[China Aluminum Industry Network] This article describes the experimental setup and procedures conducted in a real room environment. Unlike standard radiator testing, this experiment takes into account variable outdoor weather conditions, different radiator configurations, and fluctuating supply water temperatures and flow rates. The data collected includes supply and return water temperatures, room temperature, and flow rate. Temperature measurements were taken using platinum resistance sensors, while flow was measured with a turbine flow meter of class 3 precision.
Under these experimental conditions, a series of tests were carried out on an aluminum radiator under both constant and variable flow scenarios to determine the relationship between heat output and calculated temperature difference. Through detailed analysis of the collected data, we explored the thermal characteristics of the radiator in greater depth. This specific type of radiator is a hood-style LLD aluminum tube and aluminum fin radiator produced by Tianjin Tailai HVAC Equipment Co., Ltd. The experiment was designed with consideration for its low thermal inertia, quick temperature response, and clean internal structure, which makes it less prone to clogging and more suitable for use in heat metering systems that operate with variable flow.
Thermal characteristics analysis of the LLD-type aluminum convection radiator was performed under both constant and variable flow conditions. For example, during the 50 kg/h constant flow test, the supply water temperature was recorded at X°C, with a flow rate of Y kg/h, resulting in a temperature difference of Z°C. The calculated temperature difference was also determined, and the heat output was measured at W watts. Similarly, during the 150 kg/h constant flow test, the results showed a higher heat output. In variable flow tests, the supply water temperature remained consistent, but the flow rate varied, leading to changes in the temperature difference and heat dissipation.
From the fitted function formula, it's clear that the radiator's heat output varies depending on the flow rate. At lower flow rates, the change in heat output is more pronounced. This behavior is due to the thermal properties of the radiator, where a smaller flow rate allows for better control over heat output. Compared to single-pipe systems, dual-pipe systems exhibit a larger temperature difference between the inlet and outlet of each radiator, making the relationship between heat output and flow rate more sensitive and adjustable.
When comparing the curve obtained from a fixed flow of 15 kWg with that from the variable flow test, the two are quite similar. The heat transfer formulas derived from both tests show minimal differences. As the calculated temperature difference increases, the gap between the two becomes even smaller. In variable flow conditions, with a constant supply temperature, an increase in flow through the radiator leads to a rise in the calculated temperature difference. The findings of this experiment further confirm that when the flow rate is high, the heat sink calculation formula developed under fixed flow conditions remains applicable to variable flow systems. However, at lower flow rates—especially when heat metering is involved, as users often adjust their valves to very low settings when away—the original formula may need revision.
Currently, many heating systems operate with large flow rates and small temperature differences, deviating from design specifications. While this approach can help address issues like cold rooms caused by hydraulic imbalance, it creates significant challenges for heat metering systems. Large flow and small temperature difference operation is based on the principle that once the flow exceeds 2 to 3 times the design flow rate, the heat output becomes less sensitive to further changes in flow.
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