Increasing Air Velocity Research Articles

The effect of air temperature, velocity and humidity on respiration rate and rectal temperature as an expression of heat stress in gestating sows.

Global warming combined with increased production (i.e. more piglets, more milk and consequently more heat) means that sows are more often challenged by heat stress. The objective was to develop an effective temperature (ET) equation to predict how air temperature, velocity and humidity affect the respiration rate (RR), rectal temperature (RT) and skin temperature (ST) as an expression of heat stress in gestating sows in order to elucidate the relationship between the thermal parameters and the sows' perception of the environment. The experimental room was equipped with a negative pressure ventilation system with diffuse air inlet through the ceiling, electrical heaters, steam generators and dehumidifiers. An air distribution unit was constructed to generate vertical air velocity. A total of 16 gestating sows were exposed to three temperatures (25°C, 29°C and 33°C), two levels of relative humidity (30% and 70%) and three levels of air velocity (0.2ms-1, 1ms-1 and 2.5ms-1). The RR, RT and ST were recorded every 30min throughout the three 2-h test periods. The estimated effects of humidity and velocity in relation to effect of temperature was nearly independent of whether it was determined from RR or RT, whereas the effect of humidity was much smaller when determined from ST. High coefficients of determination (>0.97) were found for the second order relationship between the estimated ET and RR, RT and ST. An increase in relative humidity from 50 to 70% corresponded to an increase in ET of 0.9°C, while an increase in air velocity from 0.2 to 1.0ms-1 corresponded to a decrease in ET of 1.2°C. The applied ET equation was useful for expressing the combined effect of temperature, humidity and velocity on animals exposed to heat stress. However, multiplying the effect of velocity by the temperature gradient between the animal and the surrounding air did not improve the estimation.

Field measurement and numerical simulation of dust migration in a high-rise building of the mine hoisting system.

Dust pollutants generated from the coal transfer process in a high-rise building of the mine hoisting system not only undermine the operating environment but also reduce the surrounding air quality. Therefore, this study aimed to determine the spatiotemporal distribution of coal dust in the high-rise buildings using field measurement and numerical simulation. Based on the discrete phase model (DPM), the dust migration process under the hybrid ventilation system was investigated in detail. Then, the feasibility of the established model to predict the spatiotemporal distribution of dust pollutants was proven through the measurements of both the airflow and the dust concentration. The present study showed that dust distribution is not uniform in time and space, which also differs for different floors. The dust concentration of the 3rd floor is relatively larger when compared with those of other floors. The dust concentration increases for the upper floors when the upward air velocity increases, while those of the lower floors are not always low due to the backflows, particularly for the 2nd floor. PM2.5 takes up more than 20% of all discharged particles.

Effects of hot air assisted radio frequency drying on heating uniformity, drying characteristics and quality of paddy

In order to solve the big challenge of cracking during paddy drying, this research revealed the application of hot air assisted radio frequency (HA-RF) drying technology on paddy grains based on its volumetric heating advantage. Drying characteristics and paddy quality were investigated at various combinations of air temperatures (50 °C, 55 °C and 60 °C), air velocities (0.5 m/s, 1.5 m/s and 2.5 m/s) and electrode gaps (100 mm, 110 mm and 120 mm). A comparison between the tempering-intermittent hot air (HA) drying was investigated to demonstrate the applicability of HA-RF drying on paddy grains. Increase in temperature and air velocity, while decrease in electrode gap resulted in increased average heating rate. The RF assistance significantly enhanced the drying rate of paddy grains and reduced drying duration and energy consumption by up to 62.5% and 42.9%, respectively, as compared to HA drying. A higher color and taste value, while a lower crack ratio (CR) without damage in starch granules of microstructure which caused formations of internal fissures were observed in HA-RF dried samples than HA dried ones. The findings of this study demonstrated that HA-RF drying is a good alternative of HA for industrial-scale drying of paddy grains.

Study on wind environment of semi-open space in hot-arid and hot-humid climate zones in rural areas

To explore the coupling effect of open space temperature and air velocity in hot-arid and hot-humid climate regions in rural China, 1690 valid data were obtained by long-term field tests and questionnaires were carried out in hot-arid and hot-humid regions. Results indicated that when the operative temperature is below 33.5 °C, the mean thermal sensation decreases with the increase of air velocity in the hot-humid region. When the operative temperature rose to greater than 33.5 °C, the mean thermal sensation could be significantly reduced only when the air velocity is over 1.0 m/s. However, increasing air velocity in hot-arid regions can significantly improve the thermal sensation. In addition, residents in hot-humid regions were more willing to increase airflow than those in hot-arid regions. These results support the theory of climate adaptation and can provide a reference for the design of semi-open space buildings in rural regions.

Numerical Simulation of Bus Bar Hole Ventilation in Jinghe Dongzhuang Hydropower Station

Based on the boundary conditions obtained from the actual measurements during the infrastructure period of Jinghe Dongzhuang Power Station, a calculation model of the predicted bus bar hole environment was established, and a full-scale numerical simulation of the bus bar hole environment was performed based on CFD to analyze the effect of air supply velocity changes on the temperature and velocity fields in the working area. The ventilation effect is evaluated and compared by calculating the inhomogeneity coefficient and air distribution characteristic index. The study shows that an appropriate increase in air velocity can reduce the thermal impact of the internal heat source on the surrounding environment and can effectively control the air quality in the work area. Considered comprehensively, the work area has better comfort when V/V0 is slightly greater than 1. The research results have some guiding significance for the design of bus bar hole air supply system in Jinghe Dongzhuang Power Station.

Performance evaluation of hybrid desiccant air conditioning system regenerated by waste heat from air cooled condenser: Experimental Investigation

Heating ventilation and air conditioning units reject a large quantity of heat to the surroundings as waste. Thus proper reclamation of this unused heat could also enhance the COP of such arrangements and their lesser adverse effect on the environment. Therefore hybrid desiccant air conditioning unit using unused heat from condenser for regeneration can be more effective than the conventional air conditioning unit under hot and humid climatic conditions. In this paper, various performance parameters of hybrid desiccant air conditioning unit using unused heat from condenser is determined at different process air inlet temperatures (28, 29.5, 31, 32.5, 34, 35.5 and 37°C) and different process air inlet velocities, i.e. (1.5, 2.5, 3.5 and 4.5 m/s) and at fix (2.5 m/s) air velocity at regeneration inlet. Refrigerating effect, heat rejection rate, VCOP, ECOP, dehumidification effectiveness, moisture removal capacity and DCOP decreases with increment in different air temperatures at process inlet. While compressor work, regeneration effectiveness and regeneration rate increases with increment in different air temperatures at process inlet. On the other hand, refrigerating effect, heat rejection rate, VCOP, ECOP, dehumidification effectiveness, regeneration effectiveness, and regeneration rate decrease with increased air velocities at process inlet. Whereas compressor work, moisture removal capacity and DCOP increases with an increase in air velocities at the process inlet. Thus, optimization of these performance parameters is determined to achieve the maximum efficiency of the hybrid desiccant air conditioning system under the above operating states.

Performance analysis of air curtains on indoor environment and dehumidification energy consumption in a low humidity plant

The purpose of this study is to evaluate the effect of air curtains on indoor environment and dehumidification energy consumption for different air supply angle and velocity. The numerical investigation was conducted in a low-humidity plant located in the atmospheric boundary layer. The standard k-epsilon turbulence model was used in simulation study. The optimum air supply angle and velocity were evaluated based on temperature and humidity distribution. The simulation cases range in air supply angle from 0° to 20° and velocity from 6m/s to 14m/s, which were studied by means of orthogonal experiments. Simulation results show that air curtain can reduce the average indoor temperature of the plant by up to 3.9°C and reduce the average moisture content by up to 86.6% compared to the cases without air curtains. The energy saving assessment of the dehumidification rotor system shows a parabolic variation in energy consumption with increasing air velocity at a certain air supply angle. The optimum energy consumption occurs at the range of 9-11m/s for air supply velocity. When air supply velocity is over 11m/s, the airflow exchange is enhanced by air curtain at the plant opening, resulting the higher energy consumption from air leakage for dehumidification.

Effect of condensate flow rate, surface tension, density and vapor velocity on condensate retention of wire wrapped tubes

Simulated condensation has been conducted on three wire wrapped tubes having same root diameter but different fin spacing of 1.5 mm, 2 mm, and 2.5 mm. Different fluids (ethanol, ethylene-glycol, and water) are used for condensation by providing them to the tubes through tiny holes in inter-fin spacing on the top of the surface of tubes. The major parameters are to be controlled in this research are fin spacing, vapor velocity, condensate flow rate and ratio of surface tension density of the fluid. Obtained results show that flooding angle (calculated from the top of the tube to the level where fluid fills the fin) rises by increasing fin spacing. Also, retention angles increase by reducing ratio of surface tension density of fluid. Acute flooding angles at zero air velocity and zero flow rate, elevates by increasing air velocity. However, obtuse flooding angles at static conditions drop by reducing air velocity. An interesting result is obtained regarding retention angle which remains almost even for the higher condensation flow rates until the tube gets inundated with condensation. Moreover, critical flow rates for all the tubes against using different working fluids are measured. Results obtained for static conditions have good correspondence with already available authentic data for flooding angle. Pictures showing condensate retention angles have been included in this paper.

Experimental study of a natural draft hybrid (wet/dry) cooling tower with a splash fill type

<abstract> <p>Cooling towers have such a significant influence on work and efficiency that researchers and designers are working tirelessly to enhance their performance. A prototype design for a natural draft hybrid (wet/dry) cooling tower has been created, relying on geometrical, dynamic, and thermodynamic similarities. Based on Iraqi weather, experiments have been conducted using splash fill (150 mm) in summer (hot and dry) weather conditions. This study investigated heat transfer mechanisms of both air and water in a natural draft hybrid cooling tower model(NDHCTs), both directly (wet section) and indirectly (dry section). The tower is filled with splash-style packing, and the warm water is spread throughout the building using sprayer nozzles. The influences of water flow rates, fill thickness, and air velocity on the cooling range, approach, cooling capacity, thermal efficiency of the cooling tower, water evaporation loss into the air stream and water loss percentage were explored in this study. The experimental were carried out with four different water flow rates, ranging from 7.5 to 12 (Lpm) litres per minute, and eight different air velocities, all while keeping a constant inlet water temperature and a zero (m/s) crosswind. Data has been gathered, and performance variables have been determined. The findings demonstrate that the cooling tower's efficacy increases when the water flow rate is low, and the cooling range increases with increasing air velocity and decreases with increasing water flow rate; for a 7.5 Lpm water flow rate and a 2.4 m/s air velocity, it expanded to 19.5 ℃. The cooling capacity increased to 23.2 kW for a water flow rate of 12 Lpm and an air velocity of 2.4 m/s.</p> </abstract>

A Study on Computational Analysis for Natural Convection in Tall Building – A Macroscopic Approach

The development of convective heat transfer in buildings are found to be due to the movement of air with respect to the turbulence in air to the temperature. The heat transferred is observed in 3 levels ‐ the roof exposed floor, the seventh floor and the lower floor of the 14 storey naturally ventilated tall building. This paper discusses the eulerian approach which is a macroscopic approach to understand the temperature in the building since the density stratification occurs in the indoor volume of the building. The volume averaged data is considered to be in eularian approach. The CFD analysis is used to artificially create the environment with the different temperatures and velocities. Heat transfer happens due to convection, hence the boundary conditions ‐ initial outdoor temperature has been kept constant at 30°C and 23°C. The change in the outdoor temperature at the air velocities 10 m/sec at 12 noon were observed as 29.37°C, 29.49°C, 29.89°C at constant temperature 30 with respect to 1st floor, 7th floor and roof. Finally, it is noted that, as the air velocity increases, the outdoor temperature also increases. Conjugate heat transfer analysis is followed in CFD analysis to include the resistance of the exterior concrete wall to transfer the temperature to the control volume. K‐omega model is used to resolve the turbulence and to analyse the interior domain with Boussinesq hypothesis in the momentum equation to include the effect of the density difference in heat transfer. It is observed the velocity helps to take the temperature from the exterior domain to the interior part of the building. Hence the results clearly indicate that when the outdoor temperature is higher and the outdoor velocity is also higher, the temperature which enters the indoor environment is also high.

Performance analysis of aqueous LiCl and CaCl2 based falling film dehumidifier with surface modification

• Analysis is carried out on a falling film based liquid desiccant dehumidifier. • The surface is modified with sinusoidal profile to increase the dehumidification. • The sinusoidal wavy profile increases the desiccant surface area by 7%. • Aqueous LiCl solution enhances the dehumidification by 29.15% compared to CaCl 2 . • With aqueous LiCl, the modified surface increases the dehumidification by 33.18%. In summer air-conditioning, conventional vapor compression systems cool the process air to its dew point temperature for dehumidification and further heat it to required supply temperature. This involves extra cooling and subsequent heating. Liquid desiccant systems avert this issue by separately handling latent and sensible loads, while running primarily on low grade thermal energy. Falling film type liquid desiccant dehumidifiers are advantageous over other types, mainly, as they reduce desiccant carryover into supply air stream. The current work aims towards the analysis and the performance improvement of a falling film type dehumidifier with the help of wavy profile of the working surface. Detailed comparison of the two commonly used desiccants, i.e., LiCl and CaCl 2 are carried out to analyse the performance of the dehumidifier. The present work also includes the characterisation of the wave profile and the analysis in terms of various important parameters, such as, the dehumidification effectiveness, the moisture removal rate and the change in specific humidity, missing in earlier studies. In order to study the performance, a simplified 2–D transient finite volume model is taken into consideration to simulate a multiphase, multi-component conjugate heat and mass transfer system using ANSYS Fluent 19.2. The volume of fluid method is used to trace out the liquid–gas interface. With back-end modification of the solver, the thermophysical properties of the liquid film are evaluated using empirical relationships, as a function of temperature and concentration. The penetration model of mass transfer provides the local mass transfer coefficients. The moisture removing the potential of the aqueous solutions of LiCl and CaCl 2 are evaluated at quasi steady-state conditions. The numerical solver is validated with the already published experimental results with a maximum deviation of 10.31%. A sinusoidal wavy profile of the wall introduced in the system enhances the turbulence intensity by 3.8% and the dehumidification performance by 33.18% and 18% for LiCl and CaCl 2 , respectively. It is due to the enhanced liquid–gas interface area. The mean film thickness is found to improve by 15.25% and 13.38% for LiCl and CaCl 2 , respectively. The effect of process parameters on the performance of the dehumidifier is also studied. It has been observed that the dehumidification effectiveness decreases from 86.14% to 31.1% with increase in inlet air velocity from 0.2 m/s to 2.0 m/s. It has also been found that a lower concentration of the desiccant solution and lower velocity of air yield higher dehumidification effectiveness. However, the moisture removal rate of the system will be compromised. Compared to the previously studied cases, the current configuration of the sinusoidal profile with amplitude to wavelength ratio of 1:15, yields superior dehumidification performance.

Computational Modeling of Drying of Pharmaceutical Wet Granules in a Fluidized Bed Dryer Using Coupled CFD-DEM Approach.

Drying of wet granules in a fluidized bed dryer is an important part of the pharmaceutical tablet manufacturing process. Complicated gas-solid flow patterns appear in the fluidized bed dryer, and interphase momentum, heat, and mass transfer happen during the drying process. A coupled computational fluid dynamics (CFD)-discrete element method (DEM)-based approach was used to model the drying process of pharmaceutical wet granules in a fluidized bed dryer. The evaporation of water from the surfaces of the particles and the cohesion force between the particles due to the formation of liquid bridges between the particles were also considered in this model. The model was validated by comparing the model predictions with the experimental data available from the literatures. The validated model was used to investigate the drying kinetics of the wet granules in the fluidized bed dryer. The results from numerical simulations showed that the dynamics and rate of increase of temperature of wet particles were considerably different from those of dry particles. Finally, the model was used to investigate the effects of inlet air velocity and inlet air temperature on the drying process. The model predicted increase in drying rate with the increase of inlet air velocity and inlet air temperature. This model can help not only to understand the multiphase multicomponent flow in fluidized bed dryer but also to optimize the drying process in the fluidized bed dryer.

Experimental and numerical investigation of heat transfer in a channel with multiple phase change materials (PCMs)

In this study, the thermal performance of an air-phase change material (PCM) unit used in free cooling applications was examined experimentally and numerically by Comsol finite element simulation software. Effects of the air inlet temperature, velocity and also PCM configuration on the efficiency of the air-PCM unit were investigated. Experiments were performed on PCM unit, which is a channel including PCM plates inside and exposed to medium air entrance from one side. The air in contact with the plates inside this unit is cooled and contributes the room temperature to decrease. The experimental work was carried out at two different ambient temperatures in a well-insulated room. Three different configurations of paraffin-based pure RT22HC and RT25HC were studied. Effects of air inlet temperature and velocity on the heat transfer, channel outlet temperature, performance of the air-PCM heat exchanger, cooling power of the system and also total amount of heat absorbed by the PCM were investigated. The initial temperature of the PCMs is 16 ᵒC and experiments were carried out for two different average inlet temperature values (27 and 29 ᵒC) and two different average velocities (1.3 and 1.8 m/s) of the air at the channel entrance. According to the results, it was concluded that the air inlet temperature and air inlet velocity have a substantial effect on the thermal performance of the air-PCM unit. It was observed that the melting time decreased and the channel outlet temperature increased with the increase of air inlet temperature and velocity. 2 ᵒC increase of in the inlet temperature increased the total amount of heat absorbed by PCMs by 31%, while an increase of the inlet velocity by 0.5 m/s increased it by 16%. The results revealed that the increase of the inlet velocity and with the inlet temperature increased the thermal energy absorbed by 44%. In addition, it was observed that the average efficiency increased by 37% with 2 ᵒC increase of inlet temperature and 0.5 m/s decrease in the inlet velocity.

Chemical study of bottom ash sintering in combustion of pelletized residual agricultural biomass

Although residual agricultural biomass is a high-potential energy source, its use is curtailed by the characteristics of its ash (quantity and composition). This ash can cause problems during combustion, including bottom ash sintering, which is the main focus of this study. Results of bottom ash proportion and sintering degree yielded by combustion tests carried out with four different agropellets (one was exclusively woody, and the others were blended with various herbaceous components –mixed agropellets) under different operating conditions in a laboratory fixed-grate reactor were presented in a previous paper. The inlet air temperature and the excess air were the two controlled operating parameters in the tests. To bring the analysis further, samples of bottom ash collected during these tests have been characterized using SEM-EDS and P-XRD techniques. The results confirmed that, given its high content of alkali metals and its high ratio (K+Na)/(Si+P), the differences in sintering behavior presented by the four agropellets are related to the formation of alkali metal silicates and phosphates; Si+P is the limiting and determining content that condition the sintering severity. Regarding the influence of operating conditions, only small variations in the composition of both the sintered and not sintered fractions of the bottom ash have been detected when varying inlet air temperature and excess air in the analyzed range. Nevertheless, these SEM-EDS results have led to the detection of two opposing phenomena related to increased excess air: higher ash entrainment and lower vaporization, which are associated with the increase of air velocity and the reduction of combustion temperature, respectively. Whereas in the mixed agropellets and in the range of excess air tested these two effects offset each other, woody agropellet is significantly affected by entrainment due to its lack of sintered matter. These results provide useful information towards a solution of the problem posed by sintering in the combustion of residual agricultural biomass.

Determination of Pneumatic Conveying Characteristics of Canola

In this study, it was aimed to determine the pneumatic conveying characteristics of canola seeds (Brasicca napus Oleifera sp). The physical properties, pressure drop, air velocity, power consumption characteristics of Turan variety canola seeds were investigated. Three different canola moisture, three different pipe diameters, three different material feed flow rates and five different air velocities were used and the effects of these factors on the pneumatic conveying characteristics of the canola were examined. The pneumatic conveying of canola seeds was carried out at the positive pressure pneumatic conveyor. The pressure drop and power consumption have increased with the increase of air velocity. The lowest pressure drop and power consumption values were obtained in conveying with pipe diameter of 70.3 mm, canola moisture of 16.54%, compressor speed of 1150 rpm and conveying capacity of 3.89 t/h. The lowest power consumption was achieved with the conveying of the canola at 6.36% moisture, 7.49 t/h material feed flow rate and 1150 rpm compressor speed. In trials, the pressure drop decreased when the pipe diameter was increased.

Air-side heat transfer characteristics of ambient air vaporizers with various geometric parameters under cryogenic frosting conditions

Ambient air vaporizers (AAVs), which utilize air as a heat source, have been widely used for natural gas regasification. Under cryogenic frosting conditions, the heat transfer performance of AAVs is gradually reduced owing to frost growth on the fin surface. In this study, the heat transfer characteristics of AAVs were measured and analyzed by varying the geometric design parameters and operating variables under cryogenic frosting conditions. The air velocity, relative humidity, and temperature were selected as the operating variables, and the fin height, fin tip distance, and fin pitch were considered as design parameters. The frost growth was accelerated with increasing air velocity, humidity, and temperature under cryogenic frost conditions. Furthermore, as the fin height, fin tip distance, and fin pitch increased, the heat transfer reduction and pressure drop with respect to time decreased owing to the decrease in the blockage ratio. In addition, an empirical correlation for the Nusselt number in AAVs was developed as a function of the operating variables and geometric parameters based on the measured data. The present results can be used as practical design guidelines for AAVs under actual operating conditions.

Performance enhancement of a liquid desiccant absorber with triangular corrugated structured packing

Energy crisis and environmental concerns have initiated momentum to look for an alternative to the vapor compression systems (VCS). The present study involves 2-D numerical modelling of a liquid desiccant absorber (LDA), a potential alternative to the VCS. Low effectiveness is a major challenge in the development of an LDA. The present study aims to improve the effectiveness of the absorber of LDA by replacing the flat solution surface with a triangular corrugated one. The modelling involves multiphase flow with conjugate heat-mass interaction. The finite volume method-based software ANSYS Fluent 19.2 is used for the study. The liquid-gas interface is tracked using the volume of fluid method. The SIMPLE scheme is used in pressure velocity coupling. The ever-changing properties of the desiccant solution, along with various source terms are taken into consideration using user-defined functions. The mass transfer coefficients are calculated using the penetration theory. The incorporation of corrugation having a pitch to height ratio of 10:2, enhances the desiccant-air interface area by 6.4%, compared to a flat surface. The dehumidification and the enthalpy effectiveness are improved by over 26%, whereas, the Nusselt number has augmented by 47%. The effectiveness of the absorber maximizes when the desiccant solution at the inlet is maintained at 298 K and 35% concentration. Also, the increase in air velocity reduces the dehumidification and the enthalpy effectiveness of the system. The current study indicates that the incorporation of corrugation affects the effectiveness of the absorber and maximizes with pitch to height ratio of 10:2.

Separation of switchgrass seeds by aerodynamic properties as a way of quality improvement

The article presents the research results on the effect of seed separation (by aerodynamic properties) regime on germination energy and germination in order to reduce the biological dormancy of seeds and significantly improve the quality.
 Methods. Laboratory, measuring and weighing, mathematical and statistical.
 Results. With speed increasing in the aspiration column channel from 2.5 to 5.2 m/sec there was a slight change in the 1000-seed weight. There was not dependency in increase in the 1000-seed weight along with increasing air velocity. Thus, if in the control the 1000-seed weight was 1.65 g, then at the maximum 5.2 m/sec air velocity in the aspiration channel it was 1.68 g (SSD0.05 = 0.10 g). Germination energy and seed germination significantly increased in all separation modes except for the mode with 2.50 m/sec air velocity in the aspiration channel. The 1000-seed weight that fell into the waste naturally increased with increasing air velocity in the aspiration channel from 0.15 g to 0.40 g, and germination energy and seed similarity were at the level of 0−1%. Increasing the air speed to 7.87 m/sec provided a significant increase in seed germination energy and germination compared to the control and sorting of seeds at an air speed of 5.6 m/sec and 7.49 m/sec, and waste losses in waste increased by 28.0%.
 Conclusions. Separation of switchgrass seeds of different years of vegetation, collected from panicles of different tiers and maturation dates provided a significant increase in its germination energy and germination and can be introduced into production but it does not completely solve the problem of reducing the biological dormancy of seeds.

Influencing factors for transpiration rate: A numerical simulation of an individual leaf system

This paper establishes a 3-dimensional mathematical model to investigate the relationship between transpiration rate and environmental factors via a finite element and controlled variable method. The results show that an increase in photosynthetically active radiation (PAR), ambient temperature and air velocity promote transpiration, and an increase in relative humidity (RH) leads to a decrease in the transpiration rate. However, the transpiration rate decreases with increasing relative humidity. The reason for this phenomenon is that the vapour pressure deficit (VPD), the diffusion resistance of vapour through the boundary layer, and leaf stomatal conductance are strongly affected by these environmental factors. Stomatal conductance controls the diffusion of water vapour from the mesophyll interstitial spaces to the stomatal surface. The boundary layer resistance and VPD control the diffusion of water vapour from the pore surface to the environment. When the boundary layer resistance does not change, VPD determines the transpiration rate of the leaf. In contrast, the transpiration rate of the leaf is synergistically affected by the VPD, boundary layer resistance and stomatal conductance (gs). Due to the influence of the transpiration rate and energy exchange, the leaf temperature increases with increasing PAR, RH and ambient temperature and decreases with increasing air velocity. This research can provide some guidance for agricultural production and the development of bionic materials with thermal infrared properties similar to those of natural leaves.

Experimental Investigation to Evaluate the Effective Moisture Diffusivity and Activation Energy of Cassava (Manihot Esculenta) under Convective Drying

Investigation of effective moisture diffusivity (Deff) and activation energy (Ea) of cassava were conducted under convective drying at temperature and velocity of 60, 70 and 80 °C, and 1.0, 1.5 and 2.0 m/s, respectively. In the experiment, cassava was sliced into 3 mm-thickness and dried under given conditions until mass was saturated. Deff and Ea were described by Fick’s second law and Arrhenius-type equation, respectively. The experimental results indicated that the increase in Deff was significantly affected by increasing the hot air temperature and velocity. The slope method was used to calculate average Deff, and results were found to range from 3.83 × 10–9 – 9.86 × 10–9 m2/s. The Ea was found to decrease with an increase in hot air velocity, ranging from 21.23– 24.92 kJ/mol. Additionally, Moisture content (Mw) and Drying rate (DR) were also used to describe the drying kinetics. From the experimental results, Mw and DR decreased with an increase in drying time. DR increased with an increase in temperature and velocity causing Mw to rapidly decrease and drying time to reduce. The highest DR was found to be 0.55 gwater/min at temperature of 80 °C and velocity of 2.0 m/s.