel by means of Comsol software. Modeling results are validated by an experimental data base. They serve as a base for the determination of the SDP wheel effectivenesses ԑ1 and ԑ1 which are equal to 0.02 and 0.83, respectively. The application of desiccant cooling system performance with SDP desiccant wheel in a hot and dry weather of the region of Gabes (south-eastern Tunisia) leads to a coefficient performance (COP) value equal to 1.1. This result is better than the COPs of other air conditioning desiccant systems which use zeolites and silica gel wheels. Moreover, the COP of desiccant cooling system with SDP desiccant wheel is the best for a wide range of operating conditions.

Analysis of the multi-stage desiccant cooling system performance in Wrocław (Poland)

In this study, the application potential of desiccant cooling system with indirect evaporative precooling is analyzed for moderate climatic conditions. Wrocław (Poland) was selected as a representative city. On the base of summer season weather parameters different system running modes were proposed such as cooling and dehumidification mode (Mode 1) and only cooling mode (Mode 2). The average month Thermal and Electrical COP were established for selected climatic conditions. It was concluded that proposed system allows to cool the air without occurrence of condensation in Mode 2 with high average monthly electrical COP (COPel = 62.2 in August). On the other hand when dehumidification is needed, system operates in Mode 1 and obtains relatively high average Thermal COP values (COPth = 2.2).

Parametric analysis of components effectiveness on desiccant cooling system performance

A number of studies have been conducted for investigating parameters that influence the performance of desiccant cooling systems. Many of these rely on intricate numerical simulations, especially due to coupled non-linear transport equations associated with a desiccant dehumidifier. In this study, a simple numerical procedure for designing desiccant cooling systems has been employed for analyzing the impact of cycle components’ characteristics on the overall system performance. The methodology is based on solving a non-linear algebraic system stemming from heat and mass transfer balances associated with the operation of each component. The required input data involves user-prescribed inlet and room conditions, a regeneration temperature, and cycle components’ effectiveness values. With the proposed methodology, results of different cooling cycles are presented in an informative graphical fashion that can readily be used as a design tool for desiccant cooling systems. The results show that COP values clearly over one can be obtained for ideal ventilation cycles, which have 100% heat wheel effectiveness. Nevertheless, a great reduction, by factors of two and higher, are obtained when this effectiveness is reduced to 0.8. In addition, the results show that a 20–30% decrease in dehumidifier performance can lead to 30–50% reduction in the overall ventilation cycle performance.

Experimental and numerical investigations on the performance of dehumidifying desiccant beds composed of silica-gel and thermal energy storage particles

Enhanced efficiency of the adsorption process in the dehumidifier is a key element for improved performance of desiccant cooling systems. Due to the exothermic nature of the adsorption process, the dehumidification and cooling capacity are limited by significant temperature changes in the adsorption column. In the present study, the effects of integration of sensible and latent heat storage particles in the desiccant bed for in situ management of released adsorption heat are investigated. For this purpose, column experiments are performed using an initially dry granular bed made of silica-gel particles or a homogeneous mixture of silica gel and inert sensible or latent heat storage particles. The packed bed is subject to a sudden uniform air flow at selected values of temperature and humidity. Also, a packed bed numerical model is developed that includes the coupled non-equilibrium heat and moisture transfer in the solid and gas phases. Investigations of the heat and mass transfer characteristics are reported using the composite structure and the results are compared with the base case of simple silica gel bed. Improved desiccant cooling system performance can be obtained by appropriate adjustment of desiccant cycle operation and proper choice of the volume ratio of thermal energy storage particles.

Desiccant aging and its effects on desiccant cooling system performance

Desiccants used for the purpose of space conditioning or enthalpy transfer can be subjected to hundreds of thousands of adsorption/regeneration cycles over their useful life. Studying the loss of a desiccant's equilibrium water adsorption capacity after exposure to thermal cycling is a common method for quantifying desiccant aging. Since isotherm shape and desiccant capacity can be related to overall cooling-system performance, system cooling capacity and coefficients of performance over time can be predicted. Adsorption isotherms for several different desiccants have been determined after subjecting the materials to varying numbers of thermal cycles in a specially designed test unit capable of adsorption/desorption cycling every 10 min. Aging curves for a new Type 1M desiccant developed specifically for desiccant cooling applications by LaRoche Industries Inc. are compared to other commonly used desiccants.

The influence of altitude on the performance of desiccant-cooling systems

The impact of height above sea level (i.e. ambient pressure) on the performance of the ventilation cycle desiccant-cooling system and its components has been studied using computer simulations. The impact of ambient pressure depends on whether the system was designed for fixed-mass flow rate or fixed-volume flow rate operation. As the ambient pressure is decreased from 1.0 to 0.8 atm, the system thermal coefficient of performance increases by 8% for both fixed-mass and fixed-volume flow rate; the cooling capacity of the system is decreased by 14% for the fixed-volume flow rate system and increased by 7% for the fixed-mass flow rate system. The electric power requirements for the system with fixed-volume flow rate did not change; for the fixed-mass flow rate system, it increased by 44%. The overall coefficient of performance increased up to 5% for the fixed-volume flow rate system and decreased up to 4% for the fixed-mass flow rate system.

An Analytical Examination of Methods for Improving the Performance of Desiccant Cooling Systems

The conventional Pennington Cycle desiccant cooling system offers a clear opportunity for heat-actuated air conditioning. However, efforts to translate this opportunity into commercially viable hardware have not been successful. The performance of the hardware has been inadequate, resulting in excessive solar collector requirements or, in the case of gas-fired equipment, uneconomical use of natural gas. Two methods for improving the coefficient of performance (COP) of these systems are: (1) the addition of inert heat capacity to the desiccant matrix, and (2) “staging” the regeneration air stream. An analysis is presented in this paper which explains the benefits and drawbacks of these methods based upon the wave nature of the heat and mass transfer processes occurring within the desiccant bed. The results indicate that the best overall system performance is obtained by staging the regeneration process while minimizing the amount of inert heat capacity.

Performance and cost evaluation of solid desiccant solar cooling system

SYNOPSIS This paper presents performance and cost-evaluation studies of a solid desiccant solar cooling system. A fixed bed adiabatic dehumidifier model and a standard flat-plate solar collector option have been considered to investigate the overall desiccant cooling system performance as a function of regeneration temperature and the effectiveness of the heat exchangers. The economics of a solar regeneration dehumidifier based cooling system has also been evaluated for one Ton of cooling capacity equivalent and a comparative study using other energy sources has also been made. It was found that the solar option would be the cheapest and hence the solid desiccant solar cooling system can be made cost effective.

Desiccant Cooling System Performance: A Simple Approach

A simple algebraic model of wave motion arising in the adiabatic fixed-desiccant bed dehumidification of an air stream is applied to the prediction of the performance potential of a desiccant air conditioning system. The model is used to explain the increase in cooling system performance that has been realized through the use of mixed inert-desiccant material adsorption beds. The response of cooling system performance to changes in external process conditions is examined and conclusions are drawn relative to optimization of system characteristics.