Advances in Gas Cooler Design and the New Gas Cooler Product Selector Simon Jones Engineering Manager Sean Armitage Sales Manager
Introduction GEA Searle Over 90 years experience in the design and manufacture of heat exchangers Many years working closely with the refrigeration industry to align with system innovations GEA Searle has embraced the re-emergence of CO 2 as a refrigerant and has worked on many customer collaborations dating back to 1997 We have just completed a 2 year research project with Brunel University on CO 2 Gas Coolers 2 Insert text with "Insert Header and Footer"
Basic Principles CO 2 is a very good working fluid with a high thermal capacity With ODP 0 and GWP 1, CO 2 is viewed by many as a future proof refrigerant, with many potential applications of which we are still only beginning to realise Different ways to work with CO 2 include direct cycle, secondary or cascade A common Transcritical Cycle is that known as the Booster System, which utilises appropriate compressor technology for the LT and MT parts of the system to improve compressor ratios / efficiency 3 Insert text with "Insert Header and Footer"
The Gas Cooler Performs the function of a conventional condenser (albeit exceptional operating conditions) while the CO 2 system is operating sub-critically in lower ambient conditions As the ambient increases, the high side system operation moves into the supercritical phase and condensation can no longer take place. Instead the properties progressively move from those of a gas to those of a mixed fluid 4 Insert text with "Insert Header and Footer"
The Gas Cooler Condensation is no longer possible as the heat rejection is taking place in the supercritical region. This supercritical / fluid region is often referred to as the gas condition; therefore it follows we are performing Gas Cooling and hence the heat exchanger is called a Gas Cooler Control of the operating pressure and switching between sub and supercritical is performed using an electronic valve (such as the Danfoss ICMT) with a control algorithm intended to achieve maximum efficiency Operating pressures and temperatures above 100 bar and inlet temperatures well above 100 C, the gas cooler construction needs special consideration 5 Insert text with "Insert Header and Footer"
The Gas Cooler Gas Cooler operating point 120 C Typical Inlet 34 C Typical Outlet 6 Insert text with "Insert Header and Footer"
Gas Cooler Development Purpose behind research project - Improve GEA Searle's understanding of Transcritical CO 2 refrigeration applications We believe we have to do more than sell a component - Optimise the design of a heat exchanger, specifically for use as a Gas Cooler With the previously defined operating characteristics, a conventional heat exchanger is not the best option - Develop and collaborate a mathematical model that can be used within a product selector for Gas Coolers The performance rating of a heat exchanger is essential to ensure the customer gets only what they need and what they pay for 7 Insert text with "Insert Header and Footer"
Gas Cooler Development CO 2 booster system incorporated as is common for UK supermarkets 8 Insert text with "Insert Header and Footer"
Gas Cooler Development 9 Insert text with "Insert Header and Footer"
Gas Cooler Development Length:1600 mm Air OFF Air ON Inlet header outlet header Height : 66 mm Fins Material : Aluminium Thickness : 0.16 mm Pithc: 12 Fins/inch Row wide: 32 Row deep: 2, 3 and 4 row options Variable circuit options Tubes Material : Copper Dia. : 8 mm Thickness : 1 mm In order to simulate as many operating conditions as possible, it was necessary to design a system with hot air recirculation the opposite to what you would want in application 10 Insert text with "Insert Header and Footer"
Gas Cooler Development 11 Insert text with "Insert Header and Footer"
Heat Exchanger Optimisation Improved thermal capacity of the working fluid means that both lower flow and reduced charge are possible This, along with the high working pressure led to the conclusion that 8mm was one of the optimised tube diameters for this application Extensive CFD analysis was used to define / optimise coil geometries 12 Insert text with "Insert Header and Footer"
Heat Exchanger Optimisation Test results and CFD analysis shows significant temperature change through at the fluid inlet region of the 13 Insert text with "Insert Header and Footer"
Heat Exchanger Optimisation Original coil geometry With a horizontal split in the coil block overall heat transfer increase of approximately 7% Addition of a vertical slit can offer a further 2% performance increase 14 Insert text with "Insert Header and Footer"
Gas Cooler Application Due to the possibilities for far greater temperature differences with gas cooler (2-3 time compared with conventional refrigerants) it can be preferable to reduce the airflow and increase the number of tube rows deep Consequently operational power input, noise and heat exchanger footprint (by increasing the number of tube rows deep) may be reduced whilst maintaining thermal capacity The relationship between air volume and capacity is dissimilar to that of an ordinary HCFC system with a condenser; i.e. a drop in air volume can lead to greater heat exchanger efficiencies as the loss in capacity is less than the loss in power input (Efficiency = Heat Rejection / Fan Power Input) 15 Insert text with "Insert Header and Footer"
Mathematical Model The mathematical model, developed for GEA Searle by Dr. Yunting Ge of Brunel university, as been extensively calibrated against test results and CFD analysis It considers cross-counter flow operation of working fluids Fluid properties are adjusted through the calculation due to the significant differences of the fluid properties at different stages of the Gas Cooling process The developed mathematical model has now been built into a product selector which filters between the extensive product range 16 Insert text with "Insert Header and Footer"
GF Gas Cooler The Range Modular range 4 fan module lengths From 1.2m long to 12 m long, up to 2.2m wide Selected units up to 700kW 15 db(a) to 72 db(a) @ 10m Single piece side plates Integral tube-sheets 17 Insert text with "Insert Header and Footer"
GF Gas Cooler The Range Modular range from one to twenty fans 1.2m to 12m long M N P1 P2 A 1200mm B 1500mm C 1800mm D 2100mm 18 Insert text with "Insert Header and Footer"
GF Gas Cooler - Features Different size expansion gas within the block to allow for expansion and contraction. Block are split into an upper section with large expansion gaps and a lower section with small expansion gaps. This feature is incorporated into all gas cooler blocks to allow for the different rates of expansion and contraction. 19 Insert text with "Insert Header and Footer"
GF Gas Cooler - Features In addition to the expansion gaps within the block, we have also implemented oversized tube plates and extended tubes to allow for movement of the block. The block is supported on each fan module by an integral steel tube sheet. Each tube sheet is fitted with re-flared Aluminium insert plates supporting each Copper tube. 20 Insert text with "Insert Header and Footer"
GF Gas Cooler - Features Gas coolers headers are manufactured from 304L Stainless Steel with NB stainless steel connections. Advantages of St/St over Mild Steel are the anti-corrosive / improved life cycle After manufacture and testing heaters are over sprayed. 21 Insert text with "Insert Header and Footer"
GF Gas Cooler - Features Initial leak test air under water at 69 Bar. Strength pressure test 170 Bar. Maximum Operating Pressure 120 Bar. 22 Insert text with "Insert Header and Footer"
GF Gas Cooler - Fans GEA Searle offer the best fan technology available in the market today This includes, AC, EC, AxiTop, ZA Plus and the soon to be released FlowGrid 23 Insert text with "Insert Header and Footer"
GF Gas Cooler Selection Software Customer Requirements 24 Insert text with "Insert Header and Footer"
GF Gas Cooler Selection Software 25 Insert text with "Insert Header and Footer"
GF Gas Cooler Selection Software Unit GF-MC101G4H-EC-P-AL (with options) GF-MC101G4H-EC-P-AL 435 1JB Unit Orientation: Horizontal (Vertical air flow) Electrical Supply: 400 V, 3 Phase, 50 Hz Fanset Description: 910 mm Ziehl EC Fanset TK Wired?: Not Applicable Isolators (one per fan)?: No Fin Material: Aluminium (AL) Fin Type and Rows: G4 Wiring or Control Type: 1 Junction Box Casing Finish: Powder RAL7032 Pebble Grey Brand: GEA Searle Transcritical Capacity kw 75 Ambient Temperature C 32 Refrigerant CO2 (R744) Noise Level db(a) 48 Mean Noise Level db(a) 50 Sound Power Level db(a) 81 Tube/Fin Material Copper/Aluminium (AL) Inlet Connection Size Outlet Connection Size Sections Per Unit 1 Circuits Per Section 11 Orientation Horizontal (Vertical air flow) Air Volume m3/s 4.9 Internal Volume dm3 12 Input Power (Total) A 0.93 Energy Rating B Fan Speed rpm 770 Electricity Supply 400/3/50 Rows Of Fans 1 Fans Per Row 1 Starting Current A 0 Full Load Current A 0 Overall Length mm 2123 Overall Width mm 1130 Overall Height mm 1333 Dry Weight kg 293 Part Number GF-MC101G4/5601379 Configuration Model Condenser version 1.0.7 date 2014/01/07 26 Insert text with "Insert Header and Footer"
Thank You GEA Searle will be exhibiting at the ACR Show in February 27 Insert text with "Insert Header and Footer"