The origin of the faster mechanism of partial enthalpy recovery deep in the glassy state of polymers

A novel finding made by Cangialosi and coworkers in physical aging of several polymers way below the glass transition temperature Tg is that equilibrium recovery occurs by reaching a plateau...

Performance Comparison of Enthalpy Recovery Devices Using Liquid Desiccant and Desiccant Wheel

Heat recovery between outdoor air and indoor exhaust air is an effective approach for energy-saving in the air-conditioning system. Performances of enthalpy recovery devices using liquid desiccant (LD) and desiccant wheel (DW) are compared in the present study. Effects of key factors including desiccant flow rate, number of transfer units (NTUm), and air inlet parameters on recovery performance are analyzed. There exists the same ideal recovery efficiency with a given NTUm for these two kinds of devices. However, an optimal solution flow rate could be achieved for enthalpy recovery device using LD, while a higher rotation speed leads to a higher recovery efficiency for that using DW. Recovery efficiencies of the two devices increase with the increase in NTUm, while they have different ranges of NTUm. NTUm of the DW is usually superior to that of the LD, due to the material difference. Then, the optimum methods to improve recovery efficiency of the two devices are clarified, i.e., increasing NTUm for an enthalpy recovery device using LD and choosing a reasonable rotation speed for that using DW, respectively. The present research will be beneficial to cast light on the relation between enthalpy recovery devices using LD and DW.

Experimental analysis and performance optimization of a counter-flow enthalpy recovery device using liquid desiccant

The liquid desiccant enthalpy recovery is an efficient way to save energy in air-conditioning systems. In this study, a counter-flow liquid desiccant enthalpy recovery device was proposed and experimentally analyzed. Enthalpy transfer capacity, enthalpy efficiency and pressure drop per height of packing were used as indices to describe its performances. Based on the experiment results, the heat and mass transfer model of a packed tower was used to simulate and optimize the performance of this device. The maximum enthalpy efficiency and enthalpy transfer capacity were achieved when the optimal air velocity (1.9–2.1 m/s in this study) maintained to be slightly below the air velocity at the loading point and the thermal capacity ratio of air to desiccant ( m*) equaled to 1. These conclusions are valuable to both design and operation of such an enthalpy recovery device. Practical application: A counter-flow enthalpy recovery device with liquid desiccant was proposed and experimentally investigated. Based on the experiment results, a numerical model for this device was built and validated. The optimal air and desiccant mass fluxes were analyzed to maximize the enthalpy efficiency of this device, which could be higher than the conventional device with cross-flow pattern. These results could provide guidelines for both design and operation management of counter-flow enthalpy recovery devices in liquid desiccant-based air-conditioning systems.