Exchanger Design Research Articles

Optimum Design and Running of PHEs in Geothermal District Heating

Plate heat exchangers and terminal heat radiators usually take a major initial capital investment in a low-temperature geothermal heating project. In this article, a method of arriving at an optimum design of the plate heat exchanger and the corresponding terminal heat radiators in a geothermal heating system is proposed. A comparison is made between the results of the optimized design and those by the conventional design. The effects of the configuration and some parameters of plate heat exchangers on the design results are discussed. Emphasis is also given to how to obtain the best operation status while a geothermal well is producing at constant flow rate and wellhead temperature.

Effect of Mixed Convection and U-Bends on the Design of Double-Pipe Heat Exchangers

For horizontal flow in the laminar flow regime, the interaction between natural and forced convection and the effect of the secondary flow induced by an unheated U-bend were considered in developing an empirical correlation for the nearly uniform heat flux condition. The correlation predicts the local peripheral average heat transfer coefficient with an absolute average deviation of 9.9%. In this article the mechanisms involved in laminar flow with the presence of a U-bend are explained. The realistic behavior of the correlation is illustrated. Also, a brief discussion of some of the existing correlations for laminar flow is presented. Four cases showing the practicality of using the correlation in the design of horizontal double-pipe heat exchangers are demonstrated.

Industrial thin-film deodorization of seed oils withSoftColumnTM technology

Development of thin-film deodorizers started in the 1970ies, and they have been in industrial use since the middle of the 1980ies. The latest type is the SoftColumn, a deodorizer specially developed for mild, low cost processing of seed oils. This deodorizer consists of a structured packing section and a flexible holding section. Regenerative oil heating/cooling and final heating is carried out in external, sparged vacuum heat exchangers, and the design of the heat exchangers leads to superior heat recovery and savings in fuel consumption. This set-up provides major advantages with regard to oil quality, economy, and flexibility. The extremely effective stripping of free fatty acids (FFAs) leads to shorter overall holding times of the oil at elevated temperatures, and steam consumption is cut to a third of the amount required in conventional deodorizers. The product oil has not only low acidity, low colour, good taste and stability, but also low trans fatty acid (TFA) concentrations. By adjusting the stripping steam flow the plant can be optimized both for tocopherol retention or removal. Flexible holding times allow optimization of heat bleaching/TFA formation without compromising on capacity. In this paper product analysis data on tocopherol and trans fatty acids from thin-film deodorizers in industrial operation are shown.

Design of a Heat Exchanger

Design of a Heat Exchanger

Second-Law and Experimental Analysis of a Cross-Flow Heat Exchanger

This article presents a cross-flow plate-type heat exchanger that has been studied and manufactured in laboratory conditions because of its effective use in waste heat recovery systems. This new heat exchanger was tested with an applicable experimental setup, considering temperatures, velocity of the air, and the pressure losses occurring in the system. These variables were measured and the efficiency of the system was determined. The irreversibility of the heat exchanger was taken into consideration, while the design of the heat exchanger was such that the minimum entropy generation number was analyzed with respect to the second law of thermodynamics in the cross-flow heat exchanger. The minimum entropy generation number depends on the parameters called the optimum flow path length and dimensionless mass velocity. Variations of the entropy generation number with these parameters are analyzed.

Heat Transfer Through an Extended Surface Containing He II

A semi-analytic solution for the heat transfer process between a He II pressurized bath and a saturated tube-type heat exchanger is presented. The problem is modeled with an extended surface heat transfer formulation analogous to that in conventional conduction. The process is governed by Kapitza conductance and counterflow within the bulk fluid in the tube. The resulting nonlinear differential equation may be integrated for the special case of constant properties, yielding a simple solution applicable to design and analysis of practical heat exchangers.

表面処理とイオン交換 イオン交換体の設計と輸送現象

表面処理とイオン交換 イオン交換体の設計と輸送現象

Passive Enhancement Technique for Free Convection-Dominated Melting of Phase Change Material in Horizontal Cylindrical Annulus.

Knowledge of heat transfer during melting and freezing in enclosures is important in the design of heat exchangers using phase change materials (PCMs) for thermal energy storage. While freezing heat transfer is governed mainly by conduction, melting of a PCM generally invokes free convective currents in the melt phase depending on the orientation and geometry of the heat transfer surfaces. In this paper, a finite element simulation is carried out to predict the flow and temperature fields as well as the rate of heat storage during melting of a PCM in a horizontal cylindrical annulus heated from an isothermal inside surface. A novel yet simple method is suggested and validated numerically to enhance the heat storage rate in a PCM. The technique involves simply “flipping” the horizontal cylinder, i.e., turning it through 180° about its own axis, at an optimum time during the melting process. It is found that up to 18% enhancement in the energy storage rate can be achieved with this simple technique.

Thermoeconomic considerations in the design and rating of two-phase heat exchangers

We discuss a closed-form model for thermoeconomic design and analysis of two-phase heat exchangers used as condensers and evaporators. The results are presented in terms of the optimum number of heat-transfer units (NTUs) as a function of the dimensionless unit-cost ratio and the exit-to-inlet absolute temperature ratio of the single-phase fluid. The sensitivities of various unit-cost parameters (UCPs) are presented. It is demonstrated that the selection of UCPs play a significant role in sizing heat exchangers.

A new type of plate heat exchangers

An original structural design of compact plate heat exchangers, which was developed at OKBM, is of practical interest.

98/04138 Contemporary developments in the thermal design of finned-tube heat exchangers

98/04138 Contemporary developments in the thermal design of finned-tube heat exchangers

98/04270 Design of a high-temperature heat exchanger for integration in a combined gas and steam turbine process with pressurized coal dust firing

98/04270 Design of a high-temperature heat exchanger for integration in a combined gas and steam turbine process with pressurized coal dust firing

Performance and endurance of a PEMFC operated with synthetic reformate fuel feed

Widespread implementation of polymer electrolyte membrane fuel cell (PEMFC) powerplants for stationary and vehicular applications will be dependent in the near future on using readily available hydrocarbon fuels as the source of the hydrogen fuel. Methane and propane are ideal fuels for stationary applications, while methanol, gasoline, and diesel fuel are better suited for vehicular applications. Various means of fuel processing are possible to produce a gaseous fuel containing H2, CO2 and CO. CO is a known electrocatalyst poison and must be reduced to low (10's) ppm levels and CO2 is said to cause additional polarization effects. Even with no CO in the feed gas a H2/CO2/H2O gas mixture will form some CO. Therefore, as a first step of developing a PEMFC that can operate for thousands of hours using a reformed fuel, we used an anode gas feed of 80% H2 and 20% CO2 to simulate the reforming of CH4. To investigate the effect of reformate on cell performance and endurance, a single cell with an active area of 58 cm2 was assembled with a membrane electrode assembly (MEA) furnished by Texas A&M University using IGT's internally manifolded heat exchange (IMHEX™) design configuration. The MEA consisted of a Nafion 112 membrane with anode and cathode Pt catalyst loadings of 0.26 and 1.46 mg/cm2, respectively. The cell was set to operate on a synthetic reformate–air at 60°C and 1 atm and demonstrated over 5000 h of endurance with a decay rate of less than 1%/1000 h of operation. The cell also underwent four successful thermal cycles with no appreciable loss in performance. The stable performance is attributed to a combination of the IGT IMHEX plate design with its inherent uniform gas flow distribution across the entire active area and MEA quality. The effects of temperature, gas composition, fuel utilization (stoics) and thermal cycle on cell performance are described.

Providing effective service of heat exchangers with heating tubes in the gas industry

A theoretically based approach to design of heat exchangers based on heating tubes or loops makes it possible to readily solve problems of design, service, and determination of capabilities of designs of heat exchangers with separate heating and cooling zones and multiflow, multizone apparatus

Fouling effect of geothermal water scale on heat transfer around a tube in a bank

Seales deposited onto the heating surfaces of heat exchangers seriously reduce the heat transfer performance and also increase the hydrodynamic drag. Accordingly, fouling is an important problem in the design and operation of heat exchangers. Present paper investigates the heat transfer around in-line four circular cylinders on which geothermal water scales are uniformly distributed. The cylinders are settled in tandem with equal distance between neighbouring cylinders and only the test cylinder is heated under the condition of constant heat flux. It is found that the heat transfer of the in-line tube banks greatly varies with the fouling of geothermal water scale, especially its scale height. Further, the local and average Nusselt numbers strongly depend upon the cylinder spacing and the Reynolds number.

Countercurrent extraction of sparingly soluble gases for membrane introduction mass spectrometry.

Membrane introduction mass spectrometry has been applied to inert gas measurements in blood and tissue, but gases with low blood solubility are associated with reduced sensitivity. Countercurrent extraction of inert gases from a blood sample into a water carrier phase has the potential to extract most of the gas sample while avoiding dependence of signal on blood solubility. We present the design of a membrane countercurrent exchange (CCE) device coupled with a conventional direct insertion membrane probe to measure partial pressure of low solubility inert gases in aqueous samples. A mathematical model of steady-state membrane CCB predicts that countercurrent extraction with appropriate selection of carrier and sample flow rates can provide a mass spectrometer signal nearly independent of variations in solubility over a specified range, while retaining a linear response to changes in gas partial pressure over several orders of magnitude. Experimental data are presented for sulfur hexafluoride and krypton in water samples. Optimal performance is dependent on adequate equilibration between the sample and carrier streams, and the large resistance to diffusion in the aqueous phase for insoluble gases presents a substantial challenge to the application of this principle.

97/02279 Calculation and design of twin-tube safety heat exchangers

97/02279 Calculation and design of twin-tube safety heat exchangers

TURBULENT FLOW AND HEAT TRANSFER IN STAGGERED TUBE BANKS WITH DISPLACED TUBE ROWS

Turbulent flow in closely spaced staggered tube bundles is numerically investigated using a finite volume approach in general curvilinear coordinates. Attention is focused on the hydrodynamic and thermal effects of the longitudinal displacement of alternate tube rows. The computations used both standard and two-layer k-ε turbulence models in conjunction with a streamwise periodic finite volume formulation. The computations are in excellent agreement with experimental data for the limiting case of flow and heat transfer in undisplaced tube banks. Furthermore, the results indicate increases in both pressure drop and heat transfer with an increase in displacement. The results of this study may serve as an aid in the design of shell and tube cross-flow heat exchangers.

General numerical scheme for heat exchanger thermal analysis and design

This article describes two personal computer–based teaching modules designed to instruct engineering students in the more fundamental thermal aspects of the analysis and design of heat exchangers. One module applies to shell-and-tube exchangers; the other applies to cross-flow types. Enhanced numerical algorithms solve discretized forms of the governing differential energy-conservation equations. Graphical user interfaces display temperature distributions along with traditional design and performance measures. © 1997 John Wiley & Sons, Inc. Comput Appl Eng Educ 5: 231–242, 1997

Denaturation of β-lactoglobulin and native enzymes in the plate exchanger and holding tube section during continuous flow pasteurization of milk

The denaturation of β-lactoglobulin, alkaline phosphatase and lactoperoxidase and changes in the proteolytic activity, were studied at the heating and holding sections of a plate heat-exchanger, during treatment of milk under different conditions of temperature and flow rate. The heating rate contributed considerably to the heat-induced changes in the milk components during continuous flow pasteurization, whereas these indicators were less susceptible to differences in the holding times. Information gained in such studies on the denaturation effects occurring in the different sections could be useful in the design of heat exchangers and holding tubes.