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Topic: Heat of vapourisation

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	Standard enthalpy change of vaporization - Wikipedia, the free encyclopedia
		The standard enthalpy change of condensation (or heat of condensation) is numerically exactly equal to the standard enthalpy change of vaporisation, but has the opposite sign: enthalpy changes of vaporisation are always positive (heat is absorbed by the substance), whereas enthalpy changes of condensation are always negative (heat is released by the substance).
		This is particularly true of metals, which often form covalently bonded molecules in the gas phase: in these cases, the standard enthalpy change of atomization must be used to obtain a true value of the bond energy.
		An alternative description is to view the enthalpy change of condensation as the heat which must be released to the surroundings to compensate for the drop in entropy when a gas condenses to a liquid.
	en.wikipedia.org /wiki/Heat_of_vapourisation (482 words)

	[No title]
		Heat energy is either the energy carried by the infra-red radiation or the energy of vibration of moving atoms.
		Heat energy is transferred from an object at higher temperature to one of lower temperature.
		Heat Capacity Heat Capacity is the energy needed to change the temperature of an object one degree Celsius.
	www.hsphys.com /heat_sum_L.doc (763 words)

	Heat - Latent Heat
		Latent heats of fusion vary widely, and values should always be accompanied by the temperatures at which they were measured (these are not necessarily the normal melting points).
		The latent heat of evaporation is the energy required to overcome the molecular forces of attraction between the particles of a liquid, and bring them to the vapour state, where such attractions are minimal.
		Latent heats of vaporization vary widely, and values should always be accompanied by the temperatures at which they were measured (these are not necessarily the normal boiling points).
	www.physchem.co.za /Heat/Latent.htm (794 words)

	[No title] (Site not responding. Last check: 2007-10-31)
		A high latent heat of vapourisation is desirable because it will reduce the weight of refrigerant to be circulated per ton of refrigeration.
		Heat transfer to the generator causes separation of water vapour thereby pure vapour flows into the condenser while the strong solution of Lithium-Bromide returns into absorber.
		Replacement of the Compressor: The object of a compressor in the vapour compression refrigeration system is to withdraw the vapour from the evaporator and compress them to such pressure corresponding to which the saturation temperature is higher than the cooling agent in the condenser.
	www.eng.buffalo.edu /~ss258/Downloads/Academic/Paper/EcoFriendlyCFCAlternative/EcoFriendlyAlternativePaper.doc (2151 words)

	Condensers and Reboilers (Site not responding. Last check: 2007-10-31)
		A condenser is used to turn the vapour leaving the top of a distillation column into a liquid, by removing is heat of vapourisation.
		A reboiler is used to turn the liquid leaving the bottom of a column into a vapour by transferring the heat of vapourisation to the liquid.
		As with heat exchangers, thermodyanmics is used to calculate the heat load, which in this case depends on the Thermodynamic property; The heat of vapourisation.
	lorien.ncl.ac.uk /ming/Webnotes/Main/Where/cond.html (75 words)

	TPX experiment
		The purpose of the TPX experiment was to demonstrate heat transport by means of two-phase loops under space conditions and to compare in-flight data with terrestrial test data and thermal modelling predictions.
		Heat, supplied to two parallel capillary pumped evaporators (a flat one and a cylindrical one), causes evaporation of the working fluid, sets the mass flow rate and generates the pumping pressure to maintain the working fluid circulation in the system.
		The heat, extracted from the fluid in the condenser sections and the subcooler, is radiated to space via the GAS canister lid.
	www.nlr-duc.nl /EXPMNT/TPX.html (980 words)

	Heat Pipe? - Overclockers Forums
		The main advantage a heat pipe of this sort would have is that it uses convection to carry the heat away from the source.
		The phase change allows more heat to be absorbed into the pipe, but convection is the method that transfers the heat from one end of the pipe to the other.
		Now 'cold' end of the heat pipe may be cooled itself on the outside by convection, but convection is not the manner that heat is being moved within the pipe itself.
	www.ocforums.com /showthread.php?p=432794 (3145 words)

	[No title]
		Heating, evaporation and diffusion of the residual droplet is accelerated by the release of reaction heat from the ignition zone.
		The heat losses in small bombs were found to be very great, and it was concluded that it is advantageous to build an engine with a few large cylinders rather than with many small ones.
		Complete vapourisation, however, would be impossible since cooling of the boost air would be too great for the process to be controllable, and at the low temperatures involved hydrogen peroxide would become solid.
	www.fischer-tropsch.org /primary_documents/gvt_reports/BIOS/bios_1612.htm (16696 words)

	The Ultimate Evaporation Dog Breeds Information Guide and Reference
		When the process of escape and return reaches an equilibrium, the vapour is said to be "saturated," and no further change in either vapour pressure and density or liquid temperature will occur.
		Water molecules are in a constant state of evaporation and condensation flux near the surface of liquid water.
		Heat can also be received by radiation from any hot refractory wall of the combustion chamber.
	www.dogluvers.com /dog_breeds/Evaporation (543 words)

	Heat of vapourisation (Site not responding. Last check: 2007-10-31)
		It is defined as the heat required to vaporize one mole of a substance at its boiling point under standard pressure (101325 Pa).
		The latter is defined as the heat released when one mole of the substance condenses at its boiling point under standard pressure.
		The heat of vaporization of water is about 2250 kJ/kg which is equal to 40,6 kJ/mol.
	aseannewsnetwork.de /articles/content/h/he/heat_of_vapourisation.html (246 words)

	SJF 1993
		For example in the domestic 'fridge the evaporator takes in heat from the body of the fridge or the 'ice box' and discards heat at the back of the fridge through a series of coiled pipework called the condenser.
		Heat is extracted from the air or water thus cooling it down.
		This heat exchanger is called an EVAPORATOR since the volatile liquid is evaporated into the vapour state from the liquid state as shown below.
	www.arca53.dsl.pipex.com /index_files/frig1.htm (404 words)

	Temperature - Vent-Axia (Site not responding. Last check: 2007-10-31)
		Sweating is highly efficient because the heat of vapourisation of water is 540 cal/g.
		For bodily comfort the heat produced by the body, which may normally vary between 120 and 440 watts depending on the amount of activity, must be dissipated to preserve the inner body temperature at about 36.9°C, and this is done naturally by heat loss from the skin.
		If the air surrounding the body is cool, heat loss is rapid, but if very warm air surround the body it may gain heat from the air, and this additional heat must be dispersed as well as that generated by the body.
	www.vent-axia.co.uk /sharing/temperature.asp (1107 words)

	Fan death - Wikipedia, the free encyclopedia
		If the fan is left on all night in a sealed and enclosed room, believers in fan death suppose that it will lower the temperature of the room to the point that it can cause hypothermia.
		Empirical measurements will show, however, that the temperature in the room does not fall, at least not due to the fan; if at all, it should rise slightly because of friction and the heat output of the fan motor, but even this is generally not significant.
		Fans actually make one cooler by increasing the convection around a person's body so that heat flows from them to the air more easily, and by the latent heat of vapourisation as perspiration evaporates from the body.
	en.wikipedia.org /wiki/Fan_death (1455 words)

	Evaporation
		The sensor also records the vapour pressure or humidity of the air at the same height as the temperatures were measured.
		Following this the partial pressure of water vapour in the air was calculated and plotted against time, however the data aquired was noisy so a spline was fitted (with lamda = 1) to both; and predicted e (partial pressure of water vapour) was saved (see graphs below).
		After the calculations of the Bowen Ratio and the soil heat flux the evaporation rate was calculated in millimetres, again the results were noisy so a spline was fitted with lamda = 2.
	www.usyd.edu.au /agric/web04/evaporation-final.htm (893 words)

	BBC - Rough Science - Ice Challenge
		The latent heat of vapourisation of a liquid is the amount of energy in joules required to turn one gram of the liquid into a vapour.
		When you get out of the shower or bath and feel cold it is because for every gram of water that evaporates from your skin 2264 joules (539 calories) of energy are being used to evaporate that gram of water.
		The energy is taken in the form of heat from you and therefore you feel cold.
	www.open2.net /roughscience2/html/challenges/ice/ice_06.htm (130 words)

	Construction of the first refrigerant to coolant heat exchanger (Designing the heat exchanger)
		This translates to a heat resistance between evaporating refrigerant and coolant of about 0.01 K/W. Based on my experience with waterjackets, this is no problem, even with a modest evaporator coil surface area and only 500L/hr coolant flow.
		The latent heat of vapourisation of R134a is 217kJ/kg of refrigerant.
		This is useful during experimenting, and the heat exchanger can serve as a direct replacement for the standard radiator used in my current watercooling system.
	www.icecoldcomputing.com /text/show_page.php?id=19 (723 words)

	Quiz 3 (PHYS262, Summer 2001)
		The change in the internal energy of a given system is equal to the sum of the heat given to it and the work done by it (i.e.
		The heat capacity of a given system is independent of the system size.
		The efficiency of a heat engine is only dependent on the highest temperature and the lowest temperature of a cycle.
	www.physics.umd.edu /courses/Phys262/hjkn/Quiz/Q4/Q4.html (289 words)

	Nat Gaz.
		When the pressure is released(when the gas supply valve is turned on), the liquid will boil and form a vapour.
		Heat is needed to convert the liquid to gas, known as the latent heat of vapourisation.
		This is why the containers feel cold to the touch and if there is heavy gas consumption, frost may appear on the outside.
	www.natgaz.com.lb /lpgproperties.html (164 words)

	ChE Forums > Latent Heat Of Vapourisation
		Aug 30 2004, 03:34 AM Generally speaking, for one given component, the latent heat of vaporization decreases as temperature increases.
		In fact, the outline of the dome by definition is precisely the conditions that define the latent heat condition: the curve on the left represents saturated liquid (& solid in some cases) while the section of the dome on the right represents the saturated vapor.
		And it is the length of the horizontal line (constant pressure) that links both sides of the dome that defines the latent heat of vaporization or sublimation.
	www.cheresources.com /invision/lofiversion/index.php/t832.html (436 words)

	Superheating and microwave ovens
		Microwave ovens heat the water directly: the microwaves pass through the container and the water, and the water itself absorbs energy from them.
		The latent heat of vapourisation of water is L = 2.23 MJ/kg.
		This means that it takes 4,200 Joules of heat to raise the temperature of 1 kg of water by 1 °C. Suppose that we heat one kilogram of water from 100 °C (its normal boiling temperature) to 101 °C, i.e.
	www.phys.unsw.edu.au /~jw/superheating.html (1573 words)

	[No title]
		Calculate the change in enthalpy, entropy and Gibbs free energy which occurs when one mole of carbon monoxide is heated from 300 K to 500 K at 1 atmospheric pressure.
		The molar heat capacity in J K-1 at this pressure is given by Cp = 26.537 + 7.6831 x 10-3 (T/K) — 11.72 x 10-7 (T/K)2 The molar entropy of carbon monoxide gas is 198.087 J K-1 mol-1 at 300 K and 1 atmosphere.
		Calculate the solubility at 298 K of a substance which melts at 323 K and has a molar latent heat of fusion of 12.29 kJ mol-1 assuming ideal behaviour.
	www.maths.tcd.ie /~pwalsht/WEBpdf/CHEMICAL_THERMODYNAMICS_PROBLEMS.doc (214 words)

	The Science behind Water Cooling [Archive] - Overclockers Forums (Site not responding. Last check: 2007-10-31)
		The latent heat of vapourisation is the amount of energy required to convert 1g of water to water vapour at the same temperature.
		The amount of energy required heat 1g of water by 1C is 1 Joule but the amount of energy required to convert 1g of water to vapour is 540 Joules.
		The heat is transfered from the water to the metal radiator by conduction and then from the metal surface by forced convection.
	www.ocforums.com /archive/index.php/t-75070.html (418 words)

	Steam Injection (Site not responding. Last check: 2007-10-31)
		Steam is a great carrier of heat and because it is at 100C to 200C in non contained systems, it can heat quickly without scorching.
		Heat losses to piping are absorbed by the superheat.
		Because it condenses and then heats the water to boil the same ammount, in a perfect system there is no loss of volume.
	brewery.org /brewery/library/SteInjCS1295.html (1715 words)

	Questions
		But if you shake the bottle and immediately take the cap off (just to see if your cap is a winning cap), the coke will spew out everywhere even though you have not changed the temperature of the coke (from the act of shaking the bottle).
		The melting point of silver is at 1235 K and the boiling point at 2323 K. Given this information, calculate the minimum amount of heat, in joules, required to completely melt 130 g of silver initially at
		Calculate the net heat added to the system during one complete cycle.
	www.physics.umd.edu /courses/Phys262/hjkn/Exams/mid2web/node1.html (416 words)

	Review of Physical Processes (Site not responding. Last check: 2007-10-31)
		The latent heat of fusion (Lf) is the energy per unit mass which must be added to cross the solid/liquid phase boundary, the latent heat of vapourisation (Lv) relates to crossing the liquid/vapour boundary and the latent heat of sublimation (Ls) relates to crossing the solid/vapour boundary.
		Finally, when the vapourisation line is hit at point C, additional heat transfer will result in a phase change (evaporation) and the liquid water will begin to change into the vapour phase (the temperature at which this takes place is called the saturation temperature and the pressure is the saturation pressure).
		This means that the rate at which the natural logarithm of the vapour pressure (P) of a liquid changes with temperature is determined by the molar enthalpy of vapourisation of the liquid (Hvap), the ideal gas constant (R) and the temperature of the system (T).
	www.enm.bris.ac.uk /teaching/projects/2002_03/jb8355/review.htm (1899 words)

	Ch 3 (Site not responding. Last check: 2007-10-31)
		, calculate the heat released when 1 tonne of the coal is burnt.
		If the temperature of the coal is 25 C, estimate the heating value of the Blair Athol coal before drying.
		for methane, calculate the heat produced by burning the 1000t of coke directly.
	www.terrace.qld.edu.au /academic/chemistry/12revision7.htm (700 words)

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