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Case Studies of Parametric Accelerated Life Testing
Published in Seong-woo Woo, Design of Mechanical Systems Based on Statistics, 2021
To store food, the refrigerator utilizing a vapor-compression refrigeration cycle has to provide cold air from the evaporator to the freezer and refrigerator compartments. The refrigeration unit consists of a compressor, a condenser, a capillary tube, and an evaporator. The compressor takes the refrigerant from the evaporator and then compresses it, which transfers it to the condenser in the refrigeration cycle. In the process, a reciprocating compressor increases the refrigerant pressure from that in the evaporator to that in the condenser and is subjected to repeated stresses by the operation of the crankshaft. As customers demand refrigerators that use less energy, it is necessary to improve the overall energy efficiency of the refrigerator. One way to improve efficiency is to redesign the compressor in the refrigerator. The primary components in a domestic compressor consist of the crankshaft, piston assembly, stator and its frame, valve plate, and suction reed valve (Figure 9.63).
Thermodynamic Cycles for Solar Cooling
Published in Sotirios Karellas, Tryfon C. Roumpedakis, Nikolaos Tzouganatos, Konstantinos Braimakis, Solar Cooling Technologies, 2018
Sotirios Karellas, Tryfon C. Roumpedakis, Nikolaos Tzouganatos, Konstantinos Braimakis
The evaporator is the heat exchanger at which the cooling effect is produced by absorbing heat from a heat source in order to evaporate the working medium of the refrigeration cycle. There are two main types of evaporators used in practice, depending on the cooling medium: (1) evaporators that cool down a liquid, most commonly water, and (2) evaporators that cool air or other gas-phased media. In the liquid cooling evaporators, as in the case of water condensers, all kinds of heat exchangers can be used, with plate-heat exchangers, tube-in-tube, and shell-and-tube heat exchangers being the most widely applied, as shown in Figure 2.9. Especially in the case of shell-and-tube heat exchangers, fluid allocation is highly dependent on the specific application, with both cases of vaporization taking place on the shell side and cases in which the vaporizing fluid is flowing inside the tubes.
Energy Transport in Thermal Energy Systems
Published in Steven G. Penoncello, Thermal Energy Systems, 2018
In many thermal energy systems, one of the working fluids passing through a heat exchanger experiences a phase change. Figure 5.21 is a schematic of two common thermal systems; a vapor power cycle and a refrigeration cycle. In both of these cycles the working fluid undergoes two phase changes in the heat exchangers. In the vapor power cycle, liquid water is converted to steam in the boiler and condensed back to a liquid in the condenser. In the refrigeration cycle, the refrigerant is converted to a vapor in the evaporator and condensed back to a liquid in the condenser. These types of heat exchangers are generally categorized as either boilers, evaporators or condensers. The heat exchangers in Figure 5.21 are shown as counter flow heat exchangers for convenience in the sketch. In applications, the heat exchangers may have several different configurations such as shell and tube or cross flow.
A Critical Review on Heat Transfer of Supercritical Fluids
Published in Heat Transfer Engineering, 2023
Qingyang Wang, Jinliang Xu, Chengrui Zhang, Bingtao Hao, Lixin Cheng
The two cycles shown in Figure 1 can help to reduce greenhouse gas emission. Supercritical CO2 Brayton cycles can use various energy sources including fossil fuel, solar energy, geothermal heat, nuclear energy, and waste heat, and have great benefit due to its flexibility and higher efficiency [7, 13]. Therefore, supercritical CO2 power generation is attracting significant interests as a possible solution to carbon emission reduction. Moreover, the traditional refrigeration cycles use chlorofluorocarbons and hydrochlorofluorocarbons as refrigerants, which causes significant global warming and ozone depletion. CO2 (R744) is a natural refrigerant, which is nontoxic, non-flammable and easy to obtain, and has an ozone depletion potential of 0 and a global warming potential of 1. Hence, transcritical CO2 refrigeration cycles are much more environmentally friendly compared to traditional refrigeration cycles.
Modeling of vertical ground heat exchangers
Published in International Journal of Green Energy, 2021
Seama Koohi-Fayegh, Marc A. Rosen
Heat pumps use the same mechanical principles as refrigerators. While refrigerators remove heat from the interior and discharge it to the environment, heat pumps take heat from the environment and concentrate it to heat the building in the summer. A heat pump is a machine that transfers heat from a source to another region by employing a refrigeration cycle. Although heat normally flows from higher to lower temperatures, a heat pump reverses that flow and acts as a “pump” to move the heat. Therefore, a heat pump can be used both for space heating in the winter and for cooling (air conditioning) in the summer. In the refrigeration cycle, a refrigerant (known as the “working fluid”) is compressed (as a liquid) then expanded (as a vapor) to absorb and remove heat. The heat pump transfers heat to a space to be heated during the winter period and, by reversing the operation, extracts (absorbs) heat from the same space to be cooled during the summer period.
Analysis of a pharmaceutical batch freeze dryer: resource consumption, hotspots, and factors for potential improvement
Published in Drying Technology, 2019
Ana Gabriela Renteria Gamiz, Pieter-Jan Van Bockstal, Steven De Meester, Thomas De Beer, Jos Corver, Jo Dewulf
The laboratory freeze dryer used for the analysis is a batch commercial unit LyoBeta 25 (Telstar, Terrassa, Barcelona) that follows the scheme presented in Figure 1. The chamber holds 4 stainless steel (316L) shelves for product and a top radiant shelf, resulting in a total loading area of 0.68 m2. The thermal fluid used for temperature control is silicone oil (KT3). The cooling system has a vapor-compression cascade refrigeration cycle using R-404a and R-23 as refrigerants. The same cooling system is used to cool down the shelves and the cold trap. The heating of the shelves is done by electrical resistance heating. It is considered that the shelf-channels have a serpentine path design since freeze dryer shelves generally hold this type of path for heat transfer enhancement.[24] The data reported by Kuu et al. from a laboratory batch freeze dryer (LyoStar II) is used as a proxy value for the shelf-channels dimensions, considering a rectangular configuration.[25]