Heat Transfer Calculations and the Typical Design Cycle

The engineer must gather sufficient information so that some basic heat transfer calculations could be made. This phase would involve consideration of the basic heat transfer modes - conduction, convection and radiation and a quantitative assessment of heat transfer modes which need to be consideredon the basis of their significance. The calculations would most likely involve the classical equations for describing heat transfer and could be simple linear equations or more complex differential equations using a math program. From this series of calculations the designer would explore key aspects of the design and various different parameters, like material selection, or heat transfer coefficients. The design would then proceed to a fabrication and test phase. Here the prototype would be built and a test regime developed that would validate (подтверждать правильность) the performance of the device. From the test data, the engineer gains the information needed to judge the appropriateness (зд. точность) of his calculations and make design improvements. This process is essentially an iterative ( повторяющийся) one and is repeated until a complex combination of time, project budget, and design objectives are reached.

Translate into English.

1. Инженеры и учёные должны знать основные законы термодинамики. 2. Теплопередача – это процесс, с помощью которого происходит перемещение энергии. 3. С первого взгляда можно было бы предположить, что принципы теплопередачи можно вывести из основных законов термодинамики. 4. Поскольку поток тепла является результатом отсутствия температурного равновесия, его количественная обработка должна основываться на других отраслях науки. 5. Если мы будем неправильно использовать энергию, которая существует в настоящее время, то мир может стать необитаемым. 6. Теплопередача широко применяется в работе (действии) многочисленных устройств. 7. Первый закон термодинамики гласит, что энергию нельзя ни создать, ни разрушить, но можно только преобразовать из одного вида в другой. 8. Понимание процесса теплопередачи очень важно (crucial) для анализа термодинамических процессов, которые происходят в тепловых двигателях и тепловых насосах.9. Термодинамика – это область физики, которая связана с соотношением тепла и других свойств, таких как давление, плотность, температура и.т.д. в веществе (substance). 10. Теплопередача управляется (to guide) некоторыми основными принципами, которые стали известны как законы термодинамики.

 

You are going to read Text 1B.

           Words and word combinations to help you:

ambient adj	окружающий, кругом обтекающий
feasibility n	возможность, вероятность (выполнения)
combustion chamber	камера сгорания
bearing n	подшипник; опора
capacitance n	эл. ёмкость, ёмкостное сопротивление
inductance n	эл. индуктивность; коэффициент (само)индукции

Translate the following attributive constructions.

Reactor burnout, ambient air temperature, carbon dioxide concentration, turbine blades, energy transport processes, radiative heat transfer, computer circuits, reaction rate, product degradation, frost formation, detailed heat transfer analysis, electrical circuit calculations.

 

Look through the text and say in what branches of engineering heat transfer processes can be found. Can you give your own examples of heat transfer processes in different branches of engineering? Share your opinion with your fellow students.

Text 1 B

Engineering Heat Transfer.

At one time or another every engineer is likely to be confronted with a heat transfer problem. In the design of computer circuits electrical engineers may be concerned with temperature variations owing to electrical heating; civil and mechanical engineers may need to assess the importance of thermal stresses and strains in the structural design of high-speed aircraft and nuclear reactors; and chemical engineers are often required to design chemical reactors that operate at temperatures high enough so that the reaction rate is reasonably fast, but low enough so that product degradation or reactor burnout is not a problem. Agricultural engineers are interested in the radiative heat transfer that often leads to frost formation when the ambient air temperature is above the freezing point, and the energy transport processes are associated with micro-meteorology. The ecologist is concerned with a variety of heat transfer processes such as the "greenhouse" effect caused by the increasing carbon dioxide concentration in our atmosphere.

To estimate the cost, the feasibility, and the size of equipment necessary to transfer a specified amount of heat in a given time, a detailed heat transfer analysis must be made. The dimensions of boilers, heaters, refrigerators, and heat exchangers depend not only on the amount of heat to be transmitted but also on the rate at which the heat is to be transferred under given conditions. The successful operation of equipment components such as turbine blades, or the walls of combustion chambers, depends on the possibility of cooling certain metal parts by continuously removing heat from a surface at a rapid rate. A heat transfer analysis must also be made in the design of electric machines, transformers, and bearings to avoid conditions that will cause overheating and damage the equipment. The listing in Table 1, which by no means is comprehensive, gives an indication of the extensive significance of heat transfer and its different practical applications. These examples show that almost every branch of engineering encounters heat transfer problems, which shows that they are not capable of solution by thermodynamic reasoning alone but require an analysis based on the science of heat transfer.

In heat transfer, as in other branches of engineering, the successful solution of a problem requires assumptions and idealizations. It is almost impossible to describe physical phenomena exactly, and in order to express a problem in the form of an equation that can be solved, it is necessary to make some approximations. In electrical circuit calculations, for example, it is usually assumed that the values of the resistances, capacitances, and inductances are independent of the current flowing through them. This assumption simplifies the analysis but may in certain cases severely limit the accuracy of the results.

 

TABLE 1Significance and diverse practical applications of heat transfer

Chemical, petrochemical, and process industry	Power generation and distribution	Aviation and space exploration	Electrical machines and electronic equipment:	Transportation	Comfort heating, ventilation, and air-conditioning
Heat exchangers, reactors, reboilers, etc.	Boilers, condensers, cooling towers, feed heaters, transformer cooling, transmission cable cooling, etc.	Gas turbine blade cooling, vehicle heat shields, rocket engine/nozzle cooling, space suits, space power generation, etc.	Cooling of motors, generators, computers and microelectronic devices, etc.	Engine cooling, automobile radiators, climate control, mobile food storage, etc.	Air conditioners, water heaters, furnaces, chillers, refrigerators, etc.

20. Write a summary of Text 1B. The following verbs in Passive and phrases are to help you to make a summary: are described; are summarized; are emphasized; are analysed; attention is given to…; a study of... was performed; it is concluded that….