ISSN:0145-7632    

DOI:10.1080/01457630050144442

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

ISSN:0145-7632    

DOI:10.1080/014576300270979

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

Heat exchanger networks (HEN) play important roles in a chemical plant. In a plant lifetime, it may be required to retrofit a HEN several times in order to improve the energy efficiency or to accommodate the increase in throughput. The network pinch method developed by Asante and Zhu [1] can identify bottlenecks, which limit the increase in heat recovery for an existing HEN and also indicate promising structure changes to overcome the bottlenecks. As a result of HEN retrofit, additional surface area is required for some heat exchangers. There are a number of options to provide additional area, such as installing new shells or new units, adding new tubes to an existing bundle, etc. If heat transfer enhancement (HTE) is applied, additional area can be reduced significantly. This can result in a great reduction in capital cost and implementation time for modifications. However, in practice, heat transfer enhancement techniques have not been applied extensively, particularly in the petroleum refining industry. Several main aspects need to be addressed when HTE is taken into consideration for HEN retrofit. The first is how to determine which heat exchangers are suitable to apply HTE in the network and the second issue is to determine what level of augmentation of heat transfer performances is required. The last is about how to select a particular enhancement technique that can fulfil the enhancement requirement. A new strategy for applying HTE in HEN retrofit at the conceptual design stage has been developed. The above issues can be addressed properly by this new method. The new procedure is demonstrated using a case study.

ISSN:0145-7632    

DOI:10.1080/014576300270988

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

Efficiency of noncircular fins circumscribing circular tubes is generally determined by one of two approximate techniques, the equivalent annulus method or the sector method. In the present work the predictions of these two methods are compared with results obtained from a semianalytical technique for square, hexagonal, and eccentric annular fins. It is observed that the accuracy of the equivalent annulus method reduces with the increase of the two-dimensionality of the fins. However, the sector method guarantees very close agreement with the semianalytical technique over a wide range of parametric variations for all the fins. An improved definition of fin efficiency for the sector method is also put forward to take care of the heat loss from fin tips. Finally, it is shown that the optimum dimensions of the fins determined by the sector method closely match the predictions of the semianalytical technique.

ISSN:0145-7632    

DOI:10.1080/014576300270997

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

An experimental investigation has been carried out for the condensation of R-134a vapor on four single horizontal circular integral-fin tubes (CIFTs) made of copper. The fins are of trapezoidal shape and the fin density of these tubes has been varied systematically from 934 fpm to 1,875 fpm. All the experimental data have been acquired at the saturation temperature of 312.4 +/- 0.5 K. The CIFT with 1,560 fpm fin density has been found to be the best-performing tube, as it has provided an enhancement factor (EF) of the order of 5.6. The experimental results are in the best agreement with Honda and Nozu model. This model has predicted 80% of the experimental results in a range of 0-30%.

ISSN:0145-7632    

DOI:10.1080/014576300271004

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

In the present work the geometry of annular ducts with asymmetrical longitudinal fins is optimized in order to enhance the heat transfer under laminar coolant flow conditions. The heat transferred is also maximized for a given amount of material or hydraulic resistance. Polynomial profiles are assigned to the two lateral fin surfaces. Velocity and temperature distributions on the annular duct cross section are determined with the help of a finite-element model. A global heat transfer coefficient and an equivalent Nusselt number are then calculated. Lastly, optimum asymmetrical fins obtained by means of a genetic algorithm are shown for different situations and their performance is compared with those of optimum symmetrical fins.

ISSN:0145-7632    

DOI:10.1080/014576300271013

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

For annular-sector ducts, steady, laminar, and constant-property forced-convection flow and heat transfer in the entrance region have been analyzed numerically using a general, marching procedure. Two types of thermal boundary conditions have been considered: (1) uniform temperature both axially and peripherally (T boundary condition); (2) uniform axial heat flux with uniform peripherally temperature at any cross section (H1 boundary condition). Numerical analysis has been conducted in the following range of parameters:Di/Do= 0.00, 0.25, 0.50, apex angle of the sector 2 alpha = 18 degrees, 20 degrees, 24 degrees, 30 degrees, 40 degrees, and Pr = 0.707. The solutions of the developing Nusselt number and friction factor are presented as functions of nondimensional axial distance. Comparisons are made between the computed results and the analytical or numerical results available in the literature. For all cases compared, satisfactory agreement is obtained.

ISSN:0145-7632    

DOI:10.1080/014576300271022

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

The present study examines the performance difference between straight and coiled capillary tubes. The test results indicate that the helical effect increased with decrease of the diameter of coiling, and the effect of inlet conditions is relatively small. Based on the present test results, a simple relation is proposed which can quantitatively describe the difference between coiled and straight capillary tubes.

ISSN:0145-7632    

DOI:10.1080/014576300271031

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

A temperature-controlled hot water heat pump was simulated using heating in a vertical, domestic hot water storage tank. The influence of the return loop flow rate on stratification was investigated experimentally. The return loop is the water line that supplies a long line of consumers with hot water, and returns colder water to the middle of the hot water storage tank. The return temperature is a function of the length of the loop, insulation, and ambient conditions. Temperatures were measured as a function of time at different vertical locations on the centerline of the storage tank. The temperature distributions in the tank were compared for different return flow rates. A return flow rate of three tank volumes per day was identified as preferable, although good results were also obtained for less than three tank volumes per day.

ISSN:0145-7632    

DOI:10.1080/014576300271040

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

ISSN:0145-7632    

DOI:10.1080/014576300271059

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor