Showing papers on "Concentric tube heat exchanger published in 2005"

Experimental and numerical investigation of thermal energy storage with a finned tube

Abstract: A latent heat thermal energy storage system using a phase change material (PCM) is an efficient way of storing or releasing a large amount of heat during melting or solidification. It has been determined that the shell-and-tube type heat exchanger is the most promising device as a latent heat system that requires high efficiency for a minimum volume. In this type of heat exchanger, the PCM fills the annular shell space around the finned tube while the heat transfer fluid flows within the tube. One of the methods used for increasing the rate of energy storage is to increase the heat transfer surface area by employing finned surfaces. In this study, energy storage by phase change around a radially finned tube is investigated numerically and experimentally. The solution of the system consists of the solving governing equations for the heat transfer fluid (HTF), pipe wall and phase change material. Numerical simulations are performed to investigate the effect of several fin parameters (fin spacing and fin diameter) and flow parameter (Re number and inlet temperature of HTF) and compare with experimental results. The effect of each variable on energy storage and amount of solidification are presented graphically. Copyright © 2005 John Wiley & Sons, Ltd.

Heat transfer characteristics of flat plate finned-tube heat exchangers with large fin pitch

Abstract: The objective of this study is to provide experimental data that can be used in the optimal design of flat plate finned-tube heat exchangers with large fin pitch. In this study, 22 heat exchangers were tested with a variation of fin pitch, number of tube row, and tube alignment. The air-side heat transfer coefficient decreased with a reduction of the fin pitch and an increase of the number of tube row. The reduction in the heat transfer coefficient of the four-row heat exchanger coil was approximately 10% as the fin pitch decreased from 15.0 to 7.5 mm over the Reynolds number range of 500–900 that was calculated based on the tube diameter. For all fin pitches, the heat transfer coefficient decreased as the number of tube row increased from 1 to 4. The staggered tube alignment improved heat transfer performance more than 10% compared to the inline tube alignment. A heat transfer correlation was developed from the measured data for flat plate finned-tubes with large fin pitch. The correlation yielded good predictions of the measured data with mean deviations of 3.8 and 6.2% for the inline and staggered tube alignment, respectively.

Helical coil-on-tube heat exchanger

Abstract: A coil on tube heat exchanger is provided that uses multiple parallel helical channels to limit liquid pressure losses while providing similar performance and production times to previous coil and tube designs. Two or more channels are wrapped together around a tube in a helical fashion, permitting the heat exchanger to be used in a counter-flow, or contra-flow, implementation. The system preferably includes a header, or manifold, to connect two or more of the channels together at the beginning and/or end of the tube. However, each individual channel may be connected to a separate load and kept independent. The plurality of channels can be implemented within a single tube or via multiple tubes, or a combination thereof. Embodiments of the present invention provide reduced pressure loss, higher performance and are generally faster to manufacture than prior heat exchangers.

Heat exchanger and water heater

Abstract: A heat exchanger A1 includes a partition 19 partitioning the space 35 surrounded by a coiled tube 60 at an axially intermediate portion of a housing 2 into a first and a second regions 35 a and 35 b and partitioning the coiled tube 60 into a first and a second heat exchanging portions HT1 and HT2. The combustion gas supplied to the first region 35 a flows to a combustion gas path 36 by passing through a clearance 61 of the first heat exchanging portion HT1 and then passes through a clearance 61 of the second heat exchanging portion HT2. With this structure, the amount of heat recovery is increased, and the heat exchange efficiency is enhanced while simplifying the overall structure of the heat exchanger A1 and reducing the size of the heat exchanger.

Heat Transfer Enhancement for Finned-Tube Heat Exchangers With Winglets

Abstract: This paper presents the results of an experimental study of forced convection heat transfer in a narrow rectangular duct fitted with a circular tube and/or a delta-winglet pair. The duct was designed to simulate a single passage in a fin-tube heat exchanger. Heat transfer measurements were obtained using a transient technique in which a heated airflow is suddenly introduced to the test section. High-resolution local fin-surface temperature distributions were obtained at several times after initiation of the transient using an imaging infrared camera. Corresponding local fin-surface heat transfer coefficient distributions were then calculated from a locally applied one-dimensional semi-infinite inverse heat conduction model. Heat transfer results were obtained over an airflow rate ranging from 1.51 x 10-3 to 14.0 x 10-3 kg/s. These flow rates correspond to a duct-height Reynolds number range of 670 – 6300 with a duct height of 1.106 cm and a duct width-toheight ratio, W/H, of 11.25. The test cylinder was sized such that the diameter-to-duct height ratio, D/H is 5. Results presented in this paper reveal visual and quantitative details of local fin-surface heat transfer distributions in the vicinity of a circular tube, a delta-winglet pair, and a combination of a circular tube and amore » delta-winglet pair. Comparisons of local and average heat transfer distributions for the circular tube with and without winglets are provided. Overall mean finsurface Nusselt-number results indicate a significant level of heat transfer enhancement associated with the deployment of the winglets with the circular cylinder. At the lowest Reynolds numbers (which correspond to the laminar operating conditions of existing geothermal air-cooled condensers), the enhancement level is nearly a factor of two. At higher Reynolds numbers, the enhancement level is close to 50%.« less

Fluid agitating fin, method of fabricating the same and heat exchanger tube and heat exchanger or heat exchanging type gas cooling apparatus inwardly mounted with the fin

Abstract: A fluid agitating plate fin is mounted to a heat exchanger tube to agitate a cooling fluid and to create a turbulent flow. Edges of the plate fins are opposed to each other and the opposed butted blade edges cross each other.

Heat transfer during annular tube contact in a helically coiled tube-in-tube heat exchanger

Abstract: Helically wound tube-in-tube heat exchangers are manufactured by coiling two tubes, one placed inside the other. This method often results in the tubes not sharing the same center line, and therefore annular contact occurs in some cases. An experimental comparison was made of such tubes in a heat exchanger with annular contact, as opposed to an aligned (concentric) device without annular contact, in order to quantify the effect of annular contact in terms of heat transfer coefficients and pressure drop. By comparing the heat transfer characteristics, it was concluded that the heat transfer coefficient in the annulus was found to increase substantially. The result was an improved performance by the heat exchanger where annular contact occurs, compared to the heat exchanger with the inner tube in a concentric position.

3D numerical heat transfer and fluid flow analysis in plate-fin and tube heat exchangers with electrohydrodynamic enhancement

Abstract: Three-dimensional laminar fluid flow and heat transfer over a four-row plate-fin and tube heat exchanger with electrohydrodynamic (EHD) wire electrodes are studied numerically. The effects of different electrode arrangements (square and diagonal), tube pitch arrangements (in-line and staggered) and applied voltage (VE=0–16 kV) are investigated in detail for the Reynolds number range (based on the fin spacing and frontal velocity) ranging from 100 to 1,000. It is found that the EHD enhancement is more effective for lower Re and higher applied voltage. The case of staggered tube pitch with square wire electrode arrangement gives the best heat transfer augmentation. For VE=16 kV and Re = 100, this study identifies a maximum improvement of 218% in the average Nusselt number and a reduction in fin area of 56% as compared that without EHD enhancement.

Dynamic model of a supercritical carbon dioxide heat exchanger

Abstract: A dynamic model of a heat exchanger for heating supercritical carbon dioxide under turbulent conditions is presented in this paper. The model takes into account the resistance to heat transfer in the gas as well as in the heating fluid (liquid water at ambient pressure) and across the stainless steel wall of the inner tube. Experimental data on convective heat transfer to supercritical carbon dioxide was measured in a vertical double-pipe stainless steel heat exchanger, in the pressure range 10–21 MPa, temperatures ranging from 313 to 343 K, and carbon dioxide mass flowrates from 3 to 12 kg/h. The corresponding Reynolds (Re) and Prandtl (Pr) numbers ranged from 5 × 103 to 3 × 104 and from 1.5 to 3, respectively. Based on the experimental data, a correlation was developed for the heat-transfer coefficient of supercritical carbon dioxide in the inner pipe as a function of Re and Pr. The dynamic model is able to predict the temperature of the outlet gas flow stream under steady-state conditions within ±2.3% of the experimental values, and the dynamic response of the heat exchanger to step disturbances in process variables.

Heat flux measuring device for pressure pipes, method for producing a measuring device, method for monitoring an operating state of a heat exchanger, heat exchanger and method for measuring a heat flux

Abstract: A measuring device for a heat exchanger includes a heat exchanger pressure pipe having a pipe wall with a circumference, and an indentation extending over and deforming a portion of the circumference At least one thermocouple is disposed eccentrically in the portion of the circumference deformed by the indentation Filling material fills the indentation A method for producing a measuring device in a pressure pipe of a heat exchanger, a method for monitoring an operating state of a heat exchanger having a pressure pipe, a heat exchanger, and a method for measuring a heat flux, are also provided The size of the indentation can be decreased for a given size of the thermocouple due to the eccentric configuration of the thermocouple, so that the heat flux is obstructed to a comparatively small degree by the pipe wall while local overheating of the pipe wall is prevented

Heat exchanger and heat pump water heater using it

Abstract: PROBLEM TO BE SOLVED: To provide a compact heat exchanger excellent in mountability in equipment and having high performance. SOLUTION: The heat exchanger 10 is constituted by a plurality of pipes 1 arranged on the same plane in parallel to each other; a first fluid flow passage comprising an entrance header 2 and an exit header 3 for communicating the plurality of pipes 1 at both ends; and a second fluid flow passage comprising an approximately flat box body 6 including the plurality of pipes 1. A dead space as occurred in a conventional one is reduced, a mounting density of the heat exchanger is enhanced and the minimization of a storage space can be realized. Further, since the heat exchanger can be constituted in an approximately flat plate-like shape, the compact heat exchanger having excellent mountability to the equipment can be provided. Further, enlargement of a heat transfer area by multi-pipe becomes relatively easy and high performance and enlargement of ability of the heat exchanger can be easily realized. COPYRIGHT: (C)2006,JPO&NCIPI