Exit Air Temperature Research Articles

Energy and exergy experimental analysis for innovative finned plate solar air heater

In this current experimental study, a flat absorber plate of a solar air heater (SAH) with innovative straight interrupted fins arranged in a V-shaped pattern is analyzed using energy and exergy approaches, as the literature clearly shows that the low rate of heat transfer of flat plate SAH remains a source of concern for energy experts. The aluminum finned absorption plate was designed, manufactured, and tested during the summer in Saudi Arabia, examining the effect of changing the SAH tilt angle of θ = 0°, θ = 10°, θ = 20°, and θ = 30°. The study found that tilting the SAH at θ = 10°, θ = 20°, and θ = 30° increases the hot air exit temperature by 7.5 %, 15.7 %, and 12.5 %, respectively, compared to the horizontal position at θ = 0°. Tilting the SAH to θ = 20° increased absorbed solar radiation and air draft, resulting in 38.2 % SAH energy efficiency, 26.4 % exergy efficiency, and a 1.36 sustainability index that increased by 5.5 %, 12.8 % and 3.8 % compared to the horizontal position θ = 0°.

A Large-Diameter Earth–Air Heat Exchanger (EAHX) Built for Standalone Office Room Cooling: Monitoring Results for Hot and Dry Summer Conditions

Earth–air heat exchangers (EAHX) use the soil thermal capacity to dampen the amplitude of outdoor air temperature oscillations. This effect can be used in hot and dry climates for room cooling, and depending on the EAHX design, this cooling can be achieved with very few resources other than those used during EAHX construction. This is an obvious advantage compared to the significant energy consumption and operational costs of refrigeration machines traditionally used in room cooling. Despite the large number of papers on EAHXs available in the scientific literature, very few deal with large-diameter EAHXs (with pipe diameters larger than 0.30 m), and even fewer present monitoring data gathered from a built and functional large-diameter EAHX. The present paper uses monitoring data and provides a detailed quantitative analysis of the performance of a large-diameter EAHX built for standalone cooling of an existing office building. The field monitoring was carried out during a characteristic hot and dry summer period of the south of Portugal. Results show that outdoor air to EAHX exit air temperature gradients reach 9 K and cooling capacities exceed 27 kW. Moreover, the studied EAHX is capable of standalone cooling for outdoor air temperatures up to 33 °C and meets more than 50% of the room design cooling demand for outdoor air temperatures as high as 37 °C. This evidences that large-diameter EAHXs have the potential to achieve significant reductions in CO2 emissions and in energy consumption associated with building cooling in hot and dry climates.

Numerical study of an infrared suppression (IRS) device with cooling hole configuration on the mixing tube

Hot walls of the infrared suppression (IRS) device intensify the infrared signature of warships, which is detrimental for attaining infrared stealth. In this work, to effectively reduce the wall temperature, hole cooling technology is innovatively adopted on a marine IRS device. Circular holes are arranged on the mixing tube of the device. Numerical simulations are conducted to predict the temperature and flow distribution. The current research comprehensively analyzes the effects of hole position, number of hole rows, and number of holes on the wall temperature of the mixing tube and heat shield. The air suction rate and the exit temperature of the whole device are considered as well. The results indicate that the air suction and exit temperature of the device do not significantly change with the hole arrangement parameters. As the hole position moves towards the mixing tube outlet, the average temperature of the mixing tube continuously increases, while the maximum temperature of the mixing tube exhibits a peak-and-valley pattern. When the holes with large diameters are located near the mixing tube inlet, a backflow occurs between the mixing tube and the heat shield, causing the heat shield temperature to rise appreciably. Increasing the number of hole rows can reduce the mixing tube temperature, but excessive hole rows lead to an elevation in the heat shield temperature. The optimal configuration for the number of hole rows is found to be 2 with a hole diameter of 80 mm. With the increment in hole number, the average temperature of the mixing tube rises due to the accelerated disappearance of the streamwise vortices behind the holes; however, the maximum temperature of the mixing tube shows a decreasing-then-increasing trend owing to that more streamwise vortices are created. This study paves the way for the practical application of hole cooling technology on marine IRS devices. The findings can provide instructive suggestions for the arrangement of cooling holes.

Improving the performance of a triple-flow solar air collector using recyclable aluminum cans as extended heat transfer surfaces: An energetic, exergetic, economic and environmental survey

In the current work, the effect of integrating recyclable aluminum cans as tubular fins to a triple-flow solar air collector (TFSAC) has been numerically and experimentally investigated. In this regard, conventional (TFSAC) and aluminum can-integrated (TFSAC/F) systems have been simulated by applying computational fluid dynamics approach. Moreover, developed TFSACs have been fabricated and experimentally analyzed at fixed flow rate of 0.01 kg/s. According to the experimentally obtained results, utilizing recyclable aluminum cans as fins improved the average temperature difference as 14.02%. Additionally, average exergetic efficiencies for TFSAC and TFSAC/F were calculated as 18.87% and 23.25%, respectively. Economic and environmental analyses have also been performed for the developed TFSACs within the scope of the present survey. The simple payback periods for TFSAC and TFSAC/F were gained as 1.178 and 1.035 years, respectively. Moreover, the yearly CO2 savings for TFSAC and TFSAC/F analyzed in this work were attained as 0.149 and 0.169, respectively. It should be stated that mean deviation between numerically and experimentally acquired exit air temperature values are 3.71% and 7.62%, respectively for TFSAC and TFSAC/F.

Flux augmentation and temperature enhancement through secondary parabolic concentrator and air recirculation for a central receiver tower system

Flat volumetric receivers for central receiver tower (CRT) systems face two critical shortcomings: light spillage nearby the receiver and low exit air temperature due to suction of air in ambient condition. Here, a thorough design modification is proposed and analyzed to address both the issues by introducing a secondary optical addendum based on the principle of compound parabolic concentrator (CPC). As a case study, existing and modified designs of PS10 plant with flat heliostats are compared. For the same receiver, the modified plant increases the intercept efficiency by 6% whereas the incorporation of CPC augments the concentrated flux by 18%. A glass covered secondary optical element not only reduces operational difficulties due to absorber-soiling, but also provides an opportunity of heated air recirculation. If the heated air is partially recirculated, it can provide a control parameter, i.e. the air return ratio (ARR), by which the exit air temperature can be enhanced. It is demonstrated here that temperature as high as 1775 K is achievable for the modified PS10 plant when significant fraction of heated air is recirculated. Hence, the present study opens up optimization routes for CRT based plants based on limited area heliostat field and volumetric porous absorber through CPC based secondary optical element and fractional recirculation of heated air.

Experimental study of vapor compression refrigeration system enhanced via tubular heat exchanger incorporating single/dual phase change materials

Vapor compression refrigeration (VCR) systems operating in hot climates suffer from high condenser temperatures that reduce their performance. One interesting approach being investigated to improve VCR performance is incorporating phase change materials (PCMs) into VCR systems that have not yet been expanded experimentally. So, this work experimentally studies the effect of using tubular PCM heat exchanger to cool the VCR condenser. The impact of two PCMs types suitable for warm climate conditions: SP24 and SP26, and combination of them on the VCR energy and exergy performance is investigated for two inlet ambient air temperatures. The impact on the exit air and PCMs temperatures, and VCR unit's pressure-enthalpy curve, VCR coefficient of performance, and power consumption is also examined. The results show that PCM-equipped systems significantly enhance the VCR exergy efficiency and coefficient of performance, especially at higher ambient temperature. Compared to the system without PCM, the power consumption can be reduced by up to 10.4% with PCM, while the exergy efficiency and coefficient of performance can be improved by 13.7% and 13.4%, respectively. While PCM SP24 provides the best performance, PCM SP26 has longer effective cooling period. A combination of SP24 and SP26 balances the performance and effective cooling period.

Effects of carbon nanodots coating and airflow rate on the thermal efficiency of flat plate collector

ABSTRACT The application of nanoparticle coating in a collector could resolve the issues of lesser heat transfer rate and lower thermal efficiency associated with the flat plate collector (FPC). In this study, carbon nanodots (CNDs) synthesized from fish scales wwere coated over the black paint coating to enhance the thermal efficiency of FPC. The effect of various concentrations (0, 0.1, 0.2, and 0.5%w/v) of CND coatings and mass flow rates of air (0.011 kg/s (natural convection) and 0.015, 0.029, and 0.044 kg/s (forced convection)) on the collector outlet air temperature and efficiency of the FPC were evaluated with a control (black paint). Solar radiation ranged from 382 to 913 W/m2 on the experimental days, and the atmospheric temperature and relative humidity values varied from 26.2 to 34.8°C and 50–72%, respectively. Fourier transform infrared spectroscopic studies of absorber plate coating revealed that the CNDs interacted with the black paint surface through phenolic OH, C=O, and NH mainly by hydrogen bonding. It was observed that the exit air temperature of the collector varied from 55 to 65°C. The thermal efficiency of 59.97%, 62.72%, 71.87%, and 67.75% was obtained for control (black-paint), 0.1%, 0.2%, and 0.5% CNDs coating, respectively, at the airflow rate of 0.044 kg/s. The coating of 0.2% CNDs recorded a maximum thermal efficiency of 71.87% at 0.044 kg/s. Overall, the CNDs coating on the absorber surface enhanced the thermal efficiency of the collector by 19.84% over the black paint-coated surface (control). It can be concluded from the study that CNDs coating resulted in enhanced outlet air temperature and improved thermal efficiency, which can be utilized for low-temperature applications like the drying of food materials.

Monitoring exhaust air temperature and detecting faults during milk spray drying using data-driven framework

The advanced data analytics platform bridges the gap between industrial automation technology and new cloud-based technology. The information on the implementation of a data analytics platform to convert huge data into valuable information and use it to serve the scheduled maintenance of the components involved in the food processing industry is rarely reported in the literature. This work reports a data-driven framework for prediction and fault detection in key performance parameters for a milk spray drying process plant. The framework consists of different data analysis methods and it helps to take decisions about the selection of key performance parameters involved in improving the spray drying thermal efficiency. The neural network-based NARX model demonstrates a better performance than the linear models in the prediction of cyclone exit air temperature which is the key performance parameter in spray drying as it governs thermal efficiency. The performance of the predictive model is validated using RMSE. The ML-based classification methods are also used in the present work to classify the different faults and the decisions regarding the maintenance of the components responsible for the faults. The performance of these models was verified using a confusion matrix. It is proposed that the decision tree classifier and random forest classifier are best suitable for fault finding as their accuracy is highest at 99.83%.

Parabolic Air Collectors with an Evacuated Tube Containing Copper Tube and Spiral Strip, and a New Cavity Receiver: Experimental Performance Analysis

Sunray thermal energy is one of the most promising and quickly growing techniques globally. In parabolic trough air collectors (PTAC), receiver design and safety are of paramount importance because of their impact on the overall effectiveness of power plants. However, experimental studies of alternative receivers to improve heat transfer are still to be performed. In this study, a PTAC system was tested experimentally with an evacuated tube: open on one end, containing a copper tube and a spiral strip (case 1), and with a new cavity receiver consisting of several arranged tetragonal pyramidal elements (case 2). Afterward, the results were compared and showed a slightly superior exit air temperature and thermal efficiency performance for case 1. The overall results demonstrate a remarkable convergence of case 2 from case 1 in terms of temperature increase across PTAC, in which the maximum exit air temperature for case 1 is 58.2 °C, a 3.4% increase over case 2 at 0.0105 kg/s mass flow rate. Lastly, the results validate the potential and clarify the specific conclusions of these methods’ application in improving heat exchange in a PTAC.

Experimental investigation of locally available Torai (luffa cylindrica) as evaporative cooling pads

ABSTRACT This work presents an experimental evaluation of the performance of a cooling pad made from the locally available material “Torai” (luffa cylindrica). Different performance parameters that define the cooling performance of the proposed pad, such as the exit air temperature, degree of cooling, saturation effectiveness, cooling potential, and coefficient of performance, have been experimentally investigated. Results show that the overall cooling performance (cooling potential, degree of cooling, effectiveness, and coefficient of performance) increases by increasing the pad thickness. For a given pad an increase in air velocity decreases the saturation efficiency and degree of cooling. The maximum saturation effectiveness and coefficient of performance found for a 7 cm pad at 1.5 m/s air velocity are 65.9% and 8.53, respectively. The rate of water evaporation increases by increasing the pad thickness and air velocity. The maximum water evaporation rate found is 1.4 g/s for a 7 cm pad at 1.5 m/s air velocity. The water retention capacity of the proposed pad material is about 78 g. Moreover, it may be concluded that the proposed pad shows reasonably good performance to be employed as a pad material for direct evaporative coolers. The cost of manufacturing a pad 30.48 cm2 is between Rs130 (US$1.625) and Rs234 (US$2.925).

Enhancing the Air Conditioning Unit Performance via Energy Storage of Different Inorganic Phase Change Materials with Hybrid Nanoparticles

Air conditioning unit performance, coupled with new configurations of phase change material as thermal energy storage, is investigated in hot climates. During the daytime, the warm exterior air temperature is cooled when flowing over the phase change material structure that was previously solidified by the night ambient air. A theoretical transient model is constructed and solved numerically for the proposed design in plate and cylinder configurations. This model is studied at different inlet hot ambient air temperatures and phase change material types (SP24E and SP26E) without and with inclusion of hybrid nanoparticles. The results affirm that the discharging and charging duration for the cylinder is minimal compared to the plate configuration. Raising the inflow air temperature lowers the exit air temperature and air conditioning coefficient of performance and power-saving but shortens the cooling time. Using phase change material with a relatively low melting temperature increases the melting time and exit air temperature but reduces the charging time. Mixing hybrid nanoparticles with phase change material has a short-term positive influence on air conditioning performance. The maximum power saving for 2 h of working is 16.4% for the cylinder, while for 10 h of working, it is 6.4% for the plate.

Exergetic optimisation of a solar-biomass hybrid greenhouse dryer in drying banana slices

In this study, an elitist non-dominated sorting genetic algorithm was applied in exergetic optimisation of a solar-biomass hybrid greenhouse dryer in drying banana slices. To develop comprehensive relationships for objective functions under each drying mode (solar, biomass, and solar-biomass), the system was linearised around drying and exit air temperatures. The objective functions involved maximising exergy efficiency and drying air temperature of the system. The trade-offs showed that solar and solar-biomass modes required the same airflow rate (0.05 kg/s) indicating that at these combinations the dryer received almost equal energy input. Biomass mode trade-offs indicated that a lower flow rate (0.01 kg/s) was required for drying. Further, both solar-biomass and biomass modes must maintain a fuel feed rate of 0.001 kg/s for maximum exergy efficiency (solar-biomass: 80.21% ± 14.26%; biomass: 79.28% ± 10.38%) and drying air temperature of 333 K. Performance evaluation of the optimised system demonstrated its superiority compared to the unoptimised system.

Experimental investigation and theoretical prediction of the multistage reciprocating evaporative cooler

Present work comprises the fabrication of a multistage reciprocating humidifier where four Celdek 7090 packings are arranged at different positions run by a motor connected to a cam follower. Packing dips in the water and comes in contact with air in cross flow direction in a duct. Air velocities and camshaft speeds are varied to evaluate the performance parameters such as outlet dry bulb temperature, outlet specific humidity, evaporation rate, coefficient of performance, cooling effect and humidification efficiency. A theoretical model is constructed to predict the performance of the multistage dynamic humidifier. Stage-wise performance is also determined to analyse the influence of number of stages on the cooler performance. The system gave a maximum evaporation rate, energy conversion factor, humidification efficiency equal to 1.864 g/s, 4.84, and 72.62 %. The predicted performance parameters for various conditions are found to be in agreement with the experimental results. Experimental and empirical results are close to each other with a maximum deviation of 2.1 %, 2.4 %, 8.3 % and 8.5 % for exit air temperature, exit humidity ratio, saturation efficiency and energy conversion factor respectively for various tested air flow rates. Stage wise performance revealed that higher number of stages will drastically deteriorate the performance and simultaneously increase the energy consumption.

Cooling Modelling of an Electrically Heated Ceramic Heat Accumulator

This paper presents a simple novel mathematical model of a heat accumulator with an arranged packing in the form of ceramic cylinders. The accumulator analysed in the paper can be heated with inexpensive electricity overnight or excess electricity from wind farms. It can be used as a heat source in a hydronic heating system or for domestic hot water. The differential equations describing the transient temperature of the accumulator packing and flowing air were solved using the explicit Euler and Crank–Nicolson methods. The accuracy of both methods was assessed using exact analytical solutions and the superposition method for a uniform initial temperature and accounted for time changes in inlet air temperature. A numerical simulation of the accumulator cooled by flowing air was carried out. The correlation for the air-side Nusselt number was determined using the method of least squares based on experimental data. The calculated exit air temperature was compared with the measured data. The accumulator can operate as a heat source with dynamic discharge. The developed mathematical model of the accumulator can be used in a system to adjust the fan rotational speed so that the air temperature in the room is equal to the preset temperature.

Efficiency and Effectiveness Method versus <i>ε</i>-NTU Method with Application in Finned Flat Tube Compact Heat Exchanger with Water-Ethylene Glycol as Nanofluid Base of Iron Oxide Nanoparticles

This work aims to establish comparisons between two models used for the performance of heat exchangers. The chosen system, in this case, consists of a heat exchanger used in automotive radiators flat finned tube type. Water and ethylene glycol compound as base fluid and volume fractions of iron oxide nanoparticles (Fe3O4) are used as a refrigerant. The quantities determined in this work are the nanofluid exit temperature, the air exit temperature, the absolute error between the models for heat transfer rate, and Effectiveness. The quantities that constitute parameters, independent variables, are the airflow, represented by the Reynolds number, and the iron oxide volume fraction. Ethylene Glycol 50% compound has slightly better thermal performance than pure water and reduces the reactive effect of water on the environment, increasing the average life of the equipment. The absolute relative error between the models is less than 20% and presents maximum values with the increase of the nanoparticle volume fraction and growth in the Reynolds number for the air.

Energy performance index of air distribution: Thermal utilization effectiveness

The energy performance index is crucial for the energy-efficient design and operation of air distribution. Heat Removal Efficiency (HRE) is a widely used energy performance index, and Energy Utilization Coefficient (EUC) and Effectiveness of Heat Removal (EHR) are alternatives to HRE. This study justifies that these existing indices are unreasonable and incompetent as energy performance indices. This study also proposes a new index called Thermal Utilization Effectiveness (TUE) and verifies its efficacy as an energy performance index via theoretical analyses and experiments on stratum ventilation, displacement ventilation, and underfloor air distribution. EUC is not a suitable energy performance index since it does not consider the relative contributions of the occupied and unoccupied zones to the energy performance of air distribution. EHR cannot qualitatively distinguish the energy performance of air distribution because of its floating benchmark point. HRE cannot quantitatively distinguish the energy performance of air distribution because it unequally weighs the thermal energy of the air temperature of the occupied zone. TUE accounts for the relative contributions of the occupied and unoccupied zones to the energy performance with the help of the exit air temperature, qualitatively distinguishes the energy performance because of its two fixed benchmark points, and quantitatively distinguishes the energy performance by equally weighing the thermal energy of the air temperature of the occupied zone. Therefore, TUE overcomes the drawbacks of EUC, EHR, and HRE, and is a reasonable and competent energy performance index of air distribution.

Experimental and numerical analysis of a three-fluid membrane-based ionic liquid desiccant absorber

Membrane-based liquid desiccant system is a promising technology for efficient humidity control. Also, in comparison to systems using conventional desiccants, ionic liquid (IL) desiccants enable increased system operational envelope and efficiency. In this study, a finite difference numerical model is developed for an IL-based counter and cross flow internally cooled polymer heat and mass exchanger (i.e. absorber). A super-hydrophobic membrane separates the IL desiccant and air flows while allowing moisture transfer from air to IL. The numerical model determines the outlet conditions of all three absorber fluids (water, desiccant, and air), establishing the absorber heat and mass transfer performance. The model was compared with the experimental data obtained from an IL desiccant absorber under a wide variety of water, desiccant, and air inlet conditions. The maximum discrepancy between the model predictions and experimental data for the air exit temperature, air exit relative humidity, cooling water exit temperature, and solution exit temperature are 4%, 9%, 5%, and 2%, respectively. A comprehensive parametric study is then conducted to evaluate the sensitivity of the absorber performance to different input conditions. This highly accurate model and parametric study of a membrane-based absorber can be utilized in design and performance analysis of emerging liquid desiccant dehumidification and separate sensible and latent cooling (SSLC) systems.

The Effect of Using a Paraffin Wax-Aluminum Chip Compound As Thermal Storage Materials in a Solar Air Heater

This paper presents an experimental investigation of a designed and fabricated air heater consisting of three cases. The first case used concrete as the main part of the air heater. The second case used paraffin wax as phase change material (PCM) accompanied with concrete as the main part of the air heater. In the third case aluminum chip was added to PCM and concrete. It was used as a thermal storage compound in a solar air heater. Results show that the exit air temperature was increased highly for the third case compared with the other cases and the efficiency of system was improved and the maximum storage efficiency achieved was 100% higher than the concrete case. The air heating gained was in its maximum value with the third case and the maximum increment achieved was 147.52% at Feb. also.

Modeling of Bifacial Photovoltaic-Thermal (PVT) Air Heater with Jet Plate

This research demonstrates how to develop a novel energy balance equation to investigate heat transmission between the components of a bifacial photovoltaic-thermal (PVT) air heater with a jet plate. The temperature output and efficiency of the system are shown. A greater mass flow rate reduces the exit air temperature and increases the thermal efficiency of the thermal component. Increased sun irradiation raises the output air temperature and thermal efficiency. In terms of electrical efficiency, a greater mass flow rate reduces the temperature of the PV panel while increasing electrical efficiency. On the other hand, higher solar irradiation raises the temperature of the PV panel, lowering its electrical efficiency. The maximum thermal efficiency of BPVTJPR is 51.09% under the circumstances of 12 PV cells with a packing factor of 0.66, a jet plate reflector with 36 holes, 900 W/m2 solar irradiances, and a mass flow rate of 0.035 kg/s. The maximum electrical efficiency of BPVTJPR is 10.73% under the circumstances of 12 PV cells with a packing factor of 0.66, a jet plate reflector with 36 holes, 700 W/m2 solar irradiances, and a mass flow rate of 0.035 kg/s.

Design, Fabrication and CFD Analysis of Jet Impingement Solar Dryer for Copra

This Paper attempts to study the variation of simulation and fabricated jet impingement dryer to define how to increase efficiency, temperature and best quality of the dryer. The jet impingement is helps to increase the overall temperature of the exhaust air. where increasing the temperature slightly and velocity ranges of drying time as been reduced. The experimental process has been carried in the copra.From the CFD analysis end results establish the flow jet impingement processing on the absorber where a strong function of heat transfer enhancement. The present process concludes that the mass flow ranges of air as been influence the heat transfer rates. At solar radiation 500-1000 (W/M2), 348K ambient temperature and 0.048(Kg/S) mass flow ranges has been get at the end analysis.Now a day the new model innovations are needed in solar dryer to fulfil the requirements of drying industrial and agricultural products. The new design process analysis and assumptions are very necessary to design any system. By comparison solar drying fulfil the requirements than sun drying processing. Under the such process and conditions Effect of mass flow ranges of air, solar radiation on exit air temperature, and efficiency has been analyzed.