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Heriot-Watt University School of Engineering and Physical Science Chemical Chemical & Petrol eum Engin Engin eeri eeri ng Stage 2 Laborator y Experiment Experiment 10: 10: Mechanical Mechanical Heat Heat Pump Contents 1 Introduction ................................. .................................................. .................................. .................................. .................................. .................................. .................1 2 Objectives................................................................... ....................................................................................................... ................................................................ ............................ 1 3 Basic Theory ................................................................... ....................................................................................................... ........................................................... ....................... 2 4 Equipment .................................................................. ...................................................................................................... ................................................................ ............................ 5 5 Operational Notes .................................................................. ..................................................................................................... .................................................... ................. 6 6 Experimental Data Sheets ..................................................................... ........................................................................................................ ................................... 8 7 Analysis and Discussion .................................. .................................................. .................................. ................................... ............................... .............. 9 8 Safety Note ..................................................................... ......................................................................................................... ........................................................... ....................... 9 9 Appendix .................................................................... ........................................................................................................ .............................................................. .......................... 10
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Introduction
The SOLTEQ® Heat Pump Equipment (Model: HE165-A) has been designed to provide students with a practical and quantitative demonstration of a vapour compression cycle, and is suitable for all course levels (intermediate and undergraduate). Refrigerators and heat
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Basic Theory
A heat pump is a mechanism that absorbs heat from waste source or surrounding to produce valuable heat on a higher temperature level than that of the heat source. The fundamental idea of all heat pump is that heat is absorbed by a medium, which releases the heat at a required temperature which is higher after a physical or chemical transformation. Heat pump technology has attracted increasing attention as one of the most promising technologies to save energy. Areas of interest are heating of buildings, recovery of industrial waste heat for steam production and heating of process water for e.g. cleaning, sanitation. Generally, there are three types of heat pump systems: i. ii. iii.
Closed cycle vapour compression heat pumps (electric and engine driven) Heat transformers (a type of absorption heat pump), and; Mechanical vapour recompression heat pumps operating at about at 200°C
3.1 Closed Cycle Vapour Compressi on Heat Pump Most of the heat pumps operate on the principle of the vapour compression cycle. In this cycle, the circulating substance is physically separated from the heat source and heat delivery, and is cycling in a close stream, therefore called „closed cycle‟. In the heat pump process, the following processes take place:
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3.2 Vapour Compression Heat Pump Principles
Figure 2: Vapor Compression Heat Pump Cycle The labelled components are:
1. Condenser
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iii) Expansion Process (t3
t4)
At Point (3), the refrigerant is in liquid state at a relatively high pressure and temperature. It flows to (4) through a restriction called the flow control device or expansion valve. The refrigerant loses pressure going through the restriction. The Pressure at (4) is so low that a small portion of the refrigerant flashes (vaporizes) into a gaseous. In order to vaporize, it must gain heat (which it takes from that portion of the refrigerant that did not vaporize). iv) Vaporizing Proc ess (t4
t1)
The refrigerant flows through a heat exchanger called the evaporator. The heat source is at a slightly higher temperature than the refrigerant, therefore heat is transferred from it to the refrigerant. The refrigerant boils because of the heat it receives in the evaporator. By the time it leaves the evaporator (4) it is completely vaporized. The refrigerant has thus returned to its initial state and is now ready to repeat the cycle, in a continuous manner. 3.3 Coefficient of Performance The Coefficient of Performance, (COP H) of a heat pump cycle is an expression of the cycle efficiency and is stated as the ratio of the heat removed in the heated space to the heat energy equivalent of the energy supplied to the Compressor.
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Equipment
Figure 3: Unit assembly of Mechanical Heat Pump (Model: HE165A) 1. Expansion valve
6. Evaporator
2. Refrigerant flowmeter
7. Low Pressure Cut Off Switch
3. Sight Glass
8. High Pressure Cut Off Switch
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Figure 4: Schematic diagram for Heat Pump Equipment (Model: HE165-A).
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5.3 Experiment 1: Determination of power input , heat o utput and coefficient of performance Procedures:
1. 2. 3. 4. 5.
Perform the general start-up procedures. Adjust the cooling water flowrate to 3.0 LPM. Allow the system to run for 15 minutes. Record all necessary readings into the experimental data sheet. Repeat the experiment with reducing water flowrate. Maintain the evaporating temperature (TT4) by covering part of the evaporator for the purpose of lowering the evaporating load. 6. Repeat similar steps until the compressor delivery pressure reaches around 14.0 bar. 7. The experiment may be repeated another constant evaporating temperature (TT4). Note:
The cooling water and refrigerant flow rate display is in percentage (%). Below is the formula to convert cooling water and refrigerant flow rate to LPM.
1. Cooling water flow rate (LPM) = Cooling water flow rate (%) × 4.5 LPM 100%
2. Refrigerant flow rate (LPM) = Refrigerant flow rate (%) × 0.8 LPM 100%
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6 Experimental Data Sheets 6.1 Experiment 1: Determination of p ower input, heat out put and coefficient of performance Results: Table 1 Test Cooling water flowrate, FT2
LPM
Cooling water flowrate, FT2
%
Refrigerant flowrate, FT1
LPM
Refrigerant flowrate, FT1
%
Refrigerant Pressure (Low), PT1
Bar(g)
Refrigerant Pressure (High), PT2
Bar(g)
Refrigerant Pressure (Low), PT1
Bar(abs)
Refrigerant Pressure (High), PT2
Bar(abs)
1
2
3
4
5
3.0
2.5
2.0
1.5
1.0
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7 Analysis and Discussions 1. Calculate the Heat output and Coefficient of performance. 2. Plot the performance curves for Heat Pump (COP, Heat Delivered, and Compressor Power Input) versus Temperature of Water Delivered. 3. Plot the experimental vapour compression cycle on the p-h diagram of R-134a and compare with the ideal cycle. 4. Perform energy balance on the condenser. 5. Perform energy balance on the compressor. 6. Plot the performance curves for Heat Pump (COP, Heat Delivered, and Compressor Power Input) versus Condensing Temperature. 7. Calculate the compressor pressure ratio and volumetric efficiency.
8 Safety Note 1. The unit must be operated under the supervision of trained personnel. 2. All operating instructions supplied with the unit must be read and understood before attempting to operate the unit. 3. Always check and rectify any leak.
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Ap pendi x: Press ur e-Enthalp y Di agr am
EPS Chemical Engineering
©Heriot-W att
University
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B49CE
January 2017 v1
