Semnan University Press Journal of Heat and Mass Transfer Research 2345-508X 13 2 2026 06 01 Numerical Investigation on Transient Heat Transfer of Different Coolants in the Cooling Channel of a Thrust Chamber بررسی عددی انتقال حرارت گذرای خنک‌ کننده‌های مختلف در کانال خنک‌ کاری محفظه تراست 206 218 10532 10.22075/jhmtr.2026.40123.1914 EN Arash Haeri Department of Aerospace Engineering, Faculty of New Science and Technologies, Semnan University, Semnan, Iran Hamidreza Farshi Fasih Department of Aerospace Engineering, Faculty of New Science and Technologies, Semnan University, Semnan, Iran Roohollah Rafee Faculty of Mechanical Engineering, Semnan University, Semnan, Iran Journal Article 2026 01 29 Controlling the nozzle wall temperature using regenerative cooling is a highly effective approach in liquid rocket engines. The selection of coolant is critical to determining the cooling system's thermal performance. In this study, the transient and steady-state heat transfer characteristics of a regenerative cooling channel are numerically investigated using two benchmark coolants, water and Ethyl-alcohol, under different coolant mass flow rates. A two-dimensional axisymmetric conjugate heat transfer model is employed, in which the thrust chamber, cooling channel, and solid walls are fully coupled. For both coolants, the maximum gas-side wall temperature occurs upstream of the nozzle throat, and increasing the coolant mass flow rate significantly reduces both gas-side and coolant-side wall temperatures throughout the thrust chamber. Specifically, for water, the maximum wall temperature decreases from 657 K to 541 K as the mass flow rate increases from 0.5 to 1.5 kg/s, whereas for Ethyl-alcohol, it decreases from 957 K to 693 K. The time required to reach steady-state conditions for Ethyl-alcohol is approximately 1.8 times longer than that of water, while reducing the coolant mass flow rate from 1.0 to 0.5 kg/s nearly doubles the steady-state time. Moreover, the coolant mass flow rate strongly influences the peak heat flux and convective heat transfer coefficient upstream of the throat. Increasing the mass flow rate enhances heat transfer, so that at 1.5 kg/s the maximum heat flux is 21.0 MW/m² for water and 19.7 MW/m² for Ethyl-alcohol. Correspondingly, the convective heat transfer coefficient attains a peak value of approximately 7.8 kW/m²·K near the throat and increases with increasing coolant mass flow rate. The results provide quantitative insights into transient thermal behavior and heat transfer mechanisms in regenerative cooling channels, offering helpful guidance for the thermal design and optimization of rocket engine thrust chambers. https://jhmtr.semnan.ac.ir/article_10532_968b94de47e2612410484039bbc426bb.pdf