Primary Air Temperature Research Articles

Optimizing a dew point evaporative cooler in data center applications

Abstract The escalating energy consumption of data centers has led to a pressing need for energy-efficient cooling solutions. This paper presents a countercurrent dew point evaporative cooler (DPEC) for data center refrigeration. We developed and experimentally validated a numerical model for DPEC, then formulated regression models using the response surface method. These models link eight key design factors, including geometrical and operational factors, to three performance indices: cooling capacity per unit volume, coefficient of performance, and outlet primary air temperature. We assessed the extent of factor influence on these indices. By using these regression models as objective functions, we used the genetic algorithm for design optimization under two climatic conditions, resulting in various optimal parameter combinations. Our findings highlight the strong predictive accuracy of these models. In comparison to the original design, the optimal design achieved an improvement of 104.8%, an increase of 23.9%, and a reduction of 13.8% in the three indices.

Influence of main operating parameters on the incineration characteristics of municipal solid waste (MSW)

To study the influence of the main operating parameters on the incineration characteristics of municipal solid waste (MSW), a 375 t/d mechanical grate incinerator is selected as the research object, and the effects of primary air temperature, secondary air arrangement, and grate speed on the MSW incineration process are simulated, and experimental tests are carried out under different primary air temperature and grate speed conditions. The results show that the relative errors between the measured and simulated values of the incinerator outlet O2 content and the measurement point temperature are within ±5% for all test conditions. When the primary air temperature increases from 423 K to 503 K, the position where the MSW incineration ends moves 3.32 m towards the front of the grate, and the moisture evaporation and fixed carbon combustion rates also increase, but the maximum volatile release rate and the optimal incineration condition of the MSW occur at the primary air temperature of 483 K. The increase in grate speed delays the incineration process of MSW and decreases the moisture evaporation rate and fixed carbon combustion rate, but it worsens the incineration effect of MSW. When the grate speed increases from 6.94 m/h to 13.88 m/h, the MSW incineration process is delayed by 3.20 m, and the moisture evaporation and fixed carbon combustion rates decrease by 43 kg·m−2·h−1 and 9 kg·m−2·h−1, respectively. To achieve the optimal operating conditions, the secondary air volume ratio of the front and rear arches is 1.59:1, the secondary air direction of the front arch is 40° and 60°, and that of the rear arch is 0° for the primary air temperature of 463 K and 483 K, respectively. This study can provide useful insights for optimizing the design and operation of mechanical grate incinerators.

Design on a novel waste heat recovery system integrated with the bypass flue and outside primary air preheater for bitumite-fired power plants

Bitumite is widely used in coal-fired power plants. However, due to its high volatile content, the temperature of primary air to coal mills is limited to a lower value because of its high risk of spontaneous combustion. The method to reduce primary air temperature by mixing with cold air leads to irreversible loss and reduces the power generation efficiency of the power plant. To address the issue, a novel flue gas waste heat recovery system integrated with the bypass flue and outside primary air preheater for bitumite-fired power plants was suggested. The thermo- and techno-economic analysis models of the waste heat recovery system were developed, and the design parameters were optimized to maximize profit. The thermo-economic analysis shows that the exergy efficiency of the waste heat recovery system can reach 49.8 %, and the coal consumption rate can be reduced by 4.75 g (kW h)−1 by integrating the optimal waste heat recovery system. The techno-economic analysis shows that the net present value of the power plant during ten years can reach 10.6 M$, and the discounted payback period is 0.6 years. The novel waste heat recovery system can effectively improve the thermo- and techno-economic performance of bitumite-fired power plants.

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.

Multi-objective optimization of dew point indirect evaporative coolers for data centers

This study introduces a novel counter-flow dew point indirect evaporative cooler (DPIEC) tailored for data center cooling. A numerical model for DPIEC was developed in COMSOL and validated experimentally, followed by the formulation of regression models using response surface methodology. Eight critical design parameters (five operational and three geometrical) were linked to three performance evaluation indexes (outlet primary air temperature T1,out, coefficient of performance COP, and cooling capacity per unit volume Qv). The magnitude of parameter influence on the evaluation indexes was assessed. Employing the three regression models as objective functions, a genetic algorithm, implemented in MATLAB, was adopted to perform multi-objective optimization for DPIEC under four climatic conditions, yielding an array of optimal parameter combinations. The results underscored the robust predictive accuracy of the established regression models, with R2 and Adeq Precision exceeding 0.96 and 53.7, respectively. The ideal point method achieved design solutions of the DPIEC with T1,out below 21.6 °C, COP above 61.3, and Qv over 15.5 kW/m3. Compared to the original design, the optimized design featured reductions of over 13.84 %, elevations of over 23.50 %, and enhancements of over 104.10 % in these three indexes, respectively. In addition, the confirmation study of the Pareto front proved the reliability of the obtained DPIEC design reference.

Prediction model of NOx emissions in the heavy-duty gas turbine combustor based on MILD combustion

A prediction model of NOx emissions in heavy-duty gas turbine combustors based on the moderate and intense low-oxygen dilution (MILD) combustion was proposed, and the inlet parameter sensitivity analysis was also investigated to identify the impact weight for the practical operation of heavy-duty gas turbines. The optimal space-filling (OSF) design was first adopted to determine the optimal combination of gas temperature (Tgas), primary air temperature (Tfirst), secondary air temperature (Tsecondary), gas mass flow (mgas), primary air mass flow (mfirst), and secondary air mass flow (msecondary) for minimum NOx emissions. Based on the results of the OSF design, the minimum NOx emissions of 24.11 mg/m3 were obtained, and the corresponding Tgas, Tfirst, Tsecondary, mgas, mfirst, and msecondary were 769.67 K, 825.10 K, 722.61 K, 1.71 kg/s, 4.29 kg/s, and 7.69 kg/s within the range of 10% fluctuation of rated input parameters. The sensitivity ranking of the six inlet parameters was secondly achieved as mfirst > Tfirst > Tsecondary > msecondary > mgas > Tgas with the base of NOx emissions. Finally, a novel prediction model with six inlet parameters was established to quickly and accurately calculate the NOx emissions influenced by complicated boundary conditions in MILD combustion of heavy-duty gas turbines.

Assessment of Thermal Performance of Non-Evaporative Cooling System Assisted with TEC Models at High Temperature Climate

In this work, a non-evaporative cooling system is used with an assisted thermoelectric cooler (TEC) devices module. The system was proposed as an alternative cooling system in the high temperature climate to overcome the high energy consumption of traditional air-conditioning compression cycle. The open source Open FOAM V.9 was used to solve the transient effect of 3D model of indirect non-evaporative cooling system. The primary air temperature was set to 319 . While, the air flow was tested under four different air inlet velocities: 0.75 m/s, 1 m/s, 1.25 m/s, and 1.5 m/s. the validation shows good and acceptable agreement in COP values of the system with both experimental and theoretical works from literature within an error between (12.9 % and 9.5 %). Results show that the temperate difference value on a slice through the length of the air channel starts to decrease as velocity increasing. For example, at the last timesteps of each velocity, the temperature difference reaches about (~10 oK) when velocity is (0.75 m/s) starting from the first quarter of the channel, while the same difference in temperature not reached until the half way of the channel from the channel inlet when velocity is (1.5 m/s). Revealing that even though the percentage increase in the velocity is about 50%, the change in the temperature difference value between the inlet and outlet of the channel is about 1.2%. The local Nusselt number shows that steady state heat transfer reached very quickly as the velocity increased (i.e., at 0.75 m/s at 12s while for 1.5 m/s at 4s). Notwithstanding, as the time processed the ( increases for all cases but becomes lower as the velocity increased. .

Investigating the thermal performance of air-cooling system integrated with TEC modules: Transient numerical simulation

The current study represents a developed 3-D numerical transient model to a complete indirect non-evaporative cooling system integrated with an assisted TEC unit using OpenFOAM V.9 source code. The TEC model was developed using a hand-written code as a source added to the energy equation. The primary air temperature was a criterion to compare between three cases of environment's temperature: low mode (299 K), medium mode (309 K), and high mode (319 K). A new dimensionless factor called by Heat Flux Ratio (HFR) is derived to evaluate the thermal performance. In addition, wall heat flux and temperature difference along the vertical air channel were the parameters used for comparison. The complete system was constructed and validated according to number of experimental and theoretical studies from literature. Furthermore, all cases were tested under five different air inlet velocities: 0.75 m/s, 1 m/s, 1.25 m/s, 1.5 m/s, and 1.75 m/s. Results show that HFR values increase as time increases. In addition, it was found that HFR increases with the reduction in the velocity. Moreover, it was found that higher temperature difference can be reached at the lowest velocity (0.75 m/s) while the minimum difference would be at the highest velocity (1.75 m/s) with the error between modes doesn't pass (2.5%). On the other hand, the highest wall heat flux approached at the highest velocity (1.75 m/s) and vice versa where the error doesn't exceed (2.85%) between the modes. Finally, the validation shows good and acceptable agreement in COP values of the system with both experimental and theoretical works form literature where the error is ranged between (20.3% and 3.64%).

On the diagnosis of a fouling condition in a kraft recovery boiler: combining process knowledge and data-based insights

Fouling is still a major challenge for the operation of kraft recovery boilers. This problem is caused by accumulation of ash deposits on the surfaces of heat exchangers in the upper part of the boiler over time. The first consequence is the reduction of steam production due to loss of heat transfer and, finally, the shutdown of the boiler due to clogging. The present work investigated the operational condition of a modern kraft boiler under a critical fouling condition. This boiler had even faced a manual cleaning due to a clogging event. This analysis combined process knowledge, plant team experience, and a data-driven approach, given the complexity of the process. In this sense, historical data covering this critical period of operation were collected. After a cleaning procedure, they were used to obtain a predictive neural network model for the flue gas pressure drop in the boiler bank, which is an indirect measure of ash deposit accumulation. Once validated, it was used for sensitivity analysis, with the aim of quantifying the effects of the model inputs. Five variables out of eighteen accounted for nearly 60% of the total effect on pressure drop. Namely, primary air temperature (21.6% of the total effect) and flow rate (11.1%), black liquor flow rate (9.9%) and temperature (8.4%), and white liquor sulfidity (8.6%). The analysis of these results mainly suggested an excess of carryover, which composes the ash deposits. Recommended actions to mitigate the fouling condition involved adjustments to the primary air system before the more drastic solution of reducing the boiler load.

Operation control and optimization of high efficiency hot primary air temperature adjustment device

Aiming at the problems existing in the control logic of the current hot primary air temperature adjustment device, such as adjustment lag, poor adjustment quality, deviation of the pulverizing system operation from the normative value and insufficient energy-saving effect in the adjustment process, a standard-based calculation method was proposed. It is a logical optimization scheme that dynamically adapts to the moisture content of raw coal and the coal volume of the pulverized. It has the advantages of faster adjustment speed, high system energy saving effect, and ensures the standard operation of the coal mill.

Research on deep utilization technology of flue gas residual heat for large-capacity coal-fired units

The utilization of flue gas waste heat is an important measure to improve the power efficiency of coal-fired units. Traditional method is to arrange the heating surface after the air preheater, which can just recover the low-grade heat, low efficiency. For the engineering practice of a 1000MW double-reheat unit, three feasible schemes are proposed, namely scheme 1 “two-stage gas cooler plus cold air heater”, scheme 2 “air preheater bypass + two-stage flue gas cooler plus cold air heating” and scheme 3 “air preheater bypass + hot primary air temperature adjustment plus two-stage flue gas cooler plus cold air heater”. For the sake of evaluating the actual effects of different schemes objectively, the thermal characteristic calculation model of the four-part rotary air preheater was established by finite difference method, and then the effect of the inlet air temperature and the share of bypass flue gas on the thermal efficiency of the boiler were studied. The equivalent enthalpy drop method was used to establish the thermal characteristic model of steam turbine, and the influence of different heat distribution modes on the heat consumption rate of steam turbine was studied.. Considering the technical economy, the optimal bypass flue gas share of this scheme is 12%, which corresponds to the reduction of coal consumption for power supply of the unit by about 3.23g/kWh. Taking into account comprehensively, scheme 3 is recommended.

Thermal economy analysis of flue gas waste heat utilization system of 1000MW secondary reheat unit

Deep utilization of flue gas waste heat is an important means to ameliorate the power generation productivity of coal-fired units. Aiming at the waste heat cascade utilization system which is composed of “air preheater bypass + two-stage low-temperature coal economizer + thermal primary air temperature regulating device” proposed in a certain project, using the energy balance method and the equivalent enthalpy drop method, the mathematical model of the impact of waste heat utilization devices at all levels on the unit economy is established from the boiler efficiency and steam engine heat rate. Combined with the rated operation data of the unit, the thermal economy of the system is analyzed. The results show that the bypass of the air preheater and the temperature regulating device of the hot primary air can effectively improve the utilization efficiency of the waste heat of the flue gas at the tail of the boiler, the coal consumption of power supply can be reduced by 3.47 g/kWh under rated working conditions.

Mixed Combustion Characteristics of Various Biomass Particles

As a promising pollutant emission reduction technology, biomass mixed combustion has attracted widespread attention worldwide. This paper aimed to study the characteristics of biomass mixed combustion and temperature distribution. A combination of simulation and experimental methods was adopted. The results showed when four kinds of biomass were burned separately, their highest temperatures in the center section of combustion chamber were corn stalk>cotton stalk>sawdust>rice straw in descending order. Compared with other three biomass, the highest temperature of corn stalk was more than 100 K higher, which mainly occurred during the full combustion stage, mainly because corn stalk had high volatile content and caught fire easily. In addition, with the optimal mixed combustion parameters, biomass mixed combustion improved the combustion characteristics of single biomass combustion. The optimal blending ratio of corn stalk to rice straw was 7:3, and the optimal primary air velocity and temperature were 48 m/s and 1300 K, respectively. With the optimal blending ratio, the maximum temperature in the center section was higher than that of single biomass combustion, with advanced ignition point, relatively uniform temperature distribution in the combustion chamber and good combustion performance, because the precipitation and combustion of high volatile components during mixed combustion caused the surface temperature of fixed carbon to rise rapidly to reach the ignition temperature. Finally, this paper studied the combustion characteristics of corn stalk and rice straw with the optimal mixed combustion parameters in mixed combustion experiment, and verified the good consistency between the simulation and experimental values. Therefore, biomass mixed combustion technology provides an important reference for solving the problem of low calorific value of single biomass combustion.

Study on Combustion Characteristics and NOx Formation in 600 MW Coal-Fired Boiler Based on Numerical Simulation

The variations in the boiler operation conditions have a great effect on the combustion characteristics and the pollutant formation in furnaces. This work aims to investigate the effects of operational parameters on NOx formation and its distribution in furnaces using the numerical simulation method to obtain the optimum control strategy for reducing NOx emissions. The numerical simulation models of pulverized coal combustion in furnaces involving flow, heat transfer, combustion and NOx formation are established. Taking a 600 MW supercritical opposed firing pulverized coal boiler as the study object, a full-scale three-dimensional physical model of the boiler is constructed with Gambit software. On this basis, the pulverized coal combustion and the NOx formation under various boiler loads are numerically simulated using the software of Ansys Fluent 2021R1, and the accuracy and the reliability of the models established are verified by comparing the simulation data with the field test data. According to the combustion numerical simulation of 128 groups of operating conditions, the effects of boiler load, the air rate and the air temperature on combustion and NOx formation have been emphatically investigated. The simulation results indicate that the formation of NOx and the NOx concentration distribution are mainly affected by the oxygen concentration and the temperature in the furnace. Especially, the effects of the variation in the excess air coefficient, the over-fire air (OFA) ratio, the primary air ratio and the internal secondary air ratio on NOx concentration distribution vary greatly. When the air temperature increases the overall NOx concentration in the furnace increases, and the influence of the secondary air temperature and the OFA temperature is greater than that of the primary air temperature. Large amounts of simulation data are a necessary data source for further study on the NOx prediction model at the economizer outlet, which can improve the prediction ability and the generalization ability of the NOx prediction model.

Experimental study of condensation characteristics and operation strategies of induction radiant air-conditioning system

To study the operation and condensation characteristics of an induction radiant air-conditioning system as a novel system that combines induction ventilation and radiant air conditioning, the characteristics of convection and condensation of an indoor terminal device radiant induction unit were studied. The mass transfer coefficient, condensation temperature, and condensation rate were analyzed experimentally. The time required to achieve a steady state indoor thermal environment was collected. The results indicated that the primary airflow rate and temperature mainly affected the mass transfer coefficient, condensation temperature, and condensation rate. When the indoor thermal environment reached a steady state, the heat transfer performance of the radiant induction unit was mainly affected by the primary air temperature. When condensation occurred, the primary airflow rate had a greater influence on the condensation rate. The start-up and response performances of the system were better than those of a traditional radiant air-conditioning system. In the condensation condition, reasonable control strategies maintain the primary air temperature and adjust the primary air flow rate, which can ensure sufficient heat transfer and stabilize the indoor thermal environment faster.

Effect of air flow rate and temperature on the atomization characteristics of biodiesel in internal and external flow fields of the pressure swirl nozzle

In this study, the flow and spray of biodiesel in the swirl atomization nozzle were analyzed. The influence of primary air flow rate and temperature on the atomization characteristics in the internal and external flow fields of biodiesel was discussed through simulation and experiments. The velocity of biodiesel in the nozzle and mixing chamber were symmetrically distributed. With increasing primary air flow rate, the maximum speed area increased and the shape of the turbulent kinetic energy of biodiesel changed from columnar to funnel. When the primary air flow rate increased from 10 to 30 L/min, the Sauter mean diameter, (SMD, d32) decreased from 95 to 28 μm, and when it increased to 50 L/min, d32 changed slightly. With increasing fuel temperature, the spray velocity increased and the particle size gradually decreased, while the particle size of each interval remained almost unchanged over 45 °C. Therefore, the best primary air flow rate and temperature for the swirling atomization of biodiesel were 30 L/min and 45 °C. It was determined that the increase in air flow rate and temperature promoted the development of atomization flow field and the breaking of droplets in biodiesel, thus optimizing the swirling atomization of biodiesel.

Multicriteria Spatial Modeling: Methodological Contribution to the Analysis of Atmospheric and Surface Heat Islands in Presidente Prudente, Brazil

Several studies demonstrate the potential of models for the representation of phenomena such as urban heat islands. This article aimed to analyze atmospheric heat islands (UHIucl) by integrating primary air temperature data with spatial information such as land use and relief from a multicriteria model based on multiple linear regression. Furthermore, we compared the measured and estimated air temperature at 11 p.m. with the surface temperature at 10:51 p.m. (local time). These temperatures were obtained through the thermal band of the Landsat 8 satellite considering extraction points of interest in Presidente Prudente city, Brazil. The multicriteria model showed reliability in UHIucl spatialization, reaching the confidence interval (p-value ≤ 0.05). The model proves that urban surface materials are the main energy sources modulating heat transfer to the atmosphere, while vegetation has a temperature-reducing effect. Precise mappings such as the one proposed here are relevant for the formulation of measures that support decision-making by public authorities. These mappings aim at urban planning that is resilient to the effects of urban climate and can be replicated in other realities.

Quantification of the effect of hydrological drivers on actual evapotranspiration using the Bayesian model averaging approach for various landscapes over Northeast Asia

Actual evapotranspiration (AET) is a critical component of hydrological processes. Accurate estimation of AET variation and its driving hydrological factors is vital for natural hazard adaptation and water resource management. This study first used AET observations from FLUXNET at 12 flux tower sites representing four different land cover types and three climate zones over Northeast Asia. Then the relationships and seasonal patterns among AET and seven hydrological variables of gross primary production (GPP), wind speed (WS), air temperature (Ta), net radiation (RN), soil moisture (SM), precipitation (P), and air pressure (Pa) were assessed using Bayesian model averaging (BMA). Finally, the performance of BMA was examined at all flux tower sites, and the impact of factor importance to predicting performance was analyzed. Generally, the results demonstrated higher AET values at sites associated with temperate and cropland areas. Analysis of the contributions of key elements to AET based on BMA suggested that RN and GPP were the two most sensitive factors for AET variation over all the selected sites. With the exception of RN and GPP, WS strongly influenced AET estimations in the wetland and cold regions. AET variation in the cropland and grassland regions was significantly affected by SM. Regardless of landscape type and climate zone, RN was the most important variable in each season, followed by GPP, WS, Ta, and SM. Ta was found to be important in spring, while WS showed a strong influence on AET in winter. In terms of prediction performance, the mean correlation coefficient and root mean square error (RMSE) of the BMA model was 0.92 and 0.49 mm/day, respectively. Using more factors with a posterior inclusion probability larger than 0.9 improved the performance of BMA. Overall, the strong correlation and low error demonstrate that BMA is an effective approach to capturing AET and exploring its interaction with climatological anomalies across different regions, especially under varied agricultural conditions, which could improve crop water management.

Heating performance of heating floor integrated with impinging jet ventilation system

Radiant floor heating systems provide comfortable indoor thermal environment. Primary air supply systems can be used to remove contaminants in the space heated by radiant floor. In this study, heating performance of integrated system of impinging jet ventilation (IJV) and heating floor was numerically investigated. The lowest floor heating capacity was 0 W/m2 and gradually increased to 50W/m2, and the primary air temperature supplied by IJV were 14, 16 and 18°C, respectively. In terms of contaminant removal efficiency, contaminant removal efficiency (CRE) was applied. The vertical dimensionless temperature distribution was used to analyse the heating performance of HF on supply air. The numerical results showed that the supply air layer of IJV could be heated by 60% to 80% under the heat effect of HF. The same is true for low supply air temperature 14 °C. The integrated system IJV/HF generated the weaken thermal stratification which is beneficial for energy saving. The CRE of IJV/HF system was influenced by the downward airflow of external wall. Sufficient supply air could overcome the downflow and effectively increase the CRE value (> 2).

Influence of multi-temperature primary air on the characteristics of MSW combustion in a moving grate incinerator

Incineration is widely applied in municipal solid waste treatment and energy recovery, especially in China. The efficiency of energy recovery does not only depend on the design and construction of equipment, but it is also highly affected by the operation. Primary air temperature is a key parameter for incinerator operation, but there is still limited information about how primary air temperature affects MSW incineration. Fluid dynamic incinerator code (FLIC) and Fluent coupled model was used to study the influence of different primary air temperatures on MSW incineration in a moving grate incinerator with five zones of primary air feeding. Four different conditions were investigated and compared, namely, control case (20 °C for five grate zones), case 180 (180 °C for five grate zones), case I (190 °C for two front zones, and 180 °C for three behind zones) and case II (190 °C for two front zones, 170 °C for two middle zones, 160 °C for the last zone). The result demonstrated, as the air preheating temperature increased, so did the rate of moisture evaporation and volatile release, the latter of which could potentially lead to higher local maximum temperature in the furnace. It was possible, by using the different primary air temperature setup, to maintain a relatively high rate of moisture evaporation and total mass loss, while having a lower rate of volatile release. Ultimately, the multi-temperature primary air setup maintained a high time-average rate evaporation of moisture at 0.04230518 kg/m2 s, and lowers the time-averaged rate of volatile release to 0.0396193 kg/m2 s, thus, maintained the local maximum furnace temperature at 1685 °C. This concept can potentially be utilized in MSW incinerators to effectively evaporate moisture from MSW while keeping the local maximum temperature in the furnace to a reasonable temperature.