Polymer Chemistry

Questions & Answers

Question 8 Creep in polymers becomes significant at temperatures above 0.4 Tm (Tm = melting temperature). O True O False

Question 9 All thermoplastics creep. O True O False

Question 10 Polymers creep below their yield point and but recover after the load is removed. O True O False

Question 11 Creep compliance is defined as? reciprocal of creep modulus ratio between time-dependent strain and stress ratio between intitial starin and imposed stress

Question 12 Relaxation modulus is measured during experimentation when? O applied load is fixed O applied strain is fixed

Question 13 How many stages are observed in the strain vs. time creep curve ?

Question 14 The creep rupture envelope are used to select and predict? Mark all that apply. safe loads acceptable temperatures acceptable time of imposed laods

Question 15 The Boltzmann superposition principle states that the response of a polymer to a given load is dependent of the response of the polymer to any load, which is already imposed on the polymer. O True O False

Question 16 According to the Boltzmann superposition principle, each loading step makes independent contribution to total loading history. O True O False

Question 1 If a load is imposed on a polymer, the strain will? O remain constant O decrease O increase

Question 2 If a load is imposed on a polymer, the strain will increase slowly with time due to? slipping of crystalline structure change in a molecular arrangement build up of tensions

Question 5 In the case of polymers and their creeping, it is necessary to consider? Mark all that apply. O temperature O applied load O time O UV radiation

Question 4 Polymers are viscoelastic at? O glass transition temperature O above glass transition temperature O below glass transition temperature O all temperatures

Question 3 The polymer is viscous in that it recovers, but elastic in that it creeps. O True O False

A straight rod of solid polymer is of length 1 m and diameter 10 mm. The polymer is linearly viscoelastic with a tensile creep compliance: D(t) = 2-exp(-0.1t), where t is in hours. The rod is suspended vertically and a mass of 10 kg is hung from it for 10 hours. A) Find the change in length of the rod. Express the result in mm, with two decimals. B) After 10 hours, the 10 kg mass is removed. Calculate the strain remaining in the rod after a further 10 hours. Express the result in percentage, with three decimals

2. Water flows through a thick-walled tube with an inner diameter of 12 mm and a length of 8 m. Thetube is immersed in a well-stirred, hot reaction tank that maintains the outer surface of the tube at85 °C. The conduction resistance of the tube wall (based on the inner surface area) is R = 0.002 m²-K/W. The inlet temperature of the water is Tmi = 20 °C, and the flow rate is 33 kg/h. Hint: seeEquation 8.45b. a. Estimate the outlet temperature of the water, Tmo. Assume, and then justify, fully developed flow and thermal conditions within the tube. b. Do you expect Tmo to increase or decrease if combined thermal and hydrodynamic entry conditions exist within the tube? Estimate the outlet temperature of the water for this condition.

3. Consider a vertical plate of dimension 0.25m x 0.50m that is at T = 100 °C in a quiescent environment at T = 20 °C. In the interest of minimising heat transfer from the plate, which orientation, (A) or (B), is preferred? What is the convective heat transfer rate from the front surface of the plate when it is in the preferred orientation?

1. Pressurized liquid water is heated by flowing through a square tube with side length s = 10 cm andlength L = 15 m and whose surface is maintained at 235 °C. a. If the flow rate and inlet temperature of the water are 0.005 kg/s and 20 °C, what is the outlet temperature Tmo? What is the total heat transfer rate q for the tube? Assume fully developed flow.

4. A thin-walled tube of 20-mm diameter passes hot fluid at a mean temperature of 45 °C in anexperimental flow loop. The tube is mounted horizontally in quiescent air at a temperature of 15 °C.To satisfy the stringent temperature control requirements of the experiment, it was decided to windthin electrical heating tape on the outer surface of the tube to prevent heat loss from the hot fluid tothe ambient air. a. Neglecting radiation heat loss, calculate the heat flux qe that must be supplied by the electricaltape to ensure a uniform fluid temperature. b. Assuming the emissivity of the tape is 0.95 and the surroundings are also at 15 °C, calculate therequired heat flux.

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