Research On Heat And Mass Transfer Performance Of Internally-cooled Liquid Desiccant Air Handling Process

The research object of this paper is the internally-cooled liquid desiccant airdehumidification method. The main contents are the heat and mass transfercharacteristics, the performance optimization criteria of this dehumidification method,as well as the performance comparison between the internllay-coold dehumidificationand the widely used adiabatic dehumidification method. Based on these ideas, thefollowing studies have been carried out in this paper:At first, a numerical model is established to simulate the performance of theinternally-cooled liquid desiccant dehumidifier and internally-heated regenerator, whichis then validated by available experimental data. The dehumidification/regenerationperformance of a novel-designed internally-coold dehumidifier/regenerator is tested,which is based on fin-tube structure and made of a special kind of plastic with highconductivity. The heat transfer coefficient between the solution and the cooling mediumand the mass transfer coefficient between the solution and the humid air are thencalculated from the experiment data, which show that the weakness of the device lies inthe heat transfer process.Secondly, the heat and mass transfer characteristics of the internally-cooled liquiddesiccant dehumidification method is analyzed. It is found that the humid air in thedehumidifier performs as the heat and moisture source, while the cooling medium as theheat sink, and the liquid desiccant as the intermediate to transfer heat from the source tothe sink. In this way, the state of the liquid desiccant is determined by both the air andthe cooling medium. The performance optimization of this kind of method shouldfollow the criteria of the uniformity of the ratio of the driving forces inside the device,with the given overall heat transfer and mass transfer coefficients KhFhand KmFm.Under the guidance of the optimization criteria, the solution flow rate should be as smallas possible to obtain better dehumidification performance in the internally-cooleddehumidification device.Thirdly, the performance comparison is conducted between the internally-cooledand the adiabatic dehumidification devices/systems. The result show that with the same KhFhand KmFm, the adiabatic dehumidification method is better when the solution flowrate is relatively large, while the internally-cooled dehumidification method is betterwhen the solution flow rate is relatively small.Finally, the material cost and occupied volume of the internally-cooled andadiabatic dehumidification method are compared. In order to achieve the same KhFhandKmFm, the internally-cooled dehumidification method has higher capital cost, butsmaller volume. As a result, the internally-cooled method has the advantage of smallerequipment size, smaller solution flow rate, less risk of solution carryover, and lessenergy consumption of the solution pump, while the disvantage is higher initial cost.The challenges of the internally-cooled liquid desiccant dehumidification method arethe poor wettability of the material surface when the solution flow rate is small and themanufacture level needs improving.