Data were taken for condensation and evaporation in a micro-fin tube at the same saturation temperature to examine similarities and differences of condensation and evaporation in micro-fin tubes. The condensation and evaporation data were taken in the same tube at 24.4 degrees C saturation temperature, for a range of mass velocities (150-327 kg/m(2)-s), and vapor qualities (0.1-0.9). If the heat transfer mechanism, is "convection dominated", one would expect that the condensation and evaporation coefficients should be nearly equal. The present data show that this behavior was verified, except for a possible nucleate boiling contribution at low vapor quality. Both vaporization and condensation show a small elfect of heat flux in the high vapor quality regions. These data provide insight of the heat transfer mechanisms, and suggest a basis for developing heat transfer correlations that may apply to both condensation and evaporation.

This paper describes the results of accelerated particulate fouling tests performed on different enhanced tubes and a plain tube. The key purpose of the tests was to investigate particulate fouling in practical heat exchanger systems where a mixture of particles exists in a flowing water stream. The applications considered are electric utility steam condensers on the Mississippi and Ohio rivers. These condensers operate with foulant materials consisting of silt and clay, having a distribution of particle sizes. Fouling data were taken for a wide range of particle concentrations, particle size, and velocity. The concentration was varied between 800 and 2,000 ppm for the particle sizes of 2,4 and 16 μm. In addition, the Reynolds number was varied between 24,000 and 65,000 for a constant concentration of 1,500 ppm. The experimental results show that the enhanced tubes foul faster than the plain tube. However, at very low concentration the enhanced and plain tubes foul at the same rate. The asymptotic fouling resistance increases as the concentration increases and it decreases as the particle diameter and velocity increase.

This paper discusses the "Inlet Temperature Difference" (ITD) based heat-exchanger (and its variants) design methodology frequently used by designers of electronic heat sinks. The methodology is at variance with the accepted methodology recommended in standard heat-transfer text books -the "Log-Mean Temperature Difference" (LMTD), or the equivalent "effectiveness-NTU" design method. The purpose of this paper is to evaluate and discuss the ITD based design methodology and its deficiencies. The paper shows that the ITD based method is an approximation at best. Variants of the method can lead to either under or over prediction of the heat transfer rate. Its shortcomings are evaluated, and it is recommended that designers of electronic cooling equipment use the well established and accepted LMTD or epsilon-NTU design methodology.

Analysis was performed to determine the performance and economic benefits of using enhanced condenser tubes in an existing nuclear plant. This work consisted of using measured heat transfer and friction performance of two enhanced tube geometries to calculate the resulting reduction of condenser saturation temperature. Using the known plant heat rate and heat rate correction factor, we calculated the increased plant generation capacity, relative to the plain tube condenser design. Detailed analysis was done for the Wieland NW-16 and the Wolverine Korodense-LPD tubes, which are estimated to cost about 23% more than plain tubes. Simple payback analysis of the Wieland NW-16 onew tube bundleo tube shows that the annual average heat rate is reduced 3.83% and the increased tube cost can be recovered in 0.036 years based on the increased generation capacity valued at $2000/kW. Tube-for-tube replacement provides a payback of 0.054 years. For the month of July, the heat rate (with new bundle) is reduced 3.83% and the increased generation rate is 37 MW. Further detail is given on accelerated particulate fouling testing, which shows that the tubes are cleanable with the sponge-ball cleaning system.

Experimental studies are presented on falling film evaporation of water on 6-row horizontal enhanced tube bundles in a vacuum condition. Turbo-CAB (19fpi and 26fpi), Korodense, and smooth tubes were tested in a range of film Reynolds number from about 10 to 110 and in the condition of only convective evaporation, without nucleate boiling. The flow modes and heat flux will affect the transition Reynolds numbers. Tubes with enhanced inner surface provide better heat transfer performance. Hotter heating water may lead to better heat transfer performance mainly due to higher heat fluxes. Correlations were also derived to predict the heat transfer coefficients and the enhancement ratio.

Enhanced condenser tube designs can significantly improve the heat rate and performance of fossil and nuclear plants. Using the optimum number of tubes and replacement tube sheets will cost more than simply replacing plain tubes. However, the investment's simple payback is measured in only weeks, which builds a strong case for using an enhanced tube design as part of your next condenser overhaul.

US rate for 2010 subscription is $654 call publisher for price information for print/online or online only subscriptions. Add $10.00 per issue for foreign airmail shipping and handling fees to all orders shipped outside the United States or Canada. All subscriptions are payable in advance. Subscriptions are entered on an annual basis, i.e., January-December. For immediate service and charge card sales, call (203) 938-1300 Monday through Friday 9 am–5 pm est. This journal contains information from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references is listed. Reasonable efforts have been made to publish reliable data and information, but the editor and the publisher assume no responsibility for any statements of fact or opinion expressed in the published papers or in the advertisements. those organizations that have been granted a photocopy license by CCC, a separate payment system has been arranged.The fee code for users of the Transactional Reporting Service is: [ISSN 1065-5131/05 $35.00+$0.00]. The fee is subject to change without notice. Begell House, Inc.'s, consent does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific permission must be obtained from Begell House, Inc., for such copying. The Journal of Enhanced Heat Transfer will consider a wide range of scholarly papers related to the subject of " enhanced heat and mass transfer " in natural and forced convection of liquids and gases, boiling, condensation, radiative heat transfer. Areas of interest include: • Specially configured surface geometries, electric or magnetic fields, and fluid additives-all aimed at enhancing heat transfer rates. Papers may include theoretical modeling, experimental techniques, experimental data, and/or application of enhanced heat transfer technology. • The general topic of "high performance" heat transfer concepts or systems is also encouraged. • The journal will also consider well-prepared review articles within the identified subject areas. • Archival quality papers previously published at limited distribution conferences are also accepted. The author may need to provide a copyright release from the conference publisher Authors should submit their manuscript electronically in Word or pdf format. Electronically transmitted manuscripts should be e-mailed to the Editor-in-Chief, Ralph.Webb@psu.edu. Authors may also electronically submit manuscripts to any of the regional editors listed on the inside Journal cover or on the Begell House website The manuscript must be accompanied by a statement that it has not been published elsewhere and …

This paper reports heat transfer and friction characteristics of three tubes having a conical, three-dimensional roughness on the inner tube surface with water flow in the tube. The TC3 truncated cone tube has twice the cone area density as TC2 and provides a Nusselt number 3.74 times that of a plain tube. The h-value is 36% higher than TC2, but it has it has nearly 60% higher pressure drop. The three-dimensional roughness offers potential for considerably higher heat transfer enhancement (e.g., 50% higher) than is given by helical ridged tubes, such as the Turbo-B type. The two truncated cone tubes provide 14–20% higher h-value than the commercial Wolverine Turbo BIII tube. Further, they have both have approximately 5% higher efficiency index than Turbo BIII. Accelerated particular fouling data are also provided for 3-D tube TC3, and for helical-ribbed tubes. The results show that although the 3-D tube provided the highest heat transfer coefficient, relative to a plain tube (h/hp), it also had the highest asymptotic fouling resistance, relative to a plain tube (Rf∗/RP∗). Significant long-term fouling would not be expected in applications using relatively clean water.

Prediction of dryout vapor quality is important for design of horizontal flow evaporators. The dryout vapor quality is defined as the local vapor quality at which the two-phase heat transfer coefficient is the maximum. A phenomenological model for predicting dryout vapor quality for annular flow with convective vaporization in plain tubes is proposed, which is comparable with dryout correlations. The model is validated by predicting dryout vapor quality for 35 different datasets, with vertical and horizontal tube orientations. The predicted datasets covers tube diameter (D) range 2 mm < D < 8 mm, a wide range of mass fluxes, heat fluxes and working fluids. The model predicts 62% of the data within +/- 30% and 37% of the data within 15% of the experimental value. It was observed that the model prediction was significantly better for data with liquid-only Reynolds number, Re-DJ > 4000. The model predicts 88% of the data with Re-DJ > 4000 within +/- 30% of the experimental value. It is concluded that the model is applicable to high mass flux annular flow in vertical tubes and horizontal tubes for which the effect of stratification due to gravity is negligible. Future work towards development of a generalized model applicable to a wider mass flux range in horizontal tubes is discussed. (c) 2007 Elsevier Ltd. All rights reserved.

Fluorine Calorimetry History, Application, Results, by V. Ya. Leonidov, P. A. G. O’Hare, Begell House, Inc., 2000, 239 pages, $94.50. Numerical Problems in Thermodynamics and Kinetics of Chemical Engineering Processes, by Stanistaw Wro ski, Ryszard Pohorecki, Jacek Siwi ski, Begell House, Inc., 1998, 415 pages, $99.00. Microgravity Fluid Physics and Heat Transfer, proceedings of the International Conference on Microgravity Fluid Physics and Heat Transfer, edited by V. Dhir, J. Straub, and Y. Fujita, Begell House, Inc., 1999, 196 pages, $97.50. Advanced Computational Methods in Heat Transfer VI, edited by B. Sundén and C. A. Brebbia, WIT Press, 2000, 669 pages, $345.00.

This paper describes the current and recent work on advanced technology concepts applied to air-cooled heat exchangers. The concepts are applicable to: 1) automotive heat exchangers (radiators, air-conditioning condensers and evaporators, and charge-air coolers) and 2) residential air conditioning. Advances in understanding of heat transfer mechanisms and predictive models are also discussed.

An analysis is presented to calculate the entrance and exit losses for developing flow in parallel plate channels. Such an analysis is of value for air-cooled heat sinks with short flow length, such as electronic heat sinks. These predictions are typically done using inlet (K c ) and exit (K e ) loss coefficients for parallel plate channels from the Kays and London book, Compact Heat Exchangers. However, the information presented in Compact Heat Exchangers assumes fully developed flow at the exit. Electronic heat sinks operate in the developing flow region. Thus, the use of the published K c and K e from Compact Heat Exchangers will result in an overestimation of the actual K c and K e values. The present author has completed an analysis that allows the accurate calculation of K c and K e values with parallel plate channels in the developing flow region. The results are presented in graphical and equation form as a function of contraction ratio and 4x+ (= 4x/D h Re). Entrance and exit losses can account for as much as 30% of the total pressure drop in electronic heat sinks having short flow lengths. Fortunately, the error associated with evaluation of K c and K e based on fully developed flow for parallel plates is small and expected to be less than 2%.

The thermal performance of plate fin, round pin-fin, and offset strip-fin heat sinks with a duct-flow type fan arrangement was analytically evaluated. Heat sinks of 65mmtimes60 mm plan areatimes50 mm height with a 4300-RPM dc fan (60mmtimes15mm) were chosen for the performance comparison. A constant temperature, 6-mm thick heat sink base plate is assumed so that thermal spreading resistance is not involved. The operating point on the fan curve is based on the flow pressure drop impedance curve through a heat sink using the friction factor correlation for the chosen heat sink. The loss coefficients at both the entrance and the exit of the heat sink are included in the flow impedance curve. The operating point is defined by the balance point of the flow impedance curve and the fan performance curve. After determining the operating air velocity, the convective thermal resistance of heat sinks is evaluated from the Nusselt number correlation for the chosen heat sink. Results obtained show that optimized round pin-fin heat sinks provide 32.8%-46.4% higher convective thermal resistance compared to an optimized plate-fin heat sink. The optimized offset strip-fin heat sink shows a slightly lower convective thermal resistance than the plate-fin heat sink. As the offset strip length decreases, however, thermal performance seriously deteriorates

This paper addresses two-phase flow distribution phenomena in multiple header-tube junctions used in heat exchangers. Because of phase separation, it is very difficult to obtain uniform two-phase flow distribution to the branch tubes. The flow distribution is strongly influenced by the header orientation (horizontal or vertical) and the number of branch tubes. Other factors that influence the flow distribution are the flow direction in the header (upflow or downflow), the header shape and tube end projection into the header, and the location and orientation of the inlet and exit connections. The source of maldistribution is the flow in the dividing headers. Work performed by the authors and others (including patents) are discussed. The possibilities for eliminating two-phase flow maldistribution are identified and discussed. This investigation shows that solutions, which provide uniform flow distribution, are very design-specific. Change of the geometry or operating parameters will require modification of the design.

Conventional technology to cool desktop computers and servers is that of the “direct heat removal” heat sink, which consists of a heat sink/fan mounted on the CPU. Although this is a very cost effective solution, it is nearing its end of life. This is because future higher power CPUs will require a lower R-value than can be provided by this technology, within current size and fan limits. This paper discusses new technology that uses “indirect heat removal” technology, which involves use of a single or two-phase working fluid to transfer heat from the hot source to an ambient heat sink. This technology will support greater heat rejection than is possible with the “direct heat removal” method. Further, it will allow use of higher performance air-cooled ambient heat sinks than are possible with the “direct heat removal” heat sink. A concern of the indirect heat removal technology is the possibility that it may be orientation sensitive. This paper identifies preferred options and discusses the degree to which they are (or not) orientation sensitive. It should be possible to attain an R-value of 0.12 K/W at the balance point on the fan curve.

This paper reports work on advanced cooling technology for servers. The air cooling load on the rack may be enhanced using highly compact Copper/Brass "flat tube" water-cooled heat exchangers that are integrated into the rack frame. The cooling water is supplied by a water chiller. Analysis shows that it is possible to provide cooling (UA/A(fr)) in the range of 670-1000 W/m(2)-K, where the m(2) is the core frontal area. Also analyzed and compared are advanced technology CPU heat sinks - a thermo-syphon concept and a liquid micro-channel heat sink. The thermo-syphon may be used in a compact thermal-bus concept for heat removal from multiple CPUs. Used with boiling on an enhanced copper boiling surface in a thermo-syphon, heat loads in excess of 75 W/m(2)-K are possible. The heat removed at each CPU in the chassis is rejected to water flow in a compact water cooled condenser. Performance results of the thermo-syphon concept are predicted, obstacles associated with increasing performance are discussed, and possible solutions are proposed. Performance predictions were also made for water cooled: (1) Copper micro-channels as an attached external sink and (2) Silicon micro-channels integral to the silicon CPU die. It is shown that micro-channels integrated into the silicon die do not offer significant advantage over copper micro-channels.

This paper traces the evolution of enhanced boiling surfaces. Early work was highly empirical and done in industrial research. The 1968 Milton patent described the first porous coated surface, and the 1971 Webb patent described a “structured” tube surface geometry. The first fundamental understanding of the “pore-and-tunnel” geometry was published by Nakayama in 1980. Webb and Chien’s flow visualization allowed observation of the evaporation in the sub-surface tunnels. They also performed an experimental parametric study that defines the effect of pore diameter and pitch on the boiling performance. The progression of work on analytical boiling models is also reviewed.