Improving the compact heat exchangers with profiled tubes for marine power plants

The design features of heat exchangers with flat tubes are considered. The stages of creating a new flat tube and its prototypes are analyzed. An oil refrigerator is chosen as a prototype of the heat exchanger because of the previous use of flat tubes with wells, now replaced with new flat profiled tubes. Thermal and hydraulic tests of a refrigerator made of such tubes are carried out at the stand. During the testing, the hydraulic resistance of the cavities of the cooled and cooling media and thermal parameters are determined: heat power, heat transfer coefficient and heat transfer coefficient from the cooled medium in the inter-tube cavity with the transverse flow of tubes to the tube wall. A satisfactory correspondence of the actual power values determined for both working environments has been established. The discrepancy does not exceed (-7.6%)-(+5%) with an average value of +0.2%. A satisfactory correspondence of the actual and calculated values of the refrigerator power has been obtained. The discrepancy does not exceed (-15%)-(+9%) with an average value of -2.8%. The calculation of the capacity of the refrigerator during its operation in the design mode of oil cooling is carried out. The oil flow is considered both through the pipe and through the inter-pipe space. A good convergence of the calculations with the experimental results has been revealed.

Study of heat transfer during steam condensation in the tubes of diesel radiator cores

The article contains an assumption about the practicability of using the processes of boiling and condensation of the coolant in the cooling system of a locomotive diesel in order to reduce the energy consumption of fans of the refrigerating chamber. The possibility of using of standard radiator cores of a diesel locomotive with flat tubes as steam condensers is considered. The results of the criterion equation of heat transfer from steam to a flat tube during condensation, obtained by the mathematical model of this process, are estimated. The assessment was carried out by comparison with experimental data. The influence of the initial steam velocity, the corresponding tube diameter, the working length of the tube, the physical properties of steam and condensate is considered. The comparison of the influence of these factors on heat transfer in round and flat tubes of a locomotive radiator core is carried out. The processed results of physical and numerical experiments for both circular and flat tubes are shown in the graphs and regression equations. The advantage of flat tubes over round ones in terms of heat transfer intensity during steam condensation, which can reach 24%, for a standard radiator core of a diesel locomotive was found.

Field Study on the Air-Side Heat Transfer Performance of Copper Finned-Flat Tubes for Heavy-Duty Truck Radiators

Heavy-duty truck cooling systems have been given low importance in the enhancement and research of heat transfer performance since off-highway conditions are hard to evaluate in laboratory essays or CFD studies. The present work is performed to evaluate the heat transfer performance of copper finned-flat tubes used in heavy-duty truck radiators. Parameters were measured in the field of two heavy-duty truck engines cooling systems. In both vehicles water is used as the cooling fluid. The results showed that the Air convective heat transfer coefficient and Overall heat transfer coefficient on the air side decreases as the Reynolds Number decreases and increases as passing through the first row to the fourth row. Additionally, the mass air flow and heat transfer rate have very high values in comparison from normal automotive radiators' operative conditions, since heavy-duty truck radiators require a large heat transfer rate. The analysis presented in this paper was used for a heavy-duty truck radiator but can be extended to any equipment with finned flat tubes. A more accurate study should be done considering vibrations and different environmental conditions.

Performance of flow distribution in a microchannel parallel flow gas cooler with stepped protrusion depth header

Microchannel parallel flow gas cooler is commonly used in transcritical carbon dioxide automotive air conditioning system. To investigate the influence of the flat tube protrusion depth on fluid distribution, a numerical calculation model of microchannel parallel flow gas cooler with D-shaped header is established. With the object of even flow distribution, a novel stepped protrusion depth header is proposed. The effects of new header on the flow distribution of gas cooler were studied by numerical simulation. The results show that the flow distribution performance of gas cooler can be improved by changing the flat tube protrusion depth. Changing the protrusion depth of three groups of flat tubes simultaneously can achieve a better flow distribution performance of gas cooler than changing the protrusion depth of only one or two groups of flat tubes. When compared with the protrusion depth of all flat tubes is 0, the novel stepped protrusion depth header reduces the total flow distribution nonuniformity of gas cooler by 34–51%. The research in this paper provides a method for improving the flow distribution performance of gas coolers.

A Method of Quantifying Refrigerant Distribution in a Two-Pass Micro-Channel Evaporator

Background: The flow rate distribution in the flat tubes of a micro-channel evaporator is essential for its heat transfer performance. Due to a large number of flat tubes in a micro-channel evaporator, the flow rate distribution is often difficult to determine. Objective: An evaporator test rig was constructed to study the quantification of the refrigerant mass flow rate distribution in a two-pass evaporator without de-stroying its structure. Methods: A heat transfer performance test rig for a two-pass evaporator was es-tablished. Subcooled refrigerant R134a was pumped into the inlet header, and infrared thermography was used to obtain the cloud map of the wall tempera-ture distribution on the surface of the evaporator. The flow rate distribution in each flat tube was calculated based on an analysis that combines the heat bal-ance between the airside and the refrigerant side with the effectiveness-Number of Transfer Units (ε-NTU) method. Results: The flow rate distribution was found to be in good agreement with the evaporator wall temperature distribution. The difference between the calculated and measured total mass flow rates was less than 15.9%, which proves that the method is simple and effective. The unevenness of flowrate distribution in the 1st and 2nd pass is 0.13 and 0.32, respectively. Conclusion: This method is simple and effective and does not destroy the structure of the micro-channel evaporator. However, it is only suitable for cases in which subcooled zone exists in a pass and is not applicable to a pass in which the refrigerant is only in a single-phase or a two-phase state.

Comparison of a Novel Polymeric Hollow Fiber Heat Exchanger and a Commercially Available Metal Automotive Radiator

A novel heat exchanger for automotive applications developed by the Heat Transfer and Fluid Flow Laboratory at the Brno University of Technology, Czech Republic, is compared with a conventional commercially available metal radiator. The heat transfer surface of this heat exchanger is composed of polymeric hollow fibers made from polyamide 612 by DuPont (Zytel LC6159). The cross-section of the polymeric radiator is identical to the aluminum radiator (louvered fins on flat tubes) in a Skoda Octavia and measures 720 × 480 mm. The goal of the study is to compare the functionality and performance parameters of both radiators based on the results of tests in a calibrated air wind tunnel. During testing, both heat exchangers were tested in conventional conditions used for car radiators with different air flow and coolant (50% ethylene glycol) rates. The polymeric hollow fiber heat exchanger demonstrated about 20% higher thermal performance for the same air flow. The efficiency of the polymeric radiator was in the range 80–93% and the efficiency of the aluminum radiator was in the range 64–84%. The polymeric radiator is 30% lighter than its conventional metal competitor. Both tested radiators had very similar pressure loss on the liquid side, but the polymeric radiator featured higher air pressure loss.