Practice questions Question 1 Baked Beans Unlimited (Pty) Ltd has been producing baked beans for over thirty years and has not upgraded their equipment. However, as of late the company has been receiving consumer complaints to say that the products flavour has changed. One complained even stated the flavour was “burnt”. Other complaints include no beans in the can, too many beans in the can and no sauce. You have been the company’s consultant food technologist for less than six months and have been asked to fix the problem. The only set of information you have been able to gather is that the viscosity of the product is 2 Pa/sec, density is 1500 kg/m3, the flow rate is 40 l/min and the diameter of the pipe moving the baked beans from the heat exchanger to the filling head is 2.5 cm. You now need to recommend to management how to fix the problem and may also need to mathematically justify your recommendations (if so show all calculations). However, as the product is one of the company’s best-selling products it is not an option to reformulate it. Question 2 A mistake has been made while mixing a batch of product in the ice cream manufacturing company you work for. As the company’s food technologist you are told that the batch is an ice-cream mix of 2000 kg containing 5% chocolate. The product should have contained 10% chocolate in the final mix. Calculate how much extra chocolate is required to meet the final value. Question 3 You are working as a Food scientist in an industry, which produces concentrated fruit juices. In a single effect evaporator, orange juice is being concentrated at steady state condition. The feeding rate of orange juice is 2160 kg/h with 10% (m/m) solids. The juice has to be concentrated to 74% total solids. The inlet feed temperature is 42°C, while product boils at 61.5°C inside the evaporator. The specific heat of orange juice is 0.93 kcal/kg°C and overall heat transfer coefficient is 808 kcal/m2hr°C. Assuming negligible boiling point elevation, calculate (a) mass flow rate of thick juice, (b) steam required and (c) total heat transfer area required. The temperature of saturated steam entering evaporator is 138°C. The latent heat of vaporization at 61.5°C is 625.1 kcal/kg and that of condensation of steam at 130°C is 651.01 kcal/kg. Question 4 You are required to design storage tanks for a newly established food industry. The manager of the industry ask you to set up a large storage tank that holds oil having a density of 917 kg/m3. The tank is required to be 3.66 m tall and is vented to the atmosphere of 1 atm abs at the top. The tank is required to be filled with oil to a depth of 3.05 m and also contains 0.61 m water in the bottom of the tank (density of water 1000 kg/m3). Calculate the pressure in Pa 3.05 m from the top of the tank and at the bottom. Also, calculate the gauge pressure at the bottom of the tank.
