Dalhousie University MECH 4010 & 4015 Design Project I Conceptual Design Report Project Name Team Number 18 Team Members Thomas Marks Ryan Gavin Dylan MacDonald Dennis McNeil Justin McPhee Submission date November 8, 2013
Contents List of Figures... 3 List of Tables... 3 1. Project Information... 4 1.1. Project Title... 4 1.2. Project Stakeholders... 4 1.3. Group Members... 4 1.4. Glossary... 4 2. Conceptual Design Summary... 5 3. Background and Context... 7 4. Requirements and Criteria... 8 4.1. Requirements and Constraints... 8 4.2. Criteria... 9 5. Functional Block Diagram... 10 6. Concept Classification Tree... 12 7. Conceptual Design... 15 8. Overview and Feasibility of Alternatives... 16 8.1. Hop Delivery... 16 8.2. Fermentation... 17 8.3. Lauter Options... 18 8.4. Milling... 19 8.5. Refrigeration vs. cold space fermentation... 19 8.6. Cooling... 20 8.7. Beer Clarification... 22 9. Testing and Verification... 23 10. Required Engineering Expertise... 24 11. Resources... 25 11.1. Facilities... 25 11.2. Advisors... 25 Appendix A Detailed Process Diagrams... 26 Dalhousie University Dept. of Mechanical Engineering Page 2 of 32
List of Figures Figure 1 - General Brewing Process Diagram... 10 Figure 2 - Concept classification tree based on functional blocks... 12 Figure 3 - Conceptual design of automated brewing system... 15 Figure 4 - Hop Delivery Alternatives - Revolver style in-line delivery and hopper style delivery... 16 Figure 5 - Boiling and Fermentation Alternatives... 17 Figure 6 - (a)false Bottom (b)copper Manifold (c)stainless Steel Screen... 18 Figure 7 - Immersion... 20 Figure 8 - Counterflow... 20 Figure 9 - Plate... 20 Figure 10 - Clarification Alternatives... 22 List of Tables Table 1 - Group Contact Information... 4 Table 2 - Process, Input, Output and Physical Requirements... 8 Table 3 - Testing and Verification Methods... 23 Table 4 - Team Expertise... 24 Dalhousie University Dept. of Mechanical Engineering Page 3 of 32
1. Project Information 1.1. Project Title - A fully automated tabletop all grain brewing machine that allows customization of recipes and process parameters. The user will load the necessary ingredients, select the process parameters, and turn the system on. The final product will be a full keg of beer. 1.2. Project Stakeholders Dalhousie University Collaborative project between Mechanical and Chemical Engineering Departments 1.3. Group Members Table 1 - Group Contact Information Thomas Marks th433667@dal.ca 902-220-4228 Ryan Gavin Ryan.Gavin@dal.ca 902-853-5335 Dylan MacDonald Dylan.MacDonald@dal.ca 902-623-2547 Dennis McNeil Dennis.McNeil@dal.ca 902-295-0587 Justin McPhee js893903@dal.ca 902-222-1640 1.4. Glossary Aeration - addition of air to the wort before fermentation to provide the yeast with the required oxygen to convert sugar to alcohol. Attenuation - a measure of the progress of fermentation. It can be calculated by examining the changes in specific gravity. Fermentation process where yeast converts sugars in the wort to ethyl alcohol and carbon dioxide gas. Lautering - Separating the wort from the grain after the mashing process. Mash - steeping milled grain to convert the grain s complex starches into fermentable sugars Mashout At the end of the mashing process, raising the mash temperature to denature (kill) the enzymes and fix the composition of the wort. Sparge - To trickle water through the grain bed to extract further sugars (typically occurs during or after lautering) Wort - the liquid extracted from the mashing process. Dalhousie University Dept. of Mechanical Engineering Page 4 of 32
2. Conceptual Design Summary This report provides a summary of the conceptual design of a fully automated all grain brewing system. A preliminary design concept was pitched at a recent design review meeting and the report includes updated requirements and some minor changes to the concept that are in line with the feedback received from industry and academic attendees. The report begins with some background information on the project, including a description of the current home brewing market and the viability of a product that can produce beer from scratch with minimum user input. The system requirements are discussed in Section 4. Requirements have been broken down into input, output, process, and physical requirements and are presented in Table 2. There are many process requirements to understand so the team developed a functional block diagram (located in Section 5) for quick visual reference of the beer making process. There are many ways to achieve the different functional blocks so the following criteria were designed to guide the design team toward a product that we believe will be marketable and innovative: The system should be powered by a standard wall outlet (110V, 15A) The design should minimize overall size and materials The system should be easy to clean A concept classification tree is presented in Section 6 that helps to show many of the options we identified that will perform the brewing process. The above list of criteria was applied to these options and our concept was narrowed down to the conceptual design presented in Section 7. The design includes an innovative process that reduces the size of the machine by reusing many of the vessels and lines during the brewing process. There is a process description in the Appendix that outlines each step of the process against a graphic of the system. The concept presented in Section 7 is the general design the team will be working to finalize over the next few weeks.. While many system components and functionalities have been decided there are still some components of the machine that require further investigation before a design selection can be made. Section 8 presents the alternatives that are yet to be finalized that the team will be focussing Dalhousie University Dept. of Mechanical Engineering Page 5 of 32
on next. It includes figures and descriptions of alternatives, as well as a quick overview of their pros and cons as well as the feasibility of each. Section 9 quickly describes the testing methods we have identified so far that will be employed to prove our system meets the requirements we have identified. The final section of the report provides some information on the resources we will be accessing throughout the project, including the roles and responsibilities of each of the group members. These resources and responsibilities are flexible and subject to change based on need as the project progresses. Dalhousie University Dept. of Mechanical Engineering Page 6 of 32
3. Background and Context All grain brewing is a method of brewing beer using only raw natural ingredients: grains, water, yeast and hops. The all grain brewing process is employed in many commercial breweries and brewpubs, and is increasingly popular amongst home brewers. All grain home brewing offers many advantages over store-bought beer. The first advantage is the level of control the brewer has over the finished product. By hand selecting the ingredients and controlling the process parameters the brewer can create any type of beer. Some home brewers duplicate their favourite brands, while many others customize recipes to create unique products. Another advantage is the decreased cost of brewing beer at home. Once the equipment is purchased, the cost per liter of homebrew is less than half that of store-bought beer. Further advantages include a fresh flavour that is unmatched in commercial beer, the knowledge of what went in to each batch, and the satisfaction of creating good beer at home. With increased interest in all grain brewing at home, many companies are starting to offer practical devices and aids for the brewing process. However, the process still takes a significant amount of time and attention from the home brewer. For example, the steps required before the fermentation process (Section 5 of this report gives a general overview of the brewing process) can take an entire day to perform. We believe a small automated all grain brewing system that offers the customization of process parameters would be an attractive product for many markets, including home brewers and breweries interested in producing small scale test batches. Our goal is to design and build a countertop automated home brewing machine that performs the mashing, boiling, fermenting and aging stages of the brewing process with no input from the brewer after turning the machine on. Dalhousie University Dept. of Mechanical Engineering Page 7 of 32
4. Requirements and Criteria 4.1. Requirements and Constraints There are many process constraints necessary to brew all grain beer. The design team has identified the absolute minimum set of requirements needed to brew almost any type of beer. Table 2 shows the process, input and output requirements, as well as the physical requirements of the system that need to be satisfied. Table 2 - Process, Input, Output and Physical Requirements Mash Boil Ferment Carbonate Water Power Ingredients PROCESS REQUIREMENTS Temperature control ± 1 C Programmable temperature range of 50-79 C for any time interval up to 90 minutes Grain bed must remain under 76 C until mashout Upon mash completion remove liquid through filter (spent grain remains) Maintain rolling boil for up to 90 minutes Programmable hop delivery - maximum 3 hop additions during boil ± 10% (wt) Wort cooled to at least 20 C after boiling Wort aerated to7-14 ppm dissolved oxygen Yeast addition after cooling and aerating Temperature control ± 1 C during fermentation Programmable temperature range of 5 C (for lagers) - 21 C (for ales) Sealed with one way vent to atmosphere CO 2 input depending on carbonation temperature (regulator manually set by user) INPUT REQUIREMENTS Plumbed in water source (municipal water supply) Standard residential electric power supply Grains, hops, yeast, Irish moss, other ingredients as needed depending on recipe Batch size 11.5 Liters ± 5% Alcohol content 3.5%-6.5% depending on recipe Food safe Size Materials OUTPUT REQUIREMENTS (pending discussion with Dalhousie Food Science to define requirement) PHYSICAL REQUIREMENTS Fit through standard 76 cm doorframe (76cm x 76cm footprint) Food grade materials for all process vessels and equipment Dalhousie University Dept. of Mechanical Engineering Page 8 of 32
4.2. Criteria The following criteria have been identified: Powered by a standard wall outlet (110V, 15A) Minimize overall size and materials Ease of cleaning These criteria were chosen to guide the design selection process towards a product that is marketable. The team believes that a countertop all grain brewing machine that is powered from a standard residential wall outlet will be a very attractive product to many home brewers. Also, maintaining a sanitized environment is critical for all brewing equipment so the system needs to be easy to clean. Dalhousie University Dept. of Mechanical Engineering Page 9 of 32
5. Functional Block Diagram Figure 1 - General Brewing Process Diagram Whole grains are milled and added to hot water in the mash tun where the grains settle to the bottom of the tun and create a grain bed. The grain bed is held at constant temperature inside the mash tun to convert the complex starches into simple sugars. Once the mashing process is complete, the liquid (now called wort) is lautered through the grain bed out of the mash tun and sent to the kettle where it is boiled. During the boil, hops are added at specific times to add flavour and complexity to the beer. Upon completion of the boil the wort is cooled quickly to at least room temperature and aerated to provide sufficient levels of oxygen for the yeast. The wort then flows to a fermentation vessel where yeast is added. The yeast reacts with the simple sugars in the wort and creates alcohol and carbon dioxide, which is vented through a one way valve to atmosphere. Once the fermentation process has completed, any remaining solids are filtered out and the beer flows to a keg where it is sealed, carbonated, and refrigerated to the desired temperature. Traditional all grain brewing systems typically use 5 vessels to complete this process: 1. A hot liquor tank - To stores and heat hot water before adding to the mash tun 2. A mash and lauter tun - to steeps the grains in the hot water 3. A kettle - to boil the wort 4. A fermentor - to ferment and age the wort Dalhousie University Dept. of Mechanical Engineering Page 10 of 32
5. A keg - to carbonate and store the beer One of the goals of this project is to design a machine that is compact so the design team challenged the need to have five separate vessels. Dalhousie University Dept. of Mechanical Engineering Page 11 of 32
6. Concept Classification Tree A concept tree (Figure 2) was used to compare options for each functional block of the system. Milling No Yes Fixed Grain Size Variable Grain Size Mashing Sparging Agitation No Sparging Recirculating Heating Propane Electric Automated Brewing System Hop Addition Cooling Metered Pre-measured Refrigeration Tap Water Gravity Fed In-Line Addition Immersion Counterflow Plate Aeration Cascade Forced Air Fermentation Removable Integrated Carbon Dioxide. Carbonation Forced Natural Nitrogen Figure 2 - Concept classification tree based on functional blocks Dalhousie University Dept. of Mechanical Engineering Page 12 of 32
Milling The feasibility of including a grain mill in our design is still being investigated (Section 8.4). At this time it can be assumed that pre-milled grains will be used in the brewing system. Mashing The sparging process was sacrificed to reduce the size and complexity of the overall design. This will compromise process efficiency, but reduce the number of mechanical systems and flowlines in the system. Recirculating the wort was chosen instead of agitation to eliminate the complexity of an agitating device from our design. Recirculation increases the efficiency of the mash and allows indirect temperature control of the mash tun. Recirculation also uses parts of our system that are used in other stages, reducing the number of system components. Heating Since our system is being designed for use in a residential setting, an electric heating element was chosen over a propane burner. Electric heat is safe and does not require ventilation. Hop Addition Pre-measured hop addition was chosen instead of metered hop addition to reduce the complexity of the control system and to ensure correct amounts of hops were added. Two methods of pre-measured hop addition are currently being evaluated and are explained in detail in Section 8.1. Cooling Wort cooling can be achieved with an open-loop tap water method (the water extracts heat from wort and is not used again) or a closed-loop water method (using a refrigeration loop to cool the water after it extracts heat from the wort). To reduce the cost and complexity of our design open-loop tap water was chosen. To make up for lost water efficiency, the cooling water will be used to flush some components of the system. The method of heat exchange between the wort and tap water has yet to be chosen, but, three options are examined in Section 8.6. Aeration Cascading the wort into the fermentor to achieve aeration was chosen because it does not require extra physical components to our design. Fermentation Integrated fermentation (i.e. fermenting within the same vessel in which boiling and cooling was done) was chosen to reduce overall system size. Fermenting in a separate removable vessel would allow another batch of beer to be started once Dalhousie University Dept. of Mechanical Engineering Page 13 of 32
fermentation begins, but it would require manual removal and sacrifice the automation of the system. Carbonation Forced carbonation was chosen because it takes significantly less time than natural carbonation. Carbonating with a CO 2 tank takes a maximum of three days, while carbonating naturally (using the CO 2 given off from the yeast to carbonate) takes two weeks. Dalhousie University Dept. of Mechanical Engineering Page 14 of 32
7. Conceptual Design The design criteria that were established in Section 4 were applied to the concept tree in Section 6 to identify an overall conceptual design, which is shown in Figure 3. Figure 3 - Conceptual design of automated brewing system A detailed overview of the process is included in Appendix A for reference. This concept provided many key benefits which are in line with our criteria, including: Compact size by reducing the number of vessels, lines, and pumps Low power requirements by only requiring heat input in one vessel and reducing the duty of the pump Maintaining customization of process parameters like temperature and hop addition Providing potential for external refrigeration and overlapping batches by allowing removal of the keg and carbon dioxide tank Dalhousie University Dept. of Mechanical Engineering Page 15 of 32
8. Overview and Feasibility of Alternatives 8.1. Hop Delivery Figure 4 shows two viable options for hop delivery. Revolver Style Delivery Hopper Style Delivery Figure 4 - Hop Delivery Alternatives - Revolver style in-line delivery and hopper style delivery For the addition of the hops during the boil, a few different processes were considered. The industry standard is to add hops by storing the hops in vessels located on a recirculation line from the kettle. Valves are opened to allow wort to run through the vessel and push the hops back into the boiling wort. One of our main criteria was to reduce the size of the machine and trying to replicate this process on a small scale will require extra lines, valves and vessels for each hop addition making it costly and more difficult to incorporate into the system s electronics. The second idea was to implement the industrial concept of using flowing wort to bring the hops into the boil by setting up a revolver type delivery system where an array of chambers, seen in Figure 4 (left), would have each section filled with the predetermined amount of hops. The revolver system would be connected such that the boiling wort would be pumped through each barrel to push the addition into the boil one at a time with a motor that turns the cylinder to the following chambers at set times. This system would be easier than the industrial process to design and program because there are less moving parts, but the lines would be prone to clogging and would also be harder to clean, and maintaining a tight seal would be difficult. Dalhousie University Dept. of Mechanical Engineering Page 16 of 32
The third option is to build a funnel-like hopper that is segmented into different sections for each hop addition. The bottom of the funnel would be capped with a disk that is free to rotate and has a section shaped hole through it where the hops can fall through. A motor is used to rotate the disk to the following section. This system has the same benefits as the revolver system, but is never in contact with flowing wort and is isolated from the rest of the system making it easier to clean. This solution can also be used as a means of adding other ingredients, such as yeast to the wort after it has been cooled. The challenge for this system is to design a way to close the lid of the fermenter immediately after it adds the yeast to the wort. 8.2. Fermentation Figure 5 - Boiling and Fermentation Alternatives For the purpose of space constraints and cost, eliminating vessels proved to be a very important step in the design process. After examining the developed brewing procedure, it was determined that combining the boil and fermentation vessels is possible. Several factors in the functionality of both vessels were considered. The boil vessel requires hop dispensing & heating systems and the fermentation vessel requires an airtight seal and aeration prior to the fermentation process. When Dalhousie University Dept. of Mechanical Engineering Page 17 of 32
combining the two vessels, using proper design of the process flow, delivery systems and heating processes, the functionality of both vessels can be achieved in a single vessel. Another option discussed during the fermentation process was a removable fermenter. If the fermenter could be removed, it would be possible to start on a second batch while the first batch is fermenting if a second fermentation vessel was used. A removable fermenter could then be placed in a temperature controlled environment to maintain constant temperature (further discussed in section 8.5). This would create the ability to produce beer at a much higher rate but requires a new vessel for each simultaneous batch, and would not allow for the easy combination of the boiling and fermentation vessel as discussed above. It also requires manual removal of the fermentor, which reduces the level of automation of the system 8.3. Lauter Options The lauter process is where the wort is removed from the grains. After the mash and lauter, grains are left remaining in the mash tun. To ensure proper drainage from the vessel, and to provide the home brewer with a cheap and easy cleaning solution for the mash tun (vessel 2 in Figure 3), three options were considered and are pictures in Figure 6. Figure 6 - (a)false Bottom (b)copper Manifold (c)stainless Steel Screen The first option is a False bottom. This is popular among home brewers because of how easily a false bottom can be used in a standard vessel. The false bottom is a pre-made component with very little set-up and little to no additional modifications or components. Its advantage is its simplicity and complete coverage of the vessel bottom however it has a slightly higher cost point than the other two options. Dalhousie University Dept. of Mechanical Engineering Page 18 of 32
A second option is to create a copper manifold. A copper manifold requires copper piping, which is cheap, and a bandsaw to create the slits in the pipe. To ensure the maximum area covered by the manifold, there must be adequate spacing to create short paths for the water to flow out of the manifold. This option will leave a small layer of wort in the mash tun after the mash and lauter are complete, but will allow the grains to be freely drained from bottom of the tank during the next step in the process (Refer to Appendix A for process description). This option uses a small amount of design and time to save on cost. The third option was a modification of a bazooka screen. A bazooka screen is a stainless steel meshsleeve that attaches to the output of the mash tun. The screen size must be sized carefully because bazooka screens can clog easily when exposed to grains. The modification of the bazooka screen is one of the more costly options however should produce the highest efficiency of all the options because the screen size can be specified and the filter covers the entire mash tun. 8.4. Milling For the milling process, there are several commercially available roller milling devices which can mill the grain to appropriate sizes. A motor with appropriate torque connected to the automation system would be able to connect directly to the commercial roller mills. A roller mill is ideal for the milling of barely grain, but for complete automation of the brewing process, there are concerns the milled grain output will not be spread evenly in the mashing tank. Automation of the milling process could require at least 2 moving components. It should be noted that milled grains are readily available at many brewing supply stores. Manually loading milled grains into the mash tun before turning the system on is an option being considered. At this point further investigation into evenly distributing the milled grains is required before a decision is made. 8.5. Refrigeration vs. cold space fermentation Lagers require temperatures as low as 5 C during fermentation. The team is investigating the feasibility of three different options at this point in the project: Integrating a refrigeration cycle to control fermentation temperature Designing a modular (removable) fermentor and assuming the brewer has access to a temperature controlled cold space Dalhousie University Dept. of Mechanical Engineering Page 19 of 32
Have an integrated fermentor without an active cooling system An integrated refrigeration cycle would allow in-situ fermentation of lagers and could also be used as a closed loop cooling system after the boil. The disadvantages are the increased complexity of design, higher costs, and the risk of refrigerant leaks. A removable fermentor would allow processing of lagers as long as a cold space was available. It should also be noted that fermentation is the longest step in the process and a removable fermentor would allow the production of multiple brews at the same time rather than waiting for a batch to finish fermenting. Disadvantages include the decrease to system automation and increased number of vessels which carries size and cost implications. The third option sacrifices the ability to brew lagers as the cold temperatures required could not be passively reached. The advantages are a smaller, more integrated design and the preservation of the automation of the system. 8.6. Cooling There are three heat exchangers being considered for cooling the wort: Immersion chillers - Figure 7 Counterflow chillers - Figure 8 Plate chillers - Figure 9. Figure 7 - Immersion Figure 8 - Counterflow Figure 9 - Plate Dalhousie University Dept. of Mechanical Engineering Page 20 of 32
The immersion chiller is very popular among homebrewers because of its simplicity. The coil is immersed into the kettle and tap water flows through the coil picking up heat from the wort. The counterflow chiller consists of a copper pipe within a copper pipe. Tap water flows through the inner pipe while hot wort flows in the opposite direction through the outer pipe. The heat exchange occurs between the wort and water through the outer wall of the inner pipe and the wort leaves the chiller at the appropriate temperature. A plate chiller consists of a number of layered plates with two inlet and outlet headers for hot wort and tap water. The wort and water flow across either side of the metal plate and heat from the wort is extracted by the water. For each of the options described above, there are certain flow rates of wort and water that will optimize cooling. The plate chiller is the most efficient because of the large surface area of the layered plates, but, it is the most difficult to clean once the cooling is complete because wort passes through the plates. At the other end of the spectrum, the immersion chiller is the least efficient option but is very easily cleaned as only tap water flows within it. Counterflow chillers offer a middling efficiency and are also difficult to clean because wort passes through the coil. There is a slight increase in system complexity for counterflow and plate exchangers due to the need to circulate two different fluids at the same time. The team is modelling the cooling system to determine how the difference in efficiency will affect the amount of water needed to cool the system and will use this model to help determine the final design. Dalhousie University Dept. of Mechanical Engineering Page 21 of 32
8.7. Beer Clarification Figure 10 - Clarification Alternatives Two different means of clarification and aging are being considered. After the fermentation process is complete, the beer should be aged in a secondary vessel. This process allows for most of the sediment to precipitate out of the beer and allow for a clear drink. To minimize the amount of vessels needed for the system, a keg can be used for this step to eliminate the in-between vessel. This is a fairly common practise among homebrewers. The problem faced with this solution is that there will be sediment at the bottom of the keg. To remedy this fault, the liquid out dip-tube used to draw beer from the bottom of the keg can be cut back roughly an inch to avoid pulling sediment out of the keg. This solution will, however, affect efficiency by increasing our amount of waste per liter of beer produced. The second consideration is to install an in-line filter between the fermentation vessel and the keg to eliminate any potential for sediment from entering the keg. This alternative will guarantee clearer beer, higher efficiency, and will avoid the need to modify the kegs. Dalhousie University Dept. of Mechanical Engineering Page 22 of 32
9. Testing and Verification The following high risk areas have been identified and tests have been developed to address them Table 3 - Testing and Verification Methods PROCESS TESTS Tests and Verifications Achieved mash temperature Maintained boil during boil process Testing and Verification Methods Integrated temperature sensor Integrated temperature sensor Hop delivery functionality Cooling model verification Adequate aeration process Food safe verification Operational testing to verify functionality Standalone testing of dispenser by comparing mass inputs to mass outputs of dispensing process Compare measured temperature changes to those predicted to theoretical models Test the dissolved oxygen content of a sample of wort after aeration process. Ensure process adheres to food safe standards (Discussions to be held with Food Science Department) PRODUCT TESTS Tests and Verifications Alcohol percentage Taste test Testing and Verification Methods Specific gravity testing of the beer Qualitative verification necessary to ensure product is as intended Dalhousie University Dept. of Mechanical Engineering Page 23 of 32
10. Required Engineering Expertise Table 4 - Team Expertise Technical Area Team Member(s) Responsible Level of Expertise Controls Dylan MacDonald C Language, Advanced Controls, Mechatronics Heating/Cooling Ryan Gavin HVAC, Thermodynamics I/II, Heat Transfer Materials/Machining Dennis McNeil Manufacturing, Engineering Co-op Power Supply Thomas Marks Li-Ion Battery Research/Development Project Management Thomas Marks Ryan Gavin Engineering Co-op Engineering Co-op CAD/CAM Justin McPhee CAD, FEM Dylan MacDonald Web Design Dylan MacDonald Personal Interest Dalhousie University Dept. of Mechanical Engineering Page 24 of 32
11. Resources 11.1. Facilities Dalhousie Food Sciences Dept. will be accessed to help determine and carry out testing on our first batch. The machine shop on Sexton Campus will be used for any machining, welding, altering of materials throughout the duration of the project. Oland Brewery hosted a detailed tour of their brewery for informative purposes and have offered further process knowledge, and some access to ingredients. Harris Industrial Testing Services have offered to test dissolved oxygen levels to verify aeration levels are met. The possibility of a cold space being available on campus is being investigated. 11.2. Advisors Aeneas Maddalena Industry Consultant (Oland Brewery) Dr. Ted Hubbard Design Supervisor Jon MacDonald Controls Assistant Dalhousie Chemical Engineering Dept. - Two design team collaborators Dalhousie University Dept. of Mechanical Engineering Page 25 of 32
Appendix A Detailed Process Diagrams Dalhousie University Dept. of Mechanical Engineering Page 26 of 32
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