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University of Bristol
Department of Mechanical Engineering
Queens School of Engineering
University Walk, Bristol BS8 1TR
MENG20600 Thermofluids 2
The Refrigerator Roshan Mohanty
Department of Mechanical Engineering Date of Laboratory: October 12, 2015 Date of Submission: October 17, 2015
Word Count: 792
ABSTRACT:
The aim of this lab experiment was to calculate the coefficient of performance (COP) of a refrigerator. The coefficient of performance of a refrigerator is basically the "efficiency" of a refrigerator. In order to calculate the COP, a set of temperatures, pressures, flow rates, compressor torque etc were measured at a steady state. These values were
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So, in order to calculate the COP, we needed the values of Qevap (per unit time) and Wcomp (per unit time).
The values of Qevap (per unit time) and Wcomp (per unit time) were calculated using the values of enthalpy obtained from the Pressure-Enthalpy graph as well as using certain equations which involved mechanical inputs. These values were then compared and a difference in the values was
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Location
Description
Temperature (°C)
T1
Compressor Inlet
4
T2
Compressor Outlet
46
T3
Condenser Outlet
20
T4
Evaporator Inlet
-6
T5
Evaporator Outlet
4
T6
Glycol Bath
4
T7
Water Inlet
16
T8
Water Outlet
22
Table 1: Temperature readings from 8 thermocouples There were 3 pressure gauges and 1 barometer. The values obtained from the gauges were added with 1 to convert them to absolute values. The readings obtained are given below in Table 2. Location
Pressure, bar (Gauge)
Converted Value (Absolute)
Barometer
1.01
Compressor Discharge
6
7
Compressor Suction
1.1
2.1
Expansion
1.2
2.2
Table 2: Pressure readings from 3 gauges and 1 barometer The flow rates and other necessary values were noted and are given below in Table 3.
Measurement
Value
Water Flow Rate
50.4 g/s
Refrigerant Flow Rate
5 g/s
Rate of Compressor Rotation
10.3 rev/s
Torque of Compressor Shaft
3.8 Nm
Current to Heater
4.62 A
Table 3: Other entities required for Calculation
*The values of Rotation, Torque, Current are average values because these values were fluctuating during the reading. So, an average of the lowest and the highest value was taken into
The user controls the pulsation frequency $f_p$, through the motor speed $\omega_m$, and the mean pressure $p_M$, through the pressure regulator in the inlet line. The pressure amplitude $p_A$, on the other hand, depends on the facility line-cavity behavior. As shown in Fig.\ref{fig:2b}, the relative pressure amplitude $\hat{p}_A= p_A/p_M$ decreases when increasing mean pressure and the pulsation frequency, though asymptotically approaching a constant
%% Init % clear all; close all; Fs = 4e3; Time = 40; NumSamp = Time * Fs; load Hd; x1 = 3.5*ecg(2700). ' ; % gen synth ECG signal y1 = sgolayfilt(kron(ones(1,ceil(NumSamp/2700)+1),x1),0,21); % repeat for NumSamp length and smooth n = 1:Time*Fs '; del = round(2700*rand(1)); % pick a random offset mhb = y1(n + del) '; %construct the ecg signal from some offset t = 1/
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Pertaining to the appearance of the oil and water before the reaction occurs, oil “sits” on top of the water because oil is less dense than water, and therefore rests on the surface of the water. The Alka-Seltzer, or effervescent tablet, reacts with the water and produces bubbles of carbon dioxide gas. This gas is less dense than both the water and oil, so it travels the the surface of the liquid, pulling a small amount of the colored water with it and creating the “lava lamp” effect. The chemical reaction that is occurring is an acid-base reaction, and results from the reaction between the ingredients in the Alka-Seltzer tablets.
Air Conditioning Heating & Refrigeration News, 217(6),
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