TECHNICAL FIELD

Embodiments of the present invention relate generally to drying systems and apparatuses required for food preservation and industrial drying and more specifically to a Phase Change Material (PCM) integrated solar dryer. BACKGROUND ART

Drying is an essential process in the preservation of food/ agricultural products and in industries, such as textile production, dairy processing, cement production, clay brick production, tile production, wood and timber processing, wastewater treatment, and biomass treatment. Systems and apparatuses for drying products for preservation and/or processing have been known in the art for some time now. Products that require drying process may be, but not limited to, agricultural crops, food products such as fruits, potatoes, onions and other vegetables, products produced in dairy industries such as milk powder, casein etc., wood and timber (for seasoning) and textile materials (for drying).

These systems are required because food/agricultural products are required to be dried (removal of moisture content) before and during storage. For other products mentioned above removal of moisture is required during processing/production. Although the use of solar radiation for drying has existed for a long time, it has not yet been widely commercialized. Solar drying may be natural or artificial. Natural drying systems include conventional sun drying. Sun being a free and renewable source of energy, this practice is very common. With the advancement in technology, artificial drying systems were invented that included hot air blowers (dryers) and unheated air blowers (dehumidifiers).

Further advancements led to solar panels being used in the drying systems, making them solar dryers. Solar dryers have been commonly used for preserving the agricultural products but they have not been widely commercialized for the industrial applications. Solar panels charge the chemical batteries that in turn provide the electrical energy to the solar dryer. But the existing dryers/ drying systems have several disadvantages. The energy requirement for running the conventional dryers is supplied from various sources, namely, electricity, fossil fuel, natural gas and wood. These sources are not environment friendly.

For sun drying of agricultural products, there are various known limitations as damage to the crops by animals, birds and rodents, leads to degradation in quality due to direct exposure to solar radiation, dew or ram, contamination by dirt, dust or debris. Also this system is labour and time intensive. Problem with solar dryers is that they work during sunshine hours only. The chemical batteries charged by solar panels work for only a limited time. Moreover, storing energy in batteries is not economical. Additionally, solar dryers are also not functional in cloudy days. Moreover, the artificial drying systems have high initial cost.

Therefore, in light of the discussion above, there is need for a Phase Change Material (PCM) integrated solar dryer which can dry food products, dairy products, textile materials etc. in a hygienic and efficient method. OBJECT OF THE INVENTION

An aspect of the present invention provides a Phase Change Material (PCM) integrated solar dryer. The PCM integrated solar dryer, is cost effective and does not suffer from above mentioned deficiencies. Further, system is designed to run for 24 hours. SUMMARY OF THE INVENTION

Embodiments of the present invention aim to provide a Phase Change Material (PCM) integrated solar dryer (hereinafter referred to as“the solar dryer”).

According to a first aspect of the present invention, there is provided a Phase Change Material (PCM) integrated solar dryer, the PCM integrated solar dryer comprising a heat storage tank having a first side and a second side, a PCM disposed in the heat storage tank, a plurality of casings disposed in a plurality of holes provided on the first side of the heat storage tank, the plurality of casings being in contact with the PCM, a plurality of heat pipes received in the plurality of respective casings and in thermal contact with the plurality of casings. The plurality of heat pipes and the plurality of casings are made up of heat conducting materials. Further, the plurality of heat pipes is configured to absorb heat energy from sunlight and transfer the absorbed heat energy to the plurality of respective casings through conduction. Also, the plurality of casings is configured to transfer the received heat energy to the PCM.

In one embodiment of the invention, the PCM integrated solar dryer as further comprises a rotatable hood adapted to cover the heat storage tank.

In another embodiment of the invention, the hood is a convertible hood having more than one layers, at least one of the layers being made of a material that is transparent and the other being an opaque layer.

In another embodiment of the invention, the hood further comprises a plurality of fans capable of drawing in ambient air.

In one embodiment of the invention, respective speeds of the plurality of fans are variable in response to one or more of a temperature value and a humidity value inside the heat storage tank.

In one embodiment of the invention, the PCM integrated solar dryer further comprises a plurality of fins disposed inside the heat storage tank, the plurality of fins being in thermal communication with the PCM.

In one embodiment of the invention, the PCM integrated solar dryer further comprises a drying tray in contact with the plurality of fins, such that the plurality of fins enables transfer of the heat energy from the PCM to the drying tray.

In one embodiment of the invention, the heat storage tank has a tapered bottom surface such that a depth of the heat storage tank at the first side is more that the depth of the heat storage tank on the second side.

In one embodiment of the invention, each casing, of the plurality of casings, includes a heat transfer component and a coupling component, the coupling component being adapted to be welded to the first side, and the heat transfer component including a front portion and an elongated portion extending from the front portion, the elongated portion being in contact with the PCM, the front portion having a cavity on an opposite side of the elongated portion, wherein the cavity is adapted to receive a heat pipe of the plurality of heat pipes.

In one embodiment of the invention, the plurality of casings includes a heat transfer component made up of aluminium and the plurality of heat pipes are made up of copper. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may have been referred by embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

These and other features, benefits, and advantages of the present invention will become apparent by reference to the following text figure, with like reference numbers referring to like structures across the views, wherein:

Fig. 1 A illustrates an exploded view of a Phase Change Material (PCM) integrated solar dryer, in accordance with an embodiment of the present invention;

Fig. IB illustrates a view of the Phase Change Material (PCM) integrated solar dryer in an open position, in accordance with an embodiment of the present invention;

Fig. 1C illustrates a partial exploded view of a casing of a heat pipe with a first side of a heat storage tank, in accordance with an embodiment of the present invention; and

Fig. ID illustrates a coupling component of a casing, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the present invention is described herein by way of example using embodiments and illustrative drawings, those skilled in the art will recognize that the invention is not limited to the embodiments of drawing or drawings described, and are not intended to represent the scale of the various components. Further, some components that may form a part of the invention may not be illustrated in certain figures, for ease of illustration, and such omissions do not limit the embodiments outlined in any way. It should be understood that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives felling within the scope of the present invention as defined bythe appended claim. As used throughout this description, the word "may" is used in a permissive sense (i.e. meaning having the potential to), rather than the mandatory sense, (i.e. meaning must). Further, the words "a" or "an" mean "at least one” and the word“plurality” means“one or more” unless otherwise mentioned. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. Language such as "including," "comprising," "having," "containing, " or "involving," and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or "containing" for applicable legal purposes. Any discussion of documents, acts, materials, devices, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention. In this disclosure, whenever a composition or an element or a group of elements is preceded with the transitional phrase“comprising”, it is understood that we also contemplate the same composition, element or group of elements with transitional phrases“consisting of’,“consisting”,“selected from the group of consisting of,“including”, or“is” preceding the recitation of the composition, element or group of elements and vice versa.

The present invention is described hereinafter by various embodiments with reference to the accompanying drawing, wherein reference numerals used in the accompanying drawing correspond to the like elements throughout the description. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiment set forth herein. Rather, the embodiment is provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art In the following detailed description, numeric values and ranges are provided for various aspects of the implementations described. These values and ranges are to be treated as examples only, and are not intended to limit the scope of the claims. In addition, a number of materials are identified as suitable for various facets of the implementations. These materials are to be treated as exemplary, and are not intended to limit the scope of the invention.

Referring to the drawings, the invention will now be described in more detail. Figures 1 A illustrates an exploded view of a Phase Change Material (PCM) integrated solar dryer (100) and Figure 1B illustrates a view of the Phase Change Material (PCM) integrated solar dryer in an open position, in accordance with an embodiment of the present invention. In general, a phase change material (PCM) is a substance with a high heat of fusion which is capable of storing and releasing large amounts of energy upon melting and solidifying at a certain temperature. Heat is absorbed or released when the material changes from solid to liquid and vice versa. When the PCMs reach their melting temperature they absorb large amounts of heat at an almost constant temperature till all the material is converted into liquid. When the ambient temperature around a liquid material falls, the PCM solidifies and releases its stored latent heat There are many options available for selecting the PCM for variety of applications. Generally used PCMs are sodium acetate, wax, gels etc. And for higher temperature ranges salts and sugar alcohols are preferred.

This unique property of storing heat energy in the form of latent heat has been used for making the solar dryer (100) work on solar energy in the present invention. As shown in Figure 1A, the PCM integrated solar dryer (100) (hereinafter referred to as“the solar dryer (100)”) comprises a heat storage tank (102) having a first side (1024) and a second side (1026). The heat storage tank (102) may be, not limited to, a cuboidal box having an open top (1022). Also, the heat storage tank (102) has a tapered bottom surface (1028) such that the depth of the heat storage tank (102) at first side (1024) is more than the depth of the heat storage tank (102) on the second side (1026). In accordance with an embodiment of the present invention, the heat storage tank (102) is made of a heat conducting material such as, but not limited to, copper and aluminium. It is envisaged that the heat storage tank (102) is insulated from the outside so as to minimise heat loss to the ambient. The insulator used may be, but not limited to, Polyurethane (PU) foam.

Further, the solar dryer (100) comprises a hood (104) rotatably connected with the first side (1024) of the heat storage tank (102). The hood (104) may be attached with the first side (1024) using a connection means such as, but not limited to, a plurality of hinges. This allows the hood (104) to rotate about a top edge of the first side (1024) and cover the open top (1022) of the box. In accordance with an embodiment of the present invention, the hood (104) may be made of same material as the heat storage tank (102). In accordance with another embodiment, the hood (104) is a convertible hood having more than one layers. While one layer is made of a material that is transparent, such that, during sunshine hours, the transparent layer allows capture of extra sunlight. Alternately, during the off-sunshine hours, an opaque layer that may also be foldable, may be located above or beneath the transparent layer. The opaque layer may be made up of an insulating material making the hood (104) act as an insulator. Additionally, a plurality of fens (1042) are disposed on a top (1044) of the hood (104). The plurality of fens (1042) are capable of drawing in ambient air through filtered channels, such as those provided along the edges and blow the ambient air into the heat storage tank (102). The same has been illustrated in Figure IB.

The plurality of fens (1042) are capable of controlling the velocity of ambient air being blown. In accordance with an embodiment of the present invention, the velocity of the ambient air being blown may be controlled by controlling a speed of the plurality of fans (1042). The speed of the plurality of fans (1042) may be controlled using a PLC (Programmable Logic Controller) in combination with a temperature sensor (not shown), installed inside the heat storage tank (102). The temperature sensor is configured to regularly sense a temperature inside the heat storage tank (102) and communicate the temperature to the PLC. Additionally, the PLC is configured to increase the speed of the plurality of fans (1042) when the temperature inside the heat storage tank (102) is increasing and vice versa. While the PLC is configured to decrease the speed of the plurality of fens (1042) if the temperature inside the heat storage tank (102) is decreasing.

Furthermore, the solar dryer (100) includes a Phase change material (PCM) (106) disposed in the heat storage tank (102). The PCM (106) may be, but not limited to, paraffin wax. The tapered bottom surface (1028) of the heat storage tank (102) ensures that a higher quantity of PCM (106) is present near the first side (1024) than the quantity of PCM (106) near the second side (1026). A conductivity of the PCM (106) may be as low as 0.1 W/mk. To enhance the conductivity of the PCM (106) and a uniform heat transfer within the heat storage tank (102), a plurality of fins (108) are placed inside the heat storage tank (102). As shown in figure IB, the plurality of fins (108) are in thermal communication with the PCM (106). The plurality of fins (108) are arranged parallel to each other within the heat storage tank (102).

The shape and profile of the plurality of fins (108) are selected such that the fins conform to the tapered bottom surface (1028) of the heat storage tank (102) while maintaining a flat top portion (1082) to provide a base for placing other components. Therefore, each of the plurality of fins (108) may have a slanted bottom portion (1084) so as to conform to the tapered bottom surface (1028) of the heat storage tank (102), when seen from a side view. The plurality of fins (108) may be made of a heat conducting material that is chemically non-reactive to PCM (106) such as, but not limited to, aluminium. Further, a drying tray (110) is placed over the plurality of fins (108). The drying tray (110) has a maximum area in contact with the plurality of fins (108) so as to maximise heat transfer. The drying tray (110) may be moved and/or slid on the top portion (1082) of the plurality of fins (108). In addition, the drying tray (110) is adapted to receive a plurality of products that require drying, kept in one or more holding means (1102). The plurality of products may be, but not limited to, agricultural crops, food products such as fruits, potatoes, onions and other vegetables, products produced in dairy industries such as milk powder, casein etc., wood and timber (for seasoning) and textile materials (for drying).

Also, included in the solar dryer (100) are a plurality of casings (112) disposed in a plurality of holes (1030) provided on the first side (1024) of the heat storage tank (102). The plurality of casings (112) are in contact with the PCM (106) disposed in the storage tank. The same has been illustrated in figure 1C. In one embodiment of the invention, each casing (112) of the plurality of casings (112) is made up of at least two components, a heat transfer component (1121) and a coupling component (1126) also illustrated in Figure ID. The coupling component (1126) is envisaged to include a first portion (1132) and a second portion (1134) and is envisaged to be made up of material suitable for welding. Such materials may include steels of different alloy compositions without departing from the scope of the invention. One such material may be mild steel. It is to be noted that although the coupling component (1126) has been shown towards an external surface of the first side (1024), in the exploded view of Figure 1 C, the coupling component (1126) in certain embodiments of the assembled solar dryer (100), may be provided along an internal surface of the first side (1024) and would be hidden from view. The welding may be performed along a boundary of the first portion (1132) touching the internal surface of the first side (1024). Additional sealing means such as chemical sealants, metal or polymer gaskets and sealing rings may also be provided to prevent any leakage of the PCM (106) between the coupling component (1126) and the heat storage tank (102).

The heat transfer component (112) includes a front portion (1124) that may be hexagonal in shape or may have some other shape and an elongated portion (1128) that may be cylindrical in shape and may be perpendicularly extending from a centre of the front portion (1124). The elongated portion (1128) has been illustrated with stippled lines because it is envisaged to be hidden in the given view of Figure 1 C. It is envisaged that internal surfaces of the coupling component (1126) and external surfaces of the elongated portion (1128) be threaded to ensure fastening between the coupling component (1126) and the heat transfer component (1121). Here again, additional sealants may be used to ensure leak proof fastening. There may be other fastening means that may be used such press-fitting and friction fit, soldering, brazing, etc. with additional use of sealants, without departing from the scope of the invention.

The front portion (1124) includes a circular cavity (1122) on the opposite side of the elongated portion (1128). The circular cavity (1122) is adapted to receiving a circular object having a smaller diameter than a diameter of the circular cavity (1122). Apart of the elongated portion (1128) (shown by dashed lines as it is hidden) remains inside the heat storage tank (102) and is in constant contact with the PCM (106) for facilitating the heat transfer. The heat transfer component (1121) of the plurality of casings (112) may be made of, a heat conducting material that is chemically non-reactive to PCM (106) such as, but not limited to, aluminium.

Returning to Figure 1A, the solar dryer (100) further comprises a plurality of heat pipes (114) connected with the respective plurality of casings (112) on the first side (1024) of the heat storage tank (102). The plurality of heat pipes (114) have a cylindrical cross-section. Each of the plurality of heat pipes ( 114) is adapted to be received in the circular cavity (1122) of each of the respective plurality of casings (112). The plurality of heat pipes (114) are made of a heat conducting material that is capable of absorbing heat from the solar radiation such as, but not limited to, copper. In accordance with an embodiment of the present invention, the plurality of heat pipes (114) may be coated with a black paint in order to absorb more heat from solar radiation, thereby increasing a heat absorption efficiency.

While in operation, the plurality of heat pipes (114) are configured to heat up on receiving solar radiation from the sun during the sunshine hours. The heated plurality of heat pipes (114) then transfer the heat to the respective heat transfer components (1121) of the respective plurality of casings (112) through conduction. After that, the plurality of casings (112) are configured to transfer the heat to the PCM (106). The heat transfer components (1121) of the plurality of casings (112) made from the material such as aluminium, are required because the plurality of heat pipes (114) made of copper if submerged in PCM (106), will react with the PCM (106). Copper-PCM (106) salts are formed as a result of the reaction which adversely affects the performance of PCM (106) as a latent heat storage medium. Hence the plurality of heat pipes (114) are embedded in the respective plurality of casings (112) containing aluminium.

So after the heat is transferred to the PCM (106) and the PCM (106) absorbs the heat during sunshine hours and starts to melt The heat storage tank (102) is meticulously designed to melt the PCM (106) completely thereby leaving no cold zones within the tank. Various studies on heat transfer contours within the heat storage tank (102) led to the tapered bottom surface (1028) design of the heat storage tank (102) such that the bottom surface (1028) of the tank is levelled up from one side. This ensures that maximum quantity of PCM (106) is in contact with the plurality of casings (112), thereby, ensuring uniform and high heat transfer rate. Then, during off-sunshine hours, when the PCM (106) starts to solidify, the PCM (106) generates heat that was absorbed during sunshine hours. The plurality of fins (108), being in contact with both the PCM (106) and the drying tray (110), are configured to transfer the heat generated by PCM (106) to the drying tray (110) via conduction. In addition, the drying tray (110) is configured to hold a plurality of products, for example, agricultural products via the holding means (1102).

Furthermore, the hood (104) is adapted to cover the open top (1022) of a drying chamber where the drying tray (110) has been located, thereby covering the plurality of products. The plurality of fans (1042) provided at the top (1044) of the hood (104) draw ambient air into the drying chamber. The plurality of fans (1042) may be powered by external AC power. The ambient air, when drawn, comes in contact with the hot drying tray (110) and temperature of the ambient air rises. The hot air travels upwards due to reduced density and suction provided by the plurality of fans (1042). The hot air is then used for drying the plurality of products placed in the holding means (1102) on the drying tray (110).

An air velocity can be controlled as per the temperature and humidity levels of the ambient air using the plurality of fans (1042). During low humidity and high temperature (summer conditions), a speed of the plurality of fens (1042) is kept high so as to allow quick heat exchange with the agricultural products. However, during high humidity, the speed of the plurality of fans ( 1042) is adjusted to maximum speed. Again in winter conditions, the speed of the plurality of fens (1042) is kept low to gain heat from the surface of the hot drying tray (110). The present invention is capable of performing the drying process at a consistent temperature range i.e. 40-60°C.

The present invention offers a number of advantages. The PCM integrated solar dryer utilises the unique property of PCM to make use of solar energy for drying a plurality of products in a cost effective, efficient and easy to implement way. Therefore, the present invention not only caters to food, agricultural and plantation sectors where the dried products are used as end products for the users but also finds its applicability in industries such as diary industries, textile industries, wood and timber etc. dehydration/drying processes are essential during production. The present invention is based on direct contact heat transfer and is developed with biodegradable, environmental friendly heat storage materials. Its sleek design combined with 24x7 operations makes it distinct and different from the prior arts of solar dryers.

Additionally, the agricultural products entail the temperature in the range of 45-60 ^* C for efficacious drying and the application of PCM in the present invention entitle it to dry at consistent temperature range i.e. 40-60 ^* C. Moreover, the arrangement of the plurality of fins in the heat storage tank is such that the plurality of fins can be assembled on site and offer ease of operation in case of any refurbishment or damage repair. Present invention caters to all the features of the existing solar dryer and also yields supreme quality products in almost one-fourth of the time taken by conventional dryers. The present invention works with almost zero electricity consumption. Conversion of solar energy to heat energy is efficient enough to work under diffused sun light.

Various modifications to these embodiments are apparent to those skilled in the art from the description and the accompanying drawings. The principles associated with the various embodiments described herein may be applied to other embodiments. Therefore, the description is not intended to be limited to the embodiments shown along with the accompanying drawings but is to be providing broadest scope of consistent with the principles and the novel and inventive features disclosed or suggested herein. Accordingly, the invention is anticipated to hold on to all other such alternatives, modifications, and variations that fall within the scope of the present invention and appended claims.