# Plz Help! How do liquid filled radiators work?

Fri 1st June, 2012 @ 18:48

# Hi,

I am currently doing a physics piece of coursework, It is a research project on radiators, I have been asked to find the answer of 3 questions and am really stuck and wondered if anyone could help me? Here are the questions:

1) How do liquid filled radiators work? Include the useful properties of the liquids they contain.
2) The specific heat capacities of Glycerol, Water and Olive Oil
3) How do the properties of these three liquids compare to the properties of the other liquids used in radiators?

P.S Could you plz post the URL of the website where this info has been found if it has been found from a website.

Fri 1st June, 2012 @ 18:53

well the liquid must be a good conductor of heat. Radiators work by a heating element which heats the water and becuz of convection currents the hot water rises, then it cools and then drops and the process continuess. ()u probably know the details of this). The liquid must not be too viscous becuz it wuld take ages too heat and it must not be the opposite (not viscous at all) becuz then it culd build up pressure if it turns to a gas.

water = 4.2 J/g

glycerol = 2.38 J/g

olive oil = 1.97 J/g

sorry i havent been much help but if i find more i will post it up immendiately = D

**

I see the question pertains to a common house radiator. Its design is such as to maximize the contact surface between air and the radiator body. Hence the thin and numerous fins.

(i) Conduction is a direct-contact transfer of heat from a region of higher temperature to a region of lower temperature. Your radiator is hot, so it heats air which surrounds it because the air is colder. The air is in contact with radiator surface, and the radiator is designed so as to have a maximum contact surface to transfer heat more efficiently.

Heat energy in a gas is, actually, in the speed the gas molecules move around: the hotter the gas is (the more heat there is), the faster its particles move. The total kinetic energy of its particles is the total heat in it. When hotter gas comes in contact with a colder one, the faster molecules collide with the slower, and they lose speed, while the slower ones gain speed. Thus, they lose kinetic energy (Ek=m*v^2/2), which the slower ones get. Macroscopically, the hot gas cools down, while the cold gas heats up.

In solids and in liquids, the situatuon is more complicated. For example, in metals, there are atoms in crystal structures, and they do not move around freely, but rather they oscillate around fixed positions. The more vigorously they oscillate, the more energy they have, the hotter the metal (more heat). If the metal is heated too much, the atoms oscillate too vigorously to stay at their fixed positions, they leave those positions and the structure break downs: the metal melts and turns into a liquid.

In essence, the metal radiator surface transfers heat from its atoms to surrounding air molecules by physical contact. The heats is conducted from metal radiator to the air in contact with it. This is conduction.

(ii) Convection, in this case, works like this. The radiator fins are vertical. They heat the air in contact with the metal fin surface. The air becomes hotter, it expands, and becomes lighter. So it goes upwards (like in a fire, when the air heats up, it runs upwards so the flames are always oriented upwards and the gases run upwards). When the heated air goes upwards, it carries heat away from the radiator. The cold air at the bottom, under the radiator, is sucked between the vertical fins, and is now heated, goes up etc. The hot air in the room loses heat to other objects, cools down and falls to the bottom of the room just to be re-sucked between the fins, reheated, and this goes on, and on. The air thus circulates. This is known as free or natural convective heat transfer.

(iii) Radiation. Well, any object at any temperature emits radiation, as described by the Stefan-Boltzmann law. The emitted energy is proportional to T^4 (T=temperature). As the surface temperature rises, obviously, the more radiation leaves that surface. Since the radiator surface has a higher temperature than its surroundings (the walls and objects in the room, that also radiate heat), it radiates more heat away, than it receives from the surroundings. Actually, radiative heat exchange happens all the time, between all the objects everywhere. The radiator loses much more heat, since T^4 rises quickly as T rises. Therefore, the net effect is that it loses heat to objects and walls in the room. It, thus, also heats the room by radiation.

Modified once, last modified by Braniac on Fri 1st June, 2012 @ 19:51

Fri 1st June, 2012 @ 18:59

this is a great start for me thank you (don't be sry). I am trying to find the SHC but not been too successful on that. I found that water has a SHC of 4810 J/kg/degree C. I am not sure if this is right. please let me know if it is wrong.

Fri 1st June, 2012 @ 19:52

No idea :)

Fri 1st June, 2012 @ 19:58

You need to press 'Start'.

Fri 1st June, 2012 @ 20:05

Yep, and then turn it up to max until ur burning hot... then you can go and open your window until your parents say 'CLOSE THE WINDOW! WE'RE NOT PAYING TO HEAT THE GARDEN!'

:D

Sat 2nd June, 2012 @ 09:20

you then say: ' SHUT UP, I'M TRYING TO REVISE' (regardless of whether you actually are or are jst chatting to people on the GR discussions)

;)

Mon 4th June, 2012 @ 10:09

beelal wrote:

well the liquid must be a good conductor of heat. Radiators work by a heating element which heats the water and becuz of convection currents the hot water rises, then it cools and then drops and the process continuess. ()u probably know the details of this). The liquid must not be too viscous becuz it wuld take ages too heat and it must not be the opposite (not viscous at all) becuz then it culd build up pressure if it turns to a gas.

water = 4.2 J/g

glycerol = 2.38 J/g

olive oil = 1.97 J/g

sorry i havent been much help but if i find more i will post it up immendiately = D

**

I see the question pertains to a common house radiator. Its design is such as to maximize the contact surface between air and the radiator body. Hence the thin and numerous fins.

(i) Conduction is a direct-contact transfer of heat from a region of higher temperature to a region of lower temperature. Your radiator is hot, so it heats air which surrounds it because the air is colder. The air is in contact with radiator surface, and the radiator is designed so as to have a maximum contact surface to transfer heat more efficiently.

Heat energy in a gas is, actually, in the speed the gas molecules move around: the hotter the gas is (the more heat there is), the faster its particles move. The total kinetic energy of its particles is the total heat in it. When hotter gas comes in contact with a colder one, the faster molecules collide with the slower, and they lose speed, while the slower ones gain speed. Thus, they lose kinetic energy (Ek=m*v^2/2), which the slower ones get. Macroscopically, the hot gas cools down, while the cold gas heats up.

In solids and in liquids, the situatuon is more complicated. For example, in metals, there are atoms in crystal structures, and they do not move around freely, but rather they oscillate around fixed positions. The more vigorously they oscillate, the more energy they have, the hotter the metal (more heat). If the metal is heated too much, the atoms oscillate too vigorously to stay at their fixed positions, they leave those positions and the structure break downs: the metal melts and turns into a liquid.

In essence, the metal radiator surface transfers heat from its atoms to surrounding air molecules by physical contact. The heats is conducted from metal radiator to the air in contact with it. This is conduction.

(ii) Convection, in this case, works like this. The radiator fins are vertical. They heat the air in contact with the metal fin surface. The air becomes hotter, it expands, and becomes lighter. So it goes upwards (like in a fire, when the air heats up, it runs upwards so the flames are always oriented upwards and the gases run upwards). When the heated air goes upwards, it carries heat away from the radiator. The cold air at the bottom, under the radiator, is sucked between the vertical fins, and is now heated, goes up etc. The hot air in the room loses heat to other objects, cools down and falls to the bottom of the room just to be re-sucked between the fins, reheated, and this goes on, and on. The air thus circulates. This is known as free or natural convective heat transfer.

(iii) Radiation. Well, any object at any temperature emits radiation, as described by the Stefan-Boltzmann law. The emitted energy is proportional to T^4 (T=temperature). As the surface temperature rises, obviously, the more radiation leaves that surface. Since the radiator surface has a higher temperature than its surroundings (the walls and objects in the room, that also radiate heat), it radiates more heat away, than it receives from the surroundings. Actually, radiative heat exchange happens all the time, between all the objects everywhere. The radiator loses much more heat, since T^4 rises quickly as T rises. Therefore, the net effect is that it loses heat to objects and walls in the room. It, thus, also heats the room by radiation.

thank you soo much I have done the first 2 questions and i'm nearly finished the 3rd.. :)

Thu 28th February, 2013 @ 09:03

Hhahahahahahaha

Thu 28th February, 2013 @ 09:04

I speak no English HAHA