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Thermodynamic Processes
Published in S. Bobby Rauf, Thermodynamics Made Simple for Energy Engineers, 2021
An isenthalpic, or isoenthalpic, process is a thermodynamic process in which no change in enthalpy occurs, or Δh = 0, or h1 = h2. A steady-state, steady-flow process, would be isenthalpic if the following conditions are met: The thermodynamic process is adiabatic—meaning, no heat is exchanged with the environment.Work is neither performed by the system onto the surroundings nor is it performed by the surroundings onto the system.There is no change in the kinetic energy of the system or fluid.
Performance of a computerized refrigeration cycle test rig for varying concentrations of (CuO-Al2O3/MO) hybrid nano-lubricants and R600a refrigerant charges: an energetic and exergetic approach
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Ankit Kumar, Satish Pal Singh Rajput
In present study, a Computerized Refrigeration Cycle Test Rig Model: RAC11 based on VCR system is utilized for experimental work shown in Figure 1. This test rig operates on the principle of a vapor compression refrigeration system. Vapor Compression refrigeration test rig is made up of four elementary components: an evaporator, a compressor, a condenser, and an expansion valve. The main function of the evaporator is to extract the amount of heat from the desired space or location so that the temperature of the space reduces. The refrigerant inside the evaporator changes its phase from liquid to gaseous phase and then goes into the compressor. The compressor, which is primarily driven by an electric motor, raises the pressure and temperature of the refrigerant. It is assumed in this study that at the entry to the compressor refrigerant is dry saturated. It means the compression is 100% dry compression and no amount of liquid particles inside the compressor. The high pressure and high temperature refrigerant is cooled inside the condenser with the help of a cooling fan (forced convection), which is also driven by an electric motor. The expansion process inside vapor compression test rig takes place with the help of an expansion valve and the process is isenthalpic process. The isenthalpic process is an irreversible process and is accompanied by an increase of entropy. In the expansion process, the refrigerant changes from liquid to the mixture of saturated liquid and saturated vapor, i.e. flash gas. The process again repeated continuously to carry out experiment.
Validated open-source Modelica model of direct evaporative cooler with minimal inputs
Published in Journal of Building Performance Simulation, 2022
Saranya Anbarasu, Wangda Zuo, Yangyang Fu, Yash Shukla, Rajan Rawal
Figure 1 shows a typical Direct Evaporative Cooler (DEC). The evaporative cooling pad is the key component of a DEC system and serves as a heat and mass exchanger. Cooling pads are generally built with layers of humidity-absorbing materials such as cellulose, aspen, paper, etc., and are wetted by a pump. A centrifugal fan blows the air through the wetted cooling pad, which cools the dry air by increasing the relative humidity. Thermodynamically, the energy required to evaporate the water is taken from the air in the form of sensible heat and is converted into latent heat. This conversion of sensible heat to latent heat, without the change in enthalpy, is known as an isenthalpic process. Figure 2 represents the direct evaporative cooling process on the psychrometric chart as a parallel line to the wet-bulb line and the enthalpy line. Evaporative cooling, therefore, causes a drop in the air temperature, proportional to the sensible heat drop, and an increase in relative humidity, proportional to the latent heat gain (Fouda and Melikyan 2011). The extent of temperature drop depends on the duration of contact, surface area of contact, and mass flow rate of air passing through the cooling pad. Additionally, there is also a significant pressure drop depending on the geometric configuration of the cooling pad, which must be catered by the fan to maintain the required mass flow rate.