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33-474: Parlux is an Italian manufacturer of hair dryers and other related hair care electrical appliances, which sells largely in the commercial side of the hair electrical appliance market, and less so the household market. It was founded in 1977 by Paolo Parodi in Corsico . In 1991 it moved to Trezzano sul Naviglio . From 2000, the appliances were no longer hand-made, but made on an automated assembly line. It

66-552: A gas stove. Godefroy invented it for use in his hair salon in France, and it was not portable or handheld. It could only be used by having the person sit underneath it. Armenian American inventor Gabriel Kazanjian was the first to patent a blow dryer in the United States, in 1911. Around 1920, hair dryers began to go on the market in handheld form. This was due to innovations by National Stamping and Electricworks under

99-428: A material can be defined for strength-controlled models by: B Δ T = σ f α E {\displaystyle B\Delta T={\frac {\sigma _{f}}{\alpha E}}} where σ f {\displaystyle \sigma _{f}} is the failure stress (which can be yield or fracture stress ), α {\displaystyle \alpha }

132-599: A reasonable ability to deflect cracks within the structure. To measure thermal shock, the impulse excitation technique proved to be a useful tool. It can be used to measure Young's modulus, Shear modulus , Poisson's ratio , and damping coefficient in a non destructive way. The same test-piece can be measured after different thermal shock cycles, and this way the deterioration in physical properties can be mapped out. Thermal shock resistance measures can be used for material selection in applications subject to rapid temperature changes. A common measure of thermal shock resistance

165-419: A reasonably wide range of temperatures. Among the best thermomechanical materials, there are alumina , zirconia , tungsten alloys, silicon nitride , silicon carbide , boron carbide , and some stainless steels . Reinforced carbon-carbon is extremely resistant to thermal shock, due to graphite 's extremely high thermal conductivity and low expansion coefficient, the high strength of carbon fiber , and

198-743: A result, a commonly chosen material index for thermal shock resistance in the poor heat transfer case is: k K I c E α {\displaystyle {\frac {kK_{Ic}}{E\alpha }}} The temperature difference to initiate fracture has been described by William David Kingery to be: Δ T c = S k σ ∗ ( 1 − ν ) E α 1 h = S h R ′ {\displaystyle \Delta T_{c}=S{\frac {k\sigma ^{*}(1-\nu )}{E\alpha }}{\frac {1}{h}}={\frac {S}{hR^{'}}}} where S {\displaystyle S}

231-401: A tube that went into a bonnet with holes in it that could be placed on top of a person's head. This worked by giving an even amount of heat to the whole head at once. The 1950s also saw the introduction of the rigid-hood hair dryer which is the type most frequently seen in salons. It had a hard plastic helmet that wraps around the person's head. This dryer works similarly to the bonnet dryer of

264-459: A year, a stark difference to the hundreds of cases of electrocution accidents during the mid-20th century. The British historical drama television series Downton Abbey made note of the invention of the portable hairdryer (blow dryer) when a character purchased one in Series 6 Episode 9, set in the year 1925. Thermal shock Methods to prevent thermal shock include: Borosilicate glass

297-463: Is a shape factor, σ ∗ {\displaystyle \sigma ^{*}} is the fracture stress, k {\displaystyle k} is the thermal conductivity, E {\displaystyle E} is the Young's modulus, α {\displaystyle \alpha } is the coefficient of thermal expansion, h {\displaystyle h}

330-448: Is made to withstand thermal shock better than most other glass through a combination of reduced expansion coefficient, and greater strength, though fused quartz outperforms it in both these respects. Some glass-ceramic materials (mostly in the lithium aluminosilicate (LAS) system ) include a controlled proportion of material with a negative expansion coefficient, so that the overall coefficient can be reduced to almost exactly zero over

363-401: Is more lightweight. This really caught on in the 1960s with the introduction of better electrical motors and the improvement of plastics. Another important change happened in 1954 when GEC changed the design of the dryer to move the motor inside the casing. The bonnet dryer was introduced to consumers in 1951. This type worked by having the dryer, usually in a small portable box, connected to

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396-541: Is situated in the Lombardy region of Italy. Hair dryer A hair dryer , hairdryer , hairdrier , or blow dryer is an electromechanical device that blows ambient or hot air over damp hair to speed the evaporation of water to dry the hair. Blow dryers enable better control over the shape and style of hair, by accelerating and controlling the formation of temporary hydrogen bonds within each strand. These bonds are powerful (allowing stronger hair shaping than

429-430: Is the coefficient of thermal expansion, E {\displaystyle E} is the Young's modulus, and B {\displaystyle B} is a constant depending upon the part constraint, material properties, and thickness. B = C A {\displaystyle B={\frac {C}{A}}} where C {\displaystyle C} is a system constrain constant dependent upon

462-521: Is the heat transfer coefficient, and R ′ {\displaystyle R'} is a fracture resistance parameter. The fracture resistance parameter is a common metric used to define the thermal shock tolerance of materials. R ′ = k σ ∗ ( 1 − v ) E α {\displaystyle R'={\frac {k\sigma ^{*}(1-v)}{E\alpha }}} The formulas were derived for ceramic materials, and make

495-408: Is the maximum temperature differential, Δ T {\displaystyle \Delta T} , which can be sustained by the material for a given thickness. Thermal shock resistance measures can be used for material selection in applications subject to rapid temperature changes. The maximum temperature jump, Δ T {\displaystyle \Delta T} , sustainable by

528-561: Is the mode I fracture toughness , E {\displaystyle E} is the Young's modulus, α {\displaystyle \alpha } is the thermal expansion coefficient, and H {\displaystyle H} is half the thickness of the plate. A material index for material selection in the fracture mechanics derived perfect heat transfer case is therefore: K I c E α {\displaystyle {\frac {K_{Ic}}{E\alpha }}} For cases with poor heat transfer,

561-643: Is the thickness, h {\displaystyle h} is the heat transfer coefficient , and k {\displaystyle k} is the thermal conductivity . If perfect heat transfer ( B i = ∞ {\displaystyle \mathrm {Bi} =\infty } ) is assumed, the maximum heat transfer supported by the material is: Δ T = A 1 σ f E α {\displaystyle \Delta T=A_{1}{\frac {\sigma _{f}}{E\alpha }}} A material index for material selection according to thermal shock resistance in

594-404: Is used as a volumizer too. There are two types of round brush hair dryers – rotating and static. Rotating round brush hair dryers have barrels that rotate automatically while static round brush hair dryers don't. In 1888 the first hairdryer was invented by French stylist Alexandre Godefroy. His invention was a large, seated version that consisted of a bonnet that attached to the chimney pipe of

627-435: Is wrapped around mica insulators. Nichrome is used due to its high resistivity , and low tendency to corrode when heated. A survey of stores in 2007 showed that most hair dryers had ceramic heating elements (like ceramic heaters ) because of their "instant heat" capability. This means that it takes less time for the dryers to heat up and for the hair to dry. Many of these dryers have "normal mode" buttons that turn off

660-460: The fracture mechanics framework. Lu and Fleck produced criteria for thermal shock cracking based on fracture toughness controlled cracking. The models were based on thermal shock in ceramics (generally brittle materials). Assuming an infinite plate, and mode I cracking, the crack was predicted to start from the edge for cold shock, but the center of the plate for hot shock. Cases were divided into perfect, and poor heat transfer to further simplify

693-457: The 1950s but at a much higher wattage. In the 1970s, the U.S. Consumer Product Safety Commission set up guidelines that hair dryers had to meet to be considered safe to manufacture. Since 1991 the CPSC has mandated that all dryers must use a ground fault circuit interrupter so that it cannot electrocute a person if it gets wet. By 2000, deaths by blowdryers had dropped to fewer than four people

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726-523: The Biot number is an important factor in the sustainable temperature jump. Δ T = A 4 K I c E α π H k h H {\displaystyle \Delta T=A_{4}{\frac {K_{Ic}}{E\alpha {\sqrt {\pi H}}}}{\frac {k}{hH}}} Critically, for poor heat transfer cases, materials with higher thermal conductivity, k , have higher thermal shock resistance. As

759-1144: The Poisson's ratio, ν {\displaystyle \nu } , and A {\displaystyle A} is a non-dimensional parameter dependent upon the Biot number , B i {\displaystyle \mathrm {Bi} } . C = { 1 axial stress ( 1 − ν ) biaxial constraint ( 1 − 2 ν ) triaxial constraint {\displaystyle C={\begin{cases}1&{\text{axial stress}}\\(1-\nu )&{\text{biaxial constraint}}\\(1-2\nu )&{\text{triaxial constraint}}\end{cases}}} A {\displaystyle A} may be approximated by: A = H h / k 1 + H h / k = B i 1 + B i {\displaystyle A={\frac {Hh/k}{1+Hh/k}}={\frac {\mathrm {Bi} }{1+\mathrm {Bi} }}} where H {\displaystyle H}

792-426: The amount of time needed to dry hair (the average dryer today can use up to 2000 watts of heat). Since the 1920s, development of the hair dryer has mainly focused on improving the wattage and superficial exterior and material changes. In fact, the mechanism of the dryer has not had any significant changes since its inception. One of the more important changes for the hair dryer is to be made of plastic, so that it

825-460: The assumptions of a homogeneous body with material properties independent of temperature, but can be well applied to other brittle materials. Thermal shock testing exposes products to alternating low and high temperatures to accelerate failures caused by temperature cycles or thermal shocks during normal use. The transition between temperature extremes occurs very rapidly, greater than 15 °C per minute. Equipment with single or multiple chambers

858-779: The fracture stress derived perfect heat transfer case is therefore: σ f E α {\displaystyle {\frac {\sigma _{f}}{E\alpha }}} For cases with poor heat transfer ( B i < 1 {\displaystyle \mathrm {Bi} <1} ), the maximum heat differential supported by the material is: Δ T = A 2 σ f E α 1 B i = A 2 σ f E α k h H {\displaystyle \Delta T=A_{2}{\frac {\sigma _{f}}{E\alpha }}{\frac {1}{\mathrm {Bi} }}=A_{2}{\frac {\sigma _{f}}{E\alpha }}{\frac {k}{hH}}} In

891-406: The handheld and the rigid-hood dryer. A hood dryer has a hard plastic dome that fits over a person's head to dry their hair. Hot air is blown out through tiny openings around the inside of the dome so the hair is dried evenly. Hood dryers are mainly found in hair salons. A hair dryer brush (also called "hot air brush" and "round brush hair dryer" and "hair styler" ) has the shape of a brush and it

924-655: The heater and blow room-temperature air while the button is pressed. This function helps to maintain the hairstyle by setting it. The colder air reduces frizz and can help to promote shine in the hair. Many feature "ionic" operation, to reduce the build-up of static electricity in the hair, though the efficacy of ionic technology is of some debate. Manufacturers claim this makes the hair "smoother". Hair dryers are available with attachments, such as diffusers, airflow concentrators, and comb nozzles. Hair dryers have been cited as an effective treatment for head lice . Today there are two major types of blow dryers (hair dryers):

957-589: The models. The sustainable temperature jump decreases, with increasing convective heat transfer (and therefore larger Biot number). This is represented in the model shown below for perfect heat transfer ( B i = ∞ {\displaystyle \mathrm {Bi} =\infty } ). Δ T = A 3 K I c E α π H {\displaystyle \Delta T=A_{3}{\frac {K_{Ic}}{E\alpha {\sqrt {\pi H}}}}} where K I c {\displaystyle K_{Ic}}

990-574: The poor heat transfer case, a higher thermal conductivity is beneficial for thermal shock resistance. The material index for the poor heat transfer case is often taken as: k σ f E α {\displaystyle {\frac {k\sigma _{f}}{E\alpha }}} According to both the perfect and poor heat transfer models, larger temperature differentials can be tolerated for hot shock than for cold shock. In addition to thermal shock resistance defined by material fracture strength, models have also been defined within

1023-436: The sulfur bonds formed by permanent waving products ) but are temporary and extremely vulnerable to humidity . They disappear with a single washing of the hair. Hairstyles using blow dryers usually have volume and discipline, which can be further improved with styling products, hairbrushes, and combs during drying to add tension, hold and lift. Blow dryers were invented in the late 19th century. The first, stationary, model

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1056-498: The white cross brand, and later U.S. Racine Universal Motor Company and the Hamilton Beach Co., which allowed the dryer to be small enough to be held by hand. Even in the 1920s, the new dryers were often heavy, weighing in at approximately 2 pounds (0.9 kg), and were difficult to use. They also had many instances of overheating and electrocution . Hair dryers were only capable of using 100 watts, which increased

1089-473: Was created by Alexandre F. Godefroy in his salon in France . The handheld, household hair dryer first appeared in 1920. Blow dryers are used in beauty salons by professional stylists and in the household by consumers. Most hair dryers consist of electric heating coils and a fan that blows the air (usually powered by a universal motor ). The heating element in most dryers is a bare, coiled nichrome wire that

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