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Law of thermodynamics
Law of thermodynamics
The law of thermodynamics
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There are many reasons for wanting to cool things, but whatever the reason, the Second Law of Thermodynamics dictates that cooling something will take effort (sorry, no spontaneously cool sodas). Different techniques have been developed to address this issue, each having its own limitations and ideal uses.
The most commonly used method of cooling is with vapor-compression cycles, because it is fairly easy to construct a cooling device employing this method and the cost is low. In fact, conventional refrigerators use this method of cooling to keep your leftovers and drinks chilled! Air conditioners also employ a vapor-compression cycle to cool the ambient air temperature in a room.
Basically, vapor-compression refrigeration employs a heat engine run backwards, so heat energy is taken from a cold reservoir and deposited into a hot reservoir. By the Second Law of Thermodynamics, heat energy does not spontaneously transfer from a cold to a hot reservoir. In order to have heat transfer in that direction (and not from from hot to cold, as the system is naturally inclined to do), it is necessary to do work on the system.
Vapor-Compression Refrigeration Cycle
This refrigeration cycle is approximately a Rankine cycle run in reverse. A working fluid (often called the refrigerant) is pushed through the system and undergoes state changes (from liquid to gas and back). The latent heat of vaporization of the refrigerant is used to transfer large amounts of heat energy, and changes in pressure are used to control when the refrigerant expels or absorbs heat energy.
However, for a refrigeration cycle that has a hot reservoir at around room temperature (or a bit higher) and a cold reservoir that is desired to be at around 34°F, the boiling point of the refrigerant needs to be fairly low. Thus, various fluids have been identified as practical refrigerants. The most common include ammonia, Freon (and other chlorofluorocarbon refrigerants, aka CFCs), and HFC-134a (a non-toxic hydrofluorocarbon).
Stages of the Vapor-Compression Refrigeration Cycle
The Vapor-Compression Refrigeration Cycle is comprised of four steps. The conceptual figure of the process shows the PV changes during each part.
Part 1: Compression
In this stage, the refrigerant enters the compressor as a gas under low pressure and having a low temperature.
Since the evaporator coil is responsible for making the air in the system cool, it’s an incredibly important part that must always be in working condition. It’s job is to turn the coolant in the unit to a gas form, which then cools down the coil. When warm air passes over this coil, it becomes chilled before passing through all the vents in your home.
The Yeti Rambler has taken off where it’s more expensive and luxurious brethren, the Yeti cooler, has left off. The explosion of demand for this particular cup is due to its highly engineered design, which features 18/8 stainless steel material and a double walled vacuum insulation, which keeps a drink hot or cold twice as long as plastic cups (“Frequently asked questions”, n.d.). The cutting edge cup also features a gasket lid that locks beverages inside of the cup, allowing one to move freely without fear of spilling (“Frequently asked questions”, n.d.). Saporito (2016) narrates the Yeti Coolers story as it was started in 2005 by Ryan Seiders and his brother Roy Seiders as a way to provide premium coolers
An Investigation Into How the Thickness of Insulation Affects the Time a Drink Takes to Cool Down
Shirley (2013) explains the steps of the theory; the first step is unfreezing. The unfreezing stage this is preparation stage. This is the stage when
In the production process of chemicals it requires to use of a average calorific value gas (MCV) also non-nitrogen diluted by minor impurities for best alteration to chemical compounds (Paisley et al., 1994). For the electricity production the used product gas should be clean from char-particles, pitch and ash etc. before it is inserted into the gas turbine or in a combustion engine. The higher temperature gases which exits from the gas turbine can be further used to generate steam from there heat for a steam turbine, like as an Integrate Gasification Combined Cycle (IGCC) generally used in power
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
heat will stay in the cup and can only escape by rising to the surface
First of all, the purpose of this lab was to determine the water’s vapor pressure at different temperatures as well as to measure the molar heat of vaporization of water using the Clausias Clapeyron equation. The first concept out of many represented in this lab is the ideal gas law. The ideal gas law is used to get the number of moles of air trapped in the 10 mL graduated cylinder. Once we cooled the system so that water vapor is extremely minute, and then we determined the number of moles of air using the ideal gas law. The number of moles of air equals to the pressure (in atm) times volume divided by constant times temperature. One would assume that when the water is heated to 80 degrees, the number of air molecules in the air bubble would decrease, but it actually stays constant. This is due to the fact that there is no air coming in or out of the cylinder. As the temperature gets closer to 80 degrees, the number of air molecules stays the same but the water vapor increases. And the bubble expands to keep the pressure at the same level. The ideal gas law was also used when the partial pressure of air in the gas mixture is calculated. This is gotten from number of moles multiplied by the constant and the constant and the whole thing divided by the volume.
Investigating Heat Loss From a Container Planning We are investigating heat loss from a container and how it is affected. We could change: Room temperature Surface area Amount of water Use a lid Insulate around it Colour of tin We could measure / observe: Amount of time Temperature We will change: Surface area We will measure / observe: Temperature (every minute for 5 minutes) Our question is: Does surface area effect the rate of heat loss? We will keep these the same: Colour of tin Room temperature Amount of water Use a lid Insulate around it Preliminary investigation = == ==
Process cd : This liquid refrigerant is collected in the liquid storage tank and later on it is expanded to low pressure and temperature by passing it through the throttle valve. At point d we have low temperature liquid refrigerant with small amounts of vapour .
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.
... 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.
Heat energy is transferred through three ways- conduction, convection and radiation. All three are able to transfer heat from one place to another based off of different principles however, are all three are connected by the physics of heat. Let’s start with heat- what exactly is heat? We can understand heat by knowing that “heat is a thermal energy that flows from the warmer areas to the cooler areas, and the thermal energy is the total of all kinetic energies within a given system.” (Soffar, 2015) Now, we can explore the means to which heat is transferred and how each of them occurs. Heat is transferred through conduction at the molecular level and in simple terms, the transfers occurs through physical contact. In conduction, “the substance
The study of the relation between internal energy, heat, and work is the basic foundation in thermodynamics. How they interact can be applied to mechanics and experiments. For example, if you add heat to a piston, the gas contained inside will begin to expand and cause displacement, doing work. Gases are heavily studied in thermodynamics, because the internal energy is easier to account for. Gases only have kinetic energy because the potential energy is negligible since the far apart molecules cannot interact with each other. The four main types of thermodynamic processes- isovolumetric, isothermal, adiabatic, and isobaric-all involve the relation between work, heat, and internal energy on gases.