A Maintenance Strategy for Heat Transfer Equipment Subject to Fouling: A Probabilistic Approach

1997 ◽  
Vol 119 (3) ◽  
pp. 575-580 ◽  
Author(s):  
S. M. Zubair ◽  
A. K. Sheikh ◽  
M. O. Budair ◽  
M. A. Badar
Keyword(s):  
Heat Transfer ◽  
Critical Level ◽  
Performance Indicator ◽  
Probabilistic Approach ◽  
Stochastic Approach ◽  
Maintenance Strategy ◽  
Scatter Parameter ◽  
Cleaning Cycle ◽  
Maintenance Schedules ◽  
Cost Implications

Fouling of heat transfer surfaces introduces a major uncertainty into the design and operation of heat transfer equipment. After a brief discussion on impact of fouling, we present and discuss a stochastic approach to the analysis of fouling models. In view of the performance indicator (U/Uc) of the heat exchangers, a maintenance strategy for planned maintenance schedules is presented. Various scenarios of reliability based maintenance strategy are introduced. The strategy is explained in terms of the scatter parameter (α) of the time-to-fouling distribution corresponding to a critical level of fouling, and the risk factor (p) representing the probability of tubes being fouled to a critical level after which a cleaning cycle is needed. In addition, the cost implications of the above mentioned strategy are explained and their impact on heat exchanger maintenance is highlighted.

Lime salts: origin and control in beet processing

2020 ◽  
pp. 282-287
Author(s):  
Jan Maarten de Bruijn
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Performance Indicator ◽  
Key Performance Indicator ◽  
Process Measures ◽  
Trouble Shooting ◽  
Important Chemical ◽  
And Control ◽  
Affect Processing ◽  
White Sugar

Lime salts in the thin juice obtained after juice purification is one of the most important chemical KPI’s (Key Performance Indicator) in beet processing. Too high lime salts content will significantly affect processing costs – particularly energy – due to scaling of heat exchange surfaces thus decreasing heat transfer. In addition, high lime salts are at the origin of turbidity and insoluble solids in white sugar. Therefore, it is of the utmost importance to understand the chemistry behind lime salts in beet processing in order to be able preventing too high lime salts contents in thin juice. This paper will explain the details of the chemistry behind the presence of lime salts. Further, a trouble-shooting guide is included to elucidate the different causes for high lime salts contents and how these causes can be identified, as well as the process measures to reduce the lime salts content in thin juice.

scholarly journals Building condition assessment: adjustments of the Building Performance Indicator (BPI) for university buildings in Brazil

2020 ◽  
Vol 20 (1) ◽  
pp. 215-230
Author(s):  
Francisco Morato Leite ◽  
Renan Alves Volse ◽  
Humberto Ramos Roman ◽  
Fernanda Aranha Saffaro
Keyword(s):  
Research Laboratory ◽  
Performance Indicator ◽  
Ease Of Use ◽  
Maintenance Management ◽  
Building Performance ◽  
Maintenance Strategy ◽  
Building Systems ◽  
Different Types ◽  
University Buildings ◽  
Building Condition

Abstract The Building Performance Indicator (BPI), not fully applied in Brazil, expresses objectively the overall condition of a building based on the performance assessment of the building systems that comprise it. Although BPI was originally developed for hospital facilities, it can be used in different types of buildings since its methodology is generic. The objective of the study is to adjust the BPI to allow its application in the maintenance management of Brazilian university buildings. The stages of the research consist of (1) adjusting the factors and criteria that comprise the BPI; (2) implementing the adapted BPI; and (3) verifying its utility and ease of use. The adjustment and implementation included a building for classrooms and another that houses a teaching and research laboratory, both located at University X. The results obtained allowed the comparison of the overall condition between the inspected buildings, which establishes the intervention priority helping to adopt the most adequate maintenance strategy.

Error Analysis of Cam-Follower Systems: A Probabilistic Approach

1984 ◽  
Vol 198 (3) ◽  
pp. 155-162 ◽  
Author(s):  
S S Rao
Keyword(s):  
Error Analysis ◽  
Probabilistic Approach ◽  
Random Variables ◽  
Stochastic Approach ◽  
Geometrical Parameters ◽  
Manufacturing Costs ◽  
Actual Output ◽  
Analysis And Synthesis ◽  
Cam Follower ◽  
Synthesis Procedure

The actual output kinematic characteristics of a cam-follower system will be different from the theoretical (desired) ones due to errors in manufacture and assembly. A method of evaluating the mechanical error in the kinematic response of cam-follower systems is presented using a stochastic approach. The tolerances on cam profiles and other geometrical parameters are treated as random variables that influence the mechanical error. The equations necessary for the mechanical error analysis of a planar cam-follower system (disc cam with translating roller follower) are derived. The equations for a spatial cam-follower system (globoidal cam with oscillating cylindrical follower) are also given at the end. An optimal synthesis procedure is outlined for the allocation of tolerances so as to minimize the manufacturing costs while satisfying a constraint on the maximum mechanical error in the kinematic response of cam-follower systems. The application of analysis and synthesis procedure is demonstrated with reference to a disc cam with translating roller follower.

scholarly journals Demographic Projections: User and Producer Experiences of Adopting a Stochastic Approach

2016 ◽  
Vol 32 (4) ◽  
pp. 947-962 ◽  
Author(s):  
Kim Dunstan ◽  
Christopher Ball
Keyword(s):  
New Zealand ◽  
Probabilistic Approach ◽  
Stochastic Approach ◽  
New Approach ◽  
Demographic Projections ◽  
Statistical Agencies

Abstract Statistics New Zealand is one of the few national statistical agencies to have applied a stochastic (probabilistic) approach to official demographic projections. This article discusses the experience and benefits of adopting this new approach, including the perspective of a key user of projections, the New Zealand Treasury. Our experience is that the change is less difficult to make than might be expected. Uncertainty in the different projection inputs (components) can be modelled simply or with more complexity, and progressively applied to different projection types. This means that not all the different demographic projections an agency produces need to adopt a stochastic approach simultaneously. At the same time, users of the projections are keen to better understand the relative certainty and uncertainty of projected outcomes, given the important uses of projections.

Stochastic approach for performance evaluation regarding water distribution systems

2007 ◽  
Vol 56 (9) ◽  
pp. 29-36 ◽  
Author(s):  
M. Möderl ◽  
T. Fetz ◽  
W. Rauch
Keyword(s):  
Performance Evaluation ◽  
Case Studies ◽  
Distribution Systems ◽  
Water Distribution ◽  
Performance Indicator ◽  
Water Distribution Systems ◽  
Stochastic Approach ◽  
Cumulative Distribution ◽  
Design System ◽  
The Impact

A traditional procedure for performance evaluation of systems is to test approaches on one or more case studies. However, it is well known that the investigation of real case studies is a tedious task. Moreover, due to the limited amount of case studies available it is not certain that all aspects of a problem can be covered in such procedure. With increasing computer power an alternative methodology has emerged, that is the investigation of a multitude of virtual case studies by means of a stochastic consideration of the overall performance. Within the frame of this approach we develop here a modular design system (MDS) for water distribution systems (WDSs). With the algorithmic application of such a MDS it is possible to create a variety of different WDSs. As an example of stochastic performance evaluation the impact of pipe breakages on WDSs is estimated applying a pressure driven performance indicator. This performance indicator is evaluated stochastically. Likewise the performance evaluation of a variety of WDSs is also performed stochastically. Cumulative distribution function, histogram and other statistical properties of 2,280×1,000 performance results of the different WDSs are calculated to highlight the applicability of the introduced stochastic approach.

Effect of Notch Location on the Stress Concentration and Reliability of Notched Composite Laminates Based on a Probabilistic Approach

2007 ◽  
Author(s):  
R. Ganesan ◽  
A. K. Arumugam
Keyword(s):  
Stress Concentration ◽  
Stress Distribution ◽  
Composite Laminates ◽  
Probabilistic Approach ◽  
Stochastic Approach ◽  
Strength Properties ◽  
Practical Reasons ◽  
Commercial Aircraft ◽  
Reinforced Plastics ◽  
Reliability Based Design

Composite materials and laminates are being widely used in aerospace and automotive industries due to their less weight to stiffness ratio. Especially the use of composite laminates, made up of Carbon or Graphite Fiber Reinforced Plastics (CFRP/GFRP), in military and commercial aircraft structures has progressed steadily over the past few decades. Drilling holes and making cutouts in these laminates are unavoidable for practical reasons. These holes (or) cutouts introduces stress concentration near the hole (or) cutout edge and reduces the load-bearing capacity of the structure. Cutouts are made at the edges of composite laminates for practical purposes, which is capable of reducing the delamination effect in notched laminates. The stress distribution in notched composite laminates can vary according to the location of the notch in the laminate, which leads to the variation in strength and reliability values of notched laminates. The objective of the present work is to study the effect of notch location on the stress concentration and reliability of notched composite laminates. Composite laminate displays significant variation in material and strength properties and the stress distribution in the laminate becomes stochastic in nature. Thus the notched laminates were analyzed using a stochastic approach and designed based on a reliability-based design approach.

A Stochastic Approach for Radiative Exchange in Enclosures With Nonparticipating Medium

1984 ◽  
Vol 106 (4) ◽  
pp. 690-698 ◽  
Author(s):  
M. H. N. Naraghi ◽  
B. T. F. Chung
Keyword(s):  
Heat Transfer ◽  
Approximate Solutions ◽  
Stochastic Approach ◽  
Absorption Factor ◽  
Heat Transfer Characteristics ◽  
Markov Chain Theory ◽  
Different Types ◽  
Chain Theory ◽  
Specular Surfaces ◽  
Radiative Exchange

A stochastic method is developed for calculating radiation interchange in enclosures with a finite number of isothermal surfaces but without a participating medium. Different types of surface properties are considered. They are diffuse and specular surfaces. In this work, a stochastic n model is proposed that is based on the Markov chain theory and leads to some explicit matrix relationships for the absorption factor from which the heat transfer characteristics of the enclosure can be determined. The present approach provides an exact solution as long as the necessary view factors can be determined. The accuracy of approximate solutions can be improved as n increases.

scholarly journals Optimal Condition-Based Maintenance Strategy for Multi-Component Systems under Degradation Failures

Energies ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 4346
Author(s):  
Kui Wang ◽  
Chao Deng ◽  
Lili Ding
Keyword(s):  
Critical Level ◽  
Condition Based Maintenance ◽  
Maintenance Strategy ◽  
Maintenance Policy ◽  
Cost Rate ◽  
Optimal Monitoring ◽  
Long Run ◽  
Component Systems ◽  
Maintenance Decision ◽  
The Impact

This paper proposes a condition-based maintenance strategy for multi-component systems under degradation failures. The maintenance decision is based on the minimum long-run average cost rate (LACR) and the maximum residual useful lifetime (RUL), respectively. The aim of this paper is to determine the optimal monitoring interval and critical level for multi-component systems under different optimization objectives. A preventive maintenance (PM) is triggered when the degradation of component exceeds the corresponding critical level. Afterwards, the paper discusses the relationship between the critical level and the monitoring interval with regards to the LACR and RUL. Methods are also proposed to determine the optimal monitoring interval and the critical level under two decision models. Finally, the impact of maintenance decision variables on the LACR and RUL is discussed through a case study. A comparison with conventional maintenance policy shows an outstanding performance of the new model.

scholarly journals Robustness Assessment of Redundant Structural Systems Based on Design Provisions and Probabilistic Damage Analyses

Buildings ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 213
Author(s):  
Panagiotis Spyridis ◽  
Alfred Strauss
Keyword(s):  
Structural Design ◽  
Performance Indicator ◽  
Probabilistic Approach ◽  
Practical Significance ◽  
Weak Links ◽  
Engineering Systems ◽  
Reliability Based Design ◽  
Component Systems ◽  
Quantitative Performance ◽  
Robustness Assessment

Typically in structural design, foreseeable loads are assumed in a structural design and dimensioning exercise and design material properties may be handled in a semi-probabilistic approach. Structures can, however, be exposed to largely unforeseeable events such as intense environmental phenomena, accidents, malicious acts, and planning or execution errors, in addition to degradation with time. Recent significant collapses have highlighted the fact that robustness is an indispensable integral part of the structural design and provisions in upcoming codes are currently expanding in this respect. The paper examines the practical significance of quantitative robustness indicators included in recent research and upcoming standards and it assesses their efficiency based on case studies. Moreover, it proposes a probabilistic numerical methodology for robustness assessment under uncertainty, and it demonstrates its practical applicability based on computations with indicative structural truss systems, i.e., multi-component systems. The proposed method allows for quantifiable and comparable robustness measures, which can be integrated in reliability-based design and structural health monitoring of engineering systems. The redundancy aspect of robustness is pronounced as a plausible quantitative performance indicator for multi-component systems. In particular, the robustness index combining reliability and redundancy of the elements is proven to be the most useful one out of the examined approaches. This probabilistic elaboration does not only account for the reasonable treatment of variability and randomness, but it allows for an inverse identification of the critical failure paths and the characterization of weak links in the systems.

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