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Plate Heat Exchangers for Refrigeration Applications

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Plate Heat Exchangers for Refrigeration Applications Plate heat exchangers for refrigeration applications Technical reference manual A Technical Reference Manual for Plate Heat Exchangers in Refrigeration & Air conditioning Applications by Dr. Claes Stenhede/Alfa Laval AB Fifth edition, February 2nd, 2004. Alfa Laval AB II No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, recording, or otherwise, without the prior written permission of Alfa Laval AB. Permission is usually granted for a limited number of illustrations for non-commer- cial purposes provided proper acknowledgement of the original source is made. The information in this manual is furnished for information only. It is subject to change without notice and is not intended as a commitment by Alfa Laval, nor can Alfa Laval assume responsibility for errors and inaccuracies that might appear. This is especially valid for the various flow sheets and systems shown. These are intended purely as demonstrations of how plate heat exchangers can be used and installed and shall not be considered as examples of actual installations. Local pressure vessel codes, refrigeration codes, practice and the intended use and in- stallation of the plant affect the choice of components, safety system, materials, control systems, etc. Alfa Laval is not in the business of selling plants and cannot take any responsibility for plant designs. Copyright: Alfa Laval Lund AB, Sweden. This manual is written in Word 2000 and the illustrations are made in Designer 3.1. Word is a trademark of Microsoft Corporation and Designer of Micrografx Inc. Printed by Prinfo Paritas Kolding A/S, Kolding, Denmark ISBN 91-630-5853-7 III Content Foreword. 1 1. Applications. The Basic Refrigeration Cycles and Applications. 2 1. The pressure-enthalpy diagram. 2 13. Heat exchanger applications in 2. The basic cycle. 2 a large supermarket. 18 14. Reversible systems. 20 3. Intercoolers & subcoolers. 4 14.1. Applications. 20 4. The components. 4 14.1.1. Cold stores. 20 4.1. The expansion process and devices. 4 14.1.2. Heat pumps. 20 4.2. The compressor. 6 14.1.3. Reversible A/C-Heat pumps units. 20 4.3. Evaporators, condensers and interchangers. 6 14.2. Design considerations. 20 4.4. The interconnecting pipe work. 6 14.2.1. Co- vs. counter current flow. 20 5. The flash economizer cycle. 6 14.2.2. Freezing risk at the flow reverse. 22 14.2.3. Suction line separators. 22 6. The evaporator economizer cycle. 8 14.2.4. Condensate subcoolers. 22 7. The real versus the ideal refrigeration cycle. 8 14.2.5. Oil separators, sight glasses and filter/driers. 22 8. Definition of capacity and 14.2.6. Liquid receivers in reversible systems. 24 coefficient of performance. 8 14.2.7. Installation of the liquid receiver. 24 9. Improvement of the cycles 14.2.8. One or two TEV systems. 24 and the use of PHE in these. 8 14.2.9. Systems with a liquid receiver. 24 14.2.10. Systems without a liquid receiver. 27 10. Subcooler/superheater cycle. 10 15. Sea water cooled systems. 28 11. The cascade cycle. 12 15.1. What is a SECOOL system? 28 12. The absorption cycles. 12 15.2. Direct vs. indirect systems. 28 12.1. Theory. 12 15.3. Components. 28 12.2. Applications. 12 16. Soluble oil in flooded systems. 32 12.3. The ammonia/water system. 14 16.1. The oil evaporator. 32 12.4. The water/lithium bromide system. 16 16.2. The oil cooler. 33 2. Optimization of Plate Heat Exchangers in Refrigeration Systems. 34 1. What is optimization. 34 2.16. Summary of PHE designs. 40 1.1. Equipment optimization. 34 2.17. Fouling factors and margins. 42 1.2. Conclusion. 34 2.18. Evaporators and condensers. 44 2. The thermal & hydraulic 2.18.1. Evaporators. 44 properties of PHEs. 34 2.18.2. Condensers. 44 2.1. Purpose of the study. 34 3. SECOOL optimization. 44 2.2. The thermal duty. 34 3.1. What is SECOOL optimization. 44 2.3. The optimally designed PHE. 35 3.2. Existing SW pumps. 45 2.4. The water flow changes. 35 3.3. Fixed pumping cost. 46 2.5. The pressure drop. 35 3.4. Summary. 46 2.6. The margin. 35 4. Optimization of PHEs in a system. 47 2.7. The complete thermal and 4.1. An intermediate circuit in a system. 47 hydraulic programs. 36 4.1.1. Indirect condenser cooling. 47 2.8. Discussion of the results. 36 4.1.2. Direct condenser cooling. 47 2.9. Further properties of the curve. 36 4.1.3. Comparison of the systems. 48 2.10. Pressure drop limit on side1. 36 4.1.4. Optimization of the systems. 48 2.11. The pressure drop varies. 36 4.1.5. Reoptimization of § 4.1.2. Direct condenser 2.12. The margin varies. 37 cooling. 48 2.13. Change in physical properties. 37 4.2. Heat exchanger duties in a supermarket. 49 2.14. The temperature difference. 38 4.2.1. Optimization of the liquid 2.15. Change of plate properties. 38 cooler - condenser circuit. 49 2.15.1. Heat transfer in a channel. 38 4.2.2. Optimization constraints. 50 2.15.2. Different channels. 39 4.2.3. Optimization of the unit cooler - 2.15.3. Cross corrugated plates. 40 evaporator circuits. 52 2.15.4. Properties of the channel types. 40 4.2.4. Change in condensation and 2.15.5. The area-flow for H, M & L channels. 40 evaporation temperatures. 52 IV Content 3. Design & Installation. 54 1. Design. 54 3.2. The multi-pass BPHE. 60 1.1. Design and material. 54 3.2.1. General. 60 1.2. Plate design. 54 3.2.2. Properties of multi-pass. 60 1.3. Plate denomination and arrangement. 54 3.2.3. Applications. 60 1.4. Nozzle directions. 56 3.2.4. Temperature difference vs. pressure 1.5. Identification of an unknown unit. 56 drop in a condenser or evaporator. 62 3.2.5. Channel arrangements. 62 2. Properties. 56 3.3. The multiple circuit BPHE. 62 2.1. Flow regime. 56 3.3.1. Applications. 62 2.2. Control. 56 3.3.2. Types. 64 2.3. Compactness. 56 3.3.3. Normal, one-pass. 64 2.4. Liquid volume. 56 3.3.4. Normal, two-pass. 64 2.5. Pressure and temperature limits. 56 3.3.5. Dual circuit BPHE. 64 2.6. Thermal efficiency. 56 3.3.6. Mixed design. 64 2.7. Fouling. 56 4. Water balancing, draining & purging. 66 3. Flow arrangement. 58 5. Instruments. 67 3.1. The one-pass BPHE. 58 6. Installation. 68 3.1.1. Evaporator. 58 6.1. Position. 68 3.1.2. Condenser. 58 6.2. Mounting. 68 3.1.3. Double nozzles. 58 6.3. Insulation. 68 3.1.4. Back end nozzles. 58 6.4. Connections. 68 3.1.5. Vents and drains. 58 7. Thermal guarantees. 68 4. Evaporators & Separators. 70 1. The evaporation process. 70 5.4. The valve-evaporator system. 84 1.1. What is boiling? 70 5.4.1. The bulb filling. 84 1.2. Boiling types. 70 5.4.2. The valve characteristic curve. 85 1.3. Flow in corrugated plate channels. 72 5.4.3. The evaporator characteristic curve. 85 2. Evaporator classifications. 72 5.5. Matching the evaporator to the valve. 86 2.1. Pool boiling units. 72 5.5.1. Operating point. 86 2.2. Flow boiling units. 72 5.5.2. Capacity of the system valve-evaporator. 86 2.3. Refrigeration evaporators. 72 5.5.3. Stability of a valve-evaporator circuit. 86 3. The flooded flow or circulation evaporator. 74 5.5.4. Noise in an evaporator. 86 3.1. General principles. 74 5.5.5. The evaporator stability curve. 87 3.2. Applications. 74 5.5.6. Feedback oscillations in a valve- 3.3. Thermosiphons. 74 evaporator loop. 88 3.4. Design considerations for thermosiphons. 76 5.5.7. Response of a valve-evaporator sys- 3.4.1. Pressure drop. 76 tem to a sudden temperature change. 88 3.4.2. Evaporation temperature. 76 5.5.8. Factors affecting the valve- 3.4.3. Flow distribution and double exits. 76 evaporator behaviour. 88 3.4.4. Minimum temperature difference. 76 5.5.9. Stability criterion of the valve- 3.4.5. Cocurrent vs. counter current flow. 76 evaporator system. 88 3.4.6. Exit vapour fraction. 76 5.5.10. Choosing & installing an expansion valve. 88 3.4.7. Oil drain 76 5.5.11. Evaporators with distributors. 90 3.5. Troubleshooting thermosiphons. 76 5.6. Troubleshooting the system 3.5.1. Instabilities. 76 valve-evaporator. 90 3.5.2. Thermal performance. 78 5.6.1. Liquid hammering. 90 3.6. Oil separation. 78 5.6.2. Hunting. 90 5.6.3. Insufficient capacity. 90 4. Vapour-liquid separators. 79 5.6.4. Too low suction pressure. 92 4.1. The purpose of this section. 79 5.7. Non-refrigerant BPHEs. 93 4.2. The function of the separator. 79 4.3. Operation. 79 6. Control. 94 4.3. Equipment of a separator. 79 6.1. Refrigerant expansion in 4.5. Separators for S&THEs and PHEs. 79 a flooded evaporator. 94 4.6. Separator types. 79 6.2. The electronic expansion valve. 94 4.7. The horizontal & hybrid separators. 81 6.3. Matching the evaporator and 4.8. Vertical separators. 82 compressor capacities. 94 4.9. Summary of separator design. 82 6.4. Capacity control. 96 5. The thermostatic expansion valve and 6.5.
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