Conservation of Mass, Flow Rates So Far: Conservation of Mass, Flow Rates Fluid Flow, Re No., Laminar/Turbulent Pressure Drop in Pipes Bernoulli’s Equation Flow Measurement, Valves Total Head, Pump Power, NPSH This Week: Pump Sizing, Types of Pumps Conservation of Energy

Pump Sizing Volume Flow Rate (m3/hr or gpm) Total Head, h (m or ft) 2a. P (bar, kPa, psi) Power Output (energy added to fluid) and Input (mechanical shaft power from motor) NPSH Required

Pumps Centrifugal Impeller spinning inside fluid Kinetic energy to pressure Flow controlled by Pdelivery Positive Displacement Flow independent of Pdelivery Many configurations

Centrifugal Pumps Delivery Impeller Volute Casting Suction

Centrifugal Pumps Flow accelerated (forced by impeller) Then, flow decelerated (pressure increases) Low pressure at center “draws” in fluid Pump should be full of liquid at all times Flow controlled by delivery side valve May operate against closed valve Seal between rotating shaft and casing

Centrifugal Pumps Advantages Simple construction, many materials No valves, can be cleaned in place Relatively inexpensive, low maintenance Steady delivery, versatile Operates at high speed (electric motor) Wide operating range (flow and head) Disadvantages Multiple stages needed for high pressures Poor efficiency for high viscosity fluids Must prime pump

Increasing Impeller Diameter Centrifugal Pumps H-Q Chart Increasing Impeller Diameter Head (or P) A B C Volume Flow Rate

Increasing Efficiency Centrifugal Pumps H-Q Chart Increasing Efficiency Head (or P) Required NPSH A B C Volume Flow Rate

Centrifugal Pumps H-Q Chart Head (or P) A B C Volume Flow Rate

Required Flow Capacity Centrifugal Pumps H-Q Chart Required Flow Capacity Head (or P) Actual Flow Capacity Required Power Volume Flow Rate

What if available NPSH is less than required NPSH? Centrifugal Pumps What if available NPSH is less than required NPSH? Increase Available NPSH 1. Increase suction static head (pump location) 2. Increase suction side pressure 3. Decrease fluid vapor pressure 4. Reduce friction losses on suction side Decrease Required NPSH 1. Reduce pump speed 2. Select a different pump

Centrifugal Pumps Curves created for specific speed, viscosity and density Often, use more charts or correction factors to “fine tune” pump selection Variable speed motor has same effect as impeller size Multiple pump/impeller combinations may work

Centrifugal Pumps Closed Impeller Most common, low solids Water, beer, wort Flash pasteurization Refrigerants Open Impeller Lower pressures Solids okay Mash to lauter turn Liquid yeast, wort, hops

Positive Displacement Pumps Theory: Volume dispensed independent of delivery head Practice: As delivery head increases, some slippage or leakage occurs Speed used to control flow rate, use of valves could cause serious damage Self-priming Good for high viscosities, avoiding cavitation

Positive Displacement Pumps Piston Pump Volumetric Efficiency High Pressures Metering hop compounds, detergents, sterilents Suction Valve Delivery Valve

Positive Displacement Pumps Peristaltic Pump

Positive Displacement Pumps Gear Pump High Pressures No Pulsation High Viscosity Fluids No Solids Difficult to Clean

Positive Displacement Pumps Lobe Rotor Pump Both lobes driven Can be sterilized Transfer Yeast Trub Bulk Sugar Syrup

Laws of Thermodynamics First Law – Energy is conserved Second Law – Energy has quality, processes go in certain directions only Forms of Energy Potential energy = mgh Kinetic energy = (0.5)mv2 Internal energy (U) – microscopic forms Conservation of Energy

Heat transfer – Temperature difference Energy Interactions Heat transfer – Temperature difference Work – Shaft, electrical, boundary, etc. Mass flow – U + PV = Enthalpy (H) Closed System Energy Equation No Phase Change

Open System Energy Equation for steady flow systems or

A 500 gallon water tank is filled with 220 gallons of hot water at 80C and 280 gallons of cold water at 10C. Assume that the specific heat of water is 4.2 kJ/kg.K. Determine the temperature in the tank after it has been filled. How much heat must be added to the tank to bring its temperature to 65C? If a 30 kW electric heater is used, how long will the heating process take?

500 kg of grain (25C) is mixed with hot (80C) and cold (10C) water for mashing. The water to grain ratio (by weight) is 3:1 and the specific heat capacities of the water and grain are 4.2 and 1.7 kJ/kg.K, respectively. a) If the desired “mash in” temperature is 38C, how much hot and cold water should be added?

(Continued) A three step mashing process, with 20 minute-long rests at 50, 62 and 72C, is desired. The mash should be heated quickly, but not too quickly between rests; with an optimal rate of 1C per minute. Neglect heat losses to the surroundings. b) Plot the mash temperature vs. time. c) Determine the heating power required, in kW. d) Determine the total heat required for the mashing process, in kJ.

Two types of heat sources are available for mashing, electric resistance heaters and steam. The steam enters a heating jacket around the mash as dry, saturated steam at 300 kPa and it exits the system as wet, saturated steam at the same pressure (enthalpy of vaporization = 2150 kJ/kg). (e) What is steam flow rate required, in kg/s? (f) If steam is used, what is the total mass of steam required, in kg?

At the location of our brewery, electricity costs $0 At the location of our brewery, electricity costs $0.14/kW-hr and the steam can be generated for $0.03 per kg. (g) What is the mashing cost when electric resistance heaters are used? (h) What is the cost with steam?

Explain the term “net positive suction head” and discuss its importance in the pumping of liquids in a brewery. A centrifugal pump with an NPSH of 5 m is pumping wort from a whirlpool, open to the atmosphere, to a wort cooler. If the wort is at 95C and has a vapor pressure of 0.8453 bar, calculate the minimum distance below the whirlpool outlet that the pump must be positioned to prevent cavitation. Data on board…