Heat exchangers are equipment that transfers heat from one medium to another. An air cooled heat exchanger, or ACHE, is simply a pressure vessel which cools a circulating fluid within finned tubes by forcing ambient air over the exterior of the tubes. In cross flow exchangers, the hot and cold fluids move perpendicular to each other. Some actual heat exchangers are a mixture of cross flow and counter flow (Known as Counter to Cross Flow Heat Exchangers) due to design features. The proper design, operation and maintenance of heat exchangers will make the process energy efficient and minimize energy losses. Heat exchanger performance can deteriorate with time, off design operations and other interferences such as fouling, scaling etc. It is necessary to assess periodically the heat exchanger performance in order to maintain them at a high efficiency level. This section comprises certain proven techniques of monitoring the performance of heat exchangers, coolers and condensers from observed operating data of the equipment. A major problem constantly faced by heat exchanger designers is to predict accurately the performance of a given heat exchanger or a system of heat exchangers for a given set of service conditions. The problem is complicated by the fact that uncertainties exist in most of the design parameters and in the design procedures themselves. The design parameters that are used in the basic thermal design calculations of a heat exchanger include process parameters, heat-transfer coefficients, tube dimensions (e.g., tube diameter, wall thickness), thermal conductivity of the tube material, and thermo physical properties of the fluids. Nominal or mean values of these parameters are used in the design calculations. However, uncertainties in these parameters prevent us from predicting the exact performance of the unit. The effect of the uncertainties is mostly in the performance degradation in service. Hence, there is an imperative need to consider all the uncertainties and to critically evaluate them and correctly predict the thermal performance of a heat exchanger. This is particularly true for critical applications. In thermal design of heat exchangers there are presently many stages in which assumptions in mathematical solution of the design problem are being made. Accumulation of these assumptions (e.g. use of mean values) may introduce variations in design as large as the uncertainties introduced in heat-transfer and flow friction correlations. The designer needs to understand where these inaccuracies may arise, and strive to eliminate as many sources of error as possible by choosing design configurations that avoid such problems at source. Heat Exchanger Thermal Design Problem referred to as the rating and sizing problems. KEYWORD:Thermal Design, Counter to cross flow heat exchanger, thermal design problems, uncertainties in design.
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Feb 18, 2020
R Siva + 3
Open Access