CN102628639A - Vacuum drying device and vacuum drying control method - Google Patents
Vacuum drying device and vacuum drying control method Download PDFInfo
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- CN102628639A CN102628639A CN2012101416439A CN201210141643A CN102628639A CN 102628639 A CN102628639 A CN 102628639A CN 2012101416439 A CN2012101416439 A CN 2012101416439A CN 201210141643 A CN201210141643 A CN 201210141643A CN 102628639 A CN102628639 A CN 102628639A
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Abstract
The invention discloses a vacuum drying device and a vacuum drying control method. The vacuum drying control method comprises the following steps: an object to be dried is placed into a closed drying chamber, and the drying chamber is heated; a vacuum pump with a gas ballast valve which is communicated with the drying chamber is started to pump the air inside the drying chamber, and the air inside the drying chamber enters the vacuum pump with the air ballast valve after being heated by a heating tube; a pressure gauge continuously monitors air pressure of the drying chamber, and an air pressure signal is transmitted to a microprocessor; and the microprocessor judges whether the object to be dried stays at a drying status according to the gas pressure change of the drying chamber. By adoption of the technical scheme, the object to be dried can be accurately dried, and the cost is reduced.
Description
Technical field
The present invention relates to the vacuum drying technique field, relate in particular to a kind of vacuum dryer and control method.
Background technology
The characteristic that vacuum drying utilizes liquid (water, chemistry or biological solvent) boiling point under the low pressure state to reduce, can be under room temperature or low-temperature condition dry thing to be dried.Vacuum drying does not destroy physics, the biological and chemical characteristic of thing to be dried, all is widely used in all trades and professions.In the process of vacuum drying, thereby how the drying regime of perception thing to be dried control dry run is a key factor.The method of present modal control dry run is regularly, promptly rule of thumb sets the needed time of thing dry run to be dried.The method shortcoming is a bad timing, if regularly too short, dry run stops too early, and thing to be dried also contains moisture, if regularly long, dry run stops too late, can lose time and the energy.
Another kind method is at the indoor installing humidity sensor of vacuum drying, and for example infrared sensor utilizes airborne moisture the absorption of infrared ray specific wavelength to be come the humidity of perception thing to be dried.But the humidity sensor temperature influence is bigger, and the temperature of thing to be dried can influence the precision of humidity sensor, and humidity sensor can increase the cost of Minton dryer.
The method that also has another kind of decision drying regime is to measure the indoor pressure of vacuum drying.When pressure is lower than a people for the particular value set, think that thing to be dried has reached drying regime.The starting point of the method is to think after thing to be dried reaches drying regime, no longer includes the liquid evaporation, and the indoor pressure of vacuum drying will reduce.But the method has been ignored the very important point, and promptly the evaporating state of thing to be dried not only depends on the content of the liquid (water, chemistry or biological solvent) that needs are dry, and depends on the evaporating temperature of thing to be dried.When the temperature reduction of thing to be dried, when dry liquid (water, chemistry or the biological solvent) steam pressure (vapor pressure) of its needs that contain was reduced, evaporation can slow down greatly, thereby caused the indoor pressure of vacuum drying to reduce.Judge that for the particular value of setting thing to be dried has reached drying regime if only use this moment, will cause erroneous judgement disconnected, evaporation process is stopped too early when pressure is lower than a people.Another shortcoming of the method is that object to be dried and class of liquids are a lot; If set a single particular pressure value for all drying objects and liquid; Usually make many objects can not reach abundant drying, thereby or overdrying destroy physics, the biological and chemical characteristic of object to be dried.If set a particular pressure value respectively, will make that the manufacturing of vacuum drying system and maintenance are very complicated for each drying objects and liquid.In addition, the operating characteristic of vacuum drying system changed along with service time, for example, the leakage of vacuum system and pollution, the variation of vavuum pump operating characteristic can make that all the particular value that begins to set is no longer suitable.
In addition, the vacuum dryer that has at present adopts condenser to reclaim the liquid that is dried, but in most of the cases, the liquid that is dried is water, there is no need to reclaim.The main effect of condenser is to prevent to get into vavuum pump from the water vapour of sample evaporation to be dried.After water vapour gets into vavuum pump, can liquefy and be dissolved in the oil, make the vacuum character deterioration of oil, thereby destroy pumping speed and vacuum that the sealing of pump, lubricated and cooling performance reduce vavuum pump.
But be to use condenser that following shortcoming is arranged, the one, increased cost; The 2nd, make vacuum dryer manufacturing and keep in repair complicatedly because the vacuum of condenser must guarantee, otherwise can destroy the vacuum of system; The 3rd, condense in the condenser moisture when reaching a certain amount of; If refrigeration source does not have enough big instantaneous power; Can not control liquid water under enough low temperature, the water that condenses can evaporate under vacuum again, not only delays the sample drying time this moment; And water vapour can get into vavuum pump, do not reach the purpose of protection vavuum pump; The 4th, behind the adding condenser, the user will often dry the moisture in the condenser, is inconvenient to use.
Summary of the invention
The objective of the invention is to propose a kind of vacuum dryer and control method, can accomplish drying exactly, and can protect vavuum pump, the convenient use thing to be dried.The present invention proposes vacuum dryer and control method is applicable to any dry liquid that needs, and below the explanation supposition need dry liquid be a water.
For reaching this purpose, the present invention adopts following technical scheme:
A kind of vacuum dryer comprises hothouse, heating tube, has vavuum pump, pressure sensor, signal amplifier and the microprocessor of gas ballasting valve, wherein; Hothouse, heating tube are connected through air duct with the vavuum pump that has the gas ballasting valve successively, and pressure sensor one end is communicated with hothouse through air duct; The other end of pressure sensor is connected with signal amplifier; Signal amplifier also is connected with microprocessor, and hothouse is airtight, is used to place thing to be dried; The vavuum pump that has the gas ballasting valve is used for extracting the air of hothouse; The air that the heating tube dry kiln transports, the steam pressure of the airborne water that lifting is sent here, pressure sensor is used for converting the air pressure in the hothouse to the signal of telecommunication and sends to signal amplifier; Signal amplifier is used for amplification signal and is transmitted to microprocessor, and microprocessor is used for the signal of telecommunication control dry run of sending according to signal amplifier and judges whether thing to be dried reaches drying regime.
Pressure sensor comprises temperature compensation means.
Also comprise heater, heater is used for heating to hothouse.
Also comprise the differential pressure transducer and first vacuum valve; One end of differential pressure transducer and the air duct connection that is communicated with pressure sensor; The other end of differential pressure transducer is through first vacuum valve and the air duct connection that is communicated with heating tube, and differential pressure transducer also is connected with signal amplifier.
Microprocessor comprises analog-digital commutator, and analog-digital commutator is used for the electrical signal conversion that signal amplifier is sent is become data signal.
Also comprise second vacuum valve, second vacuum valve is at hothouse and have between the vavuum pump of gas ballasting valve.
Also comprise the 3rd vacuum valve, the 3rd vacuum valve is connected with hothouse, and the 3rd vacuum valve is used to discharge atmosphere entering hothouse makes hothouse can open and change thing to be dried.
A kind of vacuum drying control method may further comprise the steps:
A, thing to be dried is put into airtight hothouse, and dry kiln;
The vavuum pump that has the gas ballasting valve that B, unlatching are communicated with hothouse extracts the air in the hothouse, wherein gets into the vavuum pump that has the gas ballasting valve after the heating of heating tube of the process of the air in the hothouse;
C, pressure gauge continue to monitor the air pressure of hothouse, and send to microprocessor to air pressure signal;
D, microprocessor judge according to the air pressure change of hothouse whether thing to be dried reaches drying regime.
When coming through dry kiln to heat up to object to be dried, to close at hothouse and have second vacuum valve between the vavuum pump of gas ballasting valve, the vavuum pump that has the gas ballasting valve remains in operation.
Adopted technical scheme of the present invention, can accomplish drying exactly, avoided making many objects can not reach abundant drying thing to be dried; Or thereby overdrying destroys physics, the biological and chemical characteristic of object to be dried, and pressure sensor is of many uses, and use amount is big; Produce in batches, unit price is low, and selectable model is many; Can reduce cost with respect to using other sensor to control dry run, can protect vavuum pump simultaneously, make things convenient for the use of vacuum dryer.
Description of drawings
Fig. 1 is the structural representation of vacuum dryer in the specific embodiment of the invention.
Fig. 2 is the flow chart of vacuum drying control in the specific embodiment of the invention.
Fig. 3 is the drying curve figure of thing to be dried in the specific embodiment of the invention.
The specific embodiment
Further specify technical scheme of the present invention below in conjunction with accompanying drawing and through the specific embodiment.
The main thought of technical scheme of the present invention is to utilize the variation of measuring the indoor pressure of vacuum drying to come perception thing drying regime to be dried; Rather than one the people judge drying regime for the particular value of setting, the indoor pressure of vacuum drying is that the pressure that produced during water evaporates in the thing to be dried changes and the dynamic equilibrium of vacuum pumping speed.When thing to be dried was accomplished drying as yet, the water evaporates in the thing to be dried became gaseous state, and the indoor pressure of vacuum drying is raise, and after thing drying to be dried, water no longer evaporates, and the indoor pressure of vacuum drying reduces rapidly.So, through measure pressure in the hothouse change can perception thing to be dried drying regime, thereby the control dry run.
Fig. 1 is the structural representation of vacuum dryer in the specific embodiment of the invention.As shown in Figure 1; This vacuum dryer comprises hothouse 101, heater 109, heating tube 104, the vavuum pump 105 that has the gas ballasting valve, pressure sensor 103, differential pressure transducer 111, first vacuum valve 112, second vacuum valve 113, the 3rd vacuum valve 114; Signal amplifier 110 and microprocessor 108; Wherein, hothouse, heating tube and the vavuum pump that has a gas ballasting valve are connected through air duct 106 successively, and the air duct internal diameter is 6 millimeters; Pressure sensor one end is communicated with hothouse through air duct; The other end of pressure sensor is connected with signal amplifier through lead 107, and signal amplifier also is connected with microprocessor, an end of differential pressure transducer with and air duct 106 connections that are communicated with of pressure sensor; The other end of differential pressure transducer is through first vacuum valve and the air duct that is communicated with heating tube 106 connections; Differential pressure transducer also is connected with signal amplifier through lead 107, and second vacuum valve 113 is at hothouse and have between the vavuum pump of gas ballasting valve, and the 3rd vacuum valve 114 is connected with hothouse; The 3rd vacuum valve can discharge atmosphere and get into hothouse, makes hothouse can open and change thing to be dried.
Hothouse is airtight, is used for placing thing 102 to be dried.
Heater is selected 300 watts PULSE HEATING device for use, can heat to hothouse.
The vavuum pump power that has the gas ballasting valve is 3/4 horsepower (560 watts), and 220 liters of gas pumping speed per minutes, end vacuum are used for extracting the air in the hothouse less than 2000Pa.
The air that the heating tube dry kiln transports promotes the steam pressure (vapor pressure) of airborne water.
The pressure sensor model is MPX2100DP, and range 0-0.1MPa has demarcated and has temperature compensation means, and it converts the air pressure in the hothouse to the signal of telecommunication and sends to signal amplifier.
Signal amplifier can amplification signal and is transmitted to microprocessor.
Microprocessor adopts the PIC18F452 processor; Comprise analog-digital commutator; Analog-digital commutator can become data signal with the electrical signal conversion that signal amplifier is sent, and the signal of telecommunication that microprocessor is also sent according to signal amplifier is controlled dry run and judged whether thing to be dried reaches drying regime.
The differential pressure transducer model is MPX2010, range 0-10 kPa, high ten times of pressure measurement accuracy specific pressure sensors, but little ten times of the pressure range specific pressure sensors of differential pressure transducer.One end of differential pressure transducer links to each other with air duct through first vacuum valve, and the other end directly links to each other with the air duct of pressure sensor, and the output signal of telecommunication of differential pressure transducer also links to each other with microprocessor through signal amplifier.When first vacuum valve was opened, the pressure at differential pressure transducer two ends equated that the signal of differential pressure transducer is output as zero.When the measured force value of pressure sensor reaches or during less than 40 millimetress of mercury, first vacuum valve is closed.Close the end that the back differential pressure transducer links to each other with first vacuum valve, pressure remains on a steady state value, and the pressure of the differential pressure transducer other end is along with the change in pressure in the hothouse.Like this, just cause a pressure differential at the two ends of differential pressure transducer, it is measured by microprocessor that its pressure differential converts the signal of telecommunication to.The certainty of measurement specific pressure sensor of differential pressure transducer is wanted high ten times, and the pressure that can measure more accurately in the hothouse changes.
Evaporation capacity of moisture content depends on the pressure the when steam pressure (vapor pressure) of moisture is the thermodynamical equilibrium of water vapour and condensed state water (liquid state) in the thing to be dried.When reaching thermodynamic equilibrium state, aqueous water has tendency to flash to gaseous form, and vaporous water also has tendency to be condensed into liquid state from gas form.The speed that two states changes equates.In process of vacuum drying, the water vapour that is produced during evaporation constantly shifts out outside the drying device through vavuum pump, makes that like this moisture in the thing to be dried can only unidirectionally evaporate, and can not condense.
The boiling point of liquid is the temperature of vapour pressure and the ambient pressure of liquid when equating, when boiling temperature, makes the water in the thing to be dried become gaseous state from liquid state thereby the vapour pressure of liquid can overcome environmental pressure.The vapour pressure of moisture is directly connected to evaporation of liquid speed, and under same environmental pressure, higher steam pressure energy produces bigger evaporation rate.The vapour pressure of water is along with the relation between the variations in temperature of water can be used the description of Clausius-Capeyron formula.
When with vacuum dryer drying thing to be dried, evaporation of liquid speed linear correlation in instantaneous pressure value in the hothouse and the thing to be dried.For example, when the liquid in the thing to be dried was water, the evaporation rate of moisture depended on two factors in the thing to be dried: the content of the vapour pressure of water and water in the thing to be dried.The variation of the content of water in the thing not only to be dried, the variation of the vapour pressure of water also can influence the variation of air pressure in the device in the thing to be dried.When the vapour pressure of water in the thing to be dried lowered, evaporation rate can reduce, and the pressure in the hothouse can reduce.But this does not show that thing to be dried has reached drying regime.Thing to be dried also contains moisture probably, and just evaporation rate has reduced.Iff is indicated the drying regime of thing to be dried with the atmospheric pressure value in the hothouse, usually can judge by accident disconnectedly, and it is too early to stop dry run, makes thing to be dried bone dry not as yet.
The vapour pressure of water changes along with the variations in temperature of thing to be dried in the thing to be dried.In the actual drying process, water is being converted in the gaseous process by liquid state, takes away a large amount of heats (2260 joule/gram), makes to cause the instantaneous reduction of thing temperature to be dried that vapour pressure lowers, thereby make evaporation rate reduce, and causes the minimizing of hothouse internal gas pressure.Along with the effect of the outer heater of hothouse, thing to be dried absorbs heat later on, thing temperature recovery to be dried, and the vapour pressure of moisture rises thereupon in the thing to be dried, thus evaporation rate rises, and the pressure in the hothouse also rises.So vapour pressure is a fast-changing process to the influence of air pressure in the device.
Otherwise moisture then is a slow procedure to the influence of hothouse internal pressure in the thing to be dried.Water evaporates in the thing to be dried needs a time course.The time of thing bone dry to be dried is depended on and multiple factor; The pumping speed of vavuum pump; The power of heater; The size of thing to be dried, what of moisture in the thing to be dried, but the pressure in the hothouse is a level and smooth relatively time course when not considering the variation of vapour pressure along with the variation of the water content of thing to be dried.
When the force value in using hothouse was controlled the dry run of thing to be dried, the variation of the vapour pressure of moisture was a noise to the influence of hothouse internal pressure in the thing to be dried, disturbs the observation to dry run.But the variation of vapour pressure is a quick process, and influence then is a process that changes at a slow speed to moisture to the hothouse internal pressure in the thing to be dried.Calculate the time dependent slope of hothouse internal pressure through microprocessor and can remove the interference of vapour pressure variation, correctly judge the drying regime of thing to be dried force value.
This specific embodiment has adopted the rotary-vane vaccum pump that has gas ballast valve (Ballast valve), can avoid water vapour to liquefy in oil.Its principle is to put into air in certain amount from the outside at the compression stage of vavuum pump to get into vavuum pump; To improve air and water vapor mixture body pressure; When the partial pressure of water vapour does not reach the saturated vapor pressure under the oil temperature of vavuum pump as yet; Mixture pressure surpasses the pressure of air bleeding valve and opens air bleeding valve, is rejected to outside the pump before water vapour is liquefied in pump chamber.
The rotary-vane vaccum pump that use has gas ballast valve (Ballast valve) can replace the use condenser, thus the problem of avoiding condenser to bring to vacuum dryer.But when use has the rotary-vane vaccum pump of gas ballast valve (Ballast valve); The air capacity of putting into from the outside (being called the gas ballasting amount) will cause the bigger pressure reduction of generation between pump compression chamber and the suction chamber; Make the gas regurgitation volume increase, thereby reduced the end vacuum of pump.Vacuum descends not only can influence the dry run of vacuum dryer, and vacuum descends and also can cause the water saturation vapour pressure to lower, thereby is unfavorable for the eliminating of water vapour.The gas ballasting amount is big, and the exhaust power demand also will increase.Oil spout aggravation when the gas ballasting amount greatly also can cause the pump exhaust.If the gas ballasting value selects too greatly in addition, the gas ballasting hole is corresponding wants big, has manufactured a lot of practical difficulties.Significantly, desirable situation is under the gas ballasting amount of minimum, maximum eliminating water vapour.This specific embodiment has proposed a method and apparatus, can when reducing the gas ballasting amount, strengthen water vapour eliminating amount.
By perfect gas law:
PV=NRT, wherein P is a gas pressure, and V is a gas volume, and N is the gas ear number that rubs, and R is an ideal gas constant, T is a temperature.
Can obtain the discharge rate of water from pump is:
W (Grams Per Second)=P
WSM/RT, wherein P
WBe the partial pressure (partial pressure) of water vapour in the gas in the vacuum pump chamber, S is the pumping speed of vavuum pump, and M is the molecular weight (18 restrain/rub ear) of water.
Above-mentioned formula shows that under the situation of identical vacuum pumping speed, the discharge rate of moisture is proportional to the partial pressure of the water vapour in the pump chamber, increases the partial pressure of water vapour, can increase the discharge rate of water vapour.
Water vapor pressure P in pump chamber increases, and shows that vapour content increases, and at this moment how outside the unnecessary water vapour excavationg pump, and does not increase the gas ballasting amount, and four kinds of ways can only be arranged usually:
1, reduces the pressure at expulsion of air bleeding valve when opening of vavuum pump;
2, improve the temperature of oil in the pump chamber;
3, reduce the pressure of pump intake place gas;
4, reduce vapour content in the gas of coming in from gas ballast valve, promptly add dry gas as far as possible.
But above way all has shortcoming:
1, the pressure at expulsion of reduction vavuum pump has a limit, can not be lower than atmospheric pressure.
2, the temperature of oil is also limited in the raising pump chamber, otherwise vavuum pump can be overheated.
3, the effective ways that reduce the pressure of vacuum pump inlet place gas are that cooling sucks gas, but suck after gas temperature reduces, and the water saturation steam pressure also can reduce, and the part water recovery becomes aqueous water in the gas of suction thereby make, and is unfavorable for outside the excavationg pump.
4, the water vapour that reduces in the gas of coming in from gas ballast valve is difficult to accomplish, is atmosphere because add the gas of gas ballast valve usually, and its humidity situation that depends on the weather is difficult to control.
Another way that improves the water vapor pressure in the pump chamber is to increase the steam pressure (vapor pressure) that pump sucks the water in the gas.In Minton dryer, the aqueous water in the sample evaporates in hothouse becomes gaseous state, and water vapour arrives the vacuum pump suction inlet through piping and valve, is discharged to outside the pump through vavuum pump then.Usually vavuum pump and hothouse have a segment distance, and when gas comprised that water vapour arrives vavuum pump, its temperature lowered.When gas temperature reduced, the steam pressure of wherein contained water also reduced.The steam pressure that pump sucks water contained in the gas reduces the partial pressure of water vapor reduction that directly causes in the pump chamber, makes the part water vapour be liquefied as aqueous water, be deposited in the pump oil, thus the discharge rate of reduction moisture.
This specific embodiment adds a gas heating tube (for example Universal Heated Hoses) in the porch of vavuum pump, gas heats through the gas heating tube before being inhaled into vavuum pump.Because the steam pressure of water is directly relevant with gas temperature in the gas, improve the steam pressure that sucks the water in the gas, cause the partial pressure of water vapor in the pump chamber to raise, thereby help outside the moisture excavationg pump.
The gas heating tube is by 220 volts of 300 watts of electrical heating.The temperature of heating tube is controlled at mean temperature 90 degree Celsius by temperature controller.The air inlet of gas heating tube links to each other with the pipeline that vacuum drying cabinet comes out, and the gas outlet links to each other with vavuum pump.
When gas passed through heating tube, speed was very fast.It is big that the heating power of heating tube is wanted, and makes gas effectively to heat.The heating power of heating tube is selected by the drying system decision, is to guarantee that gas is about 90 degree Celsius in the temperature of the outlet of heating tube.Why being chosen in 90 degree is because the optimum temperature that has a rotary-vane vaccum pump of gas ballast valve usually is 90 degree Celsius.Draining is best under this temperature.Temperature is low excessively, causes the partial pressure of water vapour to reduce, and the part water vapour is condensed into aqueous water.Temperature is too high, and the pump housing is overheated easily, is unfavorable for the work of pump.
The effect of heating tube is through contrast test test, use vacuum dryer at three hours inner dryings six samples, the total moisture content of six samples is 170 grams, has contrasted three kinds of equipment settings:
1, do not open the vavuum pump gas ballast valve, and do not use heating tube;
2, open the vavuum pump gas ballast valve, but do not use heating tube;
3, open the vavuum pump gas ballast valve, use heating tube simultaneously.
Ponding in the vavuum pump can be seen through the liquid level situation of observing oil in the vacuum pump chamber.When gas ballast valve and heating tube were not all opened, liquid level was presented at the black line place, far above the original liquid level of oil in the pump chamber, showed that ponding is serious in the pump.When opening gas ballast valve, when still not using heating tube, the liquid level of oil is higher than original liquid level at the green line place in the pump chamber, shows discharge fully of moisture, and along with time integral, the interior moisture of pump can get more and more, and causes the vacuum drying system duty to worsen.When opening gas ballast valve, when using heating tube simultaneously, the liquid level of oil maintains original liquid level in the pump chamber, shows and is got rid of fully from the moisture of the sample that is dried.
Another way that helps the moisture discharge is to keep vavuum pump to turn round continuously.Between heating tube and hothouse, added second vacuum valve 113.When changing sample, in the time of need stopping vacuum drying, close second vacuum valve 113, but do not stop the vavuum pump running.Beyond make getting into continual and lasting the passing through of moisture in the vavuum pump gas ballasting valve being exhausted from system.Another benefit that keeps the continuous running of vavuum pump is that the temperature of the oil in the pump chamber can not cooled off, and helps getting rid of moisture.
Fig. 2 is the flow chart of vacuum drying control in the specific embodiment of the invention.As shown in Figure 2, the flow process of vacuum drying control may further comprise the steps:
The vavuum pump that has the gas ballasting valve that step 202, unlatching are communicated with hothouse extracts the air in the hothouse, wherein gets into the vavuum pump that has the gas ballasting valve after the heating of heating tube of the process of the air in the hothouse.
In this process, in order to take into account pressure range and accuracy, pressure gauge adopts two kinds, and a kind of is pressure sensor, and another kind is a differential pressure transducer.At first adopts pressure sensor is monitored the air pressure of hothouse, and sends to microprocessor to air pressure signal, when the air pressure of hothouse is not more than 40 millimetress of mercury, adopts the air pressure of differential pressure transducer monitoring hothouse, and sends to microprocessor to air pressure signal.
In the thing dry run to be dried, microprocessor regularly obtains the air pressure in the hothouse to the continual real-time sampling of pressure sensor.Per 0.1 second of sample frequency is (10 HZ) once.After per 100 samplings, microprocessor calculates average A (i)=Σ [0.01*y (i)] to 100 force value, and y (i) is the per 0.1 second sampled value of pressure sensor.
Calculate last air pressure and the difference of working as time air pressure; It is the slope that pressure changes; (original difference is only the time dependent slope of air pressure in the hothouse divided by the time of timing microprocessor sampling air pressure to B (j)=A (i-1)-A (i); But the time because of the air pressure in the microprocessor samples hothouse is fixed, so can use difference to be equivalent to slope.If the time of the air pressure in the microprocessor samples hothouse is on-fixed, then need to replace difference) with slope.
And in the memory cell of microprocessor, preserve nearest five times difference.
If 1 difference is sometimes greater than zero, sometimes less than zero, and the absolute value of difference keeps being not more than 1 millimetres of mercury, judges that then thing to be dried has reached drying regime.
If 2 differences become less than zero (B (j) < 0), show that pressure rises, judge that thing to be dried does not reach drying regime; Moisture evaporates in the thing to be dried, and no matter force value just can not stop dry run; Keep thing temperature to be dried, get into second stage.
If 3 differences are greater than zero (B (j)>0); Difference descends slowly and greater than 1 millimetres of mercury, show that then pressure descends, but the water evaporates of thing to be dried and vacuum pumping speed does not reach balance as yet; Judge that thing to be dried does not reach drying regime, get into second stage.
If 4 differences are less than zero (B (j) < 0), but the absolute value of difference is excessive, shows that the vapour pressure of moisture in the thing to be dried rises very big; Make water evaporates too fast; The rising of the vapour pressure of moisture shows then that very greatly the temperature of thing to be dried raises too much, for some thermally sensitive things to be dried, destroys thing to be dried in order to prevent high temperature in the thing to be dried; Should slow down the heating to thing to be dried this moment, gets into second stage.
When coming through the heating, vacuum hothouse to heat up to object to be dried; When coming through dry kiln to heat up to object to be dried; Close at hothouse and have second vacuum valve between the vavuum pump of gas ballasting valve, the vavuum pump that has the gas ballasting valve remains in operation.After object to be dried heats up, open second vacuum valve again, carry out above four processes.
Fig. 3 is the drying curve figure of thing to be dried in the specific embodiment of the invention.As shown in Figure 3, the A section of curve is an initial stage of drying, and thing temperature to be dried is low, and the vapour pressure of moisture is less than the pressure of thing surrounding environment to be dried in the hothouse in the thing to be dried, and evaporation slows down or evaporates almost and stops.At this moment, the time dependent curve of pressure in the hothouse shows very large negative slope, and the force value in the hothouse is very little.Will think thing to be dried drying by mistake if only judge through the numerical value of pressure this moment, clearly, this and actual state are not inconsistent.
The B section of curve is that thing to be dried heater block outside hothouse absorbs that the vapour pressure of thing temperature to be dried and moisture raises gradually behind the heat; Evaporation recovers or accelerates; At this moment; The indoor pressure of heating in vacuum rises, and when the pumping speed of thing evaporation rate to be dried and vavuum pump reached dynamic equilibrium, the pressure in the hothouse kept value relatively stably.
The C section of curve is that thing to be dried is approaching dry, because the minimizing of moisture, evaporation capacity reduces; Pressure in the hothouse begins to descend; The D section of curve is behind thing bone dry to be dried, to evaporate to stop, and the pressure in the hothouse tends to be steady again, but remains on a lower force value.
So drying regime that force value in the hothouse and the time dependent slope of force value can be used for judging thing to be dried jointly.This method can avoid the influence of the vapour pressure variation of moisture in the thing to be dried, thereby it is disconnected to reduce erroneous judgement than the drying regime of only judging thing to be dried with force value.
The time dependent other characteristic of force value also can help to judge the degree of drying of thing to be dried.When the moist thing to be dried of drying, force value slowly descends in time; When not having thing to be dried in the hothouse, force value descends fast, keeps constant then, changes no longer in time; When dry low moisture thing to be dried, force value begins quick decline, slowly rises then.Its ascensional range depends on the water content and the evaporation rate of thing to be dried.
Use the more variation of sensitive measured pressure value of differential pressure meter.At this moment, because differential pressure instrumentation amount is the relative pressure value, so the variation of force value is opposite with the timing of use absolute pressure.The rising of differential pressure instrumentation amount is equivalent to the decline of absolute pressure timing, and vice versa.
In addition, utilize amplitude of variation, rate of change or the change histories etc. of pressure slope, can judge the degree of drying of thing to be dried.
The above; Be merely the preferable specific embodiment of the present invention, but protection scope of the present invention is not limited thereto, anyly is familiar with this technological people in the technical scope that the present invention disclosed; The variation that can expect easily or replacement all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection domain of claim.
Claims (9)
1. a vacuum dryer is characterized in that, comprises hothouse, heating tube, has vavuum pump, pressure sensor, signal amplifier and the microprocessor of gas ballasting valve; Wherein, hothouse, heating tube and the vavuum pump that has a gas ballasting valve are connected through air duct successively, and pressure sensor one end is communicated with hothouse through air duct; The other end of pressure sensor is connected with signal amplifier; Signal amplifier also is connected with microprocessor, and hothouse is airtight, is used to place thing to be dried; The vavuum pump that has the gas ballasting valve is used for extracting the air of hothouse; The air that the heating tube dry kiln transports, the steam pressure of the airborne water that lifting is sent here, pressure sensor is used for converting the air pressure in the hothouse to the signal of telecommunication and sends to signal amplifier; Signal amplifier is used for amplification signal and is transmitted to microprocessor, and microprocessor is used for the signal of telecommunication control dry run of sending according to signal amplifier and judges whether thing to be dried reaches drying regime.
2. a kind of vacuum dryer according to claim 1 is characterized in that pressure sensor comprises temperature compensation means.
3. a kind of vacuum dryer according to claim 1 is characterized in that, comprises that also heater, heater are used for heating to hothouse.
4. a kind of vacuum dryer according to claim 1; It is characterized in that; Also comprise the differential pressure transducer and first vacuum valve; One end of differential pressure transducer is communicated with the air duct that is communicated with pressure sensor, the other end of differential pressure transducer through first vacuum valve with and the air duct connection that is communicated with of heating tube, differential pressure transducer also is connected with signal amplifier.
5. a kind of vacuum dryer according to claim 1 is characterized in that microprocessor comprises analog-digital commutator, and analog-digital commutator is used for the electrical signal conversion that signal amplifier is sent is become data signal.
6. a kind of vacuum dryer according to claim 1 is characterized in that, also comprises second vacuum valve, and second vacuum valve is at hothouse and have between the vavuum pump of gas ballasting valve.
7. a kind of vacuum dryer according to claim 1; It is characterized in that; Also comprise the 3rd vacuum valve, the 3rd vacuum valve is connected with hothouse, and the 3rd vacuum valve is used to discharge atmosphere entering hothouse makes hothouse can open and change thing to be dried.
8. a vacuum drying control method is characterized in that, may further comprise the steps:
A, thing to be dried is put into airtight hothouse, and dry kiln;
The vavuum pump that has the gas ballasting valve that B, unlatching are communicated with hothouse extracts the air in the hothouse, wherein gets into the vavuum pump that has the gas ballasting valve after the heating of heating tube of the process of the air in the hothouse;
C, pressure gauge continue to monitor the air pressure of hothouse, and send to microprocessor to air pressure signal;
D, microprocessor judge according to the air pressure change of hothouse whether thing to be dried reaches drying regime.
9. a kind of vacuum drying control method according to claim 8; It is characterized in that; When coming through dry kiln to heat up to object to be dried, to close at hothouse and have second vacuum valve between the vavuum pump of gas ballasting valve, the vavuum pump that has the gas ballasting valve remains in operation.
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| CN106853417A (en) * | 2016-11-18 | 2017-06-16 | 中核兰州铀浓缩有限公司 | Centrifugation cascade a small amount of centrifuge shelves vacuum drying method |
| CN113874671A (en) * | 2018-12-19 | 2021-12-31 | 维斯有限公司 | In CO2Method for thermally drying wood in an atmosphere, and drying plant for carrying out the method and resulting product |
| CN114659341A (en) * | 2022-03-02 | 2022-06-24 | 上海兰钧新能源科技有限公司 | Control method for baking lithium ion battery |
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| CN114659341A (en) * | 2022-03-02 | 2022-06-24 | 上海兰钧新能源科技有限公司 | Control method for baking lithium ion battery |
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Application publication date: 20120808 |