Cooling capacity
The effective capacity a refrigerated equipment can provide for specimen or application system at designated room temperature (usually 20 °C) and working temperatures. Cooling capacity is specified in watt or Kcal/h. Cooling capacity is one of the most important specifications one must confirm when choosing a refrigerated equipment. It has something to do with the lowest temperature a refrigerated equipment may reach. This doesn't mean that a refrigerated equipment with lower temperature range has more cooling capacity. For example, an applica-tion system is calculated to produce 380W heat at -20 °C working temperature condition. There are 2 equipment to choose from. The tempera-ture range for the first one is -30~+90 °C, with cooling capacity 480 W @-20 °C. The temperature range for another equipment is
-50~+90 °C, with cooling capacity 350 W@
-20 °C. When only cooling capacity or even price is considered, the first unit is the right choice.
Temperature controller
Varieties of controllers with different tempera-ture stability, dynamic capability, display resolu-tion and auxiliary functions are designed and configured to be assembled to thermostatic equipment for different applications. The tem-perature stability and dynamic capability are dependent on the algorithm of the temperature controller. On/off control is the most simple, economic and reliable way for temperature regulation. The load is fully cut in and cut out from the circuit based on the setting. The on/off control is applicable to applications where temperature stability is less important or static stable system where temperature regulation is minimum. The best stability is expected to be ±0.1~0.5 °C. Improved proportion control (or PWM) regulates the load to be cut in and off the circuit at finer intervals only when temperature approaches the set point, thus keeping it precisely around the setting. Stability of around±0.02~0.1 °C is expected. Advanced PID control is able to predict the temperature change and regulate the load in advance. One doesn't have to compromise between stability and speed, which makes it applicable to ever-changing load condition or applications where precise temperature regulation is desired. The temperature stability is expected be in the range of ±0.002~0.05 °C. The display resolution is designed to match the stability of the controllers and their applications. For the above mentioned controllers, the resolutions are 0.1, 0.1/0.01 °C and 0.01/0.001 °C respectively, with the latter 2 programmable by the operator. The auxiliary functions may differ form equipment to equipment. As standard for controller design, absolute temperature calibration (ATC), safety function and auto-restart after power failure are incorporated in almost all controllers. Temperature, humidity and light editing and programming, auto-start, auto-stop and timer, and RS232/485 communication interface are included in part of Xutemp's controllers.
Pumps
All circulating baths and circulators are equipped with a pump for precise temperature control, improved temperature uniformity and sufficient heat transmission. For circulators and recirculating coolers, pumps are functioned to deliver heat transfer liquid to external applica-tion system excepts for precise temperature control, where specifications for maximum pump head, maximum flow rate and flow rate at designated head become extremely important. Because of the negative relationship between pump head and flow rate, the flow rate at designated head is more applicable. To help user understand actual flow rate of circulators, some of the chillers are equipped with pump gauges and provided with flow charts or tables. In situations where pressure loss is insignificant or flow rate is less important, the maximum data may be used for reference. The pressure pumps are applicable only to closed circulating circuit. For open circulating circuit or circuit where excess pressure is not acceptable, an open bath, glass condenser, circulators with pressure/ suction pump, or enclosed circulators are the right choice, which balance the open bath liquid level and reduce the pressure tension to the glass vessels. For open bath application with pressure/ suction pump circulator, liquid level control kit is necessary for balancing the flow rates of the pressure /suction pump, while with enclosed circulator, no level control device is necessary at any bath altitude difference.
Cooling capacity calculation
For cooling of any specimen, analytical instrument or experimental apparatus or industrial equipment, manufacturer or supplier of the equipment requiring specific cooling will give you basic information concerning temperature, cooling capacity and pump head, flow-rate to ensure optimum operation. Please always try first to acquire this information. In situations when information is unavailable, use equation below to estimate the heat energy your application system or specimen will produce. Based on the calculated result, we will help you to find the right equipment from varieties of our product line. Example:
You are condensing a rotation evaporator with tape water
Tape water into the condenser, 15 °C
Water leaving the condenser, 16.2 °C
Tape water flow rate, 6 L/min
Calculate heat energy produced by the application according to the following equation:
P=m/t×g×c×△T
Where:
m/t (tape water flow rate) =360 L/h
g (specific gravity of water) =1.0 kg/L
c (specific heat of water) =1.0 Kcal/kg/K
△T (temperature difference) =1.2 K
P (cooling capacity) =360×1.0×1.0×1.2
            =432 Kcal/h=502 W
Note: 860 Kcal/h=1,000 W
Recommended equipment: XT5718RC-E800 or equivalent