Outlet Air Temperature Research Articles

The CFD analysis of the effect of internal peak angle and mass-flow rates on the thermal performance of solar air heater with triangle cross-section

A new design of solar air heater with triangle cross-section is numerically studied. The thermal performance of solar air heater is studied at various mass-flow rates, inlet air temperatures, and solar irradiation intensities. The CFD model is developed using the software ANSYS FLUENT to study the fluid-flow and heat transfer in the solar air heater. The 3-D discretization is applied to study the thermal performance of solar collector with triangle cross-section. Mesh independence is performed in order to choose the adequate mesh. The discrete ordinate radiation model and the RNG k-? turbulence model are used to study the radiative heat transfer and the turbulent flow inside the solar air heater. Particularly, effects of different internal peak angles (145?,126?, 100?, 80?, and 67.5?) under different solar irradiation intensities (from 620-1081 W/m2) are studied to improve the thermal performance of the solar air heater. The results show a good agreement between the numerical model and the experimental data with an average error of 6%. The maximum outlet air temperature of the solar air heater reached 72 ?C for the geometries with 12 and 16 channels (internal peak angles of 80? and 67.5?, respectively) under mass-flow rate of 0.0264 kg/s. The thermal performances of the solar air heater with 16 and 12 channels are 24.2% higher than standard geometry, respectively for solar irradiation intensity of 1081 W/m2. The configuration with internal peak angle of 80? and 12 channels is selected as the optimal with a thermal efficiency of 79%, a low pressure drops compared to geometry with 16 channels and lower costs.

Investigation of the Effects of Using Plastic Instead of Aluminum in Tractor Engines, Intercooler Tanks on Engine Performance

In recent years, researchers have been working on more environmentally friendly engine systems and the efficient use of depleting fuel resources. One of these research topics is intercoolers used in turbocharged engines. Intercooler tanks are generally made of aluminum due to their good heat transfer coefficient. In this study, the suitability of the use of plastic tanks was investigated by examining the engine performance changes as a result of using plastic instead of aluminum, which is the traditional material, in the intercooler tanks of an 81 kW Perkins tractor engine. For this purpose, experiments were carried out at 1400 and 2200 rpm for intercoolers with both materials. According to the results obtained from the experiments, a 0.62% torque increase was obtained at 1400 rpm in the engine with a plastic tank material intercooler compared to the engine with an aluminum material intercooler. According to the data obtained from the experiments carried out at 2200 rpm, a power increase of 0.74% was determined. Similarly, it was determined that the effects of parameters such as radiator upper and lower hose temperatures, turbo inlet and outlet air temperatures, and intake manifold inlet temperature on engine performance were negligible. According to these findings, it has been determined that if the tanks of the intercoolers are plastic, there will be a negligible performance loss compared to the traditional material aluminum. Plastic is lighter, cheaper, and easier to manufacture than aluminum. Considering the production and operating conditions, it was concluded that such materials should be researched and developed by manufacturers.

Analysis on desiccant coated heat exchangers based on a new performance parameter and thermodynamic model

Performance of traditional vapor compression air-conditioners can be improved by achieving sensible and latent loads decoupling via the use of desiccant coated heat exchangers (DCHEs). Performance evaluation of the DCHE is mainly based on its dehumidification capacity. However, extra loss of cooling power, caused by the switch of dehumidification and regeneration phases, has not been investigated in previous articles yet. Hence, assessment for cooling power utilization efficiency (CPUE) of the DCHE is essential. In this paper, a thermodynamic model based on the first law of thermodynamics is developed and the CPUE is proposed. Further, a fundamental parametric investigation is conducted to understand the effect of different desiccant types, structure parameters and operating conditions of air and water flow. The results show that ratio of metal to desiccant and outlet air temperature in dehumidification process are the key factors on the CPUE. CPUE of metal–organic framework DCHE is more than 0.95, which is superior to the other investigated desiccant types. Then, thermodynamics model of a vapor compression air conditioner is built to evaluate the electrical coefficient of performance of the system using DCHEs. The results for different desiccant types can achieve 6.5–8.2 at 15/40 °C evaporation/condensation temperatures.

Gradient-based optimization of micro-scale pressurized volumetric receiver geometry and flow rate

This study focuses on the design optimization of a micro-scale pressurized volumetric receiver by changing geometry and flow rate constrained by the volume, outlet air temperature, and outer surface temperature. The pressurized volumetric receiver model is replicated from an existing model, which assumes constant air pressure and neglects the convection loss from the cavity. The existing model is revised from a solver to a design optimizer.The replicated model is restructured using OpenMDAO (Open-source MultiDisciplinary Analysis and Optimization) framework, and analytical derivatives are implemented for efficient derivative calculation to increase optimization performance. The replicated model is verified, and the maximum outlet air temperature difference is less than 0.05%. Optimization performance, selection of optimizers, the effect of the domain size, and radiative methods are discussed. The combined impact of the design variables is observed by selecting SLSQP (Sequential Least SQuares Programming) and trust-region optimizers. Optimization performance is tested in different domain sizes and compared with a design of experiments analysis. For testing the impact of radiative heat transfer methods to design optimization, the Rosseland approximation, and P1 method are selected. Depending on the design domain, a solution methodology is suggested for future receiver design optimizations applicable for macro-scale pressurized volumetric receivers.

Experimental studies and 3D simulations for the investigation of thermal performances of a solar air heater with different spiral-shaped baffles heights

A new design of Solar Air Heater (SAH) with spiral flow path is studied experimentally and numerically. The spiral-shaped SAH performance is studied at various mass flow rates, inlet temperatures, radiation intensity and baffle heights. Similarly, a CFD model is developed using “ANSYS Fluent” software to study the fluid flow and heat transfer in the SAH. Mesh independence is performed in order to choose the appropriate mesh. The discrete ordinate (DO) radiation model and the k-ω Shear Stress Transport (SST) turbulence model are used to study the radiative heat transfer and the turbulent flow, respectively in the SAH. Effects of different baffle heights (42 mm,50 mm,70 mm,90 mm, 110 mm and 130 mm) for different mass flow rates (input velocities:5 m/s,10 m/s,15 m/s, 20 m/s and 25 m/s) are numerically investigated. Local flow characteristics are presented and discussed. The results show a good agreement between the numerical model and the experimental data with an average error of 3.6%. The maximum outlet air temperature of the SAH during the test days reached 77.7 °C with input velocity of 5 m/s. The maximum thermal efficiency is founded for geometries having 110 mm and 130 mm baffle-heights ranges between 40% and 59% for an airflow of 0.0075 kg/s and 0.038 kg/s, respectively. The geometry having a 110 mm baffle-heights shows the optimum thermal performance of 13% higher than standard geometry (50 mm baffle height).

KINERJA GAS PENUKAR PANAS ALIRAN BALIK SHELL AND TUBE UNTUK PENGERING PERTANIAN

Abstract—One of the important post-harvest processes of rice is drying. Drying is divided into two, namely natural drying (using sunlight) and artificial drying (using tools). In this study drying utilizes heat from a biomass furnace and a configuration of heat exchanger pipes. Where the utilization of heat and the configuration of heat exchanger pipes in the design can increase thermal efficiency because the exhaust hot air mixed with smoke can still be used for drying. The configuration of the heat exchanger pipe greatly influences the expected moisture content level. The purpose of this study was carried out to determine the performance of the shell and tube counter flow heat exchanger for agricultural dryer gases with a heat source from biomass and to find the effect of the configuration of the heat exchanger pipe arrangement on the working process of the drying machine. This research is an experimental test of the performance of heat exchange pipes with a heat source from a biomass furnace. The exchange pipe performance parameters that must be known are temperature and time. The method used in this study refers to experimental and descriptive methods, namely research conducted in a systematic, factual and accurate manner. The results of this study are that the heated air flow rate affects LMTD, heated air outlet temperature, heat transfer coefficient, and efficiency, with variations in the heated air flow rate of 0.11 kg/s, 0.16 kg/s, 0.20kg/s, 0.24kg/s. Highest efficiency of 94% at a heated air flow rate of 0.24 kg/s. and the smallest efficiency of 74% is found in the value of the heated air flow rate of 0.11 kg/s.
 Keywords : dewatering, biomass, pipe configuration, heat exchanger pipe

Temperature estimation of a receiver equipped with a 3D compound parabolic concentrator

Solar Tower Power Plant (STPP) require a high concentration ratio to provide high working fluid temperatures for power generation. Three-dimensional Compound Parabolic Concentrator (3D-CPC) can be used to increase the concentration ratio in the receiver. This paper estimates the air outlet temperature of an indirectly irradiated solar receiver equipped with a 3D-CPC for STPP. For this purpose, the STPP subsystems such as the heliostat field, the 3D-CPC and the receiver are sized for an electrical power of 30 kW. An in-house Matlab code is developed and executed the configuration of the heliostats in the field. The result of the Monte Carlo ray tracing (MCRT) method is used to provide boundary conditions to the Computational Fluids Dynamics (CFD) model. The CFD model is used to simulate the conjugate heat transfer in the receiver. Based on this, a heat source is created from the solar rays absorbed in the receiver. This heat source is implemented as a volumetric heat source in Ansys Fluent by UDFs functions. Thus, the in-house Matlab code is validated by simulating the PS-10 heliostat field and the CFD model is also validated by simulating the Weizmann heliostat field. The results show that the solar field is consisted of 175 heliostats of 2 m2 surface area and 1.5 m height each. The 3D-CPC truncated at 35° increased the concentration ratio by a factor of 4.91 for an optical efficiency of 80.66 %. A receiver mesh count of 1,076,958 gave convergence of the air outlet temperature. 1.5 × 106 rays are found to get independence of the absorbed heat flux in the receiver. The temperature found on the heated solid is 1063.4 K. For a porosity of 56.02 % and a mass flow rate of 0.11 kg/s, a temperature of 1218 K is reached at the outlet of the receiver. The results show that the use of a 3D-CPC increase the concentration ratio and, consequently improve the thermal performance of the receiver. It is important to note that, parameters such as mass flow rate and porosity have a strong influence on the air outlet temperature.

Visualized study of wetting enhancement and thermal performance of fiber-coated indirect evaporative cooler

Poor wetting is a serious problem facing the traditional aluminum and polymer indirect evaporative cooler, which largely deteriorates its cooling performance. Therefore, a fiber coating (70% rayon + 30% polyester textile) is proposed to be attached to the plate heat exchanger walls to improve the wetting condition by its good moisture diffusion. Firstly, the characteristics of the fiber are evaluated by a laser microscope, wicking height and diffusivity tests. Then, its application on an indirect evaporative cooler is investigated. On one hand, to quantitatively evaluate the wetting enhancement by the fiber, comparative visualized experiments are carried out between fiber-coated and non-coated cooler to investigate the water distribution, wetting ratio and water retention at three typical core positions under different spraying time (5 s–180 s), water flow rate (2 L/min–6 L/min) and nozzle height (50 mm to 250 mm). The visualized experiment innovatively combines fluorescence display and digital image processing methods. On the other hand, the thermal conductivity of the fiber-coated plate is tested and used as input for the heat and mass transfer model of indirect evaporative cooler to predict the outlet air temperature. The results show that the non-coated plate suffers from uneven water distribution and low wetting ratio, but the fiber coating can significantly improve the wetting conditions by providing 100% wetting ratio in only 30 s under 150 mm nozzle height and 5 L/min flow rate. The influence of thermal resistance of wetted fiber on outlet air temperature is negligible, but the dry fiber will increase the supply air temperature by 0.3 °C.

Digital twin model and global sensitivity analysis of an indirect type solar dryer with sensible heat storage material: An approach from exergy sustainability indicators under tropical climate conditions

This research study presents the development of a digital twin model using artificial neural networks and global sensitivity analysis to estimate different exergy sustainability indicators (improvement potential, waste exergy ratio, and sustainability index) of a conventional indirect type solar dryer and an indirect solar dryer with a thermal storage system (ITSD-TSS) from the experimental evaluation of tomato drying under tropical climate. The artificial neural network was trained using the database generated from the solar drying process, where solar radiation, ambient temperature, wind velocity, and relative humidity were considered model inputs to estimate the annual values of the absorber plate, solar collector, and drying chamber outlet air temperatures. Subsequently, these temperatures were used to determine the exergetic sustainability indicators from a solar dryer energy balance. On the other hand, the Sobol method was used for the global sensitivity analysis, which allowed obtaining the sensitivity indices and the percentage contribution of each input variable. The experimental results demonstrated that the minimum drying time was reached at 22 h with ITSD-TSS with limestone and the drying efficiency was 12.57 %. Regarding the artificial neural network, a maximum R2 value of 0.9896 was achieved between the experimental and simulated data obtained using the Levenberg-Marquardt algorithm, and the maximum values of the absorber plate, solar collector, and drying chamber outlet air temperatures were 98.62, 81.71, and 81.64 °C, respectively. The best annual average values obtained for the improvement potential and waste exergy ratio were 389.87 W and 0.49, respectively, for the conventional dryer, and the sustainability index was 1.58, corresponding to the ITSD-TSS with beach sand. The global sensitivity analysis revealed maximum values of 0.6096 and 0.8911 for the first-order and total-order Sobol indices, respectively, and the percentage with the highest contribution was 58.4 %, corresponding to the ambient temperature in the drying chamber outlet air temperature. Finally, the economic evaluation indicated that the ITSD-TSS with limestone presented the highest annual savings with $ 1264 USD, but the conventional dryer reported the lowest payback period of 0.12 years. The methodology used in this work allows a more representative estimation of the storage system integration in an indirect solar dryer from an exergetic approach, which is essential for evaluating new technologies that integrate energy storage or other processes to improve its performance.

Optimization of spray-drying process parameters on strawberry (Fragaria ananassa D.) extracts microcapsules quality

BACKGROUND: The strawberry is a fruit with great acceptance by the consumer due to its pleasant flavor and functionality; It is rich in vitamin C, tannins, flavonoids, anthocyanins, catechin, quercetin and kaempferol, organic acids and minerals. OBJETIVE: The objective of the research was to evaluate the effect of the feed formulation and the spray-drying process on the quality of strawberry extract microcapsules (EMs). METHODS: The response surface methodology was used with a central composite design centered on the face (α= 1), considering the factors: maltodextrin (MD), inlet air temperature (IAT), outlet air temperature (OAT) and atomizing disk speed (ADS), and the response variables: humidity (Xw), water activity (aw), solubility (S), wettability (We), hygroscopicity (Hy), bulk density (ρb), compacted density (ρc), total phenols (TP), antioxidant capacity, angle of repose (AR), strawberry powder particle size (D[3 ;2]), color (CIE-Lab), and process yield (Y). RESULTS: The aw and Xw values guarantee microbiological stability and control over degradation reactions in EMs. For the levels evaluated, the S was affected by OAT and ADS, and interaction IAT*MD, ADS*MD, IAT2, and MD2. The We depended on the factors IAT, OAT, and the interactions IAT*OAT and IAT*MD. ABTS activity was affected by the factors ADS, ADS*MD and IAT2. The Y was affected by OAT, MD, IAT*OAT, IOT*ADS, IOT*MD, OAT*ADS, ADS*MD, IOT2, and OAT2. The increase in MD caused a decrease in Hy. The value of L* was affected by ADS and MD, effects due to temperature did not affect the levels evaluated, and chromaticity a* was positively affected by the increase in ADS. IAT and MD presented a statistical effect on AR. CONCLUSIONS: The experimental optimization reached a desirability of 73.7%, being the optimal conditions: IAT (154°C), OAT (89°C), ADS (16,805 rpm), and MD (11.5%).

Investigation of the integrated fuel cell, battery, and heat pump energy systems

The integration of an advanced fuel cell battery electric vehicle was proposed to extend the driving range, increase the overall energy efficiency, and produce an additional cabin space heating service for on-board vehicle application in winter. The adopted heat pump absorbs heat from the fuel cell and battery during charging and discharging scenarios at the heat pump's cold end and transfers it to the cabin supply air for cabin heating. A numerical model for the proposed system was developed and validated by published experimental results. A comprehensive evaluation of the influence of fuel cell output current, battery discharging rate, ambient air temperature, evaporator coolant inlet temperature and refrigerant subcooling degree on the Coefficient of Performance (COP), outlet air temperature, and Equivalent Effective Battery Capacity (EEBC) were conducted. In addition, in this study, a detailed comparison of proposed system to previously published existing systems was carried out in terms of COP, heating capacity, EEBC, and operating price in order to examine the advantages of the proposed system. Results showed that the proposed system was not sensitive to ambient air temperature, but evaporator coolant inlet temperature had the greatest impact on COP, compared to other defined independent variables. A maximum COP of 6.07 could be observed when the evaporator coolant inlet temperature was 32 °C. Although increasing fuel cell output current and battery discharging rate could increase heating capacity, it would decrease outlet air temperature as well. The price of a single charging cycle for running for a 4-hour period was estimated. Compared to conventional Electric Vehicle Air Source Heat Pump (EVASHP) system and Positive Temperature Coefficient (PTC) heaters, the proposed system has the lowest cost which was £10.40per charging cycle while the others are £13.8 and £19.2 respectively when providing the same EEBC and heating capacity. Additionally, the payback period was 10,500 charging cycles. Overall, this study provides a potential solution for efficient cabin heating of electric vehicles in extremely cold weather with twice the EEBC of the existing EVASHP system and with 2.8 times of a PTC system both at −20 °C and the operating price is also 1/3 lower than the existing EVASHP. Meanwhile, the COP of the proposed system is 2.3 times that of the existing systems. It can sufficiently increase the driving range of electrical vehicles in winter and eliminate driving range anxiety.

A comparison of steady-state and transient modelling approaches for the performance prediction of solar air heaters

• A transient solar air heater model using high resolution weather data is developed. • Transient model is compared to stationary model using hourly averaged weather data. • Steady approach results in large deviations, especially under variable cloud cover. • Large differences between approaches in useful energy above threshold temperatures. • Potential implications for latent heat storage, solar drying and other processes. Due to the nature of solar energy, the operation of solar air heaters is fundamentally transient, but most mathematical modelling published to describe their behavior has used stationary models coupled with hourly-averaged weather data. Little attention has been paid to the transient behavior of solar air heaters under real, highly variable weather conditions. In this study, the common modelling approach using a steady-state description of solar air heaters is compared to predictions of using a transient model to which minute resolution weather data is given as input. The steady-state approach was found satisfactory, although not optimal, only under clear sky conditions, with relatively small outlet air temperature errors compared to the results obtained with the transient model. Under less favorable conditions with partial cloud cover, the outlet air temperature with the transient model presented large variations due to the sudden changes in solar radiation not captured in the steady-state approach. With the solar air heater parameters employed, instantaneous deviations of almost 15 °C were found, as well as errors in the predicted useful energy above threshold temperature levels. These results support the use of transient models of solar air heaters and high resolution weather data for accurate, short-term modelling of solar drying, latent heat storage and other highly temperature dependent processes.

Energy effectiveness analysis of desiccant coated heat exchanger based on numerical method

The conventional air-to-air heat pumps rely heavily on the condensation dehumidification principle to regulate air humidity, thereby severely limiting the system energy efficiency. Significant energy efficiency improvements can be realized by coating high-performing solid desiccants on both evaporator and condenser heat exchangers. Thus far, existing fundamental analysis developed to evaluate energy performance improvement and achieve accurate performance prediction of desiccant coated heat exchangers with two-phase refrigerant (DCHERs) has been impeded by the complex physical phenomena, approximations in the heat/mass transfer paths, and the severe reliance on the use of empirical correlations. Therefore, in this work, a mathematical approach has been judiciously developed based on mass, momentum, energy, and species conservation principles in order to study the flow field distribution within DCHERs and predict their performance. The model is extensively validated with experimental data obtained under various working conditions with discrepancies of ±10 % and ±9 % for outlet air temperature and humidity, respectively. The model provides essential information on local temperature and humidity distributions, and key insights on the transient heat and mass transfer phenomena. Further, a general design guideline for the performance enhancement of DCHERs is established. Key results from the study reveal that the air RH varies within 15 % along the DCHER’s flow channel. Thick desiccant coating, high inlet air relative humidity, and long air-desiccant contact time markedly improve latent energy effectiveness to a maximum of 0.51. Lastly, employing the proposed guideline to design the heat exchanger with optimal tube configurations yields a 23 % enhancement of latent energy effectiveness.

Experimental and Theoretical Investigations of a Plate-Fin Water Intercooler Equipped in a Boosted Diesel Engine

Abstract Intercoolers utilized in turbocharged engines are critically essential to efficiently improve the engine volumetric efficiency and therefore the engine specific power. Although boosting the internal combustion engines has been extensively investigated, further studies are required to provide relevant approaches to optimize the heat transfer coefficient. This paper experimentally and theoretically investigates the influence of inlet coolant velocity on heat transfer characteristics of an air-to-water intercooler equipped in a turbocharged diesel engine. This aims to optimize the heat transfer rate from water to air under typical engine operating conditions. The experiment has been conducted using a fully equipped engine testbed. The engine is turbocharged with a plate-fin intercooler. The intercooler is a perpendicular air–water heat transfer system that could be suitable for boosted marine engines or power generators. A simulation model was also developed using the finite volume model in the ansysfluent package. The distributions of inlet and outlet temperature, pressure, and velocity of air and coolant under various inlet water velocity and engine operating conditions are examined. The optimal heat transfer rate from air to water was achieved for this intercooler. The outlet air temperature after the intercooler decreases by about 10 °C, engine thermal efficiency increases by 0.7% approximately, engine power enhances by 2.5%, and the specific fuel consumption decreases by 0.82%. The CFD simulation and experiment model developed in this study for the plate-fin water intercooler could be a useful approach to optimize other intercooler systems. In this study, with a 270 × 270 × 10 mm plate-fin perpendicular air–water intercooler, an optimal cooling water velocity of 1.0 m/s, corresponding with a flowrate of 1780 liter/hr, is achieved.

Modeling the impact of spray drying conditions on some Maillard reaction indicators in nano‐filtered whey

AbstractThe objective of this study was to develop a mathematical model to predict the loss of available lysine and the formation of Maillard reaction (MR) compounds in sweet whey during spray drying process. The heat damage and other spray drying process‐related variables were estimated with the compartment model coupled to the drying kinetics of droplets. The model was adequate to determine the outlet temperature of air and the final moisture content of the product. The model predicted available lysine losses like those found experimentally. However, the model predicted a higher furosine concentration than that found experimentally. The browning index exhibited no significant increase for experimental and calculated results during the spray drying, possibly because the MR did not reach the final stages. The model showed to be comparable to those reported in the literature, with the advantages of being computationally less time‐consuming and providing confidence intervals for the response variables.Practical applicationsThis work presents the integration of several mathematical models to predict the loss of available lysine and the formation of some heat damage indicators during the spray drying of whey. The model contributes to the understanding of relevant variables—such as residence time distribution, global heat transfer coefficient of the dryer, thermal properties of the drying media, glass transition temperature, drying kinetics, drying air inlet, and outlet temperature among others—on the loss of food quality regarding the thermal process. This information could help the decision‐making process that can lead to the optimization of spray drying to obtain food with minimal thermal damage and therefore the maximum amount of available nutrient content.

Prediction of outlet air characteristics and thermal performance of a symmetrical solar air heater via machine learning to develop a model-based operational control scheme-an experimental study.

This study develops reliable and robust machine learning (ML) models to predict the outlet air temperature and humidity and thermal efficiency of a solar air heater (SAH). Also, the application of predictive models for optimal control of the SAH operation is proposed. For this, the work contains three main parts: (a) a vertically-mounted symmetrical SAH was installed outside of a building room and operated throughout the winter of 2022. (b) By conducting experiments for five air mass flow rates, a large dataset with more than 62,500 sample points was collected. (c) Six input features containing time, environmental-related attributes, and SAH variables were applied to develop several state-of-the-art ML algorithms. To figure out the most accurate models for predicting output variables, the dataset was partitioned into three parts. Also, various modeling performance evaluation criteria were calculated and compared on the validation and test sets. Among these models, the gradient boosting machine algorithm based on LightGBM implementation achieved the best degree of generalization in modeling the target variables. The results demonstrated that the developed models obtained the lowest R-squared and the highest mean absolute percentage error of 0.9827 and 2.95%, respectively, on the test set. Moreover, the offline analysis of SAH operation based on the proposed control scheme demonstrated that 350 kWh of thermal energy can be generated during the application in the one-year winter season, 24% more than SAH operation without a model-based control strategy.

Four-Lobe Blower Performance Assessment

Abstract This paper presents a new 4-lobe blower for supercharging a two-stroke engine. Based on a modified Roots compressor manufactured prototype shows pros and cons of an innovative profile. The results demonstrate that the shape of rotor edges effect out pressure stability. The measurement results include the main assessed parameters: outlet pressure, overall efficiency, losses and outlet air temperature.

Prototype of a Solar Collector with the Recirculation of Nanofluids for a Convective Dryer

Solar collectors are thermal devices that can trap solar energy and convert it to heat. This heat can be used for different industrial applications, for example, the drying of food is one of the most useful applications of solar collectors. This work aims to design and build a solar collector using nanofluids for the convective drying of food. The dimensions of the solar collector were 1 m2 by 20 cm with an angle of inclination of 45°. The collector was composed of 9-mm thick tempered glass and a heat exchanger in which the nanofluids circulate. Nanofluids were designed based on canola oil and nanopowders (>50 nm) of Al2O3, CuO, and a 1:1 (w/w) mixture of both. Thermal profiles were determined using differential scanning calorimetry (DSC). The solar collector temperatures were recorded using an Agricos® unit. The maximum temperatures of the air leaving the collector were 39.1°C, 44°C, 54°C, and 47.1°C for canola oil, and the nanofluids composed of Al2O3, CuO, and the 1:1 mixture, respectively, with a maximum efficiency of 65.09%. An increase in the outlet air temperature was observed using the nanofluids compared to canola oil alone

Evaporative cooling performance prediction and multi-objective optimization for hollow fiber membrane module using response surface methodology

• A counter-flow hollow fiber membrane-based evaporative cooler is proposed. • A numerical model is established and validated by experimental data. • The regression models for performance prediction are derived by response surface methodology. • The desirability function is adopted to perform multi-objective optimization. • The accurate regression models can facilitate the regional applicability analysis. The proposed hollow fiber membrane-based evaporative cooler (HFMEC) is expected to be an alternative to the conventional direct evaporative cooler because of its advantages such as the isolation of air from liquid water and the large specific surface area. For the common counter-flow HFMEC with many influencing parameters, it is a bit laborious or even incompetent to rely on experiment or numerical simulation for the parametric study and optimization. Therefore, this study aims to develop accurate and rapid performance prediction models for the proposed HFMEC with the statistical method. An experimental test system for a counter-flow HFMEC was set up. 120 sets of simulations were carried out based on the experimentally validated numerical model and the response surface methodology. Five accurate and practical empirical equations were derived using simulated data: the considered eight input factors consisted of four operating parameters and four membrane module design parameters; the five output responses included the outlet air temperature, outlet air relative humidity, saturation effectiveness, cooling capacity per unit volume, and COP. These simplified equations were adopted to facilitate parameter sensitivity analysis and multi-objective optimization. A case study on the regional applicability of the counter-flow HFMEC demonstrated the ability of the derived equations to conveniently make performance predictions. The results indicated that the regression models could contribute to the rapid performance prediction of the counter-flow HFMEC, aiding in optimization and design.

CFD analysis of the performance impact of geometrical shape on volumetric absorbers in a standard cup

The effect of three geometrical parameters of volumetric absorbers in a standard cup –height of the chamfer, the angle of the chamfer and the height of the straight protruding side– on the air temperature at the receiver outlet, the receiver's thermal efficiency and the temperature of the interface between the absorber and the cup are analysed. For the study, 126 different geometrical configurations have been checked in a two-dimensional CFD model. A silicon carbide (SiC) ceramic foam volumetric absorber was selected for the study, and the numerical model adopted includes the simulation of the performance of both the porous media and the cup body. The modelling strategy used was implemented in the commercial CFD code STAR-CCM+ v16.02.009® with a local thermal non-equilibrium model and the Rosseland approximation for the volumetric absorber. The results conclude that different sets of geometrical parameters can produce similar results in terms of air temperature at the cup outlet, thermal efficiency of the system and temperature at the interface between the volumetric absorber and the cup. Emphasizing that the larger the chamfer height the lower the air temperature at the outlet and that the effect of the protruding absorber parameter is influenced by two possible boundary conditions, inlet fluid velocity and wall, and the latter produces the higher air outlet temperature.