Abstract—This paper addresses the industrial challenge of sizing chiller capacity in rapid chilled-water generation systems under limited cooling time windows. The core heat transfer challenge lies in the transient nature of single-tank configurations; under low Richardson number (Ri) conditions, mixing-dominated behavior occurs, to eliminate the steady temperature differences assumed in conventional sizing methods. To address this, this study develops an explicit analytical model based on a quasi-steady-state heat transfer assumption, which is physically justified by the large mismatch in thermal time constants between the water tank and the heat exchanger. The model was validated experimentally using a 3-kW mini-chiller, a 60-L tank, and a plate heat exchanger across four flow-rate conditions. The experimental results support the use of the quasi-steady-state heat transfer assumption within the system. Furthermore, while the heat exchanger effectiveness varies continuously over time due to changes in operating conditions, it can be represented by a time-averaged value because the narrow operating temperature range produces limited variations in the thermophysical properties of water. Finally, the empirical data indicate mixing-dominated conditions at low Ri values, under which the proposed transient cooling model reasonably predicts the bulk temperature decline, with R² values ranging from 0.8738 to 0.9978 across the tested conditions. The resulting non-dimensional NTU–effectiveness design equation provides a practical basis for first-pass chiller and heat exchanger sizing in rapid chilled-water generation systems operating under similar mixed-tank conditions.

Keywords—chiller sizing, tank-based cooling system, rapid cooling, thermal mixing

Cite: Nopparat Katkhaw, Wichaphon Fakkeaw, Sutham Arun, and Rachaneewan Aungkurabrut, "Transient Cooling Model for Rapid Chilled-Water Generation in a Single-tank Chiller–Heat Exchanger System," International Journal of Mechanical Engineering and Robotics Research, Vol. 15, No. 5, pp. 445-457, 2026. doi: 10.18178/ijmerr.15.5.445-457

Copyright © 2026 by the authors. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).