It is not direct sunlight that is melting your ice mate. Let’s say the scoop has 10 cm² getting blasted from the sun, that’s 1 Watt of heat under maximum possible conditions (Sun vertically above you, perfectly black ice, etc.).
tl;dr:
In total from convention 1.8 W and condensation 2.5 W and radiation 0.65 W = 4.95 W -> maximum possible sunlight on earth would only increase this by 20 %, more realistic sunlight something like 10 %.
Actual math:
Compare that to ambient temperatures of say, 30 °C, and let’s again say 10 cm² cross section, which translates to a diameter of 3.57 cm, so a sphere with a surface of 40 cm². The heat transfer coefficient under normal conditions is about 15 W/(m²K), so we get:
15 W/(m²K) * 0.004 m² * 30 K = 1.8 W
Additionally, we have latent heat from water (humidity) condensing on the cold surface:
Let’s assume a Schmidt number of 0.6, so we get a mass transfer coefficient of:
15 W/(m²K) / [1.2 kg/m³ * 1000 J/(kgK)] * 0.6^(-2/3) = 0.0176 m/s
Specific gas constant:
8.314 J/(molK) / 0.018 kg/mol = 462 J/(kgK)
So the mass flux (condensation speed) is:
0.0176 m/s * 2000 Pa / [462 J/(kgK) * 273 K] = 0.00038 kg/(m²s)
Given the heat of condensation of 2257 kJ/kg water we thus get:
0.00038 kg/(m²*s) * 2257000 J/kg = 632 W/m²
And thus for our little sphere:
632 W/m² * 0.004 m² = 2.5 W
… Then we also have radiation from the hot surrounding, let’s assume 30 °C again, we get:
Q = 5.67E-8 W/(m²*K^4) * 0.004 m² * (303 K^4 - 273 K^4) = 0.65 W (omitting radiation from the sky)
JohnDClay@sh.itjust.works 1 week ago
So made this meme is eating ice cream when it’s below or near freezing? Because you still get ice melting below freezing due to radiation.
Eheran@lemmy.world 1 week ago
Yes, while the radiation puts more energy in than the convective etc. cooling removes. So near 0 this is guaranteed, since the temperature difference from ice to ambient is almost 0 while radiation keeps pumping in something like 0.5 W. But who eats ice at freezing temperatures… And outside?
CrazyLikeGollum@lemmy.world 1 week ago
I have eaten ice cream outside when temperatures were sub-zero Fahrenheit. It’s not something I do regularly but it’s happened and will probably happen again.
If I want ice cream, then I want ice cream. No other considerations matter.
Eheran@lemmy.world 1 week ago
Alright then. But at 0 °F it is not going to melt without your intervention, no matter how sunny it is.