A practical reference on primary drying: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2026-08-01. Anything still debated is marked as such rather than presented as settled.
The physics of lyophilization depends on phase boundaries and heat and mass transfer. During primary drying, heat supplied to the product must equal the latent heat of sublimation, while water vapor moves through the drying cake to the condenser. If shelf temperature or pressure is set too high, the ice front can exceed the collapse temperature, causing meltback or pore collapse. If conditions are too cold, drying slows and costs rise. Formulation excipients, vial geometry, and freezing rate alter these limits.
Equipment for lyophilization includes a vacuum chamber, temperature-controlled shelves, a condenser, and a vacuum pump. A refrigeration system cools the shelves and condenser below the product's freezing point. Process monitoring often uses Pirani and capacitance manometers, thermocouples, and resistance sensors. Cycle development balances product quality with time and energy use. Some products are annealed during freezing to improve crystallization of bulking agents. Open questions remain about scaling cycles between laboratory, pilot, and production freeze-dryers.
Freeze-drying is used for materials whose activity or structure depends on low temperature and low water content. Examples include certain biologics, diagnostic reagents, starter cultures, coffee, and porous inorganic precursors. The dried product forms a cake whose porosity aids rapid wetting and dissolution. Main drawbacks are high energy use, long cycle times, and sensitivity to formulation and equipment variation. Questions remain about how freezing rates and ice morphology affect batch uniformity, especially when moving from laboratory to production scale.
Lyophilization, also called freeze-drying, is a dehydration process in which a solvent, usually water, is frozen and then removed by sublimation under reduced pressure. The method preserves heat-sensitive materials that would degrade in conventional drying. Large-scale use grew during the mid-twentieth century for blood plasma and antibiotics, and it later expanded to vaccines, enzymes, foods, and advanced materials. The process produces a dry, porous solid that usually reconstitutes rapidly. It is distinct from simple evaporation because the solvent bypasses the liquid phase during primary removal.
The process generally proceeds in three stages: freezing, primary drying, and secondary drying. During freezing, controlled cooling converts water into ice and may also crystallize or vitrify solutes. In primary drying, the pressure is lowered below the triple point, and heat is supplied so ice sublimes directly to vapor. Secondary drying removes water that remains bound to the solid matrix, yielding a low final water content. Product temperature must stay below the collapse or glass transition temperature to maintain structure. Cycle design therefore balances shelf temperature, chamber pressure, and time.
| Property | Value | Notes |
|---|---|---|
| Common synonyms | Freeze-drying; lyophilisation; cryodesiccation | Regional spelling and historical terms. |
| Primary drying pressure | 0.05-0.5 mbar (5-50 Pa) | Kept below the triple point of water; product-specific. |
| Shelf temperature range | -40 to +40 °C | Freezing, primary, and secondary stages use different set points. |
| Cycle duration | 12-72 hours | Depends on fill volume, formulation, and equipment. |
| Condenser temperature | -50 to -80 °C | Must remain below the product's ice temperature. |
Freezing determines ice crystal structure and pore size, which affect drying speed and product uniformity. Rapid freezing creates small crystals, while slow freezing creates larger crystals and often faster sublimation. During primary drying, chamber pressure is held below the vapor pressure of ice, and shelf temperature supplies heat for sublimation. The ice front recedes, leaving a porous matrix. Thermal limits such as collapse and eutectic temperatures set safe boundaries for formulation. These limits vary with solute composition and concentration.
Secondary drying removes bound water that remains after ice sublimation. Shelf temperature is raised gradually while pressure remains low, reducing water content to a target range. Over-drying can cause brittleness or electrostatic issues, while under-drying affects stability. The endpoint is often judged by pressure rise tests, temperature measurements, or water content analysis. Scale-up depends on matching heat and mass transfer across equipment sizes. Small changes in shelf temperature or pressure can alter cycle length substantially.
A formulation often contains excipients that protect the active ingredient during freezing and drying. Bulking agents provide structure, while lyoprotectants stabilize sensitive molecules. The freezing step can produce ice crystals whose size and distribution affect the drying rate, and cycle design includes freezing, annealing, and drying phases. If the product temperature rises above a critical value, the cake may collapse or lose its porous structure. Successful lyophilization therefore depends on the interaction between formulation, equipment, and cycle design.
Lyophilization is a dehydration process that removes water from a frozen material by sublimation under low pressure. The material is first frozen to convert liquid water into ice. Next, the pressure is reduced below the triple point of water so that ice changes directly into vapor without passing through a liquid phase. This step is called primary drying. The result is a porous solid or cake that retains the original shape of the frozen solution.
Autoimmune diseases predominantly begin in adulthood, although they can start at any age. The initial recognition of autoimmune diseases dates back to the early 1900s, and since then, advances in understanding and management of these conditions have been substantial, though much more is needed to fully unravel their complex etiology and pathophysiology.
These are available salted or in brine and they are primarily used by medium to large sausage makers who do not want to pay the additional cost for the tubed casing and do not have automatic sausage stuffing and linking machines (which require tubed casings to operate efficiently). These are available in all diameters and in lengths greater than 2 meters. Beef casings are primarily available only salted or in brine. They are measured in sets, not hanks, and the length is 32 meters; this is for beef "rounds" and "middles" only, as beef bung caps are only about 1 meter in length.
=== Tobacco usage === The use of tobacco can cause damage to the skin's collagen layer. It can cause the skin around the lips to lose collagen when in contact with the smoke or due to puckering of the lips around the cigarette. It may also cause blood vessels to constrict and reduce blood flow. Due to this, perioral collagen (connective tissue around the mouth below the skin) may show signs of damage. When collagen is lost in large amounts, it may cause wrinkles to emerge. Tobacco use can also result in slow collagen healing.
In some organisms, notably birds, and ornithischian dinosaurs, portions of the tendon can become ossified. In this process, osteocytes infiltrate the tendon and lay down bone as they would in sesamoid bone such as the patella. In birds, tendon ossification primarily occurs in the hindlimb, while in ornithischian dinosaurs, ossified axial muscle tendons form a latticework along the neural and haemal spines on the tail, presumably for support.
Three "File" editions reprinted selected content originally published between 1993 and 1996 in Edge issues 1–36. Each volume of "File" covered 12 issues. "Edge presents... The Art Of Videogames" (2007)
Sources: en.wikipedia.org
One death in Poland in December 2011 was also believed to have been caused by krokodil use, and its use has been confirmed among Russian expatriate communities in other European countries. In 2013 two cases of Krokodil use were reported in the United States. A single case of oral desomorphine use was reported in Spain in 2014. There are reports of krokodil use in the United Kingdom.
=== Crack tip plastic zone === In theory the stress at the crack tip where the radius is nearly zero, would tend to infinity. This would be considered a stress singularity, which is not possible in real-world applications. For this reason, in numerical studies in the field of fracture mechanics, it is often appropriate to represent cracks as round tipped notches, with a geometry dependent region of stress concentration replacing the crack-tip singularity. In actuality, the stress concentration at the tip of a crack within real materials has been found to have a finite value but larger than the nominal stress applied to the specimen. Nevertheless, there must be some sort of mechanism or property of the material that prevents such a crack from propagating spontaneously. The assumption is, the plastic deformation at the crack tip effectively blunts the crack tip. This deformation depends primarily on the applied stress in the applicable direction (in most cases, this is the y-direction of a regular Cartesian coordinate system), the crack length, and the geometry of the specimen. To estimate how this plastic deformation zone extended from the crack tip, Irwin equated the yield strength of the material to the far-field stresses of the y-direction along the crack (x direction) and solved for the effective radius. From this relationship, and assuming that the crack is loaded to the critical stress intensity factor, Irwin developed the following expression for the idealized radius of the zone of plastic deformation at the crack tip:
=== Electrical neuromodulation === Several forms of electrical neuromodulation, including transcutaneous electrical nerve stimulation (TENS) and transcranial direct current stimulation (tDCS), have been used to treat fibromyalgia. In general, they help reduce pain and depression and improve functioning. Transcutaneous electrical nerve stimulation (TENS) is the delivery of pulsed electrical currents to the skin to stimulate peripheral nerves. TENS is widely used to treat pain and is considered to be a low-cost, safe, and self-administered treatment. As such, it is commonly recommended by clinicians to people suffering from pain. In 2019, an overview of eight Cochrane reviews was conducted, covering 51 TENS-related randomized controlled trials. The review concluded that the quality of the available evidence was insufficient to make any recommendations. A 2020 review concluded that transcutaneous electrical nerve stimulation may diminish pain in the short term, but there was uncertainty about the relevance of the results. Preliminary findings suggest that electrically stimulating the vagus nerve through an implanted device can potentially reduce fibromyalgia symptoms. However, there may be adverse reactions to the procedure. Noninvasive brain stimulation includes methods such as transcranial direct current stimulation and high-frequency repetitive transcranial magnetic stimulation (TMS). Both methods have been found to improve pain scores in neuropathic pain and fibromyalgia.
itself should increase with temperature and be independent of density at fixed temperature. In fact, both of these predictions persist in more sophisticated treatments, and accurately describe experimental observations. By contrast, liquid viscosity typically decreases with temperature. For rigid elastic spheres of diameter
Sources: en.wikipedia.org
== Derivation by dimensional analysis == Away from the ends of the pipe, the characteristics of the flow are independent of the position along the pipe. The key quantities are then the pressure drop along the pipe per unit length, Δp/L, and the volumetric flow rate. The flow rate can be converted to a mean flow velocity V by dividing by the wetted area of the flow (which equals the cross-sectional area of the pipe if the pipe is full of fluid). Pressure has dimensions of energy per unit volume, therefore the pressure drop between two points must be proportional to the dynamic pressure q. We also know that pressure must be proportional to the length of the pipe between the two points L as the pressure drop per unit length is a constant. To turn the relationship into a proportionality coefficient of dimensionless quantity, we can divide by the hydraulic diameter of the pipe, D, which is also constant along the pipe. Therefore,
The Parliament of Canada passes all federal statute laws. It comprises the monarch, the House of Commons, and the Senate. While Canada inherited the British concept of parliamentary supremacy, this was later, with the enactment of the Constitution Act, 1982, all but completely superseded by the American notion of the supremacy of the law. Each of the 343 members of Parliament in the House of Commons is elected by simple plurality in an electoral district or riding. The Constitution Act, 1982, requires that no more than five years pass between elections, although the Canada Elections Act limits this to four years with a "fixed" election date in October; general elections still must be called by the governor general and can be triggered by either the advice of the prime minister or a lost confidence vote in the House. The 105 members of the Senate, whose seats are apportioned on a regional basis, serve until age 75. Canadian federalism divides government responsibilities between the federal government and the 10 provinces. Provincial legislatures are unicameral and operate in parliamentary fashion similar to the House of Commons. Canada's three territories also have legislatures, but these are not sovereign, have fewer constitutional responsibilities than the provinces, and differ structurally from their provincial counterparts.
=== Prevalence of use === The use of herbal remedies is more prevalent in people with chronic diseases, such as cancer, diabetes, asthma, and end-stage kidney disease. Multiple factors such as gender, age, ethnicity, education and social class are also shown to have associations with the prevalence of herbal remedy use.
==== On-screen authority figure (2003–2004) ==== The following month, Linda McMahon brought Austin back to be the co-general manager of the Raw brand, a role he played for the remainder of the year, often getting into physical altercations with talent and personnel. Austin and Bischoff continued to feud over control of the brand. On the July 21 episode of Raw, McMahon informed Austin he could not get physical with anyone unless provoked. At Survivor Series on November 16, Austin's hand-picked team of Booker T, Bubba Ray Dudley, D-Von Dudley, Rob Van Dam and Shawn Michaels faced Bischoff's team of Chris Jericho, Christian, Mark Henry, Randy Orton and Scott Steiner in a 5-on-5 Survivor Series elimination match. Austin's team lost after Batista interfered on behalf of Bischoff. After the match Jonathan Coachman came out to gloat and got beat up by Austin. As a result, Austin was "fired" from his position as co-general manager. Mick Foley took over Austin's former role and began petitioning to have Austin re-instated. Austin returned before the end of 2003, appearing at Tribute to the Troops. He posed as Santa Claus before delivering a "Stone Cold Stunner" to both Vince McMahon and John Cena. Austin returned to Raw on December 29 as its "Sheriff", giving a Stone Cold Stunner to Bischoff and rehiring Michaels, who had just been "fired" by Bischoff. Austin appeared on-and-off as 2004 began, culminating in him being the special guest referee for the Brock Lesnar vs. Goldberg match at WrestleMania XX on March 14.
Tamales – although largely associated with Mexico, and its indigenous Mesoamerican origin, records from the Iroquoian people show that they too made such a dish. Taxation – the Inca had a sophisticated taxation system, the mit'a, using quipus (knotted strings) as recording devices. Quipus were transported through the Inca road network messengers (chaskis) and administered by the quipu authorities (quipucamayoc). Tipi – a cone-shaped, portable dwelling popularized by Plains Indians (Native Americans and First Nations) of the Great Plains and the Canadian Prairies. Tipis were warm, durable, comfortable, and could be easily disassembled and packed. A settlement could be ready to move in about one hour. Tlingit armor – Tlingit armor was worn by coastal Indigenous nations in Alaska and British Columbia. Tlingit warriors wore battle helmets depicting either crest animals or ancestors, along with wooden visors, thick leather tunics, and body armor covered with wooden slats or coins. This battle attire combines technology, ingenuity, and symbolic power and protection. Tobacco – tobacco was used in the Americas for many centuries prior to the arrival of white Europeans. Consumed in high doses, tobacco can become highly hallucinogenic and was accordingly used by many indigenous peoples in the Americas to inspire dreams and dreamtime. Tobacco was also often consumed as a medicine amongst some tribes, although this was strictly practiced by experienced shamans and medicine men.
Sources: en.wikipedia.org
Simple drying usually removes water by evaporation from a liquid or solid, often with heat. Lyophilization first freezes the material and then removes ice by sublimation under vacuum. This avoids prolonged exposure to liquid water and high temperatures.
Reduced pressure lowers the boiling point of water and allows ice to sublime at temperatures below freezing. It also helps remove water vapor from the product toward the condenser. The exact pressure is chosen to stay below the triple point of water.
No. Materials with low solids content or high volatile solvents may form weak or collapsed cakes. Some proteins and cells require stabilizers to survive freezing and drying stresses. Feasibility depends on formulation and process design.
Yes. Lyophilization and freeze-drying are synonyms for the same vacuum-assisted sublimation process. The term lyophilization is more common in pharmaceutical and laboratory settings, while freeze-drying is widely used in food and general contexts.