Showing papers on "Micro heat exchanger published in 1987"

Effects of fin pattern on the air side heat transfer coefficient in plate finned tube heat exchangers

Abstract: The effects of air velocity, heat exchanger geometry and fin pattern on air side heat transfer in plate finned tube heat exchangers were investigated experimentally using a single fin passage model. The geometric parameters considered included tube diameter, transverse tube spacing, longitudinal tube spacing, number of tube rows and fin spacing. The effects of fin pattern depth and number of fin patterns per longitudinal tube row were investigated for a pattern consisting of corrugations of triangular cross section transverse to the direction of air flow. The heat transfer data were correlated in terms of the dimensionless heat transfer coefficient (Nussult number) based on the arithmetic mean temperature difference Nu/sub a/ and the Graetz number Gz, a dimensionless measure of the level of flow development.

Effects of Some Types of Maldistribution on the Performance of Heat Exchangers

Abstract: The effects of several types and patterns of maldistribution in heat exchangers on the exchanger thermal performance are investigated. For turbulent flow most exchangers show only a small reduction in performance; however, for laminar flow the reduction can be large. It is shown that substantial errors in the apparent heat transfer coefficient occur for nonuniform flows.

Pumped two-phase heat transfer loop

Abstract: A pumped loop two-phase heat transfer system, operating at a nearly constant temperature throughout, includes a plurality of independently operating grooved capillary heat exchanger plates supplied with working fluid through independent flow modulation valves connected to a liquid supply line, a vapor line for collecting vapor from the heat exchangers, a condenser between the vapor and the liquid lines, and a fluid circulating pump between the condenser and the heat exchangers

Space vehicle thermal rejection system

Abstract: A space vehicle thermal heat rejection system 10 utilizing separate optimized heat pipe components for the functions of heat acquisition, heat transport, and heat rejection. A honeycomb panel heat pipe evaporator section 20 performs the function of heat acquisition, and forms a closed thermodynamic system with a dual channel heat pipe transport section 30, which performs the function of heat transport. A plurality of truss or channel core heat pipe rejection fins 41 form the condenser section 40, which performs the function of heat rejection. A common wall 32 separates the condenser section 40 from the transport section 30. Using the above heat pipe components and having efficient interfacing between them results in high performance factors for the overall system.

Continuous Cleaning of Heat Exchanger with Recirculating Fluidized Bed

Abstract: Fluidized bed heat exchangers for liquids have been studied in the United States, the Netherlands, and the Federal Republic of Germany. Between 1965 and 1970, fluidized bed heat exchangers were developed in the United States as brine heaters in seawater desalination. Furthermore, their potential in the utilization of geothermal energy was tested between 1975 and 1980. In the Netherlands, fluidized bed heat exchangers have been developed since 1973 for brine heating and heat recovery in multistage flash evaporators for seawater desalination and, since about 1980, for applications in the process industry. The authors became interested in fluidized bed heat exchangers first in 1978 in connection with wastewater evaporation. The authors emphasize that the results of all these groups were in basic agreement. They can be summarized as follows: 1. The fluidized bed will in many cases maintain totally clean surfaces and neither scaling nor fouling will occur. In cases where even a fluidized bed cannot completely prevent scaling or fouling, the thickness of the layer is controlled. In these cases stable operation maintaining acceptable overall heat transfer coefficients is possible without cleaning. 2. There are always excellent heat transfer coefficients as low superficial velocities of less than ..nu.. < 0.5more » m/s. 3. The pressure losses are comparable with those in normal heat exchangers since fluidized bed heat exchangers are mostly operated at low superficial velocities. 4. Feed flow may be varied between 50 and 150% or more of the design feed flow. 5. Erosion is negligible. 6. Fluidized bed particles can be manufactured from all sorts of chemically and mechanically resistant materials, such as sand, glass, ceramics, and metals.« less

Earth tube heat exchanger performance correlation using boundary element method.

Abstract: THE boundary integral equation method (BIEM) was developed in this study to analyze the performance of steady state potential type problems. The numerical implementation of BIEM was done for earth tube heat exchangers as an example. Based on the steady state heat conduction equation and a constant temperature boundary condition along the soil-tube interface, an equation for predicting the thermal performance for earth tube systems was developed. The earth tube variables studied included: tube diameter, soil temperature, and ambient air temperature. The location of tubes below the ground level significantly affected the heat exchanger thermal performance. Earth tube exchangers for heating greenhouses during winter months can be economical.

Gas liquefaction method and apparatus

Abstract: A stream of compressed nitrogen (or methane) at above its critical pressure is passed along conduit 10 through heat exchangers 16, 18, 20, 22 and 24, in sequence, to cool it to below its critical temperature. The resulting fluid is then subjected to expansion and resultant liquid is collected. Refrigeration for the heat exchangers is provided by nitrogen working fluid cycles 62, 72 and 82 employing expansion turbines 64, 74 and 84 respectively. The turbines have different inlet temperatures but substantially the same outlet temperature.

Method and apparatus relating to heat exchangers

Abstract: A heat exchanger element in the form of a cylindrical tube with an integral external helical fin extending along at least the major part of the tube length; the integral finned tube being formed by an extrusion or injection moulding process from a rigid setting plastics material. The invention includes heat exchangers incorporating or formed by the heat exchanger elements.

Funnel vortex generators and heat exchange (transfer) surfaces for heat exchangers

Abstract: The invention encompasses shapes, arrangements and the production of generators of funnel vortices for increasing heat transfer at heat exchange surfaces for free and/or forced convection The axes of the funnel vortices are aligned essentially in the main flow direction and the funnel vortices circulate the heat transfer medium in a pinpointed fashion Owing to the strong rotation generated in the flow at right angles to the main flow direction, the warm or cold fluid layers near the wall continuously replace the cold or warm fluid layers away from the wall and produce a substantial rise in the heat transfer in conjunction with a relatively slight rise in the pressure losses and/or flow losses The invention further relates to heat exchange surfaces with funnel vortex generators Technical applications are heat exchange surfaces of finned (fin-and-tube) heat exchangers, gilled heat exchangers, plate heat exchangers and spiral heat exchangers, as well as heaters, radiators, convectors, housings of calorific electrical and electronic devices, radiant heat exchangers, central volumetric and/or tube-type radiation detectors for the use of solar radiation at high temperature and, furthermore, condensers and evaporators of refrigeration plants or condensers of dry-cooling towers

Testing and analysis of load-side immersed heat exchangers for solar domestic hot water systems

Abstract: This report describes work to determine the performance of load-side heat exchangers for use in residential solar domestic hot water systems. We measured the performance of four heat exchangers: a smooth coil and a finned coil having heat transfer areas of 2.5 m/sup 2/ (26 ft/sup 2/) and those having areas of 1.7 m/sup 2/ (19 ft/sup 2/). A numerical model using the thermal network program MITAS was constructed, and results were compared to the experimental results. Research showed a smooth coil with only 70% of the surface area of a finned coil performed better than the finned coil. Also, load-side heat exchangers can maintain and enhance stratification in storage tanks, permitting the use of control strategies that take advantage of stratified storage tanks to increase system performance. The analytical model, which agreed reasonably well with the experimental results, was used to vary heat exchanger flow rate and area and initial tank temperature for both a smooth- and a finned-coil heat exchanger. Increasing the heat exchanger flow rate and area results in higher heat transfer rates but not necessarily optimal performance. Lower initial tank temperatures resulted in reduced tank stratification. The smooth heat exchanger outperformed the finned heat exchanger withmore » the same outside surface area. 15 refs., 37 figs., 9 tabs.« less

Efficiency of heat and moisture exchangers.

Abstract: We wish to report an unusual case of difficulty in arresting the heart with cold cardioplegic solution. A 62-year-old woman with angina and heart block, treated by unipolar endocardial pacing (Meditronic multiprogrammable pulse generator), presented for coronary artery surgery. A plastic occlusive drape (Johnson and Johnson) was stuck to the chest wall after induction of anaesthesia and skin preparation, and the paccmaker was taken from its infraclavicular pocket and laid on the drape. This insulated the pacemaker’s casing from the patient and interrupted the circuit between the pacemaker and the patient’s heart. Artificial pacing stopped and the patient’s own pacemaker successfully took over control of her heart rate. Surgery continued uneventfully, the sternum was divided, the heart cannulated and, after aortic cross clamping, 500 ml of cold cardioplegic solution (St Thomas’ Hospital) was infused rapidly into the aortic root. The heart stopped beating and the ECG tracing became isoelectric. However, this effect was short-lived and three additional boluses of cardioplegic solution (total 600 ml) were required ovcr thc next 10 minutcs to keep the heart in asystole. The heart was immobile after infusion of the third additional bolus of cardioplegic solution but electrical activity was still seen on the ECG monitor. Inspection of the pacemaker revealed that it was in contact with surgical drapes which were soaked in blood and saline and acted as an electrical pathway back to the patient. The pacemaker was electrically isolated from the patient by placing it inside a latex surgical glove and the ECG became isoelectric again. No more cardioplegia was required and the patient’s surgery and postoperative course continued uneventfully. The rapid return of electromechanical activity in this patient’s heart may have been due partly to a Failure of the cardioplegic solution to reach poorly perfused areas of her myocardium. However, these irritable foci were being inadvertently stimulated, and only when the circuit between the patient and her artificial pacemaker was interrupted did satisfactory cardiac arrest occur. We recommend that great care is taken to ensure that the pacemaker is electrically isolated from the patient before the heart is arrested when a patient with an implanted pacemaker is to have cardiac surgery.

Process of forming enhanced heat transfer surfaces

Abstract: Aluminum alloys suitable for fabrication into plate and fin type heat exchangers are subjected to a chemical etching procedure in order to improve the heat transfer efficiency thereof. Applicants have found that a high temperature heat treatment of an aluminum alloy plate material to produce a precipitate, followed by exposure to an etching composition, results in a heat exchanger surface modified by the formation of pits. The heat exchangers so modified may be advantageously used in the reboiler/condensor section of air separation units.

Indoor unit for air conditioning apparatus

Abstract: PURPOSE:To facilitate reduction of the thickness and the size of an indoor unit, by a method wherein, since arrangement of a plurality of heat exchangers and a direction in which a coolant flows are selected so that counterflow system heat exchanger is performed, efficient heat exchange effectively utilizing a vaporization compression type freezing cycle using a non-azeotropic mixing coolant is performed. CONSTITUTION:An air flow generated through rotation of a blower 5 is sucked through a suction port 2, and is discharged in a room through a discharge port 3 by means of a second heat exchanger 4, a first heat exchanger 4a, and a blower 5. Meanwhile the first and second heat exchangers 4a and 4b are arranged in series to an air flow, and an air flow and the flow of a coolant produce a counterflow on the whole of a heat exchanger equipped with the heat exchangers 4a and 4b. Thus, the first and second heat exchangers 4a and 4b perform an action equivalent to that of heat exchangers in 4 rows in a total to perform high efficiency heat exchange. By effectively utilizing characteristics of a vaporization compression type freezing cycle using a non-azeotropic mixing coolant and providing function equivalent to that of a multi- stage type heat exchanger, heat exchange can be effected with high efficiency, and the thickness of the whole of a heat exchange part can be reduced as the area of a heat exchanger is ensured to some extent.

Heat transfer coefficients of double pipe heat exchanger with helical type roughened surface

Abstract: This work presents experimental information for single-phase forced convection in double pipe heat exchangers containing a two-dimensional helical fin roughness on the outer surface of the inner tube. The objective is to investigate the effect of augmentation heat transfer on this kind of heat exchanger and to evaluate the possibility of replacing the classical double pipe heat exchanger from the economic viewpoint. The present study experiments with a helical angle (α = 65°), a pitch-to-height ratio ( p e = 1.45 ), and three aspect ratios (shellside dia. to tubeside dia.) of D o D i = 2.68, 3.48 and 5.1 and the corresponding ratios of roughness height to hydraulic dia. ( e D H ) of 0.192, 0.13 and 0.08, respectively. Flow visualization was made and the heat transfer performance is caluclated and comparisons of these results with those of smooth tubes at the same aspect ratio are also discussed.

Heat transfer block for cross flow heat exchanger

Abstract: A heat transfer element for cross flow heat exchanger consists of ceramic corrugated and planar plates. A plurality of the heat transfer elements are stacked up in such a manner that the direction of corrugation in adjacent elements intersects at right angles to form a heat transfer block for cross flow heat exchanger. Concave portions of corrugation, which confront soot-blowing flow for removing soot deposited onto the heat transfer surfaces of heat transfer block, are filled with ceramic solids. Also concave portions of corrugation corresponding to the corners, which abut the packings attached when the heat transfer block is installed on a casing, are filled with ceramic solids.

Analysis of Laminar Flow and Heat Transfer in the Entrance Region of an Internally Finned Concentric Circular Annular Duct

Abstract: The concentric circular annular duct is a common geometry in many fluid flow and heat transfer devices. For the purpose of heat transfer augmentation, fins are often employed in the annular region, and such finned ducts find wide application in compact heat exchangers (5, 6). The analysis of flow and heat transfer in this geometry is, therefore, quite important from an engineering standpoint. For fully developed conditions, the problem has already been analyzed (7-10). However, no results are available for the developing flow in the entrance region. It is with this latter problem that the present paper is concerned.

Heat Transfer to Non‐Newtonian Fluid Foods under Laminar Flow Conditions in Horizontal Tubes

Abstract: This paper presents a study of rates of heat transfer to non-Newtonian fluid foods: mango and papaya nectars, passing through horizontal tubes of circular cross section under laminar flow conditions. Determination of the flow and thermal properties of the fluids under study was performed to adequately explain heat transfer experiences. A laminar mixed convection equation was used for describing experimental heat transfer coefficients: Nu = 1.75 [Gz + 0.0083 (Grw . PrW)0.75]1/3 . δ1/3 . (Kb/Kw)0.14 The experimental data covered Graetz numbers between 500 and 7000, and were correlated with a mean deviation of 8.4%. The results should be helpful for interpreting heat transfer to pseudoplastic materials in the design of double tube heat exchangers.

Experimental Investigation of Gas Turbine Recuperator Fouling

Abstract: This paper discusses an experimental investigation of recuperator fouling currently underway at the David Taylor Naval Ship Research and Development Center. The overall approach involves testing different heat exchangers in the exhaust gas stream of a gas turbine. The two heat exchangers initially tested were the plate-fin type and differed in the gas-side heat transfer surface geometry. Primary surface heat exchangers are being considered for future tests also. Test conditions are defined such that the critical part of full-scale recuperators (i.e., the colder end of the gas passages) is simulated in the small test heat exchangers. The composition of the gas stream is measured to determine amounts of gaseous, particulate, and condensible hydrocarbon emissions. Fuel samples taken during each test are analyzed. The test heat exchangers are specially constructed to allow inspection and measurement of the fouling film inside the unit following each test. The temperature distribution inside the test exchanger is measured, as well as air and gas inlet and exit temperatures. Measurements of fouling film thickness are made using an optical microscope and photographs of fouling deposits were taken. The early results obtained from fouling tests conducted with the first heat exchanger are discussed. Tests were also conducted to demonstrate a fouling removal technique.

Maldistribution of flow and its effect on heat exchanger performance

Abstract: This book contains 16 selections. Some of the titles are: Review of Air Flow Problems Associated with Air-Cooled Heat Exchangers in the Process, Power and Petrochemical Industries; The Effect of Nonuniform Inlet Flow and Temperature Distribution on the Thermal Performance of Air-Cooled Condensers; Heat Exchanger Flow Analysis to Resolve Potential Vibration Problems; and Modeling of Flow Maldistribution Effects in Large Steam Generator Heat Exchangers.

Heat transfer and flow studies of the liquid droplet heat exchanger

Abstract: This paper describes a lightweight, highly effective liquid droplet heat exchanger (LDHX) concept for thermal management in space. Heat is transferred by direct contact between fine droplets (100 to 300 micron diameter) of a low vapor pressure liquid and an inert working gas. Complete separation of the droplet and gas media in the microgravity environment is accomplished by configuring the LDHX as a vortex chamber. A quasi-one-dimensional, two-phase heat transfer model of the LDHX is developed and used to investigate the potential use of the LDHX for both heating and cooling the working gas in a 100-k W(e) Braytoan cycle. Experimental studies on a small scale LDHX chamber, using air and water as the two media, show excellent agreement with the theoretical model.

Heat exchanger system having adjustable heat transfer capacity

Abstract: A heat exchanger for a turbine generator power plant includes a plurality of heat transfer tubes for transferring heat from a primary fluid cooling system to a secondary water cooling system subject to variations in inlet temperature and the presence of emulsified particles. Upon a reduction in flow rate in the secondary system, as when accommodating a reduced inlet temperature, a reusable plug assembly comprising compression-actuated cap and plug members is installed on the ends of a selected portion of the heat transfer tubes to increase flow through the remaining heat transfer tubes and thereby reduce the tendency toward sedimentation of the impurities in the tubes. An alternative construction of the plug assembly allows the assembly to be installed with access to only one end of the heat transfer tubes.

低レイノルズ数域のプレートフィンチューブ熱交換器の性能 : 第2報,複数列の場合

Abstract: In the former paper the authors presented experimental data showing the effects of fin spacing, tube spacing and other geometric parameters on the heat transfer and friction performance of single row plate fin and tube heat exchangers. This paper describes the results of a continuation of that earlier study. Heat transfer and pressure drop measurements have been made for 24 plate fin and tube heat exchangers in which the primary physical variable is the flow depth, which varied from 2 to 5 tube rows. The experimental results revealed that the performance of multi row heat exchangers was affected by vortices generated from the outerwall of the tube, and the vortices are activated and strengthened with increasing Reynolds number. Dimensionless equations for the performance of multi row plate fin and tube heat exchangers were obtained.

High temperature heat exchangers

Abstract: This book contains the proceedings from the XVII Symposium of the International Center for Heat and Mass Transfer on High Temperature Heat Exchangers, held August 1985 in Yugoslavia. Papers were presented under the following topics: High Temperature Heat Exchangers Development; Basic Problem in High Temperature Heat Exchangers; Heat Exchangers for High Temperature Recovery; and High Temperature Heat Exchangers for Future Power Plants and Industrial Process Application. Some of the papers' titles are: Future Development of High Temperature Heat Exchangers; Regenerative and Direct Contact High Temperature Heat Exchangers; Heat Exchangers for Heat Recovery; High Temeprature Heat Transfer Augmentation; and Development of a BOF Slag Granulating and Heat Recovering System.