Inlet Air Humidity Research Articles

Development and verification of a novel design space and improved scale-up procedure for fluid bed granulation using a mechanistic model

A mechanistic model has been developed for scale-up of batch fluid bed (top spray) granulation, leading to a design space which was verified against experimental data at pilot-plant and commercial scales. Current published models fail to give reliable scale-up. The process is very sensitive to operating conditions, and intermittent spray and air flow during filter bag shaking is shown to substantially affect moisture content and the final granule properties. Three parameters (inlet air temperature, flow rate and humidity) are consolidated into a composite parameter Qair which, in combination with solution spray rate msol, gives a two-dimensional design space which is typically trapezoidal. Peak moisture content influences final granule attributes and depends on the ratio Qair/msol. Scale-up and product transfer between different equipment are predicted. The model has been applied to an actual pharmaceutical product, achieving robust product quality at commercial scale, and incorporated into a successful regulatory filing submission.

Airside thermal and hydraulic characteristics of compact bare tube heat exchanger under dry and wet conditions

An experimental study was conducted to investigate the thermal and hydraulic performance of a compact bare tube heat exchanger, under both dry and wet condition. Chilton–Colburn j and f power law correlations were developed for Reynolds number range of 562–1266. Discrepancies between experimental data and new correlations are within ±2%. In wet mode, experimental conditions were varied by two inlet air humidity levels, three air flow rates and three water flow rates. From the experimental results, it was found that the heat transfer performance (j factor) and friction (f factor) decrease as air flow rate increases. Heat transfer performance decreases and friction increases slightly as inlet air humidity increases. But the changes are insensitive. Mass transfer (jm factor) slightly decreases as air humidity increases. The effect of inlet air humidity, air flow rate and water flow rate on total heat transfer capacity, sensible heat, latent heat and pressure drop are discussed. Chilton–Colburn j, jm and f power law correlations were developed for Reynolds number range of 315–1080 under wet condition, with maximum deviation of ±10%, ±7% and ±7%.

State-space model for transient behavior of membrane-based liquid desiccant dehumidifier

In this paper, a state-space model for a membrane-based liquid desiccant dehumidifier with counter-flow configuration was developed and validated experimentally. Compared with experimental data, the maximum relative error of model results is less than 2%, and the mean relative error is about 1%, which indicates that the state-space model can well predict the transient characteristics of the membrane-based liquid desiccant dehumidifier. Further, the transient responses of the dehumidifier to the step changes of inlet parameters (air temperature and humidity, air flow rate, solution temperature and flow rate) were investigated in detail. This dynamic model can clearly reflect the transient relationships among input, state and output variables. It was found that the effect of perturbation of the inlet air temperature on the moisture transfer in the membrane-based dehumidifier was too small to be neglected, and the variation of the inlet air humidity had little effect on the heat transfer. The response time constant of the outlet solution temperature to the inlet perturbations was obviously larger than that of the outlet air temperature and humidity. The air and the solution flow rate can be taken as the controllable parameters for the outlet air humidity control of membrane-based liquid desiccant dehumidifier. With the advantages of short calculation time and simple solving process, the state-space model is helpful for the control design and the optimization of the membrane-based liquid desiccant dehumidifier.

Performance prediction of the combined cycle power plant with inlet air heating under part load conditions

A combined cycle power plant with inlet air heating (CCPP-IAH) system is proposed to solve the problems of ice and humidity blockages in winter climate. The performance of the CCPP-IAH system under part load conditions is analyzed via both experimental and simulation methods. The application of the inlet air heating technology significantly improves the part load efficiency and enhances the operational safety of the combined cycle power plant under complex meteorological conditions. Results show that a higher inlet air temperature will contribute a lower gas turbine thermal efficiency for proposed system. However, the heated inlet air by the recovered energy in heat recovery steam generator raises efficiencies for both the heat recovery steam generator and the overall system. The fuel consumption drops by 0.02 kg/s and 0.03 kg/s under the power load of 65% and 80%, respectively. The inlet air humidity decrease to 30% under the heated inlet air temperature of 303 K. Moreover, the exergy destruction for both Brayton cycle part and Rankine cycle part decrease with the inlet air temperature increasing. The daily fossil fuel will raise up to 2.9 ton/day and to 5.1 ton/day under the power load of 65% and 80%, respectively. The annual economic benefit from energy saving is more than $ 5.88 × 105 and the payback period is less than 3 years.

Optimal operating conditions of a hybrid humidification-dehumidification and heat pump desalination system with multi-objective particle swarm algorithm

Hybrid humidification-dehumidification (HDH) and heat pump desalination system is a newly developed type of desalination plant. The hybrid system is entirely driven by electricity, and therefore, it is essential to investigate its optimal operation for certain optimization targets. In the present work, the multi-objective particle swarm optimization (MOPSO) algorithm is introduced to discover the optimal operation of a hybrid HDH and heat pump desalination system. Based on a mathematical model of the hybrid system, multi-objective optimization is performed to obtain the optimal air flow rate and seawater flow rate in terms of the maximum system production rate, minimum unit cost of fresh water and maximum gained output ratio (GOR). It can be concluded that the inlet air temperature has insignificant impact on the optimization objectives. As the inlet air humidity ratio increases within the concerned range, the increment of optimized system production rate as well as GOR are 3.79% and 4.15% respectively, and the decrement of fresh water cost is 8.50%. The variation tendencies of optimization objectives with increasing inlet seawater temperature are similar to those with increasing inlet air humidity ratio. It is also revealed that a near-linear relationship exists between the optimized cost and electricity price.

Energy efficiency of exhaust air heat recovery while controlling building air humidity: A case study

One modern method of lowering building energy use is heat exchange between outgoing and incoming air. Exhaust air moisture (partly) condenses in the heat exchanger, giving liquid water to be removed. With low absolute humidity of inlet air especially at low outdoor temperatures, a significant drying effect results for the air inside the building. Increasing air humidity by, for example, spraying water or increasing watering of plants will give an energy penalty. This paper presents an analysis of the energy efficiency (recovered versus input exergy) of a modern house equipped an exhaust air heat recovery system and external heating supplied by a geothermal heat pump. Indoor temperature is 22 °C and relative humidity is 50 or 30%. Temperature and humidity of inlet air and ventilation flow rates are variable and the effects on power use by the heat pump are assessed. Results show that without moisture recirculation a water loss up to 1 kg/h from the building may occur. Several kWh of electricity may be consumed daily by a (geothermal) heat pump supplying heat depending on outdoor temperature, and indoor and outdoor air humidity. Besides water consumption, this may imply 10–15% of total electricity use.

Studies on cocopeat, sawdust and dried cow dung as desiccant for evaporative cooling system

The aim of the present study was to investigate the ability of natural materials, such as dried cow dung, cocopeat, and sawdust to be used as a desiccant in the evaporative cooling system to reduce the inlet air humidity. Moisture sorption and desorption characteristics of these natural materials were found out and also compared with that of silica gel. These materials were tested in different air conditions to know the sorption (28° C-85% RH, 28° C-60% RH, 33° C-60% RH) and desorption characteristics (50° C-10% RH). The materials' behavior in different humidity with the same temperature; and the same humidity with different temperature was also studied. These natural materials were studied to replace costly chemical desiccants, such as silica gel, zeolites, etc. Experimental results confirmed that cocopeat and dried cow dung have the potential to replace the chemical desiccants based on their sorption and desorption characteristics while sawdust was not found to have the desired characteristics of good desiccant. These natural materials (considered as waste) are cheap, and their reutilization will also be helpful to minimize the waste management problem.

Dynamic modeling of liquid-desiccant regenerator based on a state–space method

The regenerator is the main energy-consuming component in a liquid-desiccant-based air-conditioning system. Highly efficient control of a regenerator in dynamic operating conditions can improve system performance and reduce system energy consumption. An accurate and reliable dynamic model of a regenerator is fundamental to understand its dynamic operation characteristics and design in a high-performance control system. In this study, a state–space based model of the dynamic operation characteristics of a liquid-desiccant regenerator was developed from the control point of view. In the modeling process, the relationship between the input and output variables was reflected by constructed state–space matrixes. An experimental validation of the proposed dynamic regenerator model showed the dynamic responses of the following three case studies: (1) increase of mass flow rate of inlet desiccant solution, (2) increase in inlet desiccant solution temperature, and (3) increase in inlet air temperature and humidity. The proposed state–space model accurately reflected the dynamic response process of regeneration under different disturbances and initial conditions. Comparison between the modeling and experimental results showed that the relative errors of the outlet air temperature/humidity and outlet desiccant solution temperature were less than 5%, and the mean relative errors of their variations were less than 15%, which validates the accuracy and reliability of the proposed state–space regenerator model. This novel model can be useful for further research on the dynamic operation characteristics of regenerators and the development of high-performance control systems.

Indoor thermal comfort assessment using PCM based storage system integrated with ceiling fan ventilation: Experimental design and response surface approach

The integration of Phase Change Materials (PCMs) in buildings as a potential method to improve indoor thermal comfort can be achieved via free cooling/heating approach. This paper presents the results of a study on indoor thermal comfort and energy efficiency regarding the PCM's positive role when applied to the new constructive solutions, inside a building with a ceiling fan-assisted ventilation system. The scope was driven to investigate the potential of the solution for overheating/overcooling mitigation. The thermal performance of the proposed system was experimentally evaluated by comparing the behaviour of a prototype test room (including PCM panel), with the behaviour of a similar prototype test room, in which no PCM was added. First the experiments are conducted in an artificial climate inside a laboratory environment chamber which was controlled by harmonic and linearly rising/falling temperature changing processes. Experiments were performed based on 5 level RSM CCD method to quantify the potential effects of using PCM panels and to determine individual/interactive effect of parameters on thermal discomfort index, PPD. Results indicate that minimum discomfort level can be achieved when inlet air temperature and humidity, fan rotating speed and PCM slab height and thickness were set to 29, 48%, 115 rpm, 31 cm and 2.6 cm, respectively. PPD was obtained 4.1% in the optimized condition. Then optimised tests rooms were subjected to realistic daily temperature profiles during winter and summer. In summer case, the experiments proved that the PCM application in one of the rooms lead to an overheating reduction of 13.83% representing a PCM efficiency of 56%. Under the winter condition during two months, the experiments showed proposed hybrid system can averagely reduce discomfort level around 2.61% corresponding a PCM efficiency of about 35.49%. Based on the results, proposed system have the potential to shift cooling/heating energy demand away from peak hours.

Nitrogen oxides reduction and performance enhancement of combustor with direct water injection and humidification of inlet air

In this study, nitrogen oxides emission reduction is investigated with humid combustion in a non-premixed combustion chamber of a gas turbine that burns natural gas using computational fluid dynamics. For humidification of the combustion chamber, two methods are studied: direct water injection into the combustion chamber and increasing the inlet air humidity. The mathematical model of combustion, governing equations, numerical method, and the combustion chamber properties are extensively discussed. The mathematical model is first validated. The two approaches are then simulated and compared for low water and steam flow rates. The results show that at the water to fuel ratio of about 1, direct water injection is 1.69 times more efficient than increasing inlet air humidity in reducing nitrogen oxide emission. Finally, it is concluded that direct water injection is appropriate at low flow rates (up to the fuel flow rate) and for situations where reducing nitrogen oxide emission is highly relevant. Furthermore, increasing the humidity of the inlet air up to 25% is suitable and increases the combustion efficiency and reduces pollutants, while the outlet temperature is not decreased too much.

Experimental analysis of dehumidification performance of counter and cross-flow liquid desiccant dehumidifiers

In a liquid desiccant dehumidifier, the air-to-solution flow direction plays an important role in the dehumidification performance and the physical size of the dehumidifier tower. In this research, the dehumidification performance of counter-flow and cross-flow liquid desiccant dehumidifiers were compared via a series of experiments carried out in the environmental test chamber. To predict the dehumidification performance of both flow type dehumidifiers in various operating conditions, empirical models returning the dehumidification effectiveness and the enthalpy effectiveness, which were adopted as performance indices, were also derived based on the experimental data. From the sensitivity analysis conducted by using the proposed empirical correlations, it was observed that when the inlet air humidity ratio increased from 10.1 g/kg to 22.7 g/kg, the dehumidification effectiveness and enthalpy effectiveness of the counter-flow liquid desiccant dehumidifier increased from 51.2% to 82.4% and 40.2% to 72.5%, respectively. Meanwhile, both effectiveness values of the cross-flow dehumidifier increased from 62.3% to 63.4% and 46.3% to 55.0%, respectively. Likewise, when inlet solution temperature varied from 15.2 to 31.1 °C, the dehumidification effectiveness and enthalpy effectiveness of the counter-flow type dehumidifier decreased from 71.7 to 45.4% and 64.4 to 47.3%, respectively, while those of a cross-flow type dehumidifier decreased from 65.3 to 54.8% and 55.8 to 45.2%. Consequently, one may conclude that the cross-flow liquid desiccant dehumidifier would provide relatively stable dehumidification performance regardless of the changes in operating parameter, but the cross-flow dehumidifier may have limited dehumidification performance, especially at the lower desiccant solution temperature and in highly humid process air conditions.

Effect of Desiccant Solution Temperature on Regeneration Performance of a Cross-Flow Regenerator

The purpose of this study is to investigate the effect of the inlet solution temperature on the performance of an adiabatic cross-flow regenerator using a lithium chloride (LiCl) aqueous solution, and to propose the optimal inlet solution temperature when operating this type of regenerator. In the experimental tests, the inlet solution temperature range varied from 50 to 90°C. The tests were carried out at 10°C intervals while the other conditions remained constant. The measurement parameters for the test were the inlet air dry-bulb temperature and humidity ratio, outlet air dry-bulb temperature and humidity ratio, air volume flow, solution density, and inlet and outlet solution temperatures. The regeneration effectiveness and coefficient of performance (COP) were selected to assess the heat and mass transfer performance of the cross-flow regenerator. The most important finding of this research was to determine the optimal solution inlet temperature in the cross-flow regenerator with the LiCl aqueous solution considering both the regenerator performance and energy consumption. The test results show that the recommended inlet solution temperature is 60°C, considering both regeneration effectiveness and COP.

Experimental and model based performance investigation of a solid desiccant wheel dehumidifier in subtropical climate

This paper presents real time performance analysis of a silica gel based desiccant wheel dehumidifier. Thermodynamic model is also validated through comparison under a wide range of operating conditions for subtropical climate conditions. Initially, a mathematical model is developed by using various set of equations for desiccant wheel dehumidifier in engineering equation solver. After-wards, a parametric analysis of the system is performed including various design and climate parameters such as: inlet air humidity ratio, inlet air temperature, regeneration inlet humidity ratio, regeneration temperature, and rotation speed of the wheel. Then, an experimental set-up of the system is established in Taxila Pakistan for the real-time performance assessment. The results revealed that the optimal rotation speed of desiccant wheel ranged from 15-17 rph. The maximum model based and experimental effectiveness is 0.45 and 0.43, respectively at re-generation temperature of 80°C. The maximum and minimum root mean square error values for effectiveness are 3.2% and 2.1%, respectively. Thus, the comparison between experimental and model results showed a good agreement.

Experimental investigation on closed-type heating tower using glycerol solution

A heating tower is a key component of a heating tower heat pump. To figure out the heat and mass transfer characteristics of a cross-flow closed-type heating tower (CCHT) using a glycerol solution, an experimental investigation was conducted. The effects of fluids’ parameters on the performance of the CCHT were studied, which indicated that its performance could be improved by increasing the air flow rate, the solution flow rate, the secondary refrigerant flow rate, the inlet air temperature, and the inlet air humidity ratio, while decreased with the increase in the inlet temperature of the secondary refrigerant and remained constant with the variation of the inlet solution concentration. Based on the results, correlations of heat and mass transfer coefficients for the CCHT were developed. In addition, a quantitative performance comparison between the glycerol solution and the CaCl2 solution was also conducted, which indicated that compared with the performance of the CCHT when using the CaCl2 solution, the total heat transfer capacity when using the glycerol solution was 1.3–1.7 times higher, while the latent heat ratio was 1.9–3.3 times larger.

Experimental study and correlations for heat and mass transfer coefficients in the dehumidifier of a frost-free heat pump system

Decreasing the humidity ratio of ambient air can effectively prevent the frosting on the evaporator and improve the heat capacity of heat pump in winter. This paper conducts an experimental study and theoretical analysis on the heat and mass transfer performance of the cross-flow dehumidifier in a frost-free heat pump system. A mathematical model for predicting the heat and mass transfer performance in the dehumidifier is developed, and solved by finite difference method. Experimental study is carried out to analyze the influence of key parameters, including inlet air temperature, humidity ratio and flow rate, solution temperature, concentration and flow rate, on the coupled heat and mass transfer performance under low temperature and humidity ratio conditions. Based on the mathematical models and experimental results, the correlations of heat and mass transfer coefficients are proposed, and the deviations are within ±20%. Moreover, the effects of the inlet conditions of the liquid desiccant and air on the heat and mass transfer performance are compared with the experimental results reported in literature.

Performance investigation of the cross-flow closed-type heat-source tower using experiments and an adaptive neuro-fuzzy inference system model

In this study, a cross-flow closed-type heat-source tower (CCHT) was designed and experiments were carried out under low ambient temperature conditions. Here, a robust heuristic approach for an analysis of the performance characteristics of the CCHT was proposed. The suggested approach consisted of an Adaptive Neuro-Fuzzy Inference System (ANFIS), which was developed and validated by conducting numerous experiments. To address the problem of balancing the predictive accuracy of the model against the number of input variables, the Non-dominated Sorted Genetic Algorithm II (NSGA II) was used. In addition, by considering the optimized number of input variables, a comparative study was conducted with two other models. The integration of the ANFIS and NSGA II was proposed as the foremost model for evaluating the performance characteristics of CCHTs. Ultimately, a sensitivity analysis was carried out by utilizing the suggested predictive model to provide a comprehensive vision of the CCHT for improved understanding. For instance, it was observed that with the increase in the air inlet temperature, air inlet humidity ratio, and solution inlet temperature, the air outlet humidity ratio gradually increased, while the increase in the solution concentration led to a decrease in the air outlet humidity ratio.

Thermodynamic performance analysis of direct evaporative cooling system for increased heat and mass transfer area

Abstract This paper demonstrates the thermodynamic performance analysis of direct evaporative cooling system by increasing sides of cooling media. In this paper, a different configuration of cooling media has been developed for determining the behaviour pattern of the direct evaporative cooling system based on performance characteristics using Aspen fibers media. The effect of inlet air temperature, humidity and mass flow rate of air has been discussed in detail by using the different configuration of cooling media. The result indicates that the saturation efficiency is approximately same for entire developed top flow and ordinary lateral flow configurations excluding triangle top flow configuration. The highest saturation efficiency were observed for triangle configuration 97% for case-I. Maximum saturation efficiency of the triangular configuration of an evaporative cooling system was found to be 97%, 88%, nil and 89% for case-I, case-II, case-III and case-IV respectively, over ordinary and other top flow DEC system.

The application of dehumidified air in rapeseed and honeydew honey spray drying - Process performance and powders properties considerations

Rapeseed and honeydew honey were spray dried by dehumidified air, with NUTRIOSE® as a drying carrier, to create a product with prebiotic properties, in line with current "clean label" trend. Because of the low inlet air humidity, drying temperature was decreased (inlet/outlet: 75/50 °C). Such an approach gave the possibility to reduce the amount of added carrier. Thus, honey powders containing 80% of honey solids were produced and characterized. Drying was performed with very high powder recovery (84.4–93.9%), especially in the variants containing 80% of honey solids. Although there were some differences in the physical properties between powders produced by the application of dehumidified air and by the traditional spray drying (but containing the same ratio of honey to carrier), the overall properties were comparable: low water content (below 2.5%) and low water activity (below 0.2), medium or high cohesiveness, high hygroscopicity (above 20%), bed porosity between 50 and 70%.

Experimental and numerical analysis on total heat recovery performance of an enthalpy wheel under high temperature high humidity working conditions

Enthalpy wheels (EWs) have been extensively used for total heat recovery from ventilation air. Despite there being many studies reporting on their performances under common working conditions with a small temperature and humidity ratio difference (ΔT < 20 °C, Δω < 15 g kg−1), there are few studies reporting on their performances under high temperature high humidity (HTHH) working conditions. This study aims to investigate the total heat recovery performance of an EW under HTHH working conditions. A mathematical model is established and validated to predict the performance. The effects of rotation speed, air inlet velocity, air inlet temperature, and air inlet humidity ratio on the total heat recovery performance are numericallyinvestigated, and performance comparisons between HTHH working conditions and other common working conditions are also carried out. The comparison results show that the EW performs better for total heat recovery under HTHH working conditions, with εtotal improving by 6% compared to common working conditions. The reasons behind the discrepancies are revealed by analyzing the distributions of temperature and humidity in the EW. This study is expected to be beneficial to design EWs to recover total heat from HTHH waste gas.

Visualized experimental investigation on cross-flow indirect evaporative cooler with condensation

In hot and humid regions, condensation will easily occur in the dry channels of indirect evaporative cooler (IEC) due to high dew point temperature of primary air. However, the visualized investigation on cross-flow IEC with condensation has seldom been reported by previous studies. Therefore, a visualized cross-flow IEC was constructed with a transparent cover plate for observing the condensation in a primary air channels. A series of experiment had been carried out to investigate the comprehensive performance of IEC under different inlet primary air temperature and humidity. The outlet primary air temperature, wb-effectiveness, water consumption rate, heat transfer rate and condensation rate were analysed in detail under non-condensation, partial condensation and total condensation cases. The experimental results showed that the turning point from non-condensation to partial condensation was 33.0 °C under relative humidity of 50%, 29.0 °C under relative humidity of 60% and partial condensation to total condensation was 35.0 °C under relative humidity of 70%, 30.0 °C under relative humidity of 80%, respectively. Condensation improved the outlet primary air temperature, total heat transfer, water consumption rate and condensation rate but lowered the wb-effectiveness. Furthermore, the thermal resistance of condensate film was non-ignorable because of thick water film.