Performance Analysis on the Internally Cooled Dehumidifier Using Two Liquid Desiccant Solutions

2012 ◽  
Author(s):  
I. P. Koronaki ◽  
R. I. Christodoulaki ◽  
V. D. Papaefthimiou ◽  
E. D. Rogdakis
Keyword(s):  
Mass Transfer ◽  
Theoretical Model ◽  
Heat And Mass Transfer ◽  
Flow Rate ◽  
Air Conditioning ◽  
Cooling Water ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Liquid Desiccant ◽  
Internally Cooled

Liquid desiccant air conditioning systems have recently been attracting attention due to their capability of handling the latent load without super-cooling and then reheating the air, as happens in a conventional compression-type air conditioning system. This paper presents the results from a study of the performance of an internally cooled liquid desiccant dehumidifier. A plate heat exchanger is proposed as the internally cooled element of the dehumidifier and water as the cooling fluid. The desiccant solution is sprayed into the internally cooled dehumidifier from the top and flows down by gravity. At the same time, fresh humid air is blown from the bottom or top, counter-flowing or co-flowing with the desiccant solution. The desiccant is in direct contact with the air, allowing for heat and mass transfer. The cooling water, flowing inside the plates of the dehumidifier, carries out the heat of the crossed air and solution. A heat and mass transfer theoretical model has been developed, based on the Runge-Kutta fixed step method, to predict the performance of the device under various operating conditions. Experimental data from previous literature have been used to validate the model. Excellent agreement has been found between experimental tests and the theoretical model, with the deviation not exceeding ±4.1% for outlet air temperature and ±4.0% for outlet humidity ratio. Following the validation of the mathematical model, the dominating effects on the absorption process have been discussed in detail. Namely, effects of flow configuration, air inlet temperature, humidity and flow rate, as well as desiccant inlet temperature, concentration and flow rate have been investigated against the dehumidification rate and the cooling efficiency. The two most commonly used liquid desiccant solutions, namely LiCl and LiBr have been also evaluated against each other. The results suggested that high dehumidification mass rate can be achieved under counter flow between air and solution, low air mass flow rates, low cooling water temperature, low desiccant temperature and LiCl as the desiccant solution.

Numerical Analysis of the Heat and Mass Transfer Characteristics in an Autothermal Methane Reformer

2010 ◽  
Vol 7 (5) ◽  
Author(s):  
Joonguen Park ◽  
Shinku Lee ◽  
Sunyoung Kim ◽  
Joongmyeon Bae
Keyword(s):  
Mass Transfer ◽  
Numerical Analysis ◽  
Heat And Mass Transfer ◽  
Steam Reforming ◽  
Space Velocity ◽  
Reaction Model ◽  
Operating Conditions ◽  
Local Thermal Equilibrium ◽  
Inlet Temperature ◽  
Transfer Characteristics

This paper discusses a numerical analysis of the heat and mass transfer characteristics in an autothermal methane reformer. Assuming local thermal equilibrium between the bulk gas and the surface of the catalyst, a one-medium approach for the porous medium analysis was incorporated. Also, the mass transfer between the bulk gas and the catalyst’s surface was neglected due to the relatively low gas velocity. For the catalytic surface reaction, the Langmuir–Hinshelwood model was incorporated in which methane (CH4) is reformed to hydrogen-rich gases by the autothermal reforming (ATR) reaction. Full combustion, steam reforming, water-gas shift, and direct steam reforming reactions were included in the chemical reaction model. Mass, momentum, energy, and species balance equations were simultaneously calculated with the chemical reactions for the multiphysics analysis. By varying the four operating conditions (inlet temperature, oxygen to carbon ratio (OCR), steam to carbon ratio, and gas hourly space velocity (GHSV)), the performance of the ATR reactor was estimated by the numerical calculations. The SR reaction rate was improved by an increased inlet temperature. The reforming efficiency and the fuel conversion reached their maximum values at an OCR of 0.7. When the GHSV was increased, the reforming efficiency increased but the large pressure drop may decrease the system efficiency. From these results, we can estimate the optimal operating conditions for the production of large amounts of hydrogen from methane.

A Field Study of a Low-Flow Internally Cooled/Heated Liquid Desiccant Air Conditioning System: Quasi-Steady and Transient Performance

2016 ◽  
Vol 138 (3) ◽  
Author(s):  
Ahmed H. Abdel-Salam ◽  
Chris McNevin ◽  
Lisa Crofoot ◽  
Stephen J. Harrison ◽  
Carey J. Simonson
Keyword(s):  
Air Conditioning ◽  
Field Performance ◽  
Ambient Air ◽  
Operating Conditions ◽  
Coefficient Of Performance ◽  
Low Flow ◽  
Transient Field ◽  
Liquid Desiccant ◽  
Internally Cooled ◽  
Steady Performance

The field performance of a low-flow internally cooled/heated liquid desiccant air conditioning (LDAC) system is investigated in this paper. The quasi-steady performance (sensible and latent heat transfer rates, coefficient of performance (COP), and uncertainties) of the LDAC system is quantified under different ambient air conditions. A major contribution of this work is a direct comparison of the transient and quasi-steady performance of the LDAC system. This paper is the first to quantify the importance of transients and shows that, for the environmental and operating conditions in this paper, transients can be neglected when estimating the energy consumption of the LDAC system. Another major contribution of this work is the development and verification of a new method that quantifies (with acceptable uncertainties) the quasi-steady performance of a LDAC system from transient field data using average data.

Evaluation of Cooling Water Storage for Liquid-Desiccant Air Conditioning System

2014 ◽  
Author(s):  
Danial Salimizad ◽  
Chris McNevin ◽  
Stephen Harrison
Keyword(s):  
Air Conditioning ◽  
Electrical Power ◽  
Water Storage ◽  
Cooling Water ◽  
Operating Conditions ◽  
Coefficient Of Performance ◽  
Liquid Desiccant ◽  
Air Conditioning System ◽  
Electrical Power Consumption ◽  
Evaporative Cooling Tower

Liquid-desiccant (LD) dehumidification technology has been used to extract moisture from humid air while attempting to consume less electricity than traditional air-conditioning methods. An evaporative cooling tower (ECT) was used as a cooling device to reject the latent heat gained by the system to regenerate the desiccant solution. The performance of an ECT was evaluated both experimentally and through TRNSYS simulations to investigate optimal operating conditions. The ECT often operated in humid conditions which resulted in reduced heat rejection rates and ineffective operation. To improve performance, cooling water storage (CWS) was investigated as a way to reduce ECT usage during periods of higher ambient humidity. To undertake this study, the complete LD system, incorporating CWS, was modelled in TRNSYS for a range of typical operating conditions. The results indicated that operation of the CWS system reduced the electrical power consumption and increased the electrical coefficient of performance (COPE) of the liquid desiccant air conditioning unit system by up to 16%. The total cooling rate improved by up to 6%. Smaller gains in COPT and solar fraction were also found in the simulation results.

scholarly journals Heat and mass transfer in an adjacent internally-cooled membrane-based liquid desiccant dehumidifier (AIMLDD)

2017 ◽  
Vol 142 ◽  
pp. 3990-3997 ◽  
Author(s):  
Yu Yang ◽  
Minlin Yang ◽  
Weihao Huang ◽  
Si-Min Huang ◽  
Wei-Biao Ye ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Liquid Desiccant ◽  
Internally Cooled

An Analytical Solution to Heat and Mass Transfer in Hollow Fiber Membrane Contactors for Liquid Desiccant Air Dehumidification

2011 ◽  
Vol 133 (9) ◽  
Author(s):  
Li-Zhi Zhang
Keyword(s):  
Mass Transfer ◽  
Analytical Solution ◽  
Heat And Mass Transfer ◽  
Hollow Fiber ◽  
Hollow Fiber Membrane ◽  
System Optimization ◽  
Operating Conditions ◽  
Fiber Membrane ◽  
Liquid Desiccant ◽  
Membrane Contactors

Hollow fiber membrane contactors are used in air dehumidification. The benefit of this technology is that the liquid desiccant is not in a direct contact with the process air; therefore, the problem of liquid droplets crossover is prevented. The equations governing the heat and moisture transfer from the air to the liquid, through the membranes, are described. An analytical solution is obtained for the dimensionless differential equations, with which the dehumidification effectiveness could be estimated by simple algebraic calculations. It provides a convenient yet accurate tool for the component design and system optimization. The model is validated by experiments. The effects of varying operating conditions on system performance are investigated. It is found that the total number of transfer units for sensible heat and the overall Lewis number are the most dominant parameters influencing heat and mass transfer.

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