-+-+-+-+ One cold windy morning, my granddaughter, Eleanor, is taken to the park for fresh air in her stroller. As a top cover, there is a blanket, a quilt and a cotton sheet. Should the blanket be at the bottom or top to minimize heat loss from the body? Does it matter?.
Suppose all three covers overlap. I will briefly address the tent configuration at the end.
In the picture above you see a baby wrapped in a blanket, quilt and a sheet. We assume the existence of a small air gap between the layers. We can express the heat transfer problem graphically as follows:
![](https://substackcdn.com/image/fetch/w_1456,c_limit,f_auto,q_auto:good,fl_progressive:steep/https%3A%2F%2Fsubstack-post-media.s3.amazonaws.com%2Fpublic%2Fimages%2F7472a565-8563-49df-bef8-4a5a3adf33ba_899x410.png)
The heat flows from the body to the outside air by passing through the layers. The amount of heat loss is directly proportional to the temperature difference (eg T2-T1) and thermal conductivity (k1) of each layer and inversely proportional to the layer thickness (t1). We can write the heat transfer equations for unit area as follows:
The heat flow through the blanket:
Through the air gap between the blanket and the quilt:
Through the quilt:
Air separation between the quilt and the cover sheet:
Heat flowing through the cover sheet:
The heat removed by the wind:
Here h is the heat transfer coefficient and it varies with wind speed.
Notice that in all equations, the heat flow is expressed with the same letter, q, because the heat transferred from the body to the blanket and the heat given to the wind at the top must be the same. Otherwise, the heat will accumulate in a layer and the temperature of that layer will rise abnormally.
If we solve all of these equations for q:
The denominator is not tied to any order. So, the order of the layers doesn't matter.
Whether the blanket is at the bottom or the top, the heat loss is the same.
Tent configuration
If you use one of the covers as a windbreak tent, then choose the thinnest layer for this job. The main effect of the tent is to cut the wind, which has nothing to do with conductive thermal resistance. Those layers with the highest thermal resistance, ie t/k ratios, must be placed on the baby..
Happy grand daughter to have a caring engineer granddad! :))))
I am justified in keeping the cutest layer on top then. Great post