Effect of Operating Conditions on Optimal Performance of Rotary Dehumidifiers

1995 ◽  
Vol 117 (1) ◽  
pp. 62-66 ◽  
Author(s):  
W. Zheng ◽  
W. M. Worek ◽  
D. Novosel
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Rotational Speed ◽  
Optimal Performance ◽  
Operating Conditions ◽  
Sorption Properties ◽  
Design Point ◽  
The Real ◽  
Transfer Characteristics ◽  
The Matrix

The design-point dehumidification performance (i.e., at ARI conditions) of a rotary dehumidifier wheel depends on its rotational speed, the sorption properties of the desiccant, the heat and mass transfer characteristics of the matrix, and the size of the dehumidifier. However, the real operating conditions of a rotary dehumidifier can vary significantly from the design point, given the large variations in operating conditions (i.e., the outdoor, indoor, and regeneration temperatures and humidities) for various locations during different times of the year. This paper investigates the variability of the dehumidification performance of a rotary dehumidifier and its dependence on operating conditions. Also, the effect of the operating conditions on the optimum rotational speed of a rotary dehumidifier, where the performance of a rotary dehumidifier is optimized, is described.

Performance Optimization of Rotary Dehumidifiers

1995 ◽  
Vol 117 (1) ◽  
pp. 40-44 ◽  
Author(s):  
W. Zheng ◽  
W. M. Worek ◽  
D. Novosel
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Performance Optimization ◽  
Rotational Speed ◽  
Porous Matrix ◽  
Sorption Properties ◽  
Moisture Uptake ◽  
Adsorption Characteristic ◽  
Transfer Characteristics ◽  
Carry Over

A rotary dehumidifier consists of a rotating porous matrix made of a desiccant with mechanically supporting materials. The dehumidification performance of a rotary dehumidifier wheel depends on its rotational speed, the sorption properties of the desiccant, the heat and mass transfer characteristics of the matrix, and the size of the dehumidifier. The effect of the rotational speed on the dehumidification performance of a rotary dehumidifier has been investigated by Zheng, Worek, and Novosel (1993). This paper extends that previous work and investigates the effects of desiccant sorption properties, the heat and mass transfer characteristics, and the size of the rotary dehumidifier on the dehumidification performance. The results show that the using desiccant materials in a rotary dehumidifier with different adsorption characteristics results in a wide variation in dehumidification performance. However, the maximum performance of a rotary dehumidifier occurs for a desiccant material having an isotherm shape that can be characterized to have a separation factor of 0.07. Also, as the desiccant moisture uptake increases, the dehumidifier performance also increases. However, the performance improvement for a desiccant matrix having a maximum moisture uptake of larger than 0.25 by weight is not significant. The heat and mass transfer properties and the size of a rotary dehumidifier are characterized by the number of transfer units NTU. Generally, the larger the NTU, the better dehumidification performance. However, similar to the maximum moisture uptake, when the NTU is larger than 12, the performance will not improve significantly. Also, the dehumidifier with the most favorable adsorption characteristic has a slowest rotational speed, which results in a lower power requirements to rotate the desiccant wheel and smaller carry-over losses.

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.

Heat Transfer on Nanofluid Flow With Homogeneous–Heterogeneous Reactions and Internal Heat Generation

2014 ◽  
Vol 136 (12) ◽  
Author(s):  
Raj Nandkeolyar ◽  
Peri K. Kameswaran ◽  
Sachin Shaw ◽  
Precious Sibanda
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Heat Generation ◽  
Internal Heat ◽  
Internal Heat Generation ◽  
Heterogeneous Reactions ◽  
Transfer Coefficients ◽  
Transfer Characteristics ◽  
Fluid Properties

We investigated heat and mass transfer on water based nanofluid due to the combined effects of homogeneous–heterogeneous reactions, an external magnetic field and internal heat generation. The flow is generated by the movement of a linearly stretched surface, and the nanofluid contains nanoparticles of copper and gold. Exact solutions of the transformed model equations were obtained in terms of hypergeometric functions. To gain more insights regarding subtle impact of fluid and material parameters on the heat and mass transfer characteristics, and the fluid properties, the equations were further solved numerically using the matlab bvp4c solver. The similarities and differences in the behavior, including the heat and mass transfer characteristics, of the copper–water and gold–water nanofluids with respect to changes in the flow parameters were investigated. Finally, we obtained the numerical values of the skin friction and heat transfer coefficients.

Sign in / Sign up

Export Citation Format

Share Document