The Portable Rapid Cooler

Team Project: 2022 Spring

1. Overview

Summer is just ahead of us, a season in which people spend time on the beach under the sunshine. Getting a refreshing cold drink in front of the sea would provide extraordinary enjoyment. Typically, we will need to prepare a large cooler ahead of time, fill it with water and ice, place the drinks inside, then put the cooler in the trunk. When we arrive at the beach, we will need to carry the cooler all the way down to the waterfront, with hands full of other stuff. It takes a lot of work and time before the enjoyment begins. Let’s forget about all this heavy work. What if the drink is nice and cool, ready to drink in a minute, with just a push of a button? The goal of our project is to bring this ultimate experience to life. Our product aims to be portable, rechargeable, durable, and able to cool down can size beverages rapidly. Other beverage coolers on the market can be categorized into two main types. The first type rotates a drink submerged in an ice bath. For example, the Cooper Cooler is capable of cooling down a can size beverage in 1 minute, or a wine bottle in 6 minutes. However, it is bulky and requires 120V AC input. The other type is a portable cooler that will run on 12V DC input. It also requires putting the drink inside a water bath, then using a Peltier cooler to cool down the water bath. For example, the Xiaomi Mijia cooler requires 15 minutes for a 10°C fall. These products’ specifications do not satisfy our defined customer needs. Our product development aims to cool down a standard can size drink 10°C within 1 minute. It uses a Peltier cooler, convection, and evaporative cooling to achieve the projected result. Our cooler operates with 12V DC which is supplied by three 3.7V 15A 3000mAh Lithium-ion batteries. The total weight of the product will not exceed 5 Lbs.

2. Theory

Peltier effect

We are going to use a Thermoelectric Cooler (TEC) to reduce the temperature of the airflow. The thermoelectric effect includes the Seebeck effect, Peltier effect, and Thomson effect. Our device will only utilize the Peltier effect. When a voltage difference is applied to both ends of the TEC electrodes, a temperature difference is induced on the two flat surfaces on the TEC.

Convection Heat Transfer

When airflow enters the cooling chamber, depending on the inlet geometry, it will form a cyclone in a steady state. The surface of the can has conduction heat transfer on the wall inside the can, and convection boundary conditions at the exposed surface to the airflow. Since airflow temperature is reduced by the TEC, the airflow will remove heat from the can via convection.

Evaporative Cooling

Water has a large heat capacity. It will remove a great amount of heat when evaporated. Therefore, our device is designed to have a water sprayer to mist the can surface periodically to introduce evaporative cooling at the surface of the can. Heat would be drawn from the internal liquid through the can wall to fulfill water evaporation.

3. Analysis

CFD in ANSYS

we use ANSYS to help determine other factors that influence cooling efficiency.

As demonstrated in figure 3.3, the steady-state streamlines indicate the formation of a cyclone. Tangential Velocity to the streamlines would be much greater than the vertically upward velocity.

A transient simulation is performed using the evaporation heat rate q = 27W as the boundary conditions. In the observation of the temperature plot shown in figure 3.4, there is a large temperature gradient close to the can wall. It implies using evaporation cooling on the still beverage can will not achieve the full 27W at all times. This phenomenon is due to the surface temperature being rapidly reduced, the internal heat flow is not sufficient via conduction and free convection. Rotating the can to induce forced convection will enhance internal cooling. However, adding a rotation mechanism will increase the product cost and the overall size and weight. A further study is needed to consider if the additional cost is worth the extra parts.

4. Detail design Review (Including Ballpark Estimate)

Peltier cooler

4. Prototyping

The product prototype 1.0 was built on a plywood sheet. Due to the parts supply shortage, we used a variable AC/DC converter power supply instead of the battery pack. The prototype components include a 12V blower fan, a 12V Peltier cooler, two aluminum heat sinks and a plastic transparent cylinder shield. With the limitation of material and time, the humidity sensor and water mist humidifier are not implemented in the prototype. The first measurement we have made is the steady-state temperature of the cool side of the Peltier cooler. The heat dissipation method for the hot side of the Peltier cooler is forcing the air to flow through the heat sink. The cool side steady-state temperature was measured as 9°F (~13°C). In this case, the initial temperature of a can of the beverage was measured as 23.2°C. Before turning our cooler on, we sprayed water on the can manually. In 1 minute of operation, the drink was cooled down to 18.6 °C. The water droplets on the lower part of the can have all been evaporated. However, there are still some water droplets on the top part of the can. Compared to the theoretical analysis, the final temperature at 1 minute has not dropped to the desired temperature. The reason for that is mainly because of the limitation of water mist supply. By observation, the water droplets beneath the natural axis of the can evaporated within 20 seconds. As a result, the evaporation cooling process was focused for the first 20 seconds. By this prototyping, the concept of evaporation cooling by using a Peltier cooler is demonstrated.

Closing Remark

In this project I worked on the prototype implementation, computational model simulation. In the future implementation, instead of using a DC power supply, using a battery pack for our product is more in line with the design concept of portability. Besides that, our idealized product will implement a built-in fan blower with 3 air inlets and change the simple fin heat dissipation method to the channel-type heat sinks. The increment of the air inlets allows the cold airflow to remain in laminar flow and evenly around the drink and the heat dissipation rate directly changes the steady-state temperature of the Peltier cooler. It increases the energy using efficiency. In addition, the cylinder shield dimension could be changed due to the optimization of the cooling operation. Some constraints for this design are the airflow properties, flow velocity, and the user experience. Moreover, an idealized product will include a temperature, and humidity control system, and a humidity controller to control the humidity inside the cylinder shield and detect the number of water droplets that attach to the bottle of the beverage. While the water has evaporated, the water mist humidifier operates. It ensures that the cooling method of our product continues to be evaporative cooling. The temperature sensor will detect the temperature of the drink, with this implementation, our final product is able to contain a user control option in which the user can control the desired temperature of the drink and our system operates the cooling system and also computes the estimated required time and output that to the user.

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