The membrane dehumidifiers can be used in air conditioning systems. In this study, an experimental investigation is conducted on the planar vacuum membrane dehumidifier equipped with the four-serpentine flow channel plate. A vacuum membrane dehumidification technique is used to measure the dehumidification performance. The effects of different parameters, such as the temperature and humidity of air, the vacuum pressure, and the air flow rate, on different dehumidification performance indexes are investigated. Four dehumidification performance indexes, including the water collection of the cold trap, the water flux, the pressure drop, and the total pumping power, are investigated. The results show that the water collection capacity and water flux are increased as the inlet air temperature increases. For the air flow rate of 65 l.min−1, the water collection capacity at the inlet air humidity of 90 % is up to 2.51 times of that at the inlet air humidity of 60 %. As compared with the temperature effect, the humidity has less effect on the pressure drop. The decrease in the pressure drop and total pumping power can be observed with increasing the vacuum pressure. For example, at the air flow rate of 65 l.min−1, the pressure drop reduces about 11 % by increasing the vacuum pressure in the range of 0.66 kPa to 2.66 kPa.

In the present analysis, three potential serpentine flow channel designs for a flat-sheet membrane-based dehumidifier are designed and evaluated in terms of performance metrics such as dehumidification rate (DR), approach temperature (AT), pressure drop (ΔP), and coefficient of performance (COP). The dry side inlet air temperature and relative humidity (RH) are set at 27°C and 0%, and the wet side inlet air temperature and RH are fixed at 40°C and 85%. The inlet air flow rates of the dry and wet sides are both controlled in the range of 20-60 L min−1. The simulation results revealed that the geometrical design of the flow channels has a remarkable impact on the dehumidification performance of the dehumidifier. It is outlined that the water vapor concentration and temperature distribution at the outlet of all proposed serpentine flow channels are almost identical, showing the oversized design of the three- and six-inlet serpentine channels. Under the air flow rates of 30 ∼ 60 L min−1, it is seen that the DR, AT, and ΔP of three-, six-, and nine-inlet serpentine channels are in descending order. It is found that the size and quantity of the channel outlets and inlets have a great influence on the pressure drop. Moreover, the dehumidifier with nine-inlet serpentine flow channel can provide the highest COP with a limited increase in the pressure loss. Hence, this channel design can be a good candidate to be implemented in the flat-sheet membrane-based dehumidifier. The findings of this study could be beneficial for the design of novel dehumidifiers.

Membrane-based dehumidification system is an emerging technology which drives based on the renewable lowgrade energy sources. Water vapor selective membrane is able to separate water vapor from the air which can be used to condition air in buildings, more efficiently than conventional air-conditioning equipment. Flow channel designs (especially serpentine-type) and their impacts on the thermal-hydraulic performance of membrane-based dehumidifiers are essential and not well-studied. In the present work, a novel flat-sheet membrane dehumidifier with serpentine flow channels is designed and evaluated experimentally. The serpentine flow channel offers a long flow path that the air in the wet and dry sides of the channel interacts with each other through the membrane, thereby improving the heat and water vapor transfer. The effect of inlet air flow rate, relative humidity, and temperature of both wet and dry sides on the dehumidification rate, approach temperature, pressure drop, and coefficient of performance of the dehumidifier is examined. Results show that passing the humid air with higher flow rate, humidity, and temperature through the wet side channel leads to the higher dehumidification rate, approach temperature, and pressure drop. Increase of wet side air temperature and flow rate enhances the coefficient of performance, and the effect of inlet air relative humidity on the coefficient of performance is observed negligible at high air flow rates. Parametric study of dry side air condition reveals that the air with lower humidity improves the dehumidification rate and coefficient of performance, while its effect on the approach temperature and pressure drop is observed negligible. Elevated air temperature of dry side has positive and negative impact on the approach temperature and coefficient of performance of the dehumidifier, respectively.

In recent years, membrane dehumidification, as a novel dehumidification technology, has received many attentions for energy efficiency in air conditioning systems. Its dehumidification technology is characterized by isothermal dehumidification, which can avoid excess energy consumption. This experimental study focuses on the performance measurement of the planar vacuum membrane dehumidifier. Nafion membrane is used in combination with a planar membrane dehumidifier. A vacuum membrane dehumidification method is also employed to investigate the dehumidification performance. Four serpentine flow channel designs, including three-snake, four-snake, five-snake, and six-snake flow channel designs, are tested at the certain values of temperature and humidity and different inlet air flow rates. Different performance indexes, including water collection, dehumidification rate, pressure loss, and pumping power, are investigated. The results show that the amount of water collected by the cold trap increases with boosting the inlet flow rate in the range of 35 l/min to 55 l/min and it has the largest value when the inlet air flow rate is 55 l/min. However, the amount of water collected by the cold trap decreases with further increase of the inlet flow rate in the range of 55 l/min to 65 l/min.

The present study pertains to an experimental measurement investigation of membrane physical properties for vacuum membrane dehumidifiers. The membrane material used in an air dehumidification system is a key role for the dehumidification efficiency. To find the most suitable membrane for dehumidification, the membrane physical characteristics are examined by using three critical indexes of air permeance (AP) and water vapor permeance (WP), and selectivity (SE). Two categories of dehumidification membranes, i.e. composite and dense membranes, are applied in the vacuum membrane dehumidifier with a serpentine flow channel. Firstly, the vapor transfer rates of both composite and dense membranes are determined and the experimental data discloses that the composite membranes, such as Sulfone and Metal–organic framework (Mof) membranes, provide higher vapor transport ability, which is not suitable for the vacuum membrane-based dehumidifier. Then, the measurement of AP, WP, and SE is further performed for the dense membranes of Nafion. The result shows that the order of either AP or WP is N.211, N.212, N.115, and N.117, but the SE defined as WP/AP has a different tendency and the order is N.117, N.115, N.212, and N.211. Finally, the results of AP, WP, and SE in this dehumidifier are also compared with the previous experiment.

With the advent of 5th-generation mobile networks, the internal computing of data centers is very important. However, a server's calculations cause significant thermal problems. Therefore, this study focuses on the thermal analysis of a single rack in a data center. In this work, the airflow and temperature distributions in a single rack are examined numerically in detail. The computational fluid dynamics software is used to simulate the airflow field and temperature profile. The focus of the research is removal of heat from servers in the rack under different operating conditions and designs. The predicted results show that Case 2's size and 0.45 m of raised-floor depth would help to create a uniform airflow distribution at the same rate. Besides, the Return temperature index is used to evaluate the performance of data center. The results of Model 1 and 2 for three flow rate are presented and compared in details.

The ambient air with the excessive moisture needs to be dehumidified for a comfortable environment using air conditioning. The planar membrane-based dehumidifier (PMD) is a potential technology to remove moisture in humid air. The performance of PMDs with different operating conditions is evaluated via numerical simulations with focuses on influences of the flow channel geometry, i.e. aspect ratio (AR) of width over height, on the dehumidification performance firstly. The result discloses channels with AR = 2 have the best coefficient of performance (COP). Thus, three-dimensional dehumidifiers are simulated to further understand the physical mechanism of air dehumidification. Finally, an in-depth parametric analysis is carried out with emphasis on the influence of governing parameters on PMD performances, such as dehumidification rate (DR), dew point approach temperature (DPAT), pressure drop (Delta P), and COP. The results show that enhancing mass flow rates leads to an ascending tendency of DR, DPAT, and Delta P, but a descending tendency of COP. Increasing the inlet temperature of dry side results in the reduction of both DR and DPAT, but the increase in Delta P, resulting in the deterioration of the COP. Additionally, the counterflow PMD always has better dehumidification performance than parallel one for various governing parameters.

In this paper, a parametric study is performed on the operation of a planar membrane humidifier (PMH) for the proton exchange membrane fuel cell. The numerical method is used to simulate the heat and mass transfer in the PMH. The simulations are carried out for both counter-flow and parallel-flow arrangements. The effects of different parameters including the inlet temperatures of wet and dry channels and the inlet mass flow rates of these channels on the pressure drop, dew point approach temperature, and water recovery ratio inside the PMH are studied. The results indicate that the counter-flow arrangement provides larger values of the water recovery ratio in comparison with the case of parallel-flow one. For the counter-flow arrangement, the dew point approach temperature is decreased about 49.6% as the inlet temperature of dry channel increases in the range of 20 degrees C to 50 degrees C at inlet mass flow rate of the wet channel (m) over dot(w,i) =9 x 10(-6) kg/s, inlet mass flow rate of the dry channel (m) over dot(d,i) =18 x 10(-6) kg/s, and inlet temperature at the wet channel T-w,T-i = 80 degrees C. There is no major difference between the pressure drops of parallel-flow and counter-flow arrangements. (C) 2020 Elsevier Ltd. All rights reserved.

In this work, a numerical study is developed to examine the performance in a planar membrane-based humidifier (PMH) to optimize the operation with respect to a detailed parametric analysis. Firstly, a 3-dimensional simulation is built up to explore the heat and mass transfer in PMHs. Then, humidification performances including dew point approach temperature (DPAT), water recovery ratio (WRR), pressure drop (Delta P), and coefficient of performance (COP) are studied with focus on the effects of the duct cross-section aspect ratio (AR), defined as width/height, and the length of ducts. Among AR = 0.5, 1 and 2 with the duct length of 200, 300 and 400 mm, the maximum WRR and the best COP occur at the duct with AR = 2 for all cases of different duct lengths. Finally, influences of governing parameters named mass flow rate, inlet temperature of dry duct, and inlet relative humidity (RH) of wet duct on PMH performances are further investigated. An increase in mass flow rates both enhances DPAT and Delta P, but degrades WRR and COP of the PMH. Enhancing the inlet temperature of dry air reduces the WRR and DPAT, but increases the Delta P leading to a descending trend of the COP. Increasing the inlet RH of wet duct has a small effect on Delta P and an enhancement in the WRR and COP. (C) 2020 Elsevier Ltd. All rights reserved.

Removing excessive moisture from the ambient air by means of a selective membrane in the membrane-based dehumidifier has become a new emerging technology. The present study pertains to the experimental work on heat and mass transfer of a multi-stage planar membrane dehumidifier. Commercial Nafion 212 membranes are applied in this membrane dehumidification system because of the large selectivity. The operating conditions of inlet dry air are fixed to maintain at temperature of 27 degrees C and relative humidity of 0.1% while performing dehumidification tests. Attention is mainly paid to examining the effects of various temperature, relative humidity and flow rate of the wet side inlet air on performance indexes including the dehumidification rate (DR), dew point approach temperature (DPAT), pressure loss (Delta P), and pumping power (Omega) in planar membrane-based dehumidifiers. Measured results show that increasing inlet temperature, relative humidity and flow rate of humid air in the wet channel enhances performance indexes, that is, higher DR, DPAT, AP and n. In addition, the counter flow configuration in the dehumidifier provides better mass and heat transfer performance compared to parallel flow configuration. (C) 2019 Elsevier Ltd. All rights reserved.

The research and development of humidifiers is important to proton exchange membrane fuel cell systems. The water exchange membrane is a key component to the planar membrane humidifier. In this work, two types of low-cost membrane, the pervaperation (PV) membrane and the reverse osmosis (RO) membrane, are selected as the research targets. Their physical properties and humidification performance are tested and compared with the Nafion (R)-212 membrane. The ex-situ tests indicate that the order of air permeability is RO membrane > Nafion (R) 212 membrane > PV membrane, and the order of water vapor permeability is RO membrane similar to Nafion (R) 212 membrane > PV membrane. From the in-situ tests, the order of humidification performance is Nafion (R) 212 membrane > RO membrane > PV membrane at all air flow rates. The DPATs with the RO and PV membranes are roughly 1-2 degrees C and 2-3 degrees C higher than that with the Nafion (R) 212 membrane, respectively. The highest WRRs obtained at 30 L/min with the Nafion (R) membrane, RO membrane and the PV membrane are about 53%, 48% and 42%, respectively. The Nafion (R) membrane is most energy-efficient because it has the highest COP. Moreover, the PV and RO membranes are equally energy-efficient when considering both the water transfer performance and the power loss. (C) 2019 Elsevier Ltd. All rights reserved.

In this work, the experimental measurement is conducted to examine different membranes to find a suitable option for a planar membrane dehumidifier. The physical properties with critical characteristics of air permeance and water vapor permeance are used as the indexes to evaluate the better membrane applicability for planar dehumidifiers. The experiments contain three parts. Firstly, the air permeance rates of a variety of membranes are measured. Experimental data reveal that Nafion membranes have lower air permeance rate compared with RO membrane under the same degree of vacuum pressure. Secondly, measurements of water vapor permeance of RO and Nafion membranes are carried out. Results show that water vapor permeance of Nafion is better than RO. Finally, Nafion membranes are tested to explore the influence at various temperature, relative humidity and the vacuum side pressure on condensed water and water vapor permeance. The measurement results indicate that increasing temperature enhances the condensed water at either low or high relative humidity, while increasing the pressure on the vacuum side gets less water permeated. As a result, Nafion membranes have characteristics of low air permeance and high water vapor permeance to be candidates of the suitable membrane applied in a planar membrane dehumidifier.

Purpose The electromagnetic field and cooling system of a high power switched reluctance motor (SRM) are studied numerically. The geometry of the motor and its main components are established using a computer-aided design software in the actual size. This study aims to evaluate the resulting thermal losses using the electromagnetic analysis of the motor. Design/methodology/approach In the electromagnetic analysis, the Joule’s loss in the copper wires of the coil windings and the iron losses (the eddy currents loss and the hysteresis loss) are considered. The flow and heat transfer model for the thermal analysis of the motor including the conduction in solid parts and convection in the fluid part is introduced. The magnetic losses are imported into the thermal analysis model in the form of internal heat generation in motor components. Several cooling system approaches were introduced, such as natural convection cooling, natural convection cooling with various types of fins over the motor casing, forced conviction air-cooled cooling system using a mounted fan, casing surface with and without heat sinks, liquid-cooled cooling system using the water in a channel shell and a hybrid air-cooled and liquid-cooled cooling system. Findings The results of the electromagnetics analysis show that the low rotational speed of the motor induces higher currents in coil windings, which in turn, it causes higher copper losses in SRM coil windings. For higher rotational speed of SRM, the core loss is higher than the copper loss is in SRM due to the higher frequency. An air-cooled cooling system is used for cooling of SRM. The results reveal when the rotational speed is at 4,000 rpm, the coil loss would be at the maximum value. Therefore, the coil temperature is about 197.9°C, which is higher than the tolerated standard temperature insulation material. Hence, the air-cooled system cannot reduce the temperature to the safe temperature limitation of the motor and guarantee the safe operation of SRM. Thus, a hybrid system of both air-cooled and liquid-cooled cooling system with mounting fins at the outer surface of the casing is proposed. The hybrid system with the liquid flow of Re = 1,500 provides a cooling power capable of safe operation of the motor at 117.2°C, which is adequate for standard insulation material grade E. Originality/value The electromagnetic field and cooling system of a high power SRM in the presence of a mounted fan at the rear of the motor are analyzed. The thermal analysis is performed for both of the air-cooled and liquid-cooled cooling systems to meet the cooling demands of the motor for the first time.

This work investigates experimentally the cooling performance of Al2O3/water nanofluid with 8 wt% concentration flowing through a minichannel heat sink with a MEPCM layer in its ceiling. The hydrothermal characteristics of the nanofluid-cooled minichannel heat sink are analyzed and the dimensionless wall temperature distribution, Nusselt number, heat transfer effectiveness, coefficient of performance, figure of merit, and wall temperature thermal resistance are assessed. The measured results show that the dispersion of alumina nanoparticles inside pure water declines the wall temperature and consequently enhances the heat transfer effect and Nusselt number augments. The maximum values of average heat transfer effectiveness and FOM at the inlet of the MCHS are achieved 1.4 and 1.27 by flowing nanofluid with 8 wt% nanoparticle concentration and Re = 1549, respectively. The results revealed that embedding MEPCM layer in the ceiling of the MCHS has little influence on the cooling performance of Al2O3/water nanofluid in the minichannel heat sink.