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Abstract

Introduction

Refrigeration systems are extensively used for the intent of cooling a room and food preservation. In this experiment, R134-A will circulate through an evaporator, or a heat exchanger. The evaporator converts the fluid into vapor and in that process it takes in heats from the medium that to be cooled. After that, the vapor is passes through a compressor which compresses gas which leads to a higher temperature and pressure in the fluid. The extremely hot vapor is then passes through the condenser where it condenses, cool down. Then it passes through the expansion valve where it expands. The fluid keeps circulating in the same process which is then can be called refrigeration. The four main components of the refrigeration are Compressor, Condenser, Expansion Valve, and Evaporator. At these four main points of the refrigeration cycle temperature, pressure, fluid flow rate, and electrical output were recorded. From these values, the specific enthalpy at each of the four points was found and the Coefficient of Performance, COP, was calculated using:

COP = ṁ (h1 – h4) / Ẇelect … (1)

COPideal = (h1 – h4) / (h2 – h1) … (2)

COPCarnot = 1 / [(T2 / T4) – 1] … (3)

Where:

ṁ is the mass flow rate.

h# is the specific enthalpy at point #.

T# is the temperature at point #.

Welect is the electrical input work.

Description of Work

First, the valves that are required to be closed are kept closed, while the other valves are kept open. The system (Figure 1) was turned on and at the identified four main points of the refrigeration cycle temperature, pressure, fluid flow rate, and electrical output data were recorded before warming up the system. Then it was kept running for 5 minutes to warm up. After that, another recording of the same data has taken place again. The same data were recorded then after every 5 minutes until the cycle reached steady state. Steady state can be identified when the data start showing constant values at all four different points of the cycle. These values helped in getting the thermodynamic state of the fluid at each point, as well as the specific enthalpy associated with the cycle. Finally, a pressure vs. enthalpy graph was constructed to show the cycle, and the coefficient of performance was then calculated.

Figure 1: The entire refrigeration system used in the experiment.

Figure 2: The four main points in the refrigeration process.

Results and Discussion

The overall schematic for the whole experiment is shown below. From the pressure temperature recorded, these values are then used to calculate the enthalpy of the cycle using the thermodynamic R-134 property tables, and a P-h diagram was made for the cycle using excel. Enthalpy difference to ratio describes the cop of cycle. Nevertheless, COP ideal and COP Carnot were calculated using equations 1, 3.

Table 1: Converted refrigeration data.

Table 2: Pressure and temperature at each of the four main points.

Table 3: Pressure data and the associated specific enthalpy for all four main points

Figure 3: (P-H) diagram showing the cycle path.

Table 4: Coefficients of performance.

Conclusion

All in all, the experiment can be somehow found to be successful.

Appendix

Table 5: Raw data

Sample Calculation

· To convert pressure from inches of water to lb/ft2:

P = 0.0650 (in. of water) / 12 * 62.4 (lb/ft3)

P = 0.338 lb/ft2.

· To calculate the air velocity, V = (2 Pdynamic / ρ) 0.5 :

V = (2 * 0.338/ 0.0748) 0.5

V = 3.004 ft/s.

· To calculate the ideal work rate, Ẇideal = γ Q hf :

Ẇideal = 2.46 * 2.36 * 0.348

Ẇideal = 2.025 ft-lb/sec.

Pressure vs. Enthalpy (R-134A)

179 188 110 110 44.7 153.69999999999999 154.69999999999999 49.7

Enthalpy (Btu/lbm)

Pressure (psi)

1