Temperature of shipping container

[woody726]

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.

 

[dauto]

• 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

 

[SteamKing]

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.

 

[woody726]

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).

 

[sardar]

Calculating the surface temperature of a shipping container's roof over 24 hours can be a complex task, as it involves many variables such as weather conditions, sun exposure, and the contribution of the inside of the container. One approach to accurately calculate the surface temperature would be to use an energy balance equation, which takes into account the heat transfer between the container and its surroundings.

However, as you have mentioned, the contribution of the inside of the container can cause discrepancies between the calculated and measured values. This is because the inside of the container is an additional heat source that may not be accounted for in the energy balance equation.

To address this issue, you could try to estimate the heat flux from the inside of the container and incorporate it into the energy balance equation. This can be done by considering factors such as the temperature inside the container, the type and amount of goods being shipped, and the insulation properties of the container.

Another approach could be to use a more detailed model that takes into account the geometry and material properties of the shipping container. This can provide a more accurate representation of the heat transfer processes occurring on the container's surface.

Additionally, it may be helpful to validate your calculations by comparing them to measurements taken at different time intervals throughout the 24-hour period. This can help identify any discrepancies and refine your calculations.

In conclusion, accurately calculating the surface temperature of a shipping container's roof over 24 hours requires a comprehensive understanding of the heat transfer processes involved and careful consideration of all relevant variables. By incorporating the inside of the container and using a detailed model, you can improve the accuracy of your calculations and better understand the temperature dynamics of the shipping container.