Why do thermos cups with different mouths and capacities have different heat preservation durations?

Many friends are very concerned about the insulation market of the thermos when buying a thermos cup. They hope that the insulation market of the thermos cup will last as long as possible. http://www.zhanyict.com/While it is convenient for them to use, it also shows that the quality of the thermos cup is better. But some friends have raised questions.

Why are the insulation markets of different shapes of 500 ml thermos cups so different? Are there any standard requirements? Today, the editor will tell you why the mouth diameter of stainless steel thermos cups with the same capacity is an important factor affecting the insulation time of the thermos cup. http://www.zhanyict.com/Also, why do thermos cups with similar shapes and similar mouth diameters have longer insulation time when the capacity is larger?

Speaking of the length of heat preservation time, the editor will popularize the structure of the thermos cup. The most common thermos cup is made of stainless steel, with a double-layer structure and vacuum processing. A water cup with an opening and closing. http://www.zhanyict.com/Usually the shape of the thermos cup is cylindrical, with the top, that is, the mouth, open, equipped with a plastic or metal cup lid for sealing, and the bottom and the cup body are all designed with a double-layer vacuum.

The double-layer vacuum design can well isolate the temperature inside the cup from being transferred to the outside, forming a heat preservation function in principle. However, since the mouth of the cup is open, the heat will dissipate upward from the mouth of the cup. http://www.zhanyict.com/Although it is sealed with a cup lid, the heat will continue to dissipate outward during use and due to the limitations of the cup lid structure, so the heat preservation time of the thermos cup is limited. Then the speed of heat dissipation is closely related to the diameter of the cup mouth.

The formula for how much heat water dissipates per hour is:

Q=a(tw-to)FQ=a(tw−to)F

Where Q is the heat dissipation (unit: W), tw is the surface temperature of the heat dissipation surface (°C), to is the ambient temperature (°C), F is the area of the heat dissipation surface (m^2), and a is the comprehensive heat transfer coefficient (w/(°C×m^2).

From the formula, we can see that the larger the heat dissipation area, the more heat will be dissipated per hour, and the faster the temperature in the water cup will drop. http://www.zhanyict.com/So if you need a thermos cup with good heat preservation performance and a long time, you should choose a small mouth diameter under the same capacity. The smaller the diameter, the longer the heat preservation time.

Why is it that thermos and water cups have similar structures, although the diameters of the cup mouths are similar, the larger the capacity, the longer the heat preservation time?

Please look at this formula:

Q = mcAT

This is the water heat calculation formula. Q represents the water heat, in joules (J) or calories (ca). m represents the mass of water, in grams (g) or kilograms (kg). c represents the specific heat capacity of water, in joules/gram•degree Celsius (J/g:℃) or calories/gram•degree Celsius (cag:℃). http://www.zhanyict.com/AT represents the temperature change of water, in degrees Celsius ('C).

From this formula we can see that the greater the mass of water, the more heat it contains. Therefore, the volume of a large-capacity water cup increases and its mass also increases. http://www.zhanyict.com/Therefore, under the condition of similar heat dissipation area, naturally, the water cup with a larger water capacity will keep warm for a longer time.