Inlet Air Humidity Research Articles

Sensitivity analysis for the capacity improvement of a combined cycle power plant (100–600 MW)

Power improvement of a combined cycle power plant using inlet air cooling was analyzed in this paper. The corresponding CC capacities in a range of 100–600 MW were examined. The CC performance can be improved by decreasing an inlet air temperature and humidity to 15 °C (ISO) and 100% RH before entering air compressor of a gas turbine (GT). All year ambient temperature in Bangkok is normally higher than 15 °C. This research used a steam absorption chiller (AC) to cool intake air to the desired temperature level and no storage unit was needed. The CC uses a cooling tower (CT) for cooling purpose. In the 400 MW power plant as an example, it could increase the power output of the GT by 9.32% and the CC by 5.8%, while the ST power decreased by 3.42% annually, as some steam was supplied to the AC. In the economical analysis, the payback period (PB) will be in the range of 0.68–0.94 years, internal rate of return (IRR) 29–176%, and net present value (NPV) 116.5–154.63 MUS$. Additionally, sensitivity analysis concerning economic performance and environmental impact of the plants were also studied.

Heat and Mass Transfer in an Agitated Contact-Convective Heated Dryer

For the investigation of the drying process of a pharmaceutical fermentation waste and for determining specific heat and mass transfer coefficients an agitated contact-convective heated dryer was constructed. This dryer is also suitable for drying of other granular solids with high moisture content. Hence we investigated the drying of a by-product from bio-ethanol production, as well. The pilot-plant agitated dryer makes possible continuous measurement and data-acquisition. Data-acquisition of heated wall temperature, inlet and outlet air temperatures and humidity, mass reduction of the material makes possible the determination of transfer coefficients by the heat and mass balance of the dryer. The measured heat and mass transfer coefficients serve as proper input parameters for the simulation calculations.

Effect of compressive force on the performance of a proton exchange membrane fuel cell

The effect of the compressive force on the performance of a proton exchange membrane fuel cell has been examined experimentally. The performance has been evaluated on two polarization regions of the cell: ohmic and mass transport. Cell voltage and current density as a function of pressure were measured under constant load and various inlet air humidity conditions. The pressure distribution on the surface of the gas diffusion layer was measured using a pressure detection film and the results show that increasing the pressure improves the performance of the cell. The improvement of the cell voltage in the ohmic region was found to be greater than that in the mass transport region, whereas for the cell current density, the mass transport region exhibited higher change. The increase in the cell specific power in the ohmic and mass transport regions, as pressure increases from 0 to 2MNm-2, is estimated to be 9 and 18mWcm−2, respectively. However, the fuel cell performance in these two regions declined dramatically when excessive pressure (≥5 MNm−2) was applied. The mass transport region proved to be more susceptible to this sharp decline under excessive pressure than the ohmic region.

Bioenergy

For the investigation of the drying process of a pharmaceutical fermentation waste and for determining specific heat and mass transfer coefficients an agitated contact-convective heated dryer was constructed. This dryer is also suitable for drying of other granular solids with high moisture content. Hence we investigated the drying of a by-product from bio-ethanol production, as well. The pilot-plant agitated dryer makes possible continuous measurement and data-acquisition. Data-acquisition of heated wall temperature, inlet and outlet air temperatures and humidity, mass reduction of the material makes possible the determination of transfer coefficients by the heat and mass balance of the dryer. The measured heat and mass transfer coefficients serve as proper input parameters for the simulation calculations.

Novel description of a design space for fluidised bed granulation

The physical measurements of a fluid bed granulator can be exploited in construction of an operating window, a design space, for process performance. The purpose of this study was to determine the influence of inlet air humidity changes on temperature in different parts of a granulator system, on fluidisation behaviour and on the particle size of the final granules. A humidifying setup was constructed on a bench-scale fluid bed granulator that enabled elevated humidity levels and sharp humidity changes of the inlet air. Ibuprofen granules were produced at the various inlet air humidity levels classified as low, intermediate and high. A novel fluidisation parameter was developed. The more improperly the particles were fluidising the smaller was the relationship of airflow rate and fan speed. Four different failure modes were identified and classified, based on the fluidisation parameter: over-fluidisation, risk of improper fluidisation, improper fluidisation and collapsed bed. It was possible to construct process trajectories for smooth fluidisation, which the optimal granulation process should follow.

The development and performance evaluation of a cyclone train for the removal of contaminated hot particulate in a hot cell

A novel cyclone train was designed, fabricated and evaluated for the removal of hot particulate in a hot cell in this study. Scanning electron microscope (SEM) results show that contaminated hot particulate whose size ranged from 0.2 to 20 μm had adhered to the inner surface of a hot cell at Korea Atomic Energy Research Institute (KAERI). The developed cyclone train can be operated by a manipulator due to the higher radioactivity level in a hot cell. Collection efficiency of the cyclone was measured for different values of the inlet flow rate and the vortex finder length. It was found that the collection efficiency of the cyclone was considerably affected by the vortex finder length. A higher collection efficiency was measured with a vortex finder length of 49 mm, S/ D c = 0.64, and an inlet flow rate of 15 m/s was the best condition. Collection efficiencies were 70% for 1 μm and 97% for 10 μm, alumina mock particles at a vortex finder length of 49 mm and an inlet flow rate of 15 m/s. Measurements of the pressure drop indicate that lengthening the vortex finder length or shortening the cylinder height will both help to enhance the pressure drops of the cyclone. It is concluded that the flow in the cyclone is a turbulent flow on the basis of the Reynolds number, and that a turbulent flow causes a pressure drop in the cyclone. Value of S t k 50 1 / 2 decreased with an increase of the Reynolds number and gradually approached a constant value at a higher Reynolds number. As the temperature of the inlet air increased, the collection efficiency decreased slightly. The collection efficiency increased with an increase of the inlet air humidity in the cyclone.

A computational fluid dynamic study of a low‐humidity co‐current spray dryer

AbstractBecause spray drying uses high‐temperature gas as the drying medium and the deposits on the wall cannot be avoided in practical spray dryers, the products are subject to degradation by overheating. In order to reduce the degradation of the active components in the dried powder, a low‐dew‐point (LDP) spray dryer is proposed and evaluated via a computational fluid dynamic (CFD) model. A cylinder‐on‐cone spray dryer with pressure nozzle is investigated numerically with a commercial CFD code. The effects of low inlet air humidity and temperature on the gas flow patterns, droplet trajectories and overall dryer performance are investigated. The volumetric evaporation rate values, volumetric heat transfer intensity and thermal energy consumption per unit evaporation of water were computed and compared for evaporation of pure water in a spray chamber 2.215 m in diameter with a cylindrical top section 2.0 m high and a bottom cone 1.725 m high. Although a smaller product capacity is obtained compared with the normal spray dryer, it has advantages for drying heat‐sensitive materials. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd.

The second-law optimal operation of a paper drying machine

Paper drying is an exergy costly operation, so also a few percent saving may be of importance. The entropy production for the paper drying process was therefore optimised for a conventional multi-cylinder drying machine, the PM2 newsprint machine at Norske Skog ASA in Skogn, Norway. The machine has 51 cylinders grouped in three drying groups; the cylinders are either heated from the inside by steam, unheated or operated under vacuum conditions. The same inlet drying air is supplied in all upper air-pockets of the machine. Our drying model for the paper temperature profile was first compared with measured data from the machine. The total entropy production of the drying process was next calculated, and then minimised subject to a fixed outlet paper moisture content. Inlet humidity and cylinder group conditions were varied. Optimum conditions were obtained for a range of inlet air humidities, and for different cylinder groupings. We found that it was very favourable to increase the inlet air humidity. Other changes had a negligible effect on the total entropy production. The results further pointed to the need for a revision of the current paper drying model, as the second-law of thermodynamics was violated at high air humidities with this model.

Comparison of two non-equilibrium models for static grain deep-bed drying by numerical simulations

Non-equilibrium models of the grain stationary deep-bed drying are derived from the theoretical analysis of the physics of the drying process and consist of a set of four nonlinear partial differential equations describing, respectively, the moisture balance, air energy balance, grain energy balance and thin-layer drying rate. In these models, many authors simplify the physical description by neglecting the accumulation terms from the energy and moisture balance equations without a relevant justification. This simplification may reduce the complexity and computational time but depending of drying conditions can also reduce models’ accuracy. Accurate modelling of the drying process is a determining factor both for designing the drier, and for optimising its operation. In this paper, we use two non-equilibrium models to design two grain deep-bed drying computer codes. In the first, model 1, derived by Bakker-Arkema et al. [Bakker-Arkema, F. W., Bickert, W. G., & Patterson, R. J. (1967). Simultaneous heat and mass transfer during the cooling of a deep-bed of biological products under varying inlet air conditions. Journal of Agricultural Engineering Research, 12, 297–307] and also presented by Brooker et al. [Brooker, D. B., Bakker-Arkema, F. W., & Hall, C. W. (1974). Drying cereal grains. Westport, CT: AVI], the accumulation terms are kept, in the second, model 2, as assumed by these authors, these terms are neglected. Both models are discretized by second order semi-implicit schemes. We use these codes to simulate wheat static bed drying and we compare their predictions. We show that the transfer time, defined as the ratio of the bed height and the drying air velocity, and inlet air temperature and humidity are the main parameters which affect the behaviour of the deviation between the predictions of these models. We investigate the conditions allowing one to neglect the accumulation terms as in the model 1.

Experimental comparison of two honeycombed desiccant wheels fabricated with silica gel and composite desiccant material

Abstract Experimental comparison between two honeycombed desiccant wheels, namely, a conventional one treated with silica gel and a new one fabricated with a new kind of composite desiccant material, was made in this paper. It is found that the newly developed composite desiccant wheel performs better than the conventional one and can remove more moisture from air by approximately 50%. Also encouraging is that the new desiccant wheel can be driven by a lower regeneration temperature for acquiring the same amount of moisture removal. The reason is that the composite desiccant materials, which are constructed with LiCl and silica gel solutions in an optimal way, behave better than silica gel in moisture adsorption, according to the findings from the scanning electron microscope (SEM) pictures as well as the equilibrium adsorption test results. Some parameters, such as inlet air humidity, regeneration temperature, air mass flow rate, etc., which may affect the performance of the desiccant wheels, are also analyzed and discussed. It is further identified that the new composite desiccant wheel has potential for dehumidification applications in many fields.

Effects of potassium sulfide content in marine diesel fuel oil on emission characteristics of marine furnaces under varying humidity of inlet air

Degraded fuel oils are generally used in marine power plants for economic purposes, so as to reduce operating expenses. These marine fuel oils commonly contain various oxides or sulfide compounds of metallic elements in the fuel ash, and affect the combustion and emission characteristics of marine power plants to different extents. Moreover, marine power plants are more often operated in a highly humid environment. As a result the emission and burning process may also be altered by the various humidity level of the inlet air. The effects of potassium sulfide in marine diesel on the combustion and emission characteristics of marine furnaces under varying levels of relative humidity of inlet air were experimentally investigated in this study. A cylindrical industrial furnace made of AISI 316 stainless steel, and an automatic oil-fired burner were used for the emission characteristics measurements and observation. A mechanically homogenizing machine was used to stir potassium sulfide (K 2SO 4) powder and marine diesel with a preset K 2SO 4 concentration. The relative humidity of the inlet air and temperature were adjusted to their assigned values by a large-size air conditioner before being pumped into the burner. The marine diesel oil mixture was atomized by the inlet air consequently ignited by an electrode and then burned within the horizontal furnace. There were eight rectangular slots cut in the upper portion of the furnace wall so that the probes of a gas analyzer and a thermocouple could be inserted into radial positions in the cylindrical furnace. The concentrations of gas emission and burning gas temperature and the combustion efficiency were analyzed. The experimental results show that the burning gas temperature, carbon dioxide emission and combustion efficiency decreased when the concentrations of excess air and oxygen emission increased with the addition of potassium sulfide in the marine diesel fuel. This is primarily attributed to the fact that the sulfide of an alkali compound such as K 2SO 4 may suppress the oxidation reaction process, leading to inferior combustion characteristics.

Performance analysis of dehumidification rotating wheel using liquid desiccant

In the present work, theoretical and experimental evaluation of the effect of bed configuration and operating conditions on the performance of desiccant dehumidification system has been carried out. A new rotating absorption disk has been designed and constructed to be tested in the experimental work. The desiccant wheel has a cylindrical shape of 50-cm diameter and 10 cm thickness. The flow area of this bed is consisted of 350 narrow slots, which are uniformly distributed over the cross section of the cylindrical bed. Each slot has a cylindrical shape and constructed from a steel spring of 100 mm length and 20 mm inside diameter. To form the absorbing surface in the bed, each spring is coated with a thick cloth layer impregnated with lithium chloride solution, which is used as the working desiccant in these experiments. In the theoretical part of this study, a mathematical model has been developed where its output results are compared with the experimental data. The effect of different design parameters and operating conditions on the absorption and regeneration processes is discussed. The effect of regeneration air temperature, the process air and regeneration air inlet humidity, the rotational speed, the process and regeneration air velocity (or flow rates), the bed length, etc. on the amount of water absorbed/desorbed in a cycle is investigated. For the specific bed design parameters, actual recorded data show that an amount of 95 g of water can be absorbed in the absorption cycle per hour. This value changes with varying the operating conditions. From the theoretical investigation, it is found that at regeneration temperature of 85 °C, the amount of water absorbed is nearly equal to the amount of water desorbed (i.e. equilibrium condition) for a complete cycle. It is seen also that for moderate operating conditions (50% RH, 30 °C) and lower regeneration temperature which is suitable for solar energy application, the reduction in the humidity ratio of the process air reaches about 13% of its initial value. Finally, comparisons between theoretical and experimental results show good agreement.

Efficiency investigation of a new-design air solar plate collector used in a humidification–dehumidification desalination process

The aim of this research is to experimentally study the efficiency of a new-design plate collector used to heat air in a new desalination humidification–dehumidification process. In fact, in such processes, the air solar collectors work at unusual experimental parameters (forced convection, elevated air humidity, high solar irradiation…). At these stressed experimental conditions, few published works are available in literature. Furthermore, the comparison of the efficiency of collectors running with normal air humidity content (about 10–20 g kg −1) and air of elevated humidity (20–50 g kg −1) were not yet published as our knowledge. In the present investigation, a new air solar plate collector was designed and developed for its use in a desalination process. Moreover, a characterization of such collector was performed under different experimental conditions. The effect of different parameters, namely: the solar radiation, the wind velocity, the ambient temperature, the air mass flow rate, the inlet air humidity and temperature, on the collector efficiency was also investigated. The collector was optimized for its use in a new solar desalination process. In fact, the air solar collector was designed in order to lower its economic cost making them applicable for water desalination.

04/03136 Numerical studies and experimental observations of whirling flames: Snegirev, A. Y. et al. International of Journal Heat and Mass Transfer,2004, 47, (10–11), 2523–2539

Liquid-to-air membrane energy exchangers (LAMEEs) allow simultaneous heat and moisture transfer between salt solution flows and airflows. These exchangers can be used as air dehumidifiers for supply air or liquid desiccant regenerators in liquid desiccant air conditioning systems while the membrane eliminates entrainment of liquid desiccant as aerosols in air streams. In this study, the heat and mass transfer performance of a LAMEE used as dehumidifier and regenerator is experimentally and analytically investigated to determine the influences of air and desiccant solution flow rates, inlet air temperature and humidity, and inlet desiccant solution temperature and concentration. Using the experimental data, the analytical model for the counter-cross-flow LAMEEs is quantitatively validated for sensible and latent effectiveness during air dehumidification process for the inlet conditions tested, while agreement is not good for the salt solution regeneration or de-watering process. This discrepancy may be caused by the crystallization of LiCl aqueous solution within the membrane pores near the solution side of the membrane during the regeneration tests. The data implies that both the moisture flux ratios and the proximity of the solution concentration to the saturation concentration play a role for moisture transfer blockage within the membrane when the data for latent effectiveness is significantly below the theoretical values. The influences of inlet air and solution parameters on the mass transfer performances of the LAMEE used as dehumidifier and regenerator are also compared with those of direct-contact liquid desiccant devices available in the literature.

Effect of structured packing density on performance of air dehumidifier

Abstract An experimental study has been conducted to investigate the performance of a liquid desiccant air dehumidifier equipped with a structured packing made of wood for three different densities using triethylene glycol (TEG) as the liquid desiccant. The structured packing densities used were 77, 100 and 200 m2/m3. The performance of the dehumidifier was expressed in terms of the moisture removal rate and the dehumidifier effectiveness under different air and desiccant parameters, i.e. the air and TEG flow rates, air and TEG inlet temperatures, inlet air humidity and inlet TEG concentration. In general, the trend in the dehumidifier performance was similar to that reported by other investigators using random packing. The effect of packing density on moisture removal rate and dehumidifier effectiveness is assessed. The differences in the effectiveness of different packing densities are attributed to the wetting condition. Lower effectiveness of the column is shown with the packing density of 200 m2/m3 compared to the other two packing densities when the air flow rate, inlet concentration and desiccant flow rate are increased. However, higher effectiveness is shown when either the inlet temperature of the air or desiccant is increased.

Thermal analysis of cooling coils based on a dynamic model

A dynamic model that describes the cooling coils’ thermal qualities is developed and solved using the method of classical control theory. The dynamic relationships are obtained between the coil’s heat exchange and its five important parameters that include inlet air temperature, inlet air humidity, inlet water temperature, airflow rate and water flow rate. Experiments have been done to validate the model. Afterwards, simulations are made by the model to analyze the dynamic heat exchange of coils when some perturbations occur under different initial conditions. Then, some useful conclusions are drawn based on the analysis.

Predictions of moisture removal rate and dehumidification effectiveness for structured liquid desiccant air dehumidifier

In hot and humid climates such as in the Sultanate of Oman, the humidity puts extra load on the electric vapor-compression air conditioning (VAC) systems. Liquid and solid desiccants can reduce the moisture content of humid air and thus reduce the latent load imposed on the VAC systems. In the present work, the performance of air dehumidifiers using triethylene glygol (TEG) as desiccant was investigated. Three differently structured packing densities were used (77, 100 and 200 m 2/m 3). The performance of the dehumidifier was evaluated and expressed in terms of the moisture removal rate ( m cond) and the dehumidifier effectiveness ( ε y). The experimental work was undertaken to study the effects of several influencing design factors on this performance. The design factors covered included the air and TEG flow rates, air and TEG inlet temperatures, inlet air humidity and the inlet TEG concentration. The desiccant flow rate investigated was much less than that covered in previous studies and the range of the inlet temperatures of air and desiccant was significantly wider. The objective this study was to use the multiple regression method and the principal component analysis to obtain statistical prediction models for the water condensation rate and the dehumidification effectiveness in terms of these design factors. The results of both techniques agree with each other affirmed that the desiccant flow rate, desiccant inlet concentration and air inlet temperature are the most significant variables in predicting m cond, whereas desiccant flow rate, air inlet temperature and packing density are the most significant variables in predicting ε y.

A new process control strategy for aqueous film coating of pellets in fluidised bed.

The parameters with effect on maximum spray rate and maximum relative outlet air humidity when coating pellets in a fluidised bed were investigated. The tested variables include type of water based modified release film coating (Eudragit NE 30D, Eudragit RS 30D, Aquacoat ECD) coating principle (top spray, bottom spray), inlet air humidity and type of pellets (sugar spheres, microcrystalline cellulose pellets). The maximum spray rate was not influenced by the coating principles. The highest spray rate was obtained for the film polymer with the lowest tackiness which is assumed to be the controlling factor. The type of pellets affected the maximum spray rate. A thermodynamic model for the coating process is employed throughout the process and not just during steady state. The thermodynamic model is incorporated into a new process control strategy. The process control strategy is based on in-process calculation of degree of utilisation of the potential evaporation energy (DUE) of the outlet air and the relative outlet air humidity (RH). The spray rate is maximised using set points of DUE and RH as control parameters. The product temperature is controlled simultaneously by regulating the inlet air temperature.

Air dehumidification by triethylene glycol desiccant in a packed column

The performance of an air dehumidifier using triethylene glycol (TEG) as desiccant under hot and humid conditions was investigated. The performance of the dehumidifier was evaluated and expressed in terms of the moisture removal rate and the dehumidifier effectiveness. A packed bed column (dehumidifier) was employed, with low packing density (77 m 2/m 3), to provide direct contact between the air and the TEG. Two different structured packings were used, wood and aluminum. The experiments covered a wide range of parameter space that included the air and TEG flow rates, air and TEG inlet temperatures, inlet air humidity and inlet TEG concentration. The liquid flow rate investigated is much less than that covered in previous studies (<1 kg/m 2 s). The trend of the dehumidifier performance was similar to that reported in the literature using high density and random packing. The results were compared to the Chung and Luo correlation, which over predicted the effectiveness. The Martin and Goswami correlation failed to predict the effectiveness under the conditions of this study. In the present study, it was found that the moisture removal rate increased with increasing inlet TEG concentration, TEG flow rate and air flow rate. This was seen for both the wood and the aluminum packings. In addition, the moisture removal rate is increased with increasing the inlet air temperature for the aluminum packing only. The effectiveness of the column was increased by increasing the TEG flow rate and inlet TEG temperature for the two packings.

액체 건조제 제습을 위한 핀튜브형 재생기의 성능인자 영향 연구

Liquid desiccant dehumidification system can be used effectively to save energy consumed in air conditioning as an alternative compared with conventional air conditioning systems by reducing latent heat load. The dehumidifier and the regenerator form the heart of this system. The latent part of the cooling load is handled using liquid desiccant. In this study, the experimental regenerator has been designed to study the regeneration characteristics of the aqueous triethylene glycol(TEG) system. Thebr/ performance factors of the regenerator with finned tube heat exchanger were evaluated by a series ofbr/ experimental runs. The regeneration process is highly dependent on the liquid desiccant conditions, such as, temperature, concentration and flow rate. In addition, the effects of the inlet air temperature, humidity and flow rate were discussed. Data obtained are useful for design guidance and performance analysis of a regenerator, particularly for a liquid desiccant cooling system.br/