Numerical and Experimental Study of Heat Transfer in Pyrolysis Reactor Heat Exchange Channels with Different Hemispherical Protrusion Geometries

Abstract

One of the most effective technologies for recycling organic waste is its thermal destruction by pyrolysis methods to produce valuable products such as hydrogen and mixtures containing hydrogen. Increasing the thermal power of the flow helps to reduce the formation of secondary reactions, making the non-condensable hydrocarbon gas in the pyrolysis process cleaner, which simplifies further technology for the production of hydrogen and hydrogen-containing mixtures. In addition, the economic viability of pyrolysis depends on the energy costs required to decompose the organic feedstock. Using passive intensifiers in the form of discrete rough surfaces in heat exchanging channels is a widely used method of increasing heat transfer. This paper presents the results of numerical and experimental studies of heat transfer and hydraulic resistance in a channel with and without hemispherical protrusions applied to the heat transfer surface. The investigations were carried out for a reactor channel 150 mm long and 31 mm in diameter, with a constant pitch of the protrusions along the channels of 20 mm and protrusion heights h of 1 to 4 mm for 419 ≤ Re ≤ 2795. Compared to a smooth channel, a channel with protrusions increases heat transfer by an average of 2.23 times. By comparing the heat exchange parameters and the hydraulic resistance of the heat exchange channels, it was determined that h = 2 mm and 838 < Re < 1223 is the combination of parameters providing the best energetic mode of reactor operation. In general, an increase in h and coolant flow rate resulted in an uneven increase in heat transfer intensity. However, as h increases, the dead zone effect behind the protrusions increases and the rough channel working area decreases. Furthermore, increasing Re > 1223 is not advisable due to the increased cost of maintaining high coolant velocity and the reduced heat transfer capacity of the channel.