Ejector Based Multi Evaporator Refrigerator System Engineering Essay

Ejector Based Multi Evaporator Refrigerator System Engineering Essay

In transporting container and nutrient processing applications, three vaporizing temperatures: -300C ; -50C and +70C are frequently required for stop deading nutrient ; perished nutrient and infinite chilling, etc. A convenient manner to supply such chilling demands is to utilize different infrigidation systems to provide these different tonss. However, due to the high entire initial cost, this is non economically feasible. Another option is to utilize multi-evaporators infrigidation system ( MERS ) which consists of a individual infrigidation system with one compressor, one capacitor but three evaporators each working at the specified evaporating temperature. To cut down the force per unit area from that matching to the higher temperature evaporators to the compressor suction force per unit area, PRVs are used to keep the needed force per unit area differences in the high temperature evaporators. Since refrigerating vapour at intermediate force per unit area is foremost throttled so compressed, and compressor recess is in superheated part, the system is energy inefficient as the system force per unit area loss addition with increasing vaporizing force per unit area differences. In this research, we are seeking to suggest a novel Ejector based multi-evaporators infrigidation system ( EMERS ) constellation utilizing ousters to replace the force per unit area modulating valves such that the throttled force per unit area with high temperature evaporators can be recovered to better the system energy efficiency. The research work are to develop simple and accurate technology oriented system patterning, optimisation and dynamic control engineerings such that the operation of different evaporators can be integrated and complement each other under different on the job conditions and the whole system will ever be running most expeditiously, swimmingly and safely.

Introduction

Background and Aims

Refrigerated transportation containers are widely used in transporting perishable goods. It forms an of import portion of the planetary cold nutrient concatenation, which accounts for over 30 % of the universe ‘s nutrient supply. The figure of refrigerated transportation containers operated throughout the universe today is over 100,000 and the universe market growing for refrigerated transportation containers has been estimated at an one-year rate of about 10 % . Refrigerated transportation containers are subjected to really demanding public presentation demands because of the demand to transport a immense assortment of ladings under broad fluctuations in climatic conditions. Typically, three vaporizing temperatures: -300C ; -50C and +70C are required for stop deading nutrient ; perished nutrient and infinite chilling, severally. While the environments range can be from the cold Arctic belt to the heat of desert climes with the ambient temperature vary from ?40 to +500C. The infrigidation system needs to be designed to be energy efficient and precise temperature control is required in the iciness lading scope, peculiarly for temperature sensitive merchandises.

A convenient manner to run into the different chilling demands is to follow different infrigidation systems to provide the different tonss independently. However, this may non be economically feasible due to the high entire initial cost. Another option is to utilize multi-evaporator infrigidation systems ( MERS ) which consists of a individual infrigidation system with one compressor and three-evaporators. The schematic of conventional MERS and its matching operating rhythm on P?h diagram are shown as in Fig. 1 and Fig. 2, severally. The system consists of a individual compressor and a individual capacitor but three evaporators working at vaporizing temperature at -300C, -50C, and +70C, severally. To cut down the force per unit area of the higher temperature evaporators ( EVAP1 and EVAP2 ) to the compressor suction force per unit area which is the force per unit area of the lowest temperature evaporator ( EVAP3 ) , force per unit area modulating valves ( PRV1 and PRV2 ) are used to keep the needed force per unit area in high temperature evaporators.

As is demoing in Fig. 2, the refrigerant enters the compressor at low force per unit area PL at province ( 1 ) and is compressed isentropically to the high force per unit area PH at province ( 2 ) . The fluid enters the capacitor where it condenses to province ( 3 ) by rejecting heat to the milieus. The condensate is divided into three flows, at provinces ( 4 ) , ( 5 ) and ( 6 ) , and enters the EVAP1 ( province 7 ) , EVAP2 ( province 8 ) and EVAP3 ( province 9 ) after force per unit area decreases by EV1, EV2, and EV3, severally. Through the evaporators, the refrigerant alterations to the corresponding superheated provinces ( 10 ) , ( 11 ) and ( 14 ) . The flow at province ( 10 ) was throttled to province ( 12 ) ; while the flow at province ( 11 ) was throttled to province ( 13 ) . The flows of provinces ( 12 ) , ( 13 ) , ( 14 ) blend up into flow province ( 1 ) and return to compressor, completing the whole infrigidation rhythm. During the choking procedure, the force per unit area is exhausted inside the force per unit area modulating valves, it is irrecoverable. Since refrigerating vapour at higher force per unit areas are foremost throttled so compressed, and compressor recess is in superheated part, the system is energy inefficient as the irrecoverable system force per unit area loss additions with increasing vaporizing force per unit area differences. How to retrieve the choking force per unit area loss, find the optimized work point and command this complex system are the recent research spreads. A batch of work should be done on the MERS, particularly on optimisation and control.

Fig. 1 Schematic of CMERS

Fig. 2 Pressure-enthalpy chart of CMERS

The chief aim of this research is trying to develop a practical engineering for design and operation of EMERS to retrieve the force per unit area losingss associated with high temperature evaporators in the conventional MERS and optimizes the overall system public presentation for all possible on the job conditions. The mark is to accomplish 15 % COP betterment over the bing MERS. The background of proposed research is for the refrigerated transportation containers. However, the engineering developed in this research can be easy extended to other sectors, such as nutrient processing ; supermarket ; and chemical industries ; etc, where MERSs are required.

Previous Plants

Published literatures sing force per unit area recovering and its application in infrigidation system have been studied. To cut down the force per unit area losingss due to the throttle consequence, several system strategies have been proposed including multistage infrigidation rhythms, cascade infrigidation rhythms. However, these two methods come along with complex system hardware apparatus ; it is suited when the original system is simpler to use them. While for the MERS, the original system is much more complex than the common infrigidation system, so it is necessary to happen another attack to retrieve the loss force per unit area energy.

In Transcritical C dioxide infrigidation rhythms, the largest irreversibility ( irrecoverable energy loss ) is from restricting valve, when the force per unit area is throttled into lower force per unit area flow, the energy loss is immense due to the big force per unit area bead of the choking procedure, approximately 38 % of the rhythm ‘s entire irreversibility. When utilizing a expander to replace the choking valve in application, the entire irreversibility can be reduced by 35 % , therefore the system COP can be increased over 25 % . A typical expander based infrigidation rhythm is shown as in Fig.3.

Fig. 3 Schematic of expander based infrigidation rhythm

The working rule of expander is merely the antonym of the compressor ‘s. A compressor is utilizing other sorts of energy ( chiefly electrical power ) to bring forth the kinetic energy and compact the gas, reassign the energy into force per unit area power. While a expander makes high force per unit area flow produce the kinetic energy. The generated kinetic energy can be used to assist increasing energy efficiency ; it can bring forth electrical power for compressor to salvage entire energy cost.

The expander is really good at force per unit area energy recovery, but in order to work usually, there should be adequate force per unit area difference to drive it. So it is frequently been used in ultra-low temperature infrigidation ( cryogenic infrigidation ) or CO2 infrigidation systems where the force per unit area and temperature of the refrigerating bead greatly after enlargement procedure. While MERS applications in nutrient processing, storage and transit, the energy salvaging by such strategies are non important since the temperature and force per unit area span before and after enlargement is little. Therefore, ouster based MERS seems the lone energy salvaging alternate in such applications.

The ousters consist of three chief parts: ( 1 ) the nose ; ( 2 ) the suction chamber ; and ( 3 ) the diffusor, its working rule together with the fluctuations in the watercourse speed and force per unit area as a map of location inside the ouster are illustrated in Fig. 4 and are explained below:

The motor steam enters the ouster at point ( P ) with a subsonic speed. As the watercourse flows in the meeting portion of the ouster, its force per unit area is reduced and its speed additions. The watercourse reaches sonic speed at the nose pharynx, where its Mach figure is equal to one. The addition in the cross subdivision country in the diverging portion of the nozzle consequences in a lessening of the daze moving ridge force per unit area and an addition in its speed to supersonic conditions. At the nozzle mercantile establishment plane, point ( 2 ) , the motor steam force per unit area becomes lower than the entrained vapour force per unit area and its speed reaches highest. The entrained vapour at point ( vitamin E ) enters the ouster, where its speed additions and its force per unit area decreases to that of point ( 3 ) . The motor steam and entrained vapours watercourses may blend within the suction chamber and the meeting subdivision of the diffusor or it may flux as two separate watercourses as it enters the changeless cross subdivision country of the diffusor, where blending occurs. In either instance, the mixture goes through a daze inside the changeless cross subdivision country of the diffusor. The daze is associated with an addition in the mixture force per unit area and decrease of the mixture speed to subsonic conditions, point ( 4 ) . The daze occurs because of the back force per unit area opposition of the capacitor. As the subsonic mixture emerges from the changeless cross subdivision country of the diffusor, farther force per unit area addition occurs in the divergent subdivision of the diffusor, where portion of the kinetic energy of the mixture is converted into force per unit area, point ( degree Celsius ) . Since Pc & A ; gt ; P2, the force per unit area loss through the ouster is partly recovered at its mercantile establishment.

Fig. 4 Variation in force per unit area and speed as a map of location along the ouster

The ouster is old device and has been invented for long clip and applied to broad countries in procedure industry. The usage of ouster in infrigidation system besides has long history, the ouster infrigidation rhythm was developed, even before the visual aspect of vapor-compression infrigidation rhythm, by Maurice Leblanc in 1910, which utilized low class thermal energy or waste heat alternatively of electricity to bring forth chilling. The chief advantage of utilizing ouster as a pumping device is that it has fewer traveling parts ( no compressor ) . It is, hence, really low in wear and significantly lasting.

The application of ouster for infrigidation system can be traced back to early 1990 ‘s for domestic iceboxs, it was subsequently reported that the paradigm of a compression-injection intercrossed infrigidation rhythm system for family iceboxs with an energy ingestion decrease of 7.75 % has been achieved. An energy efficient three-evaporator infrigidation system with two ousters EJ1 and EJ2 was besides proposed late by L. Kairouani, et Al. with the conventional shown as in Fig. 5.

Fig. 5 Schematic of a fresh multi-evaporator infrigidation system with ousters

The refrigerant enters the compressor at low force per unit area PL at province ( 1 ) and is compressed isentropically to the high force per unit area PH at province ( 2 ) . The fluid enters the capacitor where it condenses to province ( 3 ) by rejecting heat to the milieus. The condensate is divided into three flows, at provinces ( 4 ) , ( 5 ) and ( 6 ) , and enters the EVAP1 ( province 7 ) , EVAP2 ( province 8 ) and EVAP3 ( province 9 ) after force per unit area decreases by EV1, EV2, and EV3, severally. Through the evaporators, the refrigerant alterations to the corresponding superheated provinces ( 10 ) , ( 11 ) and ( 15 ) . The flow at province ( 10 ) enters into the nose of EJ1 and expands to a mixture at province ( 12 ) . The concentrated secondary vapor drawn into EJ1 is at force per unit area Pevap2 ( province 11 ) . The two bluess mix in EJ1 to province ( 13 ) , flows through EJ1 diffusor where it recovers to coerce Pej1o at province ( 14 ) and so enters into the primary nose of the EJ2 pulling vapor into the EJ2 from evaporator 3 and expands to province ( 16 ) . The two bluess mix to province ( 17 ) and leave EJ2 after a recovery of force per unit area in the diffusor portion at province ( 1 ) . The pressure-enthalpy chart for ejector multi-evaporator rhythm is shown in Fig. 6.

Fig. 6 Pressure-enthalpy chart of EMERS

Through energy analysis, it is revealed that the system COP can be improved by about 8 % and 20 % , for two temperatures EMERS and three temperatures EMERS, severally, as compared to the conventional MERSs. The chief drawback of this EMERS constellation is, nevertheless, it can merely work good at the on-design status. If air-conditioning burden ( EVAP1 ) is reduced to less than 80 % of rated value, the primary mass flow rate through the nose of EJ1 and EJ2 will be cut down and the flow go throughing through EVAP2 and EVAP3 will besides be reduced. Consequently, both ousters will non work decently and even more energy will be consumed as the consequences.

Methodology

For this research, experiment is important. Suitable theoretical accounts ( inactive theoretical accounts, dynamic theoretical accounts ) will be developed for optimisation and control analysis. Then all the theoretic consequences will be tested and verified on the EMERS platform ( developing in advancement ) .

Initial consequences and future research work

Sing the infrigidation and freeze tonss are comparatively stable, and the air-conditioning burden can alter in a broad scope, we propose a new EMERS constellation to suit these facts. The schematic of the new EMERS is shown as in Fig. 7. The chief differences of the new EMERS compared with the bing EMERS are 1 ) When the air-conditioning is running, the primary and secondary recesss of EJ1 are from EVAP2 ( infrigidation ) and EVAP3 ( freezing ) , severally, and the end product of EJ1 is used as the secondary recess for EJ2 ; 2 ) When the air-conditioning is turned off, the solenoid valve is switched to the full unfastened so that the force per unit area bead in EJ2 is avoided.

Fig. 7 Schematic of the novel EMERS

The pressure-enthalpy chart utilizing R134a as refrigerant with air-conditioning running is shown in Fig. 8, where the corresponding evaporating force per unit areas and per centum refrigerating mass flow rates for air-conditioning ( EVAP1 ) , infrigidation ( EVAP2 ) and freezing ( EVAP3 ) are of 3.746 saloon and 40 % , 2.434 saloon and 20 % , and 0.847 saloon and 40 % , severally. The force per unit areas of the two flows after EJ1 and EJ2 are 0.94 saloon and 1.059 saloon, severally. For the discharge force per unit area of compressor at 8.868 saloon ( distilling temperature at 35 a„? , water-cooled capacitor ) , the compaction ratio is 8.37 ( 8.868/1.059 ) . Compared with 10.5 ( 8.868/0.847 ) compaction ratio for the conventional MERS, the energy economy is 20.3 % .

Fig. 8 Pressure-enthalpy chart of the new EMERS

In instance of air-conditioning system is away, i.e. , merely EJ1 working, the pressure-enthalpy chart is shown in Fig. 9. In such state of affairs, 10.2 % COP betterment can still be achieved compared with the conventional MERSs.

Fig. 9 Pressure-enthalpy chart of the new EMERS ( no air-conditioning )

From the above analysis, it is observed that the EMERS has a good potency to salvage energy if it can work decently. Due to the chilling burden and ambient environmental fluctuations, nevertheless, each evaporator seldom works at the designed chilling burden. Consequently, the ousters will be working at off-design conditions and effectual control of the system operation become important. Since the ouster working rule has made it structurally really hard to manage in a broad scope of operation conditions as the compaction ratio can merely be controlled in a limited grade. This has posed several challenges to the research workers in control theory and application, and to the best of our cognition, there is so far no effort to undertake such jobs. The deficiency of comprehensive and effectual solution suited to undertake off-design conditions has been, so far, the chief job that restricts the system ‘s application in the existent universe. Therefore, the research purpose is to develop an effectual operating scheme for the system under all possible on the job conditions. The chief research work including:

Ouster Parameters Optimization: The ouster public presentation is affected by both operating conditions and geometry parametric quantities. The public presentation indexs, such as, entrainment ratio, chilling capacity, COP and critical capacitor force per unit area, etc, can be varied by altering the exit place of primary noses ( NXP ) , country ratio between the nose and constant-area subdivision, diverging angle of nose, meeting angle of blending subdivision and the length of constant-area subdivision. Since the back force per unit area of the ousters are determined by suction force per unit area of the compressor in proposed system, it is different from traditional ouster based HVAC processes where the primary force per unit area demand to be fixed. In this survey, we will utilize Computational Fluid Dynamics ( CFD ) analysis combined with experimental attack to optimise the cardinal parametric quantities for such applications to run into our public presentation aims.

Mechanical Design: In the proposed design, the evaporator mercantile establishment for air-conditioning is connected to the primary recess of EJ2 to counter the consequence of burden fluctuations in air-conditioning system to the other two systems. Since the ouster merely can digest ±10 % off-design on the job conditions, this constellation may still hold jobs if the fluctuation of the air-conditioning burden is big. To work out this job, we will adding some extra devices based on the proposed mechanical design, i.e. : 1 ) Mounting a PRV before the primary recess of EJ2, as the ouster can partly recovery the force per unit area loss of PRV, certain COP betterment can be achieved ; 2 ) Using multi ousters with different country ratios in parallel to manage the variable air-conditioning burden. For illustration ; three ousters with different country ratios in parallel can manage the burden from 50 % to 100 % . In this undertaking, we will prove the public presentations of these strategies in comparing with the strategy to happen a best design in footings of public presentation and stableness.

Hybrid Mold: To develop real-time optimum operation scheme, simple and effectual constituents theoretical accounts which can suit into different sorts of operation strategies, such as single with and without air-conditioning operations, are indispensable. For both the ouster and vapour compressor rhythms, there have been many probes refering luxuriant theoretical accounts for system design and simulation of the system behaviours. However, most of these theoretical accounts are really complicated and non suited for existent clip optimisation intents. Certain constituents such as fans, pumps and valves have been good established by multinomial methods and have been proven to be simple and accurate ; we will utilize the bing theoretical accounts for these constituents. Based on energy balance and heat and mass transportation analyses, we have developed intercrossed theoretical accounts for chilling spirals, capacitors, chilling towers and ousters which merely require three characteristic parametric quantities to foretell the public presentation. Linear or non-linear least squares methods can be employed to find the parametric quantities via curve suiting makers ‘ catalog informations or existent clip experimental informations. In this undertaking, we will utilize this mold attack to pattern capacitors, evaporators and ousters. In add-on, we will widen the constituent loanblend patterning attack to develop active devices such as compressors.

Normalized Integration Error Based Input-Output ( IO ) Choice: Due to the complicated dealingss among the system variables and the ambient environment conditions, the cardinal trust for the system to be economically feasible prevarications with dependable and optimum operation under different on the job conditions and chilling burden demands. Reasonable IO choice is chiefly of import for this system since: 1 ) the improper IO set and location may restrict the public presentation, which may non be overcome by advanced accountant design ; 2 ) the IO set determines facets such as dependability and the disbursals of hardware, execution, operation, and care ; and 3 ) IO choice technique can be used to place on peculiar manner to better the system controllability and flexibleness. So far, there has been no systematic attack to this issue because of the size, complexness, and aims that are associated with the development of the systems. An effectual solution will include prioritization among viing or disparate aims, decrease in the dimensionality of the job and consistent agencies for the rating of options, such that the optimisation system can be faithfully implemented with the least cost. For this intent, an attack for control construction synthesis will be developed to find the types, Numberss and locations of detectors and actuators such that the system variables can be efficaciously and economically measured and/or controlled. The multivariable system synthesis techniques will be further developed to suit this peculiar application for the best detector and actuator arrangement and control system constellations.

Model Based Optimization: Since the heats from the air-conditioned infinite are removed by several cringles in a cascade mode ( infinite > evaporators > compressor > capacitor ) , the end product of one cringle becomes the set point or restraint of the subsequent cringle ; their operations are hence affected by each other. Hence the physical restrictions of each device, its operation window and the interactions of each cringle have to be considered in the theoretical account based public presentation optimisation. In this research, we will follow two beds optimization construction, i.e. the overall optimisation bed and the evaporator optimisation bed. The overall optimisation bed will find the operating position of each evaporator harmonizing to the chilling demand and out-of-door environment. In the evaporator optimisation bed, each evaporator will find its ain optimum set-points while taking into consideration the yokes from other evaporators and following the instructions given by the top bed. Some new issues with existent clip optimisation such as dependability, safety and hardiness will besides be addressed.

Relative Energy Based Advanced Controls: Since the system has multi-evaporator cringles and each evaporator has to run in a broad scope of burden conditions, the system is Multi-Input and Multi-Output ( MIMO ) in nature with terrible nonlinear dynamic features. Therefore, the accountants in the system which are used to keep an optimum operation, particularly, force per unit area distribution have to accommodate to the current operating conditions. Several advanced control strategies could be proposed in this research:

MIMO Control: For a given operating status, depending on the unfastened or closed cringle position, and the demand of the control system public presentation, several empirical dynamic mold methods has been developed and can be readily adopted to place the system parametric quantities. The nonlinear theoretical accounts developed for optimisation can besides assist to supply some anterior cognition such as the scope of procedure addition so that the control system can utilize it to put measure or relay size in trial experiment ; and besides to formalize the ensuing additive theoretical account from the trial by comparing its parametric quantities values with the bounds obtained from the nonlinear theoretical account. For accountant design, comparative energy based multi-input and multi-output accountant design techniques will be devised for the system. Depending on cringle features and the demands on system public presentation, decentralized, sparse or uncoupling control strategies will be implemented into the control loops. Comparisons will be made on different control schemes to happen the best solution for control.

Multi-model Control: In old studied, a multi-model control scheme for HVAC processes has been proposed where additive local theoretical accounts that describe the procedure at nominal operating points are foremost developed and their weightings on the end products are determined by fuzzed combination regulations. An extra local government is added and boundaries of fuzzed maps for partitioning are redistributed merely when an unsatisfactory accountant public presentation caused by theoretical account mismatch is detected. An extra local accountant every bit good as theoretical account is to be added to the planetary multi-model control system merely when unsated public presentation occurs. Once the multi-model construction has been determined, the overall accountant end product will be obtained by uniting the local accountant end products utilizing fuzzed combination. Consequently, the control public presentation based division will supply the proper construction, i.e. a minimal figure of local theoretical accounts, for the whole operating scope. Through rank of fuzzed sets, the combination of runing governments can be described more smoothly and of course.

Decision

The whole research is complex and we have objects covering several research countries to accomplish. Teamwork is indispensable. The consequence of this research could be widely used in nutrient storage, transit and ace market. The economic significance is obvious.