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The development of a numerical model and design for the innovative construction of a heat exchanger (HE) used in a condensation hood (being a part of the combi-steamer) are described in this work. The model covers an air-steam flow, heat transfer, and a steam condensation process. The last two processes were implemented with the use of an in-house model introduced via User Defined Functions (UDF). As the condensate volume is negligible compared to the steam, the proposed model removes the condensate from the domain. This approach enabled the usage of a single-phase flow for both air and steam using a species transport model. As a consequence, a significant mesh and computation time reduction were achieved. The new heat exchanger is characterised by reorganised fluid flow and by externally finned pipes (contrary to the original construction, where internally finned pipes were used). This allowed a reduction in the number of the pipes from 48 to 5, which significantly simplifies construction and manufacturing process of the HE. The redesigned HE was tested in two cases: one simulating normal working conditions with a combi-steamer, the other with extremely high heat load. Measurement data showed that the numerical model predicted condensate mass flow rate (3.67 g/s computed and 3.56 g/s measured) and that the condensation capability increased at least by 15% when compared to the original HE design.

An existing condensation hood has been numerically investigated using k-ε turbulence and species transport models. Due to the geometrical complexity of the appliance, two additional mathematical models were introduced with the use of User Defined Functions (UDFs). They were a model of a fan and a model of the internally finned pipes of a heat exchanger. The latter also involved a condensation model of steam implemented by mass and energy source terms. Such an approach allowed us to avoid troublesome two-phase flow simulation and thus significantly reduced the computational effort. Based on the results provided by the numerical model, potential improvements of the heat exchanger were proposed and implemented into a second, modified numerical model. Reduction of the number of the pipes by 25% is the most important change of the developed device. Its negative effect on condensation efficiency was to be compensated by improvements of steam flow in the device. Once the modifications had been evaluated, the prototype of the device was built and tested experimentally. Both the numerical and experimental results agree and show that, the modified condensation hood is comparable to the original construction in terms of condensation efficiency, despite the significant heat transfer surface area reduction.