Hot Air Temperature Research Articles

Two-Layered Model Predictive Control Strategy of the Cut Tobacco Drying Process

In this article, a two-layered model predictive control strategy is proposed for the nonsquare system of nonlinear cut tobacco drying process. The control objective is to optimize the drum dryer temperature, hot air temperature, and cut tobacco outlet temperature meet the process constraints while meeting the moisture content of cut tobacco. Firstly, the tobacco drying process system was introduced, and the nonsquare system model and performance index function were established. Then a nonlinear moving horizon estimator (NMHE) and real-time optimization (RTO) are designed. NMHE provides state and parameter estimation for the controller, and RTO provides an optimal operating setpoint for the controller. Subsequently, a two-layered model predictive control (SSTO-MPC) design integrated with a steady-state target optimization layer (SSTO) is proposed for the nonsquare system of nonlinear cut tobacco drying process. Extensive simulations under different scenarios illustrate the effectiveness of the proposed SSTO-MPC design compared with the conventional MPC.

Effect of Drying Temperatures on the Peanut Quality during Hot Air Drying.

Peanuts are usually with high moisture after harvest and must be dried to prevent mildew. Hot air drying is the most commonly used method for peanut drying. The purpose of this study was to evaluate the drying temperatures on the peanut qualities. In this paper, fresh peanuts were dried with solar radiation (control group) and hot air at 35-60°C until the moisture content of peanut reduced below 10%. The physical (texture, damaged percentage of red testa and breakage percentage of peanut kernel), physiological (germination) and biochemical (the contents of vitamin E and aflatoxin B1; acidity values, iodine values, peroxide values and fatty acid composition of peanut oil; solubility, emulsifying, foaming, water-holding capacity and oil-binding capacity of peanut protein) properties of peanut kernel were determined under different drying conditions (solar radiation, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C). The results showed that hot air temperatures had obvious influences on peanut qualities. The damaged percentage of red testa and breakage percentage of peanut kernel increased remarkably when the drying temperatures were above 45°C. Meanwhile, when drying temperatures were more than 45°C, the acid value and peroxide value of the extracted oil increased significantly. Furthermore, some properties exhibited prominent changes when the temperatures were higher than 50°C, such as hardness, brittleness, germination percentage, and the Vitamin E content of peanut kernel. In addition, the research results revealed that hot air can increase hydrophobicity of peanut protein and affect the functional properties of peanut protein. Therefore, it could be concluded that peanut should be dried by hot air below 45°C for quality maintenance. It also provided reference to choose suitable drying temperatures based on the final use of peanut.

THE EFFECT OF THE HEAT FLOW AMOUNT AND CONTINUITY ON DRIED RICE QUALITY

A research was conducted through field tests on mixed-flow rice dryer. The realization of the planned study was carried out by applying intermittent system of drying and selection of correct drying conditions. The heat flow amount and continuity were observed and evaluated in multi-thermal zoned drying process. Hot air temperatures, up to 45 oC, were used. Paddy from local rice varieties, with the initial moisture content, wet basis, up to 26 %, was processed to the desirable final oisture content, from 8% to 12%. Reached at three levels, the final moisture content depends on intended rice use: 1) for sale, 2) for one year storage and 3) for five years storage. The effect of drying air temperature level, heat flow intensity and retention time duration on dried paddy quality was analyzed.

Dead Band Zone Model Predictive Control of Cut Tobacco Drying Process

In this article, an L1-Norm model predictive controller with a dead band zone is proposed for the cut tobacco drum dryer system. The control objective is to make the drum dryer temperature, hot air temperature and cut tobacco outlet temperature meet the process constraints, and optimize the outlet moisture content of the cut tobacco. First, the cut tobacco drum dryer system is introduced, and the nonlinear open equation model is established. Then an L1-Norm moving horizon estimator (MHE) is designed to provide state and parameter estimation for the controller by using its ability to deal with nonlinearity and constraints. A model predictive control (L1-Norm zone MPC) for L1-Norm target tracking with a dead band zone is proposed for the cut tobacco drum dryer system. The simulation results show that the proposed L1-Norm zone MPC (L1-ZMPC) better-tracking performance and the controller's minimum action economic characteristics compared with the traditional setpoint tracking model predictive control.

Design and simulation of a new PCM heat exchanger for domestic hot water and air temperature control

Based on previous experiences which have proven the efficiency of PCM heat exchangers for air temperature control, we designed and simulated new PCM heat exchanger structures made of multiple PCM layers sandwiched between loading and discharge layers. By circulating air or water in the discharge circuit, these heat exchangers can be used for heating air or water, respectively. For both use cases, a three-dimensional analysis of the phase change and calculations of the charge/discharge powers were performed for the fusion and solidification processes. We obtained heating discharge powers ≥ 2.6 kW/m3 for 8 hours for air and ≥ 65 kW/m3 for 13 minutes for water with a respective total storage capacity of 28 kWh/m3 and 37 kWh/m3. The heat extraction of air and water flows and their time dependence are discussed according to the percentage of liquid PCM and the temperature profile of the discharge flow inside the heat exchanger.

Optimization of hot air drying process of corn using genetic algorithm and response surface methodology

ABSTRACT To study the effect of temperature and humidity on the drying indexes and quality indexes of corn and to optimize the corn drying process, an orthogonal experiment of hot air drying with variable temperature and humidity was designed. The drying process of the actual dryer was simulated by taking the gradient of hot air temperature (x) and the gradient of absolute humidity (y) as the experimental factors. The results showed that the drying indexes (drying time, average drying rate, accumulated temperature) reached optimal values under the drying conditions of cooling and dehumidifying; among them, the optimal value of x was 10 °C (50 °C, 40 °C, and 30 °C), and the optimal value of y was 8 g/m3 (25 g/m3, 17 g/m3, and 9 g/m3). The quality indexes (percentage of damage, fatty acid value, germination rate) reached the optimal values under the drying conditions of heating and humidifying; among them, the optimal value of y for the three quality indicators was 8 g/m3 (9 g/m3, 17 g/m3, and 25 g/m3), but the optimal value of x were different, the optimal value of x were 2.65 °C (39.35 °C, 42 °C, and 44.65 °C), 2.24 °C (39.76 °C, 42 °C, and 44.24 °C) and 6.33 °C (35.67 °C, 42 °C, and 48.33 °C). A genetic algorithm was used to transform the multi-objective function into one index, and the results show that: when x was 2.26°C (39.74°C, 42.00°C, and 44.26°C), y was 4.84 g/m3 (12.16 g/m3, 17.00 g/m3, and 21.84 g/m3), the comprehensive characteristics of the drying process can be optimized.

DESIGN AND STUDY OF DIMENSIONAL PARAMETERS INFLUENCE ON VORTEX TUBE BEHAVIOR

Vortex tube is a thermodynamic device, with no moving parts, applied to separate hot and cold air from compressed air injected into the tube. It has many applications in the industry, for example, among others, it can be mentioned electronic systems cooling, machining processes cooling and environmental chambers. This paper presents the design and tube dimensioning based on parameters and data found in the literature. Therefore, a prototype has been made and tested, which allowed the understanding of the influence of internal tube diameter and width on the hot and cold air temperatures while submitted to compressed air with pressure varying from 1 to 2.5bar. Results of tested configurations indicates that the relation between tube length and diameter (L/D) has small influence on vertex tube behavior, meanwhile, 3/8” tube diameter shows lowest temperatures on cold flow (-6.5°C, -8.0°C and -8.5°C) and higher COP (≈ 0.15).

CO-drying characteristics of sticky sewage sludge pre-conditioned with biomass and coal

The sticky sewage sludge was pre-conditioned using biomasses and pulverized coal and thin-layer drying experiments were conducted to investigate the co-drying characteristics of the mixtures. Parametric studies were carried out to investigate the effects of mixing ratio, layer thickness, hot air temperature and velocity on the drying process and to obtain the optimum drying conditions. The effective diffusivities and activation energies in the drying process of sludge and biomass/coal mixtures were determined. Experimental results showed pre-conditioning can increase the bed porosity and improve the drying rate, allowing a 50% reduction of the total drying time for the sludge/sawdust mixtures. The mixing ratio, layer thickness and hot air temperature had significant effects on the sludge drying rate. Addition of sawdust and bran reduced the drying activation energy of sewage sludge from 16.67 kJ/mol for pure sludge to 12.97 kJ/mol, 10.99 kJ/mol respectively.

Fabrication and optical properties of dichroic polarizing films based on poly(vinyl alcohol)-heteropolyacid nanocomposites

We report on a new type of poly(vinyl alcohol)(PVA)-based dichroic polarizing films whose visible dichroism is due to long-chain linear polyenes, –(CH=CH)n–, formed in the course of acid-catalyzed thermal dehydration of the polymer. The distinguishing feature of these films is that the solid acid catalyst (12-tungstophosphoric acid, TPA) is used instead of the liquid ones. Thin PVA films with embedded TPA nanoparticles were fabricated by solution casting technique. Subsequent stretching and annealing of these PVA/TPA nanocomposites produced PVA–polyene/TPA dichroic polarizing films with the thickness below 10 µm. Transmission electron microscopy, Fourier-transform infrared spectroscopy, and UV–Vis spectroscopy techniques were used to characterize the films at various stages of preparation. The fabricated polarizing films showed polarization efficiency exceeding 94% and transmittance higher than 40% in the visible range. The polarizing properties of the films did not deteriorate upon prolonged exposures to hot humid air (60 °C, 90% RH) and high temperature (90 °C). The nanocomposite polarizing film proposed in this study may have application potential in thin and flexible optoelectronic devices that must operate under harsh environmental conditions.

Thermodynamic Analysis of Packed Bed Thermal Energy Storage System

A packed-bed thermal energy storage (PBTES) device, which is simultaneously restricted by thermal storage capacity and outlet temperatures of both cold and hot heat transfer fluids, is characterized by an unstable operation condition, and its calculation is complicated. To solve this problem, a steady thermodynamics model of PBTES with fixed temperatures on both ends was built. By using this model, the exergy destruction, thermocline thickness, thermal storage capacity, thermal storage time, and other key parameters can be calculated in a simple way. In addition, the model explained the internal reason for the change of thermocline thickness during thermal storage and release processes. Furthermore, the stable operation of the PBTES device was analyzed, and it was found that higher inlet temperature of hot air, and lower temperature difference between cold and hot air can produce less exergy destruction and achieve a larger cycle number of stable operation. The work can be employed as the basis of the design and engineering application of PBTES.

Optimization of Microwave Coupled Hot Air Drying for Chinese Yam Using Response Surface Methodology

The effect of microwave coupled hot air drying on rehydration ratio (RR) and total sugar content (TSC) of Chinese yam was investigated. Single factor test and response surface methodology were used for process parameter optimization with hot air temperature, hot air velocity, slice thickness, and microwave power density as variables and RR and TSC of dried products as responses. The effect of variables on RR followed the order: slice thickness > hot air temperature > microwave power density > hot air velocity. The effect of variables on TSC followed the order: slice thickness > microwave power density > hot air velocity > hot air temperature. The optimized process parameters were hot air velocity of 2.5 m/s, hot air temperature of 61.7 °C, slice thickness of 8.5 mm, and microwave power density of 5.9 W/g. Under the optimal conditions, the predicted values of RR and TSC were 1.90 g/g and 5.74 g/100 g, respectively, which is very close to corresponding actual values (1.83 g/g and 5.72 g/100 g). The desirability of 0.913 further validated the effectiveness of the model. The findings from this work may apply to other agricultural products.

The drying rate of mushroom on tray dryer and effect of mushroom powder on organoleptic properties of Batagor

Oyster mushrooms and straw mushrooms are currently great demand in the food industry. Mushrooms have the characteristics that are easily damaged and decomposed. The effort of preserving mushrooms is by drying using hot air at a certain temperature and flow rate. The purpose of this study was to determine the drying rate of oyster mushrooms and straw mushroom in variations temperature and flow rate of hot air. In this study, the drying of mushrooms was carried out with a tray dryer that has a stacking rack with dimensions of 30 cm x 25 cm. The temperature variations used were 30, 40, 50ºC and the dryer air flow rate was 1, 2, 3 m/s. The dried mushroom with a moisture content of less than 10% is mashed to a powder then added to the food (Batagor) for an organoleptic test. The best drying result is obtained at temperature 50°C and flow rate of 3 m/s with a drying rate of 1.52 kg water/m2.h. Organoleptic test on Batagor produces the most preferred flavour by using type mushroom of Volvariella volvacea, and for aroma and texture preferably with Pleurotus ostreatus.

Heat transfer characteristics and drying kinetics of hematite thin layer during hot air convection

Heat transfer characteristics and drying kinetics of the hematite thin layer during hot air convection based on a lab-scale setup were examined at seven temperatures (100, 110, 120, 130, 140, 150, and 160 °C). Four periods during the drying process were detected, a warm-up period, a constant rate period, the first and second falling rate periods. Two isothermal temperature stages were captured during the hot air drying. The average heat transfer coefficients of the whole drying process increased by 28%, 40%, 49%, 56%, 61% and 66% as the hot air temperature rising from 100 to 110, 120, 130, 140, 150 and 160 °C. The effective moisture diffusivities of the hematite thin layer were from 8.37 × 10−9 to 2.05 × 10-8 m2 s−1 for the first falling rate period, and from 1.24 × 10−8 to 4.06 × 10-8 m2 s−1 for the second falling rate period. The isothermal temperature increased with the elevated hot air temperature, which increased by about 56% as the hot air temperature rose from 100 to 160 °C.

Experimental investigations and analysis of wet porous sand layer air-drying process

Experimental studies have been conducted to investigate the wet porous material convective air-drying characteristics. An experimental setup is designed and constructed to examine the air-drying process of a wet sand layer, and it allows dynamic measurements of both the sand layer weight and temperature. Hot air flows down towards the sand layer upper surface to realize a uniform drying of it and multiple thermocouples are embedded in the sand layer to evaluate its temperature distribution. Experiments are carried out for three sand layer thicknesses of 2, 4 and 8 mm and for three hot air temperatures of 45, 60 and 75 °C. Water film evaporation experiments are also performed to obtain the convective heat and mass transfer coefficients, which are then used for the lumped parameter analysis of the sand layer heat and mass transfer. The results show that in the water film evaporation experiment, the water temperature initially increases and then remains constant at the air wet-bulb temperature for a long period of time until the water all evaporates. In the sand layer drying experiment, however, the sand layer temperature continues to increase throughout the drying process, which can be divided into three stages, i.e. the initial rapid, intermediate slow, and final rapid increase stages. The lumped parameter method is employed to analyze the sand layer heat transfer because of the small sand layer thickness. Such analysis uses the heat transfer coefficient obtained in the water film evaporation experiment and the sand layer temperature increasing rate to calculate the sand layer moisture content and drying rate. The obtained results agree well with the experimental data. The evolution of water film cover fraction on the sand layer upper surface during drying is also discussed by assuming that the water evaporation occurs mainly at the sand layer upper surface at the drying stage at which the sand layer upper surface is fully wet or partly wet.

Modeling and Optimization of Hybrid HIR Drying Variables for Processing of Parboiled Paddy Using Response Surface Methodology

The effects of hot air temperature (40, 50 and 60 oC) and Radiation Intensity (RI) (0.21, 0.31 and 0.41 w/cm2) on the response variables (drying time, Head Parboiled Rice Yield (HPRY), color value and hardness)) of parboiled rice were investigated. The drying was performed using hybrid hot air–infrared drying. The optimization of drying variables and the relationship between response variables and the influence factors were analyzed using response surface methodology (RSM). Based on RSM results, the best mathematical model for prediction of HPRY, hardness and color value and drying time of samples was linear(R2= 0.96), quadratic(R2= 0.99), linear(R2= 0.93) and linear(R2= 0.99) equation, respectively. The HPRY (62.13- 68.13%) and hardness (130.27- 247.3 N) increased with increasing drying temperature and RI, while the color value (19.77- 18.03) and drying time (59.72- 34.41 min) decreased. The optimized parameters of drying were obtained 55 oC drying temperature and 0.41 w/ cm2 RI.

Parameter Study on Solid Oxide Fuel Cell Heat-Up Process to Reaction Starting Temperature

Solid oxide fuel cell (SOFC) is a promising fuel cell type for use in distributed generation owing to its high energy efficiency, ability to use various fuels, generation of additional heat energy, etc. These advantages arise from its high operating temperature, but this in turn imposes limitations like difficulty in selecting proper materials, restrictions in the operating environment, difficulty of thermal management, and long on/off time. A good deal of research has been conducted on thermal analysis of SOFCs, however little or none on the heat up process parameter study; such studies are required because the heat up process influences thermal stability and efficiency in terms of both time and energy. The level of effects changes depending on the heat up conditions. Accordingly, the present work deals with two heat up conditions and their effects upon the results; these conditions are hot air mass flow rate and the hot air temperature, represented as a temperature difference relative to the SOFC stack. This study is accomplished by means of modeling using MATLAB, including validation of the model by comparison to an International Energy Agency benchmark test. The results show that both conditions affect the saturation time and temperature transition of the model, but to different degrees and in different ways. Especially, saturation time depends primarily on the temperature difference, and changes in the temperature difference between the inlet and outlet is determined by linear equation with the temperature difference as domain and the mass flow rate as slope. From the results, optimal heat up conditions proper to each SOFC geometry or material can be found by changing these variables appropriately.

Experimental and numerical investigation on the evaporation performance of a cyclone-type spray desalination chamber

Complex heat and mass transfer in spray evaporators are areas of intense research due to their increasing predominance in thermal desalination industries. To improve evaporation performance, a cyclone-type spray desalination chamber is developed in this study. Influences of gas-to-liquid volume ratio, temperature and velocity of intake hot air, feeding liquid temperature and nozzle pressure upon evaporation are investigated experimentally and numerically. Thermocouples are used to obtain temperature distribution. Liquid flowmeter and hydrometer are equipped to record evaporation data. Results indicate that swirling flow prolongs the residence time of droplets in the chamber, thus evaporation efficiency can be improved. The rapid development of thermal field is closely related to the two-phase flow and intense phase change heat transfer. Evaporation increases and tends to be stable with gas-liquid ratio, intake air velocity and feeding liquid temperature. Evaporation performance can be improved significantly by increasing temperature of intake hot air. It is highly recommended to control the temperature of feeding liquid and intake air to balance between evaporation performance and energy efficiency. The two-phase flow field can be well organized by matching the spray cone angle and the swirling air flow, thus, a moderate nozzle pressure is suggested to obtain optimal evaporation performance.

Power generation characteristics of a thermoelectric modules-based power generator assisted by fishbone-shaped fins: Part II – Effects of cooling water parameters

ABSTRACT Operation control combined with the optimization of the structure for thermoelectric generators (TEGs) based on thermoelectric modules (TEMs) is an effective method to improve the power generation characteristics of TEGs. The present study is intended to experimentally investigate the power generation characteristics including voltage and power output, and conversion efficiency of a TEM-based TEG, which is added fishbone-fins aiming to enhance heat exchange of hot inlet air to the hot side of TEG. The effects of mass flow rate (MFR) of cooling water on the power generation characteristics of TEGs are analyzed in the case of the hot inlet air temperatures of 200–500°C and a constant MFR of hot inlet air. Compared to TEM-based TEG without fishbone-shaped fins, TEM-based TEG with fishbone-shaped fins has a maximum increase by 31.37 V of voltage output and 16.49 W of power output. Conversion efficiency of TEM-based TEG with fishbone-shaped fins is determined through the temperatures of hot side and cold side as well as figure-of-merit (ZT). As a result, an average increase of 2.93% of the conversion efficiency for TEM-based TEG with fishbone-shaped fins compared to the case of TEM without fishbone-shaped fins is found. In addition, the outlet temperature of cooling water is also practically measured to evaluate the influences of fishbone-shaped fins on the heat flux transferred from hot side to cold side of TEM.

Experimental investigation on a novel triple heat sources-driven absorption heat pump system

This paper presents a novel triple heat sources-driven absorption heat pump system. The exhaust gas is used as the heat source for a high-pressure generator. The superheated refrigerant vapor generated by the high-pressure generator is used for heating the solution in the low-pressure generator 1 by releasing the latent and sensible heat. The low-temperature solar thermal energy serves as the heat source of the low-pressure generator 2. The geothermal energy supplies heat to the evaporator. Heat discharged from the condenser and the absorber is supplied to the air conditioner heat medium water. The high- and low-pressure generators are coupled to each other through an ejector. The introduction of the ejector reduces the pressure of the low pressure generator 2 below the condensing pressure so that the lower temperature solar thermal energy can be utilized. An experimental setup for this heat pump cycle is built, and an experimental investigation is carried out. The influences of the independent variables on the key internal operating parameters and heating performance have been investigated. Experimental studies show that when the hot air temperature is 213 °C and the temperature of the hot water is 43.5 °C, a heating capacity of 26.6 kW can be achieved with a heating performance coefficient greater than 1.7. In this way, an efficient and full use of waste heat is realized, and the results can provide an important basis for the design and wide application of low-temperature solar thermal and geothermal energy.

Drying kinetics, quality and moisture diffusivity of spouted bed dried Sri Lankan black pepper

Drying of black pepper has been investigated in a lab-scale conventional spouted bed dryer. Spouting behavior of black pepper was studied, and the minimum spouting velocity was determined. The effect of operational conditions; drying temperature, air velocity and stagnant bed height on drying kinetics was analysed. The higher values of drying rates were achieved when the dryer was operated with moderately high temperatures, high airflow rates and shallow beds. The results show an increase in effective moisture diffusivity with increasing drying temperature. The highest effective moisture diffusivity of 2.03 × 10-10 m2/s was obtained at a hot air temperature of 75 °C. Extraction and analysis of essential oil from dried black pepper showed that the variation of oil yield with drying temperature is significant for drying temperatures from 45 °C to 75 °C 65 °C was selected as the best drying temperature for black pepper drying in the conventional spouted bed dryer.