Dew Point Effectiveness Research Articles

An Overview of Different Indirect and Semi-Indirect Evaporative Cooling System for Study Potency of Nanopore Skinless Bamboo as An Evaporative Cooling New Porous Material

The high energy consumption of compressor-based cooling system has prompted the researchers to study and develop non-compressor-based cooling system that less energy consumption, less environment damaging but still has high enough cooling performances. Indirect and semi indirect evaporative cooling system is the feasible non-compressor-based cooling systems that can reach the cooling performance required. These two evaporative cooling systems has some different in construction, porous material used, airflow scheme and secondary air-cooling method used for various applications. This paper would report the cooling performances achieved by those two-cooling systems in terms of cooling efficiency, cooling capacity, wet bulb effectiveness, dew point effectiveness, and temperature drop. Porous material used in indirect and semi-indirect evaporative cooling would be highlighted in terms of their type, size, thickness and any other feature. The introduction of nanopore skinless bamboo potency as a new porous material for either indirect or semi-indirect evaporative cooling would be described. In the future study of nanopore skinless bamboo, a surface morphology and several hygrothermal test including sorption, water vapor transmission, thermal conductivity test would be applied, before it utilizes as a new porous material for direct or semi indirect evaporative cooling.

Numerical Study and Optimization of a Combined Thermoelectric Assisted Indirect Evaporative Cooling System

This paper numerically investigates the performance of a novel combined cross-regenerative cross flow (C-RC) thermoelectric assisted indirect evaporative cooling (TIEC) system. This C-RC TIEC system combines the indirect evaporative cooling and thermoelectric cooling technologies. A heat and mass transfer model is developed to perform the performance analysis and optimization of this novel system. Performance comparison between the novel C-RC TIEC system and a regenerative cross flow TIEC system is conducted under various operating conditions. It is found that the novel system provides better performance with higher coefficient of performance (COP) and higher dew point effectiveness than the regenerative cross flow TIEC system, especially under smaller working current and smaller number of thermoelectric cooling modules. The performance optimization of the novel system is also made by investigating the influences of primary air parameters, three different mass flow rate ratios, as well as the length ratio of the left wet channel to the whole wet channel. The results show that there exist optimal mass flow rate ratios and wet channel length ratio resulting in the maximum COP.

Effect of dew point on hot-dip galvanizing behavior of a high-manganese TWIP steel for automotive application

The effect of dew points (− 50, − 10 and + 10 °C) on the galvanizing properties of a high-manganese twinning-induced plasticity (TWIP) steel was studied. Scanning electron microscopy (SEM), glow discharge optical emission spectrometry (GDOES) and X-ray photoelectron spectroscopy (XPS) were used for microscopic observation and qualitative analysis of the interfacial layer between the steel surface and the zinc layer after hot-dip galvanizing. SEM analysis results show that three different morphologies of metallic oxides are formed on the interfacial layer under the different dew points. GDOES results show that Al is present in the molten zinc, reacting with Fe on the steel surface to form Fe2Al5, which can increase the galvanizing properties. XPS results show that the valence states of Mn in the interfacial alloy layer are Mn2+ and Mn4+, and the valence states of Fe are Fe0, Fe2+ and Fe3+. The experimental results show that the hot-dip galvanizing performance is the best at − 10 °C and the formation of Mn and Fe intermetallic oxides has a bad effect on hot-dip galvanizing behavior of the high-manganese TWIP steel. The types of the formed surface oxides (MnO, Mn3O4, Mn2O3, FeO, and Fe2MnO4) on the surface of the steel sheet are confirmed. It can obtain the best hot-dip galvanizing performance of the high-manganese TWIP steel by controlling the dew point from − 10 to − 5 °C.

Comparative performance analysis of direct and desiccant assisted evaporative cooling systems using novel candidate materials

In the last decade, desiccant assisted evaporative cooling (DAEC) is emerging as an alternative air conditioning (A/c) method due to its low operating costs and environmental impacts. However, for enabling wider usage of this technology, new desiccant materials (DeMs) and evaporative cooling pad materials (ECPMs), which are low cost, natural and locally available, need to be sought.In this regard, present study aims experimental investigation of different natural ECPMs in a fixed-bed solid DAEC system, where vermiculite-calcium chloride (Vmc-CaCl2) composite is utilized as the desiccant material. The selected ECPMs were also tested in direct evaporative cooling (DIEC) mode without using the desiccant; thereby the performances of DIEC and DAEC processes with the use of different ECPMs were comparatively investigated.Comparative analysis of different materials in DIEC and DAEC processes showed that the DAEC provides between 17 and 62% higher cooling capacity (Q̇c) than DIEC. Furthermore, achieved wet-bulb (εwb) and dew point effectiveness (εdp) values were found 26–50% and 19–38% higher with DAEC for different materials. According to the testing results, wood chips (WoC) was found as the best performing ECPM in both DIEC and DAEC modes. With the use of this material, obtained εwb,ave, εdp,ave and Q̇c,ave in DAEC mode were found 50.6%, 52.5%, and 31.3% higher than EC, respectively.The cyclic performance analysis of DAEC also showed that; with the increasing charging temperature between 60 and 80 °C, moisture desorption rate rises from 6.60 to 15.27 g/min, while the system coefficient of performance (COP) drops in the range of 0.67–0.35.

The effect of Temperature, Dewpoint, and population density on COVID-19 transmission in the United States: a comparative study

The number of confirmed cases of COVID-19 peaked in the United States in the month of April, 2020 in the most populated cities. A study was done to assess if temperature, dewpoint, and population density in fifty cities had a significant effect on the number of confirmed cases of COVID-19 in the month of April. Temperature and Dewpoint data for the month of April were accessed from the National Oceanic and Atmospheric Administration (NOAA) and confirmed cases of COVID-19 was accessed from the CDC (Centers for Disease Control and Prevention). Pearson Correlation Coefficient and Multiple Regression statistical analyses were performed. COVID-19 cases in the fifty states largest cities were correlated with average temperature and dewpoint in April, as well as the city’s population density. For the Multiple Regression analysis the total number of COVID-19 cases in fifty cities served as the dependent variable and average temperature, average dewpoint, and population density comprised the predictor variables. Correlation coefficient statistics utilizing data for fifty largest cities in each state for COVID-19 cases and average temperature in April 2020 yielded an r of -.097 and P>.05; between COVID-19 and average dewpoint for April 2020 yielded an r of -.001 and P>.05, and COVID-19 and population density pairing yielded an r of .792 and P<.01 for respective cities. Multiple regression analysis yielded statistical significance for the population density variable only. This study demonstrated that cities population density had a significant effect on the number of COVID-19 cases in April 2020, and while both temperature and dewpoint resulted in a negative correlation in association with COVID-19 cases, results were not statistically significant. The seasonal uncertainty and high transmission rate of COVID-19 in the United States suggest that similar analyses should be replicated in the impending summer and winter months of 2020 to further delineate COVID-19 seasonal characteristics.

Effect of efficient multi-stage indirect evaporative cooling on performance of solar assisted desiccant air conditioning in different climatic zones.

Over the past decade, different variants of desiccant cooling system integrated with direct/indirect evaporative cooler(s) have been simulated and/or analyzed in specific climatic conditions under rather limited operating parameters and for limited durations of time. Complete seasonal and multi-climate performance analyses of solar desiccant cooling system integrated with efficient, indirect Maisotsenko Cycle based evaporative cooler, having combinational installations at process and/or regeneration sides, is rarely investigated and reported. In the current work, multiple configuration variants of solar desiccant cooling system, integrated with multi-stage indirect evaporative cooling technique based on Maisotsenko Cycle, having a designed cooling capacity of 50 kW are analyzed through a model-based transient simulation approach. Simulations are carried out for a complete typical summer season in northern hemisphere, starting from April to September, using TRNSYS in three different climatic zones including subtropical humid summer (Cfa), hot desert (Bwh) and hot semi-arid (Bsh) conditions. The three selected climatic zones cover around 20% of global world map hosting more than 37% of world population. Each configuration is analyzed in terms of wet bulb and dew point effectiveness using their respective cooling techniques, system’s thermal coefficient of performance, and solar fraction for each climate zone. It is seen that the configuration using IEC at both process and regeneration sides has the highest values of coefficient of performance and solar fraction in all selected climatic zones compared to others. The respective values of coefficient of performance is 2.28 and solar fraction of 23.84% observed in Bwh while coefficient of performance of 2.03 and solar fraction of 23.33% in Cfa; and coefficient of performance of 2.12 and solar fraction of 46.86% in Bsh climatic zones are noted. The increase of solar fraction in hot and arid climates are expected compared to Cfa. While the value of coefficient of performance for such a system is significantly improved and shows promising prospects to efficiently provide thermal comfort during summer seasons.

Analytical/experimental sensitivity study of key design and operational parameters of perforated Maisotsenko cooler based on novel wet-surface theory

Only one analytical model was previously proposed for multi-stage M-cycle cooler which is based on Sprayed-Water Theory in which the temperature of the wet plate was assumed constant, equal to water inlet temperature, (as the water flow rate was assumed so high). Said preliminary model was only able to predict outlet characteristics of the cooler (not parameters distribution along the cooler). This paper presents a new model for multi-stage M-cycle cooler based on the novel Wet-Surface theory in which the temperature of the wet-plate varies along the cooler (real working condition) and the model is able to generate the temperature/humidity distribution in addition to the outlet characteristics. The concept of the novel Wet-Surface theory and its potentials are discussed in the paper. Maximum theoretic cooling capacity of a given M-cycle cooler is obtained when it works based on Wet-Surface Theory. The model is experimentally validated with a unique test-rig and then the impacts of key operation and design parameters of multi-stage M-cycle cooler (i.e. inlet temperature, humidity ratio, mass flow rate, mass flow ratio, channel gap, channel length, channel height and the location of perforation) on its cooling characteristics (including outlet temperatures, outlet humidity ratio, wet-bulb effectiveness and dew-point effectiveness) are studied by the validated model.

Effect of Dew Point and Alloy Composition on Reactive Wetting of Hot Dip Galvanized Medium Manganese Lightweight Steel

For its application development, the medium manganese lightweight steel with 3 wt.% and 10 wt.% Mn contents was galvanized in continuous hot dip galvanizing (HDG) simulator and the process parameters on the production line were adopted. Combined with the experimental analysis and thermodynamic calculation, the effect of dew point and alloy composition on the reactive wetting of the steel was investigated. It was shown that MnO existed as a stable oxide for the medium Mn steel with 5 wt.% Al as long as Mn content exceeded 5.1 wt.%. The galvanizability of the steel with 10 wt.% Mn was deteriorated resulting from the formation of a thick and continuous external MnO layer, which had adverse effects on the wettability. MnO particles in the form of unstable phase can be found at the surface of 3Mn steel galvanized at dew point +10 °C. It distributed sparsely and the reactive wettability can be obtained by “bridging connection”, which mitigated the damage of external oxidation. Moreover, the lower dew point, the less tendency to form external oxide. Although the decrease of dew point to −30 °C had a certain benefit for coating quality, the galvanizing quality of 10Mn steel could not be improved due to the formation of a thick MnO layer. Therefore, the Mn content played a stronger role than dew point on the reactive wetting of hot dip galvanized medium manganese lightweight steel.

A Review of Recent Experimental and Theoretical Research of Dew Point Evaporative Coolers

Evaporative cooling is one of the techniques to lower the ambient air temperature according to the requirements. The technique includes the injection of moisture in the coming air, thus increasing its specific humidity. This technique can cool the air up to wet bulb temperature of the incoming air. In the recent past, the techniques are developed to lower the temperature of air without addition of moisture in the incoming air. These techniques demonstrate that the incoming air temperature can be approached near the dew point temperature of the incoming air. The present paper essentially focuses on the recent theoretical and experimental research of dew point evaporative coolers. Different flow configurations of heat exchange mediums, optimization of geometrical parameters, performance parameters (wet bulb and dew point effectiveness), energy efficiency ratio and energy saving potential are the key elements to study the prospects of dew point evaporative coolers over the conventional refrigeration systems operated by mechanical means. Dew point evaporative cooling technology is environmental friendly and has the potential in reducing the impact on earth due to global warming.

Towards a thermodynamically favorable dew point evaporative cooler via optimization

Dew point evaporative cooling is an essential alternative to conventional vapor compression chillers in air conditioning systems to reduce electricity consumption and carbon emission. In this paper, we propose a robust optimization framework of the dew point evaporative cooler towards favorable dew point effectiveness, cooling capacity and Coefficient of Performance (COP). Two optimization algorithms, i.e., multi-to-single-objective and multi-objective optimizations, are developed using genetic algorithm. Concurrently, a 2-D thermodynamic model is established for a counter-flow dew point evaporative cooler and coupled with the optimization algorithms. The model agrees well with the experimental tests on a cooler prototype, and the maximum discrepancy is within ±4.7%. The proposed optimization study is then carried out to investigate the ultimate objective functions and their corresponding decision variables. Key findings that have emerged from this study reveal that the multi-to-single-objective optimization is able to obtain appropriate objective functions according to predefined preference with less complexity and faster response, compared to a multi-objective optimization. The optimal channel length and working ratio are found to be constant in different scenarios, i.e., at 0.50 m and 0.40, respectively, hence they can be eliminated to reduce the number of decision variables.

Modelling of a dew-point effectiveness correlation for Maisotsenko cycle heat and mass exchanger

The Maisotsenko cycle heat and mass exchanger (HMX) has been proven to be a high-efficiency facility, which can be regarded as heat recovery to improve the efficiency of energy supply system or directly applied as an evaporative cooler. Many experimental tests and numerical simulations have been conducted to verify its performance and help to serve energy supply system simulation. However, it is impossible to conduct an experimental test over a wide range of working conditions and employing the numerical model for system simulation is also inconvenient. Therefore, the modelling of empirical correlations for the practical application of HMX becomes necessary. This paper conducts a detailed theoretical analysis of heat and mass transfer in HMX, and the influential dimensionless parameters on dew-point effectiveness were identified. A dew-point effectiveness correlation for HMX was proposed based on the detected parameters. The results indicated that the mean absolute deviations of the proposed correlation were 2.35% and 6.75% when compared with numerical simulation and experimental data respectively. The newly proposed correlation could be used directly to evaluate the performance of HMX or further benefit the system simulation when the HMX is used as heat recovery component.

Study of the thermal performance of a novel dew point evaporative cooler

Evaporative cooling has been proven to have higher efficiency than does mechanical vapor compression refrigeration. It has great energy saving potential, and it is also an environmentally friendly solution for air cooling systems. To improve its performance, a small size counter-cross-flow cooler coated with nylon fibers on the wet channel surface was proposed. Then, the impacts of the operating parameters on its thermal performance were analyzed. The results showed that the cooler coated with nylon fibers demonstrated better cooling performance. The dew point effectiveness of the polystyrene + nylon fiber (PS + NL) varied from 46.7% to 78.6%. Compared with previous studies, the effectiveness of the counter-cross-flow PS + NL evaporative cooler was close to that of counter-flow evaporative coolers and higher than that of cross-flow evaporative coolers. In addition, the counter-cross-flow PS + NL evaporative cooler may reduce the size and weight of the cooler while providing the same air flow rate. It would be a good solution for residential building precooling or air conditioning, improving the energy efficiency of the cooling system.

Proposal and month-wise performance evaluation of a novel dual-mode evaporative cooler

Three climatic zones (composite, hot-dry, hot-humid) cover most of the regions in India. Direct evaporative cooler is suitable for dry and indirect regenerative evaporative cooler is suitable for humid months. To avoid the use of two different coolers for the same purpose during the composite climate (significant seasonal variations of temperature and humidity), a novel two-in-one evaporative cooler is proposed and numerically investigated in this study. Proposed cooler takes advantage of both types of evaporative cooler and be operated in dual mode: acts as direct evaporative cooler for hot-dry and acts as regenerative indirect evaporative cooler for hot-wet seasons. The working of both modes (direct and regenerative) is explained with the help of a diagram. Effects of channels height and water flow rate on cooling capacity, wet bulb effectiveness, and dew point effectiveness are discussed. The month-wise performance of the proposed cooler is evaluated for five Indian cities (Bhopal, Lucknow and Varanasi of composite climate; Ahmedabad of hot-dry climate; Kolkata of hot-humid climate). Suitability of the modes in hot months (April to September) and cities are evaluated with the help of a psychometric chart. Study reveals that the proposed cooler can be effectively and economically used for composite climate.

A statistical model for dew point air cooler based on the multiple polynomial regression approach

Swift assessment of evaporative cooling systems has become a necessity in practical engineering applications of this advanced technology. This paper bypasses details of the performance process and pioneers in developing a statistical model based on the multiple polynomial regression (MPR) to predict the performance of a dew point cooling (DPC) system. Thousands of numerical and experimental data are explored and the statistical model is produced. The developed statistical model correlates the performance parameters with the key operational parameters, including the flow and geometric characteristics. The selected operational parameters are, intake air conditions, including temperature, relative humidity and flow rate as well as the working air fraction over the intake air, while cooling capacity, coefficient of performance (COP), pressure drop, dew point and wet-bulb effectiveness are selected as performance parameters. The considered geometric characteristics are channel height, channel interval and number of layers in heat and mass exchanger. The model with different polynomial degrees is assessed by R2, MRE and MSE metrics. The 8th degree polynomial model is selected. The maximum relative error of the cooling capacity, coefficient of performance, pressure drop, dew point and wet-bulb effectiveness are 6.1%, 7.54%, 0.07%, 3.54% and 2.53% respectively. Finally, as examples, the model is used to predict the performance of the DPC system in random operating conditions and in a dry climate i.e. Las Vegas. Model developed in this study would enable the swift prediction of the DPC system.

Selective Oxidation Behavior of Medium Manganese Steel in Hot-Dip Galvanizing Process

Surface oxides of medium manganese steel treated under different hot-dip galvanizing processes were analyzed by X-ray photoelectron spectroscopy, scanning electron microscope microscopy and energy dispersive spectrometer techniques. Combined with thermodynamic calculation, the effects of dew point and alloying elements on the formation of oxides were investigated. It was shown that many oxides such as Cr2O3 and Al2O3, which deteriorate galvanizing performance largely, were formed at lower dew point, and that the formation of Cr and Al oxides could be effectively inhibited at higher dew point. It was also shown that the formation of MnO could be controlled by regulating the rate of Al/Mn in the composition of experimental steel, thus reducing the surface defect.

Integrated hollow porous ceramic cuboids-finned heat pipes evaporative cooling system: Numerical modelling and experimental validation

The work presented in this paper investigates design, computer modelling and testing of a sub-wet bulb temperature evaporative cooling system for space air conditioning in buildings. The target application of evaporative cooling technology is particularly for geographical regions with hot and dry climate. A laboratory prototype made of integrated finned heat pipes and a water filled hollow porous ceramic cuboids was been built and tested. The design exploits the high thermal conductivity of heat pipes as effective heat transfer device and the good wettability characteristic of porous ceramic material. Key thermal performance metrics of the prototype were modelled and validated experimentally under controlled laboratory conditions of temperature (30, 35 and 40 °C) and relative humidity (35–55%). Under typical dry climates conditions (ambient air dry bulb temperature of 35 °C and relative humidity of 35%), the measured supply air dry bulb temperature was 22.3 °C, which is lower that the ambient air wet bulb temperature, and maximum cooling capacity of approximately 196 W per unit surface area (m2) of wet porous ceramic cuboid. Furthermore, it was shown that the measured prototype cooler wet bulb effectiveness was 1.05 while the dew point effectiveness was 0.73.

Approaches to energy efficiency in air conditioning: A comparative study on purge configurations for indirect evaporative cooling

This paper presents a mathematical model to enable a more in-depth understanding of the combined heat and mass transfer processes of a counter-flow indirect evaporative cooler operating in semi-arid regions. A series of simulation was conducted to compare the performances between a single-purge and four-purge configurations. Furthermore, the effect of several parameters on the performance of the single-purge configuration was investigated under the baseline condition. The developed model was validated against experimental data from literature to within 2% discrepancy. Key results revealed that the single-purge configuration produced higher cooling capacity (around 20% higher), as well as higher dew-point effectiveness under the same operating conditions. A parametric study was also made on the single-purge configuration. The results revealed that lower product air temperature and higher dew-point effectiveness were achieved with longer channel length and larger purge ratio. However, the maximum cooling capacity approached its maximum with longer channel length and 35% purge ratio.

Thermal Performance Enhancement of a Cross-Flow-Type Maisotsenko Heat and Mass Exchanger Using Various Nanofluids

The incorporation of a Maisotsenko (M) Cycle into an indirect evaporative cooler has led to the achievement of sub-wet bulb temperature without any humidification, thus making it a possible green and sustainable alternative for handling the cooling load of a building. In this work, the thermal performance of a cross-flow heat and mass exchanger (HMX) is enhanced by the addition of nanoparticles in the wet channel because they significantly influence the heat and mass transfer characteristics of the base fluid. A governing model for the temperature and humidity variations of the HMX is numerically simulated. Initial benchmarking is achieved using water properties. Afterward, a comparative study is conducted using aluminum-oxide-, copper-oxide-, and titanium-oxide-based nanofluids. Enhancements of 24.2% in heat flux, 19.24% in wet bulb effectiveness, 7.04% in dew point effectiveness, 29.66% in cooling capacity, and 28.43% in energy efficiency ratio are observed by using alumina-based nanofluid as compared to water in the wet channel of the cross-flow HMX. Furthermore, a particle volume concentration of 1% and a particle diameter of 20nm are recommended for maximum performance.

Effect of Dew Point on Galvanizability in 4 Mass% Al Added Low Density Steel

Effect of Dew Point on Galvanizability in 4 Mass% Al Added Low Density Steel

Performance analysis of a novel thermoelectric assisted indirect evaporative cooling system

In this paper, a novel thermoelectric assisted indirect evaporative cooling system is proposed. Specifically, thermoelectric cooling (TEC) modules are sandwiched between channels of a flat plate cross flow indirect evaporative cooler. A mathematical model of the novel system is developed, and influences of main operating and geometrical parameters on the system's performance are analyzed in detail. Analytical results show that with the assistance of the thermoelectric cooling, the proposed system is able to cool primary air to a temperature much lower than inlet air wet bulb temperature, even dew-point temperature, meanwhile keep a relatively high coefficient of performance (COP), by selecting appropriate number and electric current of TEC modules. The dew point effectiveness and COP of the proposed system change monotonously with inlet mass flow rate, temperature and humidity ratio of primary air, respectively. The dew point effectiveness also varies monotonously with the mass flow rate ratio of secondary air to primary air. However, there exists an optimal mass flow rate ratio resulting in a maximum COP. Moreover, under variable number and electric current of TEC modules, there always exist optimal widths of primary air channel and secondary air channel, leading to a maximum COP.