Optimum Air Velocity Research Articles

Enhancement of the Elastocaloric Performance of Natural Rubber by Forced Air Convection.

We study the enhancement of the elastocaloric effect in natural rubber by using forced air convection to favour heat extraction during the elongation stage of a stretching-unstretching cycle. Elastocaloric performance is quantified by means of the adiabatic undercooling that occurs after fast removal of the stress, measured by infrared thermography. To ensure accuracy, spatial averaging on thermal maps of the sample surface is performed since undercooled samples display heterogeneities caused by various factors. The influence of the stretching velocity and the air velocity is analysed. The findings indicate that there is an optimal air velocity that maximises adiabatic undercooling, with stretching velocities needing to be high enough to enhance cooling power. Our experiments allowed the characterisation of the dependence of the Newton heat transfer coefficient on the air convection velocity, which revealed an enhancement up to 600% for air velocities around 4 m/s.

Effect of installation factors on the environment uniformity of multifunctional fan-coil unit system in Chinese solar greenhouse

Airflow significantly affects crop growth, and providing adequate and uniform airflow is essential to improve crop yield and quality. This paper used computational fluid dynamics software to optimize multifunctional fan-coil unit (FCU) installation factors at different crop heights. Fan pressure jump coefficient got optimized further, and the percentage of disturbance velocity was proposed as an index to evaluate the improvement of turbulence characteristics in airflow fields. The simulation results showed that the FCU system's optimal tilt angle, swing angle, and height above the ground were 20°, 45°, and 2.9 m, respectively. The optimum spacing is related to crop height. For lower tomatoes, the optimal spacing was 4.2 m and 4.5 m for higher tomatoes. The velocity coefficients of variation (Cv-v) for different height crops before optimization were 0.58 and 0.66. The Cv-v after optimization decreased to 0.37 and 0.41, and the uniformity was improved by 36.21 % and 37.88 %; the porous medium amounts percentage in the optimum air velocity range were increased to 64.70 % and 23.50 %. Simultaneously, the homogeneous airflow distribution improved the temperature field uniformity by 46.5 % and 23.95 %. This paper can provide theoretical guidance for the design and installation of FCU systems.

Study of the enhancement in the performance of a hybrid flat plate solar collector using water and air as working fluids

AbstractA hybrid flat solar collector was manufactured from basic materials to combine the effects of both water and air solar heaters. The reason is to increase the amount of heat delivered to water by doubling the heat sources, one from the direct beam of sun and the other from the hot air delivered by the air solar heater. In addition, the flow of water inside the solar heater is made in a thin layer so that much heat can be gained by water per unit time. The outlet hot air of the solar air heater enters air ducts that pass through the solar water heater. With a constant water flowrate of 0.0167 kg/s, three different air velocities (1.7, 2.1, and 2.4 m/s) were applied to determine the optimum air velocity that results in the maximum outlet water temperature and the maximum removal factor FR for the solar water heater. The experiment was run from 10:00 a.m. to 2:00 p.m. every day during June 2023 and the data was recorded every 15 min. The data obtained from the experiment showed that the lowest air speed (1.7 m/s) results in the highest outlet water temperature (63°C) and heat removal factor FR (0.74).

Multi-objective optimization of thermal management system for multiple heat source arrays electronic chassis in a noiseless environment

Effective thermal management of electronic chassis is currently a critical concern. A heat sink with fins and heat pipes is suggested in this paper. It is intended to handle the heat produced by numerous sources within an electronic case and enhance its functionality. The parameters have been examined and improved in order to work quietly. Response surface methodology (RSM) was employed to examine the influence of fin length, fin thickness, fin spacing and Re on the junction temperature, temperature uniformity and thermal resistance of the heat sink for a printed circuit board array (PCBA). The parameter combinations were optimized using a genetic algorithm. The results indicated that the optimal fin spacing is 11 mm, optimal length is 199 m, and optimal thickness is 2.9 mm when the Reynolds number falls within the range of 2000 ≤ Re ≤ 7000. Compared to the original fins, the combined finned heat pipe heat sink decreases the temperature of the PCBA junction by approximately 10 K, enhances the temperature uniformity by around 49 %, and diminishes the total thermal resistance by nearly 48 %. The optimal air velocity is approximately 0.41 m/s. The improved heat sink can efficiently enhance the thermal management of electronic casings.

CFD analysis of airflow uniformity in a Shipping-Container vertical farm

This study focuses on optimizing airflow uniformity at canopy level in a container-sized vertical farm. Adequate air movement and uniform growth environment play a crucial role in crop production, as they significantly influence plant growth. In fully closed plant production systems, various issues such as tip-burn, low transpiration, and hindered photosynthesis can arise due to insufficient air circulation. To address these problems, four different air distribution systems were simulated using overall control or localized control techniques. A computational fluid dynamics analysis was conducted to evaluate the performance of the proposed and iteratively improved designs. Key parameters, including air velocity, CV, as well as the percentage of probe points within or outside the recommended range were investigated to identify differences between designs. The results revealed that the localized control technique, where airflow was directed straight into the canopy along a layer length, was significantly better than providing additional airflow at the end of a shelf. Air inlets along the layer length provided optimal average air velocity (0.65 m/s) and moderate airflow uniformity (coefficient of variation = 33 %) in Case 3. However, the introduction of additional outlets resulted in significantly improved uniformity compared to a single outlet and showed the lowest coefficient of variation with only 10 % in Case 4. Optimal airflow uniformity through well-designed ventilation systems is crucial, and the findings of this study contribute to a vast pool of possible designs in container farms, guiding future advancements in optimizing environmental conditions.

Mixed Combustion Characteristics of Various Biomass Particles

As a promising pollutant emission reduction technology, biomass mixed combustion has attracted widespread attention worldwide. This paper aimed to study the characteristics of biomass mixed combustion and temperature distribution. A combination of simulation and experimental methods was adopted. The results showed when four kinds of biomass were burned separately, their highest temperatures in the center section of combustion chamber were corn stalk>cotton stalk>sawdust>rice straw in descending order. Compared with other three biomass, the highest temperature of corn stalk was more than 100 K higher, which mainly occurred during the full combustion stage, mainly because corn stalk had high volatile content and caught fire easily. In addition, with the optimal mixed combustion parameters, biomass mixed combustion improved the combustion characteristics of single biomass combustion. The optimal blending ratio of corn stalk to rice straw was 7:3, and the optimal primary air velocity and temperature were 48 m/s and 1300 K, respectively. With the optimal blending ratio, the maximum temperature in the center section was higher than that of single biomass combustion, with advanced ignition point, relatively uniform temperature distribution in the combustion chamber and good combustion performance, because the precipitation and combustion of high volatile components during mixed combustion caused the surface temperature of fixed carbon to rise rapidly to reach the ignition temperature. Finally, this paper studied the combustion characteristics of corn stalk and rice straw with the optimal mixed combustion parameters in mixed combustion experiment, and verified the good consistency between the simulation and experimental values. Therefore, biomass mixed combustion technology provides an important reference for solving the problem of low calorific value of single biomass combustion.

Performance of Air Curtain located at the top of entrance opening - Difference among indoor/outdoor/double-sided installation

Large openings of buildings are often used open, which results in heat loss due to intrusion of outdoor airflow and leakage of indoor air through the opening. To reduce air-conditioning load and to improve thermal environment in such a building, installing an air curtain at the opening can be a beneficial technique. The airflow blowing out of the device suppresses the heat exchange by buoyancy-induced convection through the opening. The impact of temperature difference, blowing speed, and installation position of the air curtain on temperature distribution and invasion flow rate of outdoor air was investigated by full-scale experiment under heating operation. Thermocouples were installed to measure vertical temperature distribution. Outdoor air infiltration was measured using tracer-gas method. The amount of outdoor air infiltration was evaluated based on both temperature difference and CO2 concentration. Comparing the results, it was found that the indoor air curtain was able to suppress the airflow through the opening. The indoor-outdoor temperature difference and CO2 concentration were highest when the air velocity was 4 m/s, suggesting that there is an optimal air velocity at which the air curtain can effectively suppress the airflow through the opening.

Particle flow characteristics in the pipeline of a nonmetallic ore powder air classifier using a DPD-DEM coupled method

Understanding particle flow characteristics can help improve the efficiency of nonmetallic ore powder air classifiers. In this paper, dissipative particle dynamics (DPD) and the discrete element method (DEM) were adopted to study the interactions between the gas phase and solid particles. Gas and solid phases were coupled using the single-particle DPD model. Taking sepiolite particles as an example, at the optimal input air velocity in the pipeline, the gas particle velocity distribution, solid particle velocity distribution, solid particle concentration distribution, and solid particle position distribution were analyzed by numerical simulations. A comparison of numerical simulation and experimental results showed that when the input air velocity in the pipeline was 17 m/s, the velocity of particles and gas in the pipeline gradually increased from the wall to the center of the pipeline. The velocity near the pipeline wall changed rapidly, and the velocity in the main flow area remained basically unchanged. Particles left the pipeline in a uniform and dispersed state and were carried into the classification area. As the input air velocity increased, the pressure drop across the pipeline also increased. Therefore, the optimal input air velocity value could be reasonably selected to minimize energy consumption.

Combining artificial intelligence and building engineering technologies towards energy efficiency: the case of ventilated façades

PurposeNearly 75% of EU buildings are not energy-efficient enough to meet the international climate goals, which triggers the need to develop sustainable construction techniques with high degree of resilience against climate change. In this context, a promising construction technique is represented by ventilated façades (VFs). This paper aims to propose three different VFs and the authors define a novel machine learning-based approach to evaluate and predict their energy performance under different boundary conditions, without the need for expensive on-site experimentationsDesign/methodology/approachThe approach is based on the use of machine learning algorithms for the evaluation of different VF configurations and allows for the prediction of the temperatures in the cavities and of the heat fluxes. The authors trained different regression algorithms and obtained low prediction errors, in particular for temperatures. The authors used such models to simulate the thermo-physical behavior of the VFs and determined the most energy-efficient design variant.FindingsThe authors found that regression trees allow for an accurate simulation of the thermal behavior of VFs. The authors also studied feature weights to determine the most relevant thermo-physical parameters. Finally, the authors determined the best design variant and the optimal air velocity in the cavity.Originality/valueThis study is unique in four main aspects: the thermo-dynamic analysis is performed under different thermal masses, positions of the cavity and geometries; the VFs are mated with a controlled ventilation system, used to parameterize the thermodynamic behavior under stepwise variations of the air inflow; temperatures and heat fluxes are predicted through machine learning models; the best configuration is determined through simulations, with no onerous in situ experimentations needed.

Analysis of polishing waste ceramic foam packing in evaporative cooling

This paper proposes the use of ceramic polishing slag to make fillers for evaporative coolers. The experimental tests on the heat transfer performance of the ceramic foam packing are carried out by using the independent test bench, focusing on the effects of the packing's flow channel form, drench density, the inlet air volume and pressure drop on the heat, and the mass transfer performance of the packing. The experimental results show that the optimum drench density of the ceramic foam packing in the form of a folded runner and a linear runner is 10.0 and 6.7 kg/(m·h), respectively. The direct evaporative cooling efficiency of the ceramic foam packing in both runners tends to decrease with the decrease in the dry and wet bulb temperature difference of the inlet air and the increase of the air mass flow rate. Under the same experimental conditions, the direct evaporative cooling efficiency, optimum inlet air velocity, and pressure drop of the packing in the form of a folded flow channel are higher than those of the linear flow channel. The optimal inlet air velocities of the packing in the form of a folded runner under the conditions of Urumqi, Xi'an, and Guangzhou are 1.6, 1.4, and 1.0 m/s, respectively, and the direct evaporative cooling efficiency can reach 83.01%, 70.74%, and 66.41%. In comparison, the optimal inlet air velocity for all three conditions under the linear runner is 1.0 m/s, and the direct evaporative cooling efficiencies are 73.78%, 68.56%, and 63.28%, respectively.

General formula of cooling curve for horticultural products on forced air pre‐cooling

AbstractThe air velocity played a key role in controlling the cooling process of forced air pre‐cooling for horticultural products. However, the present general formula of cooling curve for horticultural products on forced air pre‐cooling did not reflect the influence of the air velocity on cooling rate for horticultural products on forced air pre‐cooling. This paper aimed to find the relationships among the air velocity, lag factor and cooling coefficient so as to obtain the general formula of the cooling curve for horticultural products on forced air pre‐cooling by combining the simulation and the experiment. The results showed that the lag factor had a linear relationship with the air velocity, and the cooling coefficient had a quadratic function or power function relationship with the air velocity. These two kinds of general formulas were verified by experimental data of apples, cherries and blueberries, and were also in agreement with the literature values of apples, grapes and Dutch cucumbers. Based on the accuracy and the predictability of the general formulas, the general formula has higher accuracy and predictability when the cooling coefficient had a power function relationship with the air velocity.Practical ApplicationsThis paper attempted to find a general formula to describe the cooling rates of horticultural products for the different air velocities and temperatures. The general formula was only incident the air velocity and the air temperature while the other factors were considered as the unknown variations which was obtained by the functions fitting. This could contribute to reduce the cost and time of experiments and simulations during the analysis of forced air pre‐cooling and to help the operator find the optimal air velocity effectively. To find the suitable general formula, firstly we established the simulated model to find the general formulas by using least square method. Then, the general formulas had been validated by experimental data and literature results. Finally, the predictability of these general formulas had been tested.

Development and Evaluation of an Ultrasonic Humidifier to Control Humidity in a Cold Storage Room for Postharvest Quality Management of Dates

Dates are subjected to postharvest losses in quality and quantity caused by water loss, fermentation, insect infestation, and microbial spoilage during storage. Cold storage is the main element in the postharvest quality management used for fruit preservation. Although cold storage is used for dates, precision control of the relative humidity (RH) using ultrasonic applications is not used thus far, or it is applied to other fruits on a small scale. Therefore, we designed and constructed an ultrasonic humidifier (DUH) for RH control in the cold storage room (CSR) of dates. The optimum air velocity of 3 m s−1 at the outlets of the DUH ducts produced a mist amount of 6.8 kg h−1 with an average droplet diameter of 4.26 ± 1.43 µm at the applied voltage of 48 V and frequency of 2600 kHz of the transducers. The experimental validation was carried out by comparing a CSR controlled with the DUH with two conventional CSRs. The three tested CSRs were similar in dimensions, cooling system, and amount of stored dates. The time required for cooling 800 kg of dates in the controlled CSR from 25 °C to the target temperature of 5 °C was approximately 48 h. The DUH precisely controlled the RH at the maximum RH set point of 80% in the tested CSR at 5 °C. The controlled RH at 80% has a positive impact on the physicochemical characteristics of the stored dates. It significantly reduced the weight loss of the fruits and preserved fruit mass, moisture content, water activity, firmness, and color parameters. However, no significant effect was observed on fruit dimensions, sphericity, and aspect ratio. The microbial loads of mesophilic aerobic bacteria, molds, and yeasts fell within the acceptable limits in all tested CSRs. Both stored date fruits and artificially infested dates showed no signs of insect activity in the controlled CSR at the temperature of 5 °C and RH of 80%. The DUH proved to be a promising technology for postharvest quality management for dates during cold storage.

Removal of Trace Metal Impurities from Pretreated Phosphoric Acid by Foam Fractionation

AbstractDemands for phosphoric acid are growing rapidly in various industries. This has highlighted the importance of optimizing its production and purification methods. Phosphoric acid can be produced by a wet process. However, due to the presence of many organic and inorganic impurities in the wet product, purification of the resulting product is a major concern in this industry. Removal of trace metal impurities (such as magnesium, cadmium, chromium, zinc, etc.) from produced phosphoric acid in a wet process was investigated by foam fractionation in a semi‐batch setup using sodium dodecyl sulfate (SDS) as the surfactant. Effects of inlet air velocity, surfactant concentration, and surfactant selectivity were investigated. The optimum air velocity and surfactant concentration were obtained as 0.020 cm/min and 0.7 g/L, respectively. At the optimum condition, the total removal efficiency and enrichment factor reached were 70.2% and 4.39, respectively, while the acid loss was 8.3%. The total metal removal efficiency was increased to 95.3% in a two‐stage experimental run.

Parametric study on the thermal performance of phase change material-assisted earth-to-air heat exchanger

As a passive technology, the earth-to-air heat exchanger (EAHE) can be used to reduce energy consumption within a building. This paper presents a novel design for an EAHE system assisted by a phase-change material (PCM). To study the thermal performance of the newly proposed PCM-assisted EAHE (PCM-EAHE) system, a transient three-dimensional model has been built in FLUENT. A range of validated numerical models is established and utilized to investigate the effects of design and operation parameters (i.e., phase-change temperature, PCM container diameter, pipe length, pipe diameter and air velocity) on the thermal performance of the system. The results indicated that the phase-change temperature should be consistent with the time-average ambient air temperature. Furthermore, the polynomial regression models for predicting the outlet air temperature with high accuracy are obtained using statistical product and service solutions (SPSS). The optimal air velocity levels for enhancing the heat transfer performance are 4.5 m/s and 6.8 m/s during the charging and discharging processes, respectively. Therefore, it is recommended to apply the PCM-EAHE system to new and existing buildings.

Experimental investigation on performance of desiccant coated microchannel heat exchangers under condensation conditions

Desiccant coated heat exchanger (DCHE), which can be adopted to construct a solar cooling system or desiccant heat pump system, can realize both sensible and latent load removal to provide comfortable supply air. Although it is difficult to avoid condensation in a practical application, the condensation condition of DCHEs is rarely studied. In this paper, a series of condensation experiments are carried out on the desiccant coated microchannel heat exchanger (DCMHE) under conditions with high temperature and high humidity ratio. First, by changing the temperature of cooling water, the unique dynamic characteristics of condensation different from non-condensing conditions are discussed, and the influence of desiccant coating is analyzed. Then, the parametric effects of inlet air velocity and fluid temperature on the mass transfer, heat transfer, and pressure drop performance of DCMHE are analyzed. The results show that the changing trend of the dynamic curve can be used as a sign to judge whether condensation exists or not. And the performance of DCMHE is still stable under continuous condensation conditions, which is not affected by the condensation water. In the dehumidification stage, the condensation dehumidification is dominant. In the aspect of parametric analysis, with the velocity of inlet air increasing from 0.5 m/s to 2.4 m/s, the average moisture removal in a cycle period ΔdDE,ave of DCMHE reduces by 40%, while the dehumidification results per unit time air ΔMDE of DCMHE increases by 192%. The optimal inlet air velocity range is 1.5 m/s–2.4 m/s, considering the dehumidification and heat recovery efficiency synthetically. Due to the thermal resistance of desiccant coating, total cooling load, the effectiveness of heat exchanger, and NTU of DCMHE is about 31%, 27%, and 26% lower than that of MHE. And the effect of desiccant coating on heat transfer performance is comparatively small at high wind speed. The experimental results are expected to provide a reference for the system design of desiccant coated heat exchangers.

Assessment of Mechanical Design Parameters for an Aero Gas Turbine Engine Jet Pipe Casing using Finite Element Analysis

Aero Gas Turbine engines power aircrafts for civil transport application as well as for military fighter jets. Jet pipe casing assembly is one of the critical components of such an Aero Gas Turbine engine. The objective of the casing is to carry out the required aerodynamic performance with a simultaneous structural performance. The Jet pipe casing assembly located in the rear end of the engine would, in case of fighter jet, consist of an After Burner also called as reheater which is used for thrust augmentation to meet the critical additional thrust requirement as demanded by the combat environment in the war field. The combustion volume for the After burner operation together with the aerodynamic conditions in terms of pressure, temperature and optimum air velocity is provided by the Jet pipe casing. While meeting the aerodynamic requirements, the casing is also expected to meet the structural requirements. The casing carries a Convergent-Divergent Nozzle in the downstream side (at the rear end) and in the upstream side the casing is attached with a rear mount ring which is an interface between engine and the airframe. The mechanical design parameters involving Strength reserve factors, Fatigue Life, Natural Frequencies along with buckling strength margins are assessed while the Jet pipe casing delivers the aerodynamic outputs during the engine operation. A three dimensional non linear Finite Element analysis of the Jet pipe casing assembly is carried out, considering the up & down stream aerodynamics together with the mechanical boundary conditions in order to assess the Mechanical design parameters

The optimum of heat recovery - Determination of the optimal heat recovery based on a multiple non-linear regression model

This paper is intended to answer the question of whether there can be a clear optimum according thermal efficiency and the corresponding electric effort when using heat recovery systems (HRS) under specific framework conditions. Since the benefits and the associated effort can vary widely in individual cases due to the different framework conditions, the question arises whether it is sensible to define the HRS requirements based on individual criteria, rather than blanket, rigid statutory requirements as is done with EU Regulation 1253/2014. In order to be able to find a respective economic optimum of the heat recovery in individual cases on the basis of various framework conditions without an individual optimization, a polynomial equation based on the nonlinear multiple-regression analysis has to be developed to predict the relevant optimum easily and quickly on the base of multidimensional optimizations. Thus, the determination of an optimal heat recovery in any case can prevent that with a too small or too large heat recovery an economic potential is given away. This makes sense from a business as well as from a macroeconomic point of view, since the sum of the business (microeconomic) optima must lead to a macroeconomic optimum. The influence on the heat recovery is shown on the basis of the parameters outdoor air temperature, extract air temperature and operating time. As a result, both the optimal temperature efficiency of the heat recovery, and the therefore required optimal air velocity, as well as the corresponding optimal pressure drop or the represented SFP-value depending on the general framework conditions are highlighted on the basis of two load cases and two balance limits.

Inverse design of an indoor environment using a filter-based topology method with experimental verification.

In order to create a healthy, comfortable, productive, and energy-efficient indoor environment, the computational fluid dynamics (CFD)-based adjoint method with an area-constrained topology method can be used to inversely design the optimal number, size, location, and shape of air supply inlets and air supply parameters. However, this method is not very mature, and the distribution of retained inlets is always scattered. To solve that problem, this investigation introduced a filter method that smooths the intermediate results during the inverse design process. Using a three-dimensional, non-isothermal, asymmetrical office with pre-set air supply inlets as an example, this study verified the performance of the proposed filter-based topology method. The verified method was then used to solve a multi-objective design problem and design an optimal indoor environment for a room. The results indicate that the proposed method was able to find the optimal number, location, and shape of air supply inlets and the optimal air supply temperature, velocity, and angle that led to a thermally comfortable, healthy, productive, and energy-efficient indoor environment. Finally, this investigation installed the optimal inlets in an environmental chamber to mimic the room. The measured air temperature, velocity, and mean age of air in several typical locations in the environmental chamber matched the CFD simulation results very closely.

Study on Surface Condensate Water Removal and Heat Transfer Performance of a Minichannel Heat Exchanger

The condensate on the surface of the minichannel heat exchanger generated during air cooling substantially reduces the heat transfer performance as it works as an evaporator in the air-conditioning system. This has received much attention in scientific communities. In this paper, the effect of operating parameters on the heat transfer performance of a minichannel heat exchanger (MHE) is investigated under an evaporator working condition. An experimental MHE test system is developed for this purpose, and extensive experimental studies are conducted under a wide range of working conditions using the water-cooling method. The inlet air temperature shows a large effect on the overall heat transfer coefficient, while the inlet air relative humidity shows a large effect on the condensate aggregation rate. The airside heat transfer coefficient increases from 66 to 81 W/(m2·K) when the inlet air temperature increases from 30 to 35 °C. While the condensate aggregation rate on the MHE surface increases by up to 1.8 times when the relative humidity increases from 50% to 70%. The optimal air velocity, 2.5 m/s, is identified in terms of the heat transfer rate and airside heat transfer coefficient of the MHE. It is also found that the heat transfer rate and overall heat transfer coefficient increase as the air velocity increases from 1.5 to 2.5 m/s and decreases above 2.5 m/s. Furthermore, a large amount of condensate accumulates on the MHE surface lowering the MHE heat transfer. The inclined installation angle of the MHE in the wind tunnel effectively enhances heat transfer performance on the MHE surface. The experimental results provide useful information for reducing condensate accumulation and enhancing microchannel heat transfer.

Sustainable drying of galangal through combination of low relative humidity, temperature and air velocity

Galangal (Alpinia galanga) is a herb commonly grown in Southeast Asia. The galangal rhizomes contain compounds that have antimicrobial and antioxidative properties. Longer storage of galangal can be achieved by drying. In the household-based industry, farmers use tray dryers because they are relatively cheap and easy to use. However, the quality of the products is low due to inappropriate temperature and drying time. The drying process is also energy intensive. This study investigated the effects of drying conditions such as air velocity, drying temperature and relative humidity on the drying characteristics and product quality. Drying of galangal was carried out at the following conditions: air velocities 0.25 and 0.5 m/s, drying temperatures 45 and 75 ∘C and relative humidity at 15 and 70 %RH, respectively. The mathematical modeling of thin layer drying kinetics of galangal was performed using Page model. The active ingredients in dried galangal were best preserved using a drying condition at air velocity of 0.25 m/s, 45 °C and 15%RH, in which the highest values of inhibition of free radicals by DPPH, total phenolic content (TPC) and 1’-acetoxychavicol acetate (ACA) content were 79.2 ± 1.3%, 91.9 ± 3.9 mgGAE/100 g and 384.1 ± 17.6 mg/100 g, respectively. Switching the relative humidity from low to high while keeping both air velocity and temperature low yielded a low drying rate. Hence, a combination of low relative humidity and low drying temperature at the optimum air velocity is promising for the design of more energy efficient dryer that gives desirable drying characteristics and product quality.