CLP 301 (1 st semester 2022-23) Heat Transfer and Fluid Mechanics Lab Structure: Heat Transfer Experiments: 5 Fluid Mechanics Experiments: 5 Venue: UG Lab. Slot: F (2:00 PM – 5:00 PM) Evaluation: Lab reports: 30% Session evaluation (viva/quiz): 30% End-Semester quiz: 30% Lab discipline and attendance: 10% Penalty for absence: 2 marks for every absence up to 2 sessions, and 5 marks for rest (above 2 sessions). Medical reasons will not be considered. Minimum marks for passing grade: 40 List of experiments in Heat Transfer: 1. a) Heat transfer through composite wall b) Thermal conductivity of insulating powder 2. a) Heat transfer through natural convection b) Emissivity measurement apparatus 3. Shell and tube heat exchanger 4. Vapor compression refrigeration cycle 5. Double effect evaporator List of experiments in Fluid Mechanics: 6. a) Bernoulli’s apparatu s b) Flow metering devices 7. a) Reynolds apparatus b) Forced vortex flow 8. Head loss in pipes 9. Impact of jet on vanes 10. Centrifugal pump test rig Lab report: Each group will be divided into sub-groups of 3-4 members each. Single report needs to be submitted by each sub-group. Lab report must be submitted in next turn after the experiment is performed. Late submissions may invite penalty. It is expected that each team member has contributed to report writing. The report must be handwritten and must contain the objective and theoretical background written in own language, sample calculation (absolutely must), quality graphs (preferably on graph paper), detailed discussion of findings, error analysis and scope for further improvement. The reading sheet signed by lab instructor/TA must be attached with the report. It is advisable that both sides of the paper are used in report writing. Session evaluation: Performance evaluation of an experiment performed comprises of viva or short quiz. There are marks (total 10%) for lab discipline, punctuality and cleanliness for each experiment. If you do not clean up the experimental setup and surrounding workplace after completing your experiment, you may get zero marks in lab discipline. Students are required to compulsorily submit the feedback at the end of each session at feedbackclp301@gmail.com. Important instructions: If you miss any experiment, you can perform the experiment only during the buffer session towards end of the semester. You wi ll be awarded ‘F’ grade for serious undisciplined behavior or for unsafe practices in lab or for cheating or using unfair means in end-semester quiz/session quiz. You must wear shoes to the lab, otherwise you may not be allowed to conduct the experiment. All safety rules while dealing with chemicals and heating elements must be followed strictly. Schedule of Lab Classes According to Academic Time Table: Faculty- SG MCR MKSV AV/HP Extra working day Turn Monday (G2) Tuesday (G3) Thursday (G4) Friday (G1) Saturday Intro 4-Aug 5-Aug G3 (6 Aug)/MCR 1 8-Aug Holiday Holiday 12-Aug 2 Holiday 16-Aug 18-Aug Holiday 3 22-Aug 23-Aug 25-Aug 26-Aug 4 29-Aug 30-Aug 1-Sep 2-Sep 5 5-Sep 6-Sep 8-Sep 9-Sep 6 12-Sep 13-Sep 15-Sep 16-Sep 7 19-Sep 20-Sep 22-Sep 23-Sep 8 Minor Test Minor Test G2 (29 Sep)/SG 30-Sep 9 Sem Break Sem Break 6-Oct 7-Oct G3 (8 Oct)/MCR 10 10-Oct 11-Oct 13-Oct 14-Oct 11 17-Oct 18-Oct 20-Oct 21-Oct 12 Holiday 25-Oct 27-Oct 28-Oct G2 (29 Oct)/SG 13 31-Oct 1-Nov 3-Nov 4-Nov 14 7-Nov Holiday 10-Nov 11-Nov Experiment No - 1 (a) HEAT TRANSFER THROUGH COMPOSITE WALL Aim: Study of conduction heat transfer in a composite wall and to determine. ● The total thermal resistance and thermal conductivity of composite wall. ● Thermal conductivity of individual materials in composite wall. ● The temperature profile along the composite wall. Introduction: When a temperature gradient exists in a body, there is an energy transfer from the high temperature region to the low temperature region. Conduction heat transfer in solids takes place due to flow to electrons and lattice vibrations. Many engineering appl ications of practical utility involve heat transfer through a medium composed of two or more materials of different thermal conductivities arranged in series or parallel. For example, foundry furnaces are insulated with composite walls of materials with di fferent thermal conductivity to minimize heat loss. The problem of heat transfer through the composite system can be solved by the application of thermal resistance concept. Theory: According to Fourier’s Law, Energy is transferred by conduction and heat transfer rate per unit area is proportional to the normal temperature gradient. Q T A X − T Q KA X = − Where Q is the heat transfer rate and T X is the temperature gradient in the direction of heat flow. The positive constant K is called thermal conductivity of the material. The value of the thermal conductivity depends on the type of material. It can be a function of temperature and direction. If the value of K is the same in all directions, then the material is isotropic. If it is different for different directions, then its thermal properties are anisotropic. Using Fourier’s law, heat transfer rate across a plane wall is given by the following relation – 2 1 ( ) KA Q T T X = − − Where, the thermal conductivity is considered constant. The wall thickness is , and T 1 , and T 2 are surface temperatures. If more than one material is present, as in the multilayer wall, the analysis would proceed as follows: Figure 1: One dimensional heat transfer through composite wall In the case of a composite wall where thin flat plates of more than one material are in series with the flat faces in contact, the equation for heat transfer is given by - C A B A B C B B C T T T Q K A K A K A X X X = − = − = − The above relation between the heat flow across different plates in series assumes that there is no leakage of heat from the sides of the plate. where K i = Thermal conductivity of the material of i th plates. A = Area of heat transfer which is the same fo r all the plates. T i = Temperature difference across the i th plate. X i = Thickness of the i th plate. Experimental Setup: The Apparatus consists of a heater sandwiched between two asbestos sheets. Three slabs of different material are provided on both sides of the heater, which forms a composite structure. A small press - frame is provided to ensure the perfect contact between the slabs. A Variac (Variable autotransformer) is provided for varying the input to the heater and measurement of input power is carried out by a Digital Voltmeter & Digital Ammeter. Temperature Sensors are embedded between inner faces of the slab, to read the temperature at the surface. The experiment can be conducted at various values of power input and calculations can be made accordingly. Figure 2: Schematic diagram of heat transfer through composite wall apparatus Requirements: Electricity Supply: Single Phase, 220 V AC, 50 Hz, 5 - 15Amp socket with earth Experimental Procedure: Starting Procedure: ● Ensure that the Mains ON/OFF switch given on the panel is at OFF position & dimmer stat is at zero position. Connect the electric supply to the set up. ● Switch ON the Mains ON / OFF switch. ● Set the heater input by the dimmer stat, voltmeter in the range 40 to 100 V. ● After 1.5 hrs. note down the reading of voltmeter, ampere meter and temperature sensors in the observation table after every 10 minutes interval till observing change in consecut ive readings of temperatures (± 0.2 °C). Closing Procedure: ● After the experiment is over, set the dimmer stat to zero position. ● Switch OFF the Mains ON/OFF switch. ● Switch OFF electric supply to the set up Precautions: 1. Never run the apparatus if the power supply is less than 180 volts and above than 230 volts. 2. Never switch on mains power supply before ensuring that all the ON/OFF switches given on the panel are at OFF position. 3. If the electric panel is not showing the input on the mains light, check the main supply. 4. If the voltmeter shows the voltage given to the heater but the am meter does not, check the connection of heater in the control panel. Observations: Diameter of the plates (D) = 0.25 m Cast Iron plate thickness (X 1 ) = 0.020 m Bakelite plate thickness (X 2 ) = 0.015 m Press Wood plate thickness (X 3 ) = 0.012 m Thermal Conductivity of Cast Iron (K 1 ) = 52 W /m ° C Thermal Conductivity of Bakelite (K 2 ) = 1.4 W/m ° C Thermal Conductivity of Press Wood (K 3 ) = 0.12 W/m ° C Observation Table: S. No. Voltage (V) Current (A) T 1 ( ̊C) T 2 ( ̊C) T 3 ( ̊C) T 4 ( ̊C) T 5 ( ̊C) T 6 ( ̊C) T 7 ( ̊C) T 8 ( ̊C) Calculations: To plot the temperature profile, Distance (cm) 0 20 35 47 Average temperature At distance 0, average temp T A = 1 2 2 T T + At distance 20, average temp T B = 3 4 2 T T + At distance 35, average temp T C = 5 6 2 T T + At distance 47, average temp T D = 7 8 2 T T + Rate of heat supplied by the heater Q = V I = .......W Heat flux in one direction, q = / 2 Q A = .......W/m 2 Area A = 2 4 D = ....... m 2 Temperature difference across the composite wall 1 7 2 8 ( ) ( ) 2 T T T T T − + − = =...... °C Total thermal resistance of the composite wall R t = T q = ....... ̊C m 2 /W Total thickness of the composite wall 1 2 3 X X X X = + + = ......m Thermal conductivity of the composite wall eff A D X K q T T = − = ....W/m ̊C Thermal conductivity of Cast Iron 1 1 A B X K q T T = − = ..... W/m ̊C Thermal conductivity of Bakelite 2 2 B C X K q T T = − = ..... W/m ̊C Thermal conductivity of Press Wood 3 3 C D X K q T T = − = ..... W/m ̊C Results: Report the following results ● The total thermal resistance and thermal conductivity of composite wall. ● Thermal conductivity of individual materials in composite wall. ● The temperature profile along the composite wall. Sources of errors: Report the possible sources of error found in the experiment and the observations. Discuss exactly how these affect the experimental data (i.e. will the readings be larger or will they be smaller due to the presence of a particular source). Discussions: 1. Discuss your results for conductivity with the theoretical results of conductivity provided to you. 2. Suggest some ways to lower the time it takes for your system to reach steady state. Without doing an experiment can you estimate the time scale for this system to reach steady state. 3. What will happen if the layers of the experiment are not in perfect contact, (i.e.) th ere is a layer of air between the layers? 4. What is the meaning of isotropy/ anisotropy in the context of this experiment? 5. If the two sides of the slabs are not symmetric, how will the heat(Q) be distributed between the two sides? References: 1. Holman, J.P., "Heat Transfer", 9th ed., McGraw Hill, ND, 2008, Page 23 - 24 2. Kern, D. Q. “Process Heat Transfer”, 16 th ed., McGraw Hill, ND, 2007, Page 14 - 15, Thermal Conductivity of Materials Experiment No. 1 (b) THERMAL CONDUCTIVITY OF INSULATING POWDER O bjective : To study the heat transfer through conduction in insulating powder A im : To calculate the thermal conductivity of insulating powder. Introduction : In many heat transfer equipments , heat loss to surroundings is to be minimized to achieve maximum economy. In such cases they are lagged by materials of lower thermal conductivity, which are referred as insulators. Because of demand of such insulating materials, many industries have come up to produce such material. Preference is given to produce materials having lower thermal conductivities. Also these materials are available in different shapes, sizes and forms of powders. Powders have the advantage that they can take any complicated sh ape between any two confirming surfaces. In addition its conductivity will be much lower than that of the Basic solid from which the powder has been made. This is because of a very large number of air spaces in between particles, which have much lower ther mal conductivity values. Thermal conductivity of such materials is a complicated function of the geometry of the particles, the nature of heat transfer, conduction, convection and radiation in air spaces, which is determined by the air space size and tempe rature level etc. Thus it is very difficult quantity to estimate and almost in all practical cases it is measured experimentally. T heory : Consider the transfer of heat by conduction through the wall of hollow sphere formed by the insulating powdered layer packed between two thin copper spheres. Let: r i = radius of inner sphere in m r o = radius of outer sphere in m T i = average temperature of the inner surface in ºC T o = average temperature of the outer surface in ºC From the Experimental values o f q, Ti and To, the unknown thermal conductivity k can be determined by following formulae: k = Thermal conductivity of insulating powder ( W/m o C ) Q = Amount of heat transfer (W) Experimental Setup: The apparatus consists of two thin walled concentric spheres of copper of different size. The small inner copper sphere is provided with the heater. The insulating powder (i.e. Asbestos) is packed between the two spheres. Ten temperature sensors at proper positions are fitted to measure surface t emperature of spheres. PID Controller is used for heat input & Energy meter is provided to measure the energy consumption. Figure: Block diagram of Thermal conductivity of insulating powder apparatus Requirements: Electricity Supply: Single Phase, 220 V AC, 50 Hz, 5 - 15 Amp combined socket with earth connection. Earth voltage should be less than 5 volts. Bench Area Required: 1 m x 1 m. Experimental Procedure: Starting Procedure: 1) Ensure that mains ON/OFF switch given on the panel is a t OFF position. 2) Connect electric supply to the set up. 3) Switch ON the mains ON/OFF switch. 4) Set the heater input by the PID Controller, temperature in the range 40 to 80 ̊C. 5) Switch ON the heater ON/OFF switch. 6) After 1 hrs. Note down the reading of pulses with respect to time and temperature sensors in the observation table after every 10 minutes interval till observing change in consecutive readings of temperatures (± 0.2 o C). Closing Procedure: 1) When experiment is over switch OFF the heater ON/OFF switch. 2) Switch OFF the mains ON/OFF switch. 3) Switch OFF the power supply to the set up. Precautions: • Never run the apparatus if power supply is less than 200 volts and above than 230 volts. • Never switch ON mains power supply be fore ensuring that all the ON/OFF switches given on the panel are at OFF position. • Operate selector switch of temperature indicator gently. Always keep the apparatus free from dust. Observations: Data Inner radius r i = 0.05 m Outer radius r o = 0.1 m Energy meter constant EMC = 3200 pulses/kW - hr Observation Table Sr No. P t p (sec) PV T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 P = Pulse t p = Time for pulses T 1 - T 4 = Tempe rature of temperature sensors embedded on the inner sphere ( ºC ) T 5 - T 10 = Temperatures of temperature sensors embedded on the outer sphere ( ºC ) Calculations: Amount of heat transfer A verage temperature of the inner surface A verage temperature of the outer surface Thermal conductivity Calculation T able Sr No. k (W/m 0 C) Results: Thermal conductivity of insulating powder is ... ... Sources of errors: Report the possible sources of error found in the experiment and the observations. Discuss exactly how these affect the experimental data (i.e. will the readings be larger or will they be smaller due to the presence of a particular source). References: • Holman, J.P (2008). Heat Transfer. 9th Ed. ND: McGraw Hill. pp 25 - 27. • Coulson, J.M, Richardson, J.F (1996). Chemical Engineering Vol - 1. 5th Ed. ND: Asian Books Ltd. pp 349 - 350. Experiment No - 2 (a) HEAT TRANSFER BY NATURAL CONVECTION Aim: To determine the theoretical and experimental heat transfer coefficient for transfer of heat from a heated vertical cylinder to atmosphere by free or natural convection. Introduction: The convective motion is known to enhance the heat transfer coefficien t in fluid medium. The fluid motion can be created either by external agency (forced convection) or by buoyancy of the medium (free or natural convection). The natural convection phenomenon is attributed to the flow circulation generated solely by the diff erence in temperature of the surface causing change in the density of the fluid and is not created by any external agency. This process is continuous and the heat transfer takes place due to the relative motion of hot and cold fluid particles. The energy transfer by natural convection is the dominant mode of heat transfer in many industrial devices like steam radiators, power transformers. Natural convection also plays a significant role in cooling of electronic devices. Theory: In convective cooling, as a cool fluid is passed over a heat wall, temperature profile formation takes place. . .[ ( )] s Q h A T T y = − Velocity and temperature profiles for convection Near the wall the fluid is subjected to no slip condition; that is, there is a stagnant sublayer. Since there is no fluid motion in this layer, heat transfer i s governed by conduction in this region. The layer above is a region where viscous forces oppose fluid motion. In this region, some convection may occur but conduction may well predominate. A careful analysis of this region allows us to use our conductive analysis in analyzing heat transfer. This is the basis of our convective theory. At the wall heat transfer rate can be expressed as the heat flux. .( ) conv t s T q k h T T y = − = − Hence, He at transfer coefficient ( ) t s T k y h T T − = − Dimensionless numbers ● Nusselt’s Number (Nu) h L Nu k = Heat transfer by convection Conductive resistance Heat transfer by conduction Convective resistance Nu = = A larger value of Nu implies enhanced heat transfer by conduction. ● Prandtl Number (Pr) Pr P C k = Momentum diffusivity Pr Thermal diffusivity = Pr represents the relative importance of momentum and energy transfer for diffusion. ● Grashof Number (Gr) Free stream velocity U ∞ is always zero for natural convection so the Reynolds number is also zero and is no longer suitable to describe the flow in the system unlike in forced convection. Hence, we use the Grashof number. 3 2 2 . . (Inertia force).(Buoyant force) (Viscous force) L g T Gr = = The tendency of the natural convective system towards turbulence relies on Gr. Here L = Characteristic dimension of the surface (Length in this case) k = Thermal conductivity of fluid μ = Dynamic viscosity of fluid γ = Kinematic viscosity of fluid C p = Specific capacity of fluid β = Coefficient of volumetric expansion of fluid g = Acceleration due to gravity T = T s - T a T s = Surface temperature T a = Ambie nt temperature Experimental Setup: The apparatus consists of a stainless - steel tube fitted in a rectangular duct in a vertical fashion. The duct is open at the top and bottom and forms an enclosure and serves the purpose of undisturbed surroundings. One side of the duct is made up of Perspe x for visualization. An electric heating element is kept in the vertical tube which in turn heats the tube surface. The heat is lost from the tube to the surrounding air by natural convection. The temperature of the vertical tube is measured by seven therm ocouples. The heat input to the heater is measured by an ammeter and a voltmeter and is varied by a dimmer stat. The surface of the tube is polished to minimize radiation losses. Sc hematic of heat transfer through natural convection Thermocouple no. 8 reads the temperature of air in the duct (ambient temperature). The distance between ‘point 1 and point 2’ and ‘point 2 and point 3’ is 4 cm each and the others are 7 cm each from ‘poin t 3 to point 7’. Requirements: Electric supply: Single phase 220 V AC, 50 Hz, 5 - 15 Amp socket with earth connection. Experimental Procedure: 1. Connect the equipment to power supply. Set the voltmeter reading to some value by the dimmer stat provided and k eep it constant. 2. Wait for about one hour before taking the first reading. 3. After one hour, note the temperatures T 1 to T 7 by the temperature operating switch in the interval of 30 minutes. 4. Note down the voltmeter and ammeter reading. 5. Note down the ambient temperature (T 8 ). 6. Repeat the experiment for another power input. 7. Tabulate the readings. Precautions: 1. Never run the apparatus if power is less than 180 volts and above 230 volts. 2. Never switch ON mains power supply before ensuring that all the ON/OFF switches given on the panel are at OFF position. 3. Switch OFF temperature indicator gently. 4. Always keep the ap paratus free from dust. Observations: ● Data Diameter of the tube (D) = 45 mm Length of the tube (L) = 450 mm ● Observation table S. No. T 1 T 2 T 3 T 4 T 5 T 6 T 7 T avg T 8 V I T 1 – Temperature at point 1 ( ° C) T 2 – Temperature at point 2 ( ° C) T 3 – Temperature at point 3 ( ° C) T 4 – Temperature at point 4 ( ° C) T 5 – Temperature at point 5 ( ° C) T 6 – Temperature at point 6 ( ° C) T 7 – Temperature at point 7 ( ° C) T 8 – Ambient air temperature in the duct ( ° C) Calculations: ● Experimental heat transfer coefficient exp .( ) s s a Q h A T T = − Where Q = Heat transfer rate (Watt) = V I A s = Area of the heat transferring surface = DL T s = Average surface temperature (°C) = ( ) 1 2 3 4 5 6 7 7 T T T T T T T + + + + + + T a = Ambient temperature in the duct (°C) = T 8 ● Theoretical heat transfer coefficient From a dimensionless analysis as per the Buckingham Pi theorem, a general relationship between the above dimensionless numbers has been given as: ( ) m k Nu c Gr P h L r = = 3 2 . . L g T Gr = 2 s a T T + = (Kelvin - 1 ) Where m and c are constants and they are evaluated as follows: