Calculating Temp Difference in a hot water tank

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Discussion Overview

The discussion revolves around calculating the temperature difference between the bottom and top of a hot water tank, considering factors such as tank dimensions, heat input, and time. The context includes assumptions of no heat loss and the dynamics of heat transfer in a closed system.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant seeks to calculate the temperature difference using variables like tank height, diameter, actual temperature, and time, assuming no heat loss.
  • Another participant requests clarification on whether the problem is homework or self-study and what specific subject it pertains to, such as heat transfer methods.
  • A participant describes a central heating system using a copper coil to heat water in a sealed tank and questions the expected temperature difference between the top and bottom of the tank.
  • One participant argues that if there is no heat loss, the water should theoretically be at the same temperature as the coil, suggesting that temperature differences arise only with heat loss.
  • Another participant expresses uncertainty but suggests that circulating hot water through the coil would eventually lead to a uniform temperature throughout the tank at steady state.
  • A participant questions the initial temperature of the water before circulation and speculates on the chaotic nature of convection currents, indicating that determining the temperature difference solely from a bottom sensor may be challenging.

Areas of Agreement / Disagreement

Participants express differing views on whether a temperature difference can exist without heat loss, and there is no consensus on how to approach the calculation of temperature differences in the context provided.

Contextual Notes

Assumptions regarding uniform initial temperature, the nature of convection currents, and the impact of time on temperature distribution remain unresolved. The discussion does not clarify the specific heat transfer mechanisms involved.

Alan A
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I want to calculate the difference in temp between the bottom & top of a hot water tank,
Presumably the height of the tank, the diameter, the actual temp and time would be the variables. I will assume no heat loss. The heat input would be at the base of the tank.
 
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More information is needed to answer the question. Is this a homework or a self-study problem? Is it from a textbook, and if so what subject does this section of the book deal with (i.e., heat transfer by conduction? Convection? Other?)
 
I have a central heating system which passes hot water in through a copper coil pipe to heat water in a sealed tank. The warm water rises naturally with no mechanical agigitation. My question is if the coil is at the bottom of the tank what is the approx difference between the temp at the bottom of the tank and that at the top. The tank is approx 50cm diam and 1.3 m high. Let's assume no heat loss for the tank. Obviously time will be a factor
 
It seems to me if there is no heat loss from the system, all the water would have to be at the same temperature as the coil. It is only if there is a heat loss that there would be a temperature difference. Am I missing something here?
 
Thank you for your reply. I really don't know very much but imagine that if you circulate hot water through a coil at the bottom of a tank that heat will be passed to the surrounding water and will rise to the top. Only when the system has reached a steady state will both temperatures be the same at the top & bottom of the tank. The application is if I have a temperature probe at athe the bottom of the tank what will be he temp difference at the top?
Thanks
 
Can one assume that before water is circulated through the coil, the water is uniformly at ambient temperature? Then at the instant hot water is first circulated through the coil, presumably warmer water would begin rising from the coil. Without any heat loss I don't know if there would be any convection currents or how they would flow. My guess is that they would be chaotic. It sounds like you are asking what the temperature difference would be at some time after heat is applied to the coil. To deduce the temperature at the top of the tank solely from a sensor at the bottom of the tank I think would be next to impossible.
 

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