Mechanical Engineering Laboratory

Mechanical Engineering Laboratory MEE 416 Professor H. Ezzat Khalifa Syracuse University http://lcs.syr.edu/faculty/khalifa/mee416/ MEE416 1 A. Experiment 1 Air-Conditioning: Air-side Experiment 0031 Link Hall MEE416 2 1

Outline of Experiment 1 Lecture Air-Conditioning (A/C). Basic Components of an A/C System. Properties of Moist Air. Psychrometrics. Objectives of this Experiment. Air-Conditioning Demonstrator (Laboratory System). Lab Assignments. MEE416 3 Air-Conditioning (A/C) Process: Heating/Cooling/Humidifying/Dehumidifying and filtering of indoor air. Purpose: To achieve desired air temperature, humidity and quality (cleanliness). Applications: Space conditioning for human comfort. Process control (e.g., printing and textile, datacenters). Food preservation. Animal care. MEE416 4 2

Basic Components of an A/C System Heat exchanger for cooling/dehumidifying, or for heating the air. Water or refrigerant on one side and air on the other). Air movers (fans and blowers) to move the air within the system and into and from the conditioned space. Humidifier (steam or evaporative) for adding moisture to the air. Air ducts to carry the circulated air within the A/C system and into and from the conditioned space. Air control dampers to control air flow paths and quantity. Sensors and controls (e.g., thermostats). Air filters to remove gaseous and particulate contaminants. MEE416 5 Typical A/C System (Air-Side) MEE416 6 3

Properties of Moist Air - Psychrometrics Moist indoor air is a mixture of dry air and water vapor. Indoor air for human comfort typically contains ~1% moisture by mass. Moist air conditions are determined by properties such as: Dry-bulb temperature (DBT, F). Wet-bulb temperature (WBT, F). Dew point temperature (DPT, F) Relative humidity (RH, %). Humidity Ratio (HR, lb of H 2 O/lb of dry air). Enthalpy (h, Btu/lb of dry air). Specific volume (v, ft 3 /lb) For a given pressure, the thermodynamic properties of humid air can be fully determined by the specification of two independent properties (e.g., DBT and WBT, or DBT and RH). MEE416 7 Properties of Moist Air - Psychrometrics Any state property of moist air, S can be expressed as: S = F(DBT, HR), where HR = m(h 2 O)/m(dry air), HR = m(h 2 O)/[m(mixture) m(h 2 O)], HR = γ/(1 γ); γ = 1/(1/HR 1), in which γ is the mass fraction of water vapor in moist air. But mole fraction of water vapor in moist air is given by: x = γ/m w /[(1-γ)/M a + γ/m w ] = P w /P t, which allows us to determine partial pressure of H 2 O vapor from HR. RH = P w /P w (sat at DBT)*100% MEE416 8 4

Psychrometric Chart (ASHRAE) MEE416 9 Psychrometric Processes Air Conditioning Systems Cool & Dehumidify Air Cool Humidify Heat Cool & Dehumidify Dehumidify MEE416 10 5

Laboratory Groups Divide into groups of 6-8: Lab 2: M 09:45 12:45 PM 0031 Link Hall Lab 3: W 12:45 03:35 PM (Cancelled) Lab 4: Th 05:30 8:30 PM 0031 Link Hall Lab 5: F 03:45 6:30 PM 0031 Link Hall MEE416 11 Lab Assignments Draw a schematic of the air circuit of the Hampden Model H-ACD-2 Recirculating Air Conditioning Demonstrator, indicating each of the components in the air circuit. Conduct the following experiments in the Student Manual of the Hampden H-ACD-2 Recirculating Air Conditioning Demonstrator: Experiment 1: Air Flow measurement Experiment 2: Wet bulb temperature measurement Experiment 9: Air conditioning process Write a report to summarize the experimental results and answer the following questions regarding the results of Experiment 9: Why the cooling capacities were different for the two test conditions (i.e. with vs. without the heater)? What is the amount of sensible heat, latent heat and moisture removed under each test condition (Hint: Figure 8-10 of Reference 1)? MEE416 12 6

Lab Report Requirements Each student must submit a lab report that includes the following components (with % of grade points indicated in the parenthesis): Introcution (5%). Objectives (5%). Experimental apparatus (10%). Methods and procedure (15%). Experimental uncertainity analysis (10%). Measured parameters. Calculated parameters. Results and discussions (30%). Conclusions and recommendations (20%). References (5%). Papers or report referenced Attach a copy of the team presentation Note: Team presentation and class/lab participations account for 20% of final grade. MEE416 13 B. Experiment 2 Air-Conditioning: Refrigeration Cycle Experiment 0031 Link Hall MEE416 14 7

Outline of Experiment 2 Lecture Air-Conditioning: Why do we need Refrigeration? Basic Components of a Vapor Compression System. Properties of Refrigerants. Objectives of this Experiment. Lab Assignments. MEE416 15 Typical A/C System (Air-Side) MEE416 16 8

Basic Components of an A/C System Heat exchanger for cooling/dehumidifying, or for heating the air. Water or refrigerant on one side and air on the other. Air movers (fans and blowers) to move the air within the system and into and from the conditioned space. Humidifier (steam or evaporative) for adding moisture to the air. Air ducts to carry the circulated air within the A/C system and into and from the conditioned space. Air control dampers to control air flow paths and quantity. Sensors and controls (e.g., thermostats). Air filters to remove gaseous and particulate contaminants. Why do we need a water or a refrigerant cooled heat exchanger? MEE416 17 A/C System Psychrometric Processes Coil temperature must be cooler than room dew point (DP) to dehumidify the air Room DP Outdoor Air Coil Inlet Room Return Air Coil Exit Room Condition Line MEE416 18 9

Refrigeration Cycle Experiment How the cooling capacity is provided Principles of Refrigeration. What are the basic properties of a refrigerant. How to represent the thermodynamic conditions of the refrigerant, and analyze/visualize a refrigeration cycle using a pressure enthalpy (P-h) chart. How to measure and determine the operating status and performance of a refrigeration system. MEE416 19 Basic Components of a Refrigeration System A refrigerant as a working medium (e.g., tetra-fluoroethane R134a). An evaporator in which the refrigerant changes phase from liquid to vapor, thus absorbing heat from the air and producing a refrigeration efect (cooling for air-conditioning). A compressor for pumping the refrigerant vapor to a pressure whose saturation temperature is higher than the the outdoor temperature. A condenser in which superheated refrigerant vapor is condensed to a subcooled liquid. A liquid receiver for collecting the condensed liquid refrigerant. An expansion valve for throttling the refigerant liwuid from the condenser pressure to the evaporator pressure; also controls refrigerant flow. MEE416 20 10

Simple Vapor Compression Cycle 3 2 Condenser Expansion Valve Compressor Ecaporator 4 1 MEE416 21 Properties of Refrigerant (P-h Chart). Temperature (F or R). Pressure (absoluate value in psia; gage value in psig). Enthalpy (Btu/lb). Saturation temperature and pressure (saturated vapor, saturated liquid, and two-phase mixture of liquid and vapor). Critical temperature and pressure. Entropy (Btu/lb R) Quality or dryness fraction (mass fraction of vapor in a vapor-liquid mixture). MEE416 22 11

Refrigeration Cycle The P-h chart (Mollier chart) for the refrigerant (R134a here) is a powerful tool for analyzing the refrigeration cycle process: Expansion (e.g., from subcooled point A: 100 F & 153.7 psia condenser pressure to point B at 49.7 psia evaporator pressure). Evaporation (e.g., from point B at 49.7 psia evaporator pressure to saturated vapor point C, and on to superheated vapor point D at 50 F). Compression (e.g., from point D at 50 F tp Point E). Condensation (e.g., from point E at 160 F and 153.7 psia to point G at 153.7 psia saturated liquid, then to subcooled liquid at point A to complete the cycle). MEE416 23 Single-Stage Vapor Compression Cycle P ΔT SC P C A E P E B C D Δh W o ΔT SH Δh E Δh W h MEE416 24 12

Real Vapor Compression Cycle P P D P C 3 2d 2 P E P S 4 1a 1 1b 1c h MEE416 25 P-h Chart for R134a (SI Units) MEE416 26 13

Lab Assignments Conduct the following experiments in the Student Manual of the Hampden Model H-ACD-2 Recirculating Air Conditioning Demonstrator: Experiment 5: Humidity and Dew Point. Experiment 6: The Refrigeration Cycle. Experiment 7: Effect of Humidity on refrigeration. Write a report to summarize the experimental results and discuss the findings from Experiment 7 above. Refrence: Student Manual of the Hampden Model H-ACD-2 Recirculating Air- Conditioning Demonstrator: Chapter 1, 2, 3; and Experiments 5, 6 & 7. MEE416 27 Lab Report Requirements Each student must submit a lab report that includes the following components (with % of grade points indicated in the parenthesis): Introcution (5%). Objectives (5%). Experimental apparatus (10%). Methods and procedure (15%). Experimental uncertainity analysis (10%). Measured parameters. Calculated parameters. Results and discussions (30%). Conclusions and recommendations (20%). References (5%). Papers or report referenced Attach a copy of the team presentation Note: Team presentation and class/lab participations account for 20% of final grade. MEE416 28 14

C. Experiment 3 Air-Conditioning: Fan Experiment 0025 Link Hall MEE416 29 Outline of Experiment 3 Lecture Role of fans in an Air-Conditioning System Introduction to Turbomachines Fan Performance Characteristics. Fan Scaling Laws. Objectives of this Experiment. Lab Assignment. Report Format. MEE416 30 15

Typical A/C System (Air-Side) MEE416 31 Fluid Movers in an Air-Conditioning System Refrigerant side: Refrigerant compressor. Water pumps for hydronic systems. Air Side: Indoor air fans. Outdoor fan (condenser fan). MEE416 32 16

Role of fans in HVAC Systems To deliver air flow to the conditioned space. To overcome air-flow resistance (pressure drop) in the air paths (in ducts, across dampers and through heat exchanger surfaces). To enhance heat transfer through the outdoor section (condenser in an air-conditiong system). MEE416 33 Classification of Fluid Machines Positive Displacement Machines [PD]: Hydraulic Pumps & Motors; Gas Compressors & Expanders: Piston, Sliding Vane, Scroll, Screw, Lobed (Roots) Most refrigerant compressors are of this kind. Rotodynamic (Turbo) Machines [RD]: Hydraulic Pumps & Turbines; Gas Compressors; Steam and Gas Turbines; Hydraulic Couplings; Windmills; Propellers and Fans: Radial, Mixed-flow, Axial; Impulse & Reaction; Single and Multi-stage. Air conditioning system fans Centrifugal refrigerant compressors for large chillers. MEE416 34 17

Classification of Fluid Machines Positive Displacement Machines Rotodynamic (Turbomachines) Pumps; Compressors; Propulsion Devices Piston, Vane, Scroll, Screw, Roots, Rolling Piston Centrifugal, Mixed, Axial Flow; Ship Screws; Aircraft Propellers Motors; Turbines; Expanders Hydraulic Motors; Piston, Vane, Screw Expanders Centripetal, Mixed, Axial Flow; Impulse and Reaction Turbines, Windmills MEE416 35 Axial and Radial Flow Fans Backward Swept Blades Axial Usually used in the outdoor section of an air-conditiong system Radial Usually used in the indoor section of an air-conditiong system MEE416 36 18

Axial Flow Turbomachines Titanic MEE416 37 Radial & Mixed-Flow Turbomachines MEE416 38 19

Fan Performance Characteristics Fan performance is characterized by the following parameters: Pressure rise (head) expressed in inch water, Pa, 1 inch W.G. = 5.204 lb f /ft 2 Volumetric flow rate expressed in cfm, m 3 /s Fan efficiency (fluid power divided by shaft input power). Fan rotational speed (RPM, radians/s ). Fan shaft horsepower (shaft power input). Fan performance is presented as either tables or charts showing: Pressure rise (ΔP), efficiency (η) and power (W) as a function of volume flow rate (Q) for different speeds (RPM). MEE416 39 Fan Performance Curves Increasing RPM MEE416 40 20

Fan Power Fluid power W f is the useful power imparted to the fluid by the fan: W& f = ΔP.Q ΔP could be the static pressure rise, the total pressure rise or the totalto-static pressure rise. Shaft power W s is the mechanical (shaft) power input to the fan: The term brake horsepower (BHP) should be used only for power generating machines, like engines and turbines. The correct term for power consuming machines like pumps, fans and compressors is shaft horsepower (SHP). Efficiency, η = Wf Ws MEE416 41 Dimensional Analysis of a Fan For geometrically similar fans we ΔPs = f (Q,D,N, ρ, μ ) obtain the following relations, using the Buckingham Pi theorem. ΔPs Ψs = 2 2 ρn D ΔP s = the static pressure rise; Q Q = the volumetric flow rate; Φ = 3 ND D = characteristic diameter; N = rotational speed W& Λ = 3 5 ρ = density ρn D W = fluid power; 2 ρnd Ψ s = static head coefficient; Re = μ Φ = flow coefficient; Re = Reynolds Number; L = power coefficient; Ψs = F( Φ,Re) η = aerodynamic efficiency. η = f ( Φ, Re) MEE416 42 21

Scaling of Fan Performance Curves MEE416 43 Dimensionless Representation Head (Pressure) Coefficient ΔP Ψ = 2 D 2 ρn Flow Coefficient Q Φ = 3 ND MEE416 44 22

Fan Scaling Laws For geometrically similar machines operating under similar operating conditions, dynamic similarity implies: Φ 1 = Φ 2 Ψ 1 = Ψ 2 η 1 = η 2 Λ 1 = Λ 2 These laws are valid if the effects of reynold numbers are negligible, i.e., Re is very high, which it often is. MEE416 45 Fan Test Tunnel: 0025 Link Hall Stroboscope The lab set-up has a supply fan upstream of the test fan. MEE416 46 23

Lab Assignment (1) Objective: Learn how to map fan performance data. Enhance understanding of fan performance characteristics, dimensional analysis and fan scaling laws. Obtain hands-on experience on fan testing. Test Facility: Fan test tunnel. Instruments for measuring pressure, flow rate, power and speed (RPM). Fan performance to be measured: Fan static pressure rize versus flow rate. Shaft power input versus flow rate. MEE416 47 Lab Assignment (2) Task 1: Perform fan testing at 1600 RPM and plot results graphically as: Task 2: ΔP vs. Q and η vs. Q. Using fan scaling laws, predict performance at 1200 and 2000 RPM. Task 3: Using fan scaling laws, predict the performance of a geometrically similar fan with a diameter that is 50% larger than the tested fan and with 1600 RPM. Plot the data in dimensional form. MEE416 48 24