Solar dryers are devices that use solar energy to dry substances, especially food. Solar dryers use the heat from the Sun to reduce the moisture content of food substances. There are two general types of solar dryers: direct and indirect. [1]
Direct solar dryers expose the substance to be dehydrated to direct sunlight. Historically, food and clothing was dried in the sun by using lines, or laying the items on rocks or on top of tents. [2] In Mongolia cheese and meat are still traditionally dried using the top of the ger (tent) as a solar dryer. [3] In these systems the solar drying is assisted by the movement of the air (wind) that removes the more saturated air away from the items being dried. [2] More recently, complex drying racks [4] and solar tents [5] were constructed as solar dryers.
One modern type of solar dryer has a black absorbing surface which collects the light and converts it to heat; the substance to be dried is placed directly on this surface. These driers may have enclosures, glass covers and/or vents in order to increase efficiency. [6]
In indirect solar dryers, the black surface heats incoming air rather than directly heating the substance to be dried. This heated air is then passed over the substance to be dried and exits upwards often through a chimney, taking moisture released from the substance with it. [2] They can be very simple, just a tilted cold frame with black cloth [7] to an insulated brick building with active ventilation and a back-up heating system. [8] One of the advantages of the indirect system is that it is easier to protect the food, or other substance, from contamination whether wind-blown or by birds, insects, or animals. [2] [8] Also, direct sun can chemically alter some foods making them less appetizing. [2] [8]
Solar drying is mostly carried out between 50-70 degree Celsius. Solar dryers such as Vyom and many other models now use polycarbonate sheets or UV preventive glass so that UV rays of the sun do not penetrate the food which leads to degradation of dried food. Solar dryers not only make the drying faster, it also prevents dust, pathogens, bird droppings, and interference of external agents that affect the quality of the food. Food items such as fruits, vegetables, spices and other items once dried in solar can be stored for longer period of time.[ citation needed ]
Grilling is a form of cooking that involves heat applied to the surface of food, commonly from above, below or from the side. Grilling usually involves a significant amount of direct, radiant heat, and tends to be used for cooking meat and vegetables quickly. Food to be grilled is cooked on a grill, using a cast iron/frying pan, or a grill pan.
Roasting is a cooking method that uses dry heat where hot air covers the food, cooking it evenly on all sides with temperatures of at least 150 °C (300 °F) from an open flame, oven, or other heat source. Roasting can enhance the flavor through caramelization and Maillard browning on the surface of the food. Roasting uses indirect, diffused heat, and is suitable for slower cooking of meat in a larger, whole piece. Meats and most root and bulb vegetables can be roasted. Any piece of meat, especially red meat, that has been cooked in this fashion is called a roast. Meats and vegetables prepared in this way are described as "roasted", e.g., roasted chicken or roasted squash.
Copra is the dried, white flesh of the coconut from which coconut oil is extracted. Traditionally, the coconuts are sun-dried, especially for export, before the oil, also known as copra oil, is pressed out. The oil extracted from copra is rich in lauric acid, making it an important commodity in the preparation of lauryl alcohol, soaps, fatty acids, cosmetics, etc. and thus a lucrative product for many coconut-producing countries. The palatable oil cake, known as copra cake, obtained as a residue in the production of copra oil is used in animal feeds. The ground cake is known as coconut or copra meal.
In passive solar building design, windows, walls, and floors are made to collect, store, reflect, and distribute solar energy, in the form of heat in the winter and reject solar heat in the summer. This is called passive solar design because, unlike active solar heating systems, it does not involve the use of mechanical and electrical devices.
Spray drying is a method of forming a dry powder from a liquid or slurry by rapidly drying with a hot gas. This is the preferred method of drying of many thermally-sensitive materials such as foods and pharmaceuticals, or materials which may require extremely consistent, fine particle size. Air is the heated drying medium; however, if the liquid is a flammable solvent such as ethanol or the product is oxygen-sensitive then nitrogen is used.
Food drying is a method of food preservation in which food is dried. Drying inhibits the growth of bacteria, yeasts, and mold through the removal of water. Dehydration has been used widely for this purpose since ancient times; the earliest known practice is 12,000 B.C. by inhabitants of the modern Middle East and Asia regions. Water is traditionally removed through evaporation by using methods such as air drying, sun drying, smoking or wind drying, although today electric food dehydrators or freeze-drying can be used to speed the drying process and ensure more consistent results.
Jerky is lean trimmed meat cut into strips and dried (dehydrated) to prevent spoilage. Normally, this drying includes the addition of salt to prevent some forms of bacteria growth, and encourages others; before the meat has finished the dehydrating process. The word "jerky" derives from the Quechua word ch'arki which means "dried, salted meat". All that is needed to produce basic "jerky" is a low-temperature drying method, and salt to inhibit bacterial growth.
A clothes dryer, also known as tumble dryer or simply dryer, is a powered household appliance that is used to remove moisture from a load of clothing, bedding and other textiles, usually after they are washed in a washing machine.
Solar thermal energy (STE) is a form of energy and a technology for harnessing solar energy to generate thermal energy for use in industry, and in the residential and commercial sectors.
Dried fruit is fruit from which the majority of the original water content has been removed either naturally, through sun drying, or through the use of specialized dryers or dehydrators. Dried fruit has a long tradition of use dating back to the fourth millennium BC in Mesopotamia, and is prized because of its sweet taste, nutritive value, and long shelf life.
A clothes line, also spelt clothesline and also known as a washing line, is a device for hanging clothes on for the purpose of drying them. It is any type of rope, cord, or twine that has been stretched between two points, outside or indoors, above the level of the ground. Clothing that has recently been washed is hung along the line to dry, using clothes pegs or clothespins. Washing lines are attached either from a post or a wall, and are frequently located in back gardens, or on balconies. Longer washing lines often have props holding up sections in the middle due to the weight of the usually wet clothing.
Freeze drying, also known as lyophilization or cryodesiccation, is a low temperature dehydration process that involves freezing the product and lowering pressure, removing the ice by sublimation. This is in contrast to dehydration by most conventional methods that evaporate water using heat.
Dielectric heating, also known as electronic heating, radio frequency heating, and high-frequency heating, is the process in which a radio frequency (RF) alternating electric field, or radio wave or microwave electromagnetic radiation heats a dielectric material. At higher frequencies, this heating is caused by molecular dipole rotation within the dielectric.
Drying is a mass transfer process consisting of the removal of water or another solvent by evaporation from a solid, semi-solid or liquid. This process is often used as a final production step before selling or packaging products. To be considered "dried", the final product must be solid, in the form of a continuous sheet, long pieces, particles or powder. A source of heat and an agent to remove the vapor produced by the process are often involved. In bioproducts like food, grains, and pharmaceuticals like vaccines, the solvent to be removed is almost invariably water. Desiccation may be synonymous with drying or considered an extreme form of drying.
A food dehydrator is a device that removes moisture from food to aid in its preservation. Food drying is a method of preserving fruit, vegetables and meats that has been practiced since antiquity.
Solar air heating is a solar thermal technology in which the energy from the sun, insolation, is captured by an absorbing medium and used to heat air. Solar air heating is a renewable energy heating technology used to heat or condition air for buildings or process heat applications. It is typically the most cost-effective out of all the solar technologies, especially in commercial and industrial applications, and it addresses the largest usage of building energy in heating climates, which is space heating and industrial process heating.
Vacuum drying is the mass transfer operation in which the moisture present in a substance, usually a wet solid, is removed by means of creating a vacuum.
Food powder or powdery food is the most common format of dried solid food material that meets specific quality standards, such as moisture content, particle size, and particular morphology. Common powdery food products include milk powder, tea powder, cocoa powder, coffee powder, soybean flour, wheat flour, and chili powder. Powders are particulate discrete solid particles of size ranging from nanometres to millimetres that generally flow freely when shaken or tilted. The bulk powder properties are the combined effect of particle properties by the conversion of food products in solid state into powdery form for ease of use, processing and keeping quality. Various terms are used to indicate the particulate solids in bulk, such as powder, granules, flour and dust, though all these materials can be treated under powder category. These common terminologies are based on the size or the source of the materials.