Thermodynamic Assessment of Using Water as a Refrigerant in Cascade Refrigeration Systems with other Environmentally Friendly Refrigerants

For current and future sustainability, refrigerants with high global warming potential (GWP) are being phased out and replaced with environmentally friendly refrigerants. To this end, research into the current and possible future low-GWP refrigerant alternatives in cascade refrigeration systems caught much attention. In this paper, a mathematical model is developed to assess the optimum energetic, exergetic, and operational parameters of a cascade refrigeration system using water as a refrigerant in the upper cycle with R744, N2O, R41, R717, R290, and R1270 in the lower cycle for a cooling load of 10 TR (35.2 kW). Multiple studies have been conducted for evaporator temperatures between -25 and 5 °C. Results show that R41 and R717 as low- and intermediate-temperature refrigerants, respectively, are recommended for the bottom cycle. Furthermore, R717-water showed improved COP compared to other top cycle refrigerants, with a COP improvement of 2.9% to 8.6%. This study demonstrates the thermal feasibility of using water as a refrigerant in low-temperature cascade systems. Using water as a refrigerant in the top cycle showed good results in low-temperature applications without the risk of solidification. However, the drawbacks are the high volumetric flow rate and compressor discharge temperature, requiring a large capacity water injected compressor.

Research and Policy Suggestions on Promoting the Greenization of the Lifecycle of Automobile Products

The greenization of product cycle is the current development trend. Production and consumption are two important links in the lifecycle of automobiles. Therefore, these two links play an important role during the promotion of the greenization of the lifecycle. Through carrying out the evaluation of the environmental benefits of the automobile air conditioning refrigerant alternatives and the analysis of the implementation effect of the automobile taxation scheme, this paper makes suggestions of the greenization of the production and consumption links, thus accelerating the progress of the lifecycle.

Vortex Tube Expansion Transcritical CO2 Heat Pump Cycle

The application of natural refrigerant CO2 is of great significance to reduce the greenhouse effect and ozone depletion. Transcritical CO2 heat pump cycle is presently an important aspect of natural refrigerant alternatives research. In this paper, a vortex tube expansion transcritical CO2 heat pump cycle is established and compared to that of the transcritical CO2 refrigeration cycle with throttle valve. Thermodynamic analysis results indicate that the system performance of vortex tube expansion transcritical CO2 heat pump cycle is better than the transcritical CO2 heat pump cycle with throttle valve, and the COPh improvement is 5.8%~13.9% at given conditions. The gas-cooler outlet temperature has a great impact on the system performance, there is a higher COPh improvement when the cycle at lower evaporation temperature or higher gas-cooler outlet temperature.

Experimental Investigation on Transcritical CO2 Refrigeration System

The application of natural refrigerant CO2 is of great significance to reduce the greenhouse effect and ozone depletion. Transcritical CO2 refrigeration cycle is presently an important aspect of natural refrigerant alternatives research. In this paper, the transcritical CO2 refrigeration cycle system is experimentally studied, effect on performance of heat rejection pressure, gas-cooler outlet temperature and evaporation temperature is analyzed. The experimental results show that there is an optimum high pressure to achieve the maximum COP, the evaporation temperature and gas-cooler exit temperature have great impact on the COP. Increase of gas-cooler outlet temperature led to a rapid increase in the optimal high pressure, but effect of evaporation temperature is not obvious. So in order to obtain the optimum performance, the influence of heat rejection pressure, evaporating temperature and gas-cooler outlet temperature should be considered during the designing and operating CO2 refrigeration cycle system.

A case study in Green chemistry: Developing replacements for CFCs

Chlorofluorocarbons, CFCs, were developed in the late 1920s for use as safe refrigerant alternatives to sulphur dioxide and ammonia. They were welcomed by industry because of their low toxicity, chemical stability, low flammability, low cost and ease of synthesis. They found wide application as refrigerants, blowing agents, propellants and cleaning agents. Over more than 40 years, applications of CFCs expanded into a wide variety of areas, and grew into a multibillion-dollar industry. Unfortunately, CFCs are not ecologically benign. It became increasingly clear that CFCs were responsible for ozone depletion. In the early 1970s the leading manufacturers of CFCs met to discuss the possible environmental impact of their products.This case study uses a problem based learning approach to take students through the development of replacements for CFCs from the 1970s to today. They investigate the background to the CFC problem and consider data that leads to the decision to investigate possible replacements. They must select and design replacement molecules (HFCs), devise syntheses and then consider the challenge to develop the replacements in a socio-economic and political framework. They also consider the problems posed by existing CFCs, the ‘fridge mountain’ and possible disposal and containment alternatives.The case study brings the story up to date with an investigation of the problems now being associated with HFCs and the search for new alternatives. This activity successfully teaches applied and ‘green’ chemistry via a real life context. The chemistry encountered is of an applied/industrial nature and is set in a socioeconomic context. The influence of political pressures is also brought in when appropriate. Because the activity adopts a problem based approach it is also successful in developing a range of transferable skills, particularly problem solving, teamwork plus verbal and written communication.