Primary Air Inlet Research Articles

Numerical Analysis on Performance Improvement of a Vertical Plate Indirect Evaporative Cooler with Baffles

The performance of the Plate Indirect Evaporative Cooler (PIEC) can be effectively improved by incorporating baffles in the dry channel. However, in the dimensional influence of the baffles on PIEC performance there remains a research gap. In order to investigate the impact of baffle dimensions on the wet bulb efficiency, namely the average heat transfer coefficient and the cooling capacity of the PIEC, this paper proposed and verified a three-dimensional numerical model and method based on the species transport model and the Euler wall film model. At the same time, in order to obtain the equilibrium point between the enhanced heat transfer performance and the additional resistance induced by baffles, a comprehensive performance evaluation index is introduced. The results indicate that, under the same conditions, (1) the baffle effect on PIEC performance is significant at a lower inlet air velocity, and the wet bulb efficiency of the PIEC with baffles can be improved by 22.8%; (2) the baffle effect on PIEC performance is negative if its relative length exceeds 60% or the primary air inlet velocity surpasses 4 m/s under the conditions specified in this paper; and (3) the baffle effect on PIEC performance is significant when its channel height is lower and its channel width is larger, and the wet bulb efficiency of the PIEC with baffles can be improved by 29.3%.

Experiments and modeling on thermal performance evaluation of standalone and M-cycle based desiccant air-conditioning systems

This study aims to evaluate the performance of standalone and Maisotsenko-cycle based desiccant air-conditioning systems with silica gel through experimental and explainable artificial intelligence methods. In order to examine the desiccant systems' performance, deep neural networks have been constructed based on the optimal hyper-parameters provided by the Bayesian surrogacy. The influential factors, such as regeneration air temperature and relative humidity, primary air temperature and relative humidity, among other system features like regeneration temperature and humidity, are chosen as the inputs using feature engineering and correlation heat maps. The results indicated that with the right framework and training data, the proposed model can forecast the performance of the standalone and M-cycle-based desiccant air conditioning systems with a great accuracy (i.e. R2 = 0.99). In addition, regeneration temperature and humidity, and inlet regeneration air temperature are considered to be the primary parameters that affect the thermal performance of Maisotsenko-cycle and stand-alone desiccant systems. The regeneration conditions are shown to have a positive correlation with the primary and regeneration outlet temperatures while having a negative correlation with the primary and regeneration outlet relative humidity. The primary inlet relative humidity has the greatest impact on the primary outlet relative humidity while the regeneration inlet temperature has the highest impact on the regeneration outlet relative humidity of the system. In addition, the primary inlet relative humidity is found to have positive correlations with the outlet regeneration and primary relative humidity and outlet regeneration temperature. Also, the primary air inlet temperature is found to be directly associated with the outlet primary relative humidity and temperature for the considered systems.

Investigation of aerodynamics in combustion of vegetative waste on isothermal models

Modern agricultural vehicles contain a large number of components, which include micro Abstract. Conventional furnaces using alternative fuels, such as vegetable waste (VW), are widely used instead of furnaces operating on conventional fuels. The furnaces aggregated with dryers of SZT and SP type are widely used in agriculture and food industry. Two models with a suspended bed were investigated: with flare-vortex and cyclone-vortex modes. The first model assumes the presence of an inclined grate in a rectangular chamber with a concentrated supply of secondary blast, primary blast with material is supplied above the grate in its lower part, and the second model assumes a cylindrical-shaped chamber with primary air inlet in the center and cyclonic secondary blast inlet at a certain height. This scheme is close to the first, only in the lower part of the model concentrated input of primary blast with material. The methodology of aerodynamics studies included: feeding of material from the hopper; material cutoff after steady-state mode; collection and weighing of fallen particles from the model; determination of the time of material presence in the model by labeled particles. Modeling of aerodynamics for different schemes of furnace process organization showed the possibility of creating two-span or single-span furnace blocks depending on the required operating mode. The results of comparative studies of aerodynamics of flare-vortex and cyclone-vortex modes are given. The results of comparative studies of aerodynamics of flare-vortex and cyclone-vortex modes are given. Optimal blowing parameters, secondary and primary air ratio, furnace design parameters contributing to the maximum specific volume heat stress are determined.

Counter-crossflow indirect evaporative cooling-assisted liquid desiccant dehumidifier: Model development and parameter analysis

Using auxiliary internal cooling is an effective way to improve the dehumidification effectiveness of the liquid desiccant dehumidifier (LDD) compared with the adiabatic dehumidifier. Indirect evaporative cooling (IEC) is a promising solution for internal cooling owing to its high efficiency and environmentally friendly features. A hexagonal plate heat exchanger (PHE) consisting of both counterflow and cross flow was used as a core in an IEC-internally-cooled LDD to ensure efficient heat transfer and facilitate easy installation simultaneously. A numerical heat and mass transfer model was established and validated, and an intensive parameter analysis of the thermal performance of the dehumidifier was conducted. The influential parameters include inlet primary air conditions (temperature, humidity, and velocity), inlet solution conditions (temperature, mass flow rate, and concentration), secondary to primary airflow ratio, the geometry of the heat exchanger, and channel gap. The performance of the newly developed counter-cross flow LDD with IEC-assisted cooling was improved by 16 % and 8.4 %, respectively, compared to the adiabatic and staggered flow type dehumidifiers. Among all the design parameters of the heat exchanger, the channel gap has the most significant effect on the dehumidification efficiency, and the recommended optimum height is 0.004 m. The air velocity is the most influential operating parameter on the dehumidification efficiency. The dehumidification effectiveness is reduced by 23 % as the primary air inlet velocity decreases from 4.5 m/s to 0.5 m/s.

Effect of Diffusers Installation in Inlet Primary Air Coal Pulverizer on Airflow Characteristic and Wear Concentration using CFD Modeling

This paper investigates the effect of installing several diffuser models in the pulverizer ZGM123-GII inlet ducting on air flow characteristics and wear concentration. Results of the internal check found that an area of the wall and the surrounding components were wearing abnormally or faster than usual. This condition will affect the availability of the pulverizer. There are 6 variations model used in this study to solve this problem. The 2 variations in the number of blade, there are 2 and 3 blades, combined with 3 angle variations, namely 30 o , 45 o , and 50 o . In this study, the viscous k-omega SST model was used to simulate airflow from the primary inlet to the area above the throat ring. The results show the contours of velocity of the air and the velocity vector on the pulverizer. Model with an angle of 45 degrees and the number of blade 3, is able to circulate air dominantly on the left side of the primary air inlet ducting, according to the reference study. From all variations, the model 45 o angle with 3 blades and 50 o angle with 3 blades are able to overcome the wear concentration problem.

Energy, exergy, economic and environmental analysis of an indirect evaporative cooling integrated with liquid dehumidification

To reduce the energy consumption and CO2 emission of the air conditioning system, an integrated system of indirect evaporative cooling (IEC) and liquid dehumidification (LD) named IECL is investigated. The energy and exergy performance of the IEC and IECL are compared under different the primary air inlet temperature and moisture content, the economic and environmental analysis of the IECL is presented. The results show that IECL saves 97% of the energy consumption compared with traditional air conditioning for dealing with fresh air temperature and humidity. The IECL shows better energy conversion and utilization efficiency than the IEC. The maximum exergy efficiency ratio and exergy efficiency of the IECL are 3.75 and 56.99%, respectively. Moreover, the IECL shows great economic benefits than IEC. The STP of the IECL is 7.55% lower and the NPV of the IECL is 42.42% higher than that of the IEC. The CO2, SO2, and NOx emissions of the IECL are 53.12 kg/year, 1.60 kg/year, and 0.80 kg/year, respectively.

Development of a three-dimensional numerical model of indirect evaporative cooler incorporating with air dehumidification

Indirect evaporative cooler (IEC) is treated as an energy-efficient and low carbon-emission air conditioning solution without utilizing the mechanical compressor and chemical refrigerants for cooling production. Currently, the widely-used one-dimensional (1-D) and two-dimensional (2-D) numerical models of IEC can expose the temperature and humidity variations of the airflow direction for predicting the cooling performance. However, the air profile along the channel width direction is usually simplified as constant in those models, neglecting the effect of non-uniformity distribution in the normal direction of heat exchanger plates. In this paper, a novel 3-D IEC numerical model of a cross-flow IEC was developed based on the computational fluid dynamics (CFD) method. The judgment on moist air condensation was incorporated in the model by a built-in generalized minimum residual iterative solver, which enables the performance prediction of IEC in hot and humid areas. Detailed air temperature and moisture content distributions along and perpendicular to the air channels were obtained with sufficient validations from published and experimental data. Parameter analysis was conducted on the primary air inlet properties and the channel gap distance. Results show that the prediction accuracies of temperature and humidity were improved by 5.8 and 6.7% compared with the 2-D model. The air dehumidification process started to appear from 27 ℃ given the 70% RHp,in. Under the circumstance of condensation state, the highest wet-bulb efficiency was 0.8 given the 0.5 m/s air velocity against 4 mm optimized gap distance, while the greatest dehumidification rate was 0.3 in the studied ranges. The maximum net energy saving was obtained as 4.7 kW under scorching and wet climate conditions. The proposed 3-D model can benefit future study on the heat and mass transfer mechanism of advanced plate materials by providing the non-uniformity of air profiles along the Y-axis, and thus contribute to the development of next-generation IEC technology.

Experimental and CFD analysis of multi nozzle ejector system for aircraft compact heat exchanger applications

ABSTRACT In the present study, analysis of multi-nozzle ejector systems for aircraft compact heat exchanger applications is performed. CFD procedure is validated with experimental data of a single-nozzle ejector. Experimentation is carried out with a multi-nozzle ejector to evaluate the performance of the system at ambient temperature (307 K). Based on the pressure drop data obtained from the experiment, the computational domain for CFD studies is simplified. Further the analysis of air ejector systems at higher operating temperature (813 K) is performed. Primary air inlet temperatures and pressure are varied as parameters. Velocity contour, pressure contour and temperature contours are plotted for cold and hot fluid cases. High pressure zones are observed in the mixing regime of primary and secondary fluid. Improper mixing of primary and secondary fluid is observed. The mass ratio is reduced with increase in primary pressure. Based on the CFD results at high temperature, the performance of the compact heat exchanger is computed using the heat exchanger carpet curve for the different secondary (cold) air flows induced by the ejector.

Numerical Analysis of the Effects of Oxygen-Enriched and Different Inlet Conditions on Performance of an Indirect Reheating Furnace with Pulse Combustion.

The requirement of improving efficiency and performance leads to the continuous development of furnaces and burners. For this purpose, it is necessary to establish a model suitable for industrial production and adjust it according to industrial demand. In this paper, a comprehensive numerical model is developed to characterize the combustion, heat transfer, and slab heating in an indirect reheating furnace with pulse combustion. To realize the pulse combustion process, a pulse control approach based on a user-defined function (UDF) was proposed to control the radiant tube burner state. Indirect heat transfer in the furnace was realized by coupling the radiant tubes and the furnace as a whole. In a simulation with the eddy dissipation concept (EDC) model, results from the four-step mechanism were in close accordance with those of the GRI 3.0 mechanism, and both mechanisms could describe the combustion process in detail. However, the calculation time of the EDC model with the four-step mechanism was reduced significantly. Thus, the EDC model with the four-step mechanism was selected as the ideal combustion model used for further simulation research. Through experimental validation, the simulation results of the developed model using the EDC model with the four-step mechanism showed a good agreement with the experimental results. Additionally, with this model, the effects of oxygen-enriched combustion with 74 vol % N2 and 26 vol % O2 in the oxidizer and inlet-change case with a fuel inlet and a primary air inlet on the performance of an indirect reheating furnace with pulse combustion were specially studied. The maximum flame temperature and the average temperature of the furnace atmosphere increased from 2046 to 2175 K and from 1241 to 1279 K for increased oxygen concentration, respectively. Compared with air-fuel combustion, the discharging slab temperature reached a growth of 2.9% in oxygen-enriched combustion. After changing the inlet boundary of the radiant tube burners, since the excessive combustion in the burner’s combustion chamber was avoided and the full combustion of fuel in the radiant tubes was promoted, the flame intensity in the radiant tubes was enhanced and the maximum flame temperature reached 2196 K. At the same time, the mole fraction of CO at the outlet became smaller and the slab temperature in all zones of the furnace increased by more than 3.5%. This study showed that higher efficiency of an indirect reheating furnace with pulse combustion can be achieved by oxygen-enriched combustion and changing the inlet boundary of the burners.

Exergy analysis of two indirect evaporative cooling experimental prototypes

This paper deals with the exergy analysis of two experimental prototypes consisting of indirect evaporative cooling systems with different constructive characteristics. Both prototypes have been designed and manufactured in the Thermal Engineering Laboratory of the University of Valladolid. They are made of polycarbonate hollow panels of different cross section and connected into a heat recovery cycle. Each prototype has been tested at 4 levels of outdoor air volume flow (from 125 to 400 m3·h−1) and 4 levels of dry bulb temperature (from 25 to 40 °C). For each of the 16 different operating conditions the exergy destructed by each prototype has been calculated. Results show that the higher the dry bulb temperature at the primary air inlet, the higher the exergy destruction and the exergy losses. The exergy destruction increases when the wet bulb depression temperature of the secondary air inlet decreases, leading to more inefficient configurations. The value of the exergetic efficiency is in the order of 2–12 %. The optimum combination of operating conditions at any inlet temperature of the primary air can be proposed as: 300 m3h−1 and 200 m3h−1. for the wide and narrow plates prototype, respectively.

Quality Function Deployment (QFD) and TRIZ in Briquette Cookstove Design and Simulation

Poor cookstove design can harm the user's health and environment. This research aims to obtain an efficient cookstove design, environmentally friendly and operated easily. The cookstove design process using a combination of QFD and TRIZ. QFD able to capture customer needs through a questionnaire and interview. The data collected then processed to build a House of Quality (HoQ), one of the tools in QFD. QFD results in the design parameter of the briquette cookstove, which is incorporated in the concept design. The TRIZ method is utilized to understand the problem that might occur in the concept design and focus on solving the root causes. The next step is a detailed design where the dimensions, combustion chamber capacity, and supporting features are explained. The combination of QFD and TRIZ result in a briquette cookstove concept design which is easy to clean and operate. The combustion system is Top-lit Up-Draft (TLUD). The burning chamber has two air inlets, namely primary and secondary. The primary air inlet supplies the air from the bottom of the burning chamber, partially burns the briquette, and produces flue gas. The secondary air inlet is in the shape of an oval to supply air in the burning chamber's upper part to burn the flue gas completely. A complete combustion process will increase combustion efficiency and reduce emissions. A computational simulation shows the velocity distribution inside the burning chamber.

Investigation on the performance of an indirect evaporative cooling system integrated with liquid dehumidification

Indirect evaporative cooling (IEC) and liquid dehumidification (LD) have a great energy-saving potential in air conditioning. This article presented a novel heat and mass exchanger integrating the IEC and LD (IECL), which can save the space of the air conditioning system and stably use the latent heat generated by the primary air condensation to improve the heat transfer rate. To investigate the performance of the IECL, a model was established to simulate the heat and mass transfer processes and validated by the experimental data. The pressure loss, total energy consumption, and COP were obtained under different heat exchanger structural parameters. Additionally, the moisture content and temperature difference between the primary air inlet and outlet, dehumidification efficiency, wet-bulb efficiency, and cooling capacity of the optimized IECL were investigated under different operating conditions. The results indicated that the optimized channel gap and length should be set as 5 mm and 600 mm, respectively, and the peak value of the COP is 173.3. Moreover, the IECL showed a good cooling capacity in hot and humid areas. Under the simulated conditions, the dehumidification efficiency ranges from 50% to 77%, and the wet-bulb efficiency ranges from 21% to 60%.

Experimental and normalized sensitivity based numerical analyses of a novel humidifier-assisted highly efficient indirect evaporative cooler

Indirect evaporative cooling technology has emerged as an energy-efficient, low-cost, and sustainable alternative to conventional air conditioning systems for space cooling. This is because of its significant (40–50%) energy-saving potential compared to ventilation, vapor compression cooling, and desiccant cooling systems. The current paper presents a novel humidifier-assisted regenerative indirect evaporative cooler that eliminates the use of hydrophilic surfaces within the system and mitigates the fouling propensity and water management issues. A generic cell of the proposed system is fabricated and tested for different operating scenarios along with the uncertainty propagation analysis. Thereafter, a normalized sensitivity analysis is performed to identify the most influential parameters on the cooler performance. The experimental data shows an effective cooling performance with a temperature drop of 20 °C of outdoor air and cooling capacity of 175 watts of 1800 mm × 300 mm generic cell. The cooling coefficient of performance was calculated as 44 and maximum effectiveness of 83.82% for the proposed configuration. The sensitivity analysis reveals scaling trends of the coefficient of performance in the following order of primary air inlet temperature > primary air outlet temperature > primary air velocity and the cooler effectiveness as secondary air outlet temperature > primary air inlet temperature > primary air humidity > primary air outlet.

Design Features and Performance Evaluation of Natural-Draft, Continuous Operation Gasifier Cookstove

Biomass cookstoves are used as a common source of heating and cooking in developing countries with most improved cookstove design focusing on developing efficiency in thermal conversion of fuels and safer operation than open flame fires. A top-lit-up-draft (TLUD) cookstove utilizes a gasification process similar to pyrolysis where the solid biomass fuels are heated within a oxygen-limited environment and the syngas are burned which reduces carbon content and particulate matter being introduced into the air. The new continuous-operation design is described to have features for: (1) safe addition of solid fuels during combustion of syngas, (2) removal of biochar at the primary air inlet to manage gasification location, and (3) temperature control of the cooksurface through adjustable exhaust paths. The designed cookstove is found to have a diameter to height ratio 0.42-0.47 in order to offer the cleanest burning of the biofuel. The cooking surface is experimentally studied and the thermal gradient is found for compressed wood pellets. Tracking of the coal-bed is studied as a function of time in order to better understand when additional fuel should be added to ensure constant cooking temperature and operation. Numerous exhaust paths explore the cookstove user’s ability to control the temperature contour of the cooksurface.

Swirled Jet Flame Simulation and Flow Visualization Inside Rotary Kiln—CFD with PDF Approach

CFD (computational fluid dynamics) simulation using a commercial package (Fluent-ANSYS) on industrial rotary kilns using annulus-type burners and methane gas was carried out to examine the characteristics of the flame length and flow visualization. New influencing design and operating parameters—primary air swirl number, primary air inlet annulus diameter, and secondary air temperature—were investigated and discussed. The influence of these parameters on axial temperature distribution, axial mean mixture fractions, velocity vectors, mixture fractions, and temperature contours were investigated. The current numerical findings were compared with existing experimental results to validate the simulation approach. The results showed that the primary air swirl number had a remarkable influence on the flame length at a lower primary air inlet annulus diameter ratio of 2.3. Moreover, the flame length increased by 20% and 6% with increasing the swirl number from zero to one for primary air inlet annulus diameter ratios of 2.3 and 5, respectively, and it also increased by 19% with increasing primary air inlet annulus diameter ratio from 2.3 to 5.

Optimization design of the key structural parameters of an aggregate drying pulverized coal burner

ABSTRACTIn order to reduce the costs of drying aggregate, an efficient coal-fired aggregate pulverized coal burner was optimized. A transient numerical simulation of the internal flow field of pulverized coal burner was carried out by means of computational fluid dynamics (CFD) to obtain the experimental data needed for structural optimization. Taking the straight length, radius, primary air inlet diameter, front cone angle, rear end cone angle, tertiary air inlet diameter, and secondary air inlet size as the optimization variables, and the production amount of CO was taken as the optimal target. The Box-Behnken Design response surface was established to optimize seven structural parameters through grouping. The results showed that the first structural parameter optimization demonstrated that the production amount of CO was decreased 34%, the second structural parameter optimization demonstrated that the production amount of CO was decreased by 58%.

Measurement and calculating of supersonic ejectors

This paper deals with numerical and experimental investigation of the flow in an air to air supersonic ejector with constant area mixing chamber. The mixing chamber of previous ejector was completely repaired since a scratch from previous turning had been found. As a result, a new geometry of the mixing chamber was created. Several measurements were conducted with different nozzle position (NP): 1 mm, 2 mm and 3 mm. Furthermore, for a given NP, two different values of stagnation pressure of 200 kPa and 300 kPa at the primary air inlet were investigated in more detail. All numerical simulations were performed in the ANSYS Fluent software. It was found that the influence of the position of the nozzle influences the ejection factor only to a certain extent. For the other parameters of the ejector is also a need to find the optimum position of the nozzle. Repair of the mixing chamber has contributed to reduce the pressure difference at the wall of the mixing chamber.

Investigation of the heat-recovery/non-recovery coke oven operation using a one-dimensional model

In order to predict the behaviour of the heat-recovery (HR) /non-recovery (NR) coke oven during the coke-making process, time-dependent numerical simulations have been carried out. A one-dimensional (1D), self-made (non-commercial) mathematical model has been used to predict temperatures, pressure and gas composition within upper-oven, down-comers and sole-flue of the oven analyzed. Moreover, mass flow rates of primary and secondary air, entrained from the surroundings, have been calculated. The results of the simulations indicate that the carbonization process performed in HR/NR ovens is slightly affected by surrounding conditions. A 15.8% (from 253 K to 293 K) increase in surroundings temperature has resulted in a 0.6% of temperature change within the upper-oven and the sole-flue. The same variation in ambient temperature affects slightly (0.3%) the primary and secondary air mass flow rate entrained from the environment. The increase in surroundings temperature reduces the natural draft by about 6 Pa, but pressure losses in the air ducts become higher. The usage of the so-called “sliding gates” installed in the primary and secondary air inlets is of great importance for coke-making. Changing the closure level of the primary air inlets by 25% causes the gas temperature to be altered by 4.3%. Another important factor is suction generated by a fan/stack. This parameter (suction increased by 40 Pa) changes the temperature inside the oven by about 9.7% for the upper-oven and 3.7% for the sole-flue. Both parameters have key significance for the carbonization process. The gathered data provides an improved understanding of the HR/NR coke oven operation and allows optimizing HR/NR coke oven design and the carbonization process itself.

Numerical study and performance correlation development on counter-flow indirect evaporative air coolers

In this paper, a numerical study of heat and mass transfer in counter-flow indirect evaporative air coolers is presented using an approach proposed by previous work. The mathematical model equations of continuity, momentum, energy and concentration are solved by the finite volume method to obtain the value of primary outlet dimensionless temperature. This mathematical model developed is validated against published data acquired from literature. The key target of presented analysis is to develop a performance correlation based on five dimensionless factors: ratio of channel length to half width of secondary air channel, ratio of water to secondary air mass flow rate, primary air inlet Reynolds number, secondary air inlet dimensionless temperature and water film inlet dimensionless temperature. Numerical simulations are performed by changing the value of each dimensionless factor under a constant value for other parameters. The simulation results are regressed to obtain the empirical constants of the correlation. The value of outlet dimensionless temperature is varied from 0.47 to 0.92. The developed correlation can predict the performance of the counter-flow indirect evaporative air coolers within a discrepancy of 12.6%. The correlation would be helpful to provide a simpler equation to improve the calculation speed within the engineering allowable accuracy range.

A Review Paper on CFD Analysis of Tri-sector Air Preheater for different Primary Air Inlet Opening

A Review Paper on CFD Analysis of Tri-sector Air Preheater for different Primary Air Inlet Opening