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K J Chua - One of the best experts on this subject based on the ideXlab platform.

  • similarity analysis and comparative study on the performance of counter Flow dew point evaporative coolers with experimental validation
    Energy Conversion and Management, 2018
    Co-Authors: K J Chua
    Abstract:

    Abstract This paper entails a comparative study on the performance of counter-Flow dew point evaporative coolers with two different Configurations (type A and type B). Type A refers to the Flow Configuration where the supply air Flows parallel to the water film, while type B refers to the Flow Configuration where the supply air Flows counter to the water film. Both cooler types, when compared with a conventional indirect evaporative cooler, have better potential of lowering the product air temperature below its wet bulb temperature approaching the dew point temperature. A two-dimensional computational fluid dynamics model based on the continuity, momentum, energy and diffusion equations is firstly formulated and then employed to simulate the heat and mass transfer processes. The model, when validated with experimental date, shows a maximum discrepancy of 6.0%. A similarity analysis is then performed to structure the original governing equations of the model into dimensionless forms so as to evolve a fundamental platform that allows key dimensionless parameters to be determined. By regulating these key dimensionless parameters, distributions of the dew point and wet bulb effectiveness and the dimensionless product temperature are plotted via numerical simulation method. Additionally, key simulated data are regressed to obtain the empirical correlation of the dimensionless product air temperature. The key findings that emerged from the present study include: (1) the key dimensionless parameters that are essential to evaluate the performance of the counter-Flow dew point evaporative cooler are supply air Reynolds number, water Reynolds number, working air to supply air mass Flow rate ratio, water inlet dimensionless temperature, channel length to half width of dry channel ratio and half width of wet channel to half width of dry channel ratio; (2) comparatively, type B Configuration has a higher cooling effectiveness and lower product temperature than type A Configuration; and (3) the developed dimensionless product air temperature correlation for type B adhered closely to simulated results.

  • Numerical heat and mass transfer analysis of a cross-Flow indirect evaporative cooler with plates and flat tubes
    Heat and Mass Transfer, 2016
    Co-Authors: K J Chua, X. Cui, M. R. Islam
    Abstract:

    In this study the performance of an indirect evaporative cooling system (IECS) of cross-Flow Configuration is numerically investigated. Considering the variation of water film temperature along the Flowing path and the wettability of the wet channel, a two-dimensional theoretical model is developed to comprehensively describe the heat and mass transfer process involved in the system. After comparing the simulation results with available experimental data from literature, the deviation within ±5 % proves the accuracy and reliability of the proposed mathematical model. The simulation results of the plate type IECS indicate that the important parameters, such as dimension of plates, air properties, and surface wettability play a great effect on the cooling performance. The investigation of Flow pattern shows that cross-Flow Configuration of primary air with counter-Flow of secondary air and water film has a better cooling performance than that of the parallel-Flow pattern. Furthermore, the performance of a novel flat tube working as the separating medium is numerically investigated. Simulation results for this novel geometry indicate that the tube number, tube long axis and short axis length as well as tube length remarkably affect its cooling performance.

  • study on dew point evaporative cooling system with counter Flow Configuration
    Energy Conversion and Management, 2016
    Co-Authors: Kyaw Thu, R Z Wang, K J Chua
    Abstract:

    The authors gratefully acknowledge the generous funding from (1) the National Research Foundation (NRF) Singapore under the Competitive Research Programme (CRP) Funding Scheme (R-265-000-466-281), (2) the National Research Foundation (NRF) Singapore under the Energy Innovation Research Programme (EIRP) Funding Scheme (R-265-00-543-279), (3) the National Research Foundation Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) programme and (4) the China Scholarship Council (CSC).

  • study on dew point evaporative cooling system with counter Flow Configuration
    Energy Conversion and Management, 2016
    Co-Authors: Jie Lin, R Z Wang, Kyaw Thu, T D Bui, K J Chua
    Abstract:

    Abstract Dew point evaporative cooling has great potential as a disruptive process for sensible cooling of air below its entering wet bulb temperature. This paper presents an improved mathematical model for a single-stage dew point evaporative cooler in a counter-Flow Configuration. Longitudinal heat conduction and mass diffusion of the air streams, channel plate and water film, as well as the temperature difference between the plate and water film, are accounted for in the model. Predictions of the product air temperature are validated using three sets of experimental data within a discrepancy of 4%. The cooler’s heat and mass transfer process is analyzed in terms of its cooling capacity intensity, water evaporation intensity, and overall heat transfer coefficient along the channel. Parametric studies are conducted at different geometric and operating conditions. For the conditions evaluated, the study reveals that (1) the saturation point of the working air occurs at a fixed point regardless of the inlet air conditions, and it is mainly influenced by the working air ratio and channel height; (2) the intensity of the water evaporation approaches a minimum at 0.2 to 0.3 m from the entrance; (3) the wet channel can be separated into two zones, and the overall heat transfer coefficient is above 100 W/(m2·K) after the temperature of water film becomes higher than the working air temperature.

A Basile - One of the best experts on this subject based on the ideXlab platform.

  • an experimental study on bio ethanol steam reforming in a catalytic membrane reactor part ii reaction pressure sweep factor and whsv effects
    International Journal of Hydrogen Energy, 2010
    Co-Authors: A Iulianelli, S Liguori, T Longo, Silvano Tosti, P Pinacci, A Basile
    Abstract:

    Abstract A catalytic Pd–Ag membrane reactor has been packed with a Co–Al 2 O 3 catalyst to perform the ethanol steam reforming reaction using a simulated bio-ethanol mixture (H 2 O/C 2 H 5 OH feed molar ratio = 18.7/1). In Part I of this work, low hydrogen recovery (≤30%) and CO-free hydrogen yield (≤20%) were obtained. In this second study the influence of higher pressure and sweep-gas Flow rate was studied in order to improve the membrane reactor performances in terms of higher ethanol conversion, CO-free hydrogen yield and hydrogen recovery. The counter-current sweep-gas Flow Configuration was used for studying the effect of the reaction pressure and the sweep factor on the reaction system, while the co-current Flow Configuration was also considered for analysing the weight hourly space velocity effect. Moreover, a comparison with a traditional reactor working at the same MR operating conditions was also realized. As best results, the membrane reactor showed 100% ethanol conversion, 95.0% CO-free hydrogen recovery and ∼60.0% CO-free hydrogen yield, operating at 400 °C and 3.0 (abs) bar.

  • an experimental study on bio ethanol steam reforming in a catalytic membrane reactor part i temperature and sweep gas Flow Configuration effects
    International Journal of Hydrogen Energy, 2010
    Co-Authors: A Iulianelli, A Basile
    Abstract:

    Abstract A bio-ethanol mixture was used for carrying out the ethanol steam reforming (ESR) reaction in a Pd–Ag dense membrane reactor (MR) in order to produce a CO-free hydrogen stream. The MR was packed with a commercial Co-based catalyst and the experimental tests were performed between 250 and 400 °C, at 1.5 bar of reaction pressure and in both co-current and counter-current Flow Configurations. Experimental results in terms of ethanol conversion, products selectivities and CO-free hydrogen yield are reported as well as a discussion on the CO-free hydrogen stream recovered in the permeate side of the MR (directly suitable for feeding a PEM fuel cell system) is also presented. Moreover, a comparison with a traditional reactor (TR) working at the same MR operating conditions is realized, pointing out that the MR is able to give ethanol conversions higher than the TR in all the experimental tests realized in this work.

Shahab Moshari - One of the best experts on this subject based on the ideXlab platform.

  • numerical study of regenerative evaporative coolers for sub wet bulb cooling with cross and counter Flow Configuration
    Applied Thermal Engineering, 2015
    Co-Authors: Shahab Moshari, Ghassem Heidarinejad
    Abstract:

    Abstract In this study, the numerical simulations of Cross- and Counter-Flow Regenerative Evaporative Coolers (REC) and a Cross-Flow Indirect Evaporative Cooler (IEC) are presented, using one set of the governing equations. The governing equations of heat and mass transfer are discretized using Finite Difference Method (FDM) and solved by an iterative method in MATLAB. The numerical results of the presented simulation are validated for Cross Flow IEC, Cross and Counter Flow REC against experimental data, which resulted good agreement between aforementioned simulations and experimental data. The Numerical simulation shows contour plots of two-dimensional temperature across the exchanger for Cross-Flow REC with two directions of air Flows in wet channel. The impacts of pre-cooling the working air of REC are investigated and compared to a four-stage IEC, which shows that the Counter-Flow REC can produce the lowest temperature of the inlet air in comparing to both Cross-Flow REC (around 30%higher wet-bulb effectiveness) and four-stage IEC with the same air and exchanger parameters of this study. The impacts of the working air to total air ratio are also investigated for Counter-Flow REC which show that product air temperature decreases (10%–20% higher wet-bulb effectiveness) as the working air to total inlet air ratio increases (0.2 kg/kg–0.9 kg/kg).

  • novel modeling of an indirect evaporative cooling system with cross Flow Configuration
    Energy and Buildings, 2015
    Co-Authors: Ghassem Heidarinejad, Shahab Moshari
    Abstract:

    Abstract In this paper a new modeling of an indirect evaporative cooling system (IEC) with consideration of wall longitudinal heat conduction (LHC) and effect of spray water temperature variation along the exchanger surface in a cross-Flow Configuration is presented. The resultant coupled equations of heat and mass transfer are discretized using finite difference method (FDM) and solved by an iterative method. Comparing the numerical results of the presented simulation against experimental data revealed excellent agreement with them, this shows a small margin of error in the calculation (around 3%). After validation, this mathematical model is used in a two-stage system of indirect/direct evaporative cooling system, which shows that a two-stage indirect/direct evaporative cooling system in comparing to a one-stage IEC has around 50%higher wet-bulb effectiveness with the same parameters of inlet air and exchanger. Furthermore, the presented model is used for numerical simulation of a counter-Flow regenerative evaporative cooler which shows around 60%higher wet-bulb effectiveness in comparing to a one-stage IEC. The numerical results of this study show applicability of the presented model for both sub-and above-wet bulb cooling applications.

Ghassem Heidarinejad - One of the best experts on this subject based on the ideXlab platform.

  • numerical study of regenerative evaporative coolers for sub wet bulb cooling with cross and counter Flow Configuration
    Applied Thermal Engineering, 2015
    Co-Authors: Shahab Moshari, Ghassem Heidarinejad
    Abstract:

    Abstract In this study, the numerical simulations of Cross- and Counter-Flow Regenerative Evaporative Coolers (REC) and a Cross-Flow Indirect Evaporative Cooler (IEC) are presented, using one set of the governing equations. The governing equations of heat and mass transfer are discretized using Finite Difference Method (FDM) and solved by an iterative method in MATLAB. The numerical results of the presented simulation are validated for Cross Flow IEC, Cross and Counter Flow REC against experimental data, which resulted good agreement between aforementioned simulations and experimental data. The Numerical simulation shows contour plots of two-dimensional temperature across the exchanger for Cross-Flow REC with two directions of air Flows in wet channel. The impacts of pre-cooling the working air of REC are investigated and compared to a four-stage IEC, which shows that the Counter-Flow REC can produce the lowest temperature of the inlet air in comparing to both Cross-Flow REC (around 30%higher wet-bulb effectiveness) and four-stage IEC with the same air and exchanger parameters of this study. The impacts of the working air to total air ratio are also investigated for Counter-Flow REC which show that product air temperature decreases (10%–20% higher wet-bulb effectiveness) as the working air to total inlet air ratio increases (0.2 kg/kg–0.9 kg/kg).

  • novel modeling of an indirect evaporative cooling system with cross Flow Configuration
    Energy and Buildings, 2015
    Co-Authors: Ghassem Heidarinejad, Shahab Moshari
    Abstract:

    Abstract In this paper a new modeling of an indirect evaporative cooling system (IEC) with consideration of wall longitudinal heat conduction (LHC) and effect of spray water temperature variation along the exchanger surface in a cross-Flow Configuration is presented. The resultant coupled equations of heat and mass transfer are discretized using finite difference method (FDM) and solved by an iterative method. Comparing the numerical results of the presented simulation against experimental data revealed excellent agreement with them, this shows a small margin of error in the calculation (around 3%). After validation, this mathematical model is used in a two-stage system of indirect/direct evaporative cooling system, which shows that a two-stage indirect/direct evaporative cooling system in comparing to a one-stage IEC has around 50%higher wet-bulb effectiveness with the same parameters of inlet air and exchanger. Furthermore, the presented model is used for numerical simulation of a counter-Flow regenerative evaporative cooler which shows around 60%higher wet-bulb effectiveness in comparing to a one-stage IEC. The numerical results of this study show applicability of the presented model for both sub-and above-wet bulb cooling applications.

Kyaw Thu - One of the best experts on this subject based on the ideXlab platform.

  • study on dew point evaporative cooling system with counter Flow Configuration
    Energy Conversion and Management, 2016
    Co-Authors: Kyaw Thu, R Z Wang, K J Chua
    Abstract:

    The authors gratefully acknowledge the generous funding from (1) the National Research Foundation (NRF) Singapore under the Competitive Research Programme (CRP) Funding Scheme (R-265-000-466-281), (2) the National Research Foundation (NRF) Singapore under the Energy Innovation Research Programme (EIRP) Funding Scheme (R-265-00-543-279), (3) the National Research Foundation Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) programme and (4) the China Scholarship Council (CSC).

  • study on dew point evaporative cooling system with counter Flow Configuration
    Energy Conversion and Management, 2016
    Co-Authors: Jie Lin, R Z Wang, Kyaw Thu, T D Bui, K J Chua
    Abstract:

    Abstract Dew point evaporative cooling has great potential as a disruptive process for sensible cooling of air below its entering wet bulb temperature. This paper presents an improved mathematical model for a single-stage dew point evaporative cooler in a counter-Flow Configuration. Longitudinal heat conduction and mass diffusion of the air streams, channel plate and water film, as well as the temperature difference between the plate and water film, are accounted for in the model. Predictions of the product air temperature are validated using three sets of experimental data within a discrepancy of 4%. The cooler’s heat and mass transfer process is analyzed in terms of its cooling capacity intensity, water evaporation intensity, and overall heat transfer coefficient along the channel. Parametric studies are conducted at different geometric and operating conditions. For the conditions evaluated, the study reveals that (1) the saturation point of the working air occurs at a fixed point regardless of the inlet air conditions, and it is mainly influenced by the working air ratio and channel height; (2) the intensity of the water evaporation approaches a minimum at 0.2 to 0.3 m from the entrance; (3) the wet channel can be separated into two zones, and the overall heat transfer coefficient is above 100 W/(m2·K) after the temperature of water film becomes higher than the working air temperature.