Download 5 Questions with Solution - Food Process Engineering Technology - Quiz 2 | FSTC 315 and more Quizzes Food science in PDF only on Docsity! AGSM-FSTC 315 – Fall 2012 – QUIZ # 2 (20 pts.) – September 13, 2012 1 NAME: ___________KEY_____________________ UIN: ___________________________ Show all your work to get full credit for your answer. Include all the units. Be neat. 1. (10 pts.) Calculate how much energy is required to heat a pot of water (2.5 liters) from 20 o C to 95 o C. Give your answer both in SI and English units. Density of water = 1 kg/m 3 . Given: substance = water. Volume of water = 2.5 liters. T1 = 20 o C. T2 = 95 o C. Want: Q in SI (kJ) and English (BTU) units Approach: 1. Use )( 12 TTmCpQ 2. Check for consistency of units. Mass (m) is not given so we must find mass using the concept of density = mass/volume. Thus, mass (kg) = volume (m 3 ) x density (kg/m 3 ) Mass of water = [(2.5 L x 0.001 m 3 )]x[1000 kg/m 3 ]= 2.5 kg Then, )( 12 TTmCpQ = (2.5 kg)(4.186 kJ/kg o C)(95-20) o C = 784.88 kJ (SI units) In English units: 784.88 kJ 1 BTU 1.055 kJ = 743.96 BTU Answer: 784.9 kJ (744 BTU) of heat energy is required to increase the temperature of 2.5 liters of water by 75 o C. 2. (1 pt.) The problem above deals with sensible or latent heat? Answer: _____________SENSIBLE_____________________________________ 3. (5 pts.) Calculate the specific heat (in S.I. units) of the one apple (80% water and mass = 250g): Cp food= (Mwater/Mfood)Cpwater + (Msolids/Mfood)Cpsolids AGSM-FSTC 315 – Fall 2012 – QUIZ # 2 (20 pts.) – September 13, 2012 2 CkgkJCp CkgkJ g g CkgkJ g g Cp o food oo food /6248.3 /38.1* 250 )250*2.0( /186.4* 250 )250*8.0( Answer: Cp of apple = 3.6248 kJ/kg o C 4. (2 pts.) True or False? 4.1 The lower the Cp of a material, the larger the quantity of heat energy (Q) needed to change the temperature of a specific mass of the material TRUE FALSE 4.2 Latent heat is the amount of heat energy that must be removed/added to a system in order to change its phase. TRUE FALSE 5. (2 pts.) List the two sources of experimental error in the method of mixtures used to determine the specific heat of a material. 1: Temperature measurements 2: Heat lost to the surroundings Data Sheet )( 12 TTmCpQ With: Q = heat energy in kJ or BTU m = mass in kg or lbm T = temperature in o C or o F mass (kg) = volume (m 3 ) x density (kg/m 3 ) density of water = 1000 kg/m 3 Cpsolids = 1.38 kJ/kg o C = 1.38 kJ/kgK Cp water = 4.186 kJ/kg o C = 4.186 kJ/kgK = 1.0 Btu/lbm o F
