ISSN:0145-7632    

DOI:10.1080/01457638608939640

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

By using interchangeable novel end caps, heat exchangers can be designed for operation with a variable number of tube passes. Such flexibility can allow significant savings in operating costs, as it allows exchangers to be tuned to actual process conditions. Since the pass partitions in the end caps take up minimal space, the tube bundles contain virtually the full number of tubes of a single-pass unit: an advantage that becomes more significant as the number of tube passes increases. Other advantages include improved arrangements for gasketing, which reduce the possibility of hazardous leaks as well as reducing maintenance costs. These improved features are discussed in connection with actual exchanger applications

ISSN:0145-7632    

DOI:10.1080/01457638608939641

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

To find a simple means for monitoring the heat output of a wood stove, general engineering models of heat transfer are used to develop a model that predicts the heat output of a stove from measurements of surface temperature. Using the surface area and the measured surface temperature as inputs, the model predicts the heat output of the stove by radiation and natural convection. As a means of verification, surface temperature data from four wood stoves monitored in a calorimeter room are used to make heat output predictions. The predicted heat outputs are then compared with the actual heat outputs measured by the calorimeter room. The predictions involve several potential monitoring schemes:(J) separate temperature measurements for each surface of the stove,() an average temperature measurement for all stove surfaces, and () a single surface temperature measurement. The accuracies of the predictions are characterized by their geometric bias and scatter as well as their predictions of total energy delivered. The scatter is a measure of the trackability of the model, analogous to the arithmetic standard deviation. Predictions made from average temperature measurements are found to be as accurate as those based on individual temperature measurements, whereas single-temperature measurements cause an additional 5 % uncertainty in predictions. For both the average temperature and individual temperature predictions, the bias is between 2 % and 24%, with 16% as the typical scatter. The trend in the bias is underprediction, possible causes of which are discussed at length.

ISSN:0145-7632    

DOI:10.1080/01457638608939642

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

For complicated physical arrangements, thermal design information historically has been obtained from experimentation. By interpreting experimental data in the form of nondimensional parameters, results can be applied to situations phenomenologically similar to, but physically different from, experimental conditions. Empirically derived natural convection correlations extracted from the scientific literature are compared with nondimensionalized data obtained from physical models of uniformly heated electronic circuit cards vertically mounted in a frame. Tlie majority of data points were clustered in the modified channel Rayleigh number (Ra“) region of 15 to 100, where densely populated, narrow channeled, and intensely powered circuit card applications occur. The universal correlations of Wirtz and Stutzman [4] and Bar-Cohen and Rohsenow [5] compared quite well with experimental data collected from electronic equipment being developed at AT&T Bell Laboratories and are recommended for 10<0Ra “< 1000. For Ra “ < 10, Aung‘s [2] fully developed laminar channel flow equation is recommended; for Ra > 1000, Aung et al.‘s [3] approximation of the single vertical plate is preferred because of its conservative nature when compared with two similar correlations and its close agreement with the findings of Sparrow and Gregg [<H1>INTRODUCTION]. Computations with Coyne's I13J algorithms also compared very favorably with experimental data for symmetrically heated sections of an equipment frame for 10<Ra“< 1000 and demonstrated acceptable accuracy for Ra values between 1000 and 10,000. The designer or analyst can confidently use these correlations, obtained primarily from ideal flow channels, to estimate the maximum average temperature rise in a vertical bank of electronic circuit boards cooled by natural convection

ISSN:0145-7632    

DOI:10.1080/01457638608939643

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

This paper describes the derivation of a critical heat flux (CHF) lookup table, which may be used for predicting CHF for water over a very wide range of conditions. The CHF table is based on the Chalk River Nuclear Laboratories' CHF data bank, which contains more than 15.000 CHF data points for water. A comparison of the prediction accuracy of the CHF lookup table and selected CHF correlations is presented. The table method is not designed to replace ad hoc CHF correlations derived for a given geometry over a narrow range of flow conditions; rather it is designed to provide a reasonable estimate of CHF over a very wide range of flow conditions and geometries, especially over the ranges where CHF data are scarce. It may also be used to predict CHF for nonaqueous fluids by fluid-to-fluid modeling techniques

ISSN:0145-7632    

DOI:10.1080/01457638608939644

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Experimental fouling data have been analyzed on the basis of the change in overall heal transfer coefficient of the fouling test section. It is assumed that thermal hydraulic conditions in the test section remain reasonably constant for the duration of a fouling test. The model ofTaborek et al.|I| is used, and two parameters,/8,. and Rf*, that can be determined for each fouling test are derived by regression analysis. The parameter Rf* contains all the factors that influence fouling, while 1/ ?c, contains shear stress, deposit thickness, and bonding strength of the deposit. The parameter R*is the asymptotic fouling resistance and ? is the lime constant of the fouling resistance-time curve. These parameters were determined as a function of surface temperature. Limited data were available to indicate the effect of velocity on the parameters. The parameters 1/8, and R* may be used to predict the history of fouling in a heat exchanger. Until more.data are obtained and analyzed in this fashion, the values of 1/ ?c. and R* obtained in this paper should be applied at conditions for which the fouling data were obtained. A numerical example is presented.

ISSN:0145-7632    

DOI:10.1080/01457638608939645

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A method is proposed for computing the upper hound on the local water temperature rise with respect to the hulk temperature in a spent fuel pool. The solution involves casting the continuity and momentum relationships in integral form in terms of the unknown velocity functions. The method of collocation is used to solve the problem. Computer application of this method shows it to he an efficient and cost-effective design tool.

ISSN:0145-7632    

DOI:10.1080/01457638608939646

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The entropy generation (irreversibility) concept founded on the second law of thermodynamics may be applied in heat exchanger analysis. In this paper the quantity termed enthalpy exchange irreversibility norm (EEIN) is the measure of the internal heat exchanger irreversibilities. The behavior of EEIN as a function of the heat exchanger thermal size is discussed for an arbitrary flow arrangement and more precisely for two characteristic limiting cases: cocurrent and countercurrent heat exchangers.

ISSN:0145-7632    

DOI:10.1080/01457638608939647

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor