## 3 Experimental Research Results, Analysis and Discussion
There is a similarity of scientific results that gas-dynamic non-stationarity causes an intensification of heat exchange within 20-40%. There are also data from other authors that suggest an increase in the TI values causes a rise in the HTC [39]. The detected intensification of heat exchange in pulsating flows may be associated with large- and small-scale oscillations in the flow, and the corresponding restructuring and weakening of the boundary layer, which contributes to improved heat transfer. Gas-dynamic non-stationarity has a similar effect on the heat exchange level of flows in a TrP: there is an intensification of the HTC \(\alpha\) by 24-36% compared to a steady flow (Figure 11). Also, an increase in the pulsation frequency from 3 Hz to 15.8 Hz does not actually affect the heat transfer intensity (an insignificant decrease in \(\alpha\) by 2-11% is observed, which is within the uncertainty limits of the experiment). Accordingly, it can be stated that gas-dynamic non-stationarity has a similar effect on the heat exchange level of the air flow in round and triangular pipes. Accordingly, the creation of flow pulsations in a gas-dynamic system can be considered an effective way to intensify heat exchange. This can be applied in the field of heat exchangers, heat pumps, and engines. It should be noted that the HTC values of pulsating flows in a TrP are 6.5-13.5% lower than those in a round pipe. This can be explained by the previously discovered effect of stabilizing the pulsating flow in a TrP and lower TI values. Suppression of heat transfer in a TrP has practical application in cases where it is necessary to impair heat exchange between the gas flow and the wall. The influence of turbulence of a pulsating flow on the heat transfer intensity in pipes with different cross-sectional shapes can be assessed based on Figures 12 and 13. These figures also show the dependence \(\alpha=f\) (\(w\)) for steady flows without a turbulizer as a baseline for comparison. Juxtaposition of the dependencies in Figure 10 (data without a turbulator) and Figure 12 (data with flow turbulence) shows that:  
* A rise in TI from 0.04 to 0.08 leads to an increase in the HTC \(\alpha\) of pulsating flows in a round pipe by 11-16%, which is in good agreement with [39];
* A further rise in the TI of the pulsating flow causes an additional small increase in \(\alpha\) within 5-8%;
* Accordingly, there is reason to state that turbulization of the pulsating flow in a round pipe intensifies heat transfer;  
Figure 11: Dependences of the average HTC \(\alpha\) in a triangular straight pipe without a turbulator on the air flow velocity \(w\) for different conditions: 1—steady flow with TI = 0.03; 2—pulsating flow with \(f\) = 3.0 Hz and TI = 0.03; 3—pulsating flow with \(f\) = 15.8 Hz and TI = 0.04. The pulsation frequency \(f\) has a weak effect on the heat transfer level of pulsating flows in a round pipe. Comparison of the patterns in Figure 11 (data without flow turbulence) and Figure 13 (data with a turbulence generator in the pipe) shows that:  
* An increase in the TI of the pulsating flow (from 0.04 to 0.08) in a TrP leads to a suppression of heat transfer by up to 24%;
* An increase in the TI of the pulsating flow from 0.04 to 0.15 in a TrP causes a decrease in the HTC to 10.6% (which is within the uncertainty limits of the experiment);
* Accordingly, it can be concluded that turbulization of the pulsating flow in a TrP suppresses heat transfer; the discovered effect requires additional research to clarify the physical mechanism. The obtained results indicate that the heat transfer intensity of air flows in pipes with different cross-sections has noticeable differences. This must be taken into account when designing gas-dynamic systems for heat exchange equipment, heat engines, and power plants. Thus, experimental data on the influence of the geometry of a straight pipe, pulsations, and turbulence of the air flow on the heat transfer intensity were obtained.