Surface Microfouling During the Induction Period

1983 ◽  
Vol 105 (3) ◽  
pp. 618-624 ◽  
Author(s):  
R. E. Baier ◽  
A. E. Meyer ◽  
V. A. DePalma ◽  
R. W. King ◽  
M. S. Fornalik
Keyword(s):  
Heat Transfer ◽  
Induction Period ◽  
Heat Exchangers ◽  
Transfer Coefficients ◽  
Flow Cells ◽  
Heat Transfer Coefficients ◽  
Water Side ◽  
Second Wave ◽  
Initial Pattern ◽  
Rapid Adsorption

The time during which newly installed or cleaned heat transfer surfaces remain free of fouling deposits thick enough to diminish heat transfer coefficients or energy efficiency is often called the “induction period,” a term disguising lack of knowledge of the microfouling events actually occurring. Using novel flow cells to conduct water of fresh, brackish, and oceanic quality, natural and treated with antifouling chemicals, over test surfaces of different clean and coated metals, it has been observed that the initial pattern of fouling deposits is remarkably similar in all circumstances. Rapid adsorption of protein-dominated films is followed by attachment of rodlike bacteria, bacterial exudation, colonization by a second wave of prosthecate microorganisms, additional secretion, and growth of debris-trapping filamentous appendages. Although inappropriate to extrapolate the noted rates of these processes to in-plant heat exchangers at present, this sequence of microfouling events seems universal enough to characterize the induction period of all water-side biofouling phenomena.

Comparison of 30 Boiling and Condensation Correlations for Two-Phase Flows in Compact Plate-Fin Heat Exchangers

2017 ◽  
Author(s):  
Wenhai Li ◽  
Ken Alabi ◽  
Foluso Ladeinde
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Flow Boiling ◽  
Transfer Coefficients ◽  
Two Phase Flows ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
Heat Exchanger Design ◽  
Micro Channels ◽  
Vertical Tubes

Over the years, empirical correlations have been developed for predicting saturated flow boiling [1–15] and condensation [16–30] heat transfer coefficients inside horizontal/vertical tubes or micro-channels. In the present work, we have examined 30 of these models, and modified many of them for use in compact plate-fin heat exchangers. However, the various correlations, which have been developed for pipes and ducts, have been modified in our work to make them applicable to extended fin surfaces. The various correlations have been used in a low-order, one-dimensional, finite-volume type numerical integration of the flow and heat transfer equations in heat exchangers. The NIST’s REFPROP database [31] is used to account for the large variations in the fluid thermo-physical properties during phase change. The numerical results are compared with Yara’s experimental data [32]. The validity of the various boiling and condensation models for a real plate-fin heat exchanger design is discussed. The results show that some of the modified boiling and condensation correlations can provide acceptable prediction of heat transfer coefficient for two-phase flows in compact plate-fin heat exchangers.

Analysis of Composite Fouling in Corrugated Plate Heat Exchangers

2013 ◽  
Author(s):  
Guanmin Zhang ◽  
Guanqiu Li ◽  
Wei Li
Keyword(s):  
Heat Exchangers ◽  
Transfer Coefficients ◽  
Plate Height ◽  
Plate Heat ◽  
Heat Transfer Coefficients ◽  
Plate Spacing ◽  
Friction Factors ◽  
Water Side ◽  
Theoretical Investigations ◽  
Pitch Ratio

Experimental and theoretical investigations of water-side fouling have been performed inside four corrugated plate heat exchangers. They have different geometric parameters, such as plate height, plate spacing, and plate angle. Heat transfer coefficients and friction factors have been obtained in clean tests. Composite fouling experiments have also been performed. The tests are primarily focused on the effects of average velocity. Scanning electron microscope (SEM) was used to investigate the microscopic structures of composite fouling and analyze the fouling characteristics in composite fouling tests. The plate heat exchanger with the largest de and height to pitch ratio shows the best anti-fouling performance.

MEMS Impinging-Jet Cooling

2000 ◽  
Author(s):  
Qiao Lin ◽  
Shuyun Wu ◽  
Yin Yuen ◽  
Yu-Chong Tai ◽  
Chin-Ming Ho
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Jet Impingement ◽  
Impinging Jet ◽  
Impinging Jets ◽  
Measured Temperature ◽  
Transfer Coefficients ◽  
Element Analysis ◽  
Heat Transfer Coefficients ◽  
Jet Cooling

Abstract This paper presents an experimental investigation on MEMS impinging jets as applied to micro heat exchangers. We have fabricated MEMS single and array jet nozzles using DRIE technology, as well as a MEMS quartz chip providing a simulated hot surface for jet impingement. The quartz chip, with an integrated polysilicon thin-film heater and distributed temperature sensors, offers high spatial resolution in temperature measurement due to the low thermal conductivity of quartz. From measured temperature distributions, heat transfer coefficients are computed for single and array micro impinging jets using finite element analysis. The results from this study for the first time provide extensive data on spatial distributions of micro impinging-jet heat transfer coefficients, and demonstrate the viability of MEMS heat exchangers that use micro impinging jets.

The Impact of Fin Deformation on Condensation Heat Transfer Coefficients in Internally Grooved Tubes

2013 ◽  
Author(s):  
Sunil Mehendale
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Thermal Contact ◽  
Heat Pumps ◽  
Condensation Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Condensing Heat Transfer ◽  
The Impact ◽  
Tube Expansion

In HVACR equipment, internally enhanced round tube (microfin) designs such as axial, cross-grooved, helical, and herringbone are commonly used to enhance the boiling and condensing performance of evaporators, condensers, and heat pumps. Typically, such tubes are mechanically expanded by a mandrel into a fin pack to create an interference fit between the tube outside surface and the fin collar to minimize the thermal contact resistance between tube and fin. However, during this expansion process, the internal enhancements undergo varying amounts of deformation, which degrades the in-tube thermal performance. Extensive data on condensing heat transfer coefficients in microfin tubes have been reported in the open literature. However, researchers have seldom used expanded tubes to acquire and report such data. Hence, it is always questionable to use such pristine tube data for designing heat exchangers and HVACR systems. Furthermore, the HVACR industry has been experiencing steeply rising copper costs, and this trend is expected to continue in coming years. So, many equipment manufacturers and suppliers are actively converting tubes from copper to aluminum. However, because of appreciable differences between the material properties of aluminum and copper, as well as other manufacturing variables, such as mandrel dimensions, lubricant used, etc., tube expansion typically deforms aluminum fins more than copper fins. Based on an analysis of the surface area changes arising from tube expansion, and an assessment of the best extant in-tube condensation heat transfer correlations, this work proposes a method of estimating the impact of tube expansion on in-tube condensation heat transfer. The analysis leads to certain interesting and useful findings correlating fin geometry and in-tube condensation thermal resistance. This method can then be applied to more realistically design HVACR heat exchangers and systems.

Conjugate Heat Transfer in Air-to-Refrigerant Airfoil Heat Exchangers

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
Yutaka Ito ◽  
Naoya Inokura ◽  
Takao Nagasaki
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Heat Exchangers ◽  
Transfer Coefficients ◽  
Exchange System ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Heat Exchange System ◽  
Inverse Heat Transfer ◽  
Transfer Method

A light and compact heat exchange system was realized using two air-to-refrigerant airfoil heat exchangers and a recirculated heat transport refrigerant. Its heat transfer performance was experimentally investigated. Carbon dioxide or water was used as a refrigerant up to a pressure of 30 MPa. Heat transfer coefficients on the outer air-contact and inner refrigerant-contact surfaces were calculated using an inverse heat transfer method. Correlations were developed for the Nusselt numbers of carbon dioxide and water on the inner refrigerant-contact surface. Furthermore, we proposed a method to evaluate a correction factor corresponding to the thermal resistance of the airfoil heat exchanger.

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