How to calculate the time and distance needed to heat an object

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Discussion Overview

The discussion revolves around calculating the time and distance required to heat a small rubber object to a specific temperature. Participants explore various formulas and concepts related to heat capacity, heat transfer, and the practicalities of heating methods.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant mentions having a formula for heat capacity but seeks clarification on how to calculate the time and distance for heating the object.
  • Another participant explains that heat capacity is the amount of heat needed to raise the temperature by 1 degree Kelvin or Celsius and suggests using a water bath or oven for controlled heating.
  • A participant provides the formula q = mc (Tf-Ti) and questions whether the calculated 1100 Joules is needed to raise the temperature by 1 degree Celsius or to reach the desired temperature.
  • One participant proposes using Newton's law of cooling to estimate the time required to heat the object.
  • Another participant cautions that the formula for heat capacity is only valid if all energy goes into the object and notes the low heat conductivity of rubber, suggesting that heating must be done slowly to avoid overheating.
  • A participant introduces the 1-D heat equation using Green's functions and mentions Heisler Charts as an easier method for solving heat problems.
  • One participant emphasizes that the rate of reaching a uniform temperature depends on factors like the object's shape and surrounding conditions, and introduces the concept of the Overall Heat Transfer Coefficient (U) in heat transfer problems.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of Newton's law of cooling and the validity of the heat capacity formula in practical scenarios. There is no consensus on the best method to calculate the time and distance for heating the rubber object.

Contextual Notes

Participants highlight limitations such as the dependence on the shape of the object, surrounding conditions, and the need for accurate heat transfer coefficients, which complicate the calculations.

thepok
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Hi,

I have a small rubber object that I want to heat to a particular temperature. I have done some research and I have found a formula to determine the heat capacity that I need in order to reach the specified temperature.

However, the formula does not tell me :

1.) How long will it take to reach the temperature?

2.) What distance does the source of the heat need to be from the target of the heat?


I would like to know how I can calculate both 1 and 2?


Much appreciated,
--thepok
 
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What formula is that? Heat capacity of an object is the amount of heat that is needed to raise the temperature of the object by 1 degree kelvin (or celsius)

The easiest way of to get the right temperature would be to put in in a water bath, or oven with the temperature controlled by a thermostat.
 
willem2 said:
What formula is that?

q = mc (Tf-Ti)

It roughly came to about 1100 Joules

willem2 said:
Heat capacity of an object is the amount of heat that is needed to raise the temperature of the object by 1 degree kelvin (or celsius)

Are you saying that I need 1100 Joules in order to raise the temperature of the object with 1 degree celsius? Or does the formula mean that I need 1100 Joules in order to raise the temperature to the desired temperature?
 
It would seem that I could use Newton's law of cooling to calculate the time it would take to heat the object.

Can anybody please verify?
 
The formula is only valid if you can make sure that all your energy goes into the object that you want to heat, like heating a liquid in a thermosflask with electric current.
This is probably the only case where you can get an accurate answer.

One problem with heating a rubber object, is that the heat conductivity of rubber is
low, so you'll have to heat the rubber very slowly if you don't want to overheat the outside. Newton's law of cooling is probably not very useful, because it's valid for an
object that has a single temperature.
 
Last edited:
Remember the rate at which the object will reach a uniform equilibrium temperature is dependent on many factors.

One of which is the shape of the object

A rubber cube will take longer than a rubber strip that has the same mass (more surface area)

You need to determine the surrouding conditions and the heat transfer coefficients so as to get an estimate of the Overall Heat Transfer Coefficient (U). Q=UA[T-To]. So UA[T-To] = mCDT

Knowing the Heat Capacity which is simply a thermal property of the solid material is insufficient to answer your question.

Treat it like a standard heat transfer or heat exchange problem between two substances
1145382473_6fed16f624.jpg


and this may be a useful analogy
http://www.picotech.com/experiments/heat_transfer_coefficient/graphics/heat_der.gif
 
Last edited:

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