Davood Ghadiri Moghaddam

Steady-State Performance of a Small-Scale Liquid-to-Air Membrane Energy Exchanger for Different Heat and Mass Transfer Directions, and Liquid Desiccant Types and Concentrations: Experimental and Numerical Data

A liquid-to-air membrane energy exchanger (LAMEE) is an energy exchanger that allows heat and moisture transfer between air and salt solution flows through a semipermeable membrane. For the first time, a novel small-scale single-panel LAMEE test facility is used to experimentally investigate the effect of the direction of heal and mass transfers for the air and salt solution flows, and the effect of different salt solution types and concentrations on the LAMEE effectiveness. The data for steady-state effectiveness of the LAMEE are compared to the simulation results of a numerical model. Two studies are conducted; first a study based on different heat and mass transfer directions (four test cases), and second a study focused on the influence of solution types and concentration on LAMEE performance. For the first study, NTU = 3 and four different heat capacity ratios (i.e., Cr* = 1, 3, 5, 7) are used, with a LiCl salt solution in the exchanger. Mass and energy balances for all the test cases and the repeatability of the experimental data for the air cooling and dehumidifying test case show that the experimental data are repeatable and within an acceptable uncertainty range. The results show increasing effectiveness with increasing Cr*, and good agreement between the numerical and experimental results for both air cooling and dehumidifying and air heating and humidifying test cases. In the second study, two different salt solutions (i.e., LiCl and MgCl 2 ), and three different concentrations for the LiCl solution (i.e., 25%, 30%, and 35%) are selected to investigate the effect of different salt solution types and concentrations on the performance of the LAMEE. A maximum difference of 10% is obtained for the LAMEE total effectiveness data with the different salt solution types and concentrations. The results show that both the salt solution type and concentration affect the LAMEE effectiveness, and changing the concentration is one way to control the supply air outlet humidity ratio.

Steady-State Performance of a Prototype (200 cfm) Liquid-to-Air Membrane Energy Exchanger (LAMEE) Under Summer and Winter Test Conditions

Liquid-to-air membrane energy exchangers (LAMEEs) are a new generation of energy exchangers in air-conditioning systems to transfer both heat and moisture. In this paper, the performance of a 200 cfm LAMEE is numerically and experimentally investigated under summer and winter test conditions when Lithium Chloride (LiCl) is used as a salt solution in the exchanger. The results show that the LAMEE has almost the same total effectiveness at summer and winter conditions, but the latent effectiveness of the LAMEE is higher at the summer conditions. Also, the agreement between the experimental and numerical results is acceptable for all the tests, and they are within their uncertainty ranges except for the latent effectiveness of the LAMEE tested under winter test conditions.Copyright

Measurement of Heat Transfer Enhancement and Pressure Drop Across Eddy Promoter Air Screens in a Liquid-to-Air-Membrane Energy Exchanger (LAMEE)

In liquid-to-air membrane energy exchangers (LAMEEs), the heat and mass transfer resistances in the air channel are dominant. An eddy promoter air screen can effectively enhance the heat and mass transfers in the air channel. In this study, the heat transfer enhancement and pressure drop across three different eddy promoter air screens in an air channel are experimentally investigated. Eddy promoter air screens are comprised of plastic ribs in the stream-wise direction and aluminum cross-bars normal to the air flow direction. A low speed wind tunnel test facility, which simulates the air channel of a LAMEE is designed to measure the friction factor and enhanced convective heat transfer coefficient in the air channel with an eddy promoter air screen. Tests were conducted at Reynolds numbers of 920, 1550, and 2160. In this paper, the effects of the spacing of the cylindrical bars and plastic ribs on the heat transfer performance are studied experimentally. Also, the performance of eddy promoter air screens as a function of enhanced heat transfer coefficient and increased pressure drop is investigated. Results show that the eddy promoter air screens have the highest efficiencies at Reynolds of 1550 and double the convective heat transfer coefficient of the air with respect to a smooth channel.Copyright