Mr. Rajesh, as you know, the dew formation in early morning hours, rain and fog formation inside a car window glass during raining etc. are examples of condensation of water vapour in atmospheric air. In these cases also the principle of condensation is one and the same but the process is so complex due to the simultaneous change in total pressure (ambient pressure), partial pressures, temperature, air velocity etc.

Take for example the dew formation in the early  morning hours. During night the temperature of atmospheric air (a mixture of gases and water vapour) decreases due to heat transfer from it to the surrounding objects. The decrease in temperature is associated with an increase in relative humidity or partial pressure of water vapour in air. When a certain lower temperature is reached the relative humidity will be equal to 100%. Any further heat transfer from air do not (cannot also) lower the temperature of air but phase change of water vapour to liquid water (condensation) begins. Any further decrease in air temperature occur only when all the water vapour in air condenses to liquid water. Therefore, the enthalpy of condensation is transferred to the immediately surrounding air particles and further transferred to other objects including space.

Thus, the condensate is not sharing any part of the latent heat and it can be better said that heat is not released during condensation instead it is being taken off to force condensation.

Based on condenser interaction area with atmospheric air. It cannot be less than atmospheric air. In some cases it may reach to atmospheric temp. when heat transfer area is more than what it is required.

@ venkatesh, thanks for the update. So you mean to say that the heat released will be taken up by the condensate itself, which makes its temperature higher than surrounding air. Can you give me a better insight, i mean what is the physic behind this.

If I understand the question correctly, you want to condensate some gaseous substance. Thereby the condensation enthalpy will be available to the surrounding. That could result in a temperature rise, but, in my eyes, only if you have are below the condensation point of that substance. If you condense without subcooling any rise in temperature would result in a partial evaporation as the condensation temperature will be exceeded as you would already be at the temperature. Therefor I would say, the temperature will stay at condensate temperature and any excess energy will be taken up by partial evaporation until an equilibrium is reached. 

As for pure substances like water is concerned, condensation (changing from gaseous to liquid phase) take place at constant temperature. The heat released by the condensation process (latent heat) will be taken away by the cooling medium. If the latent heat is not fully taken off phase change or condensation won't happen completely. If some additional cooling is provided, it is technically called under cooling in which case the final temperature depends on the temperature of the cooling medium and the lowest temperature that can be achieved (theoretically) is the that of the cooling medium. But, among other factors the actual temperature depends on the heat exchanger effectiveness also.

I guess RKK is right.

@ Niels, thanks for the update. But I am bit confused, according to you, the excess energy will be utilized for partial evaporation. Since the latent energy remains the same whether the transformation is from liquid to gas or vice verse, this process continues right. I mean condensation, energy again used for evaporation and so on. Of course neglecting entropy loss. So can you provide a better insight.  

Again thanks for your time, appreciated. 

@ Ramachandran  @ Sunil  , thank you for the info. But I doubt, why is it that the heat released is taken up only by the cooling medium. Because at the interface both phases co-exit, why is it not shared. It would be kind of you if you could throw more light on this.

Thanks for your time, appreciated.

I am making this discussion and also made the previous one with the assumption that the pressure remains constant.

Dear Mr. Rajesh, at the point of condensation both the liquid and gaseous phases exist in equilibrium at the same temperature and pressure. It should be noted that the process of condensation is not activated by the system internally. In fact certain degree of under cooling is required to initiate the formation of liquid molecules. The atoms in the gaseous state is having higher free energy when compared to the liquid state.So at the condensation temperature the free energy change is zero. in order to create a driving force for condensation, therefore, some under cooling (lower temperature than the boiling point) is to be created. Once the nucleation of liquid crystals is started even at a lower temperature difference, the process of condensation continues by taking away the excess free energy from the system.

In actual condenser heat exchanger the cooling temperature will be much less than the minimum under cooling requirement. The condensing fluid nearer to the tube walls get condensed by transferring heat to the surrounding cooling fluid and try to get sensible cooled, also. The inner gar molecules transfer heat to the nearby condensed molecules and the process continues. 

In fact there is no heat release as in exothermic chemical reactions, but heat is taking away artificially from the system to condense.

@Ramachandran, thank you sir, it makes sense. 

Condensation of a vapour occurs at constant temperature (as Ramachandaran K K mentioned). Condensation happens at the equilibrium between the vapour and liquid phases. Any sub-cooling of the condensed liquid is achieved by further cooling in a separate heat exchanger. For example, when steam is condensed at the extraction of a turbine in a condenser any decrease in temperature of cooling media would affect the extraction temperature, i.e. a new equilibrium condition happens, but notice that equilibrium is always maintaned. 

At a given pressure/temperature condition, the heat released from condensing a gaseous substance (i.e., cooling) will be transferred to the cooling medium (heating) - the heat sink (e.g., condensing unit of a vapour compression system).

@ Matt, thanks for the info.

@ Boukhanouf, thanks for the info.

While it is possible to have a system that is not in equilibrium for a time, it will eventually reach equilibrium. Condensation will not occur in a system at equilibrium unless there is energy leaving the system (i.e., negative heat transfer). By the way, if you are dealing with water condensing in air and want the highest accuracy, you should be aware that there are numerous errors in the literature related to the properties of moist air.  The original data trace back to Hyland & Wexler, who worked for the National Bureau of Standard (NBS), which is now called the National Institute of Standards and Testing (NIST). The tabulated values in the recent editions of the ASHRAE Handbook of Fundamentals are correct, but the equations are wrong. If you put the equations in Excel and calculate the table, you will find that the values don't match. These errors go back for decades, in which errata were issued which fixed some errors but introduced new errors. NIST has lost H&W's original documents, but there was a copy in the archives at the Library of Congress. Several years ago a colleague, Al Feltzin, went to the LOC and made a photocopy of the original data, which matched the tabulated data, not the equations. The table has since been updated, but the equations are still wrong. Do not use the saturation pressure of water vapor over water liquid when calculating the properties of water vapor in air. It's not the same. The equations in the ASHRAE handbook for enthalpy are also wrong. Again, use the table, which doesn't match the equations.

@ Dudley, thanks for the updates.

 If we treat Air as heat sink,  by definition of heat sink , It can absorbs amount of energy without changing its temperature.Take example of cup of hot coffee in surrounding  ,eventually  cools without changing temperature of surrounding .same thing happens with the bottle of cold water . During phase change process,steam is condensed into water, sufficient amount of energy released  to make hydrogen bond or water molecule. There will not be fall or rise in temperature during this bond formation. It takes time to recover all water molecule . Once all hydrogen bond in water molecule has formed , It will show fall in temperature provided that water temperature is greater than Air temperature or atmospheric temperature

@ Somanath, Thanks for the info. Whatever you said is applicable if you consider the whole system. But at the interface or at the point of condensation, the heat of condensation do alter the temperature. I am curious to know which medium takes this heat at that instant of time, ambient air or the condensate formed.

Hello Rajesh. How are you?

During condensation you there is a periodic heat transfer. As the most clear example , I mean the refrigeration cycle in a refrigerator shows us , the heat produced by compressor loses it`s heat right after entering  the condenser. Although the amount of transferred heat depends on the condensate or refrigerant that you are using , but you will absolutely have heat transfer between condenser and environment(Air). In most condensation terms , lots of amounts of the heat is transferred from condenser(system) to the environment which can be air or water according to the system. It aslo depends on the system and the environment that you choosing to do your project or solve your problem. In the closed systems for example a condensing unit of an air-conditioner we use a fan to force the heat to go out.

I think that first of all you must pay attention to what you choose at environment and system.

Good luck.

For the first part, simply no. The energy released must be removed by a heat sink, i.e. by cooling, which was already said in contributions further up.

@ Ali, thanks for the update.

@ Ferdinand, thanks for the info.

I would try to find professor Jim Braun's work from Purdue University on cooling coil algorithms. That may give you the answer.

Hi Rajesh

During phase change, yes, energy transfer accors as enthalpy of the stream decreases. this energy is absorbed by the secondary (cooling) condesner flow, obviously. But sth interesting regarding phase change, for instase in air-source heat pumps, input work to our system is 1 unit, but output heat is for example 3 units, the other two iunit comes from phase change which cannot be shown in energy flow diagrams llike Sankey diagram. Lets discuss if you have questions.

All the best

Reza

@Fred, thanks for your time, it might help me.

@ Reza, i got your point. But my actual question was, if condensation happens in atmosphere. Whether the energy released during condensation is taken by the condensate or the air surrounding it. If it is carried by the condensate, its temperature goes up. I would like to now the physic happening at the very instant of condensation.

By the way thanks for the info.

Hi Rajesh,

Can you describe your problem little bit. If it is condensation inside the heat exchanger the condensate will have a higher temperature as the cooling fluid (e.g. air). In case of humid air the temperature of the air and the condensate should be the same, but it depends on the reason of the condensation (temperature change, pressure change or contact with the cold surface).

@ Jiri, thanks for the info. I am just curious to know, during any condensation process what happens to the latent heat released. Or indirectly will the temperature of the condensate increase after condensation, assuming that the heat is taken up by the condensate. Or is it the other way around, i.e. surrounding air temperature goes up, by absorbing the heat released. Or is it like the heat released will be shared among the surrounding air and the condensate.

In short i would like to know energy balance at the very instant of condensation.

Hope this gives you a picture.

@ Rajesh

In my opinion. If the latent heat is absorbed by the condensate it will evaporate again. The heat can be only transferred to the surroundings and there must be some temperature difference to do this. In other words the amount of condensate corresponds to the heat transferred to the surroundings.

Have a nice time

Jiri

Mr. Rajesh, as you know, the dew formation in early morning hours, rain and fog formation inside a car window glass during raining etc. are examples of condensation of water vapour in atmospheric air. In these cases also the principle of condensation is one and the same but the process is so complex due to the simultaneous change in total pressure (ambient pressure), partial pressures, temperature, air velocity etc.

Take for example the dew formation in the early  morning hours. During night the temperature of atmospheric air (a mixture of gases and water vapour) decreases due to heat transfer from it to the surrounding objects. The decrease in temperature is associated with an increase in relative humidity or partial pressure of water vapour in air. When a certain lower temperature is reached the relative humidity will be equal to 100%. Any further heat transfer from air do not (cannot also) lower the temperature of air but phase change of water vapour to liquid water (condensation) begins. Any further decrease in air temperature occur only when all the water vapour in air condenses to liquid water. Therefore, the enthalpy of condensation is transferred to the immediately surrounding air particles and further transferred to other objects including space.

Thus, the condensate is not sharing any part of the latent heat and it can be better said that heat is not released during condensation instead it is being taken off to force condensation.

@ Ramachandran Sir, thanks for the update. This makes sense..... thanks a lot. 

@ Jiri, thanks for the update.

Typically, the condensate is at a temperature lower than ambient temperature. To check - Experiments on the precipitation of the dew point at the mirror cooling. This experiment shows that the temperature of water vapor condensation on the mirror during cooling is different from the temperature of the condensation to disappear when it is heated. Next - think for yourself, experiment.

The condensation is a exothermic process in which heat energy is lost; so the condensate has a lower temperature than the surrounding air.

It depends on the temperature limits of the fluids.  You got to consider the sub cooling at the inlets and outlets.  Pl re-check the properties of the fluids and the working pressures.  Dr.S.Ravindran

@ Vyatcheslav, thanks for the update

@Francisco, thanks for your time.

@Ravindran, thanks for your update.

Check the Dew Point of the Fluid concern

@Mohamad, thanks for the update.

The temperature of the air drops as it ejects heat to the surroundings. In this process, if the temperature of air decreases to dew point temperature condensate is formed. The condensate formed if is surrounded by much lower temperature then the the temperature of condensate tend to decrease further. There is a energy release causing the condensate to form. So if there is scope of increase in the temperature of condensate because of external sources, it can retain as condensate for an instantaneous time if there is considerable change in the partial pressure its got. So, yes its possible sometimes for the condensate to

have a higher temperature than the surrounding air.

Rajesh Alayil,

As I understand, you are interested in Condensation, Ref & A/c, phase change, heat transfer and you are from IIT, Chennai.

It will be good, if you can define your system in a better manner.

1. If your question is about the air cooled Condensers of Ref and / Ac units, you can check a refrigeration cycle. Heat will be lost by the vapour from compressor (possibly 65 to 75 deg C), to cooling air (possibly 20 to 40 deg C). For the heat transfer to take place between the condensing vapour and cooling air. Naturally, after Condensation and little subcooling, condensate will be at a temperature higher than the cooling air. Temperature of condensate and cooling air will be equal only if the condenser is very large in heat transfer area.

2. If your question is about dew formation, estimate the dew point. Dew point will be less than dry bulb temperature. If you collect the condensed water in a vessel, steady state will occur with air, that is, equal temperature with air.

Dr.S.Ravindran