1.6.4. Adiabatic Demagnetization Refrigeration (ADR) Cycle:-
The adiabatic demagnetization refrigeration (ADR) cycle, or “one-shot,” cycle. This cycle was first proposed by Debye (1926) and Giauque (1927) as a means of achieving temperatures below the boiling point of helium [13]. Whereby, early magnetic coolers were used to achieve extreme cryogenic temperatures [11]. This magnetic cycle is equivalent to the Carnot cycle for vapor compression systems, shown in Fig.(1.8). However, in practice, it is difficult to reject heat isothermally, since the magnetic field must also be modulated properly in order to achieve this condition; this requires complex heat switches that limit heat flux rates. Also, the temperature lift of an ADR cycle
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(1.8): Adiabatic demagnetization refrigeration (ADR) or magnetic Carnot cycle for gadolinium, “one-shot,” [13].
1.6.5. Active Magnetic Regenerative Refrigeration (AMRR) Cycle:-
The MCE is typically in the range of (1-5) k/T (in terms of the adiabatic temperature change). This modest change in temperature is obviously not sufficient for applications such as domestic refrigeration etc. [24]. On the other hand, the experiments near room temperature are using
Gadolinium and its performance were limited by the use of passive regenerators and heat exchangers in the refrigeration cycle [25]. So, a magnetic refrigeration device must utilize a regenerative process to produce a large enough temperature span to be useful for refrigeration purposes [26]. However, in 1982 a new concept was introduced by Barclay that became known as an Active Magnetic Regenerator (AMR). Unlike previous gas cycles, or magnetic cycles, the AMR concept coupled what had been two separate processes into a single component. Fig.(1.9) illustrated the AMR cycle
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Whereby, instead of using a separate material as a regenerator to recuperate the heat from the magnetic material, the AMR concept made use of the refrigerant itself as the regenerator [6], thus, making it an active part of the refrigeration cycle. This is possible due to the high heat capacities of common magnetocaloric materials near their Curie temperatures [25].
Furthermore, AMR should be recognized as the combined solid -fluid system, whereby, in essence, a temperature gradient is established throughout the AMR and a fluid is used to transfer heat from the cold end to the hot. This subtle but important idea produced a new magnetic cycle distinct from Carnot, Ericsson, Brayton, or Stirling [6].
On the other hand, the active magnetic refrigeration cycle is similar to the ADR cycle, but heat addition and rejection occurs at a constant magnetic field rather than at constant temperature. Isothermal heat rejection and addition is impractical to implement since the applied magnetic field must be modulated to match the temperature with the heat rejection rate [13],
1.6.5.1. Some Theoretical Background for the (AMRR)
Ruth Schwartz Cowan wrote “How the Refrigerator Got Its Hum” in 1983. It was included in the section, “Failed Machines” of her book. I never thought about why most refrigerators are electric. We have owned gas stoves and dryers, but never a gas refrigerator. Gas appliances cost more upfront, but are inexpensive to run over time. Personally, I would rather have gas appliances than electric and believe many other people would too; however, there are major factors that caused the gas refrigerator to fail.
"Refrigerators." Canada Science and Technology Museum. Canada Science and Technology Museum, 2014. Web. 15 Feb. 2014. .
The electronics industry relies heavily on devices that acquire, store and transmit data. NVE Corp’s spintronics technology focuses on magnetic sensors, couplers, and memory which perform these activities w...
In warmer climates such as Egypt they used techniques as evaporative cooling, “if water is placed in shallow trays during the cool tropical nights, its rapid evaporation can cause ice to form in the trays, even if the air does not fall below freezing temperatures”. Although refrigeration developed in the 18th century it wasn’t until the mid-19th century when the first refrigerator built using vapor technology was build by American John Gorrie in 1844. A few years later commercial refrigeration was introduced as well as vapor compression technology which was the beginning of our modern refrigeration. Later that century ammonia was popularized as the evaporation chemical in refrigeration. All the trials and tribulations of refrigeration where all stepping stones to the 20th century and the introduction of modern refrigeration as we know it
A thermistor is used to sense the alterations in temperature. It does this by altering its resistance, but not in proportion to the change of temperature. When the temperature increases the resistance of the thermistor drops, but not linearly. This is due to electrons in the thermistor gaining more energy because of the temperature increase.
Refrigeration Refrigeration is defined as “The process of removing heat from an enclosed space, or from a substance, to lower its pressure.” (First website given in bibliography) In simpler terms, it is removing heat from states of matter in order to keep them cooler. The basic need for refrigeration is to cool food and beverages, as they often get spoilt if the temperature is high. Before actual refrigerators and other such mechanical systems were introduced, it was very common for people to cool their food with ice and snow.
The air coming from the Secondary heat exchanger now expands through the ACM Turbine side which brings the temperature down between 2 to 10 degree Centigrade after expansion at Turbine exit.
The first step of understanding the APB mechanism is to predict temperature profiles in the wellbores accurately. Almost all practical methods for calculation of temperature profiles in the wellbores go back to the work by Ramey (1962) on wellbore heat transmission published in early 1960’s.
To demonstrate the versatility of the PTC thermistor; below are some examples where their use as an Inrush Current Limiter is the optimal choice.
A ferromagnetic material is composed of many microscopic magnets known as domains. Each domain is a region of the magnet, consisting of numerous atomic dipoles, all pointing in the same direction. A strong magnetic field will align the domains of a ferromagnet, or in other words, magnetize it. Once the magnetic field is removed, the domains will remain aligned, resulting in a permanent magnet. This effect is known as hysteresis.
... temperature of 112 0C also and a pressure 2.5 bar. Cooling water is used to condense the vapor exiting column. Remaining methane and hydrogen are separated in reflux drum where the vapor stream is combined with other gases streams. The overhead of first and second separator are combined to form fuel gas. The liquid stream exiting in the bottoms of the reflux drum is pumped at pressure of 3.3 bar for discharging pressure. The pump stream is separated in two streams. One stream is to feed to tray one of the column and the other one stream is cooled down to 38 0C in heat exchanger. Then, the cooled product stream is sent to storage.
The development of superconductors has been a working progress for many years and some superconductors are already in use, but there is always room for improvement. In 1911, Dutch physicist Heike Kamerlingh Onnes first discovered superconductivity when he cooled mercury to 4 degrees K (-452.47º F / -269.15º C). At this temperature, mercury’s resistance to electricity seemed to disappear. Hence, it was necessary for Onnes to come within 4 degrees of the coldest temperature that is theoretically attainable to witness the phenomenon of superconductivity. Later, in 1933 Walter Meissner and Robert Ochsenfeld discovered that a superconducting material will repel a magnetic field. A magnet moving by a conductor induces currents in the conductor, which is the principle upon which the electric generator operates. However, in a superconductor the induced currents exactly mirror the field that would have otherwise penetrated the superconducting material - causing the magnet to be repulsed- known today as the “Meissner effect.” The Meissner effect is so strong that a magnet can actually be levitated over a superconductive material, which increases the use of superconductors. After many other superconducting elements, compounds, and theories related to superconductivity were developed or discovered a great breakthrough was made. In 1986, Alex Muller and Georg Bednorz invented a ceramic substance which superconducted at the highest temperature then known: 30 K (-243.15º C). This discovery was remarkable because ceramics are normally insulators – they do not conduct electricity well. Since their discovery the highest temperature for superconductivity to occur is 138 K (-130.15º C).
The topic of magnetic disks is one that involves many physics related phenomenon. The intricate structure and design of “Magnetic Disks” (or hard disks) in computers include the principles of Fluid Flow, Rotational Motion, Electromagnetism, and more. This paper will focus mainly on the previously listed physics occurrences, and the design that goes into engineering the magnetic disk to include them. These physics principles are utilized in such a way that makes the hard disk a very common and useful tool, in this day and age. To most people, the magnetic disk is the most important, yet most mysterious, part of a computer system. A hard disk is a seal unit that holds computer data in the form of magnetic patterns.
In thermodynamics Refrigeration is the major application area, in which the heat is transferred from a lower temperature region to a higher temperature region. The devices which produce refrigeration are known as Refrigerators and the cycle on which it operates are called refrigeration cycles. Vapour compression refrigeration cycle is the most regularly used refrigeration cycle in which the refrigerant is alternately vaporized and condensed and in the vapor phase it is compressed. Gas refrigeration cycle is the well-known refrigeration cycle in which cycle refrigerant remains in the gaseous phase throughout the cycle. Cascade refrigeration are the other refrigeration cycles discussed in this chapter; absorption refrigeration is the one more refrigeration cycle which is used where the refrigerant is dissolved in liquid before it is compressed. One more refrigeration in which refrigeration is produced by passing the electric current through two dissimilar materials is called as the thermoelectric refrigeration.