Heat capacity of a heating element, in a flow of air

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Discussion Overview

The discussion revolves around calculating the heat capacity of a heating element within a flow of air, considering varying flow rates, inlet temperatures, and heater power. Participants explore the relationship between these variables and the heat capacity of the heater matrix.

Discussion Character

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

Main Points Raised

  • One participant questions whether it is possible to calculate the heat capacity of the heater matrix using inlet and outlet temperatures, power, and flow, while assuming no heat loss to the pipe walls.
  • Another participant requests a more detailed description of the configuration and clarification on what is meant by the heat capacity of the matrix.
  • Several participants express a desire to determine the heat capacity of the heater and the resulting temperature.
  • A reference is provided that relates power to temperature differential, flow volume, air density, and specific heat, noting that specific heat can vary with water vapor content in the air.
  • Concerns are raised about the behavior of the heater element when air flow decreases, including the risk of overheating and melting, and the role of safety thermostats in preventing this.
  • One participant points out that the initial post implies that certain variables are known, prompting a request for clarification on what is given and what needs to be calculated.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus, as there are multiple competing views on how to approach the calculation and what factors should be considered.

Contextual Notes

Limitations include assumptions about heat loss, the need for clarity on the configuration, and the influence of varying specific heat due to humidity in the air.

Who May Find This Useful

Individuals interested in thermodynamics, heating systems, and fluid dynamics may find this discussion relevant.

James125
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Air is flowing through a pipe, through a heater matrix.

Flow, Inlet temperature and heater power vary. Is it possible to calculate the heat capacity of the matrix by using the Inlet & outlet temperatures, power & flow?

I'm assuming no heat loss to the pipe walls to make it easier, but I'm not sure how to do this.
 
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Please describe the actual configuration more completely and explain what you mean by heat capacity of the matrix .
 
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I want to work out the heat capacity of the heater and thus the temperature that it will be.

Heating.png
 
James125 said:
I want to work out the heat capacity of the heater and thus the temperature that it will be.

View attachment 211151
Reference from Engineering Toolbox
Power = temperature differential * flow volume * air density * specific heat. Keep in mind that specific heat is influenced by how much water vapor is in the air.

Also, consider that happens to the heater element when air flow falls below a certain point - surface temperature climbs as flow decreases - flow too low, and the element melts. To prevent this, electrical resistance space heaters often incorporate a safety thermostat clamped to the element surface.
 
James125 said:
I want to work out the heat capacity of the heater and thus the temperature that it will be.

View attachment 211151
Sure. Your opening post implies all of those are given though. So what is given and what do you want to calculate?
 

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