An aerospace thermal regulation system uses an organic phase-change gel to stabilize the temperature of sensitive satellite instrumentation.
Calculate the energy required by the cooling system to lower the temperature of 0.75 kg0.75\text{ kg}0.75 kg of the solid phase-change gel from 25∘C25^\circ\text{C}25∘C to −15∘C-15^\circ\text{C}−15∘C.
Assume the specific heat capacity of the solid gel is 1800 J/(kg ∘C)1800\text{ J/(kg }^\circ\text{C)}1800 J/(kg ∘C).
Energy=………………………… J\text{Energy} = \dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\text{ J}Energy=………………………… J
It takes 12 minutes12\text{ minutes}12 minutes for the cooling system to lower the temperature of the solid gel across this range.
Calculate the average thermal power removed from the gel by the cooling system.
Power=………………………… W\text{Power} = \dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\text{ W}Power=………………………… W
Suggest two reasons why the actual electrical power drawn by the cooling system's power supply during this process is greater than the thermal power calculated in part (a)(ii).
During orbit, the satellite is exposed to direct sunlight, and the temperature of the solid gel rises back to its melting point. During the melting transition, the temperature of the gel remains constant.
Explain two reasons why heat energy must still be supplied to transition the solid gel into a liquid at its melting point.
Calculate the number of 25 mg25\text{ mg}25 mg micro-heat-sink gel pockets that can be fully melted from solid at its melting point using 18000 J18000\text{ J}18000 J of energy.
Assume the specific latent heat of fusion for the gel is 240000 J/kg240000\text{ J/kg}240000 J/kg.
Number of gel pockets=…………………………\text{Number of gel pockets} = \dots\dots\dots\dots\dots\dots\dots\dots\dots\dotsNumber of gel pockets=…………………………