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I have one question regarding total heat losses from water surface. Water is heated with immersion heater in open condition in a room. Heat losses from the top of the pan to air is to be calculated. And basically three mechanisms of heat transfer viz. by convection, evaporation and radiation is associated with it. (Conduction through walls negligible, insulated from sides). So my question is can I consider following combinations.​

  1. Both convection and evaporation along with radiation.
  2. only evaporation and radiation.
  3. only convection and radiation.

And what will be the exact formula for evaporation heat loss if considered. **water is heated in room.

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3 Answers 3

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Under atmospheric conditions , the most important heat loss mechanism is convection as this involves the physical medium , which is air. That is the most abundant element in a room atmosphere. Conduction needs to be considered if the physical solid material area is significant. Radiation in most cases is not very relevant in local conditions. It is however important when you oversee even the medium of heat transfer to compute the heat transfer anyways.

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Since it is being heated by an immersion heater,so convection process is must along with radiation which increases with the increase of temp.but since surface area is not so large,evaporation process can be neglected, i think. Let me know what you think.

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  • $\begingroup$ Heating of water is done in a 64 mm dia open cylinder within temperature range of 50-60 deg C and cooling is done simultaneously from top of the cylinder i.e. heat losses to air. The question is that Should I consider convection and radiation only or consider evaporation also along with convection and radiation to calculate total heat loss from the water surface. $\endgroup$
    – Ruchika Bakshi
    Commented Mar 19, 2015 at 18:31
  • $\begingroup$ Since the surface area of the vessel is not that large so evaporation needn't be considered,though i have not done the maths... $\endgroup$
    – Avisek
    Commented Mar 20, 2015 at 11:52
  • $\begingroup$ Thanks for your valuable answer. You means I have to consider only convection and radiation only. Consideration of evaporation is not required. $\endgroup$
    – Ruchika Bakshi
    Commented Mar 22, 2015 at 8:38
  • $\begingroup$ That's what i think.. :) $\endgroup$
    – Avisek
    Commented Mar 22, 2015 at 15:35
  • $\begingroup$ Ok thanks for ur last answer. I have One more question. If I supply heat of rate 10W to water of mass 250g and initial temperature of water is 29 degC then what will be the final temperature of water when steady state is reached. **Water is heating in open pan. $\endgroup$
    – Ruchika Bakshi
    Commented Mar 31, 2015 at 6:51
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It's good to consider both radiation along with conduction and convection. Evaporation is also in a way convection only as it happens through the medium of heat transfer. In your case , please give maximum attention to convective heat transfer for all practical purposes. If you are working on a practical design problem , then also consider radiation and conduction mechanisms and also include a degree of safety or tolerance.

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