Analysis of the development of heat pump fluidized bed dryer
2021-07-04 08:05:07
ã€Abstract】The heat pump drying can recover the latent heat and sensible heat in the dry exhaust gas, which has significant energy saving effect. Heat pump drying has been widely used for drying grain, seed and food materials. In this study, a heat pump fluidized bed dryer was designed. The compressor was 5 hp and the refrigerant was R22. The carrot was used as raw material for drying experiments. Experiments show that during the fluidized bed drying process, the material is suspended in the air and continuously tumbling, so that the thickness of the boundary layer of the material surface becomes smaller, and the heat transfer and mass transfer resistance are reduced. Therefore, the heat pump fluidized bed has stronger drying strength than the box heat pump. High drying efficiency and short drying time.
[Keywords] heat pump; fluidized bed; dry drying is a process that consumes a lot of energy. In developed countries, about 10% of fuel is used for drying, so reasonable processes and equipment are essential for energy saving in the drying process. . Heat pump drying has the characteristics of high thermal efficiency, energy saving, low drying temperature, hygienic safety and environmental friendliness. It is especially suitable for the drying of heat sensitive materials such as grains, seeds and food materials. Japanese scientists using a heat pump to dry the grain showed that the average energy consumption of removing 1kg of water from the grain was 2063kJ; the experimental data of Russian scientists was 1624kJ, which was lower than the average energy consumption of the conventional airflow drying method;
GiocoM 1982, 1983, 1984 three years of production experiments prove that: heat pump drying for grain drying is about 30% more energy efficient than conventional airflow drying method, zui can save 50% energy, currently in the UK, Germany and other developed countries, heat pump drying has been dry in the grain It has been widely used in the actual production and processing. Drying experiments were carried out on corn, soybean and rice seeds by heat pump dryer.
The results show that the heat pump is a technology that is suitable for various sub-drying processes. It not only maintains the quality of the seed, but also increases the germination rate of the seed by 5% compared with the sun. However, most of the heat pump drying devices currently used are box-type structures, and the heat transfer and mass transfer efficiency in the drying chamber are low, and the drying is uneven, so that the drying time is as long as 12 to 16 hours. Long-term drying processes cause microbial contamination of the product,
Affect product quality. The heat pump fluidized bed drying device can further exert the advantages of low temperature drying and fluidized bed drying of the heat pump, improve drying efficiency and shorten drying time.
1 heat pump drying principle The heat pump drying device consists of two major systems: heat pump and dryer. The heat pump is mainly a closed circuit system composed of a compressor, an evaporator, a condenser and an expansion valve. The working medium (referred to as working medium) in the heat pump system first absorbs the heat from the exhaust gas discharged from the drying process in the evaporator, and then evaporates from the liquid into steam; after being compressed by the compressor, it is sent to the condenser;
Under high pressure, the heat pump working fluid condenses and liquefies, releases high temperature condensation heat to heat the low temperature dry air from the evaporator, and heats the low temperature dry air to the required temperature and then enters the drying chamber as a drying medium for recycling; after liquefaction The heat pump working fluid returns to the evaporator again through the expansion valve, and thus circulates. Most of the water vapor in the exhaust gas is condensed in the evaporator and discharged directly to achieve the purpose of dehumidifying and drying.
Since the heat pump drying is also convective drying, there is also a problem of heat and mass transfer efficiency. The drying process involves not only the efficiency of the heat pump dehumidification unit, but also the drying medium (air)
The increase in heat and mass transfer efficiency in the drying chamber also enhances the performance of the entire drying system. In the drying system, a fluidized bed dryer is adopted. Since the particles are suspended in the drying medium, the contact area between the drying medium and the solid is large, and the material is vigorously stirred, the gas film resistance is greatly reduced, and the heat and mass transfer efficiency is high. .
2. Design of heat pump fluidized bed dryer 2.1 Design principle of heat pump fluidized bed dryer In order to conduct a comprehensive experimental study on the heat pump fluidized bed dryer, the design of the dryer should follow the following design principles:
(1) According to the modern design concept, the building block structure is adopted, and the units are independent of each other and assembled as needed;
(2) In order to simulate different drying processes and different operating conditions of the heat pump, the main parameters (temperature, speed and humidity) of the drying medium (air) can be adjusted within a certain range and can be measured in real time;
(3) In order to be able to conduct open-circuit, semi-open and closed-circuit cycle test studies on the heat pump fluidized bed drying unit, the test device should be able to switch between various cycles;
(4) The speed of the compressor and the speed of the air circulation fan in the test device are adjusted by the inverter.
According to the above design principles, a heat pump fluidized bed drying unit is designed, which is mainly composed of heat pump (refrigeration).
Systems (fully enclosed compressors, condensers, evaporators, throttles, filters, etc.) and drying media (air) circuits (centrifugal fans, dryers, heaters, piping, etc.)
composition. The working principle of the heat pump fluidized bed dryer is shown in Figure 2.
Shown. The valve in the drying line and the regulating door at the air inlet and outlet can regulate the flow rate of the air in the drying chamber. The wind speed in the drying chamber can be arbitrarily adjusted within the range of 0.5~3m/s.
Can meet different drying process requirements.
The basic flow of the heat pump drying device is open circuit, semi-open circuit and closed circuit. In order to carry out comparative experiments on the three main cycles of the heat pump drying system,
The device can be completed by adjusting each damper and baffle. In order to ensure that the system is running, reduce the heat loss in the dry high temperature section, and the cooling loss in the low temperature section of the refrigeration, the heat pump drying system is fully insulated and treated.
2.2 Thermal calculation of heat pump unit 2.2.1 Analysis of heat pump dry air circulation system The cycle of air (drying medium) during heat pump drying process can be drawn on the wet air map, as shown in Figure 3. Point a is the inlet state of the drying chamber, point b
For the outlet state of the drying chamber, point c is the air state point after dehumidification and cooling by the heat pump evaporator. Process ca is the heating process of air in the heat pump condenser,
In the process, the moisture content of the air remains unchanged, so it is a heating process with equal moisture content; the process ab is the moisture absorption of the dry material in the drying chamber.
If it is assumed that the heat exchange between the drying chamber and the outside is negligible, the process can be regarded as equalizing the humidification process; bc is the cooling and dehumidifying process of the circulating air in the evaporator.
In the actual process, the circulating air has gone through the bb`c route, first cooling down, then dehumidifying.
From the above analysis, the required cooling capacity of the evaporator is:
Q cold = G · (hb-hc) (1)
The heat required by the condenser is:
Q heat = G · (ha-hc) (2)
Thus, if the various heat losses generated by the drying chamber are neglected, that is, ha = hb, then Q cold = Q heat.
In the actual process, there must be some heat exchange between the drying chamber and the outside world, heat exchange with the outside world around the drying chamber, and heat exchange caused by temperature difference between the inlet and outlet. Generally speaking,
When the drying chamber air temperature is higher than the ambient temperature, the drying chamber emits heat outward, and there is ha
Have ha>hb.
In order to ensure the normal and stable operation of the heat pump drying system, prevent the evaporator from generating frost during the operation of the heat pump and reduce the heat transfer effect of the evaporator, usually take c
The air design temperature of the point is 5 °C. Obviously there are Φc=100%, other state parameters of point c check the air hd diagram, you can get:
Hc=18.5kg/kgdc=5.4g/kg
For point a, there is da=dc=5.4g/kg, and for ta=30°C, the state parameter of point a is:
Ha=44kJ/kgΦa=12.5%
For point b, there is ha=hb=44kJ/kg, and the size of da depends on the amount of circulating air G.
And the moisture W extracted from the dry material in the drying chamber during the drying process, db = da + (W / G) × 1000.
According to the preliminary design scheme of the drying device, the feeding time is 25kg, and the materials such as carrot and diced are dried from about 90% of water to less than 20% within 6 hours.
The total moisture released is 21.875 kg, then W = 21.875 / 6 = 3.646 kg / h.
Take G=3200kg/h, then Q cold=Q heat=Q·(ha-hc)=3200×(44-18.5)=81600kJ/h
2.2.2 Thermal calculation of heat pump refrigeration cycle The thermal process of the internal working fluid cycle of each working process of single-stage vapor compression heat pump refrigeration cycle is shown in Fig. 4.
According to the design requirements, the heat pump unit of the dryer uses a compressor to complete the task of cooling, dehumidifying and heating the circulating air. Take the evaporation temperature of 1.0 ° C, the condensation temperature is 40 ° C,
Other parameters can be found in the chart of the literature. The design conditions and design calculation results of the heat pump are shown in Tables 1 and 2, respectively.
2.2.3 Selection of main components (1) Dryer The dryer of the drying equipment is a horizontal multi-chamber fluidized bed dryer. The bottom is a perforated plate with an area of ​​0.36 m2 (length 1.2 m, width 0.3 m).
The pore diameter is Φ2.0 mm, and the opening ratio is 8%. There is a vertical baffle above the sieve plate to divide the fluidized bed into 4 small chambers. Each baffle can move up and down.
To adjust the distance between it and the sieve plate. At the lower part of each chamber is an intake branch pipe having a valve for regulating the flow of gas.
(2) Condensing unit The condensing unit includes compressors, condensers, liquid storage tanks, etc., in which the compressor is a key component. Considering the stability of operation and convenient maintenance, through calculation and analysis comparison,
We selected the TAG4561THR model produced by “100-year Taikang Refrigeration Equipment (Shanghai) Co., Ltd.†and the fully enclosed compressor unit with 3.7kW power.
(3) The evaporator is designed according to the characteristics of the device, and is entrusted to the domestic refrigeration enterprise for processing and manufacturing, which not only ensures the performance of the device is close to the imported equipment, but also significantly reduces the cost.
(4) Main fan main circulation fan According to the characteristics of the drying equipment, the rated power is 5.5kW, the flow rate is 2198~3847m3/h, and the wind pressure is 2940~3.
9-26.No.4A fan of 851.4Pa water column. The actual wind pressure and flow of the main circulation fan can be adjusted by the frequency converter.
3 Heat pump fluidized bed drying test 3.1 Test materials 1. Materials: The carrots used for testing were purchased from the farmers' market.
The test sample requires fresh, non-rotted red-skinned carrots. The main considerations for the selection of carrots as raw materials for testing are the low price, the less impact of raw materials on the season and the typicality of materials.
2. The pretreatment process before the carrot drying test is:
Raw material selection, finishing → cleaning → cutting root tip → cutting strip → dicing (6mm × 6mm × 10mm) → 5
Double boiling in water → rapid cooling → draining → evenly placed on the fluidized bed sieve plate according to drying requirements.
3.2 Test methods (1) Temperature and humidity: The temperature and humidity were measured using the WSB-005 transmitter from Wuhan Institute of Instrument and Measurement.
(2) Wind speed: The wind speed is measured by the KA22 type thermal anemometer of Shenyang Kaye Max Instruments Co., Ltd.
(3) Determination of water content: atmospheric drying oven drying method. That is, the drying method was performed once at 105 ° C for 8 hours to detect the moisture of the sample.
3.3 Test Results Figure 5 is a fluidized drying curve of a typical carrot diced heat pump. The test conditions are: drying temperature 40 ° C, dry medium air relative humidity 24.5%, the raw material is carrot diced (
6mm × 6mm × 10mm). It can be seen from the figure that there is a clear constant-speed drying section from 0 to 0.5 h. This is because the carrot has a large amount of attached water on the surface when it starts to dry.
At this time, the moisture inside the material does not change much. 0.5~4.0h is the deceleration zone, the water content of the material shows a significant decrease, and after 4h, the drying speed is very small.
The internal moisture of carrots changes very slowly. Especially in the late dry season,
It takes 4~5h to reduce the water content from 20% to 10%, which is a problem that is difficult to solve by low temperature drying. However, heat pump fluidized bed combined drying is much shorter than heat pump box drying, usually within 9 hours.
The moisture content of carrots can be dried from about 90% to less than 10%.
The drying test conditions are that the temperature of the air entering the drying chamber is 38 ° C, the relative humidity of the air is 35%, and the thickness of the carrot pieces is 3 mm when the flow is dry.
When the fluidized bed is dried, the scale of the carrot is 6 mm × 6 mm × 10 mm. When the fluidized bed is dry, the frequency of the circulating main fan is 45Hz, 40Hz and 35Hz, respectively.
To ensure that the material is in a normal fluidized state. The frequency of the circulating main fan during flow drying is 40 Hz, 35 Hz and 32 Hz, respectively, to ensure that the material is not blown up. As can be seen from Figure 6,
During the fluidized bed drying process, the carrot diced is suspended in the air and continuously tumbling, so that the thickness of the boundary layer of the material surface is reduced, and the heat transfer and mass transfer resistance are reduced.
Therefore, the fluidized bed has a higher drying strength than the through-flow drying.
The energy consumption of the heat pump fluidized bed drying fan and the total power consumption of the system are shown in Figure 7. The energy consumption of the fan is close to 50% of the total energy consumption of the system. This is because in the fluidized bed drying process, in order to keep the material fluidized while drying, it is necessary to have a higher pressure and speed of the drying medium (air). Therefore, the proportion of electric energy consumed by the circulating fan is large.
4 Conclusions (1) A set of heat pump fluidized bed drying combined drying test device was designed, and the carrot dart was subjected to fluidized drying test. the experiment shows,
Drying the moisture content of carrots from about 90% to less than 10% takes only 9 hours, which is shorter than the drying time of the box heat pump drying, and is suitable for drying high moisture fruit and vegetable materials.
(2) A comparative test of heat pump fluidized bed drying and flow drying was carried out using carrot as raw material. Tests have shown that during fluidized bed drying,
The carrot diced is suspended in the air and continuously tumbling, so that the thickness of the boundary layer of the material surface becomes smaller, and the heat transfer and mass transfer resistance are reduced, so the fluidized bed has higher drying strength than the through-flow drying.
(3) During the drying process of the fluidized bed of the heat pump, in order to ensure that the material can be in a fluidized state during drying, the circulating air must have a certain pressure and flow rate.
The power consumption of the main circulation fan is large. The experimental results show that the energy consumption of the circulating fan accounts for about 50% of the total energy consumption of the system. therefore,
It is worth noting how the heat pump fluidized bed dryer reduces the energy consumption of auxiliary equipment other than the compressor.
3. Size: 3.0-5.0cm, 5.0-7.0cm, 7.0-10cm
4. Variety: Yellow Onion and Red Onion
5.Packing:
1) 10kg/carton, 20kg/carton, 10kgs/mesh bag,20kg/mesh bag and 25kgs/mesh bag
2) or according to the clients' requirements.
6. Supply Period:
A) Fresh season: May to the middle of August
B) Cold storage season: August to December.
7.Conveyance:26-30MT/40'HR (loading quantity depending on packing)
[Keywords] heat pump; fluidized bed; dry drying is a process that consumes a lot of energy. In developed countries, about 10% of fuel is used for drying, so reasonable processes and equipment are essential for energy saving in the drying process. . Heat pump drying has the characteristics of high thermal efficiency, energy saving, low drying temperature, hygienic safety and environmental friendliness. It is especially suitable for the drying of heat sensitive materials such as grains, seeds and food materials. Japanese scientists using a heat pump to dry the grain showed that the average energy consumption of removing 1kg of water from the grain was 2063kJ; the experimental data of Russian scientists was 1624kJ, which was lower than the average energy consumption of the conventional airflow drying method;
GiocoM 1982, 1983, 1984 three years of production experiments prove that: heat pump drying for grain drying is about 30% more energy efficient than conventional airflow drying method, zui can save 50% energy, currently in the UK, Germany and other developed countries, heat pump drying has been dry in the grain It has been widely used in the actual production and processing. Drying experiments were carried out on corn, soybean and rice seeds by heat pump dryer.
The results show that the heat pump is a technology that is suitable for various sub-drying processes. It not only maintains the quality of the seed, but also increases the germination rate of the seed by 5% compared with the sun. However, most of the heat pump drying devices currently used are box-type structures, and the heat transfer and mass transfer efficiency in the drying chamber are low, and the drying is uneven, so that the drying time is as long as 12 to 16 hours. Long-term drying processes cause microbial contamination of the product,
Affect product quality. The heat pump fluidized bed drying device can further exert the advantages of low temperature drying and fluidized bed drying of the heat pump, improve drying efficiency and shorten drying time.
1 heat pump drying principle The heat pump drying device consists of two major systems: heat pump and dryer. The heat pump is mainly a closed circuit system composed of a compressor, an evaporator, a condenser and an expansion valve. The working medium (referred to as working medium) in the heat pump system first absorbs the heat from the exhaust gas discharged from the drying process in the evaporator, and then evaporates from the liquid into steam; after being compressed by the compressor, it is sent to the condenser;
Under high pressure, the heat pump working fluid condenses and liquefies, releases high temperature condensation heat to heat the low temperature dry air from the evaporator, and heats the low temperature dry air to the required temperature and then enters the drying chamber as a drying medium for recycling; after liquefaction The heat pump working fluid returns to the evaporator again through the expansion valve, and thus circulates. Most of the water vapor in the exhaust gas is condensed in the evaporator and discharged directly to achieve the purpose of dehumidifying and drying.
Since the heat pump drying is also convective drying, there is also a problem of heat and mass transfer efficiency. The drying process involves not only the efficiency of the heat pump dehumidification unit, but also the drying medium (air)
The increase in heat and mass transfer efficiency in the drying chamber also enhances the performance of the entire drying system. In the drying system, a fluidized bed dryer is adopted. Since the particles are suspended in the drying medium, the contact area between the drying medium and the solid is large, and the material is vigorously stirred, the gas film resistance is greatly reduced, and the heat and mass transfer efficiency is high. .
2. Design of heat pump fluidized bed dryer 2.1 Design principle of heat pump fluidized bed dryer In order to conduct a comprehensive experimental study on the heat pump fluidized bed dryer, the design of the dryer should follow the following design principles:
(1) According to the modern design concept, the building block structure is adopted, and the units are independent of each other and assembled as needed;
(2) In order to simulate different drying processes and different operating conditions of the heat pump, the main parameters (temperature, speed and humidity) of the drying medium (air) can be adjusted within a certain range and can be measured in real time;
(3) In order to be able to conduct open-circuit, semi-open and closed-circuit cycle test studies on the heat pump fluidized bed drying unit, the test device should be able to switch between various cycles;
(4) The speed of the compressor and the speed of the air circulation fan in the test device are adjusted by the inverter.
According to the above design principles, a heat pump fluidized bed drying unit is designed, which is mainly composed of heat pump (refrigeration).
Systems (fully enclosed compressors, condensers, evaporators, throttles, filters, etc.) and drying media (air) circuits (centrifugal fans, dryers, heaters, piping, etc.)
composition. The working principle of the heat pump fluidized bed dryer is shown in Figure 2.
Shown. The valve in the drying line and the regulating door at the air inlet and outlet can regulate the flow rate of the air in the drying chamber. The wind speed in the drying chamber can be arbitrarily adjusted within the range of 0.5~3m/s.
Can meet different drying process requirements.
The basic flow of the heat pump drying device is open circuit, semi-open circuit and closed circuit. In order to carry out comparative experiments on the three main cycles of the heat pump drying system,
The device can be completed by adjusting each damper and baffle. In order to ensure that the system is running, reduce the heat loss in the dry high temperature section, and the cooling loss in the low temperature section of the refrigeration, the heat pump drying system is fully insulated and treated.
2.2 Thermal calculation of heat pump unit 2.2.1 Analysis of heat pump dry air circulation system The cycle of air (drying medium) during heat pump drying process can be drawn on the wet air map, as shown in Figure 3. Point a is the inlet state of the drying chamber, point b
For the outlet state of the drying chamber, point c is the air state point after dehumidification and cooling by the heat pump evaporator. Process ca is the heating process of air in the heat pump condenser,
In the process, the moisture content of the air remains unchanged, so it is a heating process with equal moisture content; the process ab is the moisture absorption of the dry material in the drying chamber.
If it is assumed that the heat exchange between the drying chamber and the outside is negligible, the process can be regarded as equalizing the humidification process; bc is the cooling and dehumidifying process of the circulating air in the evaporator.
In the actual process, the circulating air has gone through the bb`c route, first cooling down, then dehumidifying.
From the above analysis, the required cooling capacity of the evaporator is:
Q cold = G · (hb-hc) (1)
The heat required by the condenser is:
Q heat = G · (ha-hc) (2)
Thus, if the various heat losses generated by the drying chamber are neglected, that is, ha = hb, then Q cold = Q heat.
In the actual process, there must be some heat exchange between the drying chamber and the outside world, heat exchange with the outside world around the drying chamber, and heat exchange caused by temperature difference between the inlet and outlet. Generally speaking,
When the drying chamber air temperature is higher than the ambient temperature, the drying chamber emits heat outward, and there is ha
Have ha>hb.
In order to ensure the normal and stable operation of the heat pump drying system, prevent the evaporator from generating frost during the operation of the heat pump and reduce the heat transfer effect of the evaporator, usually take c
The air design temperature of the point is 5 °C. Obviously there are Φc=100%, other state parameters of point c check the air hd diagram, you can get:
Hc=18.5kg/kgdc=5.4g/kg
For point a, there is da=dc=5.4g/kg, and for ta=30°C, the state parameter of point a is:
Ha=44kJ/kgΦa=12.5%
For point b, there is ha=hb=44kJ/kg, and the size of da depends on the amount of circulating air G.
And the moisture W extracted from the dry material in the drying chamber during the drying process, db = da + (W / G) × 1000.
According to the preliminary design scheme of the drying device, the feeding time is 25kg, and the materials such as carrot and diced are dried from about 90% of water to less than 20% within 6 hours.
The total moisture released is 21.875 kg, then W = 21.875 / 6 = 3.646 kg / h.
Take G=3200kg/h, then Q cold=Q heat=Q·(ha-hc)=3200×(44-18.5)=81600kJ/h
2.2.2 Thermal calculation of heat pump refrigeration cycle The thermal process of the internal working fluid cycle of each working process of single-stage vapor compression heat pump refrigeration cycle is shown in Fig. 4.
According to the design requirements, the heat pump unit of the dryer uses a compressor to complete the task of cooling, dehumidifying and heating the circulating air. Take the evaporation temperature of 1.0 ° C, the condensation temperature is 40 ° C,
Other parameters can be found in the chart of the literature. The design conditions and design calculation results of the heat pump are shown in Tables 1 and 2, respectively.
2.2.3 Selection of main components (1) Dryer The dryer of the drying equipment is a horizontal multi-chamber fluidized bed dryer. The bottom is a perforated plate with an area of ​​0.36 m2 (length 1.2 m, width 0.3 m).
The pore diameter is Φ2.0 mm, and the opening ratio is 8%. There is a vertical baffle above the sieve plate to divide the fluidized bed into 4 small chambers. Each baffle can move up and down.
To adjust the distance between it and the sieve plate. At the lower part of each chamber is an intake branch pipe having a valve for regulating the flow of gas.
(2) Condensing unit The condensing unit includes compressors, condensers, liquid storage tanks, etc., in which the compressor is a key component. Considering the stability of operation and convenient maintenance, through calculation and analysis comparison,
We selected the TAG4561THR model produced by “100-year Taikang Refrigeration Equipment (Shanghai) Co., Ltd.†and the fully enclosed compressor unit with 3.7kW power.
(3) The evaporator is designed according to the characteristics of the device, and is entrusted to the domestic refrigeration enterprise for processing and manufacturing, which not only ensures the performance of the device is close to the imported equipment, but also significantly reduces the cost.
(4) Main fan main circulation fan According to the characteristics of the drying equipment, the rated power is 5.5kW, the flow rate is 2198~3847m3/h, and the wind pressure is 2940~3.
9-26.No.4A fan of 851.4Pa water column. The actual wind pressure and flow of the main circulation fan can be adjusted by the frequency converter.
3 Heat pump fluidized bed drying test 3.1 Test materials 1. Materials: The carrots used for testing were purchased from the farmers' market.
The test sample requires fresh, non-rotted red-skinned carrots. The main considerations for the selection of carrots as raw materials for testing are the low price, the less impact of raw materials on the season and the typicality of materials.
2. The pretreatment process before the carrot drying test is:
Raw material selection, finishing → cleaning → cutting root tip → cutting strip → dicing (6mm × 6mm × 10mm) → 5
Double boiling in water → rapid cooling → draining → evenly placed on the fluidized bed sieve plate according to drying requirements.
3.2 Test methods (1) Temperature and humidity: The temperature and humidity were measured using the WSB-005 transmitter from Wuhan Institute of Instrument and Measurement.
(2) Wind speed: The wind speed is measured by the KA22 type thermal anemometer of Shenyang Kaye Max Instruments Co., Ltd.
(3) Determination of water content: atmospheric drying oven drying method. That is, the drying method was performed once at 105 ° C for 8 hours to detect the moisture of the sample.
3.3 Test Results Figure 5 is a fluidized drying curve of a typical carrot diced heat pump. The test conditions are: drying temperature 40 ° C, dry medium air relative humidity 24.5%, the raw material is carrot diced (
6mm × 6mm × 10mm). It can be seen from the figure that there is a clear constant-speed drying section from 0 to 0.5 h. This is because the carrot has a large amount of attached water on the surface when it starts to dry.
At this time, the moisture inside the material does not change much. 0.5~4.0h is the deceleration zone, the water content of the material shows a significant decrease, and after 4h, the drying speed is very small.
The internal moisture of carrots changes very slowly. Especially in the late dry season,
It takes 4~5h to reduce the water content from 20% to 10%, which is a problem that is difficult to solve by low temperature drying. However, heat pump fluidized bed combined drying is much shorter than heat pump box drying, usually within 9 hours.
The moisture content of carrots can be dried from about 90% to less than 10%.
The drying test conditions are that the temperature of the air entering the drying chamber is 38 ° C, the relative humidity of the air is 35%, and the thickness of the carrot pieces is 3 mm when the flow is dry.
When the fluidized bed is dried, the scale of the carrot is 6 mm × 6 mm × 10 mm. When the fluidized bed is dry, the frequency of the circulating main fan is 45Hz, 40Hz and 35Hz, respectively.
To ensure that the material is in a normal fluidized state. The frequency of the circulating main fan during flow drying is 40 Hz, 35 Hz and 32 Hz, respectively, to ensure that the material is not blown up. As can be seen from Figure 6,
During the fluidized bed drying process, the carrot diced is suspended in the air and continuously tumbling, so that the thickness of the boundary layer of the material surface is reduced, and the heat transfer and mass transfer resistance are reduced.
Therefore, the fluidized bed has a higher drying strength than the through-flow drying.
The energy consumption of the heat pump fluidized bed drying fan and the total power consumption of the system are shown in Figure 7. The energy consumption of the fan is close to 50% of the total energy consumption of the system. This is because in the fluidized bed drying process, in order to keep the material fluidized while drying, it is necessary to have a higher pressure and speed of the drying medium (air). Therefore, the proportion of electric energy consumed by the circulating fan is large.
4 Conclusions (1) A set of heat pump fluidized bed drying combined drying test device was designed, and the carrot dart was subjected to fluidized drying test. the experiment shows,
Drying the moisture content of carrots from about 90% to less than 10% takes only 9 hours, which is shorter than the drying time of the box heat pump drying, and is suitable for drying high moisture fruit and vegetable materials.
(2) A comparative test of heat pump fluidized bed drying and flow drying was carried out using carrot as raw material. Tests have shown that during fluidized bed drying,
The carrot diced is suspended in the air and continuously tumbling, so that the thickness of the boundary layer of the material surface becomes smaller, and the heat transfer and mass transfer resistance are reduced, so the fluidized bed has higher drying strength than the through-flow drying.
(3) During the drying process of the fluidized bed of the heat pump, in order to ensure that the material can be in a fluidized state during drying, the circulating air must have a certain pressure and flow rate.
The power consumption of the main circulation fan is large. The experimental results show that the energy consumption of the circulating fan accounts for about 50% of the total energy consumption of the system. therefore,
It is worth noting how the heat pump fluidized bed dryer reduces the energy consumption of auxiliary equipment other than the compressor.
From the month of May, the new crop of onion from Jinxiang has harvested. After dried enough, the yellow onion can be packed and shipped from the month of June. The new crop Fresh Onion has very beautiful appearance and great quality. Jinxiang is a famous county which has large area planting garlic and onion.
1. Commodity name: Fresh Onion
2. Feature: Natural color, Thick and full skin, No stain and soil on outer skin, Firm and no rotten.3. Size: 3.0-5.0cm, 5.0-7.0cm, 7.0-10cm
4. Variety: Yellow Onion and Red Onion
5.Packing:
1) 10kg/carton, 20kg/carton, 10kgs/mesh bag,20kg/mesh bag and 25kgs/mesh bag
2) or according to the clients' requirements.
6. Supply Period:
A) Fresh season: May to the middle of August
B) Cold storage season: August to December.
7.Conveyance:26-30MT/40'HR (loading quantity depending on packing)
8.Transporting and storing temperature: 0°C -+1°C
Yellow Onion,Fresh Yellow Onion,Organic Yellow Onion,Yellow Round Onions
JINING FORICH FRUITS & VEGETABLES CO., LTD. , https://www.forichgarlic.com