Overview

As the core drying equipment in the field of fruit and vegetable processing, the hot air circulation oven achieves efficient dehydration while maintaining the nutritional content of fruits and vegetables through scientific airflow organization design and precise temperature and humidity control. China is a producer of fruits and vegetables, with an annual output of over 1 billion tons, but the post harvest loss rate is as high as 20% -30%. As the main method of fruit and vegetable preservation and processing, hot air drying can extend the shelf life of fruits and vegetables to 6-12 months. Traditional air drying has drawbacks such as poor hygiene conditions, weather constraints, and uneven quality. However, modern hot air circulation ovens use forced convection heat transfer and automation control to increase drying efficiency by 3-5 times and significantly improve product quality. They have been widely used in the fruit and vegetable processing industry.

Equipment structure

-Box system: SUS304 stainless steel insulation box (thickness 100-150mm), polyurethane foam insulation (λ ≤ 0.025W/m · K)

-Heating system: steam heat exchanger (0.2-0.8MPa), electric heating tube (nickel chromium alloy) or gas hot blast stove

-Circulating system: Multi blade centrifugal fan (air volume 10000-30000m ³/h), adjustable wind speed of 0.5-2.5m/s

-Material loading system: stainless steel mesh belt (aperture 4-20 mesh) or material tray cart, corrosion-resistant design

-Control system: PLC+touch screen, integrated temperature, humidity, and air volume multi parameter control

working principle

1. Preheating stage: After the fresh ingredients are loaded, heat them to 50-60 ℃ (leafy vegetables) or 60-70 ℃ (rhizomes)

2. Constant speed drying: Maintain a suitable temperature and allow free water to evaporate quickly (with automatic moisture removal)

3. Slow down drying: Lower the temperature (by 5-10 ℃), combined with the diffusion rate of moisture

4. Balance stage: Terminate heating and use residual heat to complete final dehydration

Drying kinetics: The rate at which water migrates from the interior to the surface of fruits and vegetables determines the drying cycle, and hot air circulation accelerates this process by increasing the convective heat transfer coefficient (h=50-100W/m ² · K).

Technical Characteristics

1. Uniformity control technology

-Multi vent design: adopting alternating up and down air supply, with a cross-sectional wind speed deviation of ≤ 15%

-Optimization of flow guide plate: Computational Fluid Dynamics (CFD) simulation of airflow organization, dead zone area<5%

-Rotating loading: The flipping device of the mesh belt equipment heats both sides of the material, resulting in a drying uniformity of ≥ 90%

2. Energy saving and consumption reducing design

3.Quality Maintenance Process

-Vitamin C retention: segmented temperature change (70 ℃ → 55 ℃ → 60 ℃) is used, with a Vc retention rate of ≥ 80%

-Color protection: Pre blanching enzyme (90-100 ℃, 1-3 minutes), combined with low-temperature drying (≤ 65 ℃)

-Hydration guarantee: porosity>60%, rehydration ratio of 1:4-1:6 (dry basis)

Innovative technology application

Joint drying technology

-Hot air microwave combination: early stage hot air dehydration (moisture content 50% → 30%), later stage microwave drying (30% → 5%), reducing time by 40%

-Hot air vacuum combination: suitable for fruits and vegetables with high heat sensitivity (such as strawberries), with a 25% increase in vitamin retention rate

intelligent control system

-Moisture online detection: Near infrared sensor for real-time monitoring of moisture content, with an accuracy of ± 1%

-Drying endpoint judgment: automatic shutdown based on power curve inflection point to avoid excessive drying

-Remote monitoring: 4G/5G module enables remote control and fault diagnosis of mobile APP

New structural design

-Through flow oven: Vertical airflow passes through the material layer, doubling the heat transfer efficiency

-Solar assisted: collector preheats fresh air, saving energy by 30% -50%

-Multi level series connection: series connection in different temperature and humidity ranges to meet the requirements of drying kinetics

Application Practice Cases

1. Dried leafy vegetables (scallions)

-Equipment selection: Multi layer belt dryer (4 layers, total length 20m)

-Process parameters: temperature 60-65 ℃, wind speed 1.2m/s, time 90-110min

-Finished product quality: moisture content ≤ 5%, chlorophyll retention rate ≥ 85%, good rehydration properties

2. Dried fruits (mangoes)

-Equipment selection: Box type hot air drying room (material tray car, 20 cars/batch)

-Process parameters: three-stage variable temperature (70 ℃ → 60 ℃ → 55 ℃), time 8-10 hours

-Finished product quality: uniform orange yellow color, sufficient sugar conversion, Vc retention rate>75%