National Exams May Agric-A6, Physical Properties of Biological Materials. 3 hours duration NOTES:

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1 National Exams May AgricA6 Physical Properties of Biological Materials 3 hours duration NOTES If doubt exists as to the interpretation of any question the candidate is urged to submit with the answer paper a clear statement of any assumptions made 2 This is a CLOSED BOOK EXAM Approved calculator is permitted One aid sheet allowed written on both sides 3 FIVE (5) questions constitute a complete exam paper The first five questions as they appear in the answer book will be marked 4 Marks for each question are given 5 Some questions require an answer in essay format Clarity and organization of the answer are important Be brief too the point and concise Marking Scheme Five questions out of nine (all questions carry 20 marks) 20 marks total 2 (a) 0 marks (b) 0 marks 3 20 marks total 4 (a) 6 marks (b) 6 marks (c) 8 marks 5 (a) 0 marks (b) 0 marks 6 (a) 0 marks (b) 5 marks (c) 5 marks 7 (a) 2 marks (b) 8 marks 8 (a) 4 marks (b) 6 marks (c) 3 marks (d) 7 marks 9 (a) 45 marks (b) 45 marks (c) 3 marks (d) 5 marks (e) 3 marks 04AgricA6 May 206 Page of 6

2 Do any 5 questions The specific heat of a 2% moisture yellowdent corn was determined using a thermos bottle as a calorimeter The mass of the thermos was 545 g and the mass of the grain sample was 90 g The thermos and corn were first heated to 73 C and then 255 g of water at 2 C was poured into the thermos When the system was sealed and at equilibrium its temperature was 30 C If the specific heat of the thermos was 0946 kj/(kg K) and of water was 487 kj/(kg K) determine the specific heat of the corn using the method of mixtures (20 marks) 2 Using bench scale laboratory tests or batch equipment tests how would you determine or estimate the following (a) The thermal conductivity and diffusivity of a food product (0 marks) (b) The maximum tolerable freezing rate in terms of some frozen product quality attributes (0 marks) 3 A rotational narrow gap viscometer with a spring constant equivalent to 787 dynes/cm full scale reading on the indicator is used on a viscometer with cm outside diameter (OD) for the inner cylinder and 5 cm inside diameter (ID) for the outer cylinder The cylinders are 6 cm high Assume that end effects are negligible The following readings as a percentage of full scale on the indicator were obtained at various spindle speeds for a food product Determine the flow behaviour index (n) and consistency coefficient (b) of the fod Speed (N) rpm Torque indicated (% full scale) Use loglog graph paper or ordinary graph provided (20 marks) 4 (a) Sketch the recovery of fluid viscosity vs time during agitation at a very low shear rate following rapid agitation Distinguish between fluids that recover consistency and those that do not (6 marks) (b) What is the rate of strain (ds /dt c is strain and t is time)? Is it dimensionally similar to Av/Ay (shear rate for viscosity v is velocity and y is displacement)? Why? (6 marks) (c) The proportionality constants between stress and strain are called moduli (M) ie M = stress/strain Define in words and then in symbols the following moduli modulus of rigidity modulus of elasticity bulk modulus and modulus of compressibility (8 marks) 5 (a) Sketch a typical General Food Textural Profile curve for a food product which also shows adhesiveness Label the curve with the primary textural parameters and areas under the curve Define in formula form cohesiveness gumminess and chewiness (0 marks) 04AgricA6 May 206 Page 2 of 6

3 (b) Sketch a forcedeformation curve for 2 cycles compression for a small strain ie 0% Assume all plastic changes have vanished after the first compression cycle Start the curve for the second compression cycle at the end of the displacement for the first cycle Label the stress at 0% compression the degree of elasticity the mechanical hysteresis loss and the secant modulus of deformability and elasticity (0 marks) 6 (a) What would be the nonnewtonian class of a biomaterial in a laminar flow pipeline if the pressure drop/pipe length versus pipe length were (a) linearly decreasing (b) exponentially increasing and (c) exponentially decaying? (0 marks) (b) Explain Kelvin model to analyse creep behaviour data of a food product (5 marks) (c) Sketch a shear stress vs shear rate diagram for a pseudoplastic fluid over a range from creeping flow to very high shear rates Show when a Newtonianlike behavior is to be expected Briefly explain why? (5 marks) 7a Given the following size analysis of a sample calculate length mean particle diameter and volume mean particle diameter Dp = mean particle diameter N = number of particles (2 marks) Dpi µm Ni NiDpi 7b Define drag coefficient frictional drag and terminal velocity in aerodynamic characteristics of particles (8 marks) 8 (a) Define the surface and interfacial tension of liquid foods (4 marks) (b) Define the work of cohesion and adhesion and spreading coefficient of liquid foods (6 marks) (c) What is the effect of temperature on surface tension of a liquid food? (3 marks) (d) Explain capillary pull (du Nouy surface tension balance) method of measuring surface tension of a liquid food (7 marks) 04AgricA6 May 206 Page 3 of 6

4 9 (a) List 3 methods of measuring volume of a fruit product (45 marks) (b) List 3 methods of porosity measurement of a fried food product (45 marks) (c) List 2 methods of measuring surface area of a vegetable product (3 marks) (d) How could you use a freezing point depression to monitor the solids concentration of a beverage? (5 marks) (e) Give a conceptual view of why the addition of a solute in a liquid lowers its vapour pressure (3 marks) 04AgricA6 May 206 Page 4 of 6

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NOTES: Marking Scheme five questions out of nine (all questions cany 20 marks) 5. (a) 10 marks, (b) 10 marks

NOTES: Marking Scheme five questions out of nine (all questions cany 20 marks) 5. (a) 10 marks, (b) 10 marks National Exams May 2016 04-Agric-Ali, Physical Properties of Biological Materials 3 hours duration NOTES: 1. If doubt cxi.st.s as to the interpretation of any question, the candidate is urged to submit