Air Impingement Research Articles

Design, numerical optimisation and experimental validation of an innovative solar-powered tube heater with multiple air impingement jets

This research investigates a novel tube heater designed for the seamless integration of an innovative solar thermal system into the powder-based coating process to heat steel tube at a temperature of 240 °C. It incorporates a comprehensive numerical model developed and assessed using ANSYS FLUENT, concentrating on seven critical parameters that significantly influence the tube heater’s performance and size. These parameters include tube heater length, jets’ length, funnel height, Z/Djet, Y/Djet and X/Djet ratios, as well as jet diameter. The findings underline the critical role of tube heater length in enhancing heat transfer and maximising thermal efficiency, while reducing jet length and funnel height demonstrated negligible effects on thermal performance, promoting material economy. A lower Z/Djet ratio enhanced heat transfer uniformity, improving thermal performance, while optimal X/Djet and Y/Djet ratios were identified as 4 maintaining a balance between heat transfer rate and energy consumption. A smaller jet diameter proved beneficial since the potential core was not achieved, increasing heat transfer to the steel tubes. The experimental model, conducted to validate the novel tube heater’s performance, remarkably aligns with the numerical model, showing an R-squared value of 0.992. These results affirm the numerical setup’s accuracy and reliability in capturing the tube heater’s thermal behaviour. It is concluded that the novel tube heater stands as a highly efficient solution for the seamless integration of solar thermal systems into the powder-based coating process of steel tubes, promising significant emissions reduction.

Utilization of waste hot air of medical oxygen plant in solar desalination unit employing jet impingement air heater for water production

ABSTRACT Many oxygen plants have been established specially during COVID-19 period and they are still serving for medical needs. The objective of the present work is to utilize solar and waste thermal energy of medical oxygen plants for water production. Humidification–dehumidification desalination (HDD) has been found suitable for this objective due to low temperature energy need during the process. The layout of an HDD unit has been presented to utilize waste heat, specially when solar energy is not much effective or absent. The system has been configured with a jet impingement solar air heater and a packed bed humidifier. A mathematical model has been developed and validated with the results of experiments. A comparative study of the proposed unit (HDD-O2) and a conventional unit has been performed in terms of yield and gained output ratio (GOR). The optimum flow rates of working fluids found in the range 0.03–0.04 kg/s and the temperature of air and water resulted in a continuous gain in yield. The average yield and GOR of the HDD-O2 unit were found to be 8.5 kg/d and 1.1 that could reach up to 11 kg/d and 1.4, respectively. The HDD-O2 unit provided yield at the cost of 0.04 $/kg with a payback period of 1.73 years. The findings of the present work indicated the suitability of the HDD-O2 plant for water production.

Enhancing brown seaweed Sargassum muticum drying using pulsed electric fields and dehydration pretreatments

The present study on the brown seaweeds Sargassum muticum focused on the application of dehydration by pressing or pulsed electric fields (PEF) pretreatment before three drying processes, namely freeze-drying, air impingement drying, and natural convection in an oven. Both pretreatments permitted to reduce significantly the initial moisture of the seaweeds with a reduction up to 50 %. The structural modifications induced by these pretreatments had a direct impact on the mechanisms of moisture retention and distribution within the seaweeds, which consequently exerted an influence on drying kinetics. The apparent moisture diffusivity for freeze-drying was significantly improved by PEF passing from 2.98 10−9 m2 s−1 to 3.62 10−9 m2 s−1 after a total disintegration. Concerning oven drying by natural convection, a dehydration by pressing will be preferred because the drying time to reach 0.45 kg kg−1 in dry basis was reduced by 61 min with this pretreatment.

The heat transfer enhancement mechanism of W-shaped micro-ribs on impingement cooling

In order to improve the performance of impingement cooling in turbine blades, W-shaped micro-ribs are arranged on the target surface to weaken the influence of cross-flow and generate longitudinal vortexes. The k-ω SST turbulence model is used for numerical simulation, and the mechanism of W-ribs on the enhancement of air impingement cooling performance and the influence of W-ribs geometry are studied. Under the condition of jet flow Reynolds number 4000 to 10000, based on the W-ribs with an angle α = 120°, width W = 0.1 mm and height H = 0.3 mm, the effects of angle (α = 90°, 120°, 150°, 180°), width (W = 0.05, 0.1, 0.2, 0.4 mm) and height (H = 1, 3, 4, 8 mm) on flow and heat transfer are investigated respectively. The results show that the W-ribs can separate the flow to both sides while generating longitudinal vortexes, which can reduce the influence of crossflow and enhance the sweep of the target surface to achieve the effect of enhancing heat transfer. α is the key factor affecting the generation of longitudinal vortex. W has little effect on the flow structure, but mainly affects the vorticity. H mainly affects the distribution of mass flow rate, which has a direct impact on the uniformity of upstream and downstream heat transfer. The W-ribs with α = 120°, W = 0.1 mm and H = 0.4 mm is recommended because of its excellent heat transfer performance and high comprehensive heat transfer performance, which are 39.7–48.9 % and 1.5–9.7 % higher than the smooth target surface, respectively.

Optimizing color enhancement in dried Penaeus vannamei through high-humidity hot air impingement cooking: Enzyme inactivation, reduced drying time, and Maillard reaction inhibition

This study was aimed to evaluate the potential of high-humidity hot air impingement cooking (HHAIC) on Penaeus vannamei, focusing on its drying characteristics, microstructure, water distribution, enzyme activity, astaxanthin content, antioxidant capacity, color, and Maillard reaction. Results demonstrated that a 3 min HHAIC significantly improved the shrimp's color and optimized astaxanthin content with a notable increase in scavenging capacity based on an in-vitro as antioxidation activity evaluation. Compared to the untreated samples, HHAIC could significantly inactivate polyphenol oxidase by 95.76%. Also, it suppressed the Maillard reaction by decreasing 5-hydroxymethylfurfural content and shortened the drying time by 40%. In addition, the low-field nuclear magnetic resonance and microstructure analysis showed alterations in the shrimp muscle fiber structure and water distribution. This study indicated that HHAIC could elevate quality, enhance appearance, and reduce the processing time of dried shrimp, presenting valuable implications for industry progress.

Design of integrated air impingement blanching and drying equipment for grape and airflow uniformity analysis and optimization of its drying material room

Design of integrated air impingement blanching and drying equipment for grape and airflow uniformity analysis and optimization of its drying material room

Effect of various different pretreatment methods on infrared combined hot air impingement drying behavior and physicochemical properties of strawberry slices

In current work, the effect of freezing (F), ultrasound (U), and freeze- ultrasound (FU) pretreatment on infrared combined with hot air impingement drying kinetics, cell ultrastructure, enzyme activity, and physicochemical properties of strawberry slices were explored. Results showed that FU pretreatment enhanced cell membrane permeability via forming micropores, altered water status by transforming bound water into free water and thus promoted moisture diffusivity and decreased drying time by 50% compared to the control group. FU pretreatment also extensively decreased pectin methylesterase enzyme activity and maintained quality. The contents of total phenols, anthocyanins, vitamin C, antioxidant activity, and a* value of dried strawberries pretreated by FU were extensively increased compared to the control group. U and FU pretreatments were beneficial for retaining aromatic components and organic sulfides according to e-nose analyses. The findings indicate that FU is a promising pretreatment technique as it enhances drying process and quality of strawberry slices.

Experimental investigation of post and vented vapor chamber designs for high heat flux dissipation

To enhance the dryout heat flux of vapor chambers over a 1 cm × 1 cm area, this study describes the testing of four different vapor chamber design architectures (each having an overall size of 50 mm × 50 mm × 5.5 mm). The designs leverage a combination of internal liquid feeding posts and evaporator vapor venting features to improve the capillary-fed boiling performance. The study provides systematic insight into increasing the dryout limit of a vapor chamber and lowering the thermal resistance by assessing the effect of each geometric feature independently. A jet impingement air cooling test facility is used to measure the total thermal resistance of the package in a representative application, while a liquid cooling test facility is used to measure the thermal resistance of the vapor chamber itself. The results show that a vapor chamber with a combination of machined posts coated with sintered wick and vapor vent features has superior performance over vapor chambers with independent features. It dissipated the highest heat flux of 589 W/cm2 and provided the lowest total package thermal resistance of 0.28 K/W for a 1 cm2 heat input area. The performance improvements are attributed to an improved liquid supply utilizing the porous-wick-coated machined posts and a reduction vapor egress pressure utilizing the vent features above the heater area.

A review of food safety in low-moisture foods with current and potential dry-cleaning methods.

Food is one of the basic needs of human life. With the increasing population, the production and supply of safe and quality foods are critical. Foods can be classified into different categories including low moisture, intermediate moisture, and high moisture content. Historically, low-moisture foods have been considered safe for human consumption due to the limited amount of moisture for microbial activity. Recalls of these foods due to pathogens such as Salmonella and undeclared allergens have brought attention to the need for improved cleaning and sanitization in dry food manufacturing facilities. In the food industry, cleaning and sanitation activities are the most efficient methods to prevent microbial contamination; however, water is most often required to deliver cleaning and sanitation agents. A well-written and properly implemented sanitation standard operating procedure can take care of microbial and allergen cross-contamination. Nevertheless, there are unique challenges to cleaning and sanitation processes for low-moisture food manufacturing facilities. The introduction of moisture into a low-moisture food environment increases the likelihood of cross-contamination by microbial pathogens. Hence, the use of water during cleaning and sanitation of dry food manufacturing facilities should be limited. However, much less research has been done on these dry methods compared to wet sanitation methods. This review discusses recent foodborne outbreaks and recalls associated with low-moisture foods the accepted methods for cleaning and sanitation in dry food manufacturing facilities and the limitations of these methods. The potential for air impingement as a dry-cleaning method is also detailed.

Evaluation of air impingement for dry-cleaning nonfat dry milk residues on a stainless-steel surface.

The use of air jet impingement to remove residues from surfaces in food manufacturing operations offers an alternative to the use of water and liquid cleaning agents. During this investigation, air impingement was used to remove nonfat dry milk (NFDM) residues from a stainless-steel surface. The influence of the water activity (aw ) of the residue, the time after the residue reached an equilibrium water activity, and the thickness of residue at the time of removal from the surface have been investigated. All three factors had a significant effect on the time for removal. An increase in the water activity, the time at equilibrium, the sample thickness, or a combination of all three resulted in an increase in the time required to remove the deposits. Visible changes in the structure of deposits were observed as NFDM samples equilibrated to water activities above 0.43. NFDM residues with water activities less than 0.33 were removed within 1s of using air impingement regardless of wall shear stress. When the water activities were greater than 0.50, the thickness of deposit was greater than 1mm, and the time after reaching an equilibrium water activity was over 7days, more than 5min of air impingement with wall shear stress over 9.48Pa was required to remove the residue. The results from these experiments indicated that air impingement has the potential to provide effective cleaning in manufacturing facilities for low-moisture foods. PRACTICAL APPLICATION: The introduction of water in low-moisture food environments is often undesirable due to the possibility of pathogenic microorganism growth. The normal cleaning operations in the food industry use water as a cleaning agent. This study evaluates the application of air impingement technology as a dry-cleaning method.

Cost economic evaluation of infrared assisted hybrid dryer for horticultural produce

Apple is one of the most widely consumed fruit all over India, loved by all age groups. To avail the product year-round, a widely accepted convectional techniques namely drying is followed in large scale. The process of drying is cost intensive and time consuming by nature. Mechanisation will act as a boon to food product developer in this field. A concise knowledge regarding ownership and operational expenses are required for a food product developer which will be helpful in choosing right one from the options like purchasing a new machine, advancement of existing one or exploring the alternative methods to enhance financial outcome. Therefore, ownership cost and operational cost of developed infrared assisted air impingement hybrid dryer were analysed. The dryer was found to be cost effective as it has low breakeven point and short payback period.

Thermo-hydraulic and exergetic analysis of rectangular channel with integrated jet impingement and roughness

ABSTRACT This experimental study investigates an innovative approach to enhance surface heat transfer efficiency by employing V-pattern protrusions in conjunction with an impinging air jet. The synergy between surface roughness and the air jet induces heightened turbulence, resulting in significantly improved heat transfer performance. Various parameters on a jet plate, such as relative streamwise spacing (X/Dh), relative spanwise spacing (Y/Dh), and relative jet diameter (dJ/Dh), were systematically explored over a Reynolds number range of 4,000 to 18,000, representing the operational range. Optimal thermo-hydraulic efficiency was achieved at specific parameter values: relative streamwise spacing (X/Dh) of 1.7, relative spanwise spacing (Y/Dh) of 0.86, and relative jet diameter (dJ/Dh) of 0.086. Statistical correlations were established based on experimental data for both Nusselt number and friction factor. Furthermore, an exhaustive exergetic analysis was conducted to evaluate the thermal system’s sustainability, potential for waste heat recovery, and avenues for improvement. This study’s significance lies in its pioneering approach to augmenting heat transfer through the novel integration of V-pattern protrusions and impinging air jets. The results not only delineate optimal parameter configurations for enhancing heat transfer but also provide insights into system sustainability, waste heat recovery potential, and broader applications. By amalgamating distinct techniques, this research advances the existing literature by achieving superior thermal performance.

Exergy assessment of infrared assisted air impingement dryer using response surface methodology, Back Propagation-Artificial Neural Network, and multi-objective genetic algorithm

This study deals with the exergy analysis of the thin-layer drying process of apple fruit via an infrared-assisted air impingement dryer. In the study, process conditions, namely, drying temperature (50–70 °C), slice thickness (2–6 mm), and recirculation ratio (10–90 %) were considered as independent parameters. The impacts of process parameters were studied over the responses, namely, exergy efficiency, exergy loss, improvement potential, and sustainability index. A comparative study was conducted between a Back-Propagation Artificial Neural Network (BP-ANN) coupled with a multi-objective genetic algorithm (MOGA) and Response Surface Methodology (RSM). It was found that both BP-ANN and RSM had good prediction ability, but BP-ANN performed slightly better with higher R2, lower RMSE, and MAE values. The optimized conditions for BP-ANN-MOGA were found to be a temperature of 50 °C, slice thickness of 3.9 mm, and recirculation ratio of 76.38 %, which yielded a response of exergy efficiency of 62.23 %, exergy loss of 221 kJ, an improvement potential of 105 kJ, and a sustainability index of 2.65. This study showed a better exergy assessment of the developed hybrid dryer from a thermodynamic point of view.

Peeling mechanism of tomato induced by HHAIB: Microscopic, ultrastructure, chemical, physical and mechanical properties perspectives

In order to better manage the peeling degree and avoid unnecessary losses, the current work aimed to explore the peeling mechanism of a novel peeling technology, high-humidity hot air impingement blanching (HHAIB). The relationships between HHAIB peeling performance and the changes in skin temperature, skin structure, water state, pectin fractions content, and skin mechanical properties of tomatoes were analyzed. Results showed, after HHAIB treatment, the epicuticular wax was disrupted, the skin exhibited more and longer random cracks, the degradation of inner skin tissue was observed by transmission electron microscopy, the free water percentage increased resulting in water loss in the whole tomato, the water-soluble pectin contents decreased in tomato fleshes, while the contents of chelate-soluble pectin and sodium-carbonate-soluble pectin increased. HHAIB heating reduced the elongation at break, and increased Young's Modulus of tomato peel. This study revealed the HHAIB peeling mechanism and provided new insights for developing HHAIB peeling technology.

Effect of jet-impingement and surface roughness on performance of solar air heater: Experimental study and its optimization

The performance of solar air heaters can be improved by either active or passive techniques. In this research manuscript, both active and passive technique is used to enhance the thermal characteristics of the solar air heater. The proposed solar air heater consists of an innovative approach in which an impinging air stream and wired ribs (arranged in the multiple V-pattern over the absorber plate) are used for performance improvement. The impinging air stream is synchronized in such a way that it strikes the ribs to promote local turbulence. The investigation has been performed considering various design parameters like relative width ratio, relative roughness height/pitch, the angle of attack, the stream-wise jet pitch, the span-wise jet-wise pitch, and the jet diameter ratio. The results have shown that the presence of the ribs opposite to the impinging air stream promotes local turbulence over the ribbed surface which ultimately enhances the thermal characteristics of the solar air heater. The proposed design is also been optimized using the surface response methodology and the significance of the various roughness parameters on the thermal characteristics has also been predicted. Additionally, the best performance observed is 3.12 at a relative width ratio of 5, relative roughness height/pitch of 0.043/10, angle of attack of 60˚, stream-wise jet pitch of 0.4, span-wise jet-wise pitch of 0.84, and jet diameter ratio of 0.064.

Effect of different drying techniques on drying characteristics, physical quality, and active components of Citri reticulatae pericarpium, and the correlation between physiochemical quality

Drying characteristics and various quality attributes were investigated to assess the adaptability of four different drying techniques (hot air impingement drying (HAID), medium- and short-wave infrared drying (MSWID), hot air drying with temperature and humidity process control (HAD-THPC), and freeze drying (FD)) for Citri reticulatae pericarpium (CRP). HAID and MSWID had higher drying rate, total flavonoid content (TFC), total volatile oil content (TVOC), aldehydes, and alkenes than those of the other drying methods, among which HAID consumed the lowest energy. FD had the highest thickness, frangibility, and larger cavities of CRP due to the optimal structure retention as compared to the thermal drying methods. According to the fingerprints and principal component analysis (PCA), the volatile organic compounds (VOCs) differed between dried and fresh samples, as well as FD and thermal dried ones. Furthermore, the oil cell number can be used to forecast and determine the TVOC and various volatile components. The findings indicate HAID would be a promising drying method for CRP with better quality, shorter drying time, and lower energy consumption.

Enhancement of heat transfer in heat sink under the effect of a magnetic field and an impingement jet

Improving the performance of heat sinks is very important in the development of cooling systems. In this study, the use of a novel combination method [magnetic field impingement jet (MF-IJ)] to improve the convective heat transfer coefficient in a designed heat sink is numerically investigated. To model heat transfer, a steady three-dimensional computational fluid dynamics (CFD) approach is employed. Numerical results including velocity and temperature contours, as well as the distribution of wall temperature of the heat sink and also the convective heat transfer coefficient are analyzed. The results show that the use of ferrofluid (Fe3O4/water) flow with an external magnetic field alone increases the heat transfer coefficient by 10%, while the use of an air impingement jet with pure water and without a magnetic field increases it by 22.4%. By using the MF-IJ method, a 32% enhancement of heat transfer coefficient is achieved compared to the case of pure water flow and without MF-IJ. Based on results, at a Reynolds number of 600, by applying the magnetic field intensities of 400, 800, and 1600 G, the average heat transfer coefficient increases by 5.35, 11.77, and 16.11%, respectively. It is also found that the cooling of the heat sink and temperature distribution is improved by increasing the Reynolds number and the inlet mass flow rate of the impingement jet. For instance, at z = 0.02 m, the application of an impingement jet with mass flow rates of 0.001, 0.004, and 0.005 kg/s results in a respective decrease of 0.36, 1.62, and 1.82% in wall temperature. The results of the current study suggest that the combination method of MF-IJ can be utilized for heat sinks with high heat flux generation as a flow control device.

Effect of cold atmospheric pressure plasma pretreatment on the drying kinetics, physicochemical properties and selected bioactive compounds of okra pods subjected to hot air impingement drying

This study aimed to evaluate the effect of cold atmospheric pressure plasma pretreatment (CP) on the drying kinetics, physicochemical properties, content of chlorophylls (alpha and beta), lycopene, phenolic compounds and antioxidant capacity of hot air impingement dried (HAID) okra pods. CP treatment significantly increased moisture diffusivity from 3.04 x 10−9 to 5.07 x 10−9 m2/s and decreased the HAID time by 38%, i.e., from 235 to 145 min. CP resulted in a reduction of alpha chlorophyll and lycopene contents, whereas the combination of CP and HAID allowed both chlorophylls to be preserved. The HPLC-MS/MS analysis revealed that CP-treated samples showed lower content of phenolic compounds, while combination of CP for 15 s and HAID provided excellent preservation of these compounds. The results show that the combination of the advanced CP treatment and HAID method was useful to obtain optimal results for both drying kinetics and the quality of okra pods.

Effect of Inclined Orifice in Air Impingement Freezer on Heat Transfer Characteristics of Steel Strip Surface

In order to improve the heat transfer characteristics of the air impingement freezer, an impingement freezer experimental table was designed as the research object in this paper. Numerical simulation technology was used to simulate the impingement freezer experimental table on the basis of test verification. When the other structural parameters in the impingement freezer experimental table were constant, the effect of the inclination angle of the orifice plate (θ = 60°, 65°, 70°, 75°, 80°, 85°, and 90°) on the heat transfer characteristics of a steel strip surface was analyzed by two aspects, the average Nusselt number and the heat transfer uniformity. The results showed that with the increase in the inclination angle of the orifice plate (60° ≤ θ ≤ 90°), the average Nusselt number of the steel strip surface was increased by 19.39%, and the heat transfer uniformity index was decreased by 33.69%. When θ = 90°, the average Nusselt number on steel strip was the maximum, which was 263.68, and the heat transfer uniformity index was the minimum, which was 0.2039. Therefore, the heat transfer intensity and heat transfer uniformity in the air impingement freezer could be improved when the inclination angle of the orifice plates was 90°. This helps to improve the output of the air impingement freezer, reduce energy consumption, and improve the quality of frozen food.

Exergetic Performance of Jet Impingement Bifacial Photovoltaic-Thermal Solar Air Collector with Different Packing Factors and Jet Distributions

Jet impingement is a promising cooling mechanism to increase the rate of heat transfer in solar air collector. However, the effects of an impinging air jet on the exergetic performance of a bifacial photovoltaic-thermal with different packing factors are entirely unclear. In this research, a jet impingement bifacial photovoltaic-thermal solar air collector was developed and its exergetic performance was assessed. Jet plate reflectors with different geometric configurations are proposed to enhance the cooling and light absorption at the rear part of the bifacial photovoltaic module. Additionally, the link between exergetic performance and each variable’s design and operational characteristics was examined through indoor experiments. The results showed that the maximum exergy efficiency of the bifacial photovoltaic-thermal with packing factor of 0.66 and 36-hole jet plate reflector has 11.88% under solar irradiance of 900 W/m2, and mass flow rate of 0.025 kg/s. The maximum exergy input, exergy destruction, and improvement potential of the proposed system are 402.81 W, 345.62 W, and 304.78 W, respectively.