Insulation materials play an important role in district heating pipeline networks. Thermal losses in pipe insulation systems depend on the thermal conductivity of insulation materials. The thermal conductivity of the insulation materials is influenced by the temperature and moisture content. In this paper the effect of moisture content on the thermal conductivity of rock wool produced by different manufacturers was considered. Experimental studies were performed using the standard guarded hot plate (GHP) method. Higher thermal conductivity is always associated with higher moisture content for all investigated samples.

The pulsating flow is one of the techniques that can enhance heat transfer, therefore leading to energy saving in tubular heat exchangers. This paper investigated the heat transfer and flow characteristics in a two-dimensional in-line tube bundle with the pulsating flow by a numerical method using the Ansys Fluent. Numerical simulation was performed for the Reynolds number Re = 500 with different frequencies and amplitude of pulsation. Heat transfer enhancement was estimated from the central tube of the tube bundle. Pulsation velocity had an asymmetrical character with a reciprocating flow. The technique developed by the authors to obtain asymmetric pulsations was used. This technique allows simulating an asymmetric flow in heat exchangers equipped with a pulsation generation system. Increase in both the amplitude and the frequency of the pulsations had a significant effect on the heat transfer enhancement. Heat transfer enhancement is mainly observed in the front and back of the cylinder. At a steady flow in these areas, heat transfer is minimal due to the weak circulation of the flow. The increase in heat transfer in the front and back of the cylinder is associated with increased velocity and additional flow mixing in these areas. The maximum increase in the Nusselt number averaged over space and time in the entire studied range was 106%, at a pulsation frequency of 0.5 Hz and pulsation amplitude of 4.5. A minimum enhancement of 25% was observed at a frequency of 0.166 Hz and amplitude of 1.25.

In this paper, the external heat transfer coefficient for cross flow around a tube bundle by a pulsating flow was studied by numerical method. ANSYS Fluent 14.0 program is used for the mathematical modeling. The Reynolds numbers lie in the range 100 ≤ Re ≤ 1000, the Prandtl numbers 215 ≤ Pr ≤ 363, the frequency and the dimensionless relative amplitude of the pulsations were in the range 0,2 ≤ f ≤ 0,5, Hz, 15 ≤ β ≤ 35, the pulsation ratio 0,25 ≤ ψ ≤ 0,5. The external heat transfer for low-frequency pulsations was studied for 9 configurations of staggered tube bundles and 3 corridor tube bundles. Based on the modeling results, a criteria equation is obtained that allows calculating the external heat transfer in pulsating flows in tube bundles of different configurations. It is established that an increase in Re, Pr, ψ leads to a decrease in heat transfer, and an increase in f and β to an increase in heat transfer.

Open-cell foams are attractive for heat transfer enhancement in many engineering applications. Forced pulsations can lead to additional heat transfer enhancement in porous media. Studies of heat transfer in open-cell foams under forced pulsation conditions are limited. Therefore, in this work, the possibility of heat transfer enhancement in porous media with flow pulsations is studied by a numerical simulation. To generate the 3D open-cell foams, the Laguerre–Voronoi tessellation method was used. The foam porosity was 0.743, 0.864, and 0.954. The Reynolds numbers ranged from 10 to 55, and the products of the relative amplitude and the Strouhal numbers ranged from 0.114 to 0.344. Heat transfer was studied under the conditions of symmetric and asymmetric pulsations. The results of numerical simulation showed that an increase in the amplitude of pulsations led to an augmentation of heat transfer for all studied porosities. The maximum intensification of heat transfer was 43%. Symmetric pulsations were more efficient than asymmetric pulsations, with Reynolds numbers less than 25. The Thermal Performance Factor was always higher for asymmetric pulsations, due to the friction factor for symmetrical pulsations being much higher than for asymmetric pulsations. Based on the results of a numerical simulation, empirical correlations were obtained to predict the heat transfer intensification in porous media for a steady and pulsating flow.

The method of determining the thermal and hydraulic efficiency η of tube bundles with a pulsating flow is given in the paper. Based on numerical simulation, the effect of the Reynolds number Re of the dimensionless pulsation amplitude β and the Strouhal number Sh on the thermal and hydraulic efficiency η of the corridor tube bundles was investigated. The optimum pulsation regimes corresponding to the maximum η are found.