CA1299011C - Method and apparatus for drying fruit pulp and the like - Google Patents
Method and apparatus for drying fruit pulp and the likeInfo
- Publication number
- CA1299011C CA1299011C CA000526172A CA526172A CA1299011C CA 1299011 C CA1299011 C CA 1299011C CA 000526172 A CA000526172 A CA 000526172A CA 526172 A CA526172 A CA 526172A CA 1299011 C CA1299011 C CA 1299011C
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- water
- film
- reservoir
- pulp
- dried
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Abstract
METHOD AND APPARATUS FOR DRYING
FRUIT PULP AND THE LIKE
Abstract of the Disclosure A method and apparatus for producing a dried material from a mixture of solid particles colloidally suspended in a liquid, for example, for the production of fruit leather from a pulp and fruit juice mass, include floating an infrared-transparent film on the surface of a body of heated water and placing the material to be dried, such as the pulp and juice mix, on top of the film to absorb heat from the water and thereby cause drying of the material. The apparatus for carrying out the method includes a reservoir of water, a film floated on the water, and a heater for maintaining the temperature of the water at a predetermined level. In a preferred embodiment, the reservoir is in the form of an elongated trough and the film comprises an endless strip of polyester material, such as Mylar, to form a conveyor belt that floats on the surface of the water in the trough and carries the material to be dried on it.
FRUIT PULP AND THE LIKE
Abstract of the Disclosure A method and apparatus for producing a dried material from a mixture of solid particles colloidally suspended in a liquid, for example, for the production of fruit leather from a pulp and fruit juice mass, include floating an infrared-transparent film on the surface of a body of heated water and placing the material to be dried, such as the pulp and juice mix, on top of the film to absorb heat from the water and thereby cause drying of the material. The apparatus for carrying out the method includes a reservoir of water, a film floated on the water, and a heater for maintaining the temperature of the water at a predetermined level. In a preferred embodiment, the reservoir is in the form of an elongated trough and the film comprises an endless strip of polyester material, such as Mylar, to form a conveyor belt that floats on the surface of the water in the trough and carries the material to be dried on it.
Description
99(~
ME~THOI~ AND APPARATiUS ~OR DRYIN~;
P~UIl PUlP AND TH~ llKE~
l~ack~round of the Invention This invention relates to the drying of fruit pulp and the like and, 5 more particularly, to the efficient transfer of heat to the material being dried.
Most presently used processes for drying fruit pulp to produce, for example, fruit leathers or.concentrates of the pulp, involve placing the pulp on a carrier and then heating the carrier to dry the pulp. In these systems the entire carrier is heated, regardless of whether it contains pulp or not and a substantial 10 heat transfer occurs from the carrier to the air in places on the carrier where there is no pulp, without any appreciable use of that heat in the drying of the pulp. For example, in the system of Shepard, shown in V.S. Patent 2,301,589, issued November 10, 1942, a metallic carrier is provided and the pulp is laid onthe metallic carrier. The carrier is then heated through electrical induction and 15 the heat used to drive the moisture from the pulp. Since the entire carrier is heated, it is necessary to ensure that every portlon of the carrier is covered with pulp in order to obtain the most efficient heat transfer from the carrier to thepulp. In actual practice, it is difficult if not impossible to obtain such complete coverage of the carrier and therefore heat is lost to the open air without doing20 any substantial work in drying the pulp, causing more heat to be consumed than is necessary simply to dry the pulp. In a sys~em like that of Shepard's, the only way to obtain 100 percent heat transfer from the carrier medium to the pulp is to have an inspection and control station to monitor the coverage of the carrier bythe pulp and adJust the pulp so that it covers every open area of the carrier. This 25 causes additional problems in labor and monitoring controls that may be enough to offset any gain in efEiciency of heating.
Summary of the Invention The present invention provides a method and apparatus for drying fruit pulp and other like materials, in which the transfer of heat from the heated 30 medium to the pulp occurs most efficiently and that substantially eliminates heat ~z~9~
loss in areas of a carrier medium carrying the pulp tllat are open to the air and are not covered by the pulp. More specifically, the present invention provides amethod of drying a product, such as pulp, that includes the steps of floating a film of transparent material on a body of water, heating the water to maintain 5 the water at a predetermined temperature, and placing the product to be dried on the floating film. In order to carry out this method, an apparatus is provided that includes a reservoir of water and means associated with the reservoir of water for heating the water to the predetermined temperature ano maintaining the reservoir of water at that predetermined temperature. A transparent, solid 10 film is floated on the surface of the heated water and is adapted to receive the pulp or other material to be dried.
In preferred forms of the invention the floating material can be a flexible plastic and can be arranged on a conveyor system so that it moves across the reservoir of water carrying the pulp from a loadlng station to a removal 15 station with the timing of the conveyor belt and the parameters of the product being applied to the conveyor belt being such that the product is applied in a colloidal suspension of solid particles in a liquid base at one end of the conveyor and removed in its dried state at the second end of the conveyor. While certain preferred materials are known for use as the floating carrier film, it is sufficient 20 if the carrier is transparent to infrared radiation and able to withstand temperatures in the range of the boiling point of water without shrinkage or deterioration of the material.
Brief Description of the Drawin,es The operation and advantages of the present invention will be 25 better understood by those of ordinary skill in the art and others upon reading the ensuing specif ication when taken in conjunction with the appended drawings wherein:
FIGURE 1 is a side elevational view of one embodiment of a fruit pulp-drying apparatus made in accordance with the principles of the presen~
30 invention; and FIGURE 2 is an isometric view of a portion of the drying apparatus of FIGURE 1 with portions removed for ease of viewing.
Detailed Description of the Preferred Embodiment In accordance with the present method, a reservoir of water, such 35 as in a trough, is heated to some predetermined temperature. Preferably, the temperature of the water is maintained as close as possible to the boiling pointof water without actually producing boiling. Therefore, at sea leYel, the temperature would be close to 100 degrees C. A thin film of transparent ~9g~
material, such as a polyester film, is floated on the water surface in the trough so that it covers substantially the entire open surface area of the water.
Because of the reflective properties of the water surface and the film covering the water, there is little, if any, evaporative heat transfer from the water to the 5 air above it. When a product to be dried, such as a puree of fruit pulp, is placed on the film, the portion oE the film carrying the product is brought into in~imate contact with the surface of the water. The contact between the film carrying the product to be dried and the surface of the water enables a transfer of heat directly from the water through the film into the product to be dried, causing the 10 moisture in the product to be driven off. There is substantially no transfer of heat from the water at those surface locations not covered by the product and still covered by the film because of the reflective properties of the water surface and therefore the heat transfer from the water is confined to the product to be dried, such that the maximum efficient use of the heat is accomplished.
It is necessary that the film covering the water be able to withstand the heat and the temperature of the water without deteriorating or shrinking. It is also necessary that the film be transparent to infrared heat radiation, which, in turn, means that it will typically be optically transparent as well, although, it is the transparency to the infrared wavelengths that is 20 important and not the passage of visible light.
An embodiment of an apparatus useful in a continuous drying process to carry out the method described above is shown in FIGURES 1 and 2. A
trough 10 is formed of some nonporous medium, such as ceramic tile, and acts as a receptacle for the heated water used in the drying process. The ceramic tile 25 trough is found to be desirable because of its low heat-conducting properties and also its ability to be easily cleaned, for use with edible foostuffs; however, any suitable rigid trough will suffice, for example, one made of stainless steel. Inorder to minimize the heat loss of water in the trough, the trough is additionally insulated by insulation layer 12S positioned below the trough. The heated water 30 14 is pumped into the trough from a source 15 of heated water, which can be an electric water heater, or a boiler fueled by any suitable fuel source, such as natural gas, wood, coal, et cetera. In practice, the water flows into the troughat a first end and the trough is preferably til~ed slightly along its len~th so that the water runs by the force of gravity to a second end of the trough from which 35 it is pumped back to the hot water source, reheated to the desired temperature, and then pumped back into the trough so that the water in the trough is always maintained at the predetermined, desired temperature. In the illustrated embodiment, a polyethylene sheet 16 lines the inner surface of the trough 10 and 1~9~11 overhangs the edges of the trough to provide an additional moisture and heat barrier between the water and the trough. In practice, it has been found that a moisture layer of condensation builds up on the underside of the polyethylene sheet 16 between the sheet and the interior of the trough, which acts as a further 5 heat barrier, thereby minimizing heat loss from the water to the walls of the trough 10. A flexible sheet of infrared transparent material 18 floats on the surface of the water 14 in the trough. A suitable material has been found to be a -~ 3-mil-thick sheet of polyester film available ~rom E.I. Dupont De Nemours Co.~` under the narne 300A Mylar. The 300A Myl~meets all of the requirements of 10 the invention in that it shows very little distortion or shrinkage in the operable temperature range. It is flexible so that it lends itself to a conveyor belt type of application and also has the strength required to operate for long periods of time without breakage. While the polyester sheet 18 only needs to float on top of thewater in the illustrated embodiment, the polyester sheet is wider than the trough 15 10 so that it not only overlies the water but also rides slightly up the sides of the trough. The extra width of the polyester sheet 18 ensures a complete coverage of the water so that there is no evaporative exposure of the water to the open air above the trough. The overwide sheet 18 also provides a channel that keeps the product to be dried, typically a Eruit pulp puree consisting of solid particles in 20 suspension in a fruit juice, from running off of the polyester sheet into the hot water. The material to be dried, for example, fruit pulp 20, is placed on top ofthe polyester sheet 18 and remains on the polyester sheet until it reaches $he proper consistency or dryness, that is, until a predetermined amount of the moisture is driven of-F the mixture by the heat transferred from the ho~ water to 25 the fruit pulp through the polyester sheet.
Depending on the final product sought, the thickness of the fruit pulp will vary; however, it has been found that a thickness of approximately one-eighth to three-sixteenths of an inch is capable of producing a satisfactory fruit leather. In the illustrated embodiment, a thin sheet 22 of material such as 30 polyethylene, for example, .5 to 1.5 mils thick, is placed between the polyester sheet 18 and the fruit pulp 20. The polyethylene sheet 22 does not enter directly into the workings of the process of the present invention, but, rather, supplies a convenient medium upon which to place the fruit pulp to prevent adherence of the pulp to the polyester sheet 18. The polyethylene sheet 22 is removed from 35 the polyester sheet 18 with the fruit pulp to maintain the polyester sheet 18 in a clean condition suitable for use with edible footstuffs. Also, the polyethylene sheet separates easily from the Mylar sheet 18 so that the Mylar sheet is not damaged as it might be if it was necessary to scrape the dried fruit leather ~ f~.~d~
~.~990~ ~
directly off of the polyester sheet. The polye-thylene sheet 22 and dried fruit leather can be rolled simultaneously from the polyester sheet to provide a convenient method by which the fruit leather is transported and/or stored after its removal from the dryer.
In one preferred form of the invention, the polyester sheet 18 is formed in an endless belt and is carried by a pair of rollers 24 and 26, respectivelyJ mounted at either end of the trough to form a conveyor belt. The fruit pulp 20 is introduced onto the polyester sheet at a first end of the trough from a discharge means 28. The polyethylene sheet 22 is fed from a roll 30, also10 at the first end of the trough 10, so that the pulp 20 lies on the polyethylene sheet 22. The pulp moves over the hot water 14 on the polyester sheet conveyor belt 18 to the second end of the trough 10. The speed of the conveyor belt is regulated so that the time that it takes for the frui~ pulp to travel from one end of the trough to $he other is sufficient to produce the proper drying of the fruit 15 pulp so that it can be removed along with the polyethylene sheet 22 at the second end of the trough. The polyester belt 18 continues on under the trough 10 in a typical conveyor fashion, while the dried pulp is moved away on a second conveyor 32. In one form of the invention, which has been tested, it has been found that a fruit pulp of one-eighth to three-sixteenths inch thickness placed on 20 a Mylar sheet 3 mils thick over a trough of water in which the water depth isapproximately one inch and the water is heated to just below the boiling point, that is, just below 100 degrees C., takes approximately two and one-half hours to dry to a suitable fruit leather dryness. It is necessary to keep a slack in the polyester conveyor belt 18 so that the film floats on the water and is not under25 such tension that it resists contact with the water surface when the pulp is placed on the belt. Typically, the fruit pulp will be open to the air during itsdrying. It is not desirable to direct any heated or dried air onto the fruit pulp as it dries because this forms an undesirable skin on the top of the pulp and actually impedes drying of the pulp by evaporation. An airflow into and out oE the room 30 in which the dryer is located is desirable to maintain the room air at a humidity that allows evaporation of the moisture in the pulp to the air and, in fact, dried heated air can be pumped into the room to lower the ambient humidity and increase the rate of absorption of water vapor by the air. In an apparatus described above with a water depth of one inch in the trough 10, and a trough of35 approximately 12 meters in length, it has been found that the temperature drop of the water from the inlet at one end of the trough to the outlet from the trough is only approximately 3 degrees C. Therefore, the hot water source does not have to expend much energy in raising the temperature of the water back to :~l29~
the desired temperature prior to reintroduction of the water into the trough.
It will be understood that while one application of the invention described herein is in the production of fruit leather from a puree of fruit pulp and juice, the invention is not limited to the use with such fruit pulps. It also can 5 be used for drying vegetables, or even soups and stews that have been blended to an even consistency prior to drying. Also, the invention, rather than completelydrying a mixture, can be used to produce juice concentrates very rapidly; for example, in the l~-meter trough above, it has been found that introduction of tomato juice on one end will produce a 50-percent concentrate in approximately 10 one and one-half hours' time from the exit end of the trough. It is important that the temperature of the fruit or other mixture be kept below the boiling point sothat there is no disruption of $he material on the polyester sheet and, typically, the fruit pulp is kept at a temperature of between 80 and 90 degrees C. Also~
the water temperature, of course, should be kept below boiling in order to 15 prevent bubbling and evaporation of the water from the trough.
While a preferred embodiment of the invention has been described and illustrated, it is clear that many changes can be made to the illustrated and described embodiment without exceeding the scope of the invention. ~or example, while particular materials such as the DuPont 300A Mylar have been 20 described as being a suitable and even a desirable medium upon which to placethe material to be dried, other media are also workable with the inven~ion and, in fact, even a sheet of glass could be used, except for its undesirable properties of inflexibility. Also, while a conveyor system has been described, it is possible simply to utili~e the invention by floating an infrared-transparent film on a body 25 of hot water and then simply placing the material to be dried on the f ilm, allowing it to sit in a stationary location on the reservoir of heated water without the use of a conveyor. The use of a conveyor does not affec~ the basic concept of the invention, but, rather, adds to the production capacity of a dryer made in accordance with the principles of the present invention. Since many 30 changes can be made to the illustrated and described embodiment without exceeding the scope of the invention, the invention should be dsfined solely with reference to the claims that follow.
ME~THOI~ AND APPARATiUS ~OR DRYIN~;
P~UIl PUlP AND TH~ llKE~
l~ack~round of the Invention This invention relates to the drying of fruit pulp and the like and, 5 more particularly, to the efficient transfer of heat to the material being dried.
Most presently used processes for drying fruit pulp to produce, for example, fruit leathers or.concentrates of the pulp, involve placing the pulp on a carrier and then heating the carrier to dry the pulp. In these systems the entire carrier is heated, regardless of whether it contains pulp or not and a substantial 10 heat transfer occurs from the carrier to the air in places on the carrier where there is no pulp, without any appreciable use of that heat in the drying of the pulp. For example, in the system of Shepard, shown in V.S. Patent 2,301,589, issued November 10, 1942, a metallic carrier is provided and the pulp is laid onthe metallic carrier. The carrier is then heated through electrical induction and 15 the heat used to drive the moisture from the pulp. Since the entire carrier is heated, it is necessary to ensure that every portlon of the carrier is covered with pulp in order to obtain the most efficient heat transfer from the carrier to thepulp. In actual practice, it is difficult if not impossible to obtain such complete coverage of the carrier and therefore heat is lost to the open air without doing20 any substantial work in drying the pulp, causing more heat to be consumed than is necessary simply to dry the pulp. In a sys~em like that of Shepard's, the only way to obtain 100 percent heat transfer from the carrier medium to the pulp is to have an inspection and control station to monitor the coverage of the carrier bythe pulp and adJust the pulp so that it covers every open area of the carrier. This 25 causes additional problems in labor and monitoring controls that may be enough to offset any gain in efEiciency of heating.
Summary of the Invention The present invention provides a method and apparatus for drying fruit pulp and other like materials, in which the transfer of heat from the heated 30 medium to the pulp occurs most efficiently and that substantially eliminates heat ~z~9~
loss in areas of a carrier medium carrying the pulp tllat are open to the air and are not covered by the pulp. More specifically, the present invention provides amethod of drying a product, such as pulp, that includes the steps of floating a film of transparent material on a body of water, heating the water to maintain 5 the water at a predetermined temperature, and placing the product to be dried on the floating film. In order to carry out this method, an apparatus is provided that includes a reservoir of water and means associated with the reservoir of water for heating the water to the predetermined temperature ano maintaining the reservoir of water at that predetermined temperature. A transparent, solid 10 film is floated on the surface of the heated water and is adapted to receive the pulp or other material to be dried.
In preferred forms of the invention the floating material can be a flexible plastic and can be arranged on a conveyor system so that it moves across the reservoir of water carrying the pulp from a loadlng station to a removal 15 station with the timing of the conveyor belt and the parameters of the product being applied to the conveyor belt being such that the product is applied in a colloidal suspension of solid particles in a liquid base at one end of the conveyor and removed in its dried state at the second end of the conveyor. While certain preferred materials are known for use as the floating carrier film, it is sufficient 20 if the carrier is transparent to infrared radiation and able to withstand temperatures in the range of the boiling point of water without shrinkage or deterioration of the material.
Brief Description of the Drawin,es The operation and advantages of the present invention will be 25 better understood by those of ordinary skill in the art and others upon reading the ensuing specif ication when taken in conjunction with the appended drawings wherein:
FIGURE 1 is a side elevational view of one embodiment of a fruit pulp-drying apparatus made in accordance with the principles of the presen~
30 invention; and FIGURE 2 is an isometric view of a portion of the drying apparatus of FIGURE 1 with portions removed for ease of viewing.
Detailed Description of the Preferred Embodiment In accordance with the present method, a reservoir of water, such 35 as in a trough, is heated to some predetermined temperature. Preferably, the temperature of the water is maintained as close as possible to the boiling pointof water without actually producing boiling. Therefore, at sea leYel, the temperature would be close to 100 degrees C. A thin film of transparent ~9g~
material, such as a polyester film, is floated on the water surface in the trough so that it covers substantially the entire open surface area of the water.
Because of the reflective properties of the water surface and the film covering the water, there is little, if any, evaporative heat transfer from the water to the 5 air above it. When a product to be dried, such as a puree of fruit pulp, is placed on the film, the portion oE the film carrying the product is brought into in~imate contact with the surface of the water. The contact between the film carrying the product to be dried and the surface of the water enables a transfer of heat directly from the water through the film into the product to be dried, causing the 10 moisture in the product to be driven off. There is substantially no transfer of heat from the water at those surface locations not covered by the product and still covered by the film because of the reflective properties of the water surface and therefore the heat transfer from the water is confined to the product to be dried, such that the maximum efficient use of the heat is accomplished.
It is necessary that the film covering the water be able to withstand the heat and the temperature of the water without deteriorating or shrinking. It is also necessary that the film be transparent to infrared heat radiation, which, in turn, means that it will typically be optically transparent as well, although, it is the transparency to the infrared wavelengths that is 20 important and not the passage of visible light.
An embodiment of an apparatus useful in a continuous drying process to carry out the method described above is shown in FIGURES 1 and 2. A
trough 10 is formed of some nonporous medium, such as ceramic tile, and acts as a receptacle for the heated water used in the drying process. The ceramic tile 25 trough is found to be desirable because of its low heat-conducting properties and also its ability to be easily cleaned, for use with edible foostuffs; however, any suitable rigid trough will suffice, for example, one made of stainless steel. Inorder to minimize the heat loss of water in the trough, the trough is additionally insulated by insulation layer 12S positioned below the trough. The heated water 30 14 is pumped into the trough from a source 15 of heated water, which can be an electric water heater, or a boiler fueled by any suitable fuel source, such as natural gas, wood, coal, et cetera. In practice, the water flows into the troughat a first end and the trough is preferably til~ed slightly along its len~th so that the water runs by the force of gravity to a second end of the trough from which 35 it is pumped back to the hot water source, reheated to the desired temperature, and then pumped back into the trough so that the water in the trough is always maintained at the predetermined, desired temperature. In the illustrated embodiment, a polyethylene sheet 16 lines the inner surface of the trough 10 and 1~9~11 overhangs the edges of the trough to provide an additional moisture and heat barrier between the water and the trough. In practice, it has been found that a moisture layer of condensation builds up on the underside of the polyethylene sheet 16 between the sheet and the interior of the trough, which acts as a further 5 heat barrier, thereby minimizing heat loss from the water to the walls of the trough 10. A flexible sheet of infrared transparent material 18 floats on the surface of the water 14 in the trough. A suitable material has been found to be a -~ 3-mil-thick sheet of polyester film available ~rom E.I. Dupont De Nemours Co.~` under the narne 300A Mylar. The 300A Myl~meets all of the requirements of 10 the invention in that it shows very little distortion or shrinkage in the operable temperature range. It is flexible so that it lends itself to a conveyor belt type of application and also has the strength required to operate for long periods of time without breakage. While the polyester sheet 18 only needs to float on top of thewater in the illustrated embodiment, the polyester sheet is wider than the trough 15 10 so that it not only overlies the water but also rides slightly up the sides of the trough. The extra width of the polyester sheet 18 ensures a complete coverage of the water so that there is no evaporative exposure of the water to the open air above the trough. The overwide sheet 18 also provides a channel that keeps the product to be dried, typically a Eruit pulp puree consisting of solid particles in 20 suspension in a fruit juice, from running off of the polyester sheet into the hot water. The material to be dried, for example, fruit pulp 20, is placed on top ofthe polyester sheet 18 and remains on the polyester sheet until it reaches $he proper consistency or dryness, that is, until a predetermined amount of the moisture is driven of-F the mixture by the heat transferred from the ho~ water to 25 the fruit pulp through the polyester sheet.
Depending on the final product sought, the thickness of the fruit pulp will vary; however, it has been found that a thickness of approximately one-eighth to three-sixteenths of an inch is capable of producing a satisfactory fruit leather. In the illustrated embodiment, a thin sheet 22 of material such as 30 polyethylene, for example, .5 to 1.5 mils thick, is placed between the polyester sheet 18 and the fruit pulp 20. The polyethylene sheet 22 does not enter directly into the workings of the process of the present invention, but, rather, supplies a convenient medium upon which to place the fruit pulp to prevent adherence of the pulp to the polyester sheet 18. The polyethylene sheet 22 is removed from 35 the polyester sheet 18 with the fruit pulp to maintain the polyester sheet 18 in a clean condition suitable for use with edible footstuffs. Also, the polyethylene sheet separates easily from the Mylar sheet 18 so that the Mylar sheet is not damaged as it might be if it was necessary to scrape the dried fruit leather ~ f~.~d~
~.~990~ ~
directly off of the polyester sheet. The polye-thylene sheet 22 and dried fruit leather can be rolled simultaneously from the polyester sheet to provide a convenient method by which the fruit leather is transported and/or stored after its removal from the dryer.
In one preferred form of the invention, the polyester sheet 18 is formed in an endless belt and is carried by a pair of rollers 24 and 26, respectivelyJ mounted at either end of the trough to form a conveyor belt. The fruit pulp 20 is introduced onto the polyester sheet at a first end of the trough from a discharge means 28. The polyethylene sheet 22 is fed from a roll 30, also10 at the first end of the trough 10, so that the pulp 20 lies on the polyethylene sheet 22. The pulp moves over the hot water 14 on the polyester sheet conveyor belt 18 to the second end of the trough 10. The speed of the conveyor belt is regulated so that the time that it takes for the frui~ pulp to travel from one end of the trough to $he other is sufficient to produce the proper drying of the fruit 15 pulp so that it can be removed along with the polyethylene sheet 22 at the second end of the trough. The polyester belt 18 continues on under the trough 10 in a typical conveyor fashion, while the dried pulp is moved away on a second conveyor 32. In one form of the invention, which has been tested, it has been found that a fruit pulp of one-eighth to three-sixteenths inch thickness placed on 20 a Mylar sheet 3 mils thick over a trough of water in which the water depth isapproximately one inch and the water is heated to just below the boiling point, that is, just below 100 degrees C., takes approximately two and one-half hours to dry to a suitable fruit leather dryness. It is necessary to keep a slack in the polyester conveyor belt 18 so that the film floats on the water and is not under25 such tension that it resists contact with the water surface when the pulp is placed on the belt. Typically, the fruit pulp will be open to the air during itsdrying. It is not desirable to direct any heated or dried air onto the fruit pulp as it dries because this forms an undesirable skin on the top of the pulp and actually impedes drying of the pulp by evaporation. An airflow into and out oE the room 30 in which the dryer is located is desirable to maintain the room air at a humidity that allows evaporation of the moisture in the pulp to the air and, in fact, dried heated air can be pumped into the room to lower the ambient humidity and increase the rate of absorption of water vapor by the air. In an apparatus described above with a water depth of one inch in the trough 10, and a trough of35 approximately 12 meters in length, it has been found that the temperature drop of the water from the inlet at one end of the trough to the outlet from the trough is only approximately 3 degrees C. Therefore, the hot water source does not have to expend much energy in raising the temperature of the water back to :~l29~
the desired temperature prior to reintroduction of the water into the trough.
It will be understood that while one application of the invention described herein is in the production of fruit leather from a puree of fruit pulp and juice, the invention is not limited to the use with such fruit pulps. It also can 5 be used for drying vegetables, or even soups and stews that have been blended to an even consistency prior to drying. Also, the invention, rather than completelydrying a mixture, can be used to produce juice concentrates very rapidly; for example, in the l~-meter trough above, it has been found that introduction of tomato juice on one end will produce a 50-percent concentrate in approximately 10 one and one-half hours' time from the exit end of the trough. It is important that the temperature of the fruit or other mixture be kept below the boiling point sothat there is no disruption of $he material on the polyester sheet and, typically, the fruit pulp is kept at a temperature of between 80 and 90 degrees C. Also~
the water temperature, of course, should be kept below boiling in order to 15 prevent bubbling and evaporation of the water from the trough.
While a preferred embodiment of the invention has been described and illustrated, it is clear that many changes can be made to the illustrated and described embodiment without exceeding the scope of the invention. ~or example, while particular materials such as the DuPont 300A Mylar have been 20 described as being a suitable and even a desirable medium upon which to placethe material to be dried, other media are also workable with the inven~ion and, in fact, even a sheet of glass could be used, except for its undesirable properties of inflexibility. Also, while a conveyor system has been described, it is possible simply to utili~e the invention by floating an infrared-transparent film on a body 25 of hot water and then simply placing the material to be dried on the f ilm, allowing it to sit in a stationary location on the reservoir of heated water without the use of a conveyor. The use of a conveyor does not affec~ the basic concept of the invention, but, rather, adds to the production capacity of a dryer made in accordance with the principles of the present invention. Since many 30 changes can be made to the illustrated and described embodiment without exceeding the scope of the invention, the invention should be dsfined solely with reference to the claims that follow.
Claims (13)
1. A method of drying a product comprising the steps of:
a) floating a film of transparent material on a body of water;
b) heating the water to maintain the water at a predetermined temperature; and c) placing the product to be dried on the film.
a) floating a film of transparent material on a body of water;
b) heating the water to maintain the water at a predetermined temperature; and c) placing the product to be dried on the film.
2. The method of Claim 1, further including the step of controlling the ambient air to maintain a level of humidity that maximizes the absorption rate of water vapor by the air.
3. The method of Claim 1, further including the step of placing a release medium between the product to be dried and the film to ease the removal of the product from the film after drying.
4. An apparatus for drying a material comprising:
a reservoir of water;
a heating means associated with the reservoir of water for heating the water to a predetermined temperature and maintaining the water in the reservoir at said predetermined temperature; and a transparent, solid film floated on the surface of the heated water for receiving the material to be dried.
a reservoir of water;
a heating means associated with the reservoir of water for heating the water to a predetermined temperature and maintaining the water in the reservoir at said predetermined temperature; and a transparent, solid film floated on the surface of the heated water for receiving the material to be dried.
5. The apparatus of Claim 4, wherein said film comprises a sheet of polyester material.
6. The apparatus of Claim 4, wherein said film substantially covers the entire surface of said reservoir.
7. The apparatus of Claim 4, wherein said heating means includes a water heater separate from said reservoir, said water being heated in said water heater, said reservoir including an inlet to receive heated water from said water heater and an outlet to discharge water back to said water heater for reheating.
8. The apparatus of Claim 4, wherein said film is moved in relation to the surface of said water in said reservoir.
9. The apparatus of Claim 4, further including a separation means between said film and said material to be dried.
10. The apparatus of Claim 8, wherein said film is in the form of an endless belt that forms a conveyor to carry the product over the reservoir of water.
11. The apparatus of Claim 9, wherein said separation means comprises a second transparent sheet.
12. The apparatus of Claim 4, wherein said film comprises a web of pliant, impervious plastic material.
13. A method of providing heat transfer between a body of liquid and a product, comprising the steps of:
a) positioning a sheet of transparent impervious material on the surface of the liquid so that the sheet is supported by a buoyant force of the liquid;
b) maintaining the temperature of the liquid at a predetermined temperature; and c) placing the product on the sheet.
a) positioning a sheet of transparent impervious material on the surface of the liquid so that the sheet is supported by a buoyant force of the liquid;
b) maintaining the temperature of the liquid at a predetermined temperature; and c) placing the product on the sheet.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000526172A CA1299011C (en) | 1986-12-23 | 1986-12-23 | Method and apparatus for drying fruit pulp and the like |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000526172A CA1299011C (en) | 1986-12-23 | 1986-12-23 | Method and apparatus for drying fruit pulp and the like |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1299011C true CA1299011C (en) | 1992-04-21 |
Family
ID=4134623
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000526172A Expired - Lifetime CA1299011C (en) | 1986-12-23 | 1986-12-23 | Method and apparatus for drying fruit pulp and the like |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1299011C (en) |
-
1986
- 1986-12-23 CA CA000526172A patent/CA1299011C/en not_active Expired - Lifetime
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed | ||
| MKEC | Expiry (correction) |
Effective date: 20121205 |