CN1090922A - vacuum drying technology and device thereof - Google Patents

Abstract

The present invention relates to a vacuum drying technology and its equipment, mainly used for drying plate blank in the field of wood processing technology. The device can solve the problem of air tightness in a vacuum system, and is formed by arranging a membrane with fine texture on an annular bracket with a groove to form an air bag. When the wet plate blank is carried by the conveying belt with good water permeability and passes through the drying chamber, the air bag is in sliding contact with the plate blank and the conveying belt, and meanwhile, an integral dynamic sealing ring is formed. Under the action of the internal and external pressure difference, the air bag forms an air wedge at the cone angle of the bracket to block air from permeating, so that the vacuum degree of the system is protected, and the aim of vacuum drying in a continuous operation state is fulfilled.

Description

Vacuum drying technique and device thereof

Aspect the machining of timber, usually can run into the problem of the drying of wood.Show according to existing data, the method that the wood materials drying is adopted, following several nothing more than having: (1) is by the heated type seasoning of medium; (2) air drying method; (3) micro-wave drying method; (4) infrared drying; (5) utilize the water imbibition seasoning of disliking aqueous medium; (6) boulton process; (7) centrifugal drying method.More than the further segmentation of 7 kinds of seasonings, its characteristics have nothing in common with each other.At this, only for vacuum drying technique, at present known have: (a) closed container formula vacuum wood dryer, dry solid wood and semi-finished product material; (b) the particieboard vacuum make-up machine of mating formation, the negative pressure with vacuum produces makes wood shavings be easy to moulding.In fact (b) plants and do not belonged to vacuum drying scope, is not for drying because it uses the purpose of vacuum technique.The present invention belongs to above-mentioned (5) category of planting seasoning-be boulton process, it is to utilize the vacuum drying principle to realize being that the wet mat of raw material carries out dry a kind of device with wooden, compare with existing vacuum drying technique, have difference in essence, one is dynamic drying, and another is static dry.The former not only has static dry characteristics concurrently, but also the own advantage of tool: it utilizes capillary crisscross, abundant in the wet mat, with atmosphere and vacuum chamber communication.Moisture in the capillary to the negative pressure space motion, thereby has been accelerated rate of drying under the effect of inside and outside differential pressure.

The purpose of this invention is to provide a kind of Minton dryer, the wet feed that it can not only dry have the slab shape, and can under the situation of working continuously, carry out drying, because it has solved the dynamic airtightness problem in the vacuum drying system.

The object of the present invention is achieved like this: a conveyer belt transmission system determines that with one mode is installed on the frame-type support.Conveyer belt is sleeved on three running rollers and is inverted triangle, and driving wheel and follower be last, i.e. the two ends, top of pedestal, horizontal positioned; Regulating wheel is descending, i.e. following " belly " of pedestal.Three limits of conveyer belt and three tangent formations of running roller " triangle ", wherein a limit-base is the level of state.

Driving wheel obtains power from power source, and drives the conveyer belt running, its startup, operation and stop all by means of gauge tap.

The locus of regulating wheel can be regulated, and the purpose of regulating it has two: (1) is convenient to the conveyer belt installation; (2) make conveyer belt have suitable rate of tension.

True worker's hothouse of this device divides upper and lower two parts.They are made of shell, external tube head, air bag carriage, diaphragm, charging valve, air gauge, temperature compensator and positioner.The top hothouse be placed in conveyer belt above, its opening is down; The bottom hothouse is located in the top of support, and below the horizontal conveying belt, its opening up and corresponding with the opening of top hothouse.Upper and lower hothouse is all determined its locus by positioner.

The shell of hothouse, an end communicates with negative pressure source through external tube head, and the other end links to each other with the annular air-pocket carriage, carriage upper edge " circular periphery " has a groove, with excellent in quality, submissive, wear-resisting and show slightly flexible diaphragm and seal this groove, just constitute air bag.Gas injects through air valve, makes air bag have certain pressure.Be installed in the size that air gauge on the carriage can predict gas pressure in the air bag.

The appearance and size of the input of top hothouse and output and wet mat matches, and its both sides and conveyer belt match.

Be formed at the annular groove on the carriage, its cross sectional shape be semicircle add one trapezoidal, trapezoidal base angle or cone angle are inwards.The air bag that is formed on the carriage is that semicircle adds an ellipse, but oval major semiaxis equals 0.5～1.5 times of semi-minor axis, so the approximate circle of the cross sectional shape of air bag.By this semiellipse that diaphragm surrounds, the variation of its cross sectional shape can only change in trapezoidal scope.

Use temperature compensator, the purpose of irradiation steel slab surface is the energy that (1) compensation consumes because of water evaporates, and (2) increase the kinetic energy of superficial water molecule, and (3) accelerate the evaporation of moisture, improve rate of drying.

Two surfaces of conveyer belt must be smooth, and its middle part is a mesh areas, and both sides are smooth areas, and the width q of mesh areas and the width of wet mat adapt, and the size of mesh adapts with the wet stock size that is dried.

Before the work of this device, the guided plate-length of a lightweight is equaled the length of support, wide and thickly equate-, pass hothouse from the front end of support with the size of wet mat, extend the rear end, place on the horizontal conveying belt.

At this moment, allow two hothouse place negative pressure state.Top hothouse opening is faced the front of conveyer belt down, and the air bag on its carriage closely contacts with the upper surface of guided plate at input and output side, closely contacts with the smooth areas of conveyer belt in both sides; Bottom hothouse opening in the face of the back side of smooth conveyer belt, all closely contacts with the back side of conveyer belt around the air bag on its carriage up.

The opening of upper and lower hothouse is relative, and purpose is: (1) is in order to make conveyer belt and the wet stock stress balance in the hothouse; (2) constitute sealing; (3) be convenient to accelerate the evaporation of water vapour.

When conveyer belt carries wet stock when passing vacuum chamber, this tight contact has just constituted the overall dynamics sealing ring.

Realize that dynamic Mi Quan has three factors:

For ease of narration, this rear end of sentencing hothouse is an example.

(1) when conveyer belt delivery wet mat passed between the upper and lower air bag of vacuum chamber, air bag formed " gas chock " naturally at the inboard cone angle of carriage place.The function of this " gas chock " is that it can block the infiltration of outside air effectively.This is because exist the reason of a pressure reduction inside and outside the vacuum chamber.

(2) because the existence of inside and outside differential pressure, outside air will pass along the slit between air bag and the slab, supposes to have one air-flow to be formed between contact-making surface, according to fluid mechanics principle: " place that flow velocity is big, static pressure is little, and the local static pressure that flow velocity is little is big." this moment the pressure in the air bag greater than the pressure between contact-making surface, this just becomes to making the air bag diaphragm to move downward to be adjacent to slab, to have hindered the inflow of air.

(3) in above-mentioned, the cross sectional shape of air bag is similar to a circle, according to geometry principle: " on the plane.In all geometric figures that girth equates, the area maximum that circle is surrounded." when air bag be squeezed and inside and outside differential pressure do the time spent, deformation will take place, its sectional area must reduce, and causes that volume reduces, and must cause the air bag internal pressure to increase, result's " gas chock " has thoroughly separated the passage of air-flow at cone angle place distending.

More than the comprehensive function of three factors, it is tighter that " gas chock " wedge is got, diaphragm is just bigger to the slab applied pressure, validity and reliability that this has strengthened sealing ring have greatly thoroughly solved the problem of dynamic seal (packing).

When wet mat is carried from a last procedure toward this device, wait wet mat one to be connected mutually with guided plate, just can start this device.At this moment, the front end face of wet mat is close to the rear end face of guided plate, and along with moving of conveyer belt passed vacuum drying cabinet inchmeal.Constitute an overall dynamics sealing ring because of " air bag on the carriage, wet mat " reaches " smooth conveyer belt " again, just make wet mat under the effect of inside and outside differential pressure, moisture constantly overflows from the capillary of wet mat, enters negative pressure space.Temperature one in hothouse is regularly regulated the speed V of conveyer belt or the moisture content that the vacuum in the control hothouse just can be regulated rate of drying or slab.When drying is about to finish, should be connected guided plate mutually with the end of wet mat, make the position before guided plate returns to original start, shut down again.

Owing to adopt such scheme, just can set up the overall dynamics sealing ring effectively, control the rate of drying of wet mat neatly, make it reduce moisture content, under the situation of working continuously, carry out dry purpose thereby reach.Whole device divides the vacuum pipe part, the vacuum drying cabinet part, and conveyer belt power train and support part, simple in structure, flexible operation.In addition, it also has following advantage:

(1) compare with the heated type seasoning that extensively adopts at present:

(a) guaranteeing that its equipment is simple, invests little under the situation of working continuously;

(b) energy-conservation, thermal losses is little;

(c) simple to operate, easy, as long as regulate the speed of conveyer belt in vacuum or the drying system, just can regulate by the moisture content of dry material;

(d) easy to maintenance, the friction member of relative motion is few.

(2) compare with the air drying method:

(a) its rate of drying is fast, stable yield.(b) be not subjected to the influence in weather and place.

(3) compare with closed container formula vacuum drier.

(a) adopt continuous drying, suitable continuous productive process;

(b) rate of drying is fast, the productivity ratio height;

(c) dry run is easy to control;

(d) Gan Zao object difference, one is based on dry solid wood; Another is based on drying slab moulding or open-textured of mating formation.The former is relatively more loose to the dimensional requirement of dry object, and the latter is tighter to the requirement of slab size.

If, this is cascaded with installing several, finally can make the moisture content of slab reduce to zero or reduce to the moisture content of our defined.

Below in conjunction with accompanying drawing the present invention is further described.

Fig. 1 is contact condition, and the localization method of top hothouse between vacuum pipe connected mode, air bag, conveyer belt and the slab.

Fig. 2 is the front view of the embodiment of the invention.

Fig. 3 and Fig. 4 are that the overall dynamics sealing ring forms schematic diagram.

Fig. 5 is the F-F view, has embodied the structure of air bag carriage.

Fig. 6 is the structure chart of smooth conveyer belt.

Fig. 7～Figure 11 is the drying principles figure of this device.

Figure 12 is another embodiment.

Among the figure: 1 bottom hothouse, 2 air intake valves (1), 3 bottom hothouse carriages, 4 smooth conveyer belts, the positioner of 5 top hothouses (1), 6 air bags, 7 slabs or lightweight guided plate, 8 top hothouse carriages, 9 air intake valves (2), 10 top hothouses, 11 external tube heads (1), the sealing ring of 12 pipeline joints, the clamping screw of 13 pipeline joints, 14 bend pipes, 15 straight tubes, 16 lead to the straight tube of negative pressure source, 17 threeways, the positioner of 18 top hothouses (2), 19 external tube heads (2), 20 bottom hothouse air bags, 21 columns (1), 22H type support, the bearing tenon of 23 regulating wheels, 24 regulating wheel tongue-and-groove breach, 25 regulating wheels are regulated bolt, 26 power switches, 27 bunchers, 28 V belts, 29 bearings (1), 30 pulley concial disks (1), 31 conveyer belt live axles, 32 driving wheels, 33 pulley concial disks (2), the anchoring bolt of 34 bunchers, hothouse location, 35 bottom angle bar, 36 bottom hothouse bolts, 37 air gauges (1), 38 positioners (3), 39 bearings (2), 40 conveyer belt follower rollers, 41 vertical equity crossbeams, 42 interties, 43 upright firmly (2), 44 drag links, the external tube head butt plate of 45 bottom hothouses, firmly upright in the middle of 46,47 tongue-and-grooves, 48 tension wheel shaft bearings, 49 tensioning running rollers, 50 Pressure gauges (2), 51 lightweight guided plates, 52 far-infrared temperature compensators (1), 53 temperature compensators (2), 54 compensators (3), 55 compensators (4), 56 bottom bracket air bags, 57 bracket air bags, 58, carriage air bag groove, 59 diaphragm hold-down screws, 60 plastic washers, 61 leatheroid packing rings, 62 air bag diaphragms, 63 rubber washers, 64 triangle compact heaps, 65 cone angle, 66 air gauge installing holes, 67 diaphragm fixing screw holes (1), 68 carriage grooves, 69 diaphragm fixing screw holes (2), 70 compress the side direction shoulder (1) of diaphragm, 71 compress the side direction shoulder (2) of diaphragm, 72 air valve installing holes, 73 smooth conveyer belts, 74 conveyer belt smooth areas, 75 conveyer belt mesh areas, 76 conveyer belt docking areas, 77 conveyer belts butt joint screw hole, 78 mesh mutual alignments, 79 conveyer belts butt joint screw, 80 conveyer belts, 81 locking nuts, 82At atmospheric pressure direction, capillary distribution map in the 83 wet bases, 84Vapor water vapour evaporation direction.

In Fig. 1, upper and lower hothouse (10) and (1) all communicate with negative pressure source by external tube head (11) and (19), bend pipe (14), straight tube (15), threeway (17) and pipeline (16).The location of the hothouse right 2 pairs of positioners (5) and (18) that keep left are fixing, and its carriage has air bag groove (6) and (10), and the interior gas of air bag is through valve (2) and (9) injection.The air bag (20) of bottom bracket (3) is close to the back side of conveyer belt (4); The air bag (6) of bracket (8) is close to the smooth areas of upper surface and the side and the conveyer belt (4) of guided plate (7).

In the embodiment of Fig. 2, the frame-type support is by four big columns (21) and (43), four centre upright firmly (46), two summers (41), drag link (44) and four pairs of braces (42) formations.The upper end of support is equipped with that driven roller (32), driven roll (40), lower abdomen are equipped with adjustable regulating wheel (49), conveyer belt (4) is enclosed within on three running rollers.Respectively there is a H type support (22) both sides of support.Adjusting handle (25) is contained on the H type support, and tension wheel shaft bearing tenon (23) is embedded in the inboard tongue-and-groove (47) of H type support, and the bearing tenon can slide up and down in groove, rotates adjusting handle (25) and just can make conveyer belt have suitable rate of tension.Starting switch (26) just can make buncher (33) running, thereby drives driven roller (32) operation by drive pulley (33), V belt (28) and negative pulley wheel (30).Hothouse (1) and (10) are housed at the middle part of support, and the location of bottom hothouse is fixing by a pair of horizontal angle steel (35) and two pairs of caging bolts (36); The location of top hothouse is fixing by two pairs of positioners (18) and (38).

In Fig. 3, the conveyer belt power train is made up of driving wheel (32), follower (40), regulating wheel (49) and conveyer belt (33).Lightweight guided plate (51) extends the rear end and is placed on the horizontal conveying belt from the front end of support.The opening of upper and lower hothouse (10) (1) and carriage are corresponding mutually.Lightweight guided plate or wet mat advance along the direction of speed V.

A pair of far-infrared temperature compensator (52) (53) (54) (55) all is equipped with in upper and lower hothouse inside, and they directionally are radiated on the slab.Dotted line is represented the path of light and the scope of irradiation.In heat radiation ray overlapping district, temperature is higher, and the energy that stream molecule obtains is big, and movement velocity is fast, causes the water evaporation quantity of steel slab surface big.The power of temperature compensator can be regulated, and V is big for the slab movement velocity, the power W of compensator _MeritAlso can be with more big.Use formula, W _Merit=f(v)=KV ^x, [R＜x＜R] represents the relation between them, wherein K is a proportionality coefficient.

In Fig. 4 A-A view, slab (7) can be read from air gauge (37) (50) with air bag (56) (57), the interior air pressure of air bag that speed V passes on the upper and lower carriage from left to right, air bag is subjected to the extruding generation deformation of slab, intracapsular pressure increases, its diaphragm also increases the pressure of slab, according to frictional force formula f _Rub=μ N(μ is a coefficient of friction, and N is a normal pressure), when diaphragm increases the slab applied pressure, f _RubAlso increase, this has just quickened the wearing and tearing of diaphragm, therefore must reduce the pressure in the air bag as far as possible under the prerequisite that guarantees sealing.The blowing pressure Pn=1.0～1.3kg/cm in the general air bag ²

Analyze the motion conditions of diaphragm now:

(a) as inside and outside differential pressure △ P≤frictional force f _RubThe time, diaphragm moves toward outside cone angle.At this moment the air bag volume reduces, and pressure increases, and at cone angle place distending, forms by " gas chock ", compresses slab, blocks air and enters.

(b) as △ P＞frictional force f _RubThe time, diaphragm moves toward inboard cone angle, forms by " gas chock ".

(c) △ P=f _RubThe time, the sheet that rubs is in the centre position.If there is one air-flow to be formed between slab and the diaphragm, this just means that diaphragm reduces the slab applied pressure, causes △ P＞f _Rub, the past interior lateral movement of diaphragm, and at cone angle place formation gas chock, block air and flow into.

Air bag also can obtain similar result in the contact situation in all the other places.This has just guaranteed the formation of overall dynamics sealing ring.

In the B-B of Fig. 4 view, the diaphragm (62) on the carriage (8) is by plastic washer (60), and semicircle has been sealed in leatheroid packing ring (61), rubber washer (63), compact heap (64) and screw (59) locking, constitutes air bag.Thickness t＜the 0.3mm of diaphragm, it is excellent in quality, and is submissive, wear-resisting and show slightly elasticity, and does not produce the pleat trace at the cone angle place.

In the F-F of Fig. 5 view, g _tThe width of expression supporter ring connected in star.J represents the inboard width of hothouse, and L represents the inside length of hothouse, and V is the movement velocity of slab.Diaphragm covers the both sides of groove respectively by row's screw (68) and (69) locking.

In Fig. 6, the middle part of smooth conveyer belt (73) is mesh areas (75), and both sides are smooth areas (74), is drilled with row's aperture (77) on docking area (76), with hiding a screw (79) and nut (81) to revolving locking.

Second embodiment that conveyer belt docks from beginning to end clings with all-purpose adhesive, and locks without screw-nut.

The two sides of conveyer belt is smooth, its translational speed V=5cm/s～50cm/s, thickness h=1～5mm.

The P-P view is a mesh structure:

A, be that the head end in last hole is to the following head end in hole.

B, be the length in hole.

C, be in the longitudinal direction distance between two holes.

D, be that the left end in left hole is to the left end in right hole.

E, be the width in hole.

F, be the spacings of two holes on width.

In actual applications, the size of mesh size a, b, c, d, e, f should be determined according to following four principles on the mesh areas:

(1) can not allow useful material drops in the slab from the hole.

(2) be convenient to sealing, i.e. two pitchs of holes d≤air bag width g.

(3) help water evaporates.

(4) dry object.

Dry order has exactly in order to allow the water evaporates of wet stock fall, and as seen, the mesh of conveyer belt is close more good more, is the bigger the better, and the thickness of conveyer belt is got over Bao Yuehao.In other words the water permeability of conveyer belt will be got well.

Fig. 7～Figure 11 is the drying principles figure of this device, and existing detailed division is as follows:

The continuous vacuum drying principles

Moisture state in § 1 timber or the slab

Moisture in the timber all is included in the capillary in lumen and the cell membrane, and capillary is relevant with its size to the binding force of moisture, generally can be divided into two big classes;

(I) big capillary system: be made of the countless lumens that interconnect, it is very little so that chainless power to the binding force of moisture.

(II) microcapillary system: be made of the microcapillarys at different levels that interconnect, it has in various degree binding force to moisture.

Generally speaking, capillary radius is more little, and the surface tension of moisture in pipe is big more, makes capillary big more to the binding force of moisture.

Moisture or the big activation of Free water in the big capillary system are evaporated with the lip-deep moisture of Free water the samely, and this system can only can not absorb moisture to air evaporation moisture from air.

The intrasystem moisture of microcapillary or say that hygroscopic water must be low to a certain degree or under the condition of extra heating in air humidity could be to air evaporation, and this system can also can absorb moisture to air evaporation moisture from air.

Moisture in the wet mat also is to be trapped in the crisscross capillary.

The correlation factor of § 2 moisture contents and air

Moisture content is exactly the content of moisture in the timber, with the weight of moisture the percentage of the ratio of absolutely dry wood weight is represented, that is:

W _Contain=(G _Wet-G _Do)/(G _Do) * 100%(2-1)

W wherein _Contain-moisture content, G _Wet-moist wood weight, G _Do-absolutely dry wood weight.

The moisture content of timber can change along with the change of environment weather factor, promptly changes along with the change of atmospheric pressure P, temperature T and air humidity φ.Air humidity φ refers to air absolute humidity r _VapourTo the air wet volume capacity r under same temperature _FullRatio.

Be φ=(r _Vapour)/(r _Full)=(P _Vapour)/(P _Full) (%) (2-2)

r _Vapour=1/ (V _Vapour) (kg/m ³) (2-3)

P _Vapour: water in air vapor partial pressure, P _Full: steam partial pressure in the saturated air

The equation of state of humid air:

P _Atmosphere=P _Empty+ P _Vapour(2-4)

P _Atmosphere-atmospheric pressure; P _Empty-air partial pressure; P _Vapour-partial pressure of water vapor.

Humidity ratio of moist air refers to the water vapour that contained in 1 kilogram of dry air, uses alphabetical d ₂Expression:

That is: d ₂=(r _Vapour)/(r _Empty) * 1000(restrains water vapour/kilogram dry air) (2-5)

The thermal content of humid air refers to belong to (1+0.001d ₃) kilogram humid air heat.Represent with alphabetical I:

Be I=0.24T+0.001d ₃(595+0.46t) [kilocalorie/(1+0.001d ₃) the kilogram humid air]

（2-6）

According to formula (2-6), can draw out ID figure.

Fig. 7 is exactly ID figure, analyzes this figure, can draw following relevant conclusion at least:

(1) temperature T is constant, steam partial pressure P _VapourMore little, air humidity φ is also more little, illustrates that the ability of holding moisture in the air is big more, and promptly the dry gesture of this air is strong more;

(2) steam partial pressure P _VapourConstant, temperature is high more, and air humidity φ is more little, and moist wood is fast more to the speed of air evaporation moisture;

(3) air humidity φ is constant, and temperature T is low more, steam partial pressure P _VapourMore little, thermal content I is also few more.

Briefly: the height of air humidity has shown that air holds the ability of water vapour at a certain temperature; The height of temperature shows the severe degree of material molecule warm-up movement; The size of pressure shows the size of macro molecules mean kinetic energy.

The characteristic of § 3, water

Water is present in occurring in nature in large quantities as a kind of liquid, and its chemical property is very stable.As other material, water also has three-state: i.e. gaseous state, liquid state, solid-state.These three kinds of states are understood along with variation of temperature the phase co-conversion under certain pressure.

0 ⁰The K(absolute temperature scale) under Yi Shang any temperature, water all can produce Evaporation Phenomenon, evaporation of liquid, if do not obtain the compensation of outside energy, can only can carry out by consuming the interior of self, the temperature of liquid reduces as a result, further causes evaporation of water speed to slow down.

Fig. 8 shows the boiling point relation of atmospheric pressure and water.

Promptly when pressure increased and decreased, the boiling point of water is increase and decrease thereupon also.

The boiling of liquid is meant the inside of liquid and the phenomenon of vaporizing simultaneously in the surface.Temperature T approaches boiling point more, and liquid gasification phenomenon is strong with regard to Shaoxing opera.

Now establish, in temperature T ₁=constant and pressure P ₁Under the situation of=constant, the molecular number that the liquid evaporation generates gas is n ₁;

If temperature T ₁Constant, and make P ₁Reduce to P ₂, then the living molecular number of liquid evaporation production is n ₂; According to the relation of pressure and boiling point, can infer n qualitatively ₂＞n ₁; If under equal conditions, P ₂＜＜P ₁, n then ₂＞＞n ₁

Usually, it is incompressible that water is considered to, and its cubic expansion coefficient is very little, thereby the variation of density can omit, and the viscosity, mu of water is very littler than being with oil phase, so variation of temperature is very little to the influence of liquid flow.

The flow behavior of § 4, liquid

For general liquid is flow to line description, at first can determine the liquid motion of a small cubes.The liquid motion of an infinitely small volume can be come definite fully by eight parameters, i.e. three dimensional space coordinate X, Y, Z, pressure, temperature, density, viscosity and time.

According to the Newton's second law and the law of conservation of momentum, can obtain three equations, i.e. Navier-Stokes equations.

Wherein: U, V and W are the velocity components on X in the cartesian coordinate system, Y, the Z direction.

X, Y, Z are the body force of unit volume on the change in coordinate axis direction, and T is the time, and P is the pressure on the unit are, and ρ is a mass density, and μ is the absolute viscosity of liquid.

The left side of above-mentioned three equations is every to be to be produced by the inertia of liquid, and the right is every to be that viscous friction by liquid produces.

According to mass conservation law, the quality that flows into a control volume deducts the quality of the quality=storage of outflow,

It is ∑ _{W goes into}-∑ _{W goes out}=g (dm)/(dt)=g (d(ρ θ))/(dt) (4-4)

Wherein θ is the volume that is stored quality

According to the law of conservation of energy and the first law of thermodynamics

The energy that flows into the control volume deducts the energy that the energy=quilt of outflow is stored

I.e. (dQb)/(dt)-(dWx)/(dt)+∑ _{W goes into}h _{0 goes into}-∑ _{W goes out}h _{0 goes out}=(dE)/(dt) (4-5)

(dQ _b)/(dt)-heat is passed to the liquid of this volume with this speed.

(dWx)/(dt)-and in this volume, the merit that liquid is done the outside.

h ₀=h+V ²Gross energy in the/2g+Z per unit weight liquid (it comprises: interior energy, pressure energy, kinetic energy and potential energy)

E is the total interior energy of liquid in the control volume.

U ' is interior energy (intrinsic energy).

P _LBe pressure, r ' is a density, and V is a speed, and g is an acceleration of gravity, and Z is a height, and W is a weight flow, h ₁=u+P/r ' is the enthalpy of liquid.

Density equation: ρ=f(PT) (4-6)

Viscosity equation: μ=F(PT) (4-7)

Wherein P is a pressure, and T is a temperature.

More than 7 equations add time t, be the equation of describing liquid flow, these equations are some non-line partial differential equation with complicated boundary condition, and their general solution can not find, therefore to each particular state of liquid, all must regard special circumstances as and handle.

In general, the power that influences liquid flow has the internal friction (viscous force), surface tension of liquid, electric field force, magnetic field force of inertia force, the liquid of body force (as gravity and buoyancy), liquid and extraneous pressure etc.

Experience shows that liquid in fact generally all is that the flow regime of liquid can be described with the zero dimension ratio-Reynolds number R of inertia force to viscous force about the viscosity or inertia institute of liquid.

Wherein, ρ is the mass density of liquid, and μ is an absolute viscosity, and u is a liquid average speed, and a is the characteristic size of liquid stream, and D is the catheter diameter that liquid flows in conduit.

Liquid stream based on viscous force is called laminar flow or viscous flow.The characteristics of laminar flow are: the motion of liquid is neat, level and smooth and is the motion of parallel lines that its flow resistance is little.

Usually be called turbulent flow based on flowing of inertia force, be characterized in that the glide path of liquid particle is irregular unsettled swirl shape, its flow resistance is big.

Liquid flowing in conduit can be laminar flow, also can be turbulent flow, and laminar flow determines that by experiment promptly Reynolds number is in the scope of 2000＜R＜4000 excessively to turbulent flow.Below R=2000, laminar flow always flows; More than R=4000, flowing often is turbulent flow.

According to formula (4-8), D is more little, and the R value is more little, and flow regime might be laminar flow more, and the liquid flow in the general capillary all is a laminar flow.

Have a pressure reduction if be full of the capillary two ends of moisture, the hydraulic pressure at capillary two ends is reduced to so:

Wherein: P ₁-P ₂Be pressure reduction; μ is a liquid viscosity, and u is the liquid mean flow rate, this internal diameter of the pipeline of D; Lg is a duct length; R is a Reynolds number.

As seen, liquid viscosity is big more, and pipe is long more, and mean flow rate is big more, and Reynolds number R value is big more or caliber is more little, all can make pressure fall greatly more.

§ 5, the situation of movement of moisture in timber or wet mat

The contained moisture of timber under certain condition can be in the inner transfer of timber, and the speed degree that moves is called the moisture conductibility of timber.Move under the constant situation of gesture at moisture, moisture moves soon more, and the conductibility of timber is good more, otherwise, poor more.Moisture in the timber can move along machine direction, discharges from two end faces of timber, also can move across machine direction.If the length of material is much larger than thickness and width, and the lateral area of material is far longer than face area, although more than across the moisture conduction of fiber easily, in dry run, what play a decisive role still conducts across the moisture of machine direction along the conduction of the moisture of fiber.

Moisture movement law in the timber can be determined by following formula:

i _ShBe discharge; A ' is coefficient of transmissibility (m ²/ h);

Negative sign is represented the direction of gradient; r ₀Over dry capacity for material;

Be moisture gradient;

Be thermograde; δ is the thermal gradient coefficient.

The moving speed of timber internal moisture is the size that depends on moisture gradient and thermograde on sizable degree.Usually, the moisture content of timber inside is higher than the external aqueous rate, so moving of moisture always flows to the low place of moisture content from the high place of moisture content.

When the timber temperature is high, the moving when always low of moisture than temperature, moisture mobile easier, therefore, the existence of thermograde also can cause moving of moisture, promptly the mobile of moisture always flows to the low place of temperature from the high place of temperature.

The moulding because the used wet mat of this device is generally all mated formation, therefore, his structure is much looser than solid wood, compresses even if slab is applied certain pressure, and the compaction rate of slab also can not show a candle to former material.So the moisture conductibility of slab is more much better than solid wood.

Block timber in the slab, also because volume is little, fiber is short, makes its transmissibility improve.No matter be, or microcosmic from macroscopic view, in the slab each to the water guide performance variation of matter is all arranged, therefore, the moisture movement law in the slab fully can be with reference to the moisture movement law in the timber.

The water evaporates intensity of § 6, wood surface

In dry run, the moisture of timber inside moves to the outside on the one hand, imports in the air stream of drying medium through wood surface and interlayer on the other hand.

Water evaporates intensity by wood surface can be determined by following formula:

i _Table=a ' r ₀(W _Table-W _{Weighing apparatus})=a ' r ₀σ (φ _Table-φ _Empty) (g/cm ²S) (6-1)

A ' is for changing water coefficient (CM/S), and it is to weigh stream molecule diffuses into air through wood surface and interlayer ability.a′＝f（T、φ、V′、r′） （6-1）′

T is an air themperature; φ is an air humidity, and V ' is an air velocity, r ' volume weight of wood.

Temperature height, humidity are low, and the water vapour that is evaporated from timber is easy to by absorption of air; When air velocity was big, the thickness of interlayer reduced and is easy to be destroyed; Timber volume hour, inner moisture is easy to exterior conductive.

r ₀Heavy (the g/cm of the volume of-absolutely dry wood ³)

W _TableThe moisture content (%) that-wood surface and vicinity thereof are all layer,

W _{Weighing apparatus}-moisture content with the corresponding wood equilibrium moisture content index of the medium state of drying schedule defined (%) or under certain air condition, when material reaches moisture absorption and stablizes,

σ is conversion between W and the φ, φ _TableBe slab top layer relative humidity, φ _EmptyRelative humidity for negative pressure space.

When water vapour entered medium, its average translational kinetic energy was directly proportional with thermodynamic temperature, that is:

E _D= 1/2

△m ₁V ²= 3/2 KT（6-2）

m ₁The quality of-steam molecule; The average speed of V-molecule,

K=1.38 * 10 ^-23Burnt/as to open (Boltzmann constant)

The T-thermodynamic temperature

By free degree principle of equipartition, under thermal equilibrium state, all have identical mean kinetic energy on each free degree of material molecule according to energy, its size equals 1/2 KT.

Water vapour H ₂O has three atoms, belongs to polyatomic molecule, so it has three translational degree of freedom and three rotational freedoms, has 6 frees degree.

Stream molecule overall average kinetic energy is

EH ₂O＝ 6/2 KT＝3KT（6-3）

Temperature is high more, and the speed of steam molecule is just big more.

The drying mechanism of § 7, this device

When this device was started working, wet mat passed vacuum drying cabinet, and in hothouse, air pressure P is at 0＜P＜1kg/cm ², relative humidity φ changes in the scope of 0＜φ＜＜100%, and the moisture on wet mat top layer is because air pressure is low, and relative humidity is low and evaporate to the low humidity low-pressure area.

At the wet mat near surface, water vapour density is big, the dividing potential drop height; Far away more from the wet mat top layer, water vapour density is more little, and dividing potential drop is also low more.According to molecule diffusion theory, molecule is always spread to the little place of concentration by the big place of concentration, and stream molecule continues to flow to negative pressure source as a result.

Capillary abundant, that extend in all direction is arranged in the wet mat, no matter slab with which kind of speed moves, always exist many such capillaries, its a termination atmosphere, the other end communicates with vacuum chamber.Two ends capillaceous have so just produced pressure differential, impel the moisture in the capillary to move along the direction that pressure potential reduces, moisture thereby taken out toward negative pressure space with the form of steam, negative pressuren zone acts on the capillary swabbing effect that Here it is.

In Fig. 9, (82) At is an atmospheric pressure, and it puts on the wet mat (7) towards the direction of arrow indication, also acts on simultaneously on the moisture in the slab inner capillary tube (83).Capillary leads to vacuum drying cabinet (10).Because air bag (53) forms the overall dynamics sealing ring with the smooth areas of slab (7) conveyer belt (4), the vacuum in the hothouse has been guaranteed in the direct interchange that has thoroughly completely cut off inside and outside air.Thereby extraneous atmospheric pressure can only be indoor to vacuum drying by the moisture transmission in the capillary.The moisture that it is promoting in the capillary moves toward negative pressure space.Water vapour Vapor(84) leaves wet mat along the direction of arrow and march on towards negative pressure source.

The transfer of moisture is except following the water transport rule in the material in the slab:

Outside, the effect of the potential energy that also should be under pressure.

In the capillary, the suffered power of arbitrary infinitesimal moisture mainly contains pressure, the resistance of ducting, the viscous force of moisture and the tension force of water.Use imfinitesimal method, obtain the translational speed τ of moisture in capillary ₁[, establishing cross section capillaceous] for circular for the simplification problem.

${\mathrm{\τ}}_1={\∫}^1\frac{{\mathrm{\πr}}^2\mathrm{\Δ}{P-F}_m}{M}\mathrm{dt}(7-1)$

Wherein: π r ²-capillary sectional area

△ P-P _Outward-P _In=external atmospheric pressure-hothouse vacuum

F _Resistance=f(ω, μ, Z ')=R Θ is a duct wall frictional force, and μ is a liquid viscosity power, and Z ' is a tension force, and R Reynolds number, Θ are correlation factor, dt is the change amount of time.

1 is along the capillary pressure gradient

Length on the direction.

Length 1 capillaceous＞＞diameter D capillaceous, the mobile of moisture is laminar-type in the capillary, frictional resistance is less.The capillary caliber is more little, and the influence of liquid tension is big more.Therefore flowing of liquid will overcome the influence of tension force.

Energy with reference to perfect gas is pressed free degree principle of equipartition, and the average translational kinetic energy of stream molecule is:

EH ₂O＝ 1/2 m V ²＝3KT

The average speed of steam molecule is

V ²H ₂O＝ (6KT)/(m) （7-2）

Velocity component on Y direction is:

V ²H ₂OY= 1/6 V ²H ₂O= (KT)/(m) V ²H ₂oy=

(7-3)

Temperature is high more, and the movement velocity of steam molecule is fast more.

To this stage, involve three kinds of speed altogether:

Moisture rate travel in (I) slab, i ' _ShAnd τ ₁'

Evaporation rate of (II) water vapour or eruption speed, i ' _TableAnd τ ₁

In (III) negative pressure space, the movement rate VH of steam molecule ₂OY.

Optimal dry situation is, these three kinds of speed equate,

That is: i ' _Sh+ τ ₁=i _Table+ τ ₁'= (7-4)

Or three kinds of flows equate:

That is:

I ' _Sh+ τ ₁S ₁=i _Table+ τ ₁' s ₂=VH ₂Oy ρ (7-5)

Wherein: s ₁-be the sectional area of a definite volume

s ₂-be the sectional area of airflow volume

ρ-gas density.

Now the rate of drying of slab is discussed.

1, works as P _Outward≈ P _InThe time, △ P＜F _Resistance, the rate of drying of wet mat mainly is that its evaporation rate depends on the relative humidity and the temperature of negative pressure space by natural evaporation.φ is more little or T is high more, and dry gesture is big more, and evaporation rate is fast more.

2, work as P _Outward＞P _InThe time, establish △ P ≈ F _Resistance, two kinds of situations are then arranged:

(a) because P _InReduce, relative humidity φ is along with reducing dry gesture increase.

(b) △ P increases.Moisture in the slab moves gesture to be strengthened, and moisture is continuously along barometric gradient

Direction move, to replenish in the low-pressure area moisture that steel slab surface evaporates.

3, work as P _Outward＞＞P _InThe time, △ P＞＞F _Resistance, the moisture in the capillary will spray into negative pressure space with the form of steam.

In sum, the evaporation rate of moisture can be formed by following two kinds of speed superpositions:

(1) under the certain situation of relative humidity φ (φ ≠ 100%), moisture evaporates to negative pressure space, and its evaporation rate is:

I ' _Table=ξ a ' r ₀(φ _Table-φ _Empty) (m/s) proportionality constant among the ξ wherein.

(2) because the effect of inside and outside differential pressure △ P makes the interior moisture of slab along barometric gradient capillaceous Direction enter negative pressure space, its speed is:

${\stackrel{\‾}{\mathrm{\τ}}}_1={\∫}^1\frac{{\mathrm{\πr}}^2{\mathrm{\ΔP}-F}_m}{M}\mathrm{dt}$

The sum velocity of water vapour evaporation:

Γ _Close=i ' _Table+ τ ₁(7-6)

Hothouse into and out of end because pipeline capillaceous is short, so resistance is little, τ ₁Bigger.Past more central region, capillary channel is long more, and the resistance of ducting is big more, τ ₁More little.

Along the direction of motion of conveyer belt, the each point Γ on inherent this direction of hothouse _CloseCouple together, form a parabola, again each the bar parabola on the same direction in the hothouse is coupled together, just constitute parabolic.

In Figure 10, the Γ of each point on the X-axis _CloseLinking to each other forms parabola, and this parabolical equation is:

Γ _Close=y=Q (X)=(C ₁-C ₀)/(4L ²) X ²-C ₀(7-7)

The span of X is in the interval of [L/2, L/2].Wherein

L is the inside length of hothouse.

C ₀And C ₁Be constant, be this parabolical primary condition.

Y=Q(X) curve for upwards evaporating y=-Q(X) is downward evaporation curve, and their boundary value is β ₄(L/2, C ₁), β (0, C ₀), β ₆(L/2, C ₁), β _X1(L/2-C ₂), β _X2(0-C ₀'), β _X2(L/2-C ' ₂).

Figure 11 shows, the water vapour evaporation capacity of wet mat in the unit interval.In hothouse, set up the three dimensions rectangular coordinate system, the central authorities of initial point due to steel slab surface.X-axis is parallel to the direction of motion of conveyer belt, and Y-axis is perpendicular to steel slab surface, and Z is perpendicular to the plane of X, Y-axis decision.

The each point Y=Γ on the plane that determines by X, Z axle _Close(X Z) couples together, and just constitutes a parabola, and the space that this parabola and plane Y=0 are surrounded is the water evaporation quantity in the unit interval, and the cubical boundary condition of this curved surface is:

Wherein j is the width of hothouse or slab.

Water vapour evaporation capacity (one-sided evaporation) in unit interval is

= 1/12 Lj(C ₁-47C ₀) （7-8）

Two-sided evaporation capacity is: Q _Two=2q=1/6 Lj(C ₁-47C ₀) (7-8)

If the permeability rate of conveyer belt reaches 100%, then moisture up evaporates with down evaporation effect is the same.

From wet mat, downcut a fritter cube, its volume arbitrarily

C _Ub=h △ X △ Z; Averag density is ρ ₀Then the gross weight of this volume is:

g ₁＝ρ·C _ub （7-9）

Wherein the weight of moisture is:

G _Water=g[weight in wet base base]-g ₂[dry body heavy] (7-10)

This fritter cube begins till leave hothouse from entering hothouse, and the time of experience is t second, and the moisture that is evaporated is d ₁Gram, so, the drying capacity of this device is:

η=(d ₁)/(G _Water)=(d ₁)/(g ₁-g ₂) * 100%(7-11)

The dry board number that needs series connection:

N=100/ (η) (platform) (7-12)

In order to improve the rate of drying of slab, can select following approach:

(1) make the wet mat quality loose, even, to reduce the resistance of ducting capillaceous.

(2) increase inside and outside differential pressure △ P, improve the pressure potential at capillary two ends.

(3) the water evaporates speed on raising wet mat top layer.

(4) movement velocity of steam molecule in the intensified negative pressure space.

(5) reduce slab thickness.

(6) mesh density of increase conveyer belt mesh areas, the water penetration of raising conveyer belt.

Consumed energy is wanted in the evaporation of moisture, causes that temperature reduces, the temperature reduction causes that again molecular thermalmotion weakens, cause the evaporation rate of moisture to reduce, for fear of this kind phenomenon takes place, this device has installed temperature compensator additional, with the loss of compensation energy, control weakening of evaporation rate.

Temperature compensator can be the far ir ray lamp, shine the surface of wet plate with it, increase the kinetic energy of slab superficial water steam molecule, promote them with fast speeds, march on towards negative pressure source, remain lower relative humidity or higher dry gesture near making the top layer of slab.

Because the fuel factor of temperature compensator just makes near the space temperature the slab top layer be higher than the interior temperature of slab.But because of slab is ceaselessly moving, the time of passing this device is shorter, and thermal-radiating transmission is very shallow, and heat energy has little time to the conduction of slab depths, so slab inside does not exist and the conflicting thermograde of moisture gradient.

In the negative pressure space, because temperature has obtained compensation, the movement velocity of steam molecule is accelerated, kept near the relative humidity φ in slab top layer at lower numerical value, stablized the water evaporates intensity on top layer, this further causes the quickening of moisture translational speed in the slab again, form in a kind of negative pressure space, the translational speed of moisture is corresponding in the evaporation rate of the movement velocity of steam molecule, slab top layer moisture and the slab, " push-pull type " balanced dry gesture has been accelerated the rate of drying of wet mat greatly.

Figure 12 is another embodiment of Minton dryer, and I, II, III are represented the hothouse of three series connection.Rate of drying (or temperature T, humidity φ, vacuum P are depended in the selection of hothouse number _Very=P _InAnd moisture content), by the internal structure of dry material and thickness thereof.

Claims (9)

1, a kind of continuous vacuum drying device, it is by the frame-type support, the conveyer belt transmission system, four most of compositions such as vacuum drying cabinet and vacuum pipe, on vacuum drying cabinet divides, following two parts, the centre can be passed wet mat and conveyer belt simultaneously, conveyer belt is placed in driving wheel, on driven pulley and the regulating wheel, the power of power source output can change as required, and flow to driving wheel through transmission mechanism, it is characterized in that: on, on the carriage of following vacuum drying cabinet, respectively be equipped with the air bag of an annular distribution, make to carry slab when passing vacuum chamber when conveyer belt, " air bag; slab " and " conveyer belt " constitute an overall dynamics sealing ring together.

2, device according to claim 1, it is characterized in that: conveyer belt is bright and clean smooth, good water permeability, there is several rows of neat and fine and close aperture its workspace, middle part, respectively there is a smooth zone on the both sides of workspace, and the width gt of adjacent two round spacing d≤air bags, and the width gt of the width 〉=air bag of smooth zone.

3, device according to claim 1 is characterized in that the gas in the air bag injects from valve.

4, device according to claim 1 is characterized in that bearing the carriage of air bag, its cross sectional shape be semicircle add one trapezoidal.

5, device according to claim 1, the diaphragm that it is characterized in that constituting air bag is submissive, wear-resisting, slightly flexible, and its thickness guarantees not produce the pleat trace at the cone angle place.

6, device according to claim 1 is characterized in that air bag can form " gas chock " at cone angle place distending.

7, device according to claim 1 is characterized in that: temperature compensator is equipped with in hothouse inside, and the power output of this compensator can change with the variation of conveyer belt movement velocity.

8, device according to claim 1 is characterized in that: it can form a kind of, the movement velocity of steam molecule in the negative pressure space, the balanced dry gesture of translational speed corresponding to " push-pull type " of moisture in the evaporation rate of slab top layer moisture and the slab.

9, device according to claim 1 is characterized in that, its use of can connecting.

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