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The
student of group ÌÀÃ-03:
Solovyeva
Svetlana Valerievna
The
supervisor of studies: prof. Markin Alexander Dmitrievich
Theme :
" The
analysis of efficiency of regenerative heaters in a contour of technical
training college at calculations of thermal circuits of blocks TPP".
The wide circulation of the phenomena of heat exchange
in power, the industries, transport, and also during interaction with an
environment has demanded a plenty of designs heat exchanges devices. These
designs in each concrete case should provide an optimum combination of thermal
efficiency, convenience of operation, whenever possible small capital
investments and working costs.
In the given work theoretical bases of
calculation heat exchanges are stated. The basic methods of the description and
elements of the theory heat exchanges are included classification of types heat
exchanges.
The
given work contains a laconic and exact statement of classical bases of the
theory of heat exchange and modern methods of calculation and designing heat
exchanges equipments of the most various purposes.
Heat
exchanges provide transfer of heat between two or the big number of streams of
the heat-carriers occurbing through the device. The basic characteristic of a
design heat exchanges is the type of relative movement of streams of
heat-carriers, mutual geometry of these currents. The most general
configurations of currents are below considered.
It
is necessary to emphasize, that the described configurations represent some
idealization of real situations. In practice never it is impossible to reach
current of the heat-carrier conterminous to ideal variant.
Under
heat exchanges it is understood such devices in which make an exchange of heat
between two working bodies. In heat exchanges devices there is an exchange
between heated up and cooling working bodies, or the ferry therefore the
modular condition of working ph changes.
Used
working bodies exchange heat and may be: water pairs, warm water, gases,
various soluble salts, liquid metals.
By
a principle of work all heat exchanges may divide on:
- recuperative;
- regenerative;
- mixing type.
The
analysis of process of designing heat exchanges devices should be based on
clear understanding of criteria on which work heat exchanges will be checked.
Basically these criteria are simple for formulating, but the problems may
appear is more complex for some special cases. The general principles of a
choice of criteria are considered below by way of a degree of their importance.
First
of all it is necessary to note, that there are two big groups heat exchanges,
and each group demands various approaches to designing and manufacturing.
Undoubtedly, the most part of existing surfaces of heat exchange is duplicated
in many devices, such as automobile radiators, household and industrial conditioners,
boilers, coolers of greasing of machines etc. For such heat exchanges are made
by the industry of thousand or even millions identical units. Basically from
economic reasons process of creation of this group heat exchanges is reduced to
manufacturing some number of devices of a various design, all-round test within
the limits of expected working parameters, to a final choice of the most
successful design and, at last, to a batch production heat exchanges, most
relatives to the chosen prototype.
In
a number of industries, for example on chemical and oil refineries, are used
heat exchanges which are developed and made by small partiess and are usually
applied in consecutive or parallel configuration. Their batch production is at
a loss, first of all, because of absence of an opportunity of wide tests
outside of industrial process. Frequently these heat exchanger are intended for
heat-carriers, structure, properties and ability to formation of adjournment,
on which surface are known insufficiently and speeds of streams (so, and
conditions of course of heat exchange) may change daily. Obviously, such
situation shows more rigid requirements to designing if any chances of success
made. The given part of a management(manual) is devoted basically to this case.
The
first criterion of satisfactory work heat exchanges the device is performance
of requirements on working parameters: required capacity of the device should
be provided in an operating time from one preventive repair up to another at
the given restrictions on difference of pressure and irrespective of increase
of adjournment at surfaces. However it is necessary to note, that at designing
always there is an element of uncertainty as warmly physical properties are
seldom known with a high degree of accuracy, settlement methods are based on
use heat exchanges the equations which accuracy is within the limits of
disorder of experimental data, itself heat exchanges is produced with the
certain admissions, real operating conditions òåïëîîáìåííèêà
in different days
íåîäèíàêîâû
and adjournment, as a rule, appear a little bit big, than it was supposed in
the beginning (besides they in due course change). Therefore requirements to
performance data are carried out in practice not always. From this point of
view it is not enough for quantitative estimations as the statistical data on
work of separate devices, and data on influence of efficiency of their work on
other processes of manufacture. Hence, the designer with the help of
calculation, considering influence of an overall performance heat exchanges on
other processes of manufacture, should guarantee reliable work of the device
with the proved probability.
The
second criterion consists that heat exchanges should satisfy to conditions,
general(common) for all equipment., first of all, the mechanical
pressure(voltage) connected not only with normal work, but also with loading,
assembly, start, a stop, and also a number(line) of the certain operations
caused by infringement of production and possible(probable) emergencies here
enter. There are the external mechanical pressure(voltage) caused by presence
of pipes in heat exchanges and arising both in a stationary condition, and in
transitive modes at change of temperature of heat-carriers. In heat exchanges,
certainly, there should not be a corrosion from influence of heat-carriers and
an environment. It can be achieved basically a choice of a material, and also a
design. Adjournment on a surface of heat exchange should be whenever possible
minimal, but means of the designer in this case are usually limited to
application probably higher speeds of pressure allowable on difference and
restrictions on erosion and vibration, and also warranting of that the surface
polluted with adjournment will be accessible to clearing
The
third criterion represents the requirement of an opportunity of periodic repair
heat exchanges which usually includes clearing surfaces, heat exchange,
replacement of pipes, condensation and any other elements of a design
especially subject to corrosion, erosion, vibration or ageing. This requirement
also may become the reason of restrictions on accommodation heat exchanges and
maintenance of free space around of him(it).
The
fourth criterion directly follows from the second and the third and consists
what the designer should take into account advantages of multisection
configuration with valves It allows to repair serially each section without
special damage for work of all device Such service in particular favourably for
condensers and coolers? When one or more sections may remain without the
heat-carrier in winter time Or be used for regenerative hot conditioning very
cold heat-carrier
The
fifth criterion is reduced to that heat exchanges should have minimally
possible(probable) cost under condition of, certainly, that it
corresponds(meets) to the listed above criteria At economy of initial cost,
however, always it is necessary to mean, that the increase of working costs
owing to reduction of the sizes and heat exchanges î the device will
result decrease(reductions) of reliability to that any possible(probable) prize
in initial cost will be spent at some o'clock or days
At
last, there may be restrictions on diameter heat exchanges, length, weight and
(or) on an assortment of pipes owing to requirements to a place of
accommodation, transportation, an opportunity of service, storage of spare
pipes and condensation
If
not it is possible to reach the efficiency given for a concrete case, never it
follows to develop heat exchanges in hope, that it may be used in other
conditions. The most part heat exchanges devices intends for the installations
having service life, equal or greater, than a resource heat exchanges. The
assumption, that heat exchanges with bad design characteristics it will be
possible to use for any other technological process, results, faster, to that
neither work heat exchanges, nor course of process will not be effective
enough. It is much better to work in the assumption, that the greatest hopes
for success as at designing heat exchanges, and development of technological
process in which it heat
participates, are given with the optimum decision of the given problem.
If
you the theme and an object of research given has interested masters works and you want to learn about it more in detail,
write to me:
My e-mail: semicvetik1925@mail.ru
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