UTILIZING WAVE ROTOR TECHNOLOGY TO ENHANCE THE TURBO COMPRESSION IN POWER AND REFRIGERATION CYCLES

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1 Proceedings of IMECE 3 3 ASME International Mechanical Engineering Congress & Exosition Washington, D.C., November -, 3 IMECE3- UTILIZING WAVE ROTOR TECHNOLOGY TO ENHANCE THE TURBO COMPRESSION IN POWER AND REFRIGERATION CYCLES Pezhman Akbari Michigan State University Det. of Mechanical Engineering Engineering Building East Lansing, Michigan 88- Phone: (7 3 Fax: ( akbari@egr.msu.edu Amir A. Kharazi Michigan State University Det. of Mechanical Engineering Engineering Building East Lansing, Michigan 88- Phone: (7 3 Fax: ( kharzia@egr.msu.edu Norbert Müller Michigan State University Det. of Mechanical Engineering Engineering Building East Lansing, Michigan 88- Phone: ( Fax: ( mueller@egr.msu.edu ABSTRACT The objective of this aer is to review and suggest wave-rotor alications in ower generation and refrigeration systems. The emhasis is on recent investigations erformed by the authors for a microturbine (3 kw and a novel enhancement of a state-of-the-art water (R78 comression refrigeration cycle. The results of thermodynamic analyses erformed for the small gas turbine toed with a -ort wave rotor show that engine overall efficiency and secific work may increase by u to about 33% without changing the comressor. Execting similar advantages, it is suggested to use wave rotors in novel R78 comression refrigeration systems. This also introduces a new concet of a condensing wave-rotor that emloys ressurized water to both ( additional rise the ressure of the vaor and ( desuerheat and condense it, all in one dynamic rocess. Adding the condensing wave-rotor to the refrigeration cycle allows for a lower ressure ratio of the comressor, which is crucial for the R78 chiller technology. Some structural and economic advantages of the roosed system are mentioned. Keywords: wave rotor, gas turbine, microturbine, refrigeration, shock wave INTRODUCTION Utilization of unsteady flow devices to enhance the erformance of thermodynamic cycles has been a major branch of study since the early twentieth century. The basic concet underlying these devices is the transfer of energy with shock waves. By generating comression waves in aroriate geometries, unsteady wave machines can transfer the energy of a high-ressure fluid directly to another low-ressure fluid. Thus, a ressure rise can be obtained without using mechanical comonents such as istons or vaned imellers. This ressure rise can be greater than those obtained in steady flow devices []. For instance as shown in Fig., for the same change from a given inlet Mach number M to a given outlet Mach number 3.. M M S M ( ( Moving shock wave η Diff =% M M ( ( Diffuser M =. M = M Figure : Comarison of ressure gain (static ressure ratio of moving shock and steady flow isentroic diffuser for =. Coyright 3 by ASME

2 Shock Comression Efficiency.8... t t = η Shock η Diff = ( [ ( ( ] η Diff = ( t M, the static ressure ratio across a single shock wave moving in a frictionless channel (solid line is always much greater than that obtained by an isentroic deceleration in a % efficient diffuser (doted line. However, it must be noted that friction effects always exist, and hence ressure gains are actually less than those redicted by Fig.. It is also useful to comare the shock wave isentroic efficiency (η Shock with the diffuser efficiency (η Diff. Figure shows variations of η Shock (solid line and η Diff (dashed line as functions of the ressure gain obtained by a moving shock wave in a frictionless channel and by a diffuser, resectively. η Diff is calculated for different values of total ressure dro across the diffuser exressed by t t. Similar flow frictioneffects would lower the efficiency of wave devices and reduces the efficiency advantage of such devices, which is not shown in Fig.. The comarison in Fig. reveals that for the same ressure gain, shock comression efficiency may far exceed the efficiency obtained by a diffuser. Thus, it is seen that for a ressure recovery of u to =., η Shock is greater about 93% and hence it is always greater than that of a usual diffuser. Therefore, by substituting a diffuser with an unsteady flow device utilizing shock waves, a gain in cycle erformance can be exected. There are at least two classes of wave machines: rotating wave machines and non rotating wave machines. Dynamic ressure exchangers and wave rotors are two tyes of rotating wave devices develoed to reach the high erformance targets of thermodynamic cycles. In Euroe, however, both terms were often used interchangeably []. The first available literature on dynamic ressure exchangers utilizing ressure waves is a atent in 99 filed by Burghard [3]. This atent has introduced the concet of the dynamic ressure exchanger. The essential feature of these devices is an array of several channels arranged around the axis of a cylindrical rotor. The assembly rotates t ( ( + ( + + [ ( + ( ] η shock Figure : Shock wave and diffuser isentroic efficiencies as a function of the static ressure ratio Diffuser Efficiency Channels Stator end late Rotating drum Figure 3: Schematic configuration of a tyical wave machine between two end lates, each of which has a few orts or manifolds that control the fluid flow through the channels. Through rotation, the channel ends are eriodically exosed to the steady state orts located on the end lates causing the initiation of comression and exansion waves within the assages. Therefore, unlike a steady-flow turbomachine comonent, which either comresses or exands the gas, both comression and exansion are accomlished within a single comonent. A reversed design with stationary rotor and rotating orts is also ossible []. Such a configuration may be referred for laboratory investigations because it easily enables flow measurement in the channels where the imortant dynamic interactions take lace. However, this arrangement rarely seems to be convenient for commercial uroses []. Figure 3 schematically reresents most of the rotating wave devices. Each end late contains a few orts, here two orts are shown on each late. The number of orts and their ositions vary for different alications. To minimize leakage, in ractice, there is only a very small ga between the end lates and the rotor and the end lates with sealing material may contact the rotor. The rotor may be gear or belt driven [] or referably direct driven by an electrical motor (not shown in the icture. The ower required to kee the rotor at a correctly designed seed is very small, it is almost zero []. It is just an amount necessary to overcome rotor windage and the friction in the bearing and contact sealing if used. Alternatively, rotors can be made self-driving. This configuration called the free running rotor can drive itself by angling the blades against the direction of rotation [7]. In this case, the momentum of the inflow or outflow rotates the rotor. In dynamic ressure exchanger and wave rotors two basic fluid-exchange rocesses usually haen at least once er revolution of the rotor: the high ressure rocess (charging rocess and the low ressure rocess (scavenge rocess. In the high ressure rocess, comression waves transfer the energy directly from a fluid at a higher ressure to another fluid at a lower ressure. The low ressure rocess emloys exansion waves to scavenge the flow from the rotor channels. Ingestion of the fresh cold fluid into the rotor channels is also erformed in this rocess. Coyright 3 by ASME

3 Combustion Chamber - b - b - b baseline engine - A - A -3 A - A - A toed engine 3 A 3 T turbine A b Wave Rotor Temerature A b Figure : A schematic of a gas turbine toed by a -ort wave rotor b = A A There are several imortant advantages of rotating wave machines. Their rotational seed is low comared with turbomachines, which results in low material stresses. From mechanical oint of view, their geometries are simler than of turbomachines. Therefore, they can be manufactured relatively inexensive. Also, the rotor channels are less rone to erosion damage than the blades of turbomachines. This is mainly due to the lower velocity of the working fluid in the channels, which is about one-third of values within turbomachines []. Another imortant advantage of rotating wave devices is their selfcooling caabilities. They are naturally cooled by the fresh cold fluid ingested by the rotor. Therefore, alied to a heat engine, the rotor channels ass through cool air and high-ressure and high-temerature gas flow in each rotor revolution. As the result, the rotor material temerature is always maintained between the temerature of the cool air which is being comressed and the hot gas which is being exanded. Entroy Figure : Schematic T-s diagram for a gas turbine baseline engine and the most common imlementation case of a toing wave-rotor GAS TURBINE CYCLE APPLICATIONS While dynamic ressure exchangers have been used for air-cycle refrigerators [,, 8] or as ressure dividers for natural-gas ieline systems [, 9], the wave rotor is one configuration of dynamic ressure exchangers, commonly designed to increase the ressure and temerature of the air entering a combustion chamber of a gas turbine engine or IC-engine. This can lead to significantly enhanced engine erformance, exressed by increased efficiency, outut ower and reduced secific fuel consumtion. Seiel s work at Brown Boveri Comany in Switzerland in 99 introduced the notion of a wave device as a toing stage for a locomotive gas turbine engine, but it was not commercially roduced []. In a conventional gas turbine alication, a wave rotor is embedded between the comressor and turbine arallel to the combustion chamber. Figure illustrates how a -ort wave rotor is used to to a gas turbine cycle. In the wave rotor channels, the hot gas leaving the combustion chamber comresses the air coming out of the comressor. After the additional comression of the air in the wave rotor, it is discharged into the combustion chamber. The burned gas reexands during the comression of the air and is afterwards scavenged toward the turbine. Then, the channels are reconnected to the comressor outlet, allowing fresh recomressed air to flow into the wave rotor channels. Due to the exansion in the wave rotor, the re-exanded gas can enter the turbine with the same or a lower temerature as the gas would have in a conventional arrangement without the wave rotor []. However, the gas ressure is higher than the comressor exit ressure by the ressure gain obtained in the wave rotor. This is in contrast to the untoed engine where the turbine inlet ressure is always lower than the comressor discharge ressure due to the ressure loss occurring in the combustion chamber. The general advantage of using a wave rotor becomes aarent when comaring the thermodynamic cycles of baseline and wave-rotor-enhanced engines. Figure shows a schematic temerature-entroy diagram of a gas turbine baseline engine and a corresonding wave-rotor-toed engine. The shown case is the one most commonly discussed in references and in this aer is referred to as Case A. It is evident that both gas turbines are oerating with the same turbine inlet temerature and comressor ressure ratio. All wave rotors considered in this reort each have zero shaft work. Therefore, the wave rotor comression work is equal to the wave rotor exansion work. Thus, the energy increase from oint b to b in the baseline engine and from oint A to A in the wave-rotor-toed engine is the same, resulting in the same heat addition for both cycles. However, the outut work of the toed engine is higher than that of the baseline engine due to the ressure gain across the wave rotor ( ta > tb where index t indicates total values. Therefore, the overall thermal efficiency for the toed engine is higher than that of the baseline engine. The inherent gas dynamic design of the wave rotor comensates for the combustor ressure loss from oint A to 3 A, meaning that the comressed air leaving the 3 Coyright 3 by ASME

4 Temerature - b - b - b baseline engine - i - i -3 i - i - i toed engine i=a, B,, E T turbine B = C B = C A = E D D b = E = A Entroy wave rotor is at higher ressure than the hot gas entering the wave rotor at oint 3 A [, 3]. There are several ossibilities to to a gas turbine with a wave rotor. Nonetheless, knowing about ossible design restrictions and references, mainly five different advantageous imlementation cases for a wave rotor into a given baseline engine can be introduced as the following: Case A: same comressor, same turbine inlet temerature Case B: same overall ressure ratio, same turbine inlet temerature Case C: same combustor Case D: same turbine Case E: same comressor, same combustion end temerature Figure visualizes all five cases in a schematic T-s diagram. Path - b - b - b reresents the baseline cycle and - i - i -3 i - i - i with index i=a, B,, E indicates the various wave-rotor-toed cycles. One of the five cases might be referred for a ractical design. However, intermediate design cases are ossible. In Case A (- A - A -3 A - A - A the ressure ratio of the comressor is ket unchanged, so the hysical comressor of the baseline engine can also be used for the wave-rotorenhanced engine, rovided the mass flow is ket aroximately the same. The ressure in the combustion chamber of the enhanced engine is increased by the wave-rotor comression ratio and the turbine inlet ressure is higher. The turbine inlet temerature, however, is the same as it is for the baseline engine. The thermal efficiency is higher, because the turbine roduces more secific work, while consumtion of secific work by the comressor and secific heat addition to the cycle 3 E 3 A E 3 D b = D =3 C A C 3 B C B B b = D Figure : Schematic T-s diagram for a gas turbine baseline cycle and five different wave-rotor-toed cycles are the same as for the baseline engine. This imlementation case gives the highest erformance increase and is commonly discussed in the literature. In Case B (- B - B-3 B- B - B the overall ressure ratio for the wave-rotor-enhanced engine is ket equal to that of the baseline engine, so that the combustor works under the same ressure. However, for the wave-rotor-toed engine, the heat addition in the combustor and the combustion end temerature are higher than those of the baseline engine. For both the turbine and the comressor, the required ressure ratios are less. This case not only demonstrates an attractive erformance enhancement, additionally it rovides the highest turbine outlet temerature. Therefore this case is esecially attractive for an external heat recovery alication or for internal recueration enhancing the erformance even more. Case C (- C - C -3 C - C - C assumes that the overall ressure ratio for the wave-rotor-enhanced engine is ket equal to that of the baseline engine, as is the combustor inlet and outlet temerature. So the combustor of the baseline engine can be used unmodified. Here, the main advantage is that comressor and turbine work with a smaller ressure ratio. Case D (- D - D -3 D - D - D emloys the same hysical turbine as the baseline engine instead of the same comressor in Case A. The ressure in the combustion chamber is higher than that for the baseline engine but lower than it would be in Case A. Case E (- E - E -3 E - E - E is similar to Case A but the combustion end temerature - the maximum cycle temerature - is restricted to the turbine inlet temerature of the baseline engine, in order to not imose additional thermal requirements for the combustor. The overall ressure ratio is the same as in Case A. Performance estimations To evaluate the erformance enhancement of toing micoturbines with wave rotors, a thermodynamic aroach is used calculating the theoretic erformance (exressed by secific cycle work w and overall thermal efficiency η of wave-rotor-toed and baseline engines. The methodology is similar to the one introduced by Wilson and Paxson [] with some modifications []. In the calculations, it is assumed that the comressor inlet condition is known and is the same for both the baseline engine and the wave-rotor-enhanced engine. A comression ratio of t t =3. is assumed for the here considered stationary 3 kw baseline engine. The comressor and turbine isentroic efficiencies are C =79.% and T =8.% resectively. Considering the same aerodynamic quality of the wheels, the olytroic efficiencies are ket the same for the enhanced and baseline engine, for the comressor ( C =8.9% and turbine ( T =8.7% resectively. Incomlete combustion of the fuel is reflected by a combustor efficiency of Q =98.%. Further, a.% ressure dro in the combustor is considered by Π comb =.98. The fuel mass addition is ignored. No ressure losses in intake air filter, exhaust silencer and additional iing, or heat losses or mechanical losses are considered here. Such loses will reduce the redicted erformance. Air is entering the Coyright 3 by ASME

5 Relative Increase of Efficiency and Secific Work in % 3 3 Overall Thermal Efficiency Overall Pressure Ratio η η% and w% Wave Rotor Comression Ratio (PR W Figure 7: Overall thermal efficiency and secific work of the wave-rotor-toed engines versus wave rotor ressure ratio and overall ressure ratio (Case A comressor at.3 kpa and 3 K. The maximum allowable turbine inlet temerature is set to T t. K. According to revious wave rotor investigations [,, 7], the wave rotor comression and exansion efficiencies are assumed with WC = WE =.83. A wave rotor comression ratio of PR W = t t =.8 aears to be conceivable for the envisioned alication and is chosen for the discussion of reresentative values. However, lots are shown for various wave rotor ressure ratios indicating its effect on the erformance enhancement. Predicted erformance results Comarisons between the above cases and advantages and disadvantages of each case are extensively discussed in Ref. []. The results have indicated a 33.%,.%,.%,.%,.% relative increase in the overall thermal efficiency for each case resectively and corresondingly a relative increase in the secific shaft work of 33.%, 7.3%,.7%, 3.%, 7.%. Figure 7 illustrates the increase of cycle overall thermal efficiency (green and secific work (blue by increasing values of the wave rotor ressure ratio PR W for Case A. The lot visualizes how the effect develos from the baseline engine with PR W = until PR W =, which might be a ractical uer limit for the investigated alication. However, if the wave rotor ressure ratio increases beyond this limit the trend shows that the increasing effect becomes less, while technical roblems may increase. With a conceivable wave rotor ressure ratio of.8, the overall thermal efficiency of the baseline cycle increases from.7% to 9.% for the enhanced engine. Simultaneously the secific work increases from kjkg to 3 kjkg. This means an attractive relative erformance imrovement in overall thermal efficiency and secific work (red line in Fig. 7 of about 33.% for the baseline engine. w Secific Work (kj kg Overall Thermal Efficiency B. B D t t =3. t t =3. A D A b b PR W = Comressor Pressure Ratio ( t t Figure 8 shows a ma of the relevant design sace, which allows redicting the erformance of the wave-rotor-enhanced engine in terms of overall thermal efficiency (green and secific work (blue for any combination of comressor ressure ratio (abscissa and wave rotor ressure ratio PR W (arameter labeled in black. In this ma, the multilication of comressor ressure ratio t t and wave rotor ressure ratio PR W determines the overall cycle ressure ratio t t (red. The otimum comressor ressure ratio oints for highest overall efficiency and secific work at each achievable wave rotor ressure ratio are connected by black solid lines. This erformance ma is general. The only secific arameters are indicated in the uer right corner of the ma. They are mainly turbine inlet temerature and olytroic efficiencies of comressor and turbine, which corresond to the baseline engine. Such a ma is not only useful to exlore the ossible enhancement of already existing baseline engines, but it also serves very well for selecting a design oint or region when designing a new wave-rotor-toed engine. In the ma the erformance oints of the baseline engine and the wave-rotor-enhanced engine of Case A, B and D with a wave rotor ressure ratio of PR W =.8 are indicated, searately for overall thermal efficiency and secific work. Starting from the erformance oint of the baseline engine, the erformance values for Case A are found by moving vertically uwards (along a line for constant comressor ressure ratio t t until the corresonding erformance curve of the exected wave rotor ressure ratio is crossed. Case B is found by moving along a line for constant overall ressure ratio t t. Case D actually lies on a constant turbine ressure ratio line (not shown. Cases C and E can not be shown in the same ma since in both cases the turbine inlet temerature is less than that indicated in the uer right corner of the ma. 7. Otima 7. T = K η C =.83 η T =.8 Π comb =.98 Figure 8: Mas of overall thermal efficiency and secific work for wave-rotor-toing of gas turbines Secific Work (kj kg Coyright 3 by ASME

6 The results indicate that for every comressor ressure ratio in the shown design sace, the erformance of the toed engine is always higher than that of the corresonding baseline engine with the same comressor ressure ratio (Case A consideration. However, for higher comressor ressure ratios, less benefit can be obtained by using a wave rotor. In other words, the benefit is the greatest for lower comressor ressure ratios. This clearly favors the wave-rotor-toing for small gas turbines with low comressor ressure ratios such as microturbines. R78 REFRIGERATION CYCLE APPLICATIONS Water as a refrigerant (R78 is very beneficial because it is natural, absolutely harmless to man and nature, easily available and there are no roblems disosing it after use. Also it allows the use of high-efficient direct heat exchangers since cold water, refrigerant and cooling water all are the same fluid, mostly just water taken from the ta. As a challenge, relatively high ressure ratios are required since the cycle works under coarse vacuum. They are aroximately twice as high as ressure ratios when using classical refrigerants like R3a or R [8]. Combined with the thermodynamic roerties of water vaor this high ressure ratio requires aroximately a two to four times higher circumferential seed of the turbo comressor wheel, which can only be achieved economically by new secial high-erformance turbo comressors. However, for most air-conditioning alication they require two bulky comlete radial comressor stages with intercooling. The isentroic efficiencies of the turbo comressors are substantially limited by the required high ressure ratios and the efficiency of the ressure recovery of the steady-flow diffusers, which decelerate the high seed vaor flow coming from the high-seed comressor wheels. This is additionally comlicated by the fact that the Reynolds numbers of water vaor under vacuum are very low (like 3 times lower than if using R3a or R [8]. Hence, flow boundary layers can not withstand such a high ressure rise and tend to searate more easily from the walls and vanes of such steady flow devices, reducing the comressor efficiency further. Utilizing time-deended flow features, wave rotors reresent a romising technology for increasing the overall ressure ratio and the efficiency of the ressure recovery. As discussed above, for the same inlet and outlet Mach numbers, the ressure gain in time-deendent flow devices can be much higher than that obtained in steady flow devices. This also may allow for a lower total ressure ratio of the comressor wheel, which is usually associated with a higher isentroic efficiency of the comressor wheel assuming its aerodynamic quality stays the same (e.g. the same olytroic efficiency. This increases the overall efficiency additionally. Furthermore, the combination of this may then also ermit the use of more comact novel axial comressors with less stages and will further romote the new environmental friendly and energy efficient R78-technology for refrigeration, air-conditioning and heat um alications of caacities < kw, which is hardly available today in form of an economical solution.. W C. W Q. out Q. in Figure 9: Schematic of a R78 cycle enhanced by a -ort wave rotor Wave rotor in a R78 refrigeration cycle The hase change of the fluid inside the wave rotor in a R78 refrigeration alication is a major difference to the oeration of a wave rotor in a gas turbine cycle. Additionally, here the low ressure fluid is at higher temerature than the high ressure fluid. Coming from the comressor wheel at high-seed, the water vaor flows through a vaor collector that guides it to the inlet ort at an end late of the wave rotor. When a channel is oened by the interlay of end late and the rotating rotor, the vaor flows into the channel. Then, if the high ressure cooling water is introduced from the oosite side, it may be injected dynamically short before the vaor inlet ort is closed - meaning before the comression shock wave roagating into the vaor faster than the hase interface reaches the trailing edge of the vaor inlet ort. To assist uniform inflow of the high ressure cooling water, the rotor axis may be vertical and the water may be injected from the bottom. After the vaor is re-comressed by a rimary shock wave (if chosen so a reflected secondary shock wave and halted, the incoming water may comress the vaor further and fully condense it, deending on what kind of wave rotor has been chosen. A um sulies the high ressure to the cooling liquid. Its energy consumtion might be considered negligible, since the liquid is incomressible. However, the fluid now in its liquid state serves as a work caacitor storing the um work to release it for the vaors comression during its exansion in the wave rotor channels. Gravity and um ower may also assist the scavenging and charging of the channels. In advanced configurations the channels may be curved or bended for reasons like suorting or maintaining the rotation of the rotor 7 8 Coyright 3 by ASME

7 --3 b -8 b baseline cycle wave rotor enhanced cycle (high-ressure 3 (medium-ressure Temerature 3 b 7 T gain (low-ressure Figure : Dynamic-ressure equalizer 8 b 8 Entroy Figure : Schematic T-s diagram of a R78 cycle enhanced by a -ort wave rotor (Case A more efficiently like the free running rotor mentioned above. Due to the unsteady nature of the device, each channel of the wave rotor is eriodically exosed to both hot and cold flow. This can be timed in a way that the channel wall temerature stays aroximately at the same temerature like the incoming cooling fluid, suorting desuerheating and condensation of the vaor.. W C. W Q. out Q. in Figure : Schematic of a R78 cycle enhanced by a 3-ort condensing wave rotor Two ways of imlementing a wave rotor into a R78 cycle are described below. The first imlements a -ort wave rotor working more similar to a gas-turbine-toing wave rotor. This still requires an external condenser. The second emloys a 3-ort condensing wave rotor that eliminates the need of an external condenser, since full condensation occurs inside the wave rotor. R78 cycle with -ort wave rotor Similar to the conventional arrangement for imlementing a wave rotor in a gas turbine, the wave rotor is embedded between the comressor and exansion valve arallel to the condenser. Figure 9 illustrates how this wave rotor is used to to a R78 refrigeration cycle. In the wave rotor channels, the high-ressure cooling water leaving the um ( comresses the suerheated vaor coming out of the comressor (. Then the additional comressed vaor leaves the wave rotor ( to the condenser where it condenses while rejecting heat to the environment and returns to the wave rotor after a ressure boost by the um (. During the vaor comression in the wave rotor, the water re-exands (7 and is then further exanded into the -hase region by the exansion valve (8. After full evaoration while icking u the heat in the evaorator ( the refrigerant vaor is re-comressed in the comressor ( and the cycle continues as described above. In this configuration, the hase change mainly haens outside the wave rotor. Therefore, the vaor mass flows in and out of the wave rotor are nearly equal. Same is true for the mass flows of the water in and out of the wave rotor. However, the water orts are much smaller than the vaor ort. The advantage of using a wave rotor in this configuration can be realized by comaring the thermodynamics cycles of the baseline and the wave-rotorenhanced cycle shown in Fig.. The T-s diagram shows that, due to the additional comression by the wave rotor, condensation haens at higher temerature without increasing the ressure ratio of the comressor. It first and imortantly enables the system to work with a higher temerature difference and secondly results in a similarly high COP like the baseline cycle has for a smaller temerature difference. R78 cycle with 3-ort condensing wave rotor Figure shows the cycle arrangement with a condensing wave rotor. Concerning the ressure levels, its function is similar to a ressure-equalizer [] deicted in Fig.. It takes high ( and 7 Coyright 3 by ASME

8 axial length time a b Figure 3: Schematic wave and hase-change diagram for the 3-ort condensing wave rotor (high ressure art low ressure ( streams and equalizes them to a single medium ressure stream (3. However, the condensing wave rotor emloys a high-ressure, low-temerature liquid to comress and condense a low-ressure high-temerature gas. Thus, in the wave rotor channels, the high-ressure lowtemerature water coming out of um ( comresses the suerheated vaor coming out of comressor (, desuerheats and fully condenses it. This rocess is deicted in the schematic wave and hase-change diagram in Fig. 3. At the beginning of the rocess, when the high-ressure low-temerature water ( is exosed to the low-ressure high-temerature vaor (, due c d e to sudden ressure dro (from to, all the heat cannot be contained in the water as sensible heat and the heat surlus transforms into latent heat of vaorization. It is the so called flash evaoration or flashing henomenon, resulting in a temerature dro of the water. Therefore, a ortion of water suddenly vaorizes (b which causes a shock wave (c that travel through the suerheated low ressure vaor existing inside the channel (a. After the shock wave has additionally ressurized the vaor inside the channel, incoming water comresses the vaor further while desuerheating it (d. When the vaor ressure has reached saturation ressure, the continuing comression by the incoming water causes hase change (condensation of the vaor to water while further transfer of (now latent heat to the incoming water occurs (e. At the only outlet ort of the wave rotor, water is scavenged and then searated into two streams. One goes to the exansion valve (7 and the other to the heat exchanger (, where the heat is rejected to the environment. The um rovides the ressure level needed at the high ressure inlet of the wave rotor ( and the cycle continues as described above. Figure shows the schematic temerature-entroy diagram of the imlementation case similar as it is described above for the -ort wave rotor. Here the comression in the wave rotor is shown as a comression with substantial heat removal ( cooled comressor, since the condensing wave rotor comresses, desuerheates and condenses vaor in one rocess (-3. Further, the heat is rejected from liquid state (3-. The resulting necessary suercooling can be ket nearly insignificant by the usual high mass flow ratio of cooling water to refrigerant ( m& m&. This brings the states (3---3 much closer together then it is shown exaggerated in Figs. and. The exansion in the wave rotor (-3 reflects a massive heat addition ( heated turbine resulting from the desuerheating and latent heat of the refrigerant ( b -8 b baseline cycle wave rotor enhanced cycle baseline cycle wave rotor enhanced cycle Temerature 3 3 b T gain Te m erature 3 Case A eak ressure 8 b 8 8 Entroy En troy Figure : Schematic T-s diagram of a R78 cycle enhanced by a 3-ort wave rotor (Case A Figure : Schematic T-s diagram of a R78 cycle enhanced by a 3-ort wave rotor (Case B 8 Coyright 3 by ASME

9 Imlementation cases The above described imlementation case is here referred to as imlementation Case A. It enables the R78 alication for higher temerature differences as the baseline cycle with the same comressor as it is used for the baseline cycle. So, the additional comression by the wave rotor allows condensation at higher temerature without increasing the ressure ratio of the comressor. In Case B, where the goal is not a greater temerature lift, the wave rotor imlementation reduces the comression ratio of the comressor. This allows for other comressor designs, commonly increases the isentroic comressor efficiency, and consequently raises the COP of the cycle. Figure shows the imlementation Case B for a condensing wave rotor in which the comressor needs to roduce only a much lower ressure ratio than it has to roduce in the baseline cycle (oint versus and still the same temerature lift is achieved. SUMMARY A review of unsteady wave machine alications in ower generation and refrigeration systems is given. It is described how shock waves are utilized to transfer the energy of a highressure fluid directly to another low-ressure fluid. By this the overall comression ratio can be increased additional to that achieved by the turbo comressor in cycle. Five different advantageous imlementation cases of a -ort wave rotor into a given gas turbine baseline engine are considered. The comressor and turbine ressure ratios, and the turbine inlet temeratures vary, according to the anticiated design objectives of the five cases. For the imlementation of a wave-rotor in a stationary 3 kw microturbine, the investigation redicts an increase of the engine overall efficiency and secific work by u to 33%. In order to romote the modern environmental friendly and energy efficient R78 technology for refrigeration, airconditioning and heat um alications, new concets of imlementing a wave rotor in water (R78 refrigeration cycles are introduced, increasing the effective overall comression ressure ratio and otentially further enhancing the COP. Two different wave rotor configurations are suggested to enhance a R78 refrigeration cycle: a -ort wave rotor that is similar to those imlemented in a conventional arrangement of a waverotor-toed gas turbine. In this case the wave rotor only increases the effective ressure ratio, but still condensation mainly takes lace in an external condenser. Furthermore, a 3- ort condensing wave rotor is introduced, which may be referable. This is a comact unit that accomlishes comression, exansion and condensation in one device, eliminating the bulky external condenser. In a wave and hasechange diagram, the high ressure-art of a 3-ort condensing wave rotor is shown. Finally, two imlementation cases of a wave rotor into a R78 cycle are discussed, resectively mainly increasing the overall temerature lift or reducing the comressor ressure ratio and hence imroving the COP. REFERENCES [] Weber, H. E., 98, Shock-Exansion Wave Engines: New Directions for Power Production, ASME Paer 8-GT-. [] Kentfield, J. A. C., 998, Wave Rotors and Highlights of Their Develoment, AIAA Paer [3] Burghard, H., 99, German Patent 838. [] Darrieus, G., 9, Pressure Exchange Aaratus, U.S. Patent 8. [] Kentfield, J. A. C., 993, Nonsteady, One-Dimensional, Internal, Comressible Flows, Oxford University Press, Oxford. [] Gyarmathy, G., 983, How Does the Comrex Pressure-Wave Suercharger Work? SAE Paer 833. [7] Zehnder, G., Mayer, A. and Mathews, L., 989, The Free Running Comrex, SAE Paer 89. [8] Azoury P., H., 99, Engineering Alications of Unsteady Fluid Flow, Wiley, New York. [9] Kentfield, J. A. C., and Barnes, J. A., 97, The Pressure Divider: A Device for Reducing Gas-Pieline- Puming-Energy Requirements, SAE Paer 79. [] Seiel, C., Pressure Exchanger U. S. Patent 39939, 9. [] Akbari, P., Müller, N., 3, Performance Imrovement of Small Gas Turbines Through Use of Wave Rotor Toing Cycles, 3 International ASMEIGTI Turbo Exosition, ASME Paer GT [] Akbari, P., Müller, N., 3, Gas Dynamic Design Analyses of Charging Zone for Reverse-Flow Pressure Wave Suerchargers, 3 ASME Sring Technical Conference, Salzburg, Austria, ASME Paer ICES3-9. [3] Akbari, P., Müller, N., 3, Preliminary Design Procedure for Gas Turbine Toing Reverse-Flow Wave Rotors, 3 International Gas Turbine Congress Tokyo. [] Wilson, J. and Paxson, D. E., 993, Jet Engine Performance Enhancement Through Use of a Wave-Rotor Toing Cycle, NASA TM-8. [] Akbari P., Müller, N., 3, Performance Investigation of Small Gas Turbine Engines Toed with Wave Rotors, 39th AIAAASMESAEASEE Joint Proulsion Conference, AIAA-Paer 3-. [] Welch, G. E., 99, Two-Dimensional Comutational Model for Wave Rotor Flow Dynamics, ASME Paer 9-GT-. [7] Fatsis A, Ribaud Y., 999, Thermodynamic Analysis of Gas Turbines Toed with Wave Rotors, Aerosace Science and Technology, Vol. 3, No., [8] Müller N.,, Design of comressor imellers for water as a refrigerant, ASHRAE Transactions, Vol. 7, Coyright 3 by ASME