THT3701 Assignment 01 2026 |Applied Thermodynamics and Heat Transfer| Solutions Due May 2026

UNIVERSITY OF SOUTH AFRICA (UNISA)
College of Science, Engineering and Technology



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THT3701 ASSIGNMENT 01
Semester 1 Assignment 01 — 2026


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Module Code: THT3701

Module Name: Applied Thermodynamics and Heat Trans-
fer

Assignment No.: 01

Due Date: 2026

Semester: Semester 1, 2026




Submitted in partial fulfilment of the requirements for
Applied Thermodynamics and Heat Transfer (THT3701)
at the University of South Africa.

, UNISA | THT3701 Applied Thermodynamics and Heat Transfer



Question 1: Spacecraft Surface Temperature (Radiation Balance)


Question


The outer surface of a spacecraft in space has an emissivity of 0.8 and a solar absorptivity
of 0.3. Solar radiation is incident on the spacecraft at a rate of 950 W/m2 . Determine the
surface temperature of the spacecraft when the radiation emitted equals the solar energy ab-
sorbed. (5)


Solution


Given Information


• Emissivity: ε = 0.8
• Solar absorptivity: α = 0.3
• Incident solar radiation: q̇solar = 950 W/m2
• Stefan-Boltzmann constant: σ = 5.67 × 10−8 W/m2 · K4
• Space temperature: Tspace ≈ 0 K (deep space, negligible)


Assumptions


1. Steady operating conditions exist; the surface temperature remains constant.
2. Thermal properties of the surface are constant.
3. The spacecraft surface radiates to deep space, treated as a blackbody at 0 K.


Step 1: Energy Balance Condition


The condition given is that radiation emitted equals solar energy absorbed:



Q̇solar, absorbed = Q̇rad, emitted (1)


Step 2: Express Solar Energy Absorbed per Unit Area


Solar energy absorbed per unit area is:




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