Chapter 12B: PROPERTY TABLES, REFRIGERATION CYCLES AND HX 1) Boiling of pure substances: water and steam tables 2) Refrigerant tables 3) Binary mixtures 4) Carnot cycles: power, refrigeration, heat pump and combined 5)Heat exchangers: - Different types - LMTD method - Effectiveness-NTU method HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 1 Agami Reddy (July 2016)

Boiling process at atmospheric pressure (vaporization) HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 2 Pure substance From Pita, 2002

Boiling Process at Atmospheric Sea Level HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 3

Boiling at Different Pressures HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 4

5 This is called a “property diagram”- The axis used here are Temperature and Specific volume

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 6 Fig Pressure-volume diagram for water. Fig Temp-entropy diagram for water Property Diagram using other properties

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 7 Press ure, kPa Sat. temp., °C Specific volume, m 3 /kg Internal energy, kJ/kg Enthalpy, kJ/kg Entropy, kJ/(kg · K) Sat. liquid Sat. vapor Sat. liquid Evap. Sat. vapor Sat. liquid Evap. Sat. vapor Sat. liquid Evap. Sat. vapor pT sat vfvf vgvg ufuf u fg ugug hfhf h fg hghg sfsf s fg sgsg Steam Tables

Example 12.4 Wet Steam Properties HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 8

Example 12.6: Refrigerant Properties HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 9

10 Figure 12.7 Pressure-enthalpy diagram for R134a.

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 11 Binary Mixtures Fig Temperature-concentration diagram of a homogenous binary mixture A homogeneous mixture is one which is uniform in composition and cannot be separated into its constituent parts by purely mechanical means such as settling or centrifuging. The various properties such as density, pressure and temperature are uniform throughout the mixture. A common example is dry air and water vapor mixture. Binary mixtures, contrary to pure substances, do not have a single boiling or condensation points. The temperature where the two curves on the left axis meet corresponds to the boiling point of pure substance B at the corresponding pressure

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 12 Evaporation process for a homogeneous binary mixture at a constant pressure Consider a sub-cooled mixture of concentration x B,1 specified by point 1 which is heated -The concentration of the liquid mixture remains unaltered till the boiling temperature T 2 is reached. -The mass concentration of substance B in the liquid would be x B,3 while that in the vapor phase would be x B,4 – dotted line -As more heat is added, the liquid would gradually vaporize, and the relative mass concentrations of substances A and B in both liquid or vapor phases will be constantly changing with temperature during the boiling process. -When the temperature of the mixture reaches T 5, the mass concentration x B,3 of substance B (now entirely vapor) is back to its initial value x B,1. Fig. 12.9

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 13 Enthalpy-concentration diagram for a homogeneous binary mixture Needed for analyzing absorption refrigeration cycles and systems The condensing and boiling lines at a given pressure are now separated by the enthalpy of vaporization of substances A and B as shown. Several lines of constant T are shown in the liquid and vapor regions for different pressures while only one line corresponding to pressure p 1 is shown in the saturation region so as not to clutter up the diagram Fig

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 14 Heat Engines are subject to second law efficiency! Carnot was a scientist who: -pointed out that all heat cannot be converted into work -suggested the working of an ideal heat engine -derived an equation for the ideal heat engine efficiency (serves as a standard) Schematic of a steam power plant A heat engine is one which produces work with heat as its input

15 Carnot Power Cycle Most efficient heat engine (i.e., one which converts heat into work) - heat input and heat rejection done at constant temperatures - expansion and compression done REVERSIBLY (without friction and no heat exchange - isentropic) <> HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX Heat transfer from hot source Heat rejection to sink Useful work outputWork input Fig. 12.2

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 16 Carnot Refrigeration Cycle- another example of systems limited by second law efficiency Here work is put in (in the form of electricity) so as to achieve heat extraction or cooling Fig. 12.3

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 17 Carnot Heat Pump Cycle- Here work is put in (in the form of electricity) so as to pump up heat from a low to a high temperature- heating process Idealized relation:

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 18

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 19 Combined Carnot Heat Engine- Refrigerator Heat Engine Refrigerator Ta Idealized relation: Fig. 12.4

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 20 Example 12.3

Heat Exchangers in HVAC HX is any device facilitating heat exchange between two fluid streams Indirect: separated by a solid surface -Evaporators and condensers -Furnaces and boilers -Heating and cooling air coils Direct : where both fluid streams mix - Cooling tower HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 21

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 22 Parallel Flow Shell and Tube HX Overall heat conductance Figure Schematic diagram of parallel-flow shell-and-tube heat exchanger showing fluid temperatures and equivalent thermal circuit.

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 23 Two different types of problems: (1)Design: All flows and temperatures are specified, and the surface area of the HX tube is to be determined (2) Operational: For a given HX, the two flow rates and the inlet temperatures are given, and the outlet temps are to be determined Heat transfer rate Counter Flow HX

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 25 Figure Temperature profiles along the length of two basic HX configurations

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 26

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 27 Example 12.11

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 28 Eq.12.32

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 29 Fig

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 30 Effectiveness- NTU approach ∈

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 31 Effectiveness- NTU Method Figure Parallel-flow heat exchanger effectiveness as a function of NTU.

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 32 Figure Comparison of effectiveness of several heat exchanger designs for equal hot- and cold-side capacitance rates Figure Counterflow heat exchanger effectiveness as a function of NTU

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 33 Table 2.10

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 34

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 35

HCB 3- Chap 12B: Property Tables, Carnot Cycles and HX 36 Outcomes Understanding of the boiling process of pure substances under different pressures Familiarity with property diagrams and different types of scales Be able to determine property values from steam and refrigeration tables Familiarity with the boiling process of binary substances and understanding of the temperature-concentration and enthalpy-concentration diagrams Understanding of the Carnot power, refrigeration and heat pump cycles and be able to solve problems Familiarity with the different types of HX and classification terminology Understanding the thermal network diagram of a HX Understanding the LMTD method of designing HX and be able to solve design problems Understanding of the effectiveness-NTU approach and be able to analyze HX performance