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14Journal of Siberian Federal University. Engineering & Technologies 7 (2013 6) 845-850 УДК 62-713:62-82
The Experimental Stand for an Efficiency Assessment of Application of a Multiple-Pass Heater as Means of Cooling of Working Liquid of a Hydraulic Actuator
Almohammad A. Mohammad*, Nataly P. Kulikova and Evgeny A. Sorokin
Siberian Federal University, 79 Svobodny, Krasnoyarsk, 660041 Russia
Received 11.08.2013, received in revised form 04.09.2013, accepted 18.10.2013
In this article the problem of increase in operability of a hydraulic actuator by use of a multiple-pass heater as means of cooling of working liquid is considered. For studying of thermal processes, check of mathematical model and an assessment of efficiency of application of a multiple-pass heater the developed experimental stand is given.
Keywords: hydraulic actuator, means of cooling of working liquid, multiple-pass heater, experimental stand.
Modern hydroficated cars and the mechanisms applied practically in all industries, are operated in the most various conditions and quite often work in extreme conditions which are defined by production and natural factors.
The main factor defining efficiency of hydroficatedself-propelled cars is (air) ambient temperature on which temperature and viscosity of working liquid depend on. Other production and natural factors influence overall performance of a hydraulic actuator indirectly, through an operating mode of a hydraulic actuator and temperature of working liquid [1].
High temperatures have essential impact on productivity and durability of a hydraulic actuator as a whole. At increased temperatures there is an increase, both the volume of working liquid, and pressure in a hydraulic system. Viscosity decreases below admissible level, and volume losses sharply increase (internal movement and external leaks), increases direct contact of the interfaced surfaces of friction of details, local heating, there is an intensive wear and “gripping” of rubbing surfaces. It leads to partial or full loss of operability of the hydraulic equipment [13]. Therefore in hydraulic actuator system the increasing attention recently is paid to a problem of an exception of overheating of working liquid.
The vast experience of operation of hydraulic actuators shows that the specified problem can be solved successfully by reduction of losses of power and if necessary use of the corresponding heat exchangers.
© Siberian Federal University. All rights reserved
* Corresponding author E-mail address: alnaef@mail.ru
The greatest distribution was gained by heat exchangers with air cooling (oil, heaters). They are carried out as automobile radiators or in the form of pipes, ribbed for increasing a surface of a heat transfer. For increase in efficiency of a heat transfer the surface of the heat exchanger is blown by air from the fan.
The multiple-pass heater [4] (Fig. 1) belongs to heaters of cooling systems, mainly hydraulic systems of transport, hoisting-and-transport and digging cars. The multiple-pass heater contains the heating element formed by a set of heat releasing tubes 1, connected among themselves tube plates 2, a collector 3 and 4, side shields 5, input 6 and output 7 branch pipes, the top reservoir with liquid 8 with a set of ports round each heat releasing tube 1, the pump 9, the bottom reservoir10. The moistened surface of heat releasing tubes provides stronger heat sink from a surface of tubes.
To increase overall performance of a hydraulic actuator by cooling system introduction - a multiple-pass heater, it is necessary to study the thermal processes happening in use of a hydraulic actuator. Complexity of these processes demands carrying out the pilot research, allowing to check results of mathematical models. The purpose of a pilot research is the assessment of efficiency of application of a multiple-pass heater for cooling of working liquid.
When performing experiment it is necessary to solve the following problems: to study the processes happening in a hydraulic actuator; to check and modify mathematical model of a multiple-pass heater; to estimate influence on working process of the device of cooling of working liquid.
The accompanying task puts detection of dependence of intensity of cooling from parameters of a multiple-pass heater and weight of working liquid, and also temperature of liquid sprayed a heater.
Pilot research has to be conducted in the conditions close to operational operating modes. The experimental stand which scheme is submitted in Fig. 2 was for this purpose developed. The stand represents a tank with working liquid, with a heating element established in it.
For determination of temperature of working liquid, in the period of a warming up, measuring probes of TP1, TP2, TP3 which are connected to the measuring ITM-4 block by means of cables are established.
Fig. 1. Heater Device
heating
tunk element
Tight measuring probes of TP1, TP2, TP3 are executed from stainless steel. In probes thermal elements as which nickel thermal resistors are used settle; down. The measuring ITM-4 bleck represents the four-channel meesuring instiument of temperature. The range of measurement of temperature is from a minus of 40 (0/zero) °C to plus of 150 °C. Measurement error ± 0,5 °C.
When carrying out researches aossibility of change of volume of working liquid in a hydraulic tank and a way of an irrigaeion oa a heatrradiating surface of a heater is provided.
At resaarch oh tire: devicn of co hling of working liquid , the stand works as follows. Working liquid in a tank is warmed with the help of heating element, regulated by a rheostat, up) to the demanded temperature. Ely means of ttie pump working liquid gets te a heater, with eorced-ait cooling through which heah is transferred to environmeft. For increase of efficiency of heat exchange processes on a heater surface we offen uee of wetting of this surface by cooling liquid. Thus, after a heatee we receiie the cooled working liquid which arrives further on plums in a tank.
At production of a multiple-pnss heater important that the heat carrier (working liquid) and a material eh which the heater is made, possessed compatibility. When carrying out pilot studies the heat exchangen made of aluminum is useS.
In the course ofcarrying out pilot studian the following parameter were supervised:
- temperature of working liquid in a hydraulic tank;
- aih temperattiie;
- temperature on an entrance to a heater;
- temheratuee ah ehe exit from a heater;
- period of operation of a heater.
- way of an i reigation of a heat-rhdiating surface of a heater
Temperature of air was taken hy means of t°ie TLr2 thermometer. Temperature of working liquid was taken by means of submerged tight measuring probes executed of stainless steel. In probes thermal elements as which niekel thermoresistors are used are lecaled.
Temperatures of working liquid taken f alue weee fixed by the ITM-4 devica.
Values of controlled parameters, whbn carrying out exp e riment, were entered in the register.
Researchesi were conducted at the volume of working liquid in a hydraulic tank of 25, 50 both 100 liters and various ways of an irrigation of a heat-radiating surface of a heater (dispersion, drop, jet).
On received, during experimeno, to data dependences of temperature of working liquid on waaming up time, for liquid volumes in a tantr of 25, 50 and d00 liters are constructed at different ways of an irrigation of a heat-radiating surface ot a heatet (dispersion, daopjet).
Thermal colculation of tgo sCand
Capacity ofa hydraulic tank gets out on the relation:
Vl=(l -cl ,5)QH , (1)
wheee: Qh- pump output.
We coordinate with all-Union Stete Standard 12448-80 and we choose hydraulictank capacity according to an exception of everhoat oH a hydraulic actuator.
We deteamine the craa ot heat transfer ofhydeauHc hank by o formula:
F, =(6, a-6,ftym, (2)
wliere: Ft - aree of heat transfer of a rank; Vt - tank storage capacity.
Let’r dtlem/ine tlie area of heat-radiating surfaces of a hydraulic actuator by a formula:
Fea=Ft-at, (3)
where: Ft - thn tank are a; ab - coefficient
By a formula (4) we will determine quantity of heat allocated by a hydraulic actuator (at t)
Qha = (1 - n to, ) ' NH ' kt ' + Qt e (4)
where: Qha - quantity o:f haar allocated by a hydraulic aciuator, kt - coefficient of time of operation
under loading, kp - coefficksnt or cfficieney of nominal pressure, QT - quantity of heat allocated with heating element, nt - output - input aatio in total.
Lett determine established tempefatute in a hydraulic actuator:
f Qa .
teS=a—t^fa-i, (5)
where: tes - e!fti'ill:),L:Lit>]fed. temperature of working liquid, Khs - coeflfciemt of heat transfer of surfaces of the hydraulic equipment - maximum temperature of air.
If the established temperature of working liquid exceeds admissible, in a hydraulic actuator it is necessary to apply (he heat exchanger, which area is calculated according to the following equation:
F - Qx_______f . trta (6)
_ (t -1 U k ’
Cr tTmTat'kt tkT
where: FT - area of heat-radiating surfaces; of a hydraulic actuator, m sq, kt - coefficient of a heat
transfes oa the heat exc hanger.
Let’s determine the current temperature of working liquid in a hydraulic actuator by a formula:
k-F.
1 - -
s+s
T-k-F-a rc-C-t
+ toma (7)
where: t - time for wQch heat is allocatedr with c, kt - coefficient of a heat transfer of surfaces of the hydraulic equipment in -nvironment, Fha - average thermal capacity of materials of which the hydraulic actuatof ismade
C = Cf'r; + Ci - r-e (8)
1-1
where: Q- heat co nductivity o+ working liquid, ml - mass of working liquid, kg, mhe - mass of the hydraulic equipment, kg, Che- thermal capacityof the hydraulic equipment , J / kg °
Lei’s determine the mass of liquid, believing that its volume in a hydraulic system exceeds liquid volume rn a hydrauHc tank by 1,5 time s.
rf=piV, -1,5, (9)
where: p - denstty at temperature of liquid, fod used oil.
We count temperafure of working liquid in time range with, with an interval 300 with (for convenience oC caOcudation we wfll make the table and we will bring in it all parameters determined by cilculation).
Temperature of ovet +700 Cis recognized as a zone of dangerous temperatures for hydraulic actuator operation as in this range intensive oxidation of working liquid, curing of rubber consolidations, increase of wear of details of the hydroequipment, reduction of volume efficiency of a hydraulic actuator, speed of movement of a working link of hydraulic engines and car productivities, external leakages of liquid which can lead to receiving strong burns of the operator begins. Therefore at achievement of temperature of working liquid, there will be an automatic turning on of the heat exchanger.
By results of calculation we build the schedule t, - t. The schedule constructed by a settlement way allows to judge a thermal mode of a hydraulic actuator.
Thus, the stand allows to obtain data on influence of temperature of liquid sprayed a heater on intensity of cooling of working liquid, and as a result, to establish optimum design data of heatexchange devices.
References
[1] Каверзин С.В. Обеспечение работоспособности гидравлического привода при низких температурах. Красноярск, 1998. 240 с.
[2] Свешников В.К. // Журнал РИТМ. 2009. № 7. [Электронный ресурс]. Режим доступа: http://www.ritm-magazine.ru/
[3] Выбор и применение рабочей жидкости для мобильных машин с гидроприводом
[Электронный ресурс]. Режим доступа: htip://www.nmvgorad.teleweek.ruwww.ti-nn.
ru/?id=11032
[4] Патент RU № 121559 U1 / Опубл. 27.10.2012., Бюл. № 30.
Экспериментальный стенд для оценки эффективности применения многоходового калорифера как средства охлаждения рабочей жидкости гидропривода
А.А. Мохаммад, Н.П. Куликова, Е.А. Сорокин
Сибирский федеральный университет Россия 660041, Красноярск, пр. Свободный, 79
Стенд, описанный в данной статье, позволяет получить данные по влиянию температуры опрыскиваемой калорифер жидкости на интенсивность охлаждения рабочей жидкости и установить оптимальные конструктивные параметры теплообменных устройств.
Ключевые слова: гидроусилитель, средства охлаждения рабочей жидкости, частотный обогреватель, экспериментальный стенд.
