Showing papers on "Concentric tube heat exchanger published in 1995"

Heat transfer tube

Abstract: A heat transfer tube having an internal surface that enhances the heat transfer performance of and also improves the workability of the tube and a method of manufacturing such a tube The internal surface has a plurality of ribs that extend at an angle to the longitudinal axis of the tube A pattern of parallel notches, extending at an angle to the ribs, extend through the ribs and into the main inner surface of the tube wall The tube can be made by rolling embossing the pattern of ribs and notches on to one side of a flat metal strip, then roll forming the strip into a tubular shape with the embossed pattern on the interior of the tubular shape and the edges of the strip forming a longitudinal seam, then joining, preferably by welding, the edges along the longitudinal seam to form a tube In a preferred embodiment, the notches in the inner surface extend into the weld zone of the tube The pattern of ribs and notches increase the total internal surface area of the tube and also promote conditions for the flow of refrigerant within the tube that increase heat transfer performance The notches also serve to inhibit the propagation of splits in the tube wall when the tube is flared

Heat transfer during forced convection condensation inside horizontal tube

Abstract: This paper presents the results of an experimental investigation on heat transfer behaviour during forced convection condensation inside a horizontal tube for wavy, semi-annular and annular flows. A qualitative study was made of the effect of various parameters - refrigerant mass flux, vapour quality, condensate film temperature drop and average vapour mass velocity - on average condensing heat transfer coefficient. Akers-Rosson correlations have been found to predict the heat transfer coefficients within ±25% for the entire range of data. A closer examination of the data revealed that the nature of the relation for the heat transfer coefficient changes from annular and semi-annular flow to wavy flow. Akers-Rosson correlations with changed constant and power have been recommended for the two flow regimes.

X-ray tube having rotary anode cooled with high thermal conductivity fluid

Abstract: An X-ray tube rotating anode (14) is cooled with a liquid metal (40) functioning as a recirculated heat exchange fluid and/or a metal film in a gap (39) between the anode (14) and a stationary structure. The liquid metal (40) is confined to the gap (39) by (a) a labyrinth (44 or 46) having a coating that is not wetted by the liquid, (b) a magnetic structure (22), or (c) a wick (38). The liquid metal (40) recirculated through the anode (14) is cooled in a heat exchanger located either outside the tube or in the tube so it is surrounded by the anode (14). The heat exchanger in the tube includes a mass of metal in thermal contact with the recirculating liquid metal and including numerous passages (36) for a cooling fluid, e.g. water. A high thermal conductivity path (26, 48, 49) is provided between an anode region (16) bombarded by electrons and a central region of the tube where heat is extracted. In one embodiment the high thermal conductivity is achieved by stacked pyrolytic structures having crystalline axes arranged so there is high heat conductivity radially of the region and lower thermal heat conductivity normal to the high heat conductivity direction.

Conjugate heat transfer of a finned tube part a: heat transfer behavior and occurrence of heat transfer reversal

Abstract: The conjugate heat transfer in a high-performance finned-lube heat exchanger element was calculated for three-dimensional thermally and hydrodynamically developing laminar flows. The influence of Reynolds number Re and a fin efficiency parameter Fi (ratio of fin to fluid conductivity times fin thickness to fin pitch) on the heat transfer behavior has been studied. Flow patterns, pressure distribution. Nusselt number distribution, heat flux distribution, and fin efficiency are presented. The part of the fin upstream of the tube is much more efficient than the downstream part. A unique heat transfer phenomenon, a directional reversal of the heat transfer, occurred locally on the fin in the tube wake for small Fi and large Re. This can be interpreted as three-dimensional interaction of convection and the fin conduction in the tube wake, when the flow is dominated by a strong horseshoe vortex and a dead water zone with recirculation.

Multi-flow type heat exchanger

Abstract: A heat exchanger of the multi-flow type is provided with baffle members which are adapted to impart a zigzagging flow to the heat-exchange fluid in motion inside a flat tube and define, in conjunction with the inner wall of the flat tube, a flow path of a cross-sectional area having an equivalent diameter in the range of 0.4 to 1.5 mm. This heat exchanger excels in heat exchange ability and in facility of manufacture and assemblage.

Cooling tube for heat exchanger

Abstract: A heat exchanger for use in connection with engine cooling systems is disclosed herein. The heat exchanger is typically considered a heat exchanger and comprises a plurality of rows of tubes, a pair of headers secured to the ends of the tubes in a mechanical and brazed joint for providing improved vibration and torsional stress resistance and improved durability. More specifically, the tube include a plurality of dimples or tabulators arranged in opposed or non opposed relation agitate the fluid about the primary heat transfer axis to facilitate heat transfer from the hot fluid to the tube wall.

Flow and Cold Heat-Storage Characteristics of Phase-Change Emulsion in a Coiled Double-Tube Heat Exchanger

Abstract: This paper dealt with the flow and cold heat-storage characteristics of the oil (tetradecane, C{sub 14}H{sub 30}, freezing point 278.9 K)/water emulsion as a latent heat-storage material having a low melting point. A coiled double-tube heat exchanger was used for the cold heat storage experiment. The pressure drop, the heat transfer coefficient, and the finishing time of cold heat storage in the coiled tube were measured as experimental parameters. It was understood that the flow behavior of the emulsion as a non-Newtonian fluid had an important role in the present cold heat storage. The useful nondimensional correlation equations for the additional pressure loss coefficient, the heat transfer coefficient, and the cold heat storage time were derived in terms of modified Dean number and heat capacity ratio. 11 refs., 13 figs., 1 tab.

Performance of a compact, spiral coil heat exchanger

Abstract: A spiral coil heat exchanger consists of a number of horizontal layers of spirally wound, finned tubes connected to vertical manifolds at the inner and outermost turns of each coil. This design has advantages in heat recovery and air-conditioning applications. Two theoretical models to predict the performance of this compact heat exchanger are presented based upon unmixed and mixed air-flow considerations. Results of experimental studies on a laboratory model of the spiral coil heat exchanger agree well with the predicted performance of the theoretical models. Charts of effectiveness vs NTU suitable for design are presented.

Conjugate Heat Transfer of a Finned Tube Part b: Heat Transfer Augmentation and Avoidance of Heat Transfer Reversal by Longitudinal Vortex Generators

Abstract: Numerical investigations of three-dimensional flow and heat transfer in a finned tube with punched longitudinal vortex generators (LVG`s) are carried out for Reynolds number of 250 and 300. Air with a Prandtl number of 0.7 is used as the fluid. The flow is both thermally and hydrodynamically developing. The LVG is a delta winglet pair (DWP) punched out of the fin and is located directly behind the tube, symmetrically separated by one tube diameter. The DWP generates longitudinal vortices in the wake of the tube, defers flow separation on the tube, deflects the main stream into the tube wake, and strong reduces the ``dead water zone.`` Heat transfer reversal is avoided by the DWP. Comparison of the span-averaged Nusselt numbers for the fin with and without DWP shows significant local heat transfer enhancement of several hundred percent in the tube wake. For Re = 300 and Fi = 200 the global heat transfer augmentation by a DWP, which amounts to only 2.5% of the fin area, is 31%.

Three-dimensional heat pipe

Abstract: A heat pipe heat exchanger is provided in the form of a serpentine heat pipe that does not have the ends of the individual tubes manifolded to one another via a straight pipe or via any other common connector. Instead, it has been discovered that heat pipes connected via U-bends to form a continuous coil function adequately. The serpentine heat pipe may include integral condenser and evaporator portions separated by a divider to form a one-slab heat exchanger, or separate evaporator and condenser coils connected to one another by vapor and return lines to form a two-section heat pipe. The heat pipe heat exchanger may be formed in a continuous closed-loop pipe so that the heat exchanger can operate with or without the aid of gravitational effects. A method of producing a serpentine heat pipe includes providing a plurality of U-shaped tubes which are interconnected to form a single serpentine heat pipe, one of the tubes having an open end, and inserting sufficient refrigerant in the one tube to allow each of the tubes to function as a separate heat pipe. The serpentine heat pipe heat exchanger may be used to increase the dehumidification capacity of an air conditioner.

Plate fin heat exchanger

Abstract: A fin for use in a heat exchanger of the type comprising a plurality of fluid carrying tubes for transporting heat exchange fluid is disclosed. The fin includes a generally planar base 24 having a longitudinal axis generally perpendicular to the direction of air flowing entering the heat exchanger 10 and a transverse axis generally parallel to the direction of air flow. The axes define a main plane disposed at a predetermined angle (θ) relative to the direction of air flow entering the heat exchanger. The fin 22 further includes a plurality of apertures 30 for receiving tubes 20 therethrough and a plurality of louvres 32 disposed on the base 24 extending generally parallel to the longitudinal axis of the base. The angle θ can be between 140 and 175 degrees to the direction of air flow entering the heat exchanger.

Numerical laminar and turbulent fluid flow and heat transfer predictions in tube banks

Abstract: Numerical predictions of laminar and turbulent fluid flow and heat transfer around staggered and in‐line tube banks are shown to agree closely with seven experimental test cases. The steady state Reynolds‐averaged Navier‐Stokes equations are discretised by means of a cell‐centred finite‐volume algorithm. Two‐dimensional results include velocity vectors and streamlines, surface shear stresses, pressure coefficient distributions, temperature contours, local Nusselt number distributions and average convective heat transfer coefficients, and indicate very good agreement with experimental data. It is found that a relatively fine grid is required to be able to predict the surface heat transfer behaviour accurately. Also, three‐dimensional simulations are shown, which are physically consistent. The numerical procedure presented here is robust, accurate and time efficient, making it suitable as a design tool for tube banks in heat exchangers.

Finned tube heat exchanger and method of manufacture

Abstract: A heat exchanger of the finned tube (34) type in which the tubing (34) is formed in a single, continuous length which is bent into a zigzagged or serpentine shape (22) and then inserted through elongated slots (16) formed in a series of fin plates (15)

Contact resistance-regulated storage heater for fluids

Abstract: A storage fluid heater for heating a fluid, employs a heat storage unit, a heating element thermally coupled to the heat storage unit, and a heat recovery tube thermally coupled to the heat storage unit. The recovery tube is made from a material having a coefficient of thermal expansion so that as the average temperature of the heat storage unit near the heat recovery tube increases, the surface area of gaps between the heat recovery tube and the storage unit increases, causing the contact resistance between the heat storage unit and the heat recovery tube to increase. The temperature of the fluid flowing within the heat recovery tube is thereby limited to a predetermined maximum. A structure that relieves excess pressure when the flow of fluid through the tube is stopped has an expansion tank connected to the fluid inlet of the tube.

Heat transfer and pressure drop characteristics of a plate heat exchanger using a propylene-glycol/water mixture as the working fluid

Abstract: Plate heat exchangers are becoming increasingly important because of their potential applications in industrial processes, especially in terms of their thermal performance and their limited pressure drop. An experimental investigation to acquire both heat-transfer and pressure-drop data for a plate heat exchanger was conducted in order to respond to these interests. A propylene-glycol/water mixture was used as the working fluid in order to provide lower Reynolds numbers than those provided by water at similar test conditions. The plate heat exchanger was composed of 31 plates, each with a chevron angle of 30 degrees. The isothermal pressure drop data were taken in the fully laminar flow regime for Reynolds numbers from 10 to 80. The heat transfer data were taken in the fully laminar flow regime for Reynolds numbers of 80 to 720 with heat transfer rates of 1.1 {times} 10{sup 5} to 6.5 {times} 10{sup 5} W. The experimental data for the friction factor and Nusselt number were correlated using a standard power-law function. Other published heat-transfer and friction factor correlations for plate heat exchangers with similar plates at selected conditions are compared to the data.

Air conditioner and heat exchanger used therefor

Abstract: A heat exchanger mounted on an air condition is constructed such that at least one row of heat conduction pipe groups are arranged across an air passage. Each heat conduction pipe groups is constructed such that a plurality of heat conduction pipes 22 are arranged in parallel with each other and a fine wire 23 made of a metallic material having excellent heat conductivity is spirally wound around each adjacent heat conduction pipes 22. Thus, performances of the heat exchanger can be improved without a possibility that the air conditioner is designed with larger dimensions. In addition, the heat exchanger includes a plurality of heat conduction pipes 39 arranged in the form of at least one row with a constant distance between adjacent ones and a plurality of twisted wires 40. The twisted wires 40 are arranged so as to alternately come in contact with one side and opposite side of each heat conduction pipe 39 extending at a right angle relative to the row direction of each heat conduction pipe 39, and moreover, alternately come in contact with one side and opposite other side of each heat conduction pipe 39 extending in the longitudinal direction. With this construction, high heat conductivity can be realized, and an occurrence of clogging with dew droplets can be prevented while maintaining a heat conduction area.

Unit for distribution and/or collection of cold and/or of heat

Abstract: Unit for distribution and/or collection of cold and/or of heat, including: (a) a main exchanger (1) of heat between a refrigerant fluid (2, 21, 22) and a heat transfer fluid (3); (b) a means for producing cold with a means for heat exchange with the heat transfer fluid; (c) a closed main circuit (3) for continuous free circulation of the heat transfer fluid; (d) at least one heat transfer fluid drawing loop (7 to 11); characterized in that the flow cross-section of the main circuit (3), the maximum refrigerating power of the means for producing cold, Pmax, expressed in W, and the main heat exchanger (1) are sized relative to one another in order to satisfy, in operation, approximately the relationship: P Max =f m ×c×ΔT, in which: f m is the mass flow rate of the heat transfer fluid, expressed in kg/s; c is the mass heat of the heat transfer fluid, in liquid form, expressed in J/kg/°K.; ΔT is the difference in temperature of the heat transfer fluid between the exit and the entry of the main exchanger (1).

Evaporation heat transfer of falling films on horizontal tube. Part 1: Analytical study

Abstract: Evaporation heat transfer of a saturated falling film on a horizontal tube was studied analytically. For laminar flow, a model comprised of the developing, transitional, and developed regions is proposed. The boundary layer integral method was used to reach a closed-form solution. A third-order polynomial temperature profile was assumed in the developing region, and a linear profile in the developed region. Both profiles join smoothly in the transition region. From this analysis, the Nusselt number was presented as a function of film Reynolds number, Prandtl number, and dimensionless tube radius. A similar correlation was developed for turbulent flow using the eddy viscosity model, where the Nusselt number was obtained as a function of film Reynolds number and Prandtl number.

On-line fouling monitor for service water system heat exchangers

Abstract: An electro-mechanical, dual tube and plug device for on-line monitoring of performance losses due to reduced conductivity of a non condensing heat exchanger resulting from micro-bio fouling of the surfaces of said heat exchanger and for detecting change of heat transfer resistance of individual heat transfer tubes. The dual tube and plug assembly includes a first flow assembly tube and a second temperature assembly tube attached to the discharge end of a heat exchanger for providing accurate measurement of temperature and cooling water flow. The first flow assembly tube includes a tube having an inner chamber, including a flow sensor a temperature sensor for measuring discharge water temperature. The second temperature assembly tube plugs the inlet and the outlet of a heat transfer tube immediately adjacent to the flow assembly tube and includes a plurality of temperature sensors in the plugged empty heat transfer tube. Flow and discharge temperature signals from a first dual tube device are combined with other flow and discharge temperature signals, from additional dual tube devices. These signals are sent to a micro-processor which, utilizing inlet water temperature data provided by an inlet temperature sensor, continuously calculates, records and displays the individual heat transfer tube heat transfer co-efficient.

Refrigeration system and method for cooling a susceptor using a refrigeration system

Abstract: The refrigeration system according to the invention includes a vacuum jacketed pressure vessel which contains both a spray heat exchanger and a shell and tube heat exchanger. The spray heat exchanger includes one or more nozzles for directing a first refrigerant at a heat exchanger element conveying a second refrigerant. The first refrigerant is sprayed in a fine mist from the nozzles onto the heat exchanger element conveying the second refrigerant. The first refrigerant then evaporates and cools the second refrigerant within the heat exchanger element. The shell and tube heat exchanger is a counter current heat exchanger which includes an inner tube for conveying the second refrigerant to the spray heat exchanger, and an outer tube surrounding the inner tube for conveying the first refrigerant recovered from the interior of the vacuum jacketed pressure vessel out of the pressure vessel. The spray heat exchanger recovers the heat of vaporization of the primary refrigerant, while the shell and tube heat exchanger recovers the enthalpy remaining in the evaporated first refrigerant.

Shell-and-tube heat exchanger with corrugated heat transfer tubes

Abstract: A shell-and-tube heat exchanger includes a shell, heat transfer tubes, tube plates, covers, inlet and outlet for fluid flowing into and out of the shell, and inlet and outlet for fluid flowing into and out of the tubes, wherein the heat transfer tubes are corrugated heat transfer tubes, the tubing wall of the corrugated heat transfer tube is configured along the longitudinal direction of the corrugated heat transfer tube in a shape formed by tangentially connecting the crests of large arcs and the valleys of small arcs, the outside diameter D of the corrugated heat transfer tube is set at 1.3 to 1.5 times the inside diameter d, the corrugated heat transfer tubes are arranged spirally around the axis of the shell in multi-layers, and spiral plates are inserted between two layers of the corrugated heat transfer tubes.

Structure of heat exchanger

Abstract: A heat exchanger structure is disclosed including: a plurality of heat exchange fins stacked at predetermined intervals for enhanced thermal conduction; heat transfer tubes perpendicularly penetrating the heat exchange fins so that coolant conveyed there through is heated or cooled; an intake side in which a plurality of slits are cut and raised from a reference surface of the fin in a central portion between the heat transfer tubes with angled edges so that air is directed to the heat transfer tube; and an outlet side having raised slits whose edges are disposed at a larger angle than the intake side, increasing the velocity of air flow passing through the periphery of the heat transfer tube to enhance heat exchange and thereby prevent the flow from being stagnated at the rear of the heat transfer tube.

Experimental investigation for fluid flow and heat transfer in a rotating tube with twisted-tape inserts

Abstract: Experimental investigation was carried out for friction factor and heat transfer coefficient in the case of a rotating tube with a twisted-tape insert for heat transfer augmentation. The data obtained were compared with existing data for a stationary tube with a twisted-tape insert. It has been observed that the enhancement in heat transfer offsets the rise in friction factor due to rotation, with respect to a plain tube under stationary conditions. A correlation has been proposed for the data obtained.

A numerical study of flow and thermal fields in finned tube heat exchangers (Effect of the tube diameter)

Abstract: Enhancement of air-side heat transfer in heat exchangers used in air-conditioning machines can be considered as a way to solve the problem caused by use of alternative refrigerants. Related with this, the present study aims to investigate the flow and thermal fields in finned tube heat exchangers. In previous papers (Torikoshi et al., 1994 and Xi et al., 1994, 1995), numerical schemes that used a compound grid system for finned tube heat exchangers were described. The schemes were validated with experimental data. In the present paper, a three-dimensional unsteady numerical computation for a model of a two-row finned tube heat exchanger located in a uniform flow field has been performed to see the effect of tube diameter on the flow and thermal fields. Several features were found in the study. One interesting finding was that increasing the tube diameter almost does not improve heat transfer performance but increases the resistance of the fluid flow inside the heat exchanger.

Heat exchanger for a gas compression/expansion apparatus and a method of manufacturing thereof

Abstract: An improved heat exchanger for use in a gas compression/expansion apparatus. The heat exchanger comprises: a tube connected with a compression/expansion space of a compression/expansion cylinder of the apparatus; a central cylinder coaxially disposed in the tube such that a narrow gap for the working gas is formed only between the central cylinder and the tube. The heat exchanger may liberate heat from, or providing heat to, the compression/expansion cylinder through heat transfer between the working gas in the tube and an ambient medium surrounding said tube. The heat exchanger is capable to serve as a low/high temperature heat source for an external heat load.