Abstract
Plate-fin and tube heat exchangers (PFTHE) are made of round, elliptical, oval or flat tubes to which continuous fins ( lamellas) are attached. Liquid flows inside the tubes and gas flows outside the tubes perpendicularly to their axes and parallel to the surface of continuous fins. Experimental studies of multi-row plate-fin and tube heat exchangers show that the highest average heat transfer coefficient on the air side occurs in the first row of tubes when the air velocity in front of the exchanger is less than approximately 3.5 m/s when a Reynolds number based on an equivalent hydraulic diameter equal to the distance between tube rows in the direction of air flow is less than 10,000. In the subsequent rows of tubes up to about the fourth row the heat transfer coefficient decreases. In the fifth and further rows, it can, that the heat transfer coefficient is equal in each tube row. It is necessary to find the relationships for the air-side Nusselt number on each tube row to design a PFTHE with the appropriate number of tube rows. The air-side Nusselt number correlations can be determined experimentally or by CFD modeling (Computational and Fluid Dynamics). The paper presents a new mathematical model of the transient operation of PFTHE, considering that the Nusselt numbers on the air side of individual tube rows are different. The heat transfer coefficient on an analyzed tube row was determined from the equality condition of mass- average air temperature differences on a given tube row determined using the analytical formula and CFD modeling. The results of numerical modeling were compared with the results of the experiments.
Highlights
Plate-fin and tube heat exchangers (PFTHEs) are widely used in air conditioning, heating, and many industries [1,2,3,4]
This paper proposes a calculation method of PFTHEs based on the
The initial-boundary problem formulated by Eqs (1–12) applies to the heat exchangers made of smooth tubes as well as to PFTHEs
Summary
Plate-fin and tube heat exchangers (PFTHEs) are widely used in air conditioning, heating, and many industries [1,2,3,4]. The number of books and articles in journals concerning their design, mathematical modeling, and experimental studies is very large Both in the calculation of heat exchangers and in experimental studies, it has been assumed that the heat transfer coefficient (correlation for Nusselt number) on the gas side of each row of tubes is the same [1,2,3,4]. By using reliable CFD correlations to calculate air-side heat mw = Nt At Lt ρw , P=m ( Pin + Pout ) / 2 transfer coefficients and semi-empirical relationships to calculate heat transfer coefficients on the internal surfaces of tubes, the experimental studies required can be significantly reduced, especially for PFTHEs with new design, e.g. made of tubes with different cross-section shapes or with different designs of continuous fins on the air-side. The method of modeling PFTHEs in steady-state and transient states proposed in the paper together with the method of determining the air-side heat transfer correlations proposed in [12] will significantly reduce the cost and shorten the time of implementation of PFTHEs with new construction and flow system
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