Effect of Moisture Transfer Through a Semipermeable Membrane on Condensation/Frosting Limit

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
S. Niroomand ◽  
M. T. Fauchoux ◽  
C. J. Simonson
Keyword(s):  
Moisture Transfer ◽  
Air Flow ◽  
Semipermeable Membrane ◽  
Operating Conditions ◽  
Air Humidity ◽  
Liquid Desiccant ◽  
Humidity Ratio ◽  
Frost Formation ◽  
Effect Of Moisture ◽  
Cold Liquid

This paper investigates frost formation on a flat horizontal surface, with humid air flowing over the surface and a cold liquid desiccant flowing below the surface. Two different surfaces, a semipermeable membrane and an impermeable plate, are tested. The condensation/frosting limit, that is, the lowest air humidity ratio, Wair, at a constant liquid temperature, Tliq, or the highest Tliq at a constant Wair that leads to condensation/frosting, is determined for each surface. The main aim of this study is to find the effect of moisture transfer through the semipermeable membrane on the condensation/frosting limit. It is found that the semipermeable membrane has a lower condensation/frosting limit, due to the moisture transfer through the semipermeable membrane, which dehumidifies the air flow. For a given Wair, the surface temperature can be approximately 5 to 8 °C lower when using a semipermeable membrane, compared to an impermeable plate, before condensation/frosting occurs. Furthermore, it is shown that at some operating conditions, frost appears on the semipermeable membrane only at the air flow entrance of the test section, while the impermeable plate was fully covered with frost at the same operating conditions. Moreover, it is shown that increasing the moisture transfer rate through the semipermeable membrane decreases the frosting limit and delays frost formation.

scholarly journals Experimental Study and Performance Analysis of a Portable Atmospheric Water Generator

Energies ◽  
2019 ◽  
Vol 13 (1) ◽  
pp. 73 ◽  
Author(s):  
Wei He ◽  
Pengkun Yu ◽  
Zhongting Hu ◽  
Song Lv ◽  
Minghui Qin ◽  
...  
Keyword(s):  
Flow Rate ◽  
Reference Model ◽  
Air Flow ◽  
Operating Conditions ◽  
Water Yield ◽  
Air Humidity ◽  
Air Flow Rate ◽  
Thermoelectric Coolers ◽  
And Performance ◽  
The Impact

Found in some specific scenarios, drinking water is hard for people to get, such as during expeditions and scientific investigations. First, a novel water generator with only two thermoelectric coolers (Model A) is designed for extracting water from atmospheric vapor and then experimentally studied under a small inlet air flow rate. The impact of operating conditions on surface temperatures of cold/hot sides and water yield are investigated, including the air flow rate and humidity. Alternately, to determine the super performance of Model A, a comparative experiment between Model A and a reference model (Model B) is carried out. The results suggest that both the cold/hot temperature and water yield in Model A increases with the humidity and air flow rate rising. Seen in comparisons of Model A and Model B, it is found that, at an air humidity of 90% and air flow rate of 30 m3/h, the total water yield was increased by 43.4% and the corresponding value reached the maximum increment of 66.7% at an air humidity of 60% and air flow rate of 30 m3/h. These features demonstrate the advantage of Model A especially in low air humidity compared to Model B.

Experimental Study of Dehumidification Process by CaCl2 Liquid Desiccant Containing CuO Nanoparticles

2020 ◽  
Vol 28 (01) ◽  
pp. 2050009
Author(s):  
Nader Shoaib ◽  
Zahra Arab Aboosadi ◽  
Nadia Esfandiari ◽  
Bizhan Honarvar
Keyword(s):  
Experimental Study ◽  
Air Conditioning ◽  
Copper Oxide Nanoparticles ◽  
Cuo Nanoparticles ◽  
Operating Parameters ◽  
Air Humidity ◽  
Liquid Desiccant ◽  
Humidity Ratio ◽  
Cuo Nps ◽  
Simple Technology

A conditioning dehumidifier system is a simple technology to improve air quality and also reduces air conditioning costs. This experimental study evaluated the performance of a liquid desiccant system by adding copper oxide nanoparticles (NPs). The effect of operating parameters, such as inlet air humidity ratio and desiccant flow rate on air dehumidification rate, was also investigated. The desiccant solution contained 48[Formula: see text]wt.% CaCl2 and 0.35[Formula: see text]vol.% of CuO NPs. Comparison of liquid desiccants demonstrated a mean difference of 4.5[Formula: see text]g/s[Formula: see text][Formula: see text][Formula: see text]m2 in the air dehumidification rate by solutions with and without CuO NPs.

scholarly journals A Mathematical Model for Predicting the Performance of Liquid Desiccant Wheel

2017 ◽  
Vol 13 (2) ◽  
Keyword(s):  
Mathematical Model ◽  
Cooling System ◽  
Operating Conditions ◽  
Coefficient Of Performance ◽  
Cylindrical Shape ◽  
Liquid Desiccant ◽  
Humidity Ratio ◽  
Desiccant Wheel ◽  
Human Thermal Comfort ◽  
Wide Range

The liquid desiccant cooling system is found to be a good alternative of conventional air conditioning system for better control of both latent and sensible loads. The major component of a liquid desiccant cooling system is desiccant dehumidifier which controls the latent cooling load. In this paper a mathematical model for rotary type liquid desiccant dehumidifier commonly known as desiccant wheel has been presented. The desiccant wheel has a cylindrical shape with a number of identical narrow circular slots distributed uniformly over the rotor cross section. The slots are filled with a porous medium carrying the solution of liquid desiccant, to make the absorbing surface. The absorption and regeneration performance of the desiccant dehumidifier is discussed in this paper for different operating conditions. The wheel performance curves which help to determine the air outlet conditions and coefficient of performance (COP) of the system are drawn for a wide range of wheel thickness (0.06-0.6m), air mass flux (1-8 kg/m2 .s), and regeneration temperature (60- 85o C). A reduction of about 30% in outlet humidity ratio is observed with an increase in the wheel thickness from 0.06 to 0.2m. The computed results show that better supply air conditions can be obtained to provide human thermal comfort in the hot and humid climate with effectiveness of the system largely dependent on air flow rate, wheel thickness and humidity ratio of process air.

High resolution computation of compressible condensing/evaporating moist-air flow for external and internal flows

2013 ◽  
Vol 117 (1190) ◽  
pp. 427-444 ◽  
Author(s):  
S. Hamidi ◽  
M. J. Kermani
Keyword(s):  
High Resolution ◽  
Air Flow ◽  
Internal Flow ◽  
Operating Conditions ◽  
Numerical Code ◽  
Moist Air ◽  
Humidity Ratio ◽  
Low Humidity ◽  
External Flows ◽  
Pure Steam

Abstract In this paper computation of high resolution, compressible condensing/evaporating moist-air flow for a series of two-dimensional internal and external flows is performed. It has been observed that the inflow wetness content can change the aerothermodynamics of the flow field, e.g. the shock angles. In the case of flow expansion through nozzles, it has also been observed that the content of wetness at nozzles exit in the case of moist-air is more than five times higher than that of pure steam under similar operating conditions. The reason is due to the internal flow of heat from steam portion toward air that accelerates the steam condensation rate. The solver is spatially third- and temporally second-order accurate. Validations of the numerical code are performed versus the experimental data of Moore et al (1973) in the case of very large humidity ratio, ω→∞ (pure steam). Also in the case of low humidity ratio, ω→0 (dry air), the exact solution of shock tube and wedge cases are used to validate our numerical results.

Nitrogen Removal from Anaerobically-Treated Leachate

1984 ◽  
Vol 19 (1) ◽  
pp. 87-100
Author(s):  
D. Prasad ◽  
J.G. Henry ◽  
P. Elefsiniotis
Keyword(s):  
Nitrogen Removal ◽  
Air Flow ◽  
Operating Conditions ◽  
Air Flow Rate ◽  
Flow Rates ◽  
Anaerobic Filter ◽  
Ph Values ◽  
Wide Range ◽  
Ammonia Desorption ◽  
Effects Of Ph

Abstract Laboratory studies were conducted to demonstrate the effectiveness of diffused aeration for the removal of ammonia from the effluent of an anaerobic filter treating leachate. The effects of pH, temperature and air flow on the process were studied. The coefficient of desorption of ammonia, KD for the anaerobic filter effluent (TKN 75 mg/L with NH3-N 88%) was determined at pH values of 9, 10 and 11, temperatures of 10, 15, 20, 30 and 35°C, and air flow rates of 50, 120, and 190 cm3/sec/L. Results indicated that nitrogen removal from the effluent of anaerobic filters by ammonia desorption was feasible. Removals exceeding 90% were obtained with 8 hours aeration at pH of 10, a temperature of 20°C, and an air flow rate of 190 cm3/sec/L. Ammonia desorption coefficients, KD, determined at other temperatures and air flow rates can be used to predict ammonia removals under a wide range of operating conditions.

Determination of cost-efficient cooling power range for improving the performance of internally cooled ultrasonic atomization liquid desiccant dehumidifiers

2020 ◽  
Vol 29 (9) ◽  
pp. 1260-1276
Author(s):  
Zili Yang ◽  
Lu-An Chen ◽  
Ruiyang Tao ◽  
Ke Zhong
Keyword(s):  
Power Efficiency ◽  
Removal Rate ◽  
Operating Conditions ◽  
Cooling Power ◽  
Internal Cooling ◽  
Liquid Desiccant ◽  
Improvement Rate ◽  
Ultrasonic Atomization ◽  
Internally Cooled ◽  
Cost Efficient

Liquid desiccant dehumidifiers (LDDs) can be improved by adding internal cooling. However, the addition of excessive cooling power may deteriorate the system‘s cost-efficiency, whereas the addition of insufficient cooling power leads to negligible performance improvements. The objective of this study is to determine the suitable cost-efficient cooling power range for improving the performance of internally cooled LDDs (IC-LDDs). A novel method and a set of criteria related to the moisture removal rate, cooling-power efficiency ( ηc) and coefficient of dehumidification performance from cooling power ( DCOPcooling) were proposed to determine cost-efficient cooling power. The internally cooled ultrasonic atomization liquid desiccant system (IC-UADS), together with a well-validated model based on the conservation laws of mass and energy and the sensible heat balance, was adopted to demonstrate the analysis. The results showed that, although the dehumidification performance improves with increasing cooling power, the improvement rate decreases, while ηcand DCOPcoolingdecline quickly (by 87.9%). For cost-efficient improvement, the necessary power proportion of internal cooling to the system‘s target dehumidification capacity tends to be stable, which was about 29% for the IC-UADS, and independent of the operating conditions. The results may help to determine the reasonable cooling power range for cost-efficient improvement of IC-LDDs.

Performance Definitions for Three-Fluid Heat and Moisture Exchangers

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Mohamed R. H. Abdel-Salam ◽  
Robert W. Besant ◽  
Carey J. Simonson
Keyword(s):  
Moisture Transfer ◽  
Operating Conditions ◽  
Air Cooling ◽  
Heat And Moisture Exchanger ◽  
Moisture Exchanger ◽  
Heat And Moisture Exchangers ◽  
Overall Performance ◽  
Liquid Heat ◽  
Heat And Moisture ◽  
Design And Testing

This paper presents performance definitions for calculating the overall effectiveness of three-fluid heat and moisture exchangers. The three-fluid heat and moisture exchanger considered in this paper is a combination of a liquid-to-liquid heat exchanger for heat transfer between a desiccant solution and a refrigerant and an energy exchanger for heat and moisture transfer between desiccant solution and air streams. The performance definitions presented in this paper are used to calculate the overall sensible and latent effectivenesses of a three-fluid heat and moisture exchanger, which has been tested under air cooling and dehumidifying operating conditions in a previous work (Abdel-Salam et al., 2016, “Design and Testing of a Novel 3-Fluid Liquid-to-Air Membrane Energy Exchanger (3-Fluid LAMEE),” Int. J. Heat Mass Transfer, 92, pp. 312–329). The effectiveness of this three-fluid heat and moisture exchanger is compared when calculated using the traditional energy exchanger effectiveness equations and the overall performance definitions. Results show that the overall performance definitions provide effectiveness values that are less sensitive to changes in the inlet refrigerant temperature and therefore are more generally applicable for energy exchanger design than the traditional effectiveness equations used in the literature.

scholarly journals Optimized Thermal Efficiency of Rotor and Stator Using CFD

2020 ◽  
Vol 6 (6) ◽  
pp. 29-37
Author(s):  
Md. Shahwaz Hussain ◽  
Sujata Pouranik
Keyword(s):  
Temperature Distribution ◽  
Air Flow ◽  
Operating Conditions ◽  
Electrical Machine ◽  
Total Efficiency ◽  
Transfer Pattern ◽  
Turbulence Effect ◽  
Total Temperature ◽  
Simulation Results ◽  
And Performance

The space between rotor and stator plays a very important role in the design and performance of rotating machinery. The thickness of the gap can vary considerably depending on the size and operating conditions for the different types of rotating machines. Analysis the air velocity and temperature distribution over the air flow gap in stator and motor. Changing the design of rotor to develop turbulence in air flow gap. Compare the velocity and temperature distribution of proposed design with previous studies. The simulation results pinpoint also the periodic heat transfer pattern from the rotor surface and this provides useful information for the prediction of the temperature distribution inside the rotating electrical machine. The simulation results of case-1 show about 117°C temperature inside the rotor machine. Then increase the number of slot inside the rotor machine the total temperature of the rotor machine decreases up to 76°C. Due to low temperature total efficiency of the system increases. And also reduces the loss due to heat. The turbulence effect inside the rotor increase in third case. Due to turbulence effect the air cover large amount of area inside the rotor. So total temperature of the rotor casing decreases. In a system where volume is held constant, there is a direct relationship between Pressure and Temperature. For this case, when the pressure increases then the temperature also increases. When the pressure decreases, then the temperature decreases. So pressure in third case decrease upto1.26Pa and temperature 76 °C.

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