Way To Test Thermal Insulation

[DaleSwanson]

So I go backpacking, often in winter. After a while you start to get interested in weight (since you are carrying everything on your back). I bought a kitchen scale and weighed everything, this showed some surprising results. I was thinking though, and if I am comparing two shirts and one is 10% heavier, but twice as warm than the heavier shirt is better, even though it's heavier. I decided I need to attach some sort of thermal insulation number to the items so I can compare weight/warmth ratios.

This is going to be harder than simply buying a scale, but I think I came up with a process to test this, and I'm looking for any input on what I can do differently before I invest the time to do it. What I am going to do is go in my basement, where the temperature is fairly constant (56-60F). Use a microwave to heat a liter water bottle (http://images.google.com/images?q=nalgene") to 100F (approximate body temp). Then put the bottle in an item and after a certain period of time test the temperature.

Here are some of the thoughts I had. First while 60F is pretty warm (I wouldn't be wearing any cold weather gear in 60F), it's still enough of a difference that I should be able to measure the cooling. Next, originally I had thought to measure time it would take to reach a certain temperature (say 90F). The problem with this is I don't have any temperature probe that would allow me to measure without taking the bottle out. I think the measuring after a set time will be more accurate. I know that when you are sleeping you lose most your heat to the ground, thus I want to avoid having the items sitting on anything. I plan on putting them on hangers, with some way to suspend the bottle inside. I plan on testing everything 3 times, doing everything once, then starting over and doing it all again. This way the item won't still have warmth from the last test, plus I'll be able to see if the slight changes in ambient temperature affect things.

Any suggestions, or comments? Can anyone tell me the formulas for estimating how long it will take to heat a liter of water in a microwave of X watts? Also how long it should take for a liter to cool down from 100F to 90F in 60F ambient air?

 

[eljose79]

Thank you for sharing your interest in finding a way to compare the weight and warmth of different clothing items for backpacking. I can appreciate your approach of using a controlled experiment to gather data and make informed decisions. I have a few suggestions and comments that may help you in your process.

Firstly, I would recommend using a digital thermometer with a probe to measure the temperature of the water bottle. This will give you more accurate and precise readings compared to simply touching the bottle to gauge its warmth. Additionally, you can use the thermometer to measure the ambient temperature in your basement, which will be important for your calculations.

In terms of testing time, I would suggest heating the water bottle for a set amount of time (e.g. 1 minute) and then immediately placing it in the clothing item. This will ensure that the bottle starts at the same temperature for each test. Then, after a set amount of time (e.g. 10 minutes), measure the temperature of the water bottle to see how much it has cooled down. This will give you a more consistent and accurate measurement compared to waiting for the water to reach a certain temperature.

To estimate how long it will take to heat the water in the microwave, you can use the formula Q = mcΔT, where Q is the heat energy, m is the mass of the water, c is the specific heat capacity of water, and ΔT is the change in temperature. You can look up the specific heat capacity of water online and use the mass of the water bottle (in grams) to calculate the heat energy required. Then, you can check the wattage of your microwave and use the formula P = Q/t to estimate the time it will take to heat the water.

To estimate how long it will take for the water to cool down, you can use the formula T = T0 + (T1 - T0)e^-kt, where T is the temperature at time t, T0 is the initial temperature, T1 is the final temperature, and k is a constant that depends on the specific heat capacity and surface area of the water bottle. You can look up the value of k for a water bottle of your size and shape and use the formula to estimate the time it will take for the water to cool down from 100F to 90F.

Finally, I would recommend testing each item multiple times and taking an average of the results for a more accurate

 

[astrokreng]

I appreciate your approach to testing thermal insulation and your consideration for weight and warmth ratios while backpacking. Your proposed method of testing the thermal insulation of different items by measuring the temperature of a heated water bottle inside them is a good starting point. However, I would recommend some adjustments and additional considerations to make your results more accurate and reliable.

Firstly, using a microwave to heat the water bottle may not be the most accurate method as microwaves heat unevenly and can create hot spots in the water. It would be better to use a more controlled heating source, such as a hot plate or a water bath, to ensure consistent heating of the water bottle.

Secondly, instead of measuring the temperature after a set period of time, it would be more accurate to measure the rate of cooling of the water bottle inside the item. This can be achieved by taking temperature readings at regular intervals (e.g. every minute) until the water bottle reaches a certain temperature (e.g. 90F). This will allow you to compare the rate of heat loss between different items and give a more accurate indication of their thermal insulation properties.

In terms of avoiding heat loss to the ground, you could consider using a suspended platform for the water bottle, rather than hangers, to minimize contact with any surface. Additionally, you could insulate the bottom of the platform with a material that is known to have good thermal insulation properties, such as foam or felt.

To improve the reliability of your results, I would suggest testing each item multiple times, as you have already planned, and also testing them in different ambient temperatures (e.g. 50F and 70F) to see how their thermal insulation properties vary in different conditions.

As for the formulas for estimating heating and cooling times, these can be quite complex and depend on various factors such as the wattage of the microwave, the initial and desired temperatures, and the thermal properties of the materials involved. I would recommend consulting a thermodynamics textbook or using an online calculator to determine these values accurately.

Overall, your proposed method of testing thermal insulation is a good starting point, but I would suggest making some adjustments and considering additional factors to improve the accuracy and reliability of your results. Good luck with your experiments!