Temperature of shipping container

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    Container Temperature
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Discussion Overview

The discussion revolves around calculating the surface temperature of a shipping container's roof over a 24-hour period, incorporating various weather and solar parameters. Participants explore the complexities of energy balance equations and the influence of the container's contents on temperature measurements.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant seeks to calculate the surface temperature using an energy balance equation but notes discrepancies between calculated and measured values due to the influence of the container's interior.
  • Another participant requests clarification on the assumptions made in the model, emphasizing the importance of understanding the model to provide effective assistance.
  • A third participant highlights the potential for hazardous materials within containers to affect calculations, suggesting that treating the container as a 'black box' may limit the accuracy of the model.
  • The original poster clarifies that the container is empty and describes their model, which includes factors like solar absorption, longwave atmospheric irradiance, and convection, while expressing uncertainty about the impact of the container's interior on the temperature calculations.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of accurately modeling the temperature of the container's roof, particularly regarding the unknown effects of the container's contents. There is no consensus on how to account for these factors in the calculations.

Contextual Notes

The discussion reveals limitations related to assumptions about the container's contents and their impact on heat absorption, as well as the complexity of accurately modeling the energy balance without complete information.

woody726
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How do I calculate the surface temperature of a shipping container's roof over 24 hours? All weather and sun parameters are known and I use an energy balance equation, but the contribution of the inside of the container causes the calculated values (rise too fast) to differ from the measured ones.
 
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  • Can you give more details of what your assumptions are? How are we supposed to help you fix your model when we don't know anything about your model?
  • The unknown contentents of the containers will produce - well - unknown effect on the result
 
Sometimes, the contents of shipping containers have been known to ignite (see calcium hypochlorite). That could really throw off your calculations.

If you are treating the container as a 'black box' (where the contents are unknown), I don't know if it is feasible to construct a very accurate model, since you have no practical way to account for the heat absorption of the contents during the day.
 
The container is empty (air), and I use a model considering solar (shortwave) absorption, longwave atmospheric irradiance aborption, graybody emission from the container and convection. But the contribution of the inside of the container is what I am not sure of since currently the roof is considered simply as a sheet of metal. I assume net heat flux=0 for a given set of environmental parameters that are known for every minute over 24 hours: air temperature, solar irradiance, relative humidity, air pressure, wind velocity. The thermodynamic parameters for the container roof are also know: specific heat capacity (600 J/(kgK)), conductivity (50 W/(mK) ), density (7000 kgm-3), short (0.88) and longwave (0.9) absorption coeff, emissivity (0.88), and thickness (3mm).
 

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